Relationships between heart rate and PR interval during physiological and pharmacological interventions

Area of Science:

• Cardiology
• Physiology

Background:

• The relationship between heart rate (HR) and PR interval (PR) is crucial for understanding cardiac conduction.
• Investigating these relationships under various physiological conditions and pharmacological interventions provides insights into cardiac electrophysiology.

Purpose of the Study:

• To investigate the relationship between heart rate (HR) and PR interval (PR) in healthy subjects during rest, exercise, and isoprenaline infusion.
• To evaluate the effects of beta-adrenoceptor blocking drugs and calcium channel antagonists on atrioventricular conduction using an exercise model.

Main Methods:

• Studied 12 healthy young subjects at rest, standing, and during graduated treadmill exercise.
• Administered isoprenaline infusion to increase heart rates.
• Utilized an exercise model to assess the effects of beta-blockers and calcium channel antagonists on HR and PR intervals.

Main Results:

• A negative linear correlation was observed between HR and PR during exercise (PR = -0.351 HR + 176.7) and isoprenaline infusion (PR = -0.582 HR + 186.5).
• Beta-blocker administration resulted in PR prolongation beyond expected values at observed HRs.
• Rate-adjusted PR prolongation was greatest during exercise, followed by standing, then rest, indicating more significant beta-blockade in the atrioventricular nodal tissue.

Conclusions:

• Inverse linear relationships exist between HR and PR in healthy individuals under various conditions.
• Beta-blockers exert a rate-dependent effect on atrioventricular conduction, with a more pronounced impact on the atrioventricular node compared to the sinoatrial node.