Cardiac Beta-Adrenergic Receptor Downregulation, Evaluated by Cardiac Positron Emission Tomography, in Chronotropic Incompetence

Abstract

The mechanism of chronotropic incompetence (CI), which has been associated with autonomic dysfunction, has not been elucidated in patients without heart failure (HF). Methods: Cardiac positron emission tomography using ¹¹C-CGP12177 was performed to investigate the cardiac beta-adrenergic receptor density (β-ARD) in 13 patients with CI without HF and six healthy controls. The maximum number of available specific ¹¹C-CGP12177 binding sites per gram of tissue was calculated in regions of interest using an established graphical method. Results: Peak heart rate was significantly lower in CI patients than in controls (116.9 ± 11.0 vs. 154.8 ± 14.4 beats/min, p < 0.001). β-ARD of the total myocardium was significantly lower in CI patients than in controls (4.3 ± 1.7 vs. 7.0 ± 1.7 pmol/mL, p = 0.005). Conclusion: Beta-adrenergic receptor downregulation was demonstrated in patients with CI without HF. Decreased β-ARD is a common feature in patients with CI, with or without HF.