Background

Despite the high rate of sudden death after myocardial infarction among patients with a low ejection fraction, implantable cardioverter-defibrillators are contraindicated until 40 to 90 days after myocardial infarction. In order to close this potential dangerous gap the wearable defibrillator is available. Among patients with a recent myocardial infarction and an ejection fraction of 35% or less, the wearable cardioverter-defibrillator has proven to reduce mortality.

Case Report

A 67 year old, solitarily living, male patient was admitted to the hospital and immediately transferred to the cath lab with continuous cardiopulmonary resuscitation including external defibrillation due to ventricular fibrillation (VF). After return of sinus rhythm an acute anterior myocardial infarction (STEMI) and was diagnosed followed by an instant coronary revascularization of the culprit lesion (PCI LAD). After 3 weeks of hospitalization and optimal medical treatment for heart failure a severely reduced left ventricular ejection fraction (LVEF 24%) was diagnosed and a wearable defibrillator (LifeVest Zoll) was adjusted. 6 weeks later another interventional revascularization of the RCA was performed and the duration for the usage of the wearable defibrillator was extended for another 8 weeks. 

A week before a planned final outpatient cardiological visit to determine whether an ICD is indicated or not the patient called the Zoll hotline to report a gel leakage of the vest. Since a data transmission failed the patient was advised to promptly go to the hospital due to a possible previous treatment of the vest. The patient rejected emergency ambulance care and informed the hotline that his neighbor would transport him to the hospital. A day later a follow up call was unsuccessful including patient, brother, neighbor and hospital. 16 hours after the patients first contact to the hotline he died at home.

Retrospective analysis of the vest’s data showed a primary effective treatment due to VF. 16 hours later VF reoccurred due to r-on-t phenomenon which was correctly detected by the vest. 5 shocks were subsequently delivered with 4-6 joule which all remained ineffective (see figure 1). The technical report revealed multiple high impedance episodes after the first treatment accompanied by an acoustic request to apply new gel.  
Figure 1:

Conclusion

The wearable defibrillator is a semiautomatic device and its proper function relies on the patient’s interaction. Therefore it is crucial to critically reflect the patient’s cognitive capacities and therapy adherence before prescription. An ICD would have avoided this particular situation.

Time to hospital admission after gel leakage is pivotal. As soon as the gel dries on the skin, which starts after an hour, the impedance starts to rise ultimately leading to ineffective function. Bridging the time until stationary monitoring is achieved by application of new gel is key.