How Should We Use the Wearable Cardioverter-Defibrillator in Japan?

The LifeVest produced by Zoll Corporation (Pittsburgh, PA, USA) is the first wearable cardioverter-defibrillator (WCD) and was approved by US FDA in 2002, since when it has been used worldwide. The WCD has been available in Japan since April 2014 and in this issue of the Journal Sasaki et al¹ give us the very important information about its use.

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Concept and System of the WCD

Unlike an implantable cardioverter-defibrillator (ICD), the WCD is worn outside the body and continuously monitors the patient’s rhythm with dry and non-adhesive sensing electrodes (Figure). When a life-threatening rhythm is detected, the electrodes exude a Blue^TM gel over the therapy electrodes just before electrical shock to avoid discomfort related to the long-term exposure to the gel detriment during long-term ambulatory use. The WCD is equipped with special algorithms to reduce noise, an alarm system and a response button. The device alerts the patient prior to delivering a treatment shock, and thus allows a conscious patient to delay the treatment shock by pressing the response button controls the therapy. This system is useful for reducing inappropriate shocks, which have thus been a rare event in 0–3% of patients.²

Figure.

LifeVest Wearable Defibrillator (WCD). Adopted from Zoll homepage (http://lifevest.zoll.com/).

High success rates of ventricular tachycardia (VT)/ventricular fibrillation (VF) termination by the WCD have been already reported.³ Reasons for defibrillation failure were displacement of the sensing electrodes and prevention of VF detection by unipolar pacing artifacts from an implanted pacemaker. Thus, it is recommended to keep pacing artifact <0.25 mV to prevent this scenario.⁴ Induction of VF by inappropriate shock, or acceleration and deterioration of VT to VF by appropriate shock, can occur during WCD use, as with an ICD. However, neither has been reported in the clinical trials performed so far.²

Although one of the main concerns about the WCD was compliance, the actual time of wearing of the device by the patient can be automatically collected by the device. Another concern is the ability of patients to use the device correctly. Main errors are placement of the electrodes and refraining from pressing the response button by conscious patients.² Sleep disturbance caused by false alarms occurred in approximately half of the reports. However, only 5% of patients discontinued its use.³

Reality of WCD Use in Western Countries

The WCD was first reported 1998⁵ and since then, major societies have included WCD use in their guidelines.^6,7 Patients with a transient high risk for VF, such as those awaiting cardiac transplantation, those at very high risk after a recent myocardial infarction (MI) or an invasive cardiac procedure, or those requiring temporary removal of an infected implanted defibrillator for antibiotic therapy are indicated in the American and European cardiac societies guidelines,⁶ and use after device extraction because of an infection was recommended by expert consensus of the Heart Rhythm Society.⁷

As mentioned, the efficacy of the WCD in detecting and treating VT/VF has been demonstrated in patients at high risk of sudden cardiac death (SCD) who are not clearly indicative of an ICD or are at temporary high risk of SCD until ICD implantation.^8,9 It has been used worldwide for this purpose, especially in the USA and Germany. According to Zoll, the LifeVest has been prescribed to more than 100,000 patients.

Reality of WCD Use in Japan

In Japan, the WCD became available in April 2014 after medical reimbursement was approved by the Ministry of Health, Labour and Welfare in January 2014. The first statement of WCD use was from the Japanese Heart Rhythm Society on January 9th, 2014:¹⁰ (1) requirements of the faculty where WCD can be used under the cover of medical reimbursement, (2) requirements of the doctor who can decide on the use of WCD, (3) period of WCD use under medical reimbursement, up to 3 months, and (4) social management and safety, allowance of occupation and driving. However, there was no mention of utility or efficacy.

Sasaki et al¹ report only 9 patients’ experience, but there is very important information on indications, patient compliance and clinical efficacy in the Japanese medical environment.

Clinical Indications of WCD

The main indication for WCD use is as a bridge to ICD implantation or until the arrhythmic risk subsides (Table). Because there are no randomized or controlled trials studying the survival benefit with WCD, guidelines for its use are quite general and its prescription often relies on expert opinion.² Thus, there are differences in the frequency of various indications reported from Germany³ and the United States.¹¹ The main reasons for WCD use in Germany are recent MI (39%), post coronary artery bypass grafting (25%), ICD explant (10%), and myocarditis and non-ischemic cardiomyopathy (NICM; 10%).² In the USA, they are ICD explant (23%), NICM (20%) and delay in implantation (16%).¹¹

Table. Clinical Indications of WCD

1. Patients with accepted indications for ICD implantation (LVEF ≤35% and MI, NICM, or other DCM) who also usually have temporary or contraindications for ICD use

[For example]

• Patients waiting for re-implantation of ICD after extraction of an infected ICD

• Patients in NYHA class IV heart failure

• Terminal disease with life expectancy <1 year

2. Patients with a condition that temporarily places them at high risk of an arrhythmic death

[For example]

• ICM in the early period before and after CABG or PTCA

• Recent MI before and after CABG or PTCA

• Patients with low LVEF resulting from potentially reversible condition such as newly diagnosed DCM (tachycardia-induced cardiomyopathy, transient myocarditis

3. Patients under investigation for a disease with a high risk of arrhythmic death pending definitive diagnosis

[For example]

• Patients suspected of having an inheritable arrhythmic disorder who are awaiting results of confirmatory testing or survivors of a cardiac arrest of unclear origin

4. Patients listed for cardiac transplant

5. ICD explantation

CABG, coronary artery bypass grafting; DCM, dilated cardiomyopathy; ICD, implantable cardioverter-defibrillator; ICM, ischemic cardiomyopathy; LVEF, left ventricular ejection fraction; MI, myocardial infarction; NICM, nonischemic cardiomyopathy; PTCA, percutaneous transluminal coronary angioplasty; WCD, wearable cardioverter-defibrillator.

Sasaki et al¹ reported that the underlying heart diseases were prior MI (3 recent and 2 previous MI), variant angina, fulminant myocarditis, cardiac amyloidosis, and idiopathic VF (1 each). Thus, all of 8 patients were considered to be potentially indicative of ICD for SCD (89%). The other patients had reduced LVEF and heart failure, but no VT/VF after recent MI and in that case the WCD was used for the primary prevention of SCD.

Conclusions

We have much experience with ICD use in Japan,^12,13 but have only just started using the WCD. Although the difference in the frequency of various indications in different countries is understandable, it is still unclear how it will be used in the Japanese medical environment. Thus, we need further experience and examination of WCD use in Japan.

References

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• 10.    Niwano  S,  Kurita  A,  Kato  R,  Okamura  H,  Sekiguchi  Y,  Iwasaki  Y, et al. Statements of clinical use on the wearable cardioverter defibrillator (in Japanese). Japanese Heart Rhythm Society. http://jhrs.or.jp/com_device201401_01.html (accessed October 30, 2014).
• 11.    Chung  MK,  Szymkiewicz  SJ,  Shao  M,  Zishiri  E,  Niebauer  MJ,  Lindsay  BD, et al. Aggregate national experience with the wearable cardioverter-defibrillator: Event rates, compliance, and survival. J Am Coll Cardiol 2010; 56: 194–203.
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• 13.    Shimizu  A. What are the most useful predictors of cardiac mortality in patients post myocardial infarction? Circ J 2013; 77: 319–320.