Study of Survivors of Different Types of Cardiac Arrest and Their Neurological Recovery

After successful resuscitation from certain types of cardiac arrest, total body cooling is now a well established treatment that improves the chances of the brain recovering. This however, has only been definitively proven after a certain type of cardiac arrest that is "ventricular fibrillation / ventricular tachycardia". The purpose of this study is to explore if total body cooling is beneficial for patients recovering from another type of cardiac arrest that is "pulseless electrical activity".

HYPOTHESIS:

Patients undergoing post-cardiac arrest therapeutic hypothermia have better neurological outcomes if their initial arrest rhythm is pulseless electrical activity (PEA) in comparison to asystole.

STUDY RATIONALE AND BACKGROUND INFORMATION:

After successful resuscitation from cardiac arrest the body experiences a period of global reperfusion. During this period, patients may show signs of myocardial stunning, lactic acidosis, neurological injury and reperfusion syndrome. This constellation of findings constitutes what is known as post-cardiac arrest syndrome. The brain appears to be one of the most vulnerable organs to injury during this reperfusion phase and varying degrees of cognitive impairment may be the end result. Inducing mild therapeutic hypothermia has been shown to be protective for the brain in this setting and has been demonstrated to improve neurological recovery. The evidence for this however, is only conclusive in cases where the arrest is in a shockable rhythm i.e. pulseless ventricular tachycardia and ventricular fibrillation.

In 2002, two randomized controlled trials were published showing an improvement in neurological outcomes in patients treated with mild therapeutic hypothermia post resuscitation from shockable cardiac arrest. Therapeutic hypothermia has since been widely adopted by most authorities as part of the comprehensive treatment bundle for post cardiac arrest syndrome. Whether there is any benefit for patients arrested in non-shockable rhythms however, is a matter of controversy. Some have reported improved mortality and better neurological outcomes with therapeutic hypothermia in this patient population. Others have reported no benefit or even a trend towards harm. And although the matter remains controversial, the recommendation still stands for therapeutic hypothermia to be offered for all comatose survivors of cardiac arrest whatever the arrest rhythm.

Most previous reports have examined the differences between shockable and non-shockable rhythms in terms of neurological outcome and mortality rates after therapeutic hypothermia. To our knowledge, no study has examined the differences in outcome between the two types of non-shockable rhythms, that is pulseless electrical activity (PEA) and asystole. We hypothesize that during PEA arrests, patients may retain some degree of cerebral perfusion and hence have better neurological outcomes post-resuscitation. That is in contrast to asystole where patients are likely to have no cerebral perfusion. In this study we attempt to detect any possible differences in neurological recovery (as indicated by the Cerebral Performance Category scale on hospital discharge) after therapeutic hypothermia, between patients arrested in PEA arrest and those arrested in asystole.

Eligibility Criteria:
Inclusion Criteria:

* Admission to adult ICU (age ≥18 years) at London Health Sciences Centre
* Primary reason for ICU admission: postcardiac arrest
* Both in-hospital and out-of-hospital cardiac arrest will be included
* ICU admission between Jan 2008 and Dec 2012.

Exclusion Criteria:

- ICU admissions primarily for reasons other than cardiac arrest.