Ultra-early risk stratification after myocardial infarction via pharmacological stress echocardiography: the relative value of resting function, viability and myocardial ischemia.

BACKGROUND

Echocardiographically recognized resting function, myocardial viability (by low-dose dobutamine) and stress-induced ischemia (by high-dose dipyridamole) are potent predictors of subsequent events, but their relative value in patients evaluated very early after acute myocardial infarction remains to be established.

AIM OF THE STUDY

To assess the feasibility and usefulness of an integrated approach with resting and pharmacological stress echo for risk stratification in patients evaluated very early after myocardial infarction.

METHODS

Sixty acute myocardial infarction patients without contraindications to stress testing, and who were being given thrombolytic therapy, underwent resting echo (16-segment model of left ventricle, each segment scored from 1 = normo-hyperkinetic to 4 = dyskinetic), high-dose dipyridamole (up to 0.84 mg/kg over 10') and low-dose dobutamine (up to 10 mcg/kg/min) echo on the third-fourth day after drug withdrawal. The response was "ischemic" with a dipyridamole-induced increase in the regional score > 1 in segments with a resting score < 3, and "viable" with a dobutamine-induced decrease in the regional score > 1 in segments with resting score > 1. All patients underwent coronary angiography on the tenth-twelfth day after the acute event, and all of them were followed up for 15 +/- 10.04 months.

RESULTS

Ischemia elicited by dipyridamole appeared in 29 patients (48%) and dobutamine-induced viability was observed in 28 (47%). Ischemic events occurred in 26 patients (43.4%), five of which during the early in-hospital period. There were three deaths (5%), one re-AMI (1.7%), 7 Canadian Class III-IV angina (12%) and 15 (25%) early revascularization procedures undertaken independently of stress echo results. Events occurred in 21 patients (72%) with dipyridamole-induced ischemia and in 5 (16%) without it (p < 0.001). Likewise, events occurred in 13 patients (46.4%) with dobutamine-induced inotropic recovery and in 13 (40.6%) without it (p = ns). Event-free survival occurred in 64% of dipyridamole-positive patients, as opposed to 90% of dipyridamole-negative patients (p = 0.025). Dipyridamole echocardiographic test sensitivity and specificity for events were 81 and 74%, respectively. Sensitivity and specificity for events of dobutamine viability were 46 and 55%, respectively. In a multivariate logistic analysis, dipyridamole-induced myocardial ischemia was the strongest predictor of subsequent events (p = 0.01). According to Cox analysis, dipyridamole positivity had a relative risk estimate of 4.

CONCLUSIONS

Pharmacological stress echo is feasible even very early after acute myocardial infarction via a useful approach based on low-dose dobutamine to assess myocardial viability, and high-dose dipyridamole to assess ischemia. For risk stratification purposes, stress-induced myocardial ischemia outperforms resting function and myocardial viability, and it is independent of angiographic data. Revascularization procedures do not seem to be effective when only viability is present.