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Is dispersion of ventricular repolarization rate dependent?
M Zabel1, R L Woosley, M R Franz
1Georgetown University, Washington, DC, USA.
Pacing and Clinical Electrophysiology : PACE
|November 14, 1997
Summary
Ventricular repolarization dispersion remains stable despite changes in heart rate, suggesting rate correction may not be necessary for assessing arrhythmia risk. This study found no significant change in dispersion of action potential duration or recovery time with varying pacing cycle lengths.
Area of Science:
- Cardiovascular Physiology
- Electrophysiology
- Cardiac Arrhythmias
Background:
- QT dispersion is used to assess repolarization inhomogeneity and arrhythmia risk.
- Previous studies applied rate correction (e.g., Bazett formula) to QT and JT dispersion.
- The rate dependency of ventricular repolarization dispersion itself is not well understood.
Purpose of the Study:
- To investigate whether dispersion of ventricular repolarization is dependent on heart rate.
- To determine if rate correction is necessary for parameters of repolarization dispersion.
Main Methods:
- Simultaneous recording of multiple monophasic action potentials (MAPs) from rabbit ventricles.
- Electrically pacing isolated Langendorff-perfused rabbit hearts at varying cycle lengths (1200-300 ms).
- Measuring action potential duration at 90% repolarization (APD90) and recovery time (RT); calculating dispersion as maximal differences.
Main Results:
- APD90 and RT significantly shortened with decreasing cycle lengths (increasing heart rate).
- Dispersion of APD90 and RT did not change significantly across the tested range of pacing cycle lengths.
- Pacing-induced changes in cycle length did not significantly alter ventricular repolarization dispersion.
Conclusions:
- Ventricular repolarization dispersion is not significantly rate-dependent in the isolated rabbit heart.
- Rate correction for QT or JT dispersion may be unnecessary, challenging current clinical practices.
- Findings suggest that repolarization dispersion is a stable index of inhomogeneity, irrespective of heart rate.