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Non-cardioplegic coronary surgery in patients with poor left ventricular function

Antunes Manuel ; Antunes Pedro; Ferrão de Oliveira José

Cardiothoracic Surgery, University Hospital
Coimbra, Portugal

Abstract
Introduction
Material and Methods
Results
Discussion
Conclusions

Abstract
Objectives: This study evaluates the perioperative mortality and morbidity in patients with severe left ventricular dysfunction submitted to CABG using non-cardioplegic methods.
Methods: Between April 1990 and December 1997, 3180 patients were consecutively subjected to isolated CABG using non-cardioplegic methods for construction of the distal anastomoses. This prospective study is based on the 107 (3.5%) patients with severe impairment of the left ventricular function (ejection fraction < 30%). Intermittent aortic cross-clamping was used in 17 patients, until June 1992, and ventricular fibrillation in 90 patients. The mean age at operation was 57.0 ± 9.2 years and 95.3% of patients were male. Fifty three patients (49.5%) were in CCS class III / IV and 12 (11.2%) were subjected to urgent surgery. A history of previous myocardial infarction was recorded in 99 (92.5%) patients. Ninety seven (90.6%) patients had triple vessel and 17 (15.9%) left main stem disease, and 77 (71.9%) had a left ventricular end-diastolic pressure > 20 mmHg. Cardiopulmonary bypass time was 73.1 ± 21.7 min. The mean number of grafts per patient was 3.2 and at least one internal mammary artery was used in all cases (1.2 arterial grafts/patient). Endarterectomies were performed in 23 (21.5%) patients. Results: Perioperative mortality was 2.8% (respiratory-1; cardiac-2). The incidence of myocardial infarction was 2.4%. Forty one (38.3%) patients required inotropes, but for longer than 24 hours in only 12 (11.2%), two (1.9%) intra-aortic counterpulsation and three (2.8%) left ventricular assiste device. Two (2.4%) patients had reintervention for hemorrhage and another five (4.6%) for sternal complications. The incidences of supra-ventricular arrhythmias, renal failure and cerebrovascular accident were 17.0%, 3.6%, and 2.4%, respectively. The mean hospital stay was 9.3 ± 6.4 days.
Conclusion: These results appear to demonstrate that non-cardioplegic methods afford good myocardial protection and operating conditions with excellent applicability, even in patients with severe left ventricular dysfunction.

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Introduction:

There is no consensus as to the optimal method of myocardial protection during CABG. Although most surgeons use cardioplegia for myocardial protection in any of its numerous variations during CABG, some still use noncardioplegic methods. These include intermittent aortic cross-clamping and ventricular fibrillation with local control of coronary blood flow. The safety and efficacy of noncardioplegic methods have been demonstrated during elective primary and reoperative CABG, as well as in higher risk patients, and are further endorsed by some prospective randomised clinical trials. In this paper, we report the experience that we have obtained with these methods in 107 patients with severe left ventricular dysfunction.

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Material and Methods:

Patients data. Between April 1990 and December 1997, 3,180 patients were consecutively subjected to isolated CABG using noncardioplegic methods, i.e., intermittent aortic cross-clamping (initial 540 patients) or ventricular fibrillation (last consecutive 2,640 patients). This prospective study is based on the 107 (3.4%) patients with severe impairment of the left ventricular function, i. e., with an ejection fraction of less than 30% (range 14% to 29%). All patients had angina or demonstrable ischemia and significant lesions in bypassable vessels. Preoperative clinical and angiographic data are summarised in table I. Mean age at operation was 57.0 ± 9.2 years and 95.3% of the patients were male. Ninety five patients (88.8%) underwent elective and twelve (11.2%) urgent operations. As to the extent and severity of the coronary disease, 97 patients (90.6%) had triple and 10 (9.4%) double vessel disease, and 17 (15.9%) had left main disease. A left ventricular end-diastolic pressure > 20 mmHg was observed in 77 patients (71.9%).
Surgical technique. Cardiopulmonary bypass was conducted with nonpulsatile flow and mild hypothermia (32ºC). On cardiopulmonary bypass the systemic perfusion pressure was electively maintained at 55-65 mmHg. A left ventricular vent was always used, introduced through the right superior pulmonary vein into the left atrium. Ventricular fibrillation without clamping was used for construction of the distal anastomoses.
Control of the residual and/or collateral blood flow was achieved by a variety of methods. Commonly, we could obtain a dry field with the use of the coronary occluders and a soft jet of oxygen. Occasionally ,however, we would also slow down the pump flow transiently or, if necessary, even cross-clamp the aorta. Currently, all distal anastomosis are constructed first, followed by all proximal anastomoses in a single partial clamping period during which the heart is defibrillated and allowed to beat. The proximal anastomoses of free arterial grafts were usually constructed over the aortic anastomosis of a venous graft.
Bloodless prime was used in more than 90% of the cases and blood was not given unless the haematocrit dropped bellow 25% during cardiopulmonary bypass. Patients were actively vasodilated, both during and after the procedure to keep the mean arterial blood pressure at 55-65 mmHg, for cardiac outputs at normal or above normal levels.

Table I

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Results:

Internal mammary grafts were used in all patients, including 16 (14.9%) in whom both left and right internal mammary arteries were used, for a total of 132 arterial anastomoses (1.2 per patient). Additionally, 208 venous anastomoses (1.9 per patient) were constructed. Hence, an average of 3.1 coronary artery branches were bypassed per patient. Endarterectomies were performed in 23 patients (21.5%), 18 of the right and 5 of the left coronary system. In the intermittent aortic crossclamp group (17 patients) the average crossclamp time per graft was 6.4 min., adding to a global clamp time of 19.9 ± 9.1 min (range 7 - 34 min). The cardiopulmonary bypass time for all patients was 73.0 ± 21.7 min (range 39 -147 min) (table II).

Tabla II

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Mortality. There were three (2.8%) perioperative deaths. The first patient was a 67-year old man who died of respiratory failure on the 33rd postoperative day. The second was a 44-year old man who died of acute cardiac failure on the 3rd postoperative day. The third was a 46-year old man who developed severe bilateral pneumonia and acute mediastinitis and died of chronic cardiac failure on day 67th postoperative. Because there were only 3 deaths, predictors of operative mortality could not be derived from the current series.
Morbidity. Forty one patients (38.3%) required inotropic support (defined as the use of any inotropic agent after the patient left the operating room), but for longer than 24 hours in only 12 cases (11.2%). An intra-aortic ballon was used in two patients (1.9%) to assist weaning from cardiopulmonary bypass, including that which had already been inserted preoperatively. There were ECG criteria of perioperative myocardial infarction in three patients (2.8%). Two patients (1.9%) were returned to the operating room because of haemorrhage and five (4.6%) had reoperation for sternal complications, including 3 with the diagnosis of acute mediastinitis (presence of pus or bacterial growth in the mediastinal tissues sampled during surgical reexploration). Supraventricular arrhythmias necessitating medical and/or electrical treatment occurred in 18 patients (16.8%). One patient (0.9%) had an episode of ventricular fibrillation, and 3 (2.8%) transient complete AV block. Four patients (3.6%) developed acute renal failure (creatinine > 2.5 mg/dl) that did not require dialysis. Three patients (2.8%) had a cerebrovascular accident and another 3 delirium.

Table III

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Discussion:

An unlimited number of reports dealing with cardioplegia in any of its numerous variations showed unequivocally that cardioplegia affords good protection to the myocardium. However, this does not mean that noncardioplegic methods, which are still used by some, result in a lesser protection. The safety and efficacy of these methods have been demonstrated in primary and reoperative CABG as well in higher risk patients. In fact, three recent prospective randomised clinical trials (Gerola et al.,1993; Anderson et al.,1994; and Musumeci et al.,1998) have demonstrated that intermittent aortic cross-clamping provides equivalent, if not better protection than blood cardioplegia. There is also some evidence that noncardioplegic methods preserve LV diastolic function better. In a recent comparative study conducted in patients subjected to elective CABG, Casthely et al. (1997) found that impairment in LV diastolic function in the immediate perioperative period was minimal when ventricular fibrillation and intermittent cross-clamping was used, while it was highly significant when retrograde and anterograde blood cardioplegia were used.
We now prefer noncardioplegic methods, not only because they are safe and efficient but also because they are more versatile and allow greater operative flexibility. Since the middle of 1992, we have been using ventricular fibrillation, without aortic occlusion, with success for primary and reoperative CABG, as well as for resection of left ventricular aneurysms and for closure of ischemic ventricular septal defects. Supported by some experimental animal works, Akins (1992) advised the maintenance of an aortic root pressure of 80 to 100 mmHg. Based on our own clinical experience, we believe that a perfusion pressure around 60 - 65 mmHg is safe to maintain an adequate perfusion gradient across the coronary vascular bed and good subendocardial perfusion, even in hypertrophied hearts. Additionally, active peripheral vasodilatation, improves tissue perfusion and decreases the afterload when the heart beating is resumed. We have found that with this policy the requirement for inotropic support was markedly reduced.

Although the number of patients included is limited, a major relevance of this report lies in that it includes all cases with severe LV dysfunction who underwent CABG during an 8-year period in one department, all operated on by one surgeon (MA). On the other hand, and in the absence of other secure indicators of myocardial lesion, clinical performance is an acceptable way of assessing the adequacy of the myocardial protection, and this may be particularly true in this group of patients with severe left ventricular dysfunction.
Although this study was not designed to compare different techniques of myocardial protection, the perioperative clinical results provide suitable hard points to allow comparison with other series. Table IV summarises studies of CABG performed with cardioplegic techniques in patients with severe LV dysfunction published since 1990. The operative mortality ranged from 4.8% to 15.0%. Our perioperative mortality of 2.8% compares favourably with these, even considering that some of the studies were conducted in patients with an ejection fraction of 20% or less.
As occurred with other studies, we have had a higher (38.3%) requirement for inotropic support than in our patients without LV dysfunction (7.6%), although only 11.2% of the patients required it for longer than 24 hours. Besides the LV dysfunction, per se, one additional possible reason for this difference may be related to the fact that in this group of patients we may have had a greater tendency for "prophylactic" use of inotropic agents. By contrast, we report a much lower use of IABP. The incidence of perioperative myocardial infarction, which is also a good clinical indicator of myocardial protection, was 2.8% in our series, which compares favourably with those of some other studies. Finally, the low incidence of other causes of morbidity, as well as the mean time of hospital stay ( 9.3 ± 6.4 days), also constitute good clinical benchmarks for a relatively smooth perioperative period and, presumably, are an index of good myocardial performance.

Table IV

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Conclusions:

Our results appear to demonstrate that noncardioplegic methods afford good myocardial protection and operating conditions, even in patients with severe left ventricular dysfunction. They are very useful alternative techniques and should be known to everyone who does coronary surgery.

 

Questions, contributions and commentaries to the Authors: send an e-mail message (up to 15 lines, without attachments) to surgery-pcvc@pcvc.sminter.com.ar , written either in English, Spanish, or Portuguese.

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Update
Nov/13/1999