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Pacemaker current inhibition in experimental human cardiac sympathetic activation: a double-blind, randomized,
C Schroeder1, K Heusser2, A A Zoerner2
11] Institute of Clinical Pharmacology, Hannover Medical School, Hannover, Germany [2] Experimental Clinical Research Center, Charité Medical Faculty and Max Delbrück Center for Molecular Medicine, Berlin, Germany.
Clinical Pharmacology and Therapeutics
|February 11, 2014
Summary
Inhibiting hyperpolarization-activated, cyclic nucleotide-gated 4 (HCN4) channels with ivabradine partially reduced heart rate during stress. However, it did not fully reverse autonomic imbalance, unlike metoprolol.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Pharmacology
Background:
- Hyperpolarization-activated, cyclic nucleotide-gated 4 (HCN4) channels are crucial for autonomic heart rate (HR) regulation.
- Autonomic imbalance, particularly sympathetic overactivation, impacts cardiovascular health.
- Targeting HCN4 channels offers a potential strategy to modulate HR and autonomic function.
Purpose of the Study:
- To investigate the efficacy of HCN4 channel inhibition in reversing autonomic imbalance during sympathetic activation.
- To compare the effects of ivabradine (HCN4 inhibitor) with metoprolol (beta-blocker) on cardiovascular parameters under stress.
Main Methods:
- A double-blind, randomized, crossover study involving 19 healthy men.
- Administration of oral metoprolol+reboxetine, ivabradine+reboxetine, or placebo+reboxetine.
- Assessment of HR, BP, stroke volume, cardiac output, HR variability, BP variability, and baroreflex sensitivity at rest and during orthostatic stress.
Main Results:
- Metoprolol, but not ivabradine, reduced resting HR and BP.
- Ivabradine attenuated the orthostatic HR increase less effectively than metoprolol.
- Metoprolol significantly reduced stroke volume and cardiac output at a given HR.
- Ivabradine did not alter HR variability, BP variability, or baroreflex sensitivity, unlike metoprolol.
Conclusions:
- Ivabradine attenuates sympathetic HR effects at the sinus node but does not fully counteract myocardial sympathetic activation.
- The ability of ivabradine to reverse parasympathetic dysfunction appears limited.
- HCN4 inhibition offers a distinct mechanism of HR control compared to beta-blockade, with differential effects on autonomic balance.
