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State of the art in pediatric arrhythmia

Ronald J. Kanter

Duke University Medical Center Durham, NC

Introduction
Congenital complete AV block
Supraventricular tachycardia
Diagnosis of SVT
Postoperative arrythmias
References

Introduction

The care of infants, children, and teenagers having cardiac arrhythmias has become increasingly specialized due to a combination of greater understanding of the pathologic processes and newer treatment options. The latter has been facilitated by technical advances in cardiac catheterization technique and downsizing of implantable devices. In this section, we will focus on the newest diagnostic and treatment modalities for the most common arrhythmias in this age group: Congenital complete AV block, paroxysmal supraventricular tachycardia, and post-operative arrhythmias for congenital heart disease. This section will have a decidedly clinical bias with references to basic science only when appropriate.

Congenital complete AV block

Introduction

Congenital complete AV block occurs approximately once in every 22,000 live births (1). The majority of infants are born to mothers who are ANA positive. Although most mothers are asymptomatic, they may have active systemic lupus erythematosus or Sjogrne’s syndrome (2). There is now strong evidence that transplacental passage of maternal antinuclear antibodies are responsible for direct damage to the developing AV node. Atrioventricular block is most frequently noted starting at 22-24 weeks of gestation. Although these infants may be born with other signs of "congenital lupus", especially rash or cytopenias, they most frequently have no other associated abnormalities.


Congenital complete AV block unassociated with maternal ANA positivity may occur in association with other, usually severe, congenital heart defects. This is most frequently seen with left atrial isomerism ("polysplenia"), or l-TGA. Infants having left atrial isomerism and congenital complete AV block have a very poor prognosis, and hydrops fetalis frequently occurs in the late second or third trimester. The associated congenital heart defects in these infants tend to be on the severe end of the spectrum among those having left atrial isomerism, with complete AV septal defects and common atria.

Diagnostic Methods:

Congenital complete AV block is usually first diagnosed during routine fetal ultrasonography during the second trimester. Careful evaluation will reveal discordance of atrial and ventricular contraction with a faster atrial rate. Discrimination of complete AV block from other bradycardias is critical. Sinus bradycardia is almost always a sign of fetal distress from other causes. Non-conducted atrial bigeminy results in a regular slow ventricular rate and a premature atrial contraction following each conducted atrial contraction. This is generally well tolerated. In addition to rhythm diagnosis, fetal ultrasonography is important to determine the fetus’ well-being. Hydrops fetalis is suggested by the presence of increased skin thickness, acites, pleural effusions, and pericardial effusions. These findings predict a relatively higher likelihood of fetal demise, and, if possible, require early delivery. It is our practice to recommend weekly fetal ultrasounds in mothers whose babies have congenital complete AV block for purposes of determining fetal well-being. In addition, if the mother notices a decrease in fetal movement, this represents an urgent need to re-evaluate the fetus. In general, a fetal ventricular heart rate greater than 60 beats per minute is better tolerated than a slower heart rate, but we have seen exceptions to this observation.

Following birth, electrocardiographic evaluation adds additional information. Key features of this evaluation include the resting ventricular rate and the QRS morphology. It is generally recommended that a resting ventricular rate less than 55 beats per minute or an escape ventricular mechanism having a wide QRS merits early permanent pacing (3). These recommendations are based upon work by Mendelssohn and Engle (3). They noted a higher incidence of Stokes-Adams attacks in the first year of life among babies who had resting heart rates less than 55 at birth. Their additional finding of a P wave rate greater than 160 also representing risk has not been borne out. Among children who did not require pacing at birth, we follow these children at least once per year. At the time of follow-up, a history, physical examination, electrocardiogram, and 24-hour Holter are always obtained. Specific issues include signs or symptoms of congestive heart failure, reduced exercise tolerance, a history of syncope, premature ventricular beats, especially during periods of stress, and pauses greater than three times the prevailing QRS rate. Any of these findings merits serious consideration of permanent pacing. Children who are interested in athletic competition also receive treadmill testing both to determine their maximum ventricular rate as well as to be certain that exercise does not cause premature ventricular beats, a possible sign of myocardial ischemia. Although sophisticated event recorders may have value in these patients, we would view any symptoms of presyncope or syncope as meriting pacemaker implantation. That is, we would not require documentation of extreme bradycardia.

Treatment and Its Indications:

Maternal administration of steroids and plasmapharesis has been reported to be of limited success for fetuses shortly after diagnosis (4), but this has not been substantiated. There has also been limited enthusiasm for maternal administration of IgG and steroids (5) in an effort to forestall the immune damage to the developing conduction system. Finally, animal models have shown that artificial pacing of the fetus by opening the uterus is successful and probably safe. However, this has not gained acceptance for humans due to concerns over risk to the mother.

An infant delivered with hydrops fetalis necessarily requires urgent artificial pacing. If anything, cardiovascular demands increase outside the womb, and the limited heart rate may result in rapid deterioration. Artificial pacing may be provided in the delivery room with external pacing systems for a limited time. Damage to the delicate fetal skin, especially if they are immature, will occur within hours of artificial pacing. More appropriately, temporary transvenous pacing wires as small as 2 French in size may be readily placed from a femoral venous, subclavian venous, or internal jugular venous approach. It is very difficult to direct such a catheter into the right ventricle from the umbilical vein due to the posterior trajectory of this structure. In such an infant, the decision to implant a permanent epicardial pacing system depends upon the infant’s stability and expected tolerance of an opened chest or sub-xiphoid approach.

In summary, artificial pacing of the newborn with congenital complete AV block should be performed in the presence of hydrops fetalis, post-partum signs of congestive heart failure, a resting heart rate less than 55 beats per minute, a wide complex escape rate, or serious co-existing congenital heart defects. If the infant has less serious congenital heart defects, especially atrial septal defect, the intrinsic ventricular rate should be at least 75 beats per minute or else pacing should be considered.

The rate selected when artificially pacing these infants is lower than the normal sinus rate. Anecdotal experience has shown that a picture similar to "tachycardia induced cardiomyopathy" can occur in infants who are paced at too fast a rate. Furthermore, occasional infants have been noted to develop a dilated cardiomyopathy irrespective of pacing rate and mode. Some have speculated that these rare infants may have suffered generalized damage to their myocardium by maternal antibodies. We generally select a heart rate of between 100-120, bringing it down to 90 beats per minute by one year of age.

Indications for pacing the older child were previously described. We believe that all teenagers having congenital heart block should undergo implantation of a dual-chamber pacemaker once they have reached adult size, and certainly by 18 years of age. This is based in large measure upon a long term retrospective review of patients having congenital complete AV block from Uppsala, Sweden, which showed that sudden death may occur even in young adults who were previously asymptomatic (6).

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Supraventricular tachycardia

Introductory Comments and Epidemiology:

Supraventricular tachycardia remains the most common clinically relevant arrhythmia in the young. Fetal SVT is usually the orthodromic form of AV reciprocating tachycardia. Fetal echocardiography demonstrates a regular tachycardia with a 1:1 atrioventricular relationship at a rate of between 260-300 beats per minute. A regular tachycardia which is slower must raise concerns of atrial ectopic tachycardia or atrial flutter with 2:1 AV conduction. These may be discriminated by fetal echocardiography. An important sub-type of orthodromic AV reciprocating tachycardia, "the permanent form of junctional reciprocating tachycardia", may present as an incessant but non-sustained tachycardia, often manifesting as repeated short runs of tachycardia at rates less than 250 beats per minute. Any of these SVT’s may predispose to hydrops fetalis, depending upon their rate and the proportion of the day that the fetus is tachycardic.

The peak age for the presentation of supraventricular tachycardia is the neonatal period. About 90% of the supraventricular tachycardias are the orthodromic form of AV reciprocating tachycardia (7). About two-thirds of these patients have the Wolff-Parkinson-White syndrome when in sinus rhythm, with the remainder having a "concealed accessory pathway". These infants present with respiratory distress, pallor, poor feeding and vomiting, or other signs of low cardiac output. Tragically, neonates who have been in SVT for several days may present with cardiovascular collapse. The usual heart rate of SVT in this age group is 240-300 beats per minute. As many as 10%   of neonates having SVT have atrial ectopic tachycardia (7). This may be discriminated from the orthodromic form of AVRT by the fact that the R-P interval is longer than the P-R interval and by the incessant nature of the tachycardia. The heart rate is typically slower than in orthodromic AVRT, usually between 180-240 beats per minute. Unlike the orthodromic form of AVRT, atrial ectopic tachycardia is greatly influence by autonomic tone with variation in the rate. It is thought that most cases of atrial ectopic tachycardia is caused by an area of abnormal atrial tissue having enhanced automaticity. Common sites for atrial ectopic tachycardia include the orifices of the pulmonary veins in the left atrium and along the crista terminalis in the right atrium; although atrial ectopic tachycardia has been reported from everywhere in the atria, even near the AV node.

A word on Wolff-Parkinson-White and accessory pathways in children is appropriate at this point. As many as 65% of neonates having orthodromic AV reciprocating tachycardia, either caused by a pathway which is at times manifest (as a delta wave), or one that is always concealed, will lose their delta wave and have no further episodes of SVT after one year of age. This observation may be explained by a study which showed that a relatively high percent of infants not having heart disease and dying of unrelated causes, were shown to have accessory AV connections during careful dissection of the annulus fibrosis (8). Infants dying after about nine months of age tended not to demonstrate this finding. Hence, it is likely that infants having neonatal orthodromic AVRT have a reasonably high likelihood of undergoing involution of their accessory pathway by one year of age. Supraventricular tachycardia recurrences after  infancy or first episodes occurring in the later childhood years is far less likely to have a self-limited course (9).

The Wolff-Parkinson-White syndrome usually occurs in the absence of co-existing heart disease. However, a few types of uncommon congenital heart defects have a strikingly high incidence of associated WPW syndrome. About 10% of children having Ebstein’s anomaly of the tricuspid valve have WPW syndrome (10). Their accessory pathways are right freewall or septal and tend to be multiple. They also tend to have relatively slower conduction characteristics than usual accessory pathways. Radiofrequency catheter ablation of these accessory pathways are especially difficult due to the absence of tricuspid valve tissue at the level of the annulus, the overall dilation of the right atrium and atrialized right ventricle, and the tendency towards fractionation of electrograms at the level of the annulus fibrosis. Mapping and successful ablation is better achieved with the use of a very small French mapping electrode catheter in the right coronary artery. There is a higher than expected incidence of Wolff-Parkinson-White syndrome in children born with L-transposition of the great arteries (11). Their accessory pathways tend to be left freewall or septal. Wolff-Parkinson-White syndrome is also thought to be present more frequently in children having d-transposition of the great arteries, tricuspid atresia, and hypertrophic cardiomyopathy. Familial forms have been reported (12), and the genetic basis of this in affected families is being worked out.   Children who are old enough to verbalize their feelings may describe episodes of SVT in a variety of ways: palpitations, chest pain, or their heart "beeping" are among the most common complaints that we see.

Less commonly, children will present with syncope or episodes of fatigue. Starting at about the age of five years, AV node reentry tachycardia becomes an important cause of SVT, but is not as common as the orthodromic form of AVRT until the mid-teenage years.

Although the overall incidence of Wolff-Parkinson-White syndrome in the population has been shown to be 1.5/1,000 (13), the overall incidence of all supraventricular tachycardias is still not known. When SVT occurs, it is at least embarrassing and inconvenient, and, at worse, can be dangerous. However, in the absence of coexisting congenital heart disease, SVT is not thought to pose risk for sudden death in children and in teenagers.

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Diagnosis of SVT

When considering the overall population of young persons having SVT, the presence of Wolff-Parkinson-White syndrome on resting ECG represents the minority of patients. Other than the occasional patient with incessant types of SVT, therefore, most children having SVT will have a normal ECG at routine clinic visit. Because of this fact and because symptoms of SVT may be very nonspecific, documentation of the arrhythmia may require novel diagnostic tools. Twenty-four, 48, or 72-hour Holter monitoring will only be of value for children having intermittent WPW syndrome or very frequent episodes of SVT. These bulky devices are poorly tolerated by most school-age children. A variety of diagnostic ambulatory monitors which are more convenient have been developed to help in this task. Those which may be carried in the pocket (figure 1) or which may be worn like a wristwatch have the advantage of not being obvious to other children and may, therefore, be taken to school. However, they require a certain level of sophistication for proper use by the child, and, in our experience, require that the supraventricular tachycardia be of at least 2-3 minutes duration to permit documentation. Depending upon the maturity level of the child, we generally do not place any responsibility on the child for its proper use if they are under about 10 years of age. Very commonly, a child or caregiver will obtain a rhythm strip shortly after the episode has terminated, creating further confusion when the physician is confronted with little more than sinus tachycardia. While it is typical for children to describe a sudden onset to the tachycardia, when it terminates, they are often in sinus tachycardia due to the period of low blood pressure and discomfort.

 

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Fig.1: An example of a hand-held event recorder which, when placed against the chest and
activated, will record a 30 second rhythm strip. The rhythm is encoded as an audible tone
which is transmitted by telephone to a computer which generates the rhythm strip.

Attached ambulatory event recorders which have a limited "memory" provide the greatest opportunity for accurate documentation of a paroxysmal arrhythmia such as SVT. Although these have been reduced to a very small size, and usually require no more than two attached wires under the child’s clothing, children nevertheless dislike wearing these to school out of fear of being ostracized by their peers. We have found these recorders to be the least accepted by our patients. Only the mature teenager who is sufficiently motivated to obtain an answer (by other than an invasive test) will allow us to place these.

Esophageal electrophysiologic testing has been used for over 15 years in children as a diagnostic tool (14) and to terminate some forms of SVT (15). We have found this technique most useful in children with symptoms compatible with SVT and any of the following additional circumstances: 1) very infrequent but severe episodes in which the patient does not wish to carry an event recorder for many months; 2) in instances of  families who have shown an inability to properly use ambulatory event recorders; and 3) children who refuse to take event recorders to school. We also offer this technique to families whose infants had neonatal SVT, who wish to stop their antiarrhythmic drugs, who are between 12-18 months of age, and in whom the family would like to have some assurance that their infant has "outgrown" their SVT.

Esophageal electrophysiologic testing is an outpatient procedure, but it requires intravenous sedation for patients up to about 14 years of age. Risks of the procedure include those associated with sedation, epistaxis, and risk of laryngospasm if the catheter is placed across the vocal cords inadvertently. Sensitivity of the test is improved with the use of isoproterenol or isoproterenol plus atropine. Over a 10 year period, we have had only one patient later demonstrated to have SVT, who was thought to have a negative esophageal electrophysiologic study. During that patient’s study, however, what was interpreted as a "false-positive" (atrial flutter with 2:1 AV conduction), turned out in fact to be their clinical tachycardia. He had a very rapid AV node reentry tachycardia, which at times had 2:1 intrahisian block. In addition to documentation of SVT, these studies permit discrimination of most cases of orthodromic AV reciprocating tachycardia from the typical variety of AV node reentry tachycardia. In the former, the V-A interval from the esophageal catheter is greater than 70 ms, whereas in typical variety of AV node reentry, it is less than 60 ms. The response of tachycardia to intravenous adenosine and other maneuvers may also be evaluated by this technique.

Exercise testing is generally not sensitive for inducing SVT. However, in children older than about 5-6 years, whose symptoms primarily occur with exercise, a treadmill test is not unreasonable. We have also used exercise testing to evaluate patients having Wolff-Parkinson-White syndrome. Once children reach the late juvenile years, perhaps 8-10 years of age, and especially if they are involved in athletics, it is thought that there may be as much as a 1-2% risk of sudden death, should they experience atrial fibrillation (figure 2). The best means by which this risk can be assessed has been demonstrated to be induction of atrial fibrillation in a controlled environment and measurement of the shortest RR interval between consecutively preexcited beats and the average RR interval. However, most agree that evidence for intermittent preexcitation by Holter monitoring or clear-cut loss of preexcitation during exercise testing may also indicate that the patient’s pathway will not permit a rapid ventricular response to atrial fibrillation.

 

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Fig. 2: A three-lead rhythm strip from a 15 year old boy who suffered syncope while playing
tennis. The rhythm is atrial fibrillation and Wolff-Parkinson-White syndrome. He had a left
lateral accessory pathway which statistically placed him at risk for sudden death,
necessitating radiofrequency catheter ablation.

Indications for and Chronic Treatment of SVT:

Since radiofrequency catheter ablation has become an established option for young persons having supraventricular tachycardia, there is a broader spectrum of treatment philosophies among practicing pediatric cardiologists. In general, institutions having ready access to an individual skilled in catheter ablation of pediatric arrhythmias are more prone to recommend this therapy as primary therapy, whereas cardiologists not having such access are more prone to begin therapy with antiarrhythmic medications. First, it would be useful to discuss which patients deserve therapy of any kind, and this will be discussed in an age-related fashion.

1. Fetal Tachycardia:

Well-controlled trials investigating the need to treat fetuses having supraventricular tachycardia are lacking. It is agreed that the infant showing echocardiographic evidence for hydrops fetalis requires urgent treatment. Quite commonly, however, infants have intermittent episodes of SVT, and the relationship between the percentage of time that a fetus is in SVT and the risk of developing hydrops is complex, and surely much be related to a variety of factors including the rate of the SVT, co-existence of congenital heart defects, and other maternal/placental/fetal interactions. In general, we recommend treatment if the infant is in SVT at least one-third of the day. If the infant appears to be in atrial flutter with 2:1 AV conduction, careful heart rate monitoring is necessary to determine whether there are periods of 1:1 AV conduction. Conversely, the infant having a slower tachycardia, most often representing atrial ectopic tachycardia, may simply bear close watching or antiarrhythmic medications that will slow the rate a bit. There is no advantage in treating a fetus who has spontaneous terminations and re-initiations of SVT with an agent designed to only terminate a single episode. The fundamental principles involved in treatment of fetal SVT involves: 1) selection of drugs which are safe for both the mother and fetus; 2) knowledge of the placental transmission of the antiarrhythmic drug; and 3) ability to monitor the effect of this drug on the mother and on the fetus. Digoxin is considered the safest of the antiarrhythmic drugs, but its efficacy is relatively low. Fetal plasma levels are similar to those of the mother, and due to the large volume of distribution, it may take at least 1.5 mg of digoxin to load the maternal-fetal circulation. This drug is sometimes  efficacious for fetal AVRT, but not for atrial ectopic tachycardia. In both instances, however, it may improve hemodynamics, thus lowering the heart rate slightly. Sotalol appears to be safe during middle and late gestation to both the fetus and the mother. Fetal cord levels are 50-100% of maternal and fetal side effects appear to be less than those from other beta blockers. The maternal ECG must be followed for the QTc interval. Flecainide is equally safe for fetal SVT, and there is the added advantage that maternal blood levels may be monitored in many institutions. Use of this drug requires surveillance of the maternal QRS duration. Due to the large volume of distribution, it is often necessary to administer up to 150 mg every eight hours to the mother. Both of these drugs are more efficacious for SVT and atrial ectopic tachycardia than is digoxin. However, neither are as useful as amiodarone. Unfortunately, there is an increased incidence of premature delivery, small for gestational age birth weight, and hypothyroidism in fetuses exposed to this drug. Although fetal application of this drug using umbilical venous infusion has been reported, its use must be limited to brief periods only. There is the added risk of worsening of congestive heart failure with the use of either sotalol and flecainide in infants already having hydrops fetalis.

2.  Infancy:

Antiarrhythmic drug therapy is considered the treatment of choice for infants having any form of SVT, due to evidence that radiofrequency catheter ablation may pose greater hazards in children less than two years of age (16). Aggressive treatment for SVT is generally thought advisable due to the infants’ inability to convey their feelings should they have SVT recurrences. Despite this, most clinicians only treat for one year, if there are no apparent SVT recurrences. The selection of specific antiarrhythmic drugs is based upon the type of SVT, its response to previous antiarrhythmic drugs, the known risks of the agent, the presence of Wolff-Parkinson-White syndrome, and the presence of co-existing illnesses. In general, unless Wolff-Parkinson-White syndrome is present, digoxin is the first drug chosen. This may be followed by a beta blocker, including sotalol, followed by a Class I-C agent (flecainide and propafenone) or amiodarone. Digoxin may alter conduction characteristics of the accessory pathway in the patient with WPW syndrome, placing them at theoretical risk of ventricular fibrillation should atrial fibrillation occur. The extraordinarily low liklihood of atrial fibrillation in the infant coupled with the not so unusual occurrence of late-onset delta wave manifestation has prompted some pediatric cardiologists to avoid digoxin altogether.

In infants whose SVT is difficult to control, we have found the combination of amiodarone and propafenone or flecainide to be an excellent combination. Based upon experiences with life-threatening proarrhythmia from flecainide (17), we try to eliminate the Class I-C agent as soon as possible. Class IA agents (procainamide and quinidine) have fallen out of favor due to the very large volume of distribution of procainamide and the seemingly high prevalence of proarrhythmia from quinidine. Infants having Wolff-Parkinson-White syndrome are generally treated with a beta blocker, including sotalol, initially, followed by amiodarone, if necessary. Infants whose SVT does not recur beyond the neonatal period, and whose delta wave disappears if they had Wolff-Parkinson-White syndrome, are generally treated for about one year. However, parents must be carefully taught the signs of SVT recurrence. We offer families a diagnostic esophageal electrophysiologic study in the drug free state at about one year of age, to determine whether potential SVT still exist. If it does not, we feel confident that the child may discontinue antiarrhythmic medications. If it is still inducible, we recommend maintaining an antiarrhythmic drug until they are old enough to convey their feelings, usually about three years of age. Neonatal atrial ectopic tachycardia may also "burn itself out", although incessant and untreated atrial ectopic tachycardia will eventually result in a dilated cardiomyopathy (figure 3). This may be monitored in the drug-free state with Holter monitoring. Management decisions are always made more difficult when discontinuing amiodarone, due to its extremely long elimination half-life.

 

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Fig. 3: A rhythm strip from a newborn with atrial ectopic tachycardia and variable
atrioventricular conduction. This eventually resolved without therapy.

3. Children and Teenagers:

The first question the clinician must answer when confronted with the older child or teenager having documented SVT is whether it merits therapy at all. This decision must be based upon a combination of factors, including frequency of episodes, duration of episodes, symptoms associated with the episodes, the dynamics of the family, and the child’s temperament. Although episodes lasting only seconds may seem unimportant to a family, if a child alters his or her lifestyle to prevent situations which he/she believes may start SVT, the SVT is considered a handicapping condition, and should be treated. Although it is true that SVT almost never poses risk of sudden death in a child who has no co-existing heart disease, symptoms of syncope, or angina-like chest pain are very frightening, and generally elicit a greater sense of urgency to treat by patients and their families.

Once the clinician and family have decided that the SVT is of such a magnitude that treatment is indicated, treatment selection must be discussed: antiarrhythmic drugs or catheter ablation. The spectrum of attitudes ranges as follows: the most aggressive cardiologist will generally refer any child outside of infancy who has SVT for potential cure with catheter ablation. At the other end of the spectrum, clinicians will use antiarrhythmic drugs in combination (digoxin, beta blocker, and calcium channel blocker), prior to referral. Only in the presence of a life-threatening condition (children with Wolff-Parkinson-White syndrome who have syncope) does the latter group refer for catheter ablation. Even the least aggressive group rarely selects Class I or Class III antiarrhythmic drugs prior to catheter ablation. In the middle of this spectrum is a large group of clinicians who consider catheter ablation as the first mode of therapy when there are potential contraindications to the use of beta blockers, including children having reactive airway disease, attention deficit disorder, depression, and those who are involved in competitive athletics. Young persons who plan a career in the military, those about to undergo congenital heart surgery, and those who wish to engage in avocations which pose potential risks should they go into SVT (auto racing, scuba diving, and sky diving) almost invariably undergo catheter ablation as first therapy. Wolff-Parkinson-White syndrome poses a special challenge. Since risk assessment for sudden death depends on electrophysiologic measurements, any youngster who is felt to require such risk assessment will generally undergo catheter ablation at the same time. More difficult are those who are asymptomatic, but wish to participate in activities which otherwise are thought to be provocative, especially sports. It is our recommendation that those who have asymptomatic WPW, wish to participate in sports, and reach the age of 10 years merit risk assessment and possible catheter ablation.

Radiofrequency Catheter Ablation:

The efficacy and complication rate of catheter ablation procedures performed in persons 21 years and under in North America have been carefully collected and analyzed in retrospective fashion through the Pediatric Radiofrequency Ablation Registry, under the direction of Dr. John Kugler at the University of Nebraska (16). As of February of 1999, data from over 7,300 procedures in 6,600 patients has been collected and analyzed from 49 centers. These data are from procedures from 1991 to the present. Among these patients, 88% had a structurally normal heart, 12% had congenital heart disease, and 2% had tachycardia and left ventricular dysfunction. Variables which are associated with a successful acute outcome include the presence of a left freewall accessory pathway, the presence of AV node reentry tachycardia, and greater procedure experience by the operator. Associated with acute failure include the presence of co-existing heart disease, an anteroseptal accessory pathway, ventricular tachycardia, or intra-atrial reentry tachycardia. Extremes of patient weight also is associated with a lower likelihood of success. Acute success rates range from 97% for AV node reentry tachycardia and 91% for accessory pathways (figure 4) down to 75% for intra-atrial reentry tachycardia and 68% for ventricular tachycardia. Major complications have occurred in 2.9% of procedures, and include second or third degree AV block, cardiac perforation with effusion, embolization, brachial plexus injury, and pneumothorax.

Complications are associated with patient age less than four years and the presence of an anteroseptal pathway. As expected, risk of AV block is associated with the presence of an anteroseptal pathway, the presence of AV node reentry tachycardia, or smaller size.

 

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Fig. 4: Successful catheter ablation of a right anterior accessory pathway in a 6 year old girl
having medically-resistent SVT. The delta wave is seen to disappear one beat after onset of
radiofrequency energy, with normalization of the QRS morphology

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Postoperative arrythmias

Immediate Postoperative Arrhythmias:

The most important immediate postoperative arrhythmia is junctional tachycardia (JT), also called junctional ectopic or His bundle tachycardia. It generally occurs within 24 hours of congenital heart surgery and has been reported to occur in up to 8% of open heart operations (18).

Cardiac procedures most frequently identified in association with JT are tetralogy of Fallot repair, VSD closure, AVSD repair, repair of total anomalous pulmonary venous return, and following the Fontan operation. JT occurs usually due to transient edema in the bundle of His when the procedure involves suture lines in that area. However, procedures remote from this structure may also cause JT, probably from stretch on the bundle, which may occur with postoperative pulmonary artery hypertension.

Junctional tachycardia has a regular rhythm with a QRS morphology identical to that seen during sinus rhythm. There is often ventriculoatrial dissociation, with the ventricular rate faster than the atrial, and with occasional sinus capture beats. The junctional rate may be only slightly faster than sinus, or may greatly exceed 200 beats per minute. Epicardial wire electrograms may be useful to make the diagnosis. This tachycardia uses an automatic mechanism, and cannot be terminated by atrial or ventricular pacing, or by direct current cardioversion. These maneuvers may result in  brief overdrive suppression which may last a few seconds prior to gradual return to the previous rate and rhythm.

If the patient’s hemodynamic status improves, given time, JT generally resolves. However, most inotropic agents tend to increase the rate of JT. It is usually desirable to reduce the ventricular rate to less than 180 beats per minute in infants and less than 150 beats per minute in older children. Initial therapy includes weaning oxygenous catecholamines and maintenance of normal plasma electrolyte concentrations. Next, combination therapy may be required to reduce the ventricular rate and optimize AV synchrony. Antiarrhythmic drugs which have been demonstrated to be useful to reduce the rate include digoxin, flecainide, propafenone, and procainamide. Most recently, a multi-institution study demonstrated the efficacy of intravenous amiodarone for this arrhythmia (19). In this study, 13/14 patients experienced restoration of sinus rhythm or sufficient slowing to permit atrial pacing. Surface cooling to a rectal or esophageal temperature of 31-34ºC, has also been used to reduce the ventricular rate. Undesirable effects of this method include the need for paralysis, to prevent shivering, metabolic acidosis, and elevation of systemic resistance. Once the rate of JT has been reduced, if AV dyssynchrony is thought to be deleterious, atrial pacing may be employed to achieve AV association using the temporary atrial pacing wires.

Patients refractory to all measures may be considered for transcatheter or surgical His bundle ablation and dual-chamber pacemaker implantation.

Atrial Arrhythmias:

The largest experience with clinically important arrhythmias following atrial surgery has been with Mustard (figure 5) and Senning procedures for d-transposition of the great arteries. Because the arterial switch operation is now the surgical treatment of choice for the congenital heart defect, there are relatively few children suffering from this complication. However, it is estimated that there are still several thousand teenagers and young adults in North America who underwent one of these operations, and who are at risk of developing these arrhythmias. Both operations may result in damage to the sinus node, perinodal structures, and their blood supplies. Depending upon the specific surgical technique, conduction block to the posterior crista terminalis has been demonstrated intraoperatively. The combination of sinus node dysfunction and areas of conduction block in the atria predispose to both severe bradycardia and paroxysmal atrial reentrant tachycardias.

 

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Fig. 5: An illustration of the steps of the Mustard operation. After the right atriotomy (top left),
the atrial septum is largely removed, and the coronary sinus may be incised or otherwise redirected;
followed by placement of a "pant-legs" shaped baffle (right) which directs the caval returns to the
mitral valve and allowing the pulmonary venous returns to enter the tricuspid valve. The upper-most
suture line is most likely to damage the sinus node or its blood supply, and the lower/anterior suture
line may damage the AV node. Last, the right atriotomy is closed (lower).


All variations of the Fontan operation are designed to direct systemic venous return to the pulmonary arteries in patients with a functional single ventricle. With the exception of the most recent surgical technique in which an extra cardiac conduit from the inferior vena cava to the pulmonary arteries is placed, all of these operations result in at least part of the right atrium having a chronically elevated pressure
(figure 6).

 

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Fig. 6: The most commonly performed type of Fontan operation today is the "lateral tunnel",
in which a corridor of lateral right atrium is directed from the inferior vena cava to the superior
vena cava using a an artificial half-tube. Proximal superior caval return to the right pulmonary
artery must be reestablished – having been interrupted at the time of the prior "bidirectional
Glenn operation" (superior vena cava-to-right pulmonary artery). A newer modification of the
"lateral tunnel", requires that the preceding operation, known as the "hemi-Fontan", establish
continuity between the right atrial appendage and the right/main pulmonary artery. In either
instance, damage to the sinus node or its blood supply, conduction block in the crista
terminalis, and hemodynamic factors combine to make atrial brady-/tachyarrhythmias a major
long-term problem.

 

Hence, hemodynamic factors in addition to surgical scars likely account for the atrial tachycardias observed in these patients. Recent animal models have suggested certain technical considerations which may reduce this risk, including avoidance of placing sutures along the crista terminalis.
Finally, intra-atrial reentry tachycardia may occur years following repair of ostium secundum atrial septal defect or partial or total anomalous pulmonary venous return. Sick sinus syndrome may occur following repair of sinus stenosis ASD or certain forms of partial anomalous pulmonary venous return.

Incidence and Natural History:

Following the Mustard operation, there is a progressive decrease in the percentage of patients having sinus rhythm. Gewillig et. al., reported a 2.4% per year loss of sinus rhythm in a series of 249 patients (20). The finding of junctional rhythm was associated with a 2.1-fold increased risk for developing atrial flutter (P<0.05) (figure 7). In those series of at least eight years of mean follow-up following Mustard or Senning surgery, between 5% and 11% of patients had received permanent pacemakers, due to very low heart rates, syncope, or as adjunctive therapy with antiarrhythmic drugs (21-23).

 

fig7a.jpg (32354 bytes)
Fig. 7: Rhythm strips from a 21 year old man who had undergone a Mustard operation. Top
tracing shows atrial flutter ("intraatrial reentry tachycardia") with 2:1 AV conduction. The
bottom tracing shows a junctional rhythm. He suffered from recurrent syncope, most likely due
to spontaneous terminations of atrial flutter with overdrive suppression of his sinus node
followed by long pauses.


Receiving great attention is the known risk of sudden death in these patients ranging from 3% to 5% of patients. In Gewillig’s report, the presence of atrial flutter at routine follow-up increased the risk for sudden death 4.6-fold (p<0.01) (20). The mechanism for sudden death is thought to be 1:1 AV conduction during atrial flutter, resulting in ventricular tachycardia and fibrillation. Other proposed mechanisms of sudden death include prolonged asystole due to overdrive suppression of all subsidiary pacemakers following spontaneous termination of atrial flutter, or primary ventricular tachycardia.
The incidence of atrial tachyarrhythmias has been reported to be 15% to 48% at 8-11 years of follow-up among long term Fontan operation survivors (24-26). Older age, increased right atrial size, and elevated pulmonary artery pressures have been shown to be risk factors for arrhythmia development (p<0.01). Driscoll et. al. found that 20% of 352 patients required antiarrhythmic drugs and/or pacemaker implantation at 5-15 years of follow-up (27). Right atrial stretch, impaired ventricular function, and AV valve insufficiency were thought to be potential causes for "tachy-brady syndrome" (figure 8). The specific surgical technique may relate to long term incidence of atrial brady- or tachycardias. In particular, the "hemi-Fontan procedure" may be especially prone to damage arterial supply to the sinus node, and suture lines placed along the crista terminalis may create conduction block – so necessary for intraatrial reentry tachycardia. In general, it appears that the older atriopulmonary connection has a shorter freedom from atrial tachycardias than does the more contemporary "lateral tunnel" (28).

 

fig8a.jpg (70984 bytes)

Fig. 8: An example of "tachy-brady syndrome" in a 9 year old who had undergone a lateraltunnel type
of Fontan operation at 4 years of age. Demonstrated are brief self-limited runs of atrial flutter,
followed by severe sinus/junctional bradycardia.

It has been found that from 5%-15% of patient require a pacemaker following the modified Fontan operation (24,27). The indications include "tachy-brady syndrome", congenital AV block, or postoperative AV block. The reported incidence of overall late arrhythmic death is 2%-3% (27).
Murphy et. al. reported the natural history of 123 patients who had undergone repair of ostium secundum or sinus venosus ASD’s (29). Late follow-up (27 to 32 years) revealed that the incidence of atrial flutter or fibrillation increased directly with age at repair: 4% of operated on at £ 11 years of age up to 59% if operated on at > 41 years.

Noninvasive Evaluation:

The mainstays of outpatient follow-up following these operations include repeated ECGs, 24-hour Holter monitoring, and exercise testing. In asymptomatic patients, a Holter monitor and exercise test (figure 9) are probably sufficient no more often than every two-to-five years.

fig9a.jpg (43597 bytes)

Fig. 9. A resting 12-lead ECG (top) and 3-lead rhythm strip during a treadmill test (bottom)
from a 32 year old man who had undergone a Mustard operation. He claimed to be asymptomatic,
but as can be seen, he is always in atrial flutter – with high-grade AV block at rest (top)
but 1:1 conduction with exercise (bottom). This patient is at risk for sudden death.

 

However, patients suffering from severe fatigue, syncope, or dizziness at rest or with exercise require immediate testing. If symptoms do not occur during this standard testing, patients may benefit from newer ambulatory electrocardiographic monitoring systems, including portable monitors, attached "loop monitors", and even insertable "loop monitors".

Electrophysiologic Testing:

A variety of abnormalities have been demonstrated during routine electrophysiologic studies following Mustard, Senning, and Fontan operations. Such nonspecific findings include prolongation of the sinus node or pacemaker recovery times (figure 10), intra-atrial conduction delay, and inducibility of intra-atrial reentry tachycardia. Hence, indication to perform electrophysiologic study must be symptom-based, and the results must be interpreted with caution. We recommend electrophysiologic study following atrial surgery in any patient who has developed syncope, severe presyncope, or documented tachycardia other than atrial reentry tachycardia. Even if noninvasive monitoring shows bradycardia as the source for syncope, electrophysiologic study is indicated prior to pacemaker implantation. For example, the AV conduction response to atrial pacing should be assessed, and if there is 1:1 conduction of 120 beats per minute or greater, single-chamber atrial pacing may be all that is necessary. Severe palpitations or syncope may be caused by sinus node reentry tachycardia, atrial ectopic tachycardia, AV node reentry tachycardia, AV reciprocating tachycardia, and ventricular tachycardia. Therapy is dictated by the precise diagnosis.

 

fig10a.jpg (60368 bytes)

Fig. 10: "Sinus node recovery time" is very prolonged from this 4 year old boy who had
undergone a Senning operation. The last two pacing spikes are seen at top at cycle length
310 ms. Although the first sinus escape beat occurs only 890 ms after discontinuation of pacing,
he has subsidiary pauses of > 2 seconds. This kind of testing is no longer performed
routinely, because the indications to implant a pacemaker are based only upon clinical symptoms.

Management:

The recommendations of the American Heart Association and the American College of Cardiology Joint Committee on Pacing as they relate to patients who have undergone atrial surgery are to insert a pacemaker in any patient with: a) symptomatic bradycardia, defined as dizziness, light-headedness, near or frank syncope, or marked exercise intolerance (Class I indication); b) bradycardia with congestive heart failure (Class I indication); or c) in any patient with "tachy-brady syndrome" and a tachyarrhythmia requiring treatment with an antiarrhythmic drug other than digitalis that could suppress the sinus node (Class II indication).

Absent from these recommendations is "extreme" bradycardia, suggested to mean a resting heart rate <50 beats/minute in an infant younger than two years, <40 beats/minute in children aged 2-10 years, and <30 beats/minute in children older than 10 years who have undergone atrial surgery. Most such patients have accompanying episodes of tachycardia or symptoms related to bradycardia, but occasionally a patient will have no other symptoms. There probably are heart rates below which patients are at risk for life-threatening events, but there are scant data to support this. Based upon data that relates the co-existence of tachycardia and bradycardia in these patients, we would consider placing a pacemaker in such a patient in the hope of preventing tachyarrhythmias.

Several authors have described favorable experiences with atrial pacing following Mustard, Senning, or Fontan surgery (30,31). Transvenous pacing systems may be placed in most patients following Senning or Mustard operations (figure 11), including dual-chamber systems if necessary.

 

fig11a.jpg (32442 bytes)

Fig. 11: (Top) Postero-anterior chest radiograph from a 19 year old woman who had undergone a
Mustard operation, had clinical episodes of atrial flutter, and suffered from severe sinus bradycardia
due to treatment with sotalol. A single chamber AAIR pacing system was implanted pervenously and
secured to the base of the left atrial appendage (systemic venous side of the circulation) with an active
fixation lead. (Bottom) 12-lead ECG from that patient demonstrating atrial pacing, intact AV conduction,
and right axis deviation/right ventricular hypertrophy.

 

Transesophageal echocardiography or careful venography must be performed in advance to be certain that there is not an atrial level baffle leak, which may predispose to paradoxical emboli. Following the Fontan operation, patients requiring dual-chamber pacing may require novel approaches to lead placement, including transvenous atrial and epicardial ventricular lead attachments. AV synchrony is important in these patients and ventricular pacing alone, even with rate adaptiveness, may not be acceptable. Transvenous placement of the atrial lead in these patients may be challenging, especially in patients with a narrow corridor of native atrial tissue on the systemic venous side (figure 12). All Fontan patients receiving transvenous leads likely require anticoagulation due to the risk of thrombosis in areas of stagnant flow.

 

fig12a.jpg (19660 bytes)
Fig.12: Posteroanterior (left) and lateral (right) chest radiographs from a 16 year old boy who had
undergone a Fontan-type operation for single left ventricle, atrioventricular septal defect, and
pulmonary atresia ("asplenia syndrome"), and who required atenolol, digoxin, and amiodarone
to control post-operative atrial tachyarrhythmias. This resulted in prohibitive bradycardia but
adequate AV conduction. The intra-atrial baffle included a narrow strip of native atrial tissue
antero-superiorly, permitting active fixation of this lead and AAIR pacing.

Management of tachyarrhythmias following these operations is one of the great challenges in pediatric cardiology. The need for tachycardia conversion following the Mustard or Senning procedure may be controversial because some patients remain asymptomatic in the presence of atrial flutter with high-grade AV block. Patients who present with atrial flutter (with or without symptoms) should undergo transvenous or transesophageal overdrive pacing for termination, or D/C cardioversion. However, unlike adults with atrial flutter and a normal heart, there is growing evidence that atrial flutter in these patients may cause atrial thrombi. Therefore, if atrial flutter has occurred for more than 36 hours, or if the duration of atrial flutter is unknown, it may be prudent to perform a transesophageal echocardiogram. Occasionally, standard methods of cardioversion are unsuccessful, and intracardiac cardioversion may be necessary (32).

Following cardioversion, management to prevent recurrences of intra-atrial reentry tachycardia include pharmacological therapy, anti-tachycardia pacing, radiofrequency catheter ablation, or a combination of the above. Adequate pharmacologic AV nodal suppression with digoxin, a beta blocker, or a calcium channel blocker is necessary to prevent a rapid ventricular response to further episodes of atrial tachycardia. Class III antiarrhythmic agents (currently sotalol or amiodarone) are the most efficacious to prevent tachycardia recurrences.

Implantation of an anti-tachycardia pacemaker may obviate the need for second line drugs, but efficacy and safety of this modality must be demonstrated first during electrophysiologic testing. Acceleration to more dangerous arrhythmias is always a concern using this therapy. Since sudden cardiac death in patients following the Mustard or Senning procedures is most likely linked to tachyarrhythmias, complete arrhythmia suppression is the goal of therapy. Following the Fontan operation, medical suppression of tachyarrhythmias may be exceptionally difficult. The requirements for AV synchrony and adequate diastolic filling time makes arrhythmia control especially crucial. For these challenging patients, combinations of the above modalities may be necessary.

Radiofrequency catheter ablation of areas of the atria crucial to initiation and maintenance of intra-atrial tachycardia is becoming more and more of a possibility. In the few published series, short term clinical improvement or complete ablation of reentrant circuits was achieved in 100% of those who had undergone simple surgical ASD patch closure, in 71% of those who had undergone a Fontan operation, and in 71% of those who had undergone a Mustard or Senning procedure (33-35) (figure 13). Newer electroanatomic mapping systems are expanding the scope of curative ablation techniques. The complexity of these circuits has been made apparent by this technology. Surgical ablation of these circuits has also been reported, using cryo-therapy following preoperative and intraoperative mapping. This technique has been reported in combination with conversion of the atriopulmonary connection to the "lateral tunnel" in a small group of patients.
It is most likely that the best approach in patients undergoing the Fontan operation will include collaboration between the pediatric electrophysiologist and the congenital heart surgeon to devise surgical techniques which prevent the substrate for atrial reentry tachycardia.

fig13a.jpg (47918 bytes)

Fig. 13: Surface and intracardiac channels from a 12 year old boy who had undergone a
Senning operation and who had medically-resistent atrial flutter ("intraatrial
reentry tachycardia") and recurrent syncope. Illustrated is termination of atrial flutter
during radiofrequency energy delivery near the tricuspid annulus after completion
of a linear lesion across the lateral isthmus. The proposed direction of the
tachycardia circuit appears as the inset.

Ventricular Arrhythmias:

Most studies of chronic arrhythmias occurring after ventricular surgery are from patients with tetralogy of Fallot. In general, the less serious the defect, the less serious the outcome. For example, late sudden cardiac death occurs in approximately 0% to 5% of those who have had tetralogy of Fallot repair (36,37), but 18% of those who have had surgery for truncus arteriosus with a single pulmonary artery. This section will consider both postoperative conduction disturbances as well as postoperative ventricular tachyarrhythmias.

Conduction Disturbance:

After repair of tetralogy of Fallot, approximately 80% of patients have complete right bundle branch block, 11% have the combination of right bundle branch block with left axis deviation, and 3% have the combination of both defects plus first degree AV block (36). Early studies in these patients suggested that so-called "tri-fascicular block" were predictors of late sudden cardiac death. More recent experience has found this not to be the case. The incidence of complete AV block following ventricular surgery is higher in patients having l-transposition of the great arteries and VSD and in patients having partial or complete AV septal defects. This is due to the close proximity of the specialized AV conduction system to the rim of the ventricular septal defect.

In the presence of transient postoperative second or third degree AV block (lasting <14 days), 24-hour ECG monitoring should be performed prior to discharge and then regularly. Following ventricular surgery involving the ventricular septum, all patients should have Holter monitoring every five years or so. Second or third degree AV block lasting longer than 14 days mandates implantation of a permanent pacemaker.
Patients who had undergone ventricular surgery but developed syncope or presyncope merit electrophysiologic testing. The cause of syncope may be AV block, ventricular arrhythmias, or, occasionally, atrial flutter with rapid AV conduction. During this study, the observation of type AV block (in the AV node or His bundle) at atrial paced rates below 120 beats per minute or the finding of marked HV interval prolongation (>90 ms) at rest merits implantation of a pacemaker.

Occasionally, patients undergo pacemaker insertion in the postoperative period but regain AV conduction shortly thereafter. Data are not available to predict the risk of recurring AV block. The issue usually comes to bear once their pulse generator reaches depletion parameters and elective replacement is required. In such instances, we would use stringent criteria from 24-hour ECG monitoring and electrophysiologic testing before considering discontinuation of pacing.

Ventricular Arrhythmias:

During long term follow-up of repair of tetralogy of Fallot, ventricular arrhythmias are evident in 5% to 10% of patients on routine ECG, 20% to 40% on treadmill testing, and 40% to 60% on 24-hour Holter monitoring (36,38-40). The mean age at repair in these studies range from 5 to 10 years. The presence and severity of ventricular ectopy was related most frequently to older age at repair, elevation of right ventricular systolic pressure, and longer period of follow-up since surgery. Depressed right ventricular systolic function, elevation of right ventricular end diastolic pressure, duration of cardiopulmonary bypass during repair, and presence of a Potts anastomosis have also correlated with incidence of ventricular arrhythmias in single reports. A modern approach to tetralogy of Fallot is complete repair in infancy. Walsh’s report on 184 late survivors, all of whom had repair before 18 months of age, demonstrated no late deaths caused by arrhythmias and only one patient requiring a pacemaker at mean of 60 months of follow-up (41). In fact, among 41 patient who had 24-hour Holter data, only one had ventricular ectopy >Lown grade I. Repair at an earlier age very likely protects the heart from deleterious changes accrued from long-standing right ventricular hypertension, left ventricular volume overloading, and systemic desaturation.
The relevance of asymptomatic ventricular ectopy following tetralogy repair has been recently challenged in a 12 year follow-up study of 86 patients (42), originally reported in 1980 by Deanfield, et al (40). Of 39 patients believed to have complex ventricular ectopy at original follow-up, only one died suddenly, compared with two from among the group having had infrequent ectopy (p=ns).
The overall incidence of late sudden cardiac death following repair of tetralogy of Fallot ranges from 1.5% to 6% (36,37). All recent reports suggest ventricular arrhythmia to be the etiology of sudden death.

The main goal of routine evaluation of patients following ventricular surgery is to identify individuals who are at risk for symptoms or who are at risk of sudden death from ventricular arrhythmias (figure 14). Patients with both poor hemodynamics, based upon echocardiography or cardiac catheterization, and high-grade ventricular ectopy seem to be at greatest risk. However, there is no diagnostic tests that represents the "goal standard" for determining such risk. Noninvasive tests that have been used include routine ECG, 24-hour Holter monitoring, exercise testing, signal average ECG, and ambulatory event recording. Recent reports have suggested that the QRS duration may be as accurate as any test for predicting patients at risk for either ventricular tachycardia or sudden death following tetralogy repair. A QRS duration >180 ms has had good sensitivity and specificity in reports thusfar (43,44). We recommend a routine ECG, 24-hour Holter, and treadmill exercise test every 2 to 5 years. In patients with poor hemodynamics, our surveillance is stricter, and in those with excellent hemodynamics, less so. Equivocal or minor symptoms may be evaluated with event recorders, but paroxysmal palpitations, syncope, or presyncope merits invasive electrophysiologic testing.

fig14a.jpg (43164 bytes)

Fig. 14: Two 12-lead ECGs from the same 22 year old patient who had undergone repair
of tetralogy of Fallot at 6 years of age and who has recurrent palpitations and near-syncope.
The ECGs illustrate two different ventricular tachycardias. He has been well-controlled with amiodarone.


Older studies investigating the utility of invasive electrophysiologic testing in patients having complex ventricular arrhythmias on Holter have suggested that inducibility of monomorphic ventricular tachycardia is related to all forms of spontaneous ventricular ectopy, whereas polymorphic ventricular tachycardia was related to higher grades of spontaneous ventricular ectopy. Garson et al reported on 488 patients who had repair of tetralogy of Fallot (45). Of the 21 patients with spontaneous ventricular ectopy and no treatment, 33% died, whereas among the 421 patients with no ectopy, there were no deaths. The specificity of the finding of ventricular ectopy by Holter monitoring appears to be low, but may be improved when patients having impaired RV function only are considered. In a more recent study from Boston (46), the mere decision to perform electrophysiologic testing is associated with risk of ventricular tachycardia or sudden death more than any other single factor. The actual results of electrophysiologic testing were not particularly helpful in predicting which patients would have a life-threatening event, however.

Nevertheless, until prospective multi-institution studies are performed, each institution is left to make its own decisions based upon relatively anecdotal data. We recommend invasive electrophysiologic testing following ventricular surgery in patients having sustained palpitations, syncope, or presyncope. The demonstration of symptomatic sustained monomorphic ventricular tachycardia by noninvasive means is an indication for electrophysiologic testing as a guide for antiarrhythmic drug selection. In the absence of symptoms, we would also consider ventricular programmed stimulation if the patient has echocardiographic or catheterization-proven impairment of hemodynamics or marked QRS prolongation plus either Lown grade III ectopy on 24-hour Holter monitoring or high-grade ventricular ectopy during exercise testing. It is expected that the more liberal use of implantable defibrillators in these patients with their ability to document arrhythmias, will help determine the wisdom of this kind of approach.

When considering treatment for ventricular tachycardia following ventricular surgery, the two major concerns are whom to treat and by what means should efficacy be established. Symptomatic ventricular tachycardia requires treatment. Serial electrophysiologic studies have been shown to identify antiarrhythmic drugs that effectively suppress ventricular tachycardia re-inducibility. The positive predictive value of serial drug testing using ventricular programmed stimulation is less well established. The classes of drugs which have been favored in this patient population have included beta blockers, Class I-B agents, and Class III agents (figure 15). The modern approach to these patients, however, is to implant an ICD sooner rather than later, due to the deleterious side effects of drugs.

fig15a.jpg (62624 bytes)

Fig. 15: A continuous rhythm strip from a 14-year old girl who had undergone repair of
tetralogy of Fallot but who had persistently elevated right ventricular pressure due to multiple
peripheral pulmonary artery stenoses. She had been placed on quinidine for asymptomatic
non-sustained ventricular tachycardia by Holter monitoring. Illustrated is monomorphic
ventricular bigeminy, non-sustained monomorphic ventricular tachycardia, and a 4 second
episode of polymorphic ventricular tachycardia (torsade de pointes). The latter was
a proarrhythmic response to the quinidine.

Ablative methods have been reported since 1980. Surgical resection, cryo-ablation, and argon photoablation have all met with variable success. Successful radiofrequency ablation can be performed in patients with stable ventricular tachycardia, and has even been reported in one patient during unstable rapid ventricular tachycardia (47). Pace mapping, the presence of mid-diastolic electrical activity, and concealed entrainment mapping have been of value in these cases. As expected, the right ventriculotomy and/or ventricular septal defect patch represented the region of conduction block allowing macroreentry ventricular tachycardia.

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