Difference in Myocardial Flow Reserve Between Patients With Dilated Cardiomyopathy and Those With Dilated Phase of Hypertrophic Cardiomyopathy : Evaluation by ^<15>O-Water PET

Background The clinical features of patients with the dilated phase of hypertrophic cardiomyopathy (DHCM) may resemble those of patients with dilated cardiomyopathy (DCM); that is, systolic dysfunction and left ventricular dilatation. Myocardial flow reserve (MFR) is impaired in patients with nonischemic cardiomyopathy, and the reduced MFR may be related to poor prognosis. Several studies report that the mortality rate for patients with DHCM is higher than for DCM, but the difference between these 2 cardiomyopathies is still unclear. The purpose of this study was to assess the MFR of these 2 cardiomyopathies, using ^<15>O-water positron emission tomography (PET) to elucidate their differences. Methods and Results In total 30 patients were investigated: 23 with DCM (Group A) and 7 with DHCM (Group B). All those who were in a stable condition underwent cardiac catheterization. Myocardial blood flow (MBF) at rest and under ATP infusion was measured by ^<15>O-water PET, and the MFR was calculated. There were no significant differences in the hemodynamics of the 2 groups. The mean MFR in DHCM was significantly lower than that in DCM (1.49±0.31 vs 2.62±1.08; p=0.042), whereas MBF at rest did not differ (DCM vs DHCM: 0.66±0.20 vs 0.49±0.05ml-min-1-g-1; NS). The MFR in both Group A and B was significantly decreased com-pared with the normal controls (MFR in normal controls: 5.15±1.64, p=0.00015, 0.00013, respectively). Conclusions These results suggest that impaired vasodilatation (ie, dysfunction of the microcirculation) is more severe in patients with DHCM than in patients with DCM, even though patients' characteristics and hemo-dynamics do not differ.