The long and the short of long and short duration ventricular fibrillation.

See related article, pages 1256–1264 The mechanisms behind the complex activation sequences during ventricular fibrillation (VF) have been the topic of intense research over many years. Experimental studies in animal models of VF, as well as clinical studies of human VF,1–8 have provided a wealth of data on the nature of electric activity in the fibrillating heart. Supplemented by computer simulations and a theoretical framework of wave propagation in excitable media,9,10 our community has amassed significant insights into the mechanisms that lead to the degradation of electric activity into VF and of VF maintenance. However, the majority of these studies have been devoted to VF mechanisms in the short time period after VF onset (short-duration VF, lasting less than 1 minute). In an episode of cardiac arrest outside of the hospital, the median time to delivery of the first defibrillation shock is 4.4 minutes,11 with VF episodes often lasting as long as 10 minutes (long-duration VF); over this period, the heart becomes ischemic while being subjected to excessively high excitation rates. Changes in the electrophysiological properties of the myocardium take place over these long-duration VF episodes. This is reflected in the altered outcome of a defibrillation shock, with survival rates decreasing rapidly with the increase in minutes spent in VF.12 Similarly, the guidelines for optimal resuscitation therapy differ depending on VF duration: immediate defibrillation is prescribed if time from VF onset is less than 4 or …