Author + information
- Ralph J. Verdino, MD* ()
- ↵*Reprint requests and correspondence:
Dr. Ralph J. Verdino, Hospital of the University of Pennsylvania, 9th Floor Founders Pavilion, 3400 Spruce Street, Philadelphia, Pennsylvania 19104
- implantable cardioverter-defibrillator
- wearable cardioverter-defibrillator
Mention the words “life vest” to most people you meet, and you may conjure up images of a bright orange buoyancy device that you should put on a child when going for a boat ride on a lake. Others may associate these words with the yellow inflatable device found somewhere under your seat on an airplane. Although the flight attendants have told you about it many times, you are still not exactly sure how and when to operate one. Mention these words to many cardiologists these days, and you are talking about a wearable defibrillator that may be prescribed for your patient with a cardiomyopathy while he or she waits for a permanent implantable cardioverter-defibrillator (ICD) to be implanted or reimplanted.
The wearable cardioverter-defibrillator (WCD) is produced by a single manufacturer, ZOLL Lifecor Corp., Pittsburgh, Pennsylvania, and received U.S. Food and Drug Administration approval in 2002. This device is currently being marketed around the world for 4 types of patients: 1) patients with a left ventricular ejection fraction ≤35% waiting for the reimbursement-mandated 30- to 90-day window from initial diagnosis or revascularization to elapse before ICD implantation; 2) patients who do not currently meet ICD implantation criteria due to New York Heart Association functional class IV heart failure; 3) patients who meet ICD implantation criteria but whose condition delays or prohibits implantation, usually coincident infection; and 4) patients who have undergone ICD explantation, usually for infection, who are receiving a course of antibiotics or other treatment before implantation of a new ICD. Until recently, data regarding the incidence of sudden death and the utility of a wearable defibrillator for patients in these specific scenarios were scant. Also, patient compliance with this device on a large-scale level was a concern. Certainly, patients in clinical studies tend to be more compliant, but would “real-world” patients prescribed these devices actually use them long enough to receive benefit?
The paper by Chung et al. (1) in this issue of the Journalreports the outcomes in >3,500 patients from the manufacturer's database who wore this device between August 2002 and December 2006. They compared the survival rates of these patients with those of patients undergoing first ICD implantation at the Cleveland Clinic between August 1996 and 2004. Like many reviews of large databases not intended for rigorous academic scrutiny, this paper is plagued by missing information regarding patient demographics and indications for these devices. Mortality was not confirmed by personal contact of study coordinators, but instead taken from the Social Security Death Index. Yet, the paper does manage to provide important and unequivocal data.
First, the paper documents that these patients did, indeed, wear these devices. The 3,569 patients wore the WCDs for a total of 143,643 days for a mean use of >50 days and a range of 1 to 1,590 days. The investigators calculated that patients wore these devices for a mean of almost 20 h/day. Daily use was confirmed in >90% of patients, and <15% of patients stopped wearing the WCD prematurely because of comfort issues or adverse reactions.
Second, the paper documents that the WCD successfully treats tachyarrhythmias. During the time that these devices were worn, 80 sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) events were recorded in 59 patients (1.7% of the study cohort). The first shock was successful in 79 of 80 patients. The only patient who failed a WCD shock had hemodynamically tolerated VT that also failed several external shocks delivered by emergency medical service workers in the ambulance and hospital staff members in the emergency department. His VT was later terminated pharmacologically. Although the shocks were effective, 8 of these patients died, all of recurrent arrhythmias: 4 after recovering consciousness and the arrival of professional medical care, 1 whose spouse prevented a second WCD shock, 2 due to electrocardiogram signal disruption presumably after a fall, and 1 who failed detection due to a pacemaker operating in a unipolar mode. Although the success rates for treating VT and VF were excellent, not all cardiac arrests were secondary to tachyarrhythmias. Twenty-three asystolic events were recorded, resulting in 17 deaths, and 3 pulseless electrical activity events resulting in death were confirmed by medical personnel at the site. Unlike implanted defibrillators, the WCD cannot deliver antibradycardia pacing during these events but can only alert bystanders to call for an ambulance.
Third, the paper allays concerns of inappropriate shocks and device pro-arrhythmia. Once the device meets its prescribed criteria for detecting a tachyarrhythmia, it sets off a series of vibratory and auditory alerts. Because patients can prevent a shock by holding the response button, inappropriate sensing rarely resulted in a shock. Only 67 episodes of inappropriate ICD discharges were logged in these 3,569 patients during 4,788 months of use. These results are not dissimilar to those of inappropriate shocks from ICDs (2).
Finally, and I believe most importantly, this paper gives some guidance regarding which patients may benefit most from using this technology. Although by no means a randomized study, this analysis meticulously classified most patients according to common indications for prescription of this device. The authors divided the population into 2 groups: those who received the WCD for traditional ICD implantation criteria and those who received it for nontraditional ICD indications. The traditional group comprised 4 types of patients: 1) those who recently had an ICD explanted; 2) those with an episode of VT/VF awaiting ICD implantation; 3) those with a long-standing cardiomyopathy and left ventricular ejection fraction of ≤35%; and 4) those with a genetic predisposition to sudden cardiac death. Nontraditional indications mainly included 2 groups of patients: 1) those with a left ventricular ejection fraction ≤35% but who had only recently been diagnosed or had a recent myocardial infarction or recent coronary bypass surgery; and 2) those with a recent myocardial infarction and an ejection fraction >35%.
Although the 2 groups (traditional vs. nontraditional ICD indications) were very similar in patient numbers, appropriate WCD shocks were much more common (58 vs. 22) in the traditional indication group. When followed for long-term survival using the Social Security Death Index, the traditional group had a higher mortality, confirming that they are indeed a higher risk population. Almost 40% of the patients in the entire study for whom the WCD was prescribed were either awaiting reimplantation of an ICD after explantation or had experienced VT/VF and were awaiting improvement in their comorbidities before initial ICD implantation. The WCD appropriately shocked 39 of these 1,077 patients (3.6% of this cohort) for 58 separate episodes of VT/VF. Of these 39 patients, 36 survived. Clearly, this device can be lifesaving attire for these patients who have traditional indications for an ICD but must wait for an infection to clear or other comorbidities to resolve.
Yet, not all of the benefits of the WCD were realized in the traditional ICD group. Although the VALIANT (Valsartan in Acute Myocardial Infarction) study demonstrated a high incidence of sudden cardiac death in patients with early post-myocardial infarction with left ventricular ejection fractions ≤35% (3), the DINAMIT (Defibrillator in Acute Myocardial Infarction Trial) failed to show a benefit of early ICD implantation in this population, possibly because of the high incidence of heart failure deaths or possibly because ejection fractions may improve, leaving patients with a low risk of ventricular tachyarrhythmia (4). This group of patients, however, is covered by Medicare to obtain WCDs, and the device did appear to be beneficial for members of this cohort in the study. Ten of these 341 patients with early post-infarct ischemic cardiomyopathies (2.9%) received appropriate WCD shocks for 12 separate episodes of VT/VF; 8 of the 10 survived.
Some patient groups did not receive a great deal of benefit from the WCD. None of the 104 patients with recent myocardial infarction and an ejection fraction >35% received an appropriate shock from their WCD. Primary prevention with an ICD is not indicated in this patient population, and I believe that the WCD should not be prescribed in this scenario. Patients with a recent diagnosis of nonischemic cardiomyopathy accounted for 20% of the study population, but only 4 patients (0.7%) received appropriate shocks, 1 of whom later died. Patients who were early post-coronary artery bypass graft had an appropriate shock rate of 0.8%, and only 1 of those 2 patients survived. I believe that the WCD should not be routinely prescribed for these patients either.
In conclusion, the WCD is a technology that can save lives if prescribed for the correct patients. It has a high degree of success in treating ventricular tachyarrhythmias and does not appear to be very cumbersome for patient use. Not prescribing this lifesaving attire to your high-risk patient awaiting ICD implantation or reimplantation is the real faux pas.
Dr. Verdino has received lecture honoraria from Biotronik, Boston Scientific, Medtronic, and St. Jude.
↵* Editorials published in the Journal of the American College of Cardiologyreflect the views of the authors and do not necessarily represent the views of JACCor the American College of Cardiology.
- American College of Cardiology Foundation
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