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Ann Thorac Surg 1997;64:651-657
© 1997 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, Department of Surgery, and Division of Cardiology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Methods. Between January 1, 1985, and June 30, 1996, 427 patients underwent primary AVR + CABG, and 52 underwent AVR ± CABG after prior CABG. Demographics, operative characteristics, and operative results were compared between groups. Data for all patients were pooled and analyzed collectively for risk factors influencing mortality.
Results. The extent of native coronary artery disease and the incidence of prior myocardial infarction and stroke were greater in the reoperative group. Aortic cross-clamp and cardiopulmonary bypass times were slightly shorter, and fewer distal anastomoses were performed in the reoperative group. Operative mortality (primary group, 6.3% versus reoperative group, 7.4%) and morbidity were similar. Stepwise multivariate logistic regression analysis identified age, perioperative myocardial infarction, intraaortic balloon support, ventricular arrhythmia, perioperative stroke, and development of renal failure or acute respiratory distress syndrome, but not reoperative status, as predictors of mortality.
Conclusions. The risk of AVR after previous CABG is similar to that for primary AVR + CABG. Valve replacement should, therefore, be pursued despite prior CABG when hemodynamically significant aortic stenosis develops. Furthermore, a circumspect approach to "prophylactic" AVR for mild aortic stenosis at primary CABG seems warranted.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Aortic valve replacement (AVR) with or without repeat revascularization after previous coronary artery bypass grafting (CABG) is a technically challenging procedure. The associated operative risk is controversial, with some authors [1–4] citing mortality rates between 12% and 18% and others [5] reporting a much lower risk. The magnitude of this risk influences the threshold for recommending AVR in a patient who has undergone prior CABG. In addition, albeit less directly, it influences views concerning the optimal management of the mildly stenotic aortic valve at the time of primary CABG. Both issues can be expected to assume increasing clinical importance with the advancing age of patients who have had successful coronary revascularization as well as those undergoing primary CABG and the associated increasing incidence of senile aortic sclerosis.
With these concerns in mind, we reviewed our experience with AVR ± CABG for aortic stenosis (AS) after previous CABG over an 11.5-year period. Results were compared with those of primary AVR + CABG over the same interval to assess the impact of previous CABG on operative risk.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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All continuous data (including age and body surface area) were expressed as the mean ± the standard deviation. Two-group comparisons for continuous data were made using the Student's t test. Categoric data were tabulated, and two-group comparisons were made using the 
2 test for 2 x n tables. When 2 x 2 tables were analyzed, Fisher's exact test was used. Univariate, multivariate, and stepwise multivariate regression analyses were used to screen for risk factors for death. For all statistical calculations, a p value of less than 0.05 was considered significant. The SYSTAT system for statistics was used for all data analysis (Ver. 6.0 for Windows; SPSS, Chicago, IL).
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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). The mean age was nearly identical, and the sex distribution was similar. As might be expected, more patients in the reoperative group had a history of myocardial infarction (MI) or stroke. There was a trend toward more severe angina in the reoperative group, although differences in the distribution of patients by New York Heart Association class and Canadian Cardiovascular Society angina class did not reach significance. Differences in the distribution of valvular pathology are difficult to interpret in a meaningful way because of the number of valves for which the cause of disease was unspecified.
Findings at cardiac catheterization are presented in Table 2. The reoperative group was characterized by more advanced native coronary artery disease with a higher incidence of native left main and triple-vessel disease. Within the database, assessment of ventricular function was recorded by ejection fraction (EF) in some cases and by Coronary Artery Surgery Study (CASS) score [6] in others. To pool data, therefore, we classified patients as having no, mild, moderate, or severe ventricular dysfunction according to the following definitions: no dysfunction = EF greater than 0.55 or CASS score of 5 or less; mild = EF of 0.45 to 0.55 or CASS score of 6 to 10; moderate = EF of 0.35 to 0.45 or CASS score of 10 to 15; and severe = EF less than 0.35 or CASS score higher than 15. There was a trend toward more severe ventricular dysfunction in the reoperative group, although this did not reach significance.
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, both aortic cross-clamp and cardiopulmonary bypass times were longer in the primary group, possibly because of the greater number of distal coronary anastomoses and more frequent use of the internal thoracic artery in these patients. The reoperative procedures were more often carried out on an elective basis, although this difference was not significant.
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Perioperative Mortality and Morbidity
The 30-day mortality and morbidity for both groups are presented in Table 4. The incidence of ventricular arrhythmias, defined as triplets or greater, the incidence of perioperative MI, defined by the appearance of new Q waves on 12-lead electrocardiography, and the requirement of intraaortic balloon pump (IABP) support were slightly greater in the reoperative group. None reached significance. The incidence of low-output state, defined as a requirement of inotropic or IABP support for greater than 48 hours, was similar for both groups.
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Causes of Death
Myocardial infarction and complications of low-output state accounted for the majority of deaths in both groups. All four deaths in the reoperative group and 20 (75%) of 27 deaths in the primary group were attributable to this cause. Three deaths in the primary group were due to malignant cardiac arrhythmias, and sepsis, renal failure, stroke, and multisystem organ failure each accounted for one death.
Predictors of Operative Death
Data for both groups were combined, and 37 variables were subjected to statistical analysis as predictors of operative death. As shown in Table 5, univariate analysis identified age, body surface area, diabetes mellitus, hypertension, advanced New York Heart Association class, history of MI, and left main disease as preoperative predictors of mortality. Reoperative status was not predictive. Operative predictors of death included nonelective procedure, prosthesis size, and aortic cross-clamp and cardiopulmonary bypass times. Perioperative MI, development of low-output state, requirement of IABP support, mediastinal hemorrhage, and ventricular arrhythmia were associated with mortality, as were perioperative stroke, development of acute respiratory distress syndrome, and renal failure requiring dialysis.
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Further, our data do not support arguments favoring the replacement of mildly or moderately stenotic aortic valves encountered at the time of primary CABG on the basis of excessive risk of the repeat surgical procedure. A circumspect approach to "prophylactic" AVR seems warranted.
Limitations of Study
The results of the current study must be interpreted with an appreciation for the limitations inherent in any such retrospective analysis. Although both study groups appeared comparable as assessed by the clinical and hemodynamic variables already discussed, there remains the potential for systematic bias. For example, a tendency to carry out reoperative procedures only on better-risk candidates might lower the apparent mortality risk in this group. Such bias in this study seems unlikely, however, given the observation that for every criterion for which a significant difference was identified, the reoperative group had the more severe disease. An additional weakness in this retrospective study is the lack of complete data for the cause of the valvular disease, the extent of native coronary disease, and, in the reoperative group, the transvalvular gradient at the initial operation. This should not, however, affect the central finding in this study: the comparability of mortality rates between the primary and repeat surgical groups.
Comparison With Other Studies
The operative risk for the reoperative group in this series is considerably lower than that generally reported in the literature. Although over a time interval similar to ours, Hoth and associates [5] performed AVR without an operative death on 23 consecutive patients who had undergone CABG an average of 7.6 years previously, other authors [1–4] have estimated the risk of this procedure to be between 12% and 18%.
In 1994, Collins and Aranki [3] reported a series of 44 reoperative AVRs performed between 1975 and 1992 with an 18% operative mortality rate. The authors did not analyze date of operation as a risk factor for mortality despite the 17-year study interval. Fiore and co-workers [4] reported an equivalent operative risk among 28 patients undergoing reoperative AVR after CABG between 1980 and 1994. As our series is somewhat more contemporary than either of these, advances in myocardial protection and other subtle improvements in perioperative care may account, at least in part, for the lower risk we observed. In both of these reports, the interval between primary CABG and reoperative AVR (5.75 years and 8 ± 4 years, respectively) was similar to that reported by Hoth and colleagues [5].
Fighali and associates [2] from the Texas Heart Institute and Odell and co-workers [1] from the Mayo Clinic presented results for substantially larger series of patients undergoing reoperative AVR after CABG. Given the larger numbers, each group was able to perform multivariate analysis of risk factors for operative death within this specific population. In the former study, the mortality rate was 14% among 104 patients undergoing operation between 1983 and 1993. The authors identified preoperative renal failure, prior MI, multivessel coronary artery disease, and prolonged cardiopulmonary bypass time as predictors of operative mortality. Of the 145 patients in the Mayo Clinic study who had operation between 1975 and 1994, 20 had complex procedures at repeat surgical intervention, thus leaving 125 who underwent only AVR ± CABG at reoperation. The operative mortality rate for this subgroup was 12%. Only prolonged cross-clamp time was predictive of death in this series.
Among potential explanations for the higher mortality observed in these studies, the impact of era of operation must again be considered. Although year of operation was not a risk factor for death by multivariate analysis in the Mayo Clinic series, this variable was not analyzed in the Texas Heart Institute study.
A more subtle influence on the risk profile of the study population may be imposed by differences in referral patterns to particular institutions. The observations that almost half of the Mayo Clinic patients had undergone their primary operation elsewhere and that 10% had undergone a more complex primary procedure than CABG alone support the hypothesis that higher-risk patients may have been referred to this center. It is difficult, however, to prove such differences between study groups. In our reoperative group, the mean age, the only demographic predictor of risk in our study, was somewhat higher than that of patients in either the series of Fighali and colleagues [2] (67 ± 9 years) or Odell and coauthors [1] (71 ± 8 years). Fighali and associates identified renal failure and previous MI as risk factors for death. Comparing study groups for these characteristics, the incidence of renal failure was slightly greater in their population than ours (7% versus 2%); however, the prevalence of previous MI was higher in our reoperative population (37% versus 52%). These variables were not reported for the Mayo Clinic series.
Because of the time span of our study and the number of surgeons involved, it is difficult to come to conclusions regarding surgical techniques that may account for the lower risk of reoperative operation observed in our series compared with others. Analysis of risk factors for death in our reoperative group alone is problematic because of the relatively small number of patients in this group and the infrequency of adverse events. Our general policy of replacement of older or diseased grafts and the aggressive use of retrograde delivery of blood cardioplegia may have played a role in reducing mortality. The observation that perioperative MI and IABP support are risk factors for death as well as the frequency of cardiac-related causes of death supports the notion that meticulous attention to myocardial protection and satisfactory revascularization are important.
Conclusions
Aortic valve replacement after previous CABG is a technically challenging operation. The magnitude of operative risk for this procedure has direct implications for one's threshold for its recommendation. The results of our study suggest that the surgical risk is not prohibitive and that an aggressive approach to valve replacement should be undertaken when the standard clinical and hemodynamic criteria for valve replacement are met, irrespective of previous CABG, before irreversible impairment of ventricular function occurs.
The operative risk of AVR after previous CABG has had a less direct but equally important impact on recommendations concerning the management of mild aortic valve disease present at the time of primary CABG. Collins and Aranki [3], Fighali and associates [2], and Odell and co-workers [1] argued in favor of "prophylactic" AVR in this setting on the basis of what they judged to be excessive risk in the reoperative setting. Such reasoning can be challenged on several levels. Although the majority of patients in their series, like ours, had no known aortic valve gradient at primary operation, it can be argued that the subsequent operative risk may not be comparable for patients left with mildly or moderately stenotic valves at the time of primary CABG and therefore subject to deterioration in ventricular function because of the valvular disease itself. Although this is a formal possibility, it seems unlikely that the operative risks of these two groups would be widely disparate given the results of multivariate analysis of risk factors for mortality, as already discussed. Furthermore, as the interval between primary and repeat operation in our study and in others was relatively short, it is reasonable to assume that although aortic valve pathology was not recognized at the first operation, it was nonetheless present.
A more fundamental problem with these arguments in favor of "prophylactic" AVR is the failure to adequately consider the cumulative risks imposed on the individual and on the population as a whole by this policy. As enunciated by Fiore and colleagues [4], the additional risks to the individual associated with the prosthetic valve itself (eg, thromboembolism, infection, and structural dysfunction) are substantial. An aggressive approach to valve replacement would subject patients to these risks earlier than otherwise necessary if AVR were delayed until the traditional indications for valve replacement were met. The effect on cumulative risk is therefore ultimately dependent on the interval between primary and repeat operation as well as the device- and patient-specific risks such as thromboembolism and prosthetic valve infection. The expected rate of progression of AS becomes critical in determining the optimal approach for the individual patient.
Finally, if one considers the population as a whole, an aggressive approach to "prophylactic" AVR subjects all patients with mild or moderate AS to the increased operative risk of AVR + CABG over CABG alone. In contrast, an expectant approach exposes to the risks of AVR, albeit in a repeat surgical setting, only those patients whose valvular disease progresses. Therefore, the likelihood that mild to moderate AS will progress (true for a fraction of all patients) and the incremental increased risk of the combined procedure become critical factors in determining the optimal management of such patients.
The literature concerning the natural history of mild to moderate AS has recently been reviewed [7]. Although a prospective echocardiographic study by Brenner and associates [8] suggested a predictable rate of diminution of aortic valve area by 0.14 cm2 a year, most series indicate variable and unpredictable progression. Cheitlin and associates [9] and Wagner and Selzer [10] retrospectively reviewed patients with AS undergoing serial cardiac catheterization. Both groups of investigators found that patients fell into two categories in approximately equal numbers: those whose AS progressed and those in whom it remained stable. Subsequent prospective echocardiographic studies [11–14] have confirmed these results. The challenge, then, is to identify which patients will fall into each category. However, it has been difficult to define predictors of progression. In addition to extensive calcification of the valve or mixed stenotic and regurgitant disease [15], some studies have identified older age [14], poor left ventricular function [10, 11, 13], and renal failure [16] as predictive of progressive AS. The obvious difficulty in using these variables to guide a more aggressive approach to "prophylactic" AVR for mild stenosis is that they also identify the patients at the highest operative risk for AVR at the time of primary CABG.
We conclude, therefore, given the variability in the progression of AS and hence the uncertainty regarding the ultimate need of AVR in any individual patient, its timing, the risks associated with prosthetic valves, and the relatively modest risk of AVR after prior CABG, that routine replacement of mildly stenotic valves is not indicated at this time. We recognize, however, that the relative risks of both approaches to the management of the mildly stenotic valve can be most directly defined by comparison of the long-term outcome of patients fitting this profile who do not have valve replacement compared with those who do undergo concomitant AVR. Ultimately, the question of optimal management of these patients can be definitively answered only by a prospective, randomized study.
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Acknowledgments |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Address reprint requests to Dr Sundt, Division of Cardiothoracic Surgery, Washington University School of Medicine, Suite 3108 Queeny Tower, One Barnes Hospital Plaza, St. Louis, MO 63110-1013 (e-mail: sundt{at}wudos2.wustl.edu).
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References |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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