By Michael Crawford, MD, Editor

Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco

Dr. Crawford reports no financial relationships relevant to this field of study.

SYNOPSIS: A large German experience with the wearable cardioverter-defibrillator confirms the finding of U.S. registry studies and suggests that the device is useful for patients with reduced left ventricular function at high risk of sudden cardiac death who are not currently good candidates for an implantable cardioverter-defibrillator.

SOURCES: Wäßnig NK, Günther M, Quick S, et al. Experience with the wearable cardioverter-defibrillator in patients at high risk for sudden cardiac death. Circulation 2016;134:635-643.

Lee BK, Olgin JE. The wearable cardioverter-defibrillator: Is it now the standard of care? Circulation 2016;134:644-646.

After considerable research in the United States, the FDA approved the wearable cardioverter-defibrillator (WCD) in 2001, and an American Heart Association (AHA) scientific advisory panel rated it a class II indication in several specific patient categories in which a temporary external cardioverter-defibrillator would be preferable to an implantable cardioverter-defibrillator (ICD). This retrospective observational study from Germany is the first large report of WCD use outside the United States. This report of all registered WCD users in Germany from 2010 to 2013 includes 6,043 patients from 404 centers with eight indications for its use: ICD explantation (12%), heart failure (0.4%), awaiting heart transplant (0.7%), immediate post-myocardial infarction (MI) or coronary artery bypass graft (27%), newly diagnosed dilated cardiomyopathy (37%), newly diagnosed non-ischemic cardiomyopathy (12%), acute myocarditis (10%), and familial sudden cardiac death syndromes (1.4%). All patients who experienced WCD shocks were fully investigated. Most of the patients were men (79%). In 120 patients, one to five shocks were delivered per episode for a grand total of 163 shocks. In 94 patients (1.6%), the shocks were delivered for ventricular tachycardia (VT)/ventricular fibrillation (VF). Eleven percent of these episodes required more than one shock to terminate the arrhythmia. The WCD detected 242 VT episodes in 70 patients who remained conscious and manually withheld the shocks for these self-terminating episodes. Successful cardioversion occurred in 88 patients (94%), and 87 survived for 24 hours post-shock. There were seven deaths within 24 hours of treatment: four with unresponsive monomorphic VT and three with VF. One patient who was not shocked died of sustained asystole. One-half of the deaths occurred in ICD explant patients. Inappropriate shocks occurred in 26 patients (0.4%) and were due to artifact, rapid supraventricular tachycardia (SVT), or failure of the patient to press the hold button. None resulted in harm to the patient. The authors concluded that the German experience confirms the value of the WCD outside the United States.

COMMENTARY

These days, it is unusual for a new medical device to move from the United States to Europe rather than the reverse. However, despite FDA approval in 2001, guidelines for WCD use did not appear until the European Society of Cardiology guidelines on the management of ventricular arrhythmias and the prevention of sudden death in 2015 and the AHA scientific advisory in 2016. The recommendations of both organizations are very similar and can be summarized as follows. Specifically, both organizations recommended class IIa for patients post-ICD explantation until another can be implanted, as a bridge to transplant, and in the first 90 days post-MI in patients with ejection fraction (EF) < 35%. Also, patients with acute myocarditis, patients post-revascularization with low EF, and patients with new dilated or non-ischemic cardiomyopathy, in whom recovery of left ventricular function (LVF) is expected with optimal medical or device therapy, received a IIb recommendation. There are no class I indications for a WCD because there are no completed randomized trials showing efficacy. Although the WCD has been shown to effectively treat VT/VF, only a randomized, controlled trial can verify a survival benefit. This may sound nuts, but remember the ICD was not associated with improved survival in patients with low EF early after acute MI, despite being very effective at treating ventricular arrhythmias. So as Drs. Lee and Olgin opined in their editorial, the WCD is not considered the standard of care for any situation yet. Ongoing randomized trials, such as the VEST study, hopefully will help clarify the role of the WCD in the near future.

There are some other interesting aspects of this German study. There were fewer inappropriate shocks in their experience (0.4%) compared to 1-2% in the two large U.S. registry studies. Presumably, this was due to patient selection difference. The German study included a wider range of indications, and some of their patients may have been at lower risk of SVT. For example, the German study included more patients with acute myocarditis. Also, adherence was much better in Germany. Only 3% of German patients discontinued the device in less than three days. In the U.S. registry, 14% stopped using the WCD due to discomfort or adverse reactions. One problem with the German registry is that we do not have data on comorbid conditions, left ventricular ejection fraction, or medical treatment strategies. This makes using the data to guide individual patient decisions difficult.

So what should clinicians do now? Consider a WCD for patients with poor left ventricular ejection fraction at risk for sudden cardiac death who currently are not candidates for an ICD. However, discuss the risks and potential benefits with patients. Make patients aware that there is no conclusive scientific data on whether the WCD will prolong life.