Low-level exercise echocardiography detects contractile reserve and predicts reversible dysfunction after acute myocardial infarction : Comparison with low-dose dobutamine echocardiography

OBJECTIVES The aim of this study was to evaluate low-level exercise echocardiography (LLEE) in detecting contractile reserve and predicting functional improvement of akinetic myocardium early after acute myocardial infarction (AMI). BACKGROUND Experimental and clinical studies have shown that low-dose dobutamine enhances contractile function of dyssynergic but viable myocardium in patients with recent AMI. We hypothesized that endogenous catecholamines produced during LLEE test could serve as myocardial stressor to elicit contractile reserve. METHODS Fifty-two consecutive patients with first AMI and ≥2 akinetic segments in the infarct-related territory underwent 5 ± 2 days after AMI low-dose dobutamine echocardiography (LDDE) (5, 10 and 15 μg/kg/min) and LLEE (25 W during 3 min on supine bicycle, with continuous echocardiographic recording). Both tests were performed on the same day, in random order. Follow-up echocardiography was obtained one month later. Regional wall thickening was semi-quantitatively assessed using 16-segment, 5-grade scale model. Contractile reserve was defined as improvement in wall thickening of ≥1 grade. RESULTS Mean increase in heart rate during stress tests was 15 ± 7 beats/min with LLEE and 13 ± 6 beats/min with LDDE (p = NS). Contractile reserve was detected in 119 (55%) of 217 akinetic segments at LLEE and in 137 (63%) segments at LDDE. At follow-up study, functional improvement was identified in 139 (64%) segments. Sensitivity, specificity and positive and negative predictive values for predicting functional recovery were 81%, 92%, 95% and 73%, respectively, for LLEE, and 91%, 86%, 92% and 84%, respectively, for LDDE. Moreover, there was good correlation between systolic wall thickening measured in the center of the dyssynergic are during stress tests and at follow-up study: r = 0.77, p < 0.001 with exercise testing and r = 0.73, p < 0.001 with dobutamine testing. CONCLUSIONS Low-level exercise echocardiography provides promising alternative to LDDE for identifying myocardial viability and predicting reversible dysfunction early after AMI.