Bridging a temporary high risk of sudden arrhythmic death. Experience with the wearable cardioverter defibrillator (WCD).

The implantable cardioverter defibrillator (ICD) is able to reduce sudden arrhythmic death in patients who are considered to be at high risk. However, the arrhythmic risk may be increased only temporarily as long as the proarrhythmic conditions persist, left ventricular ejection fraction remains low, or heart failure prevails. The wearable cardioverter defibrillator (WCD) represents an alternative approach to prevent sudden arrhythmic death until either ICD implantation is clearly indicated or the arrhythmic risk is considered significantly lower or even absent. The WCD is also indicated for interrupted protection by an already implanted ICD, temporary inability to implant an ICD, and lastly refusal of an indicated ICD by the patient. The WCD is not an alternative to the ICD, but a device that may contribute to better selection of patients for ICD therapy. The WCD has the characteristics of an ICD, but does not need to be implanted, and it has similarities with an external defibrillator, but does not require a bystander to apply lifesaving shocks when necessary. The WCD was introduced into clinical practice about 8 years ago, and indications for its use are currently expanding. This article describes the technological aspects of the WCD, discusses current indications for its use, and reviews the clinical studies with the WCD. Additionally, data are reported on the clinical experience with the WCD based on 354 patients from Germany hospitalized between 2000 and 2008 who wore the WCD for a mean of 3 months.

Clinical efficacy of a wearable defibrillator in acutely terminating episodes of ventricular fibrillation using biphasic shocks.

The Wearable Cardioverter Defibrillator (WCD) automatically detects and treats ventricular tachyarrhythmias without the need for assistance from a bystander, while at the same time allowing the patient to ambulate freely. It represents an alternative to emergency medical services for outpatient populations with a temporary risk of sudden cardiac death. While the original devices used a monophasic truncated exponential waveform for cardioversion/defibrillation shocks, a new, biphasic shock was developed for the next device generation. In 12 patients undergoing electrophysiological testing for ventricular tachyarrhythmias, termination of electrically induced ventricular fibrillation (VF) was attempted via the WCD. In 22 episodes, induced VF was promptly terminated by the first 70 J (n=12) or 100 J (n=10) biphasic shocks. Time between arrhythmia initiation and shock delivery was 22 +/- 6 seconds (70 J) and 21 +/- 6 seconds (100 J) (P=NS). The measured transthoracic impedance was 71 +/- 5 Ohms (64-79 Ohms) for the 70 J shock and 64 +/- 8 Ohms (47-72 Ohms) for the 100 J shock. The present study demonstrates that a single low energy biphasic shock delivered by the WCD, reliably terminates electrically induced VF (100% of episodes). The results of this study suggest that there is an acceptable safety margin to the maximum output of the device (150 J). Despite our promising data, we recommend that programming all shocks for maximum energy output should be done when using the WCD in ambulatory patients.