Coronary Bypass Surgery for Patients with Chronic Poor Preoperative Left Ventricular Function (EF<30%): 5-year Follow-up

Results Mean follow-up was 3.3 years (range, 0.5–5.5); average patient age was 64.4 ± 1 years. Preoperative thallium scans were performed solely on 31 patients with none or mild angina, of which 10 (32%) demonstrated large areas of viable myocardium. Perioperative mortality was 1.9%. On multivariate analysis, factors predictive of increased perioperative death were recent myocardial infarction ( p < 0.001) and nonelective surgery ( p < 0.001). Kaplan–Meier 5-year survival and freedom from major adverse cardiac events were 72.3 and 82.3%, respectively. In 21 patients, with preoperative nil-to-mild angina and nil-to-small areas of myocardial viability, thallium scanning failed to predict a successful outcome. Conclusion Offering coronary surgery to these patients irrespective of thallium testing is safe and effective in the medium term. Early surgery is recommended. Keywords CABG Surgery Poor Ventricular Function Introduction It is perceived that offering coronary bypass grafting (CABG) to patients with chronic, severe, left ventricular dysfunction (ejection fraction (EF) ≤ 30%) is a high-risk operation of unproven survival benefit. 1 In the absence of contemporary randomized trials of revascularisation versus medical therapy, this issue remains unclear. Despite however, considerable evidence demonstrates that surgical revascularisation of patients with ischaemia and ventricular dysfunction is superior to medical management alone. 2–4 As there is no consensus, a spectrum of clinical practice therefore exists regarding which patients are offered revascularisation (CABG or percutaneous). One end of this spectrum mandates demonstrating large areas of viable myocardium usually by thallium scan or dobutamine stress echocardiography (DE). 5 However, these tests may underestimate the magnitude of cell viability in upto 20% of patients; patients potentially denied the benefit of revascularisation. 6–8 Coronary bypass surgery, in these patients, has historically produced acceptable mortality and medium term outcomes; 2 the first series in Australia by Baird recorded an operative mortality of 12% with 80 and 85% alive and free of heart failure at 2 years, respectively. 3 Importantly CABG has had three decades since to be refined. Furthermore, the current prognosis of patients with severe left ventricular dysfunction and significant coronary artery disease managed medically remains poor. 4 O’Connor reported a 5- and 10-year survival benefit in patients having CABG versus medical therapy of 61% and 42% versus 37% and 13%, respectively. 4 O’Connor concluded that “regardless of the severity of coronary artery disease, heart failure symptoms or ventricular dysfunction, CABG provides extended event-free and survival advantage over medical therapy alone in patients with ischemic cardiomyopathy”. 4 This remains the only such study comparing current medical versus surgical therapy. Some physicians thus offer CABG either without performing or irrespective of thallium studies. 7,9 This is the opposite end of the spectrum of CABG referral. This study assesses the results of this particular strategy. Methods Patient Population This is a retrospective review of 107 consecutive patients with an EF of 30% or less referred for isolated CABG from July 1, 1996 to December 31, 2001. This group represents 5–7% of our annual isolated CABG referrals. 10 Patients had documented severe chronically impaired left ventricular function, despite medical therapy, thus excluding patients with transient or nonmedically optimised ventricular dysfunction (i.e. not managed by a cardiologist with vasodilators, diuretics, beta-blockers, etc.). The EF was determined by one or several means including ventriculography, echocardiography and radionuclide scanning. The value documented for EF was the latest before surgery in stable (i.e. not in hospital) patients. Performance of preoperative echocardiography and myocardial viability studies were at the discretion of the referring cardiologist. Patients were considered suitable for CABG in the presence of severe coronary disease (i.e. >50% diameter stenosis) affecting either the left anterior and/or two major epicardial coronary arteries deemed technically graftable. Prospective data collection and monthly internal audit were performed using an Australian modified version of the U.S.A. Society of Thoracic Surgeons (STS) database. 10 This study met the criteria of continuous ongoing unit quality assurance and patient confidentiality, and patients gave informed consent to participate in this research satisfying the respective three hospital human ethics committees. 10–12 Demographic, clinical and operative characteristics are given in Table 1 . The performance of CABG has been described elsewhere. 10 Off-pump CABG was performed in 5% of cases and 3 patients were redo CABG operations. Surgical preference required an aggressive approach to preoperative optimisation of renal and cerebrovascular function. 11 Patients with carotid bruits and/ or age >80 years were screened with carotid ultrasound. Asymptomatic unilateral or bilateral high-grade (>80%) stenoses mandated carotid endarterectomy. Preoperative chronic impairment of renal function (serum creatinine (s.Cr) > 130 mmol/L) mandated a prophylactic perioperative regime of hydration and enforced diuresis. 12 Operative definitions are in accordance with STS criteria. Our aim was to assess perioperative outcomes, medium-term survival, freedom from cardiac symptoms and quality of life. Patient Follow-up Patients were contacted via a standardized telephone questionnaire in June 2002, and a standardized modified SF-36 was completed. 11 Questions selected were directed to examine patient's quality of life, current level of activity (active, sedentary or restricted), freedom from preoperative symptoms, onset of new medical problems and level of satisfaction with surgery. In total, 16 questions from the SF-36 were utilized. 11 The data was analyzed in terms of patient characteristics, type of surgery, comorbidities, complications, survival, recurrence of symptoms, cardiac events, medications, quality of life and satisfaction with surgery. Data Collection and Statistical Analysis Perioperative data was collected prospectively. The relationship between potential predictors of perioperative mortality and major complications were assessed by uni- and multivariate analysis. In univariate analysis, categorical variables were analyzed using a Pearson chi-square test or Fisher's exact test when cell frequencies were less than five. Continuous variables were compared using the Student's unpaired t -test. Data is presented as the mean ± 1 standard deviation (S.D.) for continuous variables and as a percentage for categorical variables. Differences were considered significant with p ≤ 0.05. On univariate analysis, variables with p ≤ 0.05 were included in the multivariate analysis in a stepwise logistic regression analysis to test for statistically significant predictors of mortality, perioperative major complications and medium-term survival. Actuarial survival was assessed by the Kaplan–Meier method. Results One hundred and thirteen patients were referred for surgery. Six patients were rejected because of inanition or inability to curtail smoking. Perioperative data analysis of 107 patients was performed; 4 patients were lost to follow-up. Twenty-five patients were aged >70 years. The mean follow-up was 3.3 ± 0.5 years (range, 0.5–5.5 years). The median EF was 26% (interquartile range, 24–30%; range, 11–30%); 19 patients had EF ≤ 20%. In the 31 patients with preoperative thallium scans the median EF was 20% (interquartile range, 15–26%; range, 11–28%). Of these 31 patients, three had no demonstrable reversible ischaemia; 5, 13 (42%) and 10 patients (32%) had small, moderate and large areas of reversibility, respectively. No patient had DE or positron (PET) scan. In 86 patients preoperative 2DE was performed, the median EF was 23% (interquartile range, 20–26%; range, 11–28%). At angiography left ventricular end diastolic pressures (LVEDP) were recorded in 85 patients; the mean LVEDP was 26 ± 6 mmHg. All patients had documented poor left ventricular function >6 months; urgent (31%) or emergent (6%) cases were acute exacerbations on this background. A cause for the exacerbation was identifiable in 16 patients (43%): AMI, 8; pneumonia, 4; pulmonary emboli, 2 and arrhythmia, 2. Operative Morbidity and Mortality Operative mortality was 1.9% (two patients), both nonelective cases. The causes of death were pulmonary embolus (day 7) and pneumonia (day 11), respectively. The mean number of grafts per patient was 3.3 ± 0.9; the left internal mammary artery (LIMA) was grafted to the left anterior descending coronary artery (LAD) in 96% of patients. Perioperative inotrope support for a low cardiac output state was required in 23 patients, 16 of these also required an intra-aortic balloon pump (IABP); 9 were inserted preoperatively. The incidence of major perioperative complications (i.e. stroke, return to theatre, tracheostomy) was 4.7% (five patients) Table 2 . Three patients had a stroke (2.8%); none had significant extra cranial carotid disease. Four patients, based on preoperative carotid Doppler's, underwent uneventful, unilateral internal carotid endarterectomy. Superficial sternal cellulitis occurred in one patient, and four patients developed leg wound infections responsive to antibiotics. There were no perioperative myocardial infarctions (AMI). Perioperative atrial tachyarrhythmias occurred in 36% of the patients Table 3 . Statistical analysis of clinical factors considered predictive of operative mortality and/or major perioperative complications was performed. On univariate analysis, factors associated with increased risk of death were female sex ( p < 0.01), preoperative pulmonary edema ( p < 0.01), NYHA class IV ( p < 0.05), recent AMI ( p < 0.001) and nonelective surgery ( p < 0.001). By multiple regression analysis, only two factors were predictive of increased mortality: recent (i.e. within 3 weeks from surgery), AMI ( p < 0.01) and nonelective surgery ( p < 0.01). Factors predictive of increased risk of significant perioperative complications (i.e. stroke, return to theatre, tracheostomy) after uni- and multivariate testing were nonelective surgery ( p < 0.01) and a previous history of stroke ( p < 0.01). Medium-term and Event-free Survival Kaplan–Meier 1- and 5-year survival was 94 and 72.3%, respectively ( Fig. 1 ). On univariate analysis, factors associated with reduced 5-year survival were female sex ( p < 0.01), preoperative pulmonary edema ( p < 0.01), any preoperative arrhythmia ( p < 0.05) and nonelective surgery ( p < 0.05). By multiple regression analysis, preoperative pulmonary edema ( p < 0.03), any preoperative arrhythmia ( p < 0.01) and nonelective surgery ( p < 0.05) were predictive of poorer 5-year survival. However, 66% of the hospital deaths (10 patients) were due to noncardiac causes: cancer (three), stroke (two), renal failure (two), infection (two) and pulmonary embolism (one). Kaplan–Meier event-free survival (i.e. freedom from sudden cardiac death, angina or AMI) was 99 and 83% at 1 and 5 years, respectively ( Fig. 2 ). Six patients (6%) had a subsequent AMI; five were fatal. One occurred at 10 months, two at 2 years, one at 3 years and two at 4 years postsurgery, respectively. Symptom recurrence occurred in seven patients; four had recurrence of both angina and congestive cardiac failure and three solely congestive cardiac failure. Thus postoperative hospitalizations occurred in 13 patients. Preoperative Canadian Cardiovascular Status [I, 16%; II, 18%; III, 25%; IV, 41%] and New York Heart Association class preoperatively [I, 45%; II, 5%; III, 12%; IV, 39%] were significantly ( p < 0.01) improved postoperatively [CCVS: I, 93%; II, 7%; NYHA: I, 62%; II, 31%; III, 7%] ( p < 0.01). Satisfaction with Surgery and Quality of Life Eighty-four percent of the patients reported their health as good to excellent. When asked what their current health was like compared to that before surgery, 10% stated that they were worse. Twenty patients had worsened or developed new medical problems; in eight the daily activities were impeded, only one significantly so. In total,0 94% stated that CABG had been worthwhile. Concurrent Medical Therapy At final assessment, medical treatment included aspirin or equivalent [i.e. ADP antagonists] (85%), statins (81%), ACE-inhibitors (75%), angiotensin-II antagonists (4%), beta-blockers (39%) and carvedilol (11%). Few received diuretics (33%), digoxin (17%), warfarin (17%), spironolactone (11%), nitrates (8%), calcium channel antagonists (8%) or amiodarone (6%). Discussion Patients with severe coronary artery disease (i.e. >50% reduction in lumen diameter) and poor left ventricular function (EF ≤ 30%) can be offered CABG with a low perioperative risk (i.e. mortality, 1.9%; AMI, 0%; stroke, 2.9%) and acceptable medium-term survival (5 years, 72%) and quality of life (83%). Offering CABG to these patients without documented evidence of large areas of cell viability on thallium studies appears justified. All 21 patients with less than significant (i.e. large areas) viability on thallium studies survived and achieved excellent medium-term outcomes. Currently the management of these patients lies within a clinical spectrum. At one pole, patients are offered CABG predominantly based on the presence of graftable and severely stenosed coronary arteries. The opposite pole requires, in addition to the former criteria, evidence of large areas of myocardial viability, usually by thallium studies. However, the inherent limitations of these tests are well recognized. The positive predictive power of thallium scintigraphy and DE (the two most widely used tests) is 80%; the range is broad. 16,17 PET may prove superior. 8 However, in a prospective comparison of patients with suspicion of jeopardized myocardium randomized to PET or DE, Siebelink demonstrated no difference in patient management or cardiac event-free survival at 28 months follow-up. 17 Furthermore, Allman in a meta-analysis of 24 viability studies concluded that the absence of viability on noninvasive testing was associated with no significant difference in outcomes, irrespective of treatment strategy. 5 Allman makes no comment of the impact of surgical complication rates on subsequent outcomes. 5 Importantly for surgery to demonstrate benefit in these patients the incidence of perioperative AMI must be minimal. Thus Alderman reviewing the CASS registry of patients having CABG with an EF < 0.35 was the first to note that for the benefits of CABG to be unequivocal, surgical mortality “must equal or better the 6.9% obtained in this study”. 18 Importantly, these were patients operated from 1975 to 1979 whose presenting symptom was mainly angina; their perioperative AMI rate was 5.6%. Clearly evidence of large, reversible defects on thallium scintigraphy augurs for a good prognosis post-CABG. 5,13 Buxton and Chan reported a mortality and transplantation free survival of 1.7 and 73%, respectively, in patients with stable coronary artery disease and an EF < 0.35. 13 The presence of large reversible defects on thallium studies was the sole independent predictor of a good prognosis. Our 10 patients with large areas of reversibility also had no adverse events. However, Kron, commenting on Chans’ study, noted that “the problem lies with the patients who do not have evidence of ischaemia as 19” (out of 37) “of these patients had improvement in their heart failure symptoms. This occurred without any major improvement in ventricular function.” 13 So our 21 patients without large areas of viability on thallium scanning were significantly improved by CABG. Elefteriades demonstrated that lack of improvement of left ventricular EF after CABG in these patients (i.e. EF < 0.35) was not associated with poorer outcome compared with patients (also with EF < 0.35) with improved left ventricular EF post-CABG. 9 In a series of 135 patients with an EF < 0.35, 66% of patients had no significant change in EF (i.e. less than 0.05 increase in EF) post-CABG, yet survival, freedom from cardiac death and improvement in angina and heart failure scores were similar in both the groups (i.e. those with increases in postoperative EF > 0.05). 9 Elefteriades suggests that myocardial viability should be considered a continuum “from full thickness viability without any scar to full thickness scarring without viable cells”. 14 The few studies in these patients correlating preoperative viability studies (DE or thallium) with histological biopsies of explanted or operated hearts supports this view. 6,15 Zimmerman performed biopsies at the time of CABG to correlate thallium studies assessing viability with histological findings. The spectrum of interstitial fibrosis ranged from 15 to 60 volume % regardless of the classification of these segments as either reversible or irreversible. 6 Zimmerman concluded that “this binary classification into viable or nonviable segments appears to be an oversimplification and does not reflect the continuous nature of structural damage in coronary artery disease”. 6 The folly of excluding patients from CABG based solely on a negative thallium study was evident many times in patients with a purported “full thickness scar and no evidence of reversibility”; at surgery, viable myocardium and renewed effective contraction were present. 7,9 Therefore, the opposite end of this spectrum offers CABG, irrespective of viability testing. 4,7 Mickleborough reported a consecutive series of 125 patients (EF < 20%), without case selection on the basis of viability studies or visibility of distal vessels, with an operative mortality of 4% and excellent medium-term outcomes. 7 Mickleborough concluded that “all patients with graftable coronary disease, poor left ventricular function and akinetic or dyskinetic regions of the ventricle will benefit from surgery”. 7 The surgical results in these patients have improved since the pioneering achievements of Isom and, in Australia, Baird. 2,3 Operative mortality of 15% in the 1970's was reduced to 10% in the 1980's. 9,18–25 The STS database, covering 26,000 American patients, documented a mortality rate of 7.6% in patients having CABG (EF 10–30%). 26 Within the last decade mortality rates under 5% are common. 3,7,13,26–29 Differences in surgical series may reflect patient selection. 30,31 Nevertheless, the incidence of perioperative myocardial injury is low (i.e. <2%), in series with low mortality. 3,7,13,19,26,28 Hence, attention to myocardial protection is critical. There appears to be no significant difference between the different techniques of myocardial protection. 7,20,28 The optimal technique can be tailored to a specific patient; 10% of our patients were managed with VF and intermittent aortic cross clamping; off-pump CABG (5% of our patients) may further improve outcomes. 32 Our indiscriminate use of the left IMA may be a contributing factor to our perioperative and medium-term outcomes. 7,9,10 Elefteriades noted the same benefit despite concerns regarding the IMA's ability to deliver sufficient flow in the presence of exogenous inotropes. 9 We, like others, found two factors predictive of increased perioperative death: a recent AMI and nonelective surgery. 9,21,30 Nonelective surgery also had a significant impact on the occurrence of major complications. 7,9,21,30 Autopsy findings in these medically treated patients reveal a high incidence (33%) of acute coronary events. 33 Earlier presentation for surgery therefore may produce better outcomes. Long-term survival was significantly influenced by three variables: preoperative pulmonary edema, preoperative arrhythmia and nonelective surgery. Hence, the potential exists to improve long-term cardiac events by earlier surgery. 7,20,23,30 Further benefits may be possible as 15% of our patients appeared to be suboptimally medicated. 34 A randomized trial comparing medical versus CABG versus CABG with a new technique of surgical ventricular restoration (STITCH trial) is expected to report within 5 years. In the interim this study documents that the quality of life of these patients, by NYHA and CCVS class, is significantly improved after CABG. Importantly, patients perceive their health and well being as improved; 94% are satisfied with their surgery. Limitations of this Study This study has clear limitations. This is a retrospective study of referred patients hence bias in patient selection cannot be excluded but is likely present and reflects individual cardiologists and our bias regarding treating these patients. Although a consecutive series, we cannot know if only the sturdiest were preselected for surgical consideration. Also only 4% had non-LAD coronary disease. There is no control group to verify the superiority of CABG over medical treatment or percutaneous techniques. Like many surgical series, the majority (66%) of patients had moderate to severe angina. We, like others, adopt the view that therefore some myocardial viability must be present. However, the percentage of all patients with ischaemic cardiomyopathy and significantly stenosed and graftable coronary disease offered CABG is unknown. Also there is no clear consensus in the literature as to what is a poor left ventricle. We adopted the commonest definition, an EF ≤ 0.30. Therefore, comparisons between surgical series must be viewed with caution. Our total number of patients with nil to mild angina is small (36 cases). Of these, 19 had preoperative thallium scans, 3 of which revealed no evidence of reversibility. Of patients having preoperative thallium studies only 21 had less than large areas of myocardial viability. So too, thallium testing was performed solely at the discretion of the referring cardiologist thus not performed in all patients, or at one center with standardized protocols. Hence it is unclear whether the group of patients referred for thallium testing is representative of the whole group. To assess patient satisfaction with surgery, we used relevant parts of the SF-36 questionnaire because of logistic constraints. Although we have satisfactorily used this previously, this approach is not validated. 11 Importantly however, rather than ask a solitary question: are you satisfied with your surgery? And use that as the basis to make conclusions. We used 16 relevant questions from a validated source and asked patients directly; few have done so. We conclude that CABG is safe and effective in selected patients with chronic poor LV function and significantly stenosed coronary disease affecting the LAD and/or two major epicardial coronary arteries. The 5-year survival of 72.3 and 84% with good quality of life supports this clinical approach. In these patients, thallium studies were unnecessary and nonpredictive of successful revascularisation, particularly in those with nil to mild angina and nil to moderate areas of myocardial viability. Future improvements may be expected by earlier referral, improved patient selection with new imaging (MRI) and new surgical techniques (i.e. surgical ventricular restoration). 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