Early coronary reperfusion following acute myocardial infarction (AMI) can limit myocardial necrosis and permit functional recovery of the muscle. Previous studies have shown that low-dose dobutamine echocardiography can identify viable tissue and can be used to predict functional recovery in patients who have had an AMI. However, endogenous catecholamines produced by low-level exercise echocardiography may provide a better test of myocardial recovery. Hoffer and colleagues compared the effectiveness of low-level exercise echocardiography and low-dose dobutamine echocardiography after AMI in detecting contractile reserve and predicting functional recovery.
Patients were enrolled prospectively if they had suffered an AMI and if their baseline echocardiogram showed two or more akinetic left ventricular segments in the infarct-related territory of the myocardium. Approximately five days after the acute injury, patients received low-dose dobutamine echocardiography and low-level exercise echocardiography. Both tests were done on the same day and in random order. The exercise tests were performed with the patient in a semisupine position on a tilting exercise table. A 25-lb weight was maintained for three minutes with continuous echocardiography. Dobutamine was infused intravenously at dosages of 5, 10 and 15 mg per kg per minute in periods of three minutes with patients in a left lateral decubitus position. Routine follow-up echocardiography was performed one month after the AMI. Contractile reserve and functional recovery were identified as improvement in the wall thickening of the myocardium in at least two contiguous infarct zone segments.
Fifty-two consecutive patients were enrolled in the study. Mean increases in heart rate were 15 beats per minute with low-level exercise echocardiography and 13 beats per minute with low-dose dobutamine echocardiography. However, systolic blood pressure did not increase significantly during either test. Both tests detected contractile reserve in at least two contiguous segments of akinetic myocardium, with low-level exercise echocardiography detecting reserve in 55 percent of these segments and low-dose dobutamine echocardiography detecting reserve in 63 percent. The sensitivities, specificities, and negative and positive predictive values were similar in both tests. Correlation between the two tests was also good. Neither test was associated with an increased number of adverse events.
The authors conclude that low-level exercise echocardiography is a viable alternative to low-dose dobutamine echocardiography for evaluating myocardial viability and functional recovery. Performed after an AMI, low-level exercise echocardiography is a valuable tool that can help identify viable tissue and predict functional recovery following AMI.