Effects of Acute Myocardial Ischemia on Regional Function of the Remote Nonischemic Myocardium in Dogs

Yoo, Kyung Yeon; Park, Su Tak; Lee, Jun Cheol; Park, Jong Hun; Gwak, Sang Hyun

Abstract

INTRODUCTION
During an acute myocardial ischemia, maintenance of overall ventricular function may depend on remote nonischemic myocardium. Whereas fentanyl has minimal hemodynamic effects, volatile anesthetics, including halothane and isoflurane cause negative inotropic and lusitropic effects in normal myocardium. This investigation examined the effects of volatile anesthetics in comparision with fentanyl on compensatory responses to brief left anterior descending coronary artery (LAD) occlusion in remote normal myocardium (left circumflex coronary artery (LCX) supply) in an open-chest canine model.
METHODS
Thirty-six mongrel dogs, acutely instrumented for measurement of pressure (left ventricle (LV) and aorta), flows (pulmonary trunk and LCX) and dimensions in ischemic and non-ischemic myocardium, were subjected to a 10-min LAD occlusion during fentanyl (n=10), halothane (n=13), or isoflurane (n=13) anesthesia. Regional contractile function was assessed using percent systolic shortening (%SS) and the preload recruitable stroke work slope (Mw). Diastolic function was evaluated using a regional time constant for intramyocardial pressure decline of LV (IMPtau), peak lengthening rate (dL/dtmax) and a regional chamber stiffness constant (Kp).
RESULTS
Acute LAD occlusion caused immediate deterioration of anterior wall function similarly without changes in cardiac index, mean arterial pressure and dP/dtmax in all three groups. LV end-diastolic pressure (LVEDP), LVPtau, and heart rate increased and dP/dtmin decreased to the same extent with regional myocardial ischemia in all groups. During fentanyl anesthesia, acute myocardial ischemia was associated with an increase in %SS (26%) and Mw (48%) in LCX area without changes in IMPtau and dL/dtmax. With halothane or isoflurane anesthesia, %SS, Mw and IMPtau showed similar changes as those in fentanyl in response to LAD occlusion. However, dL/dtmax was increased (47 and 45% in the halothane and isoflurane groups, respectively) and Kp was increased (34 and 33% in the halothane and isoflurane groups, respectively) less compared to fentanyl (78%). Enhanced function in LCX zone was associated with a comparable increase (21~28% from baseline) in LCX flow in all groups.
CONCLUSION
Enhanced regional contractility following acute coronary occlusion in nonischemic myocardium during fentanyl anesthesia is well-preserved with volatile anesthetics in an open-chest canine model. In addition, diastolic functions are also enhanced rather than depressed during anesthesia with volatile anesthetics. Halothane and isoflurane, however, do not differ in the compensatory responses to acute regional ischemia.