Comorbidity and survival in out-of-hospital cardiac arrest

Background: Patients suffering out-of-hospital cardiac arrest (OHCA) have a poor prognosis but survival among subgroups differs greatly. Previous studies have shown conflicting results on whether patient comorbidity affects outcome. The aim of this national study was to investigate the effect of comorbidity on outcome after OHCA in Sweden. Methods: We included all patients with bystander-witnessed OHCA from 2011 to 2015 in the national Swedish Registry of Cardiopulmonary Resuscitation. In order to assess comorbidity, the database was merged with the comprehensive National Patient Registry, which includes all out-patient and in-patient care in Sweden. The Charlson comorbidity index (CCI) and the specific comorbidity conditions constituting the CCI was used to identify whether comorbidity was associated with outcome. Results: A total of 12,012 patients were included in the study. Of these, 1598 patients survived to 30 days (13%). The most common comorbidities were a history of congestive heart failure (29%), myocardial infarction (24%), and diabetes without complications (23%). Renal disease (odds ratio [OR] 0.53; 95% CI 0.53-0.72), diabetes with complications (OR 0.65; 95% CI 0.49-0.84), diabetes without complications (OR 0.63; 95% CI 0.52-0.75), congestive heart failure (OR 0.84; 95% CI 0.71-0.99), and metastatic carcinoma (OR 0.61; 95% CI 0.40-0.93) were significantly associated with a reduced chance of 30-day survival when adjusted for demographic characteristics and also resuscitation-associated factors such as shockable initial rhythm, bystander cardiopulmonary resuscitation (CPR), and place of arrest. With increasing comorbidity, the chance of 30-day survival decreased: adjusted OR was 0.82 (59% CI 0.68-0.99) for CCI 3-4, 0.62 (95% CI 0.47-0.83) for CCI 5-6, and 0.51 (95% CI 0.36-0.72) for CCI > 6, respectively, all in relation to those with CCI 0-2. Additionally, increasing morbidity was associated with reduced odds of return of spontaneous circulation (ROSC) and ROSC at hospital admission. Conclusion: This large national study showed that increasing comorbidity decreased the chance of survival to 30 days in OHCA. This association remained after covariate adjustment.