(FIT)-Module 1, Workshop 1: Electrocardiographic/Electrophysiologic Correlation-Tomaselli Case 9 Answer

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Video Summary

The main observation is that increasing the pacing rate slows conduction velocity and shortens action potential duration (APD) due to cumulative inactivation of the sodium current. While sympathetic activation at increased heart rate normally reduces APD and refractory periods in whole systems, this is less relevant in isolated environments. Cumulative inactivation of repolarizing potassium currents hastens repolarization, while increasing rate can also deplete sodium current. This slowdown can result in rate-related conduction issues, like bundle branch blocks. Therefore, cumulative inactivation of the sodium current is identified as the key factor in conduction slowing at elevated rates.

Keywords

pacing rate

conduction velocity

sodium current inactivation

action potential duration

bundle branch block