Postoperative ventricular function and cardiac enzymes after on-pump versus off-pump CABG surgery.

I t is not known whether the extent and time course of myocardial dysfunction and recovery differ between patients undergoing off-pump coronary artery bypass surgery (CABG) and on-pump CABG. We conducted a nonrandomized pilot study to assess myocardial stunning and the time course of functional recovery in patients undergoing offand on-pump CABG. Ventricular function was assessed using myocardial contrast echocardiography because contrast-enhanced images provide better endocardial border definition and patients who have undergone cardiac surgery generally have limited acoustic windows after operation. • • • Adult patients who were eligible for both offand on-pump CABG were recruited for this study. The type of CABG was determined before study recruitment, and 2 surgeons performed all operations. Patients were excluded if they were considered ineligible for off-pump CABG (e.g. hemodynamic instability, target distal vessels 1.5 mm, vessels inadequately visualized, or heavily calcified vessels), or if they were only suited for off-pump CABG (e.g. severe lung, renal, or aortic disease). Patients were also excluded if they had undergone prior CABG, had hemodynamic instability, had associated severe cardiac or medical conditions, could not return for follow-up 3 to 4 weeks after surgery, or had prestudy echocardiographic images that were technically unsatisfactory for detailed assessment of left ventricular (LV) function. The first 12 qualifying patients were enrolled in the study: 6 underwent offand 6 on-pump CABG. Both groups of patients received the same, standardized, intraoperative and perioperative care. In patients who had undergone conventional CABG, myocardial preservation during cardiopulmonary bypass (uniformly blood plegia), topical cold drip, and aortic cross clamping were standardized. Electrocardiographic ST-segment changes were monitored with electrocardiographic recordings after operation. The outcomes for this analysis were LV function measured by ejection fraction (EF) and assessed using myocardial contrast echocardiography, and biochemical markers of procedural ischemic damage measured with cardiac enzyme markers including creatinine kinase (CK), the MB isoform of CK (CK-MB), and troponin I. Cardiac enzymes were measured before, and at 6, 12, and 24 hours after operation. Patients underwent a total of 4 contrast-enhanced echocardiographic studies: before, 1 day after, 3 days after, and 1 month after operation. Because of the fresh sternal surgical wound, only apical windows (4and 2-chamber views) were available for echocardiographic evaluation. After baseline precontrast echocardiographic images were acquired with standardized parameters, Optison contrast (3 ml) (Mallinckrodt, Inc., Hazelwood, Missouri) was infused intravenously at a rate of 80 ml/hour, and later adjusted as needed to obtain optimal myocardial opacification. Two observers, blinded to patient identification, the stage of the study, and each other’s interpretation, read each echocardiographic study to assess global LV function and to score 5 anatomic regions (anterior, apex, lateral, inferior, and septum) with respect to regional LV function before and after contrast enhancement using the semiquantitative methods recommended by the American Society of Echocardiography. Primary image analysis was limited to the contrast-enhanced images. Final scoring of images was the average of the EF estimates from the 2 observers. In the event the discrepancy between absolute EF estimates was 10%, a final estimate was obtained from a consensus reading by the blinded observers. Between-group differences in EF and cardiac enzymes were compared using analysis of variance for continuous variables with a normal distribution, and Wilcoxon’s rank-sum test for those with a non-normal distribution. The changes over time in EF and enzymes were compared between groups using repeatedmeasures regression. All scores from the 2 observers for echocardiographic image analyses were tested for interobserver variability using intraclass correlation and tests. Changes in baseline-to-peak enzyme level were compared with changes in preoperative-to-postoperative EF in each CABG group, and changes in regional wall motion were compared among wall segments, with correlation tests (Spearman’s ). Alpha levels of 0.05 based on a 2-tailed test were used to define statistical significance. The median age was 73 years in the group who had off-pump CABG and 58 years in the on-pump CABG group (Wilcoxon p 0.03) (Table 1). Off-pump From the Departments of Medicine and Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland. This study was supported by Grant M01-RR00052 from the National Institutes of Health/National Center for Research Resources, Bethesda, Maryland. Dr. Chang’s address is: Division of Cardiology, Carnegie 568, The Johns Hopkins Hospital, 600 North Wolfe Street, Baltimore, Maryland 21287. E-mail: pchang@jhmi.edu. Manuscript received October 19, 2001; revised manuscript received and accepted January 24, 2002.