Therapeutic hypothermia: is it effective for non-VF/VT cardiac arrest?

Sudden cardiac death represents a major health problem. In adults, the prevalence of out-of-hospital cardiac arrest (OHCA) attended by the emergency medical services (EMS) ranges from 52 to 112 per 100,000 person-years in developed countries [1], whereas the prevalence of adult in-hospital cardiac arrest (IHCA) ranges from 1 to 5 per 1,000 patient admissions [2]. Mortality from cardiac arrest exceeds 90 % in OHCA [1, 3] and 70 % in mo st studies on IHCA [4–6]. Patients who have a sh ock able rhythm, i. e., ventricular fi brillation (VF) or pulseless ventricular tachycardia (VT), on initial electrocardiogram (EKG) have a consistently higher survival than those whose initial cardiac rhythm is nonshockable, i. e., asysto le or pulseless electrical activity (PEA). More than two-thirds of initially resuscitated patients die before hospital discharge [7,8]. Th e m ajor causes of hospital mortality are post-resuscitation brain and myocardial dysfunction [9,10]. Mild therapeutic hypothermia can reduce the sever ity of post-resuscitation brain injury and improve survival in patients who remain comatose after resuscitation from cardiac arrest. In 2002, two randomized clinical trials showed improved neurological outcome [11,12] in a t otal of 350 comatose adults resuscitated from OHCA who were cooled to 32–34 °C for 12–24 hours shortly after recovery of spontaneous circulation. Th e largest of these trials [12] also sh owed a signifi cant reduction in mortality within six months in patients treated with mild therapeutic hypothermia. Both these trials included only patients who had VF/VT as the initial rhythm. Based on these results, subsequently confi rmed by a meta-analysis [13], the International Liaison Committee on Resuscitation (ILCOR) recommended in 2003 the use of mild therapeutic hypothermia for all comatose survivors after OHCA due to VF/VT [14]; this recommendation was confi rmed in the current 2010 Guidelines for Cardiopulmonary Resuscitation [15]. However, only 25–30 % of OHCA patients have VF/VT as the initial recorded cardiac rhythm [1], and this percentage has decreased in recent years [16,17], partly because of the advent of implantable cardioverter-defi brillators for the prevention and treatment of patients at r isk of lethal arrhythmias [18]. Th e prevalence of VF/VT rhythms in IHCA does not exceed 25–30 % either [2]. For the remaining 70–75 % of patients who under go cardiac arrest with non-VF/VT rhythms, indications for receiving therapeutic hypothermia after resuscitation are less clear.