Cardiac autonomic nerve abnormalities in chronic heart failure are associated with presynaptic vagal nerve degeneration

Background: Understanding of the functional and structural disturbances of cardiac autonomic nerves in ventricular hypertrophy and eventual chronic heart failure (CHF) remains unclear. Methods and results: ECG signals were obtained by a radio transmitter from male Wistar rats that received monocrotaline (MCT) via subcutaneous injection. Heart rate (HR) and HR variability (HRV) were analyzed. The RR interval, total power (TP), low frequency (LF) power, high frequency (HF) power, and LF/HF (L/H) power ratio were measured. Ultrastructural changes in cardiac autonomic nerves at the sinoatrial (SA) node region were studied using an electron microscope. TP and HF powers in MCT-induced right ventricular hypertrophy (RVH) and eventual CHF were significantly decreased, and HR was significantly increased at week 5 or later after the MCT injection. The electron microscopic findings indicated the depletion of neurotransmitter vesicles and degradation of parasympathetic but not sympathetic nerve endings in the SA node region of the heart. Conclusion: MCT-induced RVH and CHF rats showed presynaptic vagal nerve degradation prior to sympathetic nerve derangement in the heart.

► Monocrotaline-induced heart failure rats were examined by telemetric ECG.
► Electron microscopic findings show degradation of cardiac autonomic nerve endings.
► Heart rate variability indicates vagal nerve derangement in early heart failure.
► Heart rate variability indicates sympathetic derangement in late heart failure.
► Vagal structural and functional derangement was prior to those in sympathetic ones.