Heart rate variability alters cardiac repolarization and electromechanical dynamics.

Area of Science:

• Cardiovascular Physiology
• Computational Biology
• Cardiac Electrophysiology

Background:

• Heart rate variability (HRV) reflects autonomic nervous system activity and is crucial for normal cardiac function.
• Low HRV is linked to increased risk of cardiac arrhythmias.
• Alternans, characterized by beat-to-beat alternations in action potential duration and intracellular calcium, is a known arrhythmogenic mechanism often studied under fixed pacing rates.

Purpose of the Study:

• To investigate the impact of HRV on the interplay between action potential duration (APD), intracellular calcium (Ca) dynamics, and electromechanical properties.
• To determine if HRV can mitigate arrhythmogenic alternans.

Main Methods:

• Utilized a nonlinear discrete-time map model to simulate APD and intracellular Ca cycling.
• Incorporated a stochastic pacing period to represent HRV.
• Analyzed the effects of varying HRV on APD and Ca transients.

Main Results:

• HRV decreased variations in APD and peak Ca at fast pacing rates where alternans typically occurs.
• Increased HRV disrupted alternans patterns for both APD and peak Ca.
• HRV weakened the correlation between APD and peak Ca, decoupling Ca-mediated instabilities from repolarization alternans.
• Sarcoplasmic reticulum Ca uptake rate modulated the efficacy of HRV's effects.

Conclusions:

• HRV disrupts arrhythmogenic alternans, suggesting a protective role against cardiac arrhythmias.
• HRV may be a significant physiological factor in preventing life-threatening arrhythmias.