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J Thorac Cardiovasc Surg 1998;116:74-78
© 1998 Mosby, Inc.

Surgery For Adult Cardiovascular Disease

The increased need for a permanent pacemaker after reoperative cardiac surgery

From the Division of Cardiac and Thoracic Surgery, Henry Ford Hospital, Detroit, Mich.

Received for publication Dec. 24, 1996. Revisions requested Feb. 20, 1997; revisions received Feb. 13, 1998. Accepted for publication Feb. 13, 1998. Address for reprints: Joseph W. Lewis, Jr., MD, Division of Cardiac and Thoracic Surgery, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202.

	Abstract

Top Abstract Introduction Patients and methods Results Discussion References

 
Objective: The requirement for permanent pacemaker implantation after most initial cardiac surgical procedures generally is less than 3%. To identify the incidence and factors related to permanent pacemaker need after repeat cardiac surgery, we retrospectively studied 558 consecutive patients undergoing at least one repeat cardiac operation.
Method: Univariable and multivariable analyses of comorbidity, preoperative catheterization values, and operative data were performed to identify factors related to pacemaker implantation.
Results: In this group, 54 patients (9.7%) required a permanent pacemaker. A multivariable model showed a relationship between a permanent pacemaker and tricuspid valve replacement/annuloplasty associated with aortic/mitral valve replacement, preoperative endocarditis, increasing number of reoperations, the degree of hypothermia during cardiopulmonary bypass, and advanced age. Additional univariable predictors of pacemaker need included multiple valve replacement, increased cardiopulmonary bypass and aortic crossclamp times, and aortic valve replacement. Over 90% of patients who have or have not received permanent pacemaker implantation were in New York Heart Association class I to II, with a mean follow-up time of 6 years. Kaplan-Meier survival curves were statistically similar for both groups at 5 and 10 years after the operation.
Conclusion: Permanent pacemaker implantation was required in 9.7% of patients undergoing repeat cardiac surgery. This represented approximately a fourfold increase compared with similar primary operations reported in other series. Factors strongly related to this need included valve replacement, preoperative endocarditis, number of reoperations, advanced age, and degree of hypothermia during cardiopulmonary bypass. The need for a permanent pacemaker after reoperations did not result in significant long-term impairment of functional status or longevity compared with those who did not require a permanent pacemaker.

	Introduction

Top Abstract Introduction Patients and methods Results Discussion References

 
In a literature review of 24,729 predominantly first-time cardiac surgical procedures, ^1-21 the need for postoperative permanent pacemaker implantation (PPI) was 2.2%. For isolated coronary artery bypass grafting, 37 of 4596 patients (0.8%) required PPI. PPI was performed in 98 of 2800 (3.5%) valve replacements, 132 of 6004 (2.2%) congenital heart defect repairs, and 13 of 118 (11.0%) orthotopic heart transplantations. To define the incidence and factors relating to PPI after reoperative cardiac surgical procedures, we studied 558 consecutive patients who did receive a permanent pacemaker and who were undergoing at least one repeat operation.

	Patients and methods

Top Abstract Introduction Patients and methods Results Discussion References

 
A retrospective analysis of patients requiring repeat cardiac surgical procedures between March 1976 and December 1991 was conducted. All patients receiving PPI were included in the PPI group irrespective of their survival status. Those patients with self-limiting bradyarrhythmias that required only temporary pacing were placed in the nonpaced cohort. The remote cutoff date of 1976 was chosen because cardioplegic arrest of the heart was introduced at this institution at that time. Although multiple surgeons participated in the care of this group, surgical methods remained remarkably constant during the study period. Pericardial reentry was achieved by median sternotomy; cardiopulmonary bypass was performed with a membrane oxygenator with a crystalloid prime in most instances. Cold crystalloid cardioplegia (10° C) was used during aortic crossclamping in most of the patients. The degree of systemic cooling during perfusion varied among surgeons. Before cardiopulmonary bypass was discontinued, temporary atrial and ventricular pacing wires were placed in most patients with a sinus mechanism. Those with atrial fibrillation received ventricular leads only. Permanent screw-in epicardial leads were used in those patients with tricuspid procedures or suspected conduction injury during complicated valve reoperations. In this setting, temporary pacing in the immediate perioperative period was accomplished through disposable transcutaneous wires linked to the permanent electrode. Complete heart block or bradyarrhythmias with ventricular rates below 45 to 50 beats/min persisting 7 to 10 days after the operation received permanent pacemakers. Patients were seen in the Pacemaker Clinic 1 week, 1 month, and 3 months after discharge; thereafter, patients were examined every 6 months. Those patients with no R waves when briefly paced VVI at 30 beats/min were considered pacemaker dependent; they were seen every 3 months. Evaluation at each visit included interrogation of the programmed parameters, telemetry data, and event counters. After the underlying rhythm had been documented, sensing and stimulation thresholds were measured and final settings were programmed according to Pacemaker Clinic guidelines. In addition, transtelephonic monitoring was conducted every 2 months until the generator reached month 36 of service. Thereafter, transtelephonic monitoring was done on a monthly basis until the generator was replaced. Numeric data generated by PPI and nonpaced groups were compared by a two-sample unpaired t test. Because of the large number of variables examined, a statistical significance was achieved at p  < 0.01. Categoric data were analyzed by the ² test of association. Survival information for the two groups was compared by Kaplan-Meier curves with the log-rank test. Possible factors related to the need for PPI with p < 0.20 from univariable comparisons were entered into a stepwise multivariable logistic regression analysis. Variables examined included age, sex, number, type and currency of reoperations, preoperative conduction disturbances, preoperative catheterization values, presence of mitral annular calcification, preoperative New York Heart Association (NYHA) class, number of bypass grafts performed, hypertension or diabetes mellitus, preoperative prosthetic endocarditis, sternal reentry complications, postoperative low cardiac output, postoperative bleeding, perfusion and aortic crossclamp times, usage, type and volume of cardioplegic solutions, lowest hematocrit and temperature during cardiopulmonary bypass, need for postoperative transfusion, and emergency operation. Follow-up by clinic examination or telephone contact was complete in 96% of patients (100% in the PPI group).

	Results

Top Abstract Introduction Patients and methods Results Discussion References

 
The mean age for the entire group was 56 ± 14 years, with a range of 3 to 90 years. Mean ages for the PPI and nonpaced groups were 59.8 ± 13.9 years and 55.7 ± 15.0 years, respectively (p = 0.05). The male/female ratio was 313:245 (1.3:1). Although a slight female predominance was seen in the PPI group, it was not significantly different from the gender ratio of patients who were not paced. The types of operative procedures are summarized in Table I. The number of repeat operations in most instances was higher in the permanent pacing group (Table II). Causes of nonfatal morbidity and operative deaths are outlined in Tables III and IV, respectively. In the group that was not paced, tachyarrhythmias (ventricular fibrillation, 7 deaths; ventricular tachycardia, 1 death; atrial fibrillation, 2 deaths) contributed to operative mortality in 10 of 504 patients (2.0%). Only one patient was paced temporarily at the time of death. No bradyarrhythmia precipitated death in this group. In the PPI cohort, 10 of 12 patients (83.3%) who died in the hospital had complete heart block compared with 18 of 42 (42.9%) survivors (p = 0.01). However, no deaths in this group were attributed directly to the bradyarrhythmia that required permanent pacing.

Survival for PPI patients was 83% at 5 years and 51% at 10 years; in the cohort that was not paced, 84% of patients were alive at 5 years and 60% at 10 years (Fig. 1). The most common causes of late death in both cohorts included documented congestive heart failure, cancer, and tachyarrhythmias. Of the 42 PPI survivors, 32 (76.2%) were pacemaker dependent at the last follow-up.

View larger version (15K): [in this window] [in a new window]   Fig. 1. Kaplan-Meier survival curves for paced and nonpaced cohorts after reoperative cardiac surgery. *Log rank p value shows no significant difference in curves.

	Discussion

Top Abstract Introduction Patients and methods Results Discussion References

 
New rhythm disturbances and conduction defects are relatively common after most cardiac procedures that require cardiopulmonary bypass. These problems include sinus node dysfunction, various fascicular blocks, and complete atrioventricular block. Fortunately most are self-limiting and harmless and disappear before hospital discharge. Some, however, are permanent and require either prolonged surveillance for malignant rhythm development ^2,20 or PPI. Factors leading to these conduction defects identified by multivariate analyses are advanced age (especially older than 64 years of age), total cardiopulmonary bypass and aortic crossclamp times, significant left main coronary artery stenosis, right coronary artery occlusion with significant stenosis of the left anterior descending coronary artery, number of bypassed coronary arteries, currency of operation, presence of preoperative conduction defects, concomitant left ventricular aneurysmectomy, use of cold cardioplegia, and the maximal degree of myocardial cooling. ^{1,4,6,8,23,24} Other elements thought to be related to the genesis of these rhythm disturbances include long-standing hypertension, atherosclerotic lesions jeopardizing flow to the first septal perforating coronary artery, number of diseased coronary arteries, preoperative use of digoxin, ß-blockers or calcium channel blockers, previous inferior wall myocardial infarction, presence of mitral annular or aortic valve calcification, left ventricular ejection fraction, type of cardioplegia used, adequacy of myocardial protection, valvular surgery especially involving the tricuspid valve, less frequent use of the internal thoracic artery graft, the serum potassium level at the time of aortic crossclamp release, high postoperative creatine kinase MB levels, perioperative myocardial infarction, perioperative low cardiac output, postoperative atrial fibrillation, and no identifiable factors. ^{4-8,10,12,15,17,21-23,25} Conditions related to the specific need for permanent pacing after cardiac surgical procedures include postoperative atrial fibrillation, preoperative conduction defects (sinus and atrioventricular node dysfunction including bundle branch blocks), advanced age, dense calcium in the aortic anulus with or without mitral annular calcification, valvular operations especially involving the tricuspid valve, poor myocardial protection, and no obvious factors. ^{7,10,11,15,18,25} The increased need for PPI after orthotopic heart transplantation may reflect organ rejection, operative trauma, prolonged perioperative ischemic time, drug use, or combinations thereof. ^3,13,16

Conduction injury leading to the need for permanent pacing in patients undergoing reoperations has not been well documented. Many of the conditions detailed earlier can be seen in these patients.

In a series of 5942 mixed cardiac procedures, ¹⁰ 123 patients (2.1%) required PPI. Redo procedures accounted for 22% of these pacemaker implantations. In 227 patients surviving repeat valve surgery, ²⁶ 18 (7.9%) required permanent pacemakers. We thought that preoperative endocarditis and first-degree atrioventricular block increased the need for PPI. Because some valvular prostheses have limited viability, the subsequent need for reoperation may impose conditions that can damage the conduction system. The atrioventricular node lies close to the noncoronary cusp of the aortic valve, the posterior-medial commissure of the anterior mitral leaflet, and the septal leaflet of the tricuspid valve. Debridement of annular tissue at these areas decreases the distance between the atrioventricular node and anchoring sutures, thereby increasing the chance for conduction injury. Careful attention to this anatomy combined with judicious debridement and choice of a valvular prosthesis commensurate with the clinical setting may lessen this problem.

Although systemic hypothermia appears to have a salutary effect on myocardial protection during aortic crossclamping, injury to the conduction system may parallel the level of reduced temperature. In one series, ²³ cold myocardial "protection" (core cooling to 28° C plus cold cardioplegia) produced greater injury to the conduction system than a warm delivery system (normothermic perfusion and cardioplegia). Because all patients receiving hypothermic perfusion were cooled to the same core temperature, it is difficult to ascertain whether this injury resulted from systemic or cardioplegia cooling. In our patients, cardioplegia temperatures were kept around 10° C, but the core temperature varied by surgeons' preference. Significantly, the degree of core cooling was found to be an independent predictor of permanent pacemaker need, with a breakpoint for conduction injury below 21° C. It is difficult to understand how core cooling leads to conduction injury when this phenomenon is not seen regularly with lower temperature levels achieved during profound hypothermia and circulatory arrest. Nevertheless, avoidance of hypothermia levels below 21° C may offer some protection against the development of postoperative bradyarrhythmias requiring PPI during reoperative cardiac procedures. Because permanent epicardial leads were placed in many of our patients at the time of the operation when significant bradycardia was encountered, implantation of a permanent generator in the immediate postoperative period was relatively simple. Pacing thresholds for these leads were significantly higher than transvenous leads, leading in some instances to the need for revision. Because most currently implanted pacing units have sophisticated telemetry, frequent observation of epicardial leads should signal abnormally rising thresholds. Unless a tricuspid prosthesis has been implanted in this setting, conversion to a transvenous pacing system remains the procedure of choice.

In a collected series of 2989 patients from the general population who received a pacemaker unrelated to any cardiac surgical procedure, ^27-30 the actuarial survival at 5 years ranged from 41% to 67%. Most patients had mean ages between 67 and 80 years. In cohorts who received a pacemaker before they were 66 years of age, the 5-year survival was approximately 70% to 75%. In our PPI group, the mean age was 59.8 years with a 5-year survival of 83%. Survival time in the redo cardiac surgical group that did not require pacing also compared favorably with these values. PPI after redo cardiac surgical procedures does not seem to significantly affect longevity.

	Acknowledgments

 
We thank Jennifer Cholewa for her assistance in the preparation of this manuscript.

	References

Top Abstract Introduction Patients and methods Results Discussion References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Joseph W. Lewis, Jr. Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lewis, J. W. Articles by Jacobsen, G. Search for Related Content PubMed PubMed Citation Articles by Lewis, J. W., Jr. Articles by Jacobsen, G.