Zoll LifeVest fails to cut sudden deaths in heart attack trial

Zoll's LifeVest (Zoll Medical)

A phase 3 trial of Zoll Medical’s LifeVest has missed its primary endpoint. The study found that people who started using the wearable defibrillator the week after they had a heart attack were as likely to suffer sudden cardiac death in the next three months as patients who received conventional therapy.

Zoll designed the 2,300-patient trial to show LifeVest reduces the sudden death rate by monitoring the wearer’s heart rhythms and delivering a treatment shock if they go awry. But the study found the device was no more effective than medication alone in this key regard. Investigators claim the result may say as much about our ability to determine cause of death as the effectiveness of the device.

“While the VEST Trial did not meet the endpoint of sudden death mortality, the ability to determine the cause of death as sudden when unwitnessed is difficult and could result in misclassification,” Jeffrey Olgin, M.D., co-principal investigator on the trial, said in a statement.


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Olgin’s assessment is supported by data from a secondary endpoint that looked at all-cause mortality. The all-cause mortality rate in the control arm was 4.9%, compared to 3.1% in the LifeVest cohort. That difference amounts to a 36% reduction in mortality and a p-value of 0.04, giving Zoll a data point that, while having debatable clinical significance, doesn’t paint the study as an outright failure.

It remains to be seen whether that is enough to stop the data negatively affecting perceptions of the value of LifeVest or use of the device. The data could lead physicians to narrow use LifeVest to a smaller, higher-risk subgroup of people than was included in the 2,300-patient trial. The vast majority of patients in the trial never received a shock from the device. 

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