Abstract 40: Is Severe Post-shock Bradyarrhythmia In Patients Using Wearable Defibrillators Common or Serious?
Background: Previous studies have shown a 40% to 60% incidence of asystole immediately after transthoracic defibrillation of pulseless ventricular tachycardia/ventricular fibrillation (VT/VF). Such post-shock asystole has very poor outcomes. Wearable cardioverter defibrillators (WCD, LifeVest, ZOLL Lifecor) automatically record and treat VT/VF by delivering transthoracic defibrillation without the need for a bystander. Post-shock bradyarrhythmia (PSB) is of clinical concern in patients (pts) using WCD.
Objective: Determine the incidence and outcomes of PSB during WCD use.
Methods: ECG recordings from consecutive pts who had VT/VF while using WCD between March 2005 and March 2007 were retrospectively analyzed. All VT/VF occurring within 24 hours from the initial shock for VT/VF were defined as a single sudden death event (SDE) while those beyond 24 hours as a SDE recurrence. ECGs contained 30 seconds prior to the VT/VF detection and > 15 seconds following VT/VF termination. Severe PSB was defined as a pause longer than 10 seconds. Survival was defined as conscious at emergency department (ED) arrival or not needing to go to the ED. Pt calls and medical orders were reviewed to determine the indications for WCD use and pt post-shock status.
Results: Between March 2005 and March 2007, 3564 pts used WCD for an average of 51 days. 56 pts (51% ICD explants, 28% ischemic cardiomyopathy (ICM), 11% Non-ICM, 8% delayed ICD implant, 2% others) received 142 shocks for 79 SDE. 14 pts had > 1 SDE (max = 5). 15 SDE had >1 VT/VF (max = 47). 79/79 (100%) initial SDE shocks terminated VT/VF. 76/79 (96%) of treated SDE resulted in survival. Severe PSB was found in 4 ECGs from 4 pts. 3/4 (75%) occurred after the initial SDE shock, 1/4 (25%) after VT/VF recurrence; 2/4 (50%) developed ventricular complexes prior to the end of the recording, 2/4 (50%) did not; 3/4 (75%) pts survived, 1/4 (25%) did not. Median time from VT/VF onset to shock was 44 seconds.
Conclusions: WCD is an efficacious therapy. The majority of pts with severe PSB after WCD survived. Severe PSB was less frequent and had a better prognosis than that observed in EMS studies. This may be attributed to faster WCD shock therapy (median 44 seconds) compared with EMS (>10 minutes).