Ventricular fibrillatory frequency and its correlation with transthoracic defibrillation current requirement

Correlation between ventricular fibrillatory frequency (VFF) in patients with ventricular fibrillation (VF) and transthoracic defibrillation current was studied. Strong positive correlation between VFF and optimal defibrillation current was revealed in patients with primary VF. There was a significant negative correlation between TTI and defibrillation current, that ceased secondary VF, and there was no significant correlation between TTI and current in patients with primary VF.

Introduction

The efficacy of external defibrillation depends on various both cardial and noncardial factors. Heart function status, waveform shock (monophasic and biphasic) and chest impedance play important roles among them. The aim of this study was the research of the correlation between VFF in patients with primary (1-ry) and secondary (2-ry) VF and the value of defibrillation current.

Methods

Twenty patients with 1-ry VF and 28 patients with 2-ry VF were studied. VF mostly occurs during the acute phase of myocardial infarction. The efficacy of external defibrillation depends on various both cardial and noncardial factors. Heart function status, waveform shock (monophasic and biphasic) and chest impedance play important roles among them. The duration of VF was from 1 to 8 min (definition: 2-ry VF, fibrillation that occurs in patients with clinical signs of acute or chronic heart failure; 1-ry VF, in patients with the absence of these signs). Defibrillation was done with a biphasic quasi-sinusoidal shock through hand-held electrode paddles (12/12 cm diameter); the peak current (I [A]), delivered energy (DE [J]) and transchest impedance (TTI [Ohm]) were registered during the shock. VFF was estimated 5–7 s before the successful shock from surface ECG lead I or II.

Results

A strong positive correlation between VFF (range 310–435 per min) and the value of the optimal defibrillation current (range 8–21 A) (r = 0.81; P < 0.001) was revealed in patients with 1-ry VF. The correlation coefficient between VFF and defibrillation energy (range 16–85 J) was less to some extent (r = 0.69; P < 0.01). There was no correlation in patients with 2-ry VF (range of VFF 200–410 per min; range of I (A) 9–40 A). Meanwhile, there was a significant negative correlation between TTI (range 22–117 Ohms) and the value of the defibrillation current, that ceased 2-ry VF (r = -0.69; P < 0.01), and there was no significant correlation between TTI and I (A) in patients with 1-ry VF (r = -0.32, P = 0.11).

Conclusions

The obtained data suggest that the strong positive correlation between ventricular fibrillation frequency and defibrillation current value in patients with 1-ry VF is mainly related to electrophysiologycal heterogeneity of the myocardium. At the same time the influence of chest impedance on the value of the current depolarising critical amount of myocardium was, probably, insignificant. Fibrillation frequency obtained from the surface ECG predicts current and energy requirements in patients with primary VF undergoing external defibrillation.