Cardiac β-Adrenergic Receptor Downregulation, Evaluated by Cardiac PET, in Chronotropic Incompetence.

The mechanism of chronotropic incompetence (CTI), which has been associated with autonomic dysfunction, has not been elucidated in patients without heart failure (HF). Cardiac PET using C-CGP12177 was performed to investigate the cardiac β-adrenergic receptor density (β-ARD) in 13 patients with CTI without HF and 6 healthy controls. The maximum number of available specific C-CGP12177 binding sites per gram of tissue was calculated in regions of interest using an established graphical method. Peak heart rate was significantly lower in CTI patients than in controls (116.9 ± 11.0 vs. 154.8 ± 14.4 beats/min, < 0.001). β-ARD of the total myocardium was significantly lower in CTI patients than in controls (4.3 ± 1.7 vs. 7.0 ± 1.7 pmol/mL, = 0.005). β-adrenergic receptor downregulation was demonstrated in patients with CTI without HF. Decreased β-ARD is a common feature in patients with CTI, with or without HF.