DEPENDENCY OF CONTRACTILE RESERVE ON MYOCARDIAL BLOOD-FLOW - IMPLICATIONS FOR THE ASSESSMENT OF MYOCARDIAL VIABILITY WITH DOBUTAMINE STRESSECHOCARDIOGRAPHY

Background Contractile reserve, improvement in contractile function du ring inotropic stimulation, is a proposed marker of viable myocardium. This study was designed to address, in patients with left ventricular dysfunction due to chronic coronary artery disease, whether contracti le reserve depends on myocardial blood flow. Methods and Results We st udied 19 patients, at rest and during dobutamine, with 2D echocardiogr aphy for regional mechanical function and PET for regional myocardial blood flow ([O-15]water) and oxygen consumption ([C-11]acetate). Of 16 6 myocardial segments, 21 had normal systolic function, 56 were dysfun ctional but contractile reserve-positive, and 89 were dysfunctional an d contractile reserve-negative. Myocardial blood flow at rest was lowe r in contractile reserve-negative (0.41+/-0.18 mL.g(-1).min(-1)) than in contractile reserve-positive (0.50+/-0.22 mL.g(-1).min(-1)) and nor mal segments (0.55+/-0.20 mL.g(-1) min(-1), P<.009). After dobutamine infusion, blood flow increased less in contractile reserve-negative 60 .63+/-0.38 mL.g(-1).min(-1)) than in contractile reserve-positive (1.2 8+/-0.65 mL.g(-1).min(-1)) and normal segments (1.93+/-0.83 mL.g(-1).m in(-1), P<.0001). Likewise, myocardial oxygen consumption was lower at rest in contractile reserve-negative (clearance rate of [C-11]acetate , 0.043+/-0.012 min(-1)) than in contractile reserve-positive (0.048+/ -0.01 min(-1)) and normal segments (0.058+/-0.008 min(-1), P<.02). Myo cardial oxygen consumption with dobutamine increased less in contracti le reserve-negative (0.060+/-0.013 min(-1)) than in contractile reserv e-positive (0.077+/-0.016 min(-1)) and normal segments (0.092+/-0.021 min(-1), P<.0001). Of segments defined as viable by PET, 54% were cont ractile reserve-negative and exhibited lower blood flow with dobutamin e (0.72+/-0.36 mL.g(-1).min(-1)) than with viable, contractile reserve -positive segments (1.29+/-0.70 mL.g(-1).min(-1), P<.0001). Conclusion s Contractile reserve depends, in part, on the level of myocardial blo od flow at rest and during inotropic stimulation.