Ahmad Masri (Heart and Vascular Institute, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA) and others report in JACC: Clinical Electrophysiology that a systematic review and meta-analysis of the available evidence on the use of wearable cardiofibrillator therapy (WCD) found that the rate of patients who were appropriately treated was substantial and higher in observational studies than in the only available randomised controlled trial (RCT). They explain this was because “there was significant heterogeneity across the observational studies”, which “included mixed indications and high-risk patients”.
Masri and colleagues report that, while the first WCD was approved for use by the US Food and Drug Administration in 2001, studies about its effectiveness have had mixed findings and there have been no RCTs until the recent VEST (Vest Prevention of Early Sudden Death) trial in 2018, which compared the benefit of WCD with medical therapy in patients who had had a myocardial infarction and ejection fraction ≤35%, and which found no difference in mortality secondary to sudden cardiac death.
The authors therefore “sought to synthesise the available evidence on the use of the WCD” by performing a systematic review and meta-analysis of all published studies that reported on the rate of shocks delivered by a WCD, regardless of indication.
The authors compared the outcomes of 28 studies (27 observational studies and the WCD arm of the VEST RCT) on the use of WCDs. Reviewing data from the studies, Masri et al identified 33,242 patients who had been treated with WCD, with various indications, including ischaemic cardiomyopathy, non-ischaemic cardiomyopathy, implantable cardioverter defibrillator explant and mixed indications.
They found the incidence of appropriate WCD therapy to be 5 per 100 people over 3 months for all indications (95% confidence interval [CI] 3.0 to 6.0, p<0.001), with a high heterogeneity (I2=93%). When focusing only on studies that involved patients with ischaemic cardiomyopathy, they found the incidence of appropriate WCD therapy to be much lower in the VEST trial at only 1 per 100 people over 3 months (95% CI: 1.0 to 2.0) than in the observational studies, which had an incidence of 11 per 100 people over 3 months (95% CI: 11.0 to 20.0; I2=93%).
The incidence of inappropriately treated patients was 2 per 100 people over 3 months (95% CI: 1.0 to 3.0; I2=93%) for all indications. Mortality while wearing WCD was found to be rare, with a pooled incidence of 0.7 per 100 people over 3 months (95% CI: 0.3 to 1.7; I2=94%, p<0.001).
“Our study puts into perspective the overall published evidence evaluating WCD use,” Masri et al write. “Qualitative analysis shows that most studies were not indication-specific, thus diluting our knowledge on the indication-specific utility of WCD and in which patients it should be best used. Selection bias and including mixed indications in observational studies was likely the major determinant of the higher rate of appropriate treatment in patients prescribed a WCD as compared with the WCD arm of the VEST trial.”
The authors describe how the patients who were included in the two studies on which the FDA originally based its approval “do not represent the patients who are currently being prescribed WCD while on optimal medical therapy during the mandated 3 months waiting period before implantable cardioverter-defibrillator consideration.”
“The primary finding of our study is that the available evidence from observational studies is fraught with poor methodology, selection bias, and confounding concerns. The available evidence from the VEST trial shows that the rate of appropriate treatment by WCD was low (1 in 100 persons over 3 months) and that WCD was not associated with a decreased risk of sudden cardiac death,” Masri and colleagues state.
They conclude that “these findings suggest that WCD should not be used in primary prevention until further RCT data support its use,” and “more randomised, indication-specific clinical trials are needed to address the efficacy and cost-effectiveness of WCD and to justify its continued use.”