Abstract 21: Elevated Resting Heart Rate Is Associated with Pulseless Electrical Activity Independent of β-Blocker Use

Abstract

Introduction: Higher heart rate (HR) has been associated with increased cardiovascular mortality but mechanisms are poorly understood. Sudden cardiac arrest (SCA) presenting with pulseless electrical activity (PEA) has a significantly higher mortality than ventricular fibrillation/tachycardia (VF/VT). Hypothesis: We investigated the hypothesis that resting HR has a predictive role in subjects with future PEA versus VF/VT. Methods: Cases of out of hospital SCA, age ≥18 years, with resuscitation attempted were identified from an ongoing prospective community-based study in the Northwest US (pop. approx. 1 million). HR was measured from resting 12-lead ECG prior and unrelated to the cardiac arrest. Pearson's chi-square tests and independent samples t -tests were used for comparisons of presenting arrhythmia, arrest circumstances and heart rate. A general linear model was used to identify gender and age differences in heart rate between PEA and VF/VT. Significant predictors of PEA were determined using logistic regression. Results: A total of 913 cases (mean age 65±16 years, 68% male) with resuscitation attempted (2002-2009) presented with VF/VT (45%) or PEA (26%). PEA cases were older, more likely to be female and to arrest at home, whereas VF/VT cases were more likely to be witnessed, to have bystander CPR, return of spontaneous circulation and to survive to hospital discharge. There was no difference in the use of beta-blockers between PEA and VF/VT (p=0.19). PEA cases had higher resting HR compared with VF/VT (81 bpm vs. 74 bpm, p=0.0007, n=322). Males with PEA had higher HR than males with VF/VT (83 bpm vs. 75 bpm, p=0.001), but the difference in HR between PEA vs. VF/VT among females was smaller and borderline significant (78 bpm vs. 72 bpm, p=0.06). Heart rate was a significant predictor of PEA after adjustment for age, gender and circumstances of arrest [OR for a 10-beat per minute increase 1.35; 95% CI (1.17-1.56)]. Heart rate remained a significant predictor of PEA after additional adjustment for beta-blockers [OR 1.36; 95% CI (1.18-1.57)]. Conclusions: Resting HR is a significant predictor of future cardiac arrest manifesting with PEA, independent of beta-blocker use and could, in part, explain the association between higher HR and increased mortality.