Coronary microvascular reactivity to sympathetic stimulation in patients with idiopathic dilated cardiomyopathy

The objective of this study was to assess noninvasively the microvascular r eactivity to sympathetic stimulation in patients with idiopathic dilated ca rdiomyopathy (IDC) and in healthy volunteers, who underwent cardiac cathete rization for exclusion of coronary artery disease. Methods: Myocardial flow was quantified with N-13-ammonia PET and tracer kinetic modeling at rest a nd in response to cold presser testing (CPT), Ten healthy Volunteers (8 men , 2 women; mean age +/- SD, 50.7 +/- 15 y) and 10 matched patients (8 men, 2 women; mean age, 52.5 +/- 14 y) with IDC (mean left ventricular ejection fraction, 0.30 +/- 0.12) were included in the study. Results: Myocardial pe rfusion at rest was not significantly different between the groups. However , myocardial vascular resistance (MVR) was significantly lower in IDC patie nts at rest than in healthy volunteers. In response to CPT a significant de crease in MVR was found in healthy volunteers (1.9 +/- 0.4 to 1.5 +/- 0.4 m m Hg x 100 g/mL; 22% decrease) but not in IDC patients (1.5 +/- 0.4 to 1.4 +/- 0.3 mm Hg x 100 g/mL; 9% decrease). Consequently, the increase of the m yocardial blood flow in response to CPT was significantly lower (P < 0.008) in IDC patients (56 +/-: 17 to 66 +/- 18 mL/100 g/min; 20% increase) compa red with healthy volunteers (52 +/- 12 to 80 +/- 30 mL/100 g/min; 52% incre ase), whereas both showed comparable hemodynamic reactions. Conclusion: The data indicate that CPT in combination with N-13 PET imaging is a valuable noninvasive tool for assessment of coronary microvascular reaction to sympa thetic stimulation in IDC patients. Lower coronary vascular resistance was found in IDC patients at rest compared with healthy volunteers, suggesting possible exhaustion of sympathetically induced dilation of the coronary mic rovasculature in IDC patients at rest. This mechanism may explain the impai red flow response to cold in IDC patients in the present study.