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Technicians in Cardiology

Case Study #1, #2, #3

Mark Sweesy

Case Study 1
Case Study 2
Case Study 3
Answers and Discussion

Case Study 1

History: A 70 year old male was implanted with a DDDR pacemaker for high grade A-V block. At his 2 week follow-up, intermittent loss of ventricular capture was noted. The ventricular output was then programmed to 7.5 V & 1.0 ms PW and the patient was hospitalized for a ventricular lead repositioning. At the 2 week follow-up post-implant the patient presented with the following telemetry information, ECG Strip #1 and EGM #1.

Programmed Information

Mode DDDC Polarity Bipolar
Rate 60 ppm V. Amp. 7.5V
A-V 275 ms V. P.W. 1.0 ms
P-V 175 ms V. Sens. 2.0 mV
Max Track 100 ppm A. Amp. 5.0 V
V. Ref. 250 ms A. P.W. 0.6 ms
A. Ref. 275 ms A. Sens. 0.5 mV

ECG Strip #1
 

EGM Strip #1

Case #1: ECG Analysis and Questions 

1. What do you think is the cause of pacing at the upper rate based on the preliminary information?

A. normal sinus tracking
B. farfield oversensing
C. atrial fibrillation
D. pacemaker mediated tachycardia

 

2. What next step could be utilized to unravel the mystery?

A. program to DVIC mode at a low rate
B. increase the upper rate
C. perform an atrial electrogram without pacing
D. any or all of the above

Additional History: The arrow on ECG Strip #2 is the point at which the atrial sensitivity was programmed from 0.5 to 1.0 mV. The arrow on ECG Strip #3 shows where the sensitivity was programmed back to 0.5 mV. The arrow on ECG Strip #4 demonstrates the point at which the ventricular output was programmed from 7.5 to 6.0 V. The patient's new ventricular threshold post lead-repositioning measured 1.5 V & 0.20 ms PW at two weeks.

ECG Strip #2

ECG Strip #3

ECG Strip #4

Additional History: Increasing the upper rate to 120 ppm resulted in faster pacing (ECG Strip #5). EGM #2 (atrial) was obtained at an atrial sensitivity of 1.0 mV.

ECG Strip #5

EGM Strip #2

Case #1: ECG Analysis and Questions:

3. What is the patient's underlying intrinsic atrial rate as determined from the EGM Strip #2 with an effective paced rate of 30 ppm?

A. 71 ppm
B. 95 ppm
C. 136 ppm
D. 167 ppm

 

4. The markers with EGM Strip #2 indicate?

A. normal pacemaker function
B. loss of atrial capture
C. loss of atrial sensing
D. loss of ventricular capture

 

5. What would you now diagnose as the reason for the upper rate pacing?

A. normal sinus tachycardia
B. farfield oversensing
C. atrial fibrillation
D. pacemaker mediated tachycardia

 

6. How large is the signal that is being tracked by the ventricle in EGM Strip #2?

A. 0.5 mV
B. 1.0 mV
C. 1.5 mV
D. 2.0 mV

 

7. What would be the best way to program out of the problem?

A. decrease the atrial sensitivity
B. increase the ventricular blanking period
C. decrease the ventricular output
D. increase the atrial alert period

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Case Study 2

History: A 67 year old male had a DDDR pacemaker implanted for complete heart block. For 6 days, the patient complained of intermittent fatigue and shortness of breath. Upon arrival at the follow-up clinic, the following telemetries, ECGs, and EGMs were taken.

Programmed Telemetries, ECGs and EGMs

 

ECG Strip #1

EGM Strip #1

Telemetry Strip #2

ECG Strip #2

EGM Strip #2

Case #2: ECG Analysis and Questions

1. Based on the findings from the initial ECG Strip #1 and EGM Strip #1, what is the cause of this patient's accelerated rate?

A. sensor driven pacing
B. PMT
C. balanced endless-loop tachycardia
D. tracking atrial tachyarrhythmia

 

2. What is the most valuable tool for assessing this patient's problem?

A. atrial EGM
B. ventricular EGM
C. surface ECG
D. chest X-ray

 

3. What explains the AV interval noted on the initial atrial EGM Strip #1?

A. safety pacing
B. crosstalk
C. rate adaptive AV delay
D. magnet application

 

4. What programmed parameter could be changed to alleviate this problem?

A. sensed AV delay
B. atrial output
C. mode switching
D. rate smoothing
E. PMT termination algorithm

 

5. Which diagnostic functions could be utilized to evaluate frequency of these episodes?

A. rate response optimization episodes and high atrial rate histogram
B. high atrial rate histogram and mode switch episode
C. rate vs. time trend and percent total event summary
D. mode switch episode and AV conduction histogram

 

6. If the patient develops this arrhythmia frequently, what mode could best be utilized?

A. VVIR
B. AAIR
C. DVIR
D. DDIR

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Case Study 3

History: An 80 year-old female with history of sick sinus syndrome and atrial flutter is admitted through the Emergency Room due to unresponsiveness and bradycardia. The patient had a VVI permanent pacemaker insertion 6 years ago for symptomatic bradyarrhythmia. The patient also had an episode of atrial fibrillation and flutter requiring admission one month ago. At that time the patient was found to have asymptomatic atrial flutter with 2:1 AV conduction and was placed on digoxin and rythmol with subsequent conversion to sinus rhythm. The patient was found by EMS in the bathroom without a pulse. The patient was given atropine without response. Subsequently, the pulse was found to be about 35-40 bpm and the patient was placed on a transthoracic pacemaker at rate of 80 ppm. On arrival to the Emergency Room her blood pressure was 98/70, pulse was paced at 60 ppm by the transthoracic pacemaker and the respiratory rate 16.

Current medications include: Rythmol (150mg po qd); Calan SR (120 mg po q am).; Coumadin (2.5 mg po q day); Lanoxin (0.125 mg Monday, Wednesday and Friday); Xanax and Darvocet (prn).

Laboratory Data: Hemoglobin 10, WBC 13.2, CK 45, Sodium 156, Potassium 7.3, Chloride 104, Carbon Dioxide 22.2, Glucose 289, BUN 37, Creatinine 2.6, Digoxin 2.3, PT 16.3

Mode VVIC
Rate 70 ppm
Pulse Width 0.60 ms
Amplitude 2.7 VMode
Sensitivity 3.0 mV


Case #3: ECG Analysis and Questions

1. What problem is recorded in ECG strip #1 during magnet application?

A. oversensing
B. battery failure
C. isoelectric beats
D. intermittent capture

 

2. What is considered to be the normal range of Potassium in mEq/L?

A. 1.5-3.5
B. 3.5-5.5
C. 5.5-7.5
D. 7.5-9.5

 

3. What is the most likely cause of the loss of capture in this pacing system ?

A. electrolyte imbalance
B. hyperkalemia
C. exit block
D. all of the above

 

4. What is the first step that should be taken to restore normal pacemaker function?

A. program to asynchronous operation
B. return to nominal parameters
C. increase output to maximum
D. reposition lead

 

5. Knowing that the stimulation threshold at the previous follow-up was 2.7 V & 0.2 ms PW with a charge of 1.1 microcoulombs (uC). What can be said of the present settings of 2.7 V & 0.6 ms PW and 3.9 uC?

A. adequate for acute phase
B. adequate for chronic phase
C. inadequate in terms of charge for chronic phase
D. adequate in terms of charge for acute phase

 

6. What can be said of the rhythm in ECG Strip #2?

A. normal capture and sensing
B. intermittent capture and normal sensing
C. intermittent capture and sensing
D. normal hysteresis function

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Answers and Discussion for Case Studies with References.

Case Study 1. Overall References: Furman, et al. (Chapters 3); Schurig, et al., 2nd ed. (Chapters 5, 8, 19)

1. C. atrial fibrillation
Discussion: This is an opinion question but the first thought was atrial fibrillation since it is difficult to observe P-waves. References: Furman (182; 438)

2. D. any or all of the above
Discussion: All of the above could be helpful as will be shown.

3. A. 71 ppm
Discussion: The atrial rate measures 71 ppm on the A IEGM scale. The smaller signals are the P-waves on the electrogram with the larger signals being farfield R-waves as marked. References: Furman (108-119)

4. C. loss of atrial sensing
Discussion: The markers only identify R-waves due to the loss of atrial sensing once the pacemaker was programmed from .5 to 1.0 mV atrial sensitivity. References: Furman (319-321)

5. B. farfield oversensing
Discussion: Farfield oversensing now has the most evidence as the problem source. Reducing the ventricular output from 7.5 to 6.0 V was the best clue. Although farfield afterpotential sensing is rare in bipolar systems, the ventricular output was programmed extremely high at 7.5 V & 1.0 ms pulse width in this scenario. When troubleshooting, always evaluate the programmed settings and take note of any settings out of the ordinary. References: Furman (41-42; 92)

6. A. 0.5 mV
Discussion: The fact that the tracking stopped when the sensitivity was programmed from 0.5 to 1.0 mV as seen on the ECG demonstrates that the farfield signal is only in the 0.5 mV range as seen by the atrial sensing circuit. References: Furman (41-42; 92)

7. C. decrease the ventricular output
Discussion: Decreasing the atrial sensitivity would correct the farfield over-sensing problem but would also result in a loss of atrial sensing as evidenced on EGM #1. Increasing the ventricular blanking would not help as this is an atrial oversensing problem and creating more atrial alertness may accentuate the problem. Although, we are still in the acute phase of lead maturation and the ventricular threshold may yet rise, the stimulation threshold is very good (1.5 V & 0.20 ms PW). This would allow one to reduce the ventricular output significantly, yet maintain an adequate safety margin. References: Furman (321-323)

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Case Study 2. Overall References: Furman, et al. (Chapters 3, 4); Ellenbogen, 2nd ed. (Chapter 6).

1. D. tracking atrial tachyarrhythmia
Discussion: By looking at the initial information, it is apparent this patient is tracking an abnormally fast atrial rate interval of 280 ms (214 bpm). Note: every other atrial depolarization is not tracked as it occurs in the post ventricular atrial refractory period. References: Furman (136-141)

2. A. atrial EGM
Discussion: This atrial EGM is a real-time intracardiac recording which is accompanied by marker channels. Utilizing this tool, one is able to observe what the pacemaker is seeing, which helps to understand its function. References: Furman (89-95)

3. C. rate adaptive AV delay
Discussion: Rate adaptative AV delay is turned on in this patient with a minimal sensed AV delay of 30 ms. It has been demonstrated that rate adaptive AV delay maintains the physiological relationship between the atria and ventricle at higher rates. References: Ellenbogen (301-304)

4. C. mode switching
Discussion: Mode switching is a programmmable feature created to prevent the undesireable tracking of paroxysmal atrial tachycardias. In this patient, mode switching from DDDR to DDIR, which is a non-tracking mode, limits the ventricular response. References: (Furman 179-185)

5. B. high atrial rate histogram and mode switch episode
Discussion: High atrial rate histogram is a diagnostic function that could be utilized to show the number of atrial tachycardias occuring. The mode switch episode is another diagnostic tool that collects heart rate data useful for diagnosing the frequency of atrial tachycardias. References: Ellenbogen (439-443)

6. D. DDIR
Discussion: The DDIR mode is useful for frequent yet not chronic atrial tachyarrhythmias. This mode prevents atrial competition as well as eliminates atrial tracking which can result in unwanted tachycardias. References: Furman (182-183)

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Case Study 3. Overall Referrences: Furman, et al. (Chapters 2, 18)

1. D. intermittent capture
Discussion: Loss of capture is the problem. Nonsensing is also present but secondary to the VOO mode due to magnet application. One must be cautious about evaluating capture during magnet application in light of intrinsic refractoriness of the tissue, however, the second to the last paced complex is clearly beyond the expected time of tissue refractoriness. References: Furman (732).

2. B. 3.5-5.5
Discussion: The normal range of Potassium in mEq/L is 3.5-5.3 This is listed at the bottom of all blood testing lab results. References: Furman (678).

3. B. hyperkalemia
Discussion: Furman states that whenever the serum level exceeds 7.0mEq/L there will almost always be an increase in pacing threshold. References: Furman (678).

4. C. increase to maximum output
Discussion: Ultimately electrolyte imbalance needs to be addressed, however, in the mean time increasing the output to maximum should at least be attempted as a temporary solution.

5. B. adequate for chronic phase
Discussion: Double the charge at threshold or triple the pulse width provided the pulse width is 0.3 ms or less. Doubling the voltage or tripling the pulse width will provide a safety margin in terms of charge that is 100% of charge at threshold. References: Furman (60-62).

6. A. normal capture and sensing. References: Furman (145, Figure 10).

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References

Ellenbogen KA, ed. Cardiac Pacing, 2nd ed. Cambridge, MA: Blackwell Science, 1996.
Ellenbogen KA, Kay GN, Wilkoff BL, eds. Clinical Cardiac Pacing. Philadelphia, PA: W.B. Saunders Co., 1995
Estes NAM, Manolis AS, Wang PJ, eds. Implantable Cardioverter-Defibrillators. A Comprehensive Textbook. New York, NY: Marcel Dekker, Inc., 1994.
Forney RC, Sweesy MW, Seckinger BD, Talbott JP, Batey RL. Emergency back-up and special feature activation. (abstract) Eur J Cardiac Pacing Electrophysiol 1994; 4(2), Suppl 4:100.
Furman SF, Hayes DL, Holmes DR Jr. A Practice of Cardiac Pacing, 3rd ed. Mt. Kisco, NY: Futura Publishing Co., 1993.
Hayes DL, Maue-Dickson W, Stanton MS. Dictionary of Cardiac Pacing, Electrophysiology and Arrhythmias. Miami Lakes, Fl: Peritus Corp., 1993.
Hayes DL, Graham KJ, Irwin M, Vidallet H, Disler G, Sweesy M, Kincaid D, Osborn MJ, Suman VJ, Neubauer SA, Seebandt M, Kallinen L. Multicenter experience with a bipolar tined polyurethane ventricular lead. PACE 1995; 18 (Part I):999-1004.
Klementowicz P, Ausubel K and Furman S. The dynamic nature of ventriculoatrial conduction. PACE 1986; 9:1050-1054.
Schurig L, ed. Educational Guidelines. Pacing and Electrophysiology. Armonk, NY: Futura Publishing Co., 1994.
Sulke N, Dristas A, Chambers J, et al. Is accurate rate response necessary? PACE 1990;1031-1043).
Sweesy MW, Batey RL, Forney RC. Activation times for "emergency back-up" programs. PACE 1990; 13(10):1224-1227.
Sweesy MW, Forney CC, Hayes DL, Batey RL, Forney RC. Evaluation of an in-line bipolar polyurethane ventricular pacing lead. PACE 1992; 15:1982-1985.

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Update
14/Mar/2000