Key result
Single square wave stimuli of various durations and amplitudes applied to spontaneously beating hearts in situ were ineffective for the production of ventricular fibrillation.
Excitability recovery for a small and localized myocardial area in a normally beating heart is synchronous and smooth.
Synchronous recovery may limit single-stimulus VF risk in normal hearts; leaves open arrhythmia mechanisms in heterogeneous or diseased myocardium.
The electrical and mechanical responses to single square wave stimuli applied to spontaneously beating hearts in situ were examined. Shocks were delivered through a time delay circuit triggered by the voltage of the R wave of the ECG. The silver-silver chloride electrodes were 3 mm apart and their position on the ventricular surface kept constant throughout an experiment Stimuli were separated by 20–30 heart beats. The plotted excitability curve (strength-interval) was found to be smooth without any indication of transient variations in threshold. Single stimuli of various durations (up to 100 msec.) and amplitudes (up to 25 ma) were ineffective for the production of ventricular fibrillation. Apparently excitability recovery for a small and localized myocardial area is synchronous and smooth.
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Maaske et al. (1958) studied Normally beating heart. Single square wave stimuli was evaluated on Excitability curve and production of ventricular fibrillation. Single square wave stimuli of various durations and amplitudes applied to spontaneously beating hearts in situ were ineffective for the production of ventricular fibrillation.
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