Etiology of Cardiac Arrest in the Absence of Manifest Structural Heart Disease - Update From the Casper Prospective Cohort

Abstract

Background: The Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) enrolls patients with apparently unexplained cardiac arrest and no evident cardiac disease, and aims to identify the underlying conditions responsible for the cardiac arrest through systematic clinical testing. A combination of exercise testing, drug provocation, electrophysiological testing, advanced cardiac imaging, and targeted genetic testing may unmask the cause of cardiac arrest when a cause is not apparent. Methods and Results: The first 200 survivors (48.6 ± 14.7 years, 41% female) of unexplained cardiac arrest from CASPER, from 14 centers across Canada were evaluated to determine the results of investigation and follow-up risk of recurrence. Patients were free of evidence of coronary artery disease, left ventricular dysfunction or evident repolarization syndromes. Advanced testing determined a probable or definite diagnosis in 41% of patients. During a median follow-up of 3.15±2.34 years, 23% of patients had either a shock from their ICD or appropriate anti-tachycardia pacing or both. The annual ICD appropriate intervention rate was 0.16 per year (SEM=0.14), with no clear difference in intervention rate between diagnosed and undiagnosed subjects, or between those diagnosed with a primary electrical versus structural etiology. Conclusions: Obtaining a diagnosis in previously unexplained cardiac arrest patients requires systematic clinical testing and regular follow-up to unmask the cause of cardiac arrest. Nearly half of apparent unexplained cardiac arrest patients ultimately received a diagnosis, allowing for improved treatment and family screening. A substantial proportion of patients received appropriate ICD therapy during follow-up.