INFRA-LOW DOSE DIPYRIDAMOLE TEST - A NOVEL DOSE REGIMEN FOR SELECTIVEASSESSMENT OF MYOCARDIAL VIABILITY BY VASODILATOR STRESS ECHOCARDIOGRAPHY

Low (0.56 mg.kg(-1) over 4 min) and high (0. 84 mg.kg(-1) over 10 min) doses of dipyridamole can identify viable myocardium through the cont ractile recovery of basally dyssynergic regions; however, it also indu ces ischaemia in susceptible patients. The aim of this study was to as sess the potential of an 'infra-low' dose of dipyridamole to selective ly identify myocardial viability, independently evaluated by low dose dobutamine. Forty patients with resting dyssynergy and angiographicall y assessed coronary artery disease (1-vessel in 18, 2-vessel in 12, an d 3-vessel in 10 patients) separately underwent a low dose dobutamine (5-10 mu g.kg(-1), min(-1) for 3 min) echo test and an infra-low dose (0.28 mg.kg(-1) over 4 min) dipyridamole echo test. Systolic blood pre ssure (rest: 131+/-19 mmHg) changed slightly after dobutamine (137 +/- 21, P<0.05 vs rest) and remained stable after dipyridamole (130 +/- 1 7, P=ns vs rest). Heart rate (rest: 68 +/- 13 beats.min(-1)) was also unchanged after dipyridamole (69 +/- 12, P=ns vs rest) and increased s lightly after dobutamine (71 +/- 15; P<0.05 vs rest and vs dipyridamol e). No patient developed echocardiographic or electrocardiographic sig ns of ischaemia after either dipyridamole or dobutamine. Of the 243 se gments with baseline dyssynergy, 70 were responders (i.e. they showed an improvement of 1 grade or more, from 1=normal/hyperkinetic to 4=dys kinetic in a 16-segment model of the left ventricle) by both dipyridam ole and dobutamine, 157 were non-responders (i.e. they showed no chang e) by both dipyridamole and dobutamine, and 16 showed discordant resul ts (five responders by dipyridamole only; 11 by dobutamine only). The overall concordance of dipyridamole and dobutamine was 93%. An echocar diographic follow-up could be obtained >6 weeks after successful revas cularization (achieved with angioplasty in 17, with by pass surgery in 3) in 19 patients and showed an improvement of one grade or more in 5 0 segments (viable) and no improvement in 50 segments (necrotic). The sensitivity of dobutamine and dipyridamole for predicting recovery was 76 and 78% respectively (P=ns); the specificity of both tests was 94% . In conclusion, infra-low dose dipyridamole is a haemodynamically neu tral stress lest which does not affect either heart rate or systolic b lood pressure; it allows myocardial viability to be explored selective ly, without eliciting ischaemia; it shows excellent overall concordanc e with low dose dobutamine and has good sensitivity and excellent spec ificity for predicting functional recovery following successful revasc ularization.