Incidence, duration and survival of ventricular fibrillation in out-of-hospital cardiac arrest patients in Sweden

Abstract The chance of survival from ventricular fibrillation (VF) is up to ten times higher than those with other cardiac arrest rhythms. To calculate the effect of out-of-hospital resuscitation organisations on survival, it is necessary to know the percentage of cardiac arrest patients initially in VF and the relationship between delay time to defibrillation and survival. Aim: To study the incidence of VF at the time of cardiac arrest and on first ECG, the duration of VF and the relation between time to defibrillation and survival. Method: The Swedish Cardiac Arrest Registry has collected standardised reports on out-of-hospital cardiac arrests from ambulance organisations in Sweden, serving 60% of the Swedish population. Results: In 14 065 cases of out-of-hospital cardiac arrest collected between 1990 and 1995, resuscitation was attempted in 10 966 cases. Incidence: The first ECG showed VF in 43% of all patients. The incidence of VF at the time of cardiac arrest was estimated to be 60–70% in all patients and 80–85% in the cases with probable heart disease. Duration: The estimated disappearance rate of VF was slow. Thirty minutes after collapse ≈40% of the patients were in VF. Survival: Overall survival to 1 month was only 1.6% for patients with non-shockable rhythms and 9.5% for patients found in VF. With increasing time to defibrillation, the survival rate fell rapidly from ≈50% with a minimal delay to 5% at 15 min. Conclusions: This study suggests a high initial incidence of VF among out-of-hospital cardiac arrest patients and a slow rate of transformation into a non-shockable rhythm. The survival rate with very short delay times to defibrillation was ≈50%, but decreased rapidly as the delay increased.