Objective: Because hibernation is considered a down-regulation of contractile function in response to reduced regional myocardial perfusion, hibernating myocardium is expected to be supplied by a critically stenosed or even occluded coronary artery. Thus, high-dose dobutamine has been postulated to cause ischemia and reworsening of myocardial function (biphasic response), whereas myocardium that demonstrates sustained improvement with high-dose dobutamine should not be supplied by a significantly stenosed vessel. This study evaluates the type of dobutamine response-biphasic versus sustained improvement-of dyssynergic myocardium in relation to its angiographically documented blood supply.
Methods: In 38 patients (5 women; mean age 60 +/- 9 years) with chronic coronary artery disease and impaired left ventricular ejection fraction (</=35%), dobutamine echocardiography and quantitative coronary angiography were performed within 4 weeks. Wall-motion response of dyssynergic myocardium to dobutamine, classified as no improvement, biphasic response, or sustained improvement, was compared with the angiographically documented blood supply (presence of coronary stenosis in the corresponding artery, collaterals, and stenoses of the collateral supplying artery) in a segment-by-segment analysis.
Results: Of the 465 segments with abnormal wall motion at rest, 201 (47%) showed improvement during dobutamine infusion at low dose. Of these, 145 (72%) were supplied by significantly stenosed epicardial vessels. Only 27 (19%) of these 145 segments showed a biphasic response whereas in the remaining 118 segments wall-motion improvement persisted during high-dose dobutamine infusion. Although mean stenosis severity in the supplying vessel was significantly greater for segments presenting with biphasic response as compared with sustained improvement (95 +/- 7% and 86 +/- 12% luminal diameter reduction, respectively; P <.0001), 69% of segments with sustained improvement were supplied by a critically stenosed artery. Only 7 of 27 segments with biphasic response and 22 of 118 segments with sustained improvement had visible collaterals supplied by a vessel without significant stenosis. The percentage of segments viable by thallium-single photon emission computed tomography imaging was similar for those with sustained and biphasic response (96% and 83%, respectively).
Conclusions: In this group of patients with coronary artery disease and impaired left ventricular function, the great majority of dyssynergic segments that exhibited a sustained, rather than biphasic, dobutamine response were supplied by a critically stenosed artery. Furthermore, the percentage of segments viable by thallium-single photon emission computed tomography did not appear to be different for segments with sustained improvement and those with biphasic response. These findings challenge the hypothesis that biphasic response is the best criterion to identify viable myocardium.