Reply

We are grateful to Dr. Barletta for his comments. Obviously, the findings we have reported constitute an intermediate step of a biphasic response phenomenon, as stated by Dr. Barletta. However, a 5-min step protocol for low dose dobutamine echocardiography is common (1,2), and a biphasic response (i.e., wall motion improvement followed by worsening) is rarely observed at low doses of 5 to 10 μg/kg body weight per min (3). Nevertheless, no change in wall motion and thickening occurred during the 3 min after tracer injection, even when we used 10 μg/kg per min of dobutamine.

We also wish to emphasize that our study was not intended to describe the behavior of inotropic contractile reserve during low dose dobutamine infusion, but it was aimed at investigating the pathophysiologic and clinical implications of the presumed mismatch between perfusion and contractility in areas with severely hypoperfused viable myocardium.

• American College of Cardiology