Left ventricular myocardial adenosine triphosphate changes during reperfusion of ventricular fibrillation: the influence of flow and epinephrine

Dynamic nature of electrocardiographic waveform predicts rescue shock outcome in porcine ventricular fibrillation

STUDY OBJECTIVE

Survival decreases with duration of ventricular fibrillation, and it is possible that failed rescue shocks increase myocardial damage. Structure in the ECG signal during ventricular fibrillation can be quantified by using the scaling exponent, a dimensionless measure that correlates with ventricular fibrillation duration. This study examined whether the scaling exponent could predict rescue shock success and whether unsuccessful rescue shocks altered the structure of the ventricular fibrillation waveform and the responsiveness to subsequent rescue shocks.

METHODS

Ventricular fibrillation was electrically induced in 44 anesthetized swine, which were randomly assigned to receive 70-J biphasic rescue shocks at 2, 4, 6, 8, or 10 minutes. If rescue shocks failed, up to 2 subsequent rescue shocks were performed at 2-minute intervals. The scaling exponent was calculated at 1-second intervals from ECG to quantify the organization of the ventricular fibrillation waveform.

RESULTS

A total of 92 rescue shocks were delivered, of which 23 successfully converted ventricular fibrillation to an organized rhythm (immediate success). After these 23 rescue shocks, 14 swine sustained organized rhythms for more than 30 seconds (sustained success). Lower scaling exponent values were associated with increased probability of successful rescue shocks. Receiver operating characteristic curves had an area under the curve of 0.86 for immediate rescue shock success and 0.93 for sustained rescue shock success. Failed rescue shocks increased the rate of scaling exponent increase over time but did not appear to affect subsequent rescue shock success when the scaling exponent was taken into account.

CONCLUSION

Highly deterministic ventricular fibrillation, reflected by a low scaling exponent, predicted rescue shock success regardless of antecedent failed rescue shocks. In addition, unsuccessful rescue shocks might decrease post-rescue shock ventricular fibrillation waveform organization.

The predictive value of ventricular fibrillation electrocardiogram signal frequency and amplitude variables in patients with out-of-hospital cardiac arrest

We evaluated ventricular fibrillation frequency and amplitude variables to predict successful countershock, defined as pulse-generating electrical activity. We also elucidated whether bystander cardiopulmonary resuscitation (CPR) influences these electrocardiogram (ECG) variables. In 89 patients with out-of-hospital cardiac arrest, ECG recordings of 594 countershock attempts were collected and analyzed retrospectively. By using fast Fourier transformation analysis of the ventricular fibrillation ECG signal in the frequency range 0.333-15 Hz (median [range]), median frequency, dominant frequency, spectral edge frequency, and amplitude were as follows: 4.4 (2.4-7.5) Hz, 4.0 (0.7-7.0) Hz, 7.7 (3.7-13.7) Hz, and 0.94 (0.24-1.95) mV, respectively, before successful countershock (n = 59). These values were 3.8 (0.8-7.7) Hz (P = 0.0002), 3.0 (0.3-9.7) Hz (P < 0.0001), 7.3 (2.0-14.0) Hz (P < 0.05), and 0.53 (0.03-3.03) mV (P < 0.0001), respectively, before unsuccessful countershock (n = 535). In patients in whom bystander CPR was performed (n = 51), ventricular fibrillation frequency and amplitude before the first defibrillation attempt were higher than in patients without bystander CPR (n = 38) (median frequency, 4.4 [2.4-7.5] vs 3.7 [1.8-5.3] Hz, P < 0.0001; dominant frequency, 3.8 [0.9-7.7] vs 2.6 [0.8-5.9] Hz, P < 0.0001; spectral edge frequency, 8.4 [4.8-12.9] vs 7.2 [3.9-12.1] Hz, P < 0.05; amplitude, 0.79 [0.06-4.72] vs 0.67 [0.16-2.29] mV, P = 0.0647). Receiver operating characteristic curves demonstrate that successful countershocks will be best discriminated from unsuccessful countershocks by ventricular fibrillation amplitude (3000-ms epoch). At 73% sensitivity, a specificity of 67% was obtained with this variable.

IMPLICATIONS

In patients with out-of-hospital cardiac arrest, successful countershocks will be best discriminated from unsuccessful countershocks by ventricular fibrillation amplitude (3000-ms epoch). At 73% sensitivity, a specificity of 67% was obtained with this variable.