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Coronary Microvascular Reactivity to Sympathetic Stimulation in Patients with Idiopathic Dilated Cardiomyopathy

Departments of Nuclear Medicine and Cardiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany

Correspondence: For correspondence or reprints contact: Alexander E. Drzezga, MD, Technische Universität München, Nuklearmedizinische Klinik u. Poliklinik, Klinikum rechts der Isar, Ismaningerstr. 22, München, 81675, Germany.

ABSTRACT

The objective of this study was to assess noninvasively the microvascular reactivity to sympathetic stimulation in patients with idiopathic dilated cardiomyopathy (IDC) and in healthy volunteers, who underwent cardiac catheterization for exclusion of coronary artery disease. Methods: Myocardial flow was quantified with ¹³N-ammonia PET and tracer kinetic modeling at rest and in response to cold pressor 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 perfusion at rest was not significantly different between the groups. However, myocardial vascular resistance (MVR) was significantly lower in IDC patients at rest than in healthy volunteers. In response to CPT a significant decrease in MVR was found in healthy volunteers (1.9 ± 0.4 to 1.5 ± 0.4 mm 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 myocardial 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) compared with healthy volunteers (52 ± 12 to 80 ± 30 mL/100 g/min; 52% increase), whereas both showed comparable hemodynamic reactions. Conclusion: The data indicate that CPT in combination with ¹³N PET imaging is a valuable noninvasive tool for assessment of coronary microvascular reaction to sympathetic 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 microvas-culature in IDC patients at rest. This mechanism may explain the impaired flow response to cold in IDC patients in the present study.

Key Words: PET • idiopathic dilated cardiomyopathy • cold pressor test