Early defibrillation and out-of-hospital cardiac arrest

Cardiology Review® Online, May 2004, Volume 21, Issue 5

From the Department of Internal Medicine, Division of Cardiovascular Diseases; Department of Internal Medicine and the Department of Anesthesiology, Mayo Clinic, Rochester, Minnesotaa As a result of improvements in the “chain of survival,” including rapid access to emergency medical care, cardiopulmonary resuscitation (CPR), defibrillation, and advanced care, more patients are surviving out-of-hospital cardiac arrest.1,2 Within this chain of survival, however, rapid defibrillation after out-of-hospital cardiac arrest caused by ventricular fibrillation is the most important determinant of outcome. The hospital discharge survival rate following ventricular fibrillation arrest after initiation of an early defibrillation program in Olmsted County, Minnesota, is 40%.3,4 Despite extensive study and improvement of resuscitation variables that affect survival to hospital admission and discharge, there are few studies that address long-term outcome. How long-term survivors appraise their quality of life is important in the assessment of outcomes that may validate aggressive early defibrillation programs to improve survival. The objective of this study was to examine long-term survival and quality of life for survivors of out-of-hospital cardiac arrest caused by ventricular fibrillation. Methods This study was approved by the Mayo Clinic Institutional Review Board. It included all patients with out-of-hospital cardiac arrest caused by ventricular fibrillation from November 1990 to January 2001 who received defibrillation by emergency personnel (police, firefighters, or paramedics) in Rochester, Minnesota, and surrounding communities in Olmsted County (January 2000 populations were 85,806 and 124,277, respectively). Data regarding the cardiac arrest and subsequent outcomes were collected in a prospective manner as previously reported. The end points included all-cause mortality and quality of life. Mortality was determined through review of the Mayo Clinic patient data registry or by telephone contact with the patient’s family. Survival rates were estimated using the Kaplan-Meier product-limit method. For comparison, expected survival rates were determined from 1990 to 2000 for two different populations: an age- and sex-matched US population and an age-, sex-, and disease-matched population without out-of-hospital cardiac arrest from Olmsted County. Long-term quality of life in a subgroup of patients was measured using the Medical Outcomes Study 36-Item Short Form General Health Survey (SF-36), which assessed functional health status with eight standard subscales.5 For comparison, scores were obtained using age- and sex-matched norms from a sample of the general US population.

Results

The study included 330 patients with an out-of-hospital cardiac arrest of presumed or documented cardiac origin. Of these patients, 200 (61%) had ventricular fibrillation, 58 (18%) had pulseless electrical activity, and 72 (22%) had asystole. Of the patients with ventricular fibrillation, 138 (69%) survived to hospital admission with sustained spontaneous circulation. An additional seven patients died in the emergency department. Seventy-nine patients (40%) were subsequently discharged from the hospital. Five patients were discharged to a nursing home without neurologic recovery (three patients had severe neurologic injury rendering them completely dependent, and two patients were comatose) and were considered nonsurvivors. Two of these patients subsequently died, and the other three have not improved neurologically since hospital discharge.

The prehospital resuscitation variables included a mean time (± standard deviation [SD]) from the 911 call to the first shock, obtained by synchronization of the defibrillator times taken from the automatic external defibrillator with the public safety communications center dispatch time. The mean time was 5.7 ± 1.6 minutes (range, 2.0—9.6 minutes) for survivors versus 6.6 ± 1.5 minutes (range, 2.8–9.9 minutes) for nonsurvivors (P = .002). Sixty-eight patients (48%) received bystander CPR. Epinephrine was required for 27.8% of the survivors compared with 93.4% of the nonsurvivors (P < .001).

The table shows the admission demographic characteristics of the hospital discharge survivors versus the nonsurvivors. Of the patients surviving to hospital discharge, the structural heart disease documented during the index hospitalization was a myocardial infarction (MI) in 37 patients (47%), of which 15 (19%) received a percutaneous catheter-based intervention and four (5%) received coronary artery bypass graft (CABG) surgery. Twenty-five patients (32%) had coronary artery disease (CAD) without an MI, of which five (6%) received a percutaneous catheter-based intervention and 10 (13%) underwent CABG surgery. Ten patients (13%) had nonischemic cardiac disease, and there was no organic heart disease in seven patients (9%).

All discharge survivors underwent echocardiography less than 24 hours after out-of-hospital cardiac arrest. The average ejection fraction was 42% ± 18% (30 patients [42%] had ejection fractions < 40%). Fifty-seven patients were considered candidates for further electrophysiological studies and treatment. In these individuals, the arrest resulted from CAD without an MI or nonischemic cardiac disease. Patients with a reversible cause of cardiac arrest (peri-MI) were candidates for further electrophysiologic treatment and study if they had left ventricular dysfunction, nonsustained ventricular tachycardia, or persistent CAD. Within this cohort of survivors who received antiarrhythmic therapy, 10 patients received amiodarone alone and 35 patients received an implantable cardioverter-defibrillator (ICD), of which three also received amiodarone. Those patients who did not receive antiarrhythmic therapy typically had an MI with preserved cardiac function and received revascularization, refused additional therapy, or had severe noncardiac comorbidities. Thirteen patients with an ICD have experienced shocks for ventricular tachycardia or ventricular fibrillation.

The follow-up time to last patient contact (or death) averaged 4.8 ± 3.0 years. Nineteen patients died, but only five died from cardiac causes

(two died from recurrent cardiac arrest). This translates into a 5-year survival rate free of cardiac death of 92%. Figure 1 shows a comparison of the overall expected survival rate for this cohort of ventricular fibrillation out-of-hospital cardiac arrest survivors with the control groups; survival was less than that for the age- and sex-matched US population (P = .02) but comparable with that of the age-, sex-, and disease-matched population.

The normalized SF-36 survey scores of 50 long-term ventricular fibrillation out-of-hospital cardiac arrest survivors compared with general US controls are shown in figure 2. No difference was seen between the groups, with the exception of the vitality score (P = .01). Vitality is a measurement of the extent one feels tired or worn out. However, the vitality score crossed the normal value within 1 SD of the mean. Of the 45 patients responding to this question, 26 (58%) were able to return to work; 65% of patients younger than 65 years returned to work.

Discussion

Summary of major findings. This study has several findings with important clinical and social implications. First, survival to hospital discharge is favorable in the setting of

a rapid defibrillation program. Second, subsequent long-term survival is equivalent to that of cardiac patients without out-of-hospital cardiac arrest. Third, the collective quality

of life of the survivors and their return-to-work rate is almost normal. These data show the long-term effect of an aggressively implemented defibrillation program in a community setting.

In areas without early defibrillation systems, mortality rates in excess of 90% to 95% are common.8,9 In contrast, in those settings in which access to early defibrillation is available, a survival rate of 15% to 40% after ventricular fibrillation arrest has been observed.1-4 The impact of early de-

fibrillation is evident within our system. In a 4-year control period before 1990, the discharge survival rate from ventricular fibrillation in Rochester, Minnesota, was 28%. This increased to 40% without other changes in resuscitation practices after a police first-responder defibrillation program was instituted.3,4

Long-term survival. The long-term survival rate within this population was also favorable, with 79% of patients alive at 5 years after discharge. Furthermore, the 5-year survival rate for patients free of cardiac death was 92% over the long-term follow-up period. The observed survival rate was only slightly lower than expected rates based on healthy state and national populations, but identical to that in disease-matched controls. All-cause survival was not altered by the occurrence of the out-of-hospital cardiac arrest.

Within our cohort of survivors, many factors might have predisposed patients to a higher subsequent mortality rate. This population had already experienced a ventricular fi-

brillation arrest. The Antiarrhythmics Versus Implantable Defibrillators (AVID) study, Canadian Implantable Defibrillator Study (CIDS), and Cardiac Arrest Study Hamburg (CASH) reported improved survival for patients with cardiac dysfunction and malignant ventricular arrhythmias who received an ICD compared with antiarrhythmic therapy; however, mortality rates at 3 to 5 years remained high, ranging from 23% to 36%.10-12 Furthermore, within our study population, predictors of increased mortality in cardiac disease were prevalent, including advanced age, multivessel disease, diabetes, left ventricular dysfunction, and congestive heart failure.13 In addition, 14 patients died of noncardiac disease independent of their arrest.

Quality of life. Subsequent quality of life with return of neurologic and occupational function is a key outcome in evaluating the benefit

of early defibrillation for out-of-hospital cardiac arrest. Previous studies have focused on short-term outcomes or used subjective assessment tools with broad categories, such as the cerebral performance scale.14,15 Using the standardized SF-36, the quality of life of survivors was confirmed to be very favorable, as also validated by comparison with national age- and sex-matched controls without underlying dis-ease. The results of this survey in-dicate that ventricular fibrillation survivors have a collective quality of life similar to a healthy population. In addition, the majority of our patients returned to work despite a mean age of 58.6 ± 13.2 years (range, 12—90 years), indicating a functional quality of life. These findings extend and confirm those by Bergner and colleagues, who reported a favorable health status assessed by sickness impact profile scores and return to previous occupation at 6 months.16 Conclusion This is the first population-based study to address long-term survival and quality of life for survivors of ventricular fibrillation out-of hospital cardiac arrest. The survival rate to hospital discharge is high when a rapid defibrillation program is instituted. The majority of survivors report long-term quality of life and excellent functional outcome in most respects indistinguishable from the general healthy population. Long-term survival is also equal to disease-matched controls. These data further validate the benefit of early defibrillation as well as aggressive treatment of the under-lying cardiac disease.