Ventricular repolarization and fibrillation threshold in hibernating species

Area of Science:

• Cardiology
• Comparative Physiology
• Mammalian Hibernation

Background:

• Non-hibernating mammals typically develop ventricular fibrillation (VF) and circulatory arrest at temperatures between 15-20°C.
• Hibernators exhibit significant resistance to VF induced by hypothermia, a critical adaptation for survival during winter dormancy.

Observation:

• Hedgehogs, a hibernating species, demonstrated VF resistance across various VF-inducing procedures beyond hypothermia.
• These included epicardial aconitine application, isolated heart perfusion with CaCl2 or procaine HCl, and coronary artery ligation.
• Electrical stimulation in the vulnerable period induced VF in some hedgehogs, but required higher currents than in guinea pigs.

Findings:

• Key factors contributing to VF resistance in hibernators include a short QT duration.
• Lack of sympathetic innervation in ventricular muscle fibers of hibernators.
• Distinct metabolic factors, such as different temperature-activity curves.
• Ultrastructural differences, including less skeletin filament in the hedgehog heart's conduction system.

Implications:

• Understanding hibernator physiology may offer insights into preventing cardiac arrhythmias in non-hibernating mammals.
• Potential therapeutic targets for managing VF could be derived from studying hibernator adaptations.
• This research highlights the unique cardiovascular adaptations that enable survival during extreme physiological states.