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Refractory interval after transcardiac shocks during ventricular fibrillation
R J Sweeney1, R M Gill, P R Reid
1Department of Electrophysiology Research, Eli Lilly and Co, Indianapolis, Ind, USA. sweeneyrj@sjm.com
Circulation
|December 1, 1996
Summary
Defibrillation shocks create a brief refractory period in the heart, preventing re-fibrillation immediately after the shock. This post-shock refractory interval is shorter for biphasic shocks than monophasic shocks.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Devices
Background:
- Ventricular pacing at fast rates suggests a refractory period after defibrillation shocks.
- Experimental verification of a post-shock refractory interval during fibrillation was needed.
Purpose of the Study:
- To determine if a refractory interval exists immediately after a defibrillation shock during ventricular fibrillation.
- To compare the post-shock refractory interval duration between monophasic and biphasic shocks.
Main Methods:
- Anesthetized dogs received monophasic or biphasic shocks followed by a post-shock stimulus (PSS).
- The shock current (I50) for 50% defibrillation success was measured.
- The timing of the PSS relative to the shock was varied.
Main Results:
- A 1.0-A PSS significantly increased I50 when delivered 50-90 ms after monophasic shocks.
- A 1.0-A PSS also increased I50 after biphasic shocks, but to a greater extent than after monophasic shocks.
- A 0.5-A PSS had no effect on I50 at any tested timing.
Conclusions:
- A post-shock refractory interval exists after both monophasic and biphasic shocks during fibrillation.
- This refractory interval is shorter for biphasic shocks compared to monophasic shocks.
- Findings support the refractory period extension hypothesis for defibrillation.