Effect of beta-blockade on low-dose dobutamine-induced changes in left ventricular function in healthy volunteers: assessment by gated SPET myocardial perfusion scintigraphy

Viability studies are often performed in patients receiving beta-blocking a gents. However, the intake of beta-blocking agents could influence the iden tification of viable myocardium when low-dose dobutamine is used to demonst rate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomograph ic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once "on" and once "off" beta-blocker therapy (metoprolol succinate, 100 mg day (-1)). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosm in on a triple-headed camera equipped with focussing (Cardiofocal) collimat ors. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 mu g kg(-1) min(-1) dobutamine. Wall thickening (WT) was quantified using a method based on circumferential prof ile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were re corded at the end of each acquisition. At baseline LVEF WT and systolic BP values under beta-blockade were not significantly different from those obta ined in the non-beta-blocked state. The mean HR and diastolic BP at baselin e were lower under beta-blockade. Dobutamine administration (at 5 and 10 mu g kg(-1) min(-1)) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT. LVEF and systolic BP in the beta-blocked state were less pronounced but not sig nificantly different. HR increased significantly at 10 mu g kg(-1) min(-1) dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjec ts attenuates the inotropic and chronotropic myocardial response to low-dos e dobutamine. At doses of 5 and 10 mu g kg(-1) min(-1) dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scinti graphy acquisitions even under beta-blocker therapy.