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ORIGINAL ARTICLE |
Department of Cardiovascular and Thoracic Surgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
Shantanu Pande,, MCh, Tel: +91 5222668800, Extn 2212, Fax: +91 5222668017, Email: spande{at}sgpgi.ac.in, Department of Cardiovascular and Thoracic Surgery, Lucknow 226014, UP, India.
ABSTRACT
The outcome of multivessel off-pump coronary artery bypass grafting in cases of severe left ventricular dysfunction was studied in 58 consecutive patients with ejection fraction 
35% who were followed up for a median of 15 months. Patients with ejection fractions 25% (group 1) had the largest left ventricular dimensions preoperatively, with gradual increases during follow-up; those with ejection fractions of 26%–35% (group 2) had smaller preoperative ventricular dimensions, with left ventricular regression postoperatively. There was more improvement in ejection fraction in group 2 than group 1 (33% vs. 10%). Mitral regurgitation improved from moderate to mild in group 2; whereas in group 1, mild mitral regurgitation progressed to moderate or severe during follow-up. Ejection fraction was a predictor of more frequent use of intraaortic balloon pumping, longer duration of inotropic use, a higher mean pulmonary artery-to-systemic arterial pressure ratio, and increased postoperative drainage.
Key Words: Coronary Artery Bypass • Off-Pump • Coronary Artery Disease • Mitral Valve Insufficiency • Left Ventricular Dysfunction
INTRODUCTION
Off-pump coronary artery bypass (OPCAB) in patients with severe left ventricular (LV) dysfunction continues to be a challenge for cardiac surgeons. There are reports of poor long-term survival of patients with coronary artery disease and severe LV dysfunction under medical therapy.1 Historically, coronary artery bypass grafting (CABG) in patients with LV dysfunction was associated with high perioperative mortality.2 However, advances in surgical techniques have led to improved outcomes, making CABG a relatively safe procedure in selected high-risk patients.3 Several prospective nonrandomized studies have supported the assumption that patients with the worst preoperative prognoses would benefit most from a less invasive procedure, avoiding cardiopulmonary bypass and cardioplegic arrest.4 The safety of OPCAB techniques in multivessel revascularization has been confirmed in this group of patients.5 The purpose of this study was to assess the midterm outcome of OPCAB in patients with LV dysfunction.
PATIENTS AND METHODS
Between January 2005 and January 2007, 510 patients underwent isolated OPCAB in our institute. The records of 58 consecutive patients with ejection fraction (EF) 35% on echocardiography who underwent isolated OPCAB for multivessel disease were reviewed retrospectively. Exclusion criteria were unstable angina or myocardial infarction within 90 days preoperatively, and severe mitral regurgitation (MR) because it required concomitant mitral valve repair.6 Data were collected from medical notes, charts, and patient interviews, preoperatively and postoperatively. Postoperative myocardial infarction was documented when there were new Q waves on the electrocardiogram or an increase to 5-times the upper normal value of serum troponin T at 12 h after revascularization. Patients with severe LV dysfunction and no evidence of angina or history of dyspnea on exertion were investigated by myocardial perfusion scintigraphy. A rest-redistribution protocol with thallium-201 was used to differentiate viable and nonviable myocardium. Thallium-201 rest-redistribution myocardial perfusion scintigraphy was acquired with a dual-headed gamma camera (DST XL; SMV, France) in anterior view with a 180° orbit (from right anterior oblique to left posterior oblique) in 32 projections and a matrix size of 64 x 64, after intravenous injection of 3 mCi of thallium chloride. Viability in each myocardial segment was assessed with Emory Cardiac Toolbox software (Syntermed, Inc., Atlanta, GA, USA).
Anesthesia was induced with propofol 1–2 mg·kg–1, pancuronium 0.1 mg·kg–1, and fentanyl 8–15 µg·kg–1. It was maintained with air-oxygen and propofol 2–3 mg·kg–1·h–1. Normothermia was maintained with warm intravenous fluids, a heating mattress, and humidified airway, in addition to a warm operating room. A perfusionist was kept on standby. A midline sternotomy was performed in all patients. Systemic pressure was kept >100 mm Hg by patient positioning, intravenous fluids, and inotropics, as indicated for adequate coronary perfusion. Heparin 1 mg·kg–1 was given just before dividing the distal end of the left internal mammary artery (LIMA). Skeletonization of the artery was carried out in all cases. An Octopus 3 stabilizer (Medtronic, Inc., Minneapolis, MN, USA) was used during distal anastomoses. An intracoronary shunt (Chase Medical, Richardson, TX, USA) of appropriate size was inserted to restore the coronary circulation to avoid regional wall ischemia during distal grafting. The 1st graft in all patients was LIMA to left anterior descending artery, after placing a sponge roll between the posterior LV aspect and the pericardium. All distal arterial anastomoses were completed using 8/0 polypropylene suture, venous anastomoses were undertaken with 7/0 polypropylene suture. After distal anastomosis of the LIMA graft, proximal anastomoses of reversed saphenous vein grafts were carried out using 6/0 polypropylene suture, under partial clamping of the ascending aorta. The next distal anastomoses were to the posterior descending or right coronary artery, followed by diagonal and/or obtuse marginal grafts. For posterior and lateral grafts, LV positioning was achieved by placing 2 posterior pericardial sutures: one between the inferior vena cava and left inferior pulmonary vein, and another 1 cm above the left inferior pulmonary vein. In patients requiring conversion to cardiopulmonary bypass, aortic and 2-stage single venous cannulation was used, and the operation was performed under normothermia with an empty beating heart, without aortic crossclamping. An Intraaortic baloon pump was inserted when, systolic arterial pressure fell to <70 mm Hg with the heart in its normal pericardial position, an intraaortic balloon pump (IABP) was inserted, with moderate to high inotropic support, during cardiac arrhythmia, or by rising pulmonary arterial pressure. An 8F 40 cc balloon (Arrow International, Everett, MA, USA) was inserted percutaneously from the groin, using a sheathless technique.
All patients were studied by transthoracic echocardiography prior to hospital discharge, at 6 months, and yearly thereafter. They were clinically reviewed at 1, 3, and 6 months, then yearly. All were prescribed a beta blocker and an angiotensin-converting enzyme inhibitor. Diuretics were discontinued after 3 months if there was no dyspnea on exertion. Aspirin 150 mg per day was continued, and patient-specific pharmacologic protocols of statin or antiarrhythmic therapy were recommended.
Results are reported as median and range. Comparison of the 2 groups was performed using the Mann Whitney U test. Intragroup comparison was carried out using the Wilcoxon signed rank sum test. A p value <0.05 was considered significant. Pearson’s correlation was obtained between variables when required. Univariate analysis was undertaken to determine the effect of EF on outcome variables, using logistic regression analysis. All analyses were performed using SPSS version 10.0 software (SPSS, Inc., Chicago, IL, USA).
RESULTS
The patients were followed up for 6–38 months (median, 15 months). They were divided into 2 groups based on EF: group 1 was 21 patients with EF 25%; group 2 was 37 with EF of 26%–35%. The demographic profile and risk factors in each group are given in Table 1
. Pre- and postoperative clinical and echocardiographic parameters are compared according to group in Table 2. Improvement in functional class corresponded with a significant improvement in EF. There was a significant difference in LV dimensions pre- and postoperatively in both groups, with greater LV dilatation in group 1. There was a gradual increase in LV dilatation in group 1, whereas LV regression occurred in group 2 during follow-up. There was a greater improvement in EF in group 2 (from 33% to 40%) compared to group 1 (from 22.5% to 25%). The higher mean pulmonary artery-to-systemic arterial pressure ratio in group 1 indicates more hemodynamic instability due to handling of the heart during OPCAB. IABP usage was significantly higher in group 1 patients, who also needed more inotropic support, longer ventilation time, greater postoperative drainage, and longer hospital stay than those in group 2 (Table 3). MR was observed preoperatively in significantly more patients and with higher grades in group 1 than group 2, and this difference persisted at the latest follow-up. While MR worsened in group 1 during follow-up, it remained the same or improved in group 2. There were 4 conversions to conventional CABG on cardiopulmonary bypass: all occurred after LIMA-to-left anterior descending artery anastomosis, while performing inferior or lateral grafts. The reason for conversion was hemodynamic compromise (systolic arterial pressure <70 mm Hg with rise in pulmonary arterial pressure). Preoperatively, myocardial viability studies were performed in 19 patients. Nonviable anterior wall was observed in 6/12 patients in group 1, and 4/7 in group 2. A significant positive correlation was noted between nonviable septum and the change in LV size at end-systole (r = 0.59; p = 0.04). A strong negative correlation was found between nonviable anterior wall and mean pulmonary artery-to-systemic arterial pressure ratio (r = –0.608, p = 0.02). EF was a predictor of higher frequency of balloon pump use (p = 0.007; odds ratio = 0.14), longer inotropic use (p = 0.04; odds ratio = 0.93), higher mean pulmonary artery-to-systemic arterial pressure ratio (p = 0.04; odds ratio = 0.01), and more postoperative drainage (p = 0.01; odds ratio = 0.99) on univariate analysis of outcome variables based on EF as a dependent variable. Pre- and postoperative serum creatinine, LV dimensions, intensive care unit stay, ventilation time, hospital stay, and mortality were not dependent on EF. There was no postoperative myocardial infarction. Two (3.4%) hospital deaths occurred: one in each group; both were due to low cardiac output in the immediate postoperative period. There was 1 death during follow-up in group 1, due to severe bronchopneumonia 4 months after the operation. There was no complaint of angina during follow-up, and no interventions or coronary angiography were required. One patient in group 1 was hospitalized after 8 months due to LV failure and severe MR. This patient was managed medically, and discharged with symptomatic improvement.
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An increasing number of patients are presenting with ischemic cardiomyopathy. The shortage of cardiac transplant donors and increased age at presentation make this option questionable. Thus there is a growing need for OPCAB in patients with severe LV dysfunction. Mortality in patients with congestive heart failure is directly related to ventricular systolic function, the extent of hypercontractile myocardium, and the treatment chosen.7–9 Early and midterm mortality rates in this study were similar to previous reports.10 During follow-up, no patient required reoperation or intervention, and there was clinical improvement in symptoms.11 This is consistent with the finding that preoperative angina predicts improvement, and our observation that dyspnea does not preclude improvement.12 It is advised to confirm whether LV dysfunction is potentially reversible when considering CABG for such patients;11 however, we observed improvement in functional class even in those with nonviable myocardium.
Severe LV dysfunction (EF < 25%) tended to be associated with LV dilatation during follow-up, although it was not statistically significant. This suggests deteriorating clinical status and potential mortality in long-term follow-up. DeRose and colleagues12 reported 5- and 10-year survival rates of 68% and 45%, respectively, in similar patients. Our study showed greater EF improvement in group 2 patients, with regression of LV dimensions and decreasing MR, suggesting that the 2 groups behave differently during midterm follow-up, and may have different long-term outcomes. IABP use was higher in group 1 (47.6%) than group 2 (10.8%). The IABP was inserted before induction in these cases. Preoperative IABP use may reduce mortality.13 The incidence of ischemic MR in patients undergoing CABG varies from 4% to 7%;14 in our study, it was 24.1% (18.9% had mild MR, 5.1% had moderate MR). The incidence of ischemic MR in patients with severe LV dysfunction can be as high as 43%.15 MR improved from moderate to mild in 2 patients in group 2, and mild MR persisted in 4 others. In group 1, mild MR progressed to moderate or severe MR during follow-up. In contrast, Bouchart and colleagues16 observed a decrease in mild MR, with moderate MR remaining unchanged. They found 58% freedom from cardiac death in patients with moderate MR, compared to 88% in those with no MR. Because of the increase in MR grade in group 1, a strategy of mitral valve repair along with revascularization may benefit these patients. Despite the increased operative mortality of 15%–33% associated with mitral valve repair or replacement, patients with moderate to severe MR would avoid the 2-fold increase in risk of death at 5 years.17 Further studies are required to clarify the early and long-term outcome with moderate ischemic MR.
The positive correlation between nonviable septum and change in LV dimensions suggests continued remodeling. Lorusso and colleagues17 observed improved LV function immediately postoperatively, with a gradual fall during follow-up. Ischemic myocardial dysfunction may be associated with progressive fibrosis, in which activated interstitial fibroblasts may have a prominent role through the production of extracellular matrix.18 The highly negative correlation between nonviable anterior wall and mean pulmonary artery-to-systemic arterial pressure ratio preoperatively may indicate potential hemodynamic instability while performing OPCAB, which may explain the higher rate of IABP use in group 2.19
We concluded that OPCAB can be safely performed in patients with severe LV dysfunction. Although all patients with EF < 35% experienced improved functional class after OPCAB, those with EF 25% tended to have progressive LV dilatation and worsening MR during midterm follow-up.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:54-58
© 2009 by SAGE Publications
DOI: 10.1177/0218492309102540
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