Survival After Out-of-Hospital Cardiac Arrest
Abstract & Commentary
By John P. DiMarco, MD, PhD
Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville
Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Dumas, F, et al. Long-term prognosis following resuscitation from out of hospital cardiac arrest: Role of percutaneous coronary intervention and therapeutic hypothermia. J Am Coll Cardiol 2012;60:21-27.
In this paper, the authors reviewed long-term survival data from a large population of out-of-hospital cardiac arrest patients who were discharged alive after their arrest. All patients who have a cardiac arrest in Seattle and King County, Washington, are entered into a registry organized to follow the Utstein guidelines for reporting cardiac arrest. During the 8-year period from 2001 to 2009, the survival rate to hospital discharge was 16.8% (1101 of 5958 adult patients) after EMS treated nontraumatic out-of-hospital cardiac arrest. Factors associated with long-term survival after hospital discharge were then examined. The factors analyzed included the use of therapeutic hypothermia, percutaneous coronary interventions (PCI), implantable cardioverter defibrillators (ICDs), neurologic status upon hospital arrival, and ST-segment elevation on the initial hospital ECG. In this cohort of survivors to hospital discharge, 38% received a PCI during the hospitalization after arrest. Six percent were conscious at hospital admission and were not candidates for therapeutic hypothermia. Among the 941 patients who were unconscious at hospital admission, 245 (26%) received therapeutic hypothermia. Both PCI and therapeutic hypothermia were employed in 9.9% of the cohort, with 80% of the PCIs occurring within 6 hours of hospital arrival. Of those who received PCI within 6 hours, 71% had evidence of ST-segment elevation on the initial hospital ECG.
The median age in the group was 61 and two-thirds of the patients were male. Eighty percent had a cardiac etiology for their arrest and almost 70% had an initial shockable rhythm detected. Patients who received PCI were younger and were more likely to have the following characteristics: male gender, an arrest due to a cardiac etiology, a witnessed arrest in a public location, and bystander CPR. After hospital discharge, 348 of the 1101 patients died. Life table analysis gave survival estimates of 87% at 6 months, 82% at 1 year, and 64% at 5 years. Both PCI and therapeutic hypothermia were associated with favorable effects on mortality. Patients who received both PCI and therapeutic hypothermia had the highest survival estimates at both 1 and 5 years. Cox regression analysis showed that PCI, therapeutic hypothermia, and ICD implantation were each independently associated with improved survival after discharge. The hazard ratios for risk of death were 0.46 for PCI and 0.70 for therapeutic hypothermia. The hazard ratio for death was lowest for those who received PCI during an ST segment elevation MI (0.41). A further analysis using a nested cohort pairing for each intervention showed similar favorable hazard ratios associated with both therapeutic hypothermia and PCI.
The authors conclude that in this observational analysis, both PCI and therapeutic hypothermia produced survival benefits among patients who survived to hospital discharge. Since only patients who were discharged from the hospital were analyzed in this study, improved in-hospital survival could not be assessed but has been demonstrated in other reports.
This report from a large, well-organized registry of out-of-hospital cardiac arrest victims provides further data to support the routine use of coronary angiography followed, when indicated, by PCI and therapeutic hypothermia in resuscitated cardiac arrest victims admitted to the hospital. The largest benefit shown was for ST elevation patients and this report confirms that both PCI and therapeutic hypothermia can and should be used in these patients. In patients without STEMI, the best timing for coronary angiography remains controversial, but certainly detecting and treating high-grade coronary lesions where present should be considered at some time during the hospital stay.
Recently, some hospitals have been cited by state boards or other groups for increased adjusted mortality rates among PCI patients. In several cases, most of the PCI-related deaths occurred in patients who presented in shock or after a resuscitated cardiac arrest. The risk-adjustment schemes did not fully account for the much higher than expected mortality in such patients. Therefore, the American Heart Association has recommended that patients in shock or after arrest be separately classified from other PCI patients when data are reported. The data in this paper support this idea since we should not punish hospitals that accept the burden of treating these very high-risk patients.