Regional Left Ventricular Systolic Function in Humans During Off-Pump Coronary Bypass Surgery

Abstract

Background-Controversy exists as to whether off-pump CABG with local occlusion results in clinically significant myocardial ischemia during the occlusion period. This study was undertaken to delineate the effects of transient local coronary artery occlusion on regional systolic function. Methods and Results-Eight consenting patients undergoing left internal mammary to left anterior descending coronary artery (LAD) bypass were instrumented with a left ventricular pressure catheter and 2 subepicardial cylindrical ultrasonic dimension transducers placed in the minor axis dimension in the region served by the LAD. A digital sonomicrometer was used to collect data before, during, and after coronary occlusion from which percent systolic shortening and pressure-dimension loops were derived. Measuring devices were removed immediately after the final time point. All patients tolerated the procedure well, and there were no complications. Average duration of local occlusion needed for CABG was 15.9Ϯ4.4 minutes (range, 12 to 26 minutes). Local occlusion was associated with a decrease in peak systolic shortening from 5.8Ϯ0.8% to 1.8Ϯ0.8%. In all cases, function returned to baseline after restoration of flow. Pressure-dimension loops confirmed these findings and no evidence of diastolic creep. Linear repression analysis of degree of stenosis versus change in segmental shortening revealed a significant inverse correlation. Conclusions-Local occlusion of the LAD resulted in a transient decrease in myocardial function during occlusion with complete recovery during reperfusion. This change was less significant with increasing degrees of coronary stenosis. These data suggest that local occlusion is not associated with permanent myocardial injury but that ischemic changes do occur that may be clinically significant, especially in patients with lesser degrees of coronary stenosis. Key Words: coronary disease Ⅲ revascularization Ⅲ surgery C oronary artery bypass grafting without cardiopulmonary bypass has become an increasingly practiced technique for myocardial revascularization. This method generally uses local coronary occlusion, resulting in a brief period of myocardial ischemia. Although the effects of ischemia on regional myocardial function have been studied extensively in animal models, 1-10 the significance of limited periods of ischemia on human heart function is not well defined. The development of regional ultrasonic dimension analysis by Theroux and associates 2,3 allowed accurate determination of changes in regional myocardial function. Using this technology, Edwards et al 4 characterized the geometric alterations in myocardium during ischemia as a time-dependent stretch of myocardial segments called "creep." Glower and associates 5 showed that the reversal of diastolic creep correlated with recovery of systolic function after reversible ischemic injury.The purpose of this investigation is to define the effects of acute transient myocardial ischemia on regional systolic function in the face of chronic ischemia caused by...

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“…Subepicardial, multidirectional ultrasonic 0.7-mm dimension crystals (Sonometrics; Ontario, Canada) were implanted 10 mm apart in the minor axis plane to subtend the myocardial region supplied by the LAD and to measure longitudinal segment length shortening with highfrequency sampling (Ͼ100 Hz) (8). Segmental shortening in the ischemic and nonischemic regions was compared, at the indicated time points (Table 1), using Sonosoft sonomicrometer analysis software (version 3.1.0, Sonometrics).…”

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“…Based on measurements from ultrasonic dimensions transducers in the region served by LAD, Brown et al concluded that local occlusion is not associated with permanent myocardial injury, but that ichemic changes do occur that may be clinically significant, especially in patients with lesser degrees of coronary stenoses (23).…”

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