986-76 β·Blockade Alters the Biphasic Response of Hibernating Myocardium to Incremental Doses of Dobutamine: Implications for Dobutamine Stress Echocardiography

Abstract

We have previously shown that an incremental dobutamine infusion induces a biphasic pattern of regional LV wall thickening in hibernating myocardium, with initial improvement and subsequent deterioration. This study was designed to evaluate whether and how a, β -blocker alters this pattern. A model of myocardial hibernation was created in 6 pigs (35–45 kg). A LAD stenosis was produced to decrease LAD flow to 40–70% of baseline. This decreased regional LV wall thickening by 45 to 100% and caused transient regional lactate production. This condition was maintained for 6–8 days, at which time dobutamine echocardiography with incremental doses from 2.5–30 μ g/kg/min was performed, both with and without an esmolol infusion of 50 μ g/kg/min. The stenosis was released after dobutamine echocardiography and the animals recovered for 7 days to evaluate the reversibility of the regional wall motion abnormalities. In all 6 pigs regional wall thickening initially improved but subsequently deteriorated during the dobutamine infusion. The maximal improvement was 10 ± 5% at a dose of 4.2 ± 3.5 μ g/kg/min. Esmolol infusion during dobutamine echocardiography did not alter the magnitude of the initial improvement, 12 ± 4% (p = NS); however, the time to peak improvement was delayed, so that it occurred at a higher dose of dobutamine, 17 ± 5 μ g/kg/min (p < 0.01). Esmolol prevented the late deterioration of wall thickening to below baseline in 3 of the 6 animals. By 1 week after restoration of LAD flow, one pig had died from a non-cardiac cause and regional wall motion recovered in the 5 others. The response pattern of chronic hibernating myocardium to dobutamine stress echocardiography is modified by a β -blocker: the initial improvement, though of similar magnitude, is delayed and late deterioration of regional wall thickening is attenuated. However, if initial improvement in regional wall motion is the criterion for viability, premedication with a β -blocker will not affect sensitivity.