Predictive value of the ECG in determining cardiac resuscitation outcome in a canine model of postcountershock electromechanical dissociation after prolonged ventricular fibrillation

The purpose of our study was to determine if the surface ECG in postcountershock electromechanical dissociation (EMD) is of value in predicting return of effective myocardial contractile function during CPR. Nine dogs were subjected to five minutes of ventricular fibrillation (VF) without CPR followed by countershock and closed-chest CPR. Intravascular pressures, coronary perfusion pressure, and coronary sinus flow were measured during conventional CPR. After countershock, and before CPR, the frequencies of the following ECG variables were assessed: the presence or absence of P waves, an abnormal QRS duration (greater than 100 ms), a prolonged QTc (greater than 430 ms), and a bradyarrhythmia (QRS rate less than 60/min). Twenty-three episodes of postcountershock EMD were studied. Countershock after prolonged VF without CPR was always followed by EMD. The mean values of ECG variables were not significantly different (P greater than .05) between animals successfully resuscitated and those that were not. The sensitivity, specificity, and predictive values of individual ECG variables in estimating successful cardiac resuscitation exhibited a wide range of values. The QTc had the highest sensitivity (1.00), but the lowest specificity (0.08). The presence or absence of P waves had the highest specificity (0.62), but a sensitivity of only 0.40. QRS rate had the greatest positive predictive value (0.48) but a negative predictive value of 0.46 for successful cardiac resuscitation. The QTc had the greatest negative predictive value (1.00) but a positive predictive value of only 0.45. Multiple regression analysis using the study ECG variables as independent variables demonstrated that ECG variables were not related to outcome.(ABSTRACT TRUNCATED AT 250 WORDS)