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Ann Thorac Surg 2003;75:S2-S5
© 2003 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, Cleveland Clinic Foundation, Cleveland, Ohio, USA
* Address reprint requests to Dr Lytle, Department of Thoracic and Cardiovascular Surgery, Cleveland Clinic Foundation, 9500 Euclid Ave, F-25, Cleveland, OH 44195, USA
e-mail: lytleb{at}ccf.org
Presented at the Heart Failure & Circulatory Support Summit, Cleveland, OH, Aug 22–25, 2002.
For patients with significant coronary artery disease, abnormal left ventricular (LV) function has predicted an increased risk of death without myocardial revascularization. Natural history studies performed before the advent of coronary bypass surgery established this principle and subsequent comparative studies have confirmed it [1–6]. Soon after the advent of coronary bypass surgery a series of randomized and comparative observational studies were undertaken that compared the strategy of initial bypass surgery with initial medical management followed by surgery if symptoms worsened. Two randomized studies of patients with mild to moderate chronic stable angina, the VA Cooperative Study and the Coronary Artery Surgery Study (CASS), contained patients with abnormal left ventricular function (ejection fraction < 50%) [2–4].
In the VA Cooperative Study abnormal left ventricular function and three-vessel disease defined a "high risk" group of patients for whom bypass surgery improved the long-term survival rate. Also in the randomized portion of CASS surgery improved the survival rate of patients with ischemic cardiomyopathy and triple-vessel disease at least out to 10 years after operation. A meta-analysis of these and other smaller randomized trials confirmed the survival benefit of bypass surgery for patients with abnormal LV function [7]. Studies involving the CASS Registry, a nonrandomized portion of the CASS study that contained larger numbers of patients than the randomized arm and contained patients with mild or severe symptoms, showed that surgery prolonged the survival rate of patients with triple-vessel disease and abnormal LV function whether they had mild or severe angina [5, 6]. Other important CASS registry analyses showed that bypass surgery decreased the risk of sudden death for patients with abnormal LV function and that the surgical strategy of complete revascularization was important for patients with ischemic cardiomyopathy [8, 9]. A randomized VA Cooperative Trial involving patients with unstable angina also showed an improved survival rate for patients with triple-vessel disease and abnormal LV function who underwent bypass surgery [10].
All of these trials were initiated within the first decade of bypass surgery. Subsequent to these trials numerous factors have improved the short- and long-term outcomes associated with bypass surgery. Improvements in intraoperative myocardial protection and other aspects of perioperative care have diminished perioperative risks. Vein graft patency rates have been improved by the use of platelet inhibitors [11]. The use of statin-type drugs has been shown to decrease cardiac events within the first 3 years after bypass surgery and to decrease angiographic progression of arteriosclerosis in bypass grafts and native coronary arteries [12, 13]. In the randomized trials internal thoracic artery grafts were rarely used and a mountain of subsequent data has shown that the use of the left internal thoracic artery to graft the left anterior descending coronary artery prolongs the long-term survival rate and reduces the incidence of late cardiac events [14]. Further observational data appear to show that the use of two internal thoracic artery grafts may further improve long-term outcomes [15]. Finally surgeons are better microtechnicians today than they were during the first decade of bypass surgery.
The results of the randomized and prospective observational trials and the documented improvements in the outcomes of surgically treated patients since those trials were completed have provided the indications for bypass surgery performed for the purpose of prolonging patient survival. Numerous reviews by multiple consensus panels containing both cardiologists and cardiac surgeons have concluded that the anatomic situations of abnormal LV function combined with left main or multivessel coronary artery disease are anatomic indications for bypass surgery [16, 17].
Within the last decade pharmacologic and electrical treatments for patients with cardiomyopathy have also improved. Angiotensin-converting enzyme inhibitors, beta blockers, and diuretics may improve symptoms of congestive heart failure and in some studies have decreased mortality during short follow-up intervals. In addition implantable defibrillators decreased the risk of death due to arrhythmia in some patient subgroups. These advances have raised the question of whether revascularization is still indicated to improve the survival rate of patients with ischemic cardiomyopathy. Or stated another way, does the existence of uncorrected coronary stenoses still decrease the survival rate of patients with cardiomyopathy in the presence of modern pharmacologic and electrical therapies? It has been suggested that more current randomized trials of patients with ischemic cardiomyopathy are needed to reestablish the indications for bypass surgery.
However those trials that do show a benefit of medical therapy indicate that while improvement in mortality has occurred it is not a very large improvement and that the mortality rate is still high for patients with ischemic cardiomyopathy who have not been revascularized. For example the Atlas trial, a study comparing high- and low-dose lisinopril for 2,035 patients with ischemic cardiomyopathy, found that at a 41-month mean follow-up interval there was an 8% decrease in mortality but that the overall mortality rate was still 48%, 44% in the high-dose treatment group. Thus even in the most favorable group the risk of death was still 12% per year [18]. Similarly a randomized trial of spironolactone for 1,663 patients with ejection fraction less than 35% also showed an improved survival rate for the spironolactone group but that subgroup still had a 35% mortality at more than 24 months (17% per year) compared with a 48% mortality rate for the placebo group [19]. So although improvements in survival rate have been noted with medical therapy alone, even these very recent trials still document a high rate of death for patients with ischemic cardiomyopathy.
If patients with ischemic cardiomyopathy have coronary stenoses that produce ischemic jeopardy why would we not expect bypass grafting of these lesions to improve survival rate? There appear to be three situations where surgery might not improve mortality rate. One, if the operative risk outweighed the long-term benefit. Two, if death were unrelated to ischemia, for example if there was a high rate of death due to nonischemic arrhythmias. And three, if revascularization was ineffective in preventing ischemia. However none of these situations are reflected in current reality. First, advances in intraoperative myocardial protection have diminished the increment in the in-hospital mortality rate of bypass surgery produced by abnormal LV function. The in-hospital mortality rate for patients undergoing primary isolated bypass surgery at the Cleveland Clinic Foundation during the years 1990 to 1999 are shown in Table 1. Thus while patients with abnormal LV function are at a slight increase in risk, this in-hospital risk is a relatively small proportion of the yearly risk patients with ischemic cardiomyopathy experience without operation.
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Third, there is recent evidence from the SOLVD (Studies Of Left Ventricular Dysfunction) database that bypass surgery does decrease the mortality rate from ischemic cardiomyopathy despite treatment with modern pharmacologic therapy. One SOLVD trial was designed to test the impact of enalapril on the survival of patents with LV ejection fraction values of 0.35 or less. Of the 5,410 patients in the study (all ejection fractions < 35%), 35% had undergone previous bypass surgery a mean of 1.8 years before entry into the study [20]. The patients with prior bypass surgery experienced a 26% lower all-cause mortality rate during a 3-year follow-up than the patients who had not had bypass surgery. This decreased death rate was mostly due to a decreased risk of sudden death. Looking back at the CASS registry it is of interest that those data also showed that bypass surgery decreased the risk sudden death for patients with abnormal LV function. Another publication from SOLVD has noted that bypass surgery has a particularly strong positive impact on the survival of diabetic patients [21]. The survival benefit of bypass surgery documented by the SOLVD studies is particularly impressive because patients with clinical characteristics identifying a high risk of ischemic events, unstable angina, or myocardial infarction within 1 month were excluded from SOLVD.
In analyzing their data the authors of SOLVD cited the effect of bypass surgery in decreasing the risk of sudden death as a possible explanation for the fact that the Coronary Artery Bypass Graft (CABG) Patch trial, which involved patients with ischemic cardiomyopathy who all underwent bypass surgery, did not show a benefit from an implanted cardioverter-defibrillator (ICD) in decreasing mortality rate [22]. During the 4-year follow-up the mortality rate in the CABG Patch trial was only 6% year in the group who did not receive an ICD and equivalent in those who did. Other trials have shown a benefit from ICD implantation but in those trials fewer patients received revascularization. For example the Antiarrhythmic Versus Implantable Defibrillator (AVID) study involved patients with life-threatening ventricular arrhythmias randomized to antiarrhythmic drugs or ICD implantation [23]. In this trial approximately 80% of patients had ischemic cardiomyopathy but only approximately 30% had undergone bypass surgery. Two-year survival rates stratified according to LV ejection fraction showed that ICD implantation led to lower risk for patients with ejection fraction of 0.34 or less but not for those with ejection fraction 0.34 or greater. This improved mortality with ICD implantation was based on a particularly bad survival rate for patients in the antiarrhythmic drug group, 64% and 72% at 2 years for patients with ejection fraction 0.20 or less and 0.20 to 0.34, respectively. However even those patients with ICD implantation did not do particularly well with survival rates of 72%, 82%, and 83% for patients with ejection fraction of 0.20 or less , 0.20 to 0.34, and 0.34 or greater, respectively. The patients in AVID were almost certainly at a greater antiarrhythmic risk than those included in the CABG Patch trial. However the observation remains that the relatively unrevascularized patient subsets in the AVID trial had high mortality rates despite ICD implantation. These data suggest that ICD implantation is not a substitute for revascularization but a complementary form of therapy.
In addition to improved treatment strategies another major advance in the treatment of patients with ischemic cardiomyopathy has been the development of imaging modalities that aid in the assessment of myocardial viability. Multiple myocardial imaging techniques are available and provide different kinds of information concerning myocardial viability. The presence of cell membrane integrity, metabolic activity, and contractile reserve are addressed by single photon emission tomography (SPECT) using thallium 21 or technetium 99 perfusion tracers, positron emission tomography (PET), and dobutamine stress echocardiography (DSE), respectively. Multiple clinical studies have examined the reliability of these strategies in regard to the prediction of clinical outcomes after revascularization for patients with ischemic cardiomyopathy. Magnetic resonance imaging (MRI) may also be used to predict viability although there are fewer data correlating that imaging technique with clinical outcomes.
Allman and associates [24] performed a meta-analysis of 24 studies concerning patients with ischemic cardiomyopathy and the ability of SPECT, PET, or DSE to predict survival with or without revascularization. The studies included in the meta-analysis contained 3,088 patients with ejection fractions of 32% ± 8% followed up for 25 ± 10 months. Revascularization was of major benefit to patients who exhibited myocardial viability, decreasing the risk of death by approximately 80% and producing a 3.2% annual mortality rate for the revascularized group compared with a 16% annual mortality for patients with myocardial viability who did not undergo revascularization. Patients who were judged not to have myocardial viability in dysfunctional areas did not exhibit an improved survival rate with revascularization. Patients without viability had a worse annual mortality in the revascularized group (7.7%) and relatively better outcomes for patients treated medically (6.2% annually) when compared with patients with viability. For patients with viability the benefit of revascularization increased as ejection fraction decreased but patients without viability did not exhibit an improved survival rate with revascularization at any level of ventricular function. The authors were unable to identify a specific imaging technique that appeared to have an advantage in predicting survival benefit but regardless of variability in the techniques used to document viability the individual studies were consistent and the advantage of revascularization for patients with viability was substantial. Other authors have shown that myocardial viability studies aid in the prediction of improvement of left ventricular function and exercise capacity based on revascularization [25].
Is a randomized trial of revascularization for patients with ischemic cardiomyopathy needed or justified? The randomized trials of surgery versus medical management showed benefit for surgery in terms of survival and symptom status. Since those studies were completed the safety and long-term effectiveness of surgery has improved greatly. While medical therapy has also improved, even recent data show that patients with ischemic cardiomyopathy are at risk and that surgery diminishes that risk particularly for patients with significant myocardial viability. All the data, old and new, appear to point to a survival advantage for such patients and to randomize patients with ischemic cardiomyopathy, graftable coronary arteries, and myocardial viability seems neither necessary nor wise.
That having been said, there are subsets of patients with ischemic cardiomyopathy for whom the optimal treatment strategies are not as clear. In particular it may be that patients without demonstrable viability benefit less or not at all. Also myocardial viability is not a binary function and the amount of viability that is important is not yet clear [26]. Moreover when patients have akinetic myocardial areas that are anterior-apical in distribution the level of myocardial viability at which it makes sense to forego revascularization alone and to resect those areas for the purpose of remodeling ventricular geometry has not been resolved. These patient subsets are logical groups for investigation. Patients with substantial myocardial viability jeopardized by coronary stenoses who have abnormal LV function should have surgery.
References
This article has been cited by other articles:
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  M. H. Mandegar, M. A. Yousefnia, F. Roshanali, H. Rayatzadeh, and F. Alaeddini Interaction between two predictors of functional outcome after revascularization in ischemic cardiomyopathy: left ventricular volume and amount of viable myocardium. J. Thorac. Cardiovasc. Surg., October 1, 2008; 136(4): 930 - 936. [Abstract] [Full Text] [PDF]
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