Most Patients Willing to Wear Defibrillator on the Outside

Reed Miller

July 08, 2010

July 8, 2010 (Cleveland, Ohio) — Registry data shows that the survival rates with the wearable cardioverter-defibrillator (WCD) vest (LifeVest, Zoll Lifecor) are about as good as with an implantable cardioverter defibrillator (ICD), making it an acceptable alternative or bridge to ICD implantation [1].

Data from 3569 patients in a manufacturer-sponsored registry, published in the July 13, 2010 issue of the Journal of the American College of Cardiology, resolves doubts about patients' willingness to wear the device, which have limited the WCD's adoption. "Compliance is key. The patients need to be wearing the WCD to be effective, and proper instruction is important," study author Dr Mina Chung (The Cleveland Clinic, Ohio) told heartwire . "One reassuring finding of the study was that we also showed that the WCD was worn with good compliance by most patients."

The WCD is prescribed to patients with factors indicating a high risk of sudden cardiac death (SCD) but who cannot be implanted with an ICD immediately for a variety of clinical situations. The WCD is an alternative to giving these patients an automatic-external defibrillator, which requires a bystander to be present during a sudden cardiac arrest.

The subjects wore the device for an average of nearly 20 hours a day for 53 days, and 52% of patients wore it at least 90% of the day on average. About 14% of the subjects stopped wearing the WCD because they found it to be uncomfortable or had an adverse reaction. That is a significantly better compliance rate than in a previous published investigational study of the WCD cited by Chung et al, in which 68 of 289 patients (24.5%) stopped wearing an earlier, larger version of the WCD. Some patients in the new study complained that the device is too bulky, but the new version is 40% smaller than the older version.

During the study period, there were 80 sustained VT or VF events in 59 patients. Patients survived 72 of the 80 VT/VF events and 78 of 106 (73.6%) of all events. The first shock from the device was successful in all 76 cases of unconscious VT/VF and successful in three out of four of the other cases of VT/VF, but 17 of 23 patients experiencing asystole died. There were also two cases of pulseless electrical activity and one case of respiratory arrest. While using the WCD, 3541 of 3569 patients (99.2%) survived overall.

The authors compared the survival rates of the WCD patients with the survival of a population implanted with ICDs at the Cleveland Clinic and found that long-term mortality with the WCD was not significantly different from first-ICD-implant patients. "The long-term survival data comparing WCD and ICD survival are reassuring that WCD therapy may be comparable to ICD therapy, rationalizing the use of the WCD as an acceptable temporary alternative or a bridge to long-term ICD implantation," Chung et al conclude.

Inappropriate shocks were about as rare as they are with ICDs. In the Chung et al study, inappropriate shocks were reported by 1.9% of patients or 1.4% per month, while ICD studies show a 0.6% to 1.5% monthly rate over the first six months of use, according to the authors. The ability to prevent shocks with response buttons on the WCD may have allowed patients to minimize inappropriate shocks.

"It is interesting to speculate from these results that this type of shock-prevention feature might be useful for selected low-risk arrhythmia treatment strategies in patients with ICDs," the authors conclude.

Asystole or pulseless electrical activity accounted for a quarter of the sudden cardiac arrests and caused death in almost three-quarters of cases. "The current WCD does not have pacing capabilities, so hopefully future forms will incorporate the ability to pace and treat life-threatening slow heart rates as well," Chung said.

The authors compared outcomes of patients in the study with "traditional" ICD implantation criteria and the outcomes of those with "nontraditional" ICD indications. The traditional group included patients who recently had an ICD explanted, patients with an episode of VT/VF waiting for an ICD, patients with a long-standing cardiomyopathy and left ventricular ejection fraction of <35%, and patients with a genetic predisposition to sudden cardiac death. The nontraditional patients included patients with a left ventricular ejection fraction <35% who had only recently been diagnosed or had a recent MI or coronary bypass surgery and patients who had recently suffered an MI but maintained an ejection fraction over 35%.

Appropriate WCD shocks were much more common (58 vs 22) in the traditional-indication group, and the traditional-indication group had a higher long-term mortality, according to data from the Social Security Death Index.

In the nontraditional group, 10 of 341 patients with early postinfarct ischemic cardiomyopathies received an appropriate shock from the WCD for 12 distinct VT/VF episodes, and eight of them survived. However, none of the 104 patients with recent MI and an ejection fraction >35% received an appropriate shock from their WCD.

"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," Dr Ralph Verdino (University of Pennsylvania, Philadelphia) writes in an accompanying editorial [2]. "Most important, this paper gives some guidance regarding which patients may benefit most from using this technology."

Primary ICD therapy is not indicated in this patient population, and the results of the Chung et al study suggest they are not suitable for a WCD either, Verdino concludes. Also, the patients with a recent diagnosis of nonischemic cardiomyopathy accounted for one-fifth of the study population, but only 0.7% received an appropriate shock. Patients who recently had undergone CABG surgery had an appropriate shock rate of 0.8%, and only one of those two patients survived, so Verdino suggests the WCD should not be routinely prescribed for that type of patient.

The data was obtained from Zoll Cardiac Management Solutions, but no additional support from the company was obtained for the study. Chung participates in industry-sponsored research with Medtronic, Boston Scientific, St Jude Medical, and Biotronik. Verdino discloses that he has received lecture honoraria from Biotronik, Boston Scientific, Medtronic, and St Jude Medical.

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