Objective: The purpose of this study was to assess from the ventricular fibrillation ECG signal whether certain amplitude parameters, or frequency parameters derived using fast Fourier transform analysis, are predictive of countershock success (defined as a stable supraventricular rhythm following countershock).
Design: Retrospective, descriptive study.
Setting: Emergency medical service at a university hospital.
Patients: Twenty-six patients with out-of-hospital cardiac arrest, whose initial ECG rhythm was identified as ventricular fibrillation.
Methods and results: In all patients, advanced cardiac life support was performed in the out-of-hospital setting and a semiautomatic defibrillator was used for countershock therapy and simultaneous on-line ECG recording. For each patient, ECG data were stored in modules in digitized form over a period of 20 min and analyzed retrospectively. Using fast Fourier transform analysis of the ventricular fibrillation ECG signal in the frequency range of 0.3 to 30 Hz (mean±SD), median frequency, dominant frequency, edge frequency, and amplitude were as follows: 5.17±1.05 Hz, 4.56±0.99 Hz, 10.74±3.46 Hz, and 1.33±0.44 mV before successful countershock (n=20); and 4.21±1.17 Hz (p=0.0034), 3.31±1.57 Hz (p=0.0004), 9.46±2.93 Hz (p=0.5390), and 1.15±0.69 mV (p=0.0134) before unsuccessful countershock (n=134). Using software filters to completely eliminate interference due to manual cardiopulmonary resuscitation from the ventricular fibrillation power spectrum, only amplitude remained statistically different (p≤0.03) in predicting countershock success.
Conclusions: We conclude that in patients, median frequency, dominant frequency, and amplitude are predictive of countershock success in humans.