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Relation between repolarization and refractoriness during programmed electrical stimulation in the human right
B S Koller1, P E Karasik, A J Solomon
1Veterans Administration Medical Center, Washington, DC 20422, USA.
Circulation
|May 1, 1995
Summary
Repetitive extrastimulation shortens action potential duration and effective refractory periods, altering the repolarization-refractoriness relation. This leads to impaired impulse propagation and increased ventricular tachycardia induction risk.
Area of Science:
- Cardiac Electrophysiology
- Arrhythmogenesis Research
- Clinical Electrophysiology
Background:
- Programmed electrical stimulation is used to induce ventricular tachycardia (VT), but mechanisms remain unclear.
- The role of repetitive extrastimulation in VT induction and its effect on human ventricular repolarization and refractoriness are unknown.
- Hypothesis: Altered repolarization-refractoriness relation by extrastimulation disrupts impulse propagation, triggering VT.
Purpose of the Study:
- To investigate the effect of repetitive extrastimulation on repolarization and refractoriness in the human ventricle.
- To determine if altered repolarization-refractoriness dynamics during extrastimulation correlate with ventricular tachycardia induction.
- To elucidate the mechanism by which closely coupled extrastimuli induce VT.
Main Methods:
- Studied 21 patients undergoing electrophysiological study.
- Measured monophasic action potential durations (APDs) and effective refractory periods (ERPs) at the right ventricular apex and outflow tract during regular pacing and extrastimuli (S2-S4).
- Assessed repolarization level at capture, ERP/APD ratio, and impulse propagation time; correlated findings with VT induction.
Main Results:
- APD and ERP progressively shortened with each extrastimulus (P < .0001).
- Extrastimuli captured at progressively less repolarized levels (encroachment), correlating with delayed impulse propagation (P < .05).
- VT was induced in 11/21 patients, predominantly when significant "encroachment" and conduction slowing occurred.
Conclusions:
- Repetitive extrastimulation alters the ERP/APD relation by enabling capture at less repolarized levels.
- This "encroachment" phenomenon impairs impulse propagation and is associated with a high incidence of VT induction.
- Findings explain how repetitive, closely coupled extrastimulation can induce ventricular tachycardia.