The aim of this study was to evaluate the treatment and outcomes of patients with ST-segment elevation myocardial infarctions complicated by out-of-hospital cardiac arrest in a regional system of care. In this retrospective study, the effect of the absence of an initial shockable arrest rhythm was analyzed. The primary end point of survival with good neurologic outcome in patients with and without an initial shockable arrest rhythm was adjusted for age, witnessed arrest, bystander cardiopulmonary resuscitation, and treatment with therapeutic hypothermia and percutaneous coronary intervention. One-hundred sixty-eight of 348 patients (49%) survived to hospital discharge. Patients with a shockable initial rhythm were more likely to receive therapeutic hypothermia (48% vs 37%, risk ratio 1.2, 95% confidence interval [CI] 1.0 to 1.5) and to be treated in the cardiac catheterization laboratory (80% vs 43%, risk ratio 2.8, 95% CI 2.0 to 3.8). The likelihood of survival with good neurologic outcome in patients with a shockable initial rhythm compared with those presenting without a shockable rhythm was 4.8 (95% CI 2.7 to 8.7). In patients who underwent percutaneous coronary intervention, the likelihood of survival with good neurologic outcome was higher (risk ratio 2.7, 95% CI 1.1 to 6.8) in those with a shockable rhythm. In conclusion, the absence of an initial shockable rhythm in patients with ST-segment elevation myocardial infarctions plus out-of-hospital cardiac arrest is associated with significantly worse survival and neurologic outcome. These differences persist despite application of therapies including therapeutic hypothermia and percutaneous coronary intervention within a regionalized system of care.
Available data suggest that out-of-hospital cardiac arrest (OOHCA) and OOHCA with ST-segment elevation myocardial infarction (STEMI) represent different pathophysiologic entities with divergent outcomes. Patients with OOHCA plus STEMI have a better prognosis than the overall OOHCA population without STEMI. From a prognostic standpoint, it may be possible to further distinguish patients with OOHCA plus STEMI by initial arrest rhythm. This distinction may be of great importance to patient management, health system planning, and outcomes reporting. The purpose of this study was to compare the characteristics, treatment, and outcomes of patients with OOHCA plus STEMI with and without a shockable initial rhythm in a regional system of care with mandated therapeutic hypothermia (TH) and primary percutaneous coronary intervention (PCI).
Methods
In 2006, Los Angeles County established regionalized cardiac care for STEMI with a network of designated STEMI receiving centers. These centers are capable of providing immediate primary PCI 24 hours per day, and they are required to have robust quality improvement programs and internal policies for PCI and TH. Since 2010, all patients with OOHCA of presumed cardiac origin with restoration of spontaneous circulation in the field have been transported to these STEMI centers. Participating centers are encouraged to institute TH (target temperature 32° to 34°C) in all eligible patients <6 hours after resuscitation and to maintain it for ≥20 hours. The decision to initiate or withhold TH is at the discretion of the treating physician.
A registry is maintained by the agency, including basic demographic, arrest, and treatment data as well as patient survival and neurologic outcomes. The receiving centers are responsible for abstracting patient and chart data and entering them into the database, as previously described. This is a retrospective study of data from the registry maintained by the agency. The study was reviewed and approved with exemption of informed consent by the local facility institutional review board.
The database was queried for patients with restoration of spontaneous circulation and STEMI treated from January 1, 2011, through June 30, 2012, representing 18 months of data available since establishing regionalized care for such patients. Study variables included age, gender, race/ethnicity, initial cardiac rhythm, arrest location, witness, bystander cardiopulmonary resuscitation, and induction of hypothermia. All patients ≥18 years of age treated for nontraumatic OOHCA with return of spontaneous circulation and transported to a designated center were included. Patients with termination of resuscitation in the field were not transported by protocol and therefore were not eligible for inclusion in the database.
Outcomes were evaluated separately for patients with STEMIs with and without shockable initial arrest rhythms. Shockable rhythms included ventricular tachycardia, ventricular fibrillation, and rhythms analyzed and treated by automated external defibrillator, whereas nonshockable rhythms included pulseless electrical activity and asystole. The primary outcome of the study was survival to hospital discharge and neurologically intact survival in these 2 cohorts, as defined by a Cerebral Performance Category (CPC) at hospital discharge of 1 or 2.
All data were entered into Excel (Microsoft Corporation, Redmond, Washington) and transferred to SAS version 9.3 (SAS Institute Inc, Cary, North Carolina) for analysis. Risk ratios (RRs) and their p values were calculated using chi-square tests and Fisher’s exact tests as appropriate. The primary outcome of survival with good neurologic outcome with and without initial shockable rhythm was calculated using logistic regression, presented as an adjusted odds ratio, adjusted for age, witnessed arrest, bystander cardiopulmonary resuscitation, and treatment with TH and PCI. A separate analysis was performed on the subgroup of patients who underwent PCI with outcome adjusted for age, witnessed arrest, treatment with TH, and door-to-balloon time <90 minutes. Variables in the regression were selected on the basis of previous knowledge of their contribution to cardiac arrest outcomes and entered simultaneously into the model. Finally, an analysis stratified by initial rhythm was performed to evaluate the effect of PCI on neurologic outcome.
Results
From January 1, 2011, to June 30, 2012, a total of 1,289 patients with OOHCA with restoration of spontaneous circulation were transported to 34 participating hospitals. Of these patients, 348 patients were diagnosed with STEMIs on the basis of prehospital and/or initial hospital electrocardiographic findings made up the study cohort. Of the patients with STEMIs, a total of 52 patients (15%) died in the emergency department. Two hundred nineteen patients (63%) went to the cardiac catheterization laboratory during admission, 146 (43%) received TH, and 168 (49%) survived to hospital discharge. Good neurologic outcome (CPC 1 or 2) was present in 115 patients, representing 34% of all subjects and 68% of those surviving to hospital discharge.
Arrest rhythm data were not available for 28 patients, leaving 320 patients included in the primary analysis by initial rhythm. Patients with initial shockable rhythms were younger and more likely to be male than those without shockable rhythms ( Table 1 ). Initial Glasgow Coma Scale score was significantly lower in patients without a shockable initial rhythm. Those with a shockable initial rhythm were marginally more likely to receive TH (48% vs 37%, RR 1.2, 95% confidence interval [CI] 1.0 to 1.5) and significantly more likely to undergo cardiac catheterization (80% vs 43%, RR 2.8, 95% CI 2.0 to 3.8).
| Variable | Shockable Initial Arrest Rhythm | p-Value | |||
|---|---|---|---|---|---|
| Yes (n = 191) | No (n = 129) | ||||
| n (median) | % (IQR) | n (median) | % (IQR) | ||
| Age (years) | 62 | (53–71) | 71 | (61–82) | <0.0001 |
| Male | 148 | (77%) | 75 | (58%) | 0.002 |
| Female | 43 | (23%) | 54 | (42%) | 0.002 |
| Black | 22 | (12%) | 15 | (12%) | ns |
| White | 101 | (53%) | 61 | (47%) | ns |
| Latino/Hispanic | 44 | (23%) | 26 | (20%) | ns |
| Asian | 17 | (9%) | 19 | (15%) | ns |
| Other | 6 | (3%) | 6 | (5%) | ns |
| Initial Glasgow Coma Scale (mean/SD) | 5 | ±4.0 | 3.6 | ±2.2 | <0.001 |
All measures of neurologic status and survival were superior in the group with a shockable initial rhythm ( Figure 1 ). Glasgow Coma Scale score at time of discharge was higher in patients with shockable initial rhythm compared with nonshockable rhythm (9.7 vs 4.9), with a mean difference of 4.8 (95% CI 3.7 to 6.0, p <0.0001), and the CPC was lower (2.9 vs 4.3), with a mean difference of −1.4 (95% CI −1.8 to −1.1, p <0.0001). The adjusted odds of survival with good neurologic outcome in patients with a shockable initial rhythm compared with those presenting without a shockable rhythm was 4.8 (95% CI 2.7 to 8.7).
In the subgroup of patients who underwent PCI, there were no significant differences in age or gender, although there were numerically more female than male patients without a shockable rhythm who underwent primary PCI (25 vs 5, p = NS). The initial Glasgow Coma Scale score at emergency department admission was not significantly different between the groups (5.4 vs 4.7, mean difference 0.8, 95% CI −1.0 to 2.6).
Median door-to-balloon time was similar between those with and without a shockable rhythm. The percentages of patients with a door-to-balloon time <90 minutes, receiving TH, and achieving final Thrombolysis In Myocardial Infarction (TIMI) grade 3 flow were not significantly different ( Table 2 ). The mean CPC at discharge was 2.6 in the shockable rhythm group versus 3.5 (mean difference −0.9, 95% CI −1.6 to −0.2). Survival and survival with good neurologic outcome (CPC 1 or 2) was significantly better in patients with an initial shockable rhythm ( Figure 2 ); the adjusted odds ratio for survival with good neurologic outcome was 2.7 (95% CI 1.1 to 6.8).
| Variable | Shockable Initial Arrest Rhythm | |||
|---|---|---|---|---|
| Yes (n = 106) | No (n = 30) | |||
| n (median) | % (IQR) | n (median) | % (IQR) | |
| Door to Balloon time (minutes) | 74 | (54–93) | 86 | (59–109) |
| Door to Balloon time <90 minutes | 75 | (71%) | 17 | (59%) |
| Final Thrombolysis in Myocardial Infarction III flow | 84 | (91%) | 26 | (93%) |
| Therapeutic hypothermia | 46 | (44%) | 15 | (50%) |
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