NITROGLYCERIN ENHANCES THE ABILITY OF DOBUTAMINE STRESS ECHOCARDIOGRAPHY TO DETECT HIBERNATING MYOCARDIUM

Background A biphasic response of wall thickening with initial improve ment and subsequent deterioration during dobutamine stress echocardiog raphy (DSE) has been increasingly used for detection of hibernating my ocardium. However, the improvement of wall thickening at low-dose DSE may be limited in hibernating myocardium by severe hypoperfusion. Nitr oglycerin (NTG) improves myocardial perfusion, reduces oxygen demand, and may enhance low-dose dobutamine to improve wall thickening. Method s and Results A pig model of myocardial hibernation of 24 hours to 7 d ays was created through severe left anterior descending coronary arter y stenosis with coronary flow reductions of approximate to 40%, produc ing severe regional left ventricular dysfunction but no infarction in seven pigs. Myocardial infarction was produced in five pigs with occlu sion of the artery. DSE was performed with incremental doses with and without an NTG infusion of 50 to 100 mu g/min. In the hibernating grou p, NTG alone improved wall thickening in the hibernating region modest ly from 11.4+/-7.2% at baseline to 19.1+/-7.0%. The improvement was as sociated with increased regional coronary flow from 0.46+/-0.12 to 0.5 5+/-0.13 mL.beat(-1).100g myocardium-1 (P<.05). There was an additive effect of NTG re, low-dose (2.5 to 5 mu g.kg(-1).min(-1)) dobutamine o n wall thickening in the hibernating region. The improvement of wall t hickening of hibernating myocardium with NTG and dobutamine, from 23.7 +/-11.1% to 31.1+/-8.9% (P<.001), was associated with an increase in r egional coronary flow (P<.01). NTG did not prevent high doses of dobut amine from inducing deterioration of wall thickening in hibernating my ocardium. In the infarcted group, no improvement in wall thickening wa s observed in infarcted regions during NTG infusion, dobutamine infusi on, or the combination. Conclusions NTG enhances the improvement of wa ll thickening at low-dose dobutamine and does not prevent high-dose do butamine from inducing ischemia in hibernating myocardium. Thus, NTG a ugments the biphasic response of wall thickening and improves the accu racy of DSE for detecting viable myocardium.