Identification of viable myocardium by dipyridamole-induced improvement in regional left ventricular function assessed by echocardiography in myocardial infarction and comparison with thallium scintigraphy at rest

Abstract

In patients with coronary artery disease and left ventricular impairment, the distinction between ventricular dysfunction due to myocardial fibrosis and postischemic, viable, although dyssynergic, myocardium has important clinical implications. Experimental studies have shown that dipyridamole can increase myocardial function in stunned segments, outlining a potential role of dipyridamole-induced functional recovery as an ultrasonic marker of myocardial viability. The aim of this study was to assess whether the increase of regional left ventricular function early during dipyridamole infusion in basally asynergic segments could identify viable myocardium recognized by rest injected, delayed (>14 hours from tracer injection) thallium and (in a subset of patients) late functional recovery evaluated by a follow-up echocardiogram at rest. Twenty-two patients with angiographically documented coronary artery disease and regional dysfunction in resting conditions (average left ventricular ejection fraction 43 ± 8%) were studied by echocardiography. All patients underwent a dipyridamole-echocardiographic test (up to 0.84 mg/kg over 10 minutes) and a delayed planar thallium study. A 13-segment model was used for both techniques. A score index ranging from 1 (normokinesia) to 4 (dyskinesia) was used for echocardiography. Thallium-201 activity was expressed in each segment as the percentage of maximal activity in the corresponding view. After dipyridamole, the wall motion score was assigned to each segment in resting conditions and at peak hyperkinesia before possible mechanical signs of ischemia. A segment was considered viable when there was a regional activity >55% of peak thallium and when a resting dyssynergy (echocardiographic score ≥2) showed an improvement of ≥1 grade by dipyridamole. In all, 80 basally asynergic segments were scored. Dipyridamole and thallium had concordant results in 21 of 26 thallium-viable and 52 of 54 thallium-necrotic segments. The 23 segments viable by dipyridamole had a higher thallium score than did the 57 necrotic by dipyridamole (73 ± 9 vs 42 ± 9; p < 0.01). In a subset of 15 patients, a follow-up echocardiogram at rest was obtained at 3.4 ± 2.7 months after the initial study. A significant functional recovery (improvement of ≥1 grade) was found in 15 of 19 segments with and only 5 of 39 without dipyridamole-induced improvement (79 vs 13%; p < 0.01). These observations suggest that dipyridamole-induced recovery in the contractile function of basally asynergic segments (possibly linked to the inotropic effect of increased flow) identifies areas with myocardial viability.