MYOCARDIAL BLOOD-FLOW RESPONSE TO PACING TACHYCARDIA AND TO DIPYRIDAMOLE INFUSION IN PATIENTS WITH DILATED CARDIOMYOPATHY WITHOUT OVERT HEART-FAILURE - A QUANTITATIVE ASSESSMENT BY POSITRON EMISSION TOMOGRAPHY

Background Myocardial blood flow (MBF) impairment has been documented in advanced dilated cardiomyopathy (DCM) in which hemodynamic factors, secondary to severe ventricular dysfunction, may limit myocardial perfusion. To assess whether MBF impairment in DCM may also be present independent of hemodynamic factors, the present study was designed to quan tify myocardial perfusion in patients with mild disease without overt heart failure. Methods and Results Absolute regional MBF (milliliters per minute per gram) was measured by positron emission tomography and N-13-ammonia in resting conditions, during pacing-induced tachycardia, and after dipyridamole infusion (0.56 mg/kg over 4 minutes) in 22 DCM patients and in 13 healthy subjects. Patients were in New York Heart Association functional class I-II and showed depressed left ventricular (LV) ejection fraction by radionuclide angiography (35+/-8%; range, 21% to 48%), normal coronary angiography, and normal or moderately increased LV end-diastolic pressure (9.2+/-5.5 mm Hg; range, 2 to 20 mm Hg). There were no differences in arterial blood pressure, heart rate, and rate-pressure product between patients and control subjects in the three study conditions. Compared with control subjects, DCM patients had lower mean MBF at rest (0.80+/-0.25 versus 1.08+/-0.20 mL . min(-1). g(-1), P<.01), during atrial pacing tachycardia (1.21+/-0.59 versus 2.03+/-0.64 mL . min(-1). g(-1), P<.01), and after dipyridamole infusion (1.98+/-0.76 versus 3.78+/-0.86 mL . min(-1). g(-1), P<.01). LV MBF values were related to baseline LV end-diastolic pressure at rest (r=-.57, P<.01) and during pacing (r=-.67, P<.01) but not after dipyridamole infusion (r=.19, P=.40). Five patients had LV end-diastolic pressure >12 mm Hg; in 4, myocardial perfusion was severely depressed both at baseline and in response to stress. Conclusions In patients with DCM without overt heart failure, myocardial perfusion is impaired both at rest and in response to vasodilating stimuli. The abnormalities in vasodilating capability can be present despite normal hemodynamics; progression of the disease is associated with more depressed myocardial perfusion.