Identifying Stunned Myocardium During Cardiac Surgery: The Role of Myocardial Contrast Echocardiography

Differentiation of reversibly stunned myocardium from irreversibly damaged (infarcted) myocardium is critically important in patient management. Current methods for monitoring myocardial function yield only nonspecific assessments of myocardial viability. On the other hand, myocardial contrast echocardiography (MCE) can be used to evaluate the extent of myocardial perfusion as well as the efficacy of myocardial protection in patients undergoing coronary artery bypass graft (CABG). This system includes an external ultrasound unit and an internal tracer, usually gaseous microbubbles, which reflect the ultrasonic beam. Previous studies have shown that myocardial risk areas identified with MCE correlate with areas defined by technetium autoradiography and infarction size. We have used MCE to evaluate coronary artery bypass patients (N = 21) with regard to myocardial function and cardioplegia perfusion patterns. A significant correlation (p < 0.01) was found between abnormal contrast enhanced cardioplegia patterns and depression of left ventricular function. Refinements to ultrasound technology and contrast agents will further enhance the diagnostic power of MCE for the quantification of myocardial blood flow.