Jd Allen

Management of ventricular fibrillation outside hospital.

Abstract 55 of 126 patients with cardiac arrest outside hospital had resuscitative measures initiated within 4 minutes of the onset of arrest. 48 of the 55 had ventricular fibrillation. 39 of the 48 survived. Resuscitative measures were initiated by members of a mobile coronary-care team in 14 patients and by other individuals in 25. 27 left hospital alive and most of these patients were well at follow-up. 24 of the 27 had acute myocardial infarction, 2 had myocarditis, and 1 had been electrocuted. In 19 of the patients with myocardial infarction the coronary attack was clinically mild. These findings indicate the value of the training of medical and lay personnel in resuscitation methods provided a mobile coronary-care unit is available.

Fourier analysis of ventricular fibrillation and synchronization of DC countershocks in defibrillation

Spectral analysis of the first 40 seconds of ventricular fibrillation confirmed the presence of a large periodic component in fibrillation, with a dominant frequency of 9.9 +/- 0.7 Hz and a narrow bandwidth. To determine whether less energy was required for defibrillation at any particular phase of the ventricular fibrillation cycle, the authors studied the effect of synchronization of the countershock to the peaks and troughs of the ventricular fibrillation waveform in 12 dogs anesthetized with sodium pentobarbitone (35 mg/kg iv). There was no significant difference in threshold-delivered energy or threshold-delivered current between shocks synchronized to the peaks of ventricular fibrillation, shocks synchronized to the troughs of ventricular fibrillation, and unsynchronized shocks.

A low tilt waveform in the transthoracic defibrillation of ventricular arrhythmias during cardiac arrest

AIM Most commercially available defibrillators utilise a high tilt waveform. Work in atrial fibrillation has shown improved defibrillation success using low tilt waveforms. We hypothesise that a novel low tilt biphasic waveform will be non-inferior to a standard tilt waveform whilst delivering lower energy for the defibrillation of ventricular arrhythmias. METHODS Patients in cardiac arrest who experienced ventricular arrhythmias received shocks from a novel low tilt waveform defibrillator at 120J or a standard tilt waveform defibrillator at 150J. Resuscitation guidelines were followed as per Resuscitation Council UK, 2005. A shock was successful when the ventricular arrhythmia was terminated for ≥ 5s following shock delivery. RESULTS A total of 113 cardiac arrest cases were included. The low tilt device was used for 56 cases and the standard tilt device for 57 cases. The presenting rhythm was ventricular fibrillation (VF) in 71.7% (81/113), pulseless electrical activity (PEA) in 15.9% (18/113), ventricular tachycardia (VT) in 9.7% (11/113), asystole in 1.8% (2/113) and narrow complex rhythm in 0.9% (1/113). The low tilt device resulted in first shock success in 86% (48/56 cases) vs. the standard tilt device first shock success of 77% (44/57 cases). There was no significant difference in first shock success between the two devices (p=0.36). CONCLUSION The low tilt waveform used in this study demonstrated first shock success rates in keeping with a commercially available high tilt defibrillator which could result in less myocardial damage due to reduced energy requirements.

Radio-frequency powered atrial defibrillation with a biphasic rectangular pulse waveform: a safety study at 3 and 5 jouls

A novel device for transvenous atrial defibrillation with a biphasic rectangular pulse waveform, with instant power supplied through a radio-frequency energy-transfer link in a short air gap of up to 18 mm, has been investigated and is briefly described here. Previous waveform assessments, have suggested that a biphasic and asymmetric (second phase at 50% amplitude) pulse waveform of energy discharge is of particular clinical interest. Hence, a safety study upon the haemodynamic effects of such a novel waveform for atrial defibrillation, was carried out on 6 animal models (pigs), at energy levels of 3 J and 5 J. The results demonstrated relatively small and reversible effects on the haemodynamics and the novel waveform was comparable in effect to a conventional, capacitor-based (with RC exponential decay), biphasic waveform. Also, an assessment of the device output performance for various air gap distances is presented.