Use of a wearable cardioverter-defibrillator during the first 90 days after myocardial infarction does not provide additional protection against sudden death or death from ventricular tachyarrhythmia compared to usual care.

The wearable device was considered as a possible bridge in the immediate post-infarction period to a later implantable-ICD.

The multi-national VEST study found 1.6% of patients randomised to receive the wearable device had an arrhythmic death compared to 2.4% of patients receiving guideline-directed medical therapy, a difference that was not significant (p=0.28).

All 2,302 patients in the study had reduced left ventricular ejection fractions (<35%).

The study found total mortality was 3.1% in the patients wearing the devices and 4.9% in the control group (p=0.04).

“However, this result was not corrected for multiple testing, and given the use of most such corrections, the difference between the device and control groups would not be significant,” the study said.

The study also found no significant difference between groups with regards to non-arrhythmic deaths (1.4 v 2.2%)

There were six deaths in the 20 patients who received at least one appropriate shock while wearing in the device. Four adverse events including three hospitalisations and one death were also reported in the device group.

An adherence rate of 70% was met during the first two weeks after randomisation but then waned. Mean duration of wear was 14 hours per day, decreasing over time.

Almost 3% of participants never wore the device after randomisation while a similar proportion of patients in the control group accessed and wore a cardioverter-defibrillator against protocol.

The researchers said low adherence may be a limiting factor in the potential benefit of the wearable cardioverter–defibrillator.

“It is also evident that some patients who are successfully treated with an appropriate shock subsequently die; not all successful defibrillations prolong survival.”

“It remains unclear how to reduce the risk of arrhythmic death definitively, beyond what is possible with appropriate medical therapy, in the early period after myocardial infarction before ICDs are indicated,” the study concluded.

An editorial in the NEJM said the counterintuitive result of failure to show benefit of the wearable cardioverter–defibrillator “may be a shock to those who predicted that the trial would be positive”.

It suggested the trial was probably underpowered and acknowledged the low compliance rate of 41% at 90 days.

However in the absence of other evidence the authors said they believed it would still be reasonable to offer the device to motivated patients at high risk.

“We would advocate for a thorough discussion with the patient that both acknowledges the limitations of the available evidence and provides an understanding of the potential harms, such as frequent device alarms and potential for inappropriate shocks,” wrote Michael Field MD of theMedical University of South Carolina  and Richard Page MD of the University of Wisconsin School of Medicine.