Assessment of coronary flow reserve with transthoracic Doppler echocardiography: Comparison among adenosine, standard-dose dipyridamole, and high-dose dipyridamole

Coronary flow reserve (CFR), defined as a ratio of hyperemic-to-basal coron ary now velocity, provides important information about the functional aspec t of coronary circulation. However, it usually is determined by invasive me thods during catheterization. Recent studies have shown that transthoracic Doppler echocardiography (TTDE) may be useful in the measurement of coronar y now velocity in the distal portion of the left anterior descending corona ry artery (LAD). The vasodilators used for hyperemia are adenosine and dipy ridamole. However, the coronary vasodilative response and systemic hemodyna mic effects of the two agents have not been directly compared with TTDE. We assessed blood flow velocity and vascular resistance in the distal LAD by TTDE during an intravenous a-minute adenosine infusion (140 mu g/kg/min) an d low- (0.56 mg/kg) and high-dose dipyridamole (0.84 mg/kg) infusion in 25 patients with patent LAD. Coronary now velocity was successfully recorded i n 20 patients (80%) during baseline and the consecutive vasodilator-infusio n period. Compared with low-dose dipyridamole, adenosine infusion induced a higher CFR (3.7 +/- 0.87 vs 2.73 +/- 0.65; P < .05) and a lower coronary r esistance index (0.31 +/- 0.04 vs 0.35 a 0.08; P < .05). But by increasing the dipyridamole dose to 0.84 mg/kg, the values of the CFR and coronary res istance index became comparable to those of adenosine infusion (2.85 +/- 0. 78 vs 3.03 +/- 0.7, P = not significant [NS]; 0.33 +/- 0.04 vs 0.32 +/- 0.0 9, P = NS; respectively). We conclude that adenosine seems to be a favorabl e vasodilator for the measurement of CFR with TTDE.