Evaluation of the extent and timing of the coronary hyperemic response to dipyridamole: A study with transesophageal echocardiography and positron emission tomography with oxygen 15 water
Coronary flow reserve may be measured with Doppler-derived coronary blood-flow velocity or scintigraphic assessment of myocardial perfusion. The purpose of this study was to compare coronary flow velocity and perfusion measures of flow reserve with respect to their extent and time course. Coronary flow velocity reserve in the proximal left anterior descending coronary artery measured by pulsed-wave Doppler at transesophageal echocardiography, with measures of perfusion reserve obtained in the corresponding territory, were measured by a standard O15 water technique at positron emission tomography. Eighteen male volunteers underwent both tests on different days in random order, with dipyridamole stress (0.56 mg/kg). After correction of resting flow and perfusion measurements to a standard cardiac workload (to compensate for heterogeneity in hemodynamics between the two studies), coronary flow reserve was calculated as the ratio between dipyridamoleand corrected resting flow. The uncorrected perfusion reserve measured by positron emission tomography was 3.7 +/- 1.2, compared with a corrected perfusion reserve of 2.3 +/- 0.7. This correlated with a corrected flow velocity reserve of 2.9 +/- 1.0 at transesophageal echocardiography (R = 0.92; p < 0.001). The mean difference between these results was 0.58 +/- 0.41; discrepant results occurred at higher flows, in the presence of discordant blood pressure responses to stress, and because of intersubject variations in the timing of the peak coronary flow response, which were detected by continuous monitoring at transesophageal echocardiography. Measurement of coronary flow reserve at transesophageal echocardiography correlates well with measurements at positron emission tomography, and discrepancies are minimized if measurements are taken at the same time after dipyridamole.