Dive Brief:

• Women have a significantly higher risk of in-hospital adverse events than men after receiving Boston Scientific's Watchman device, according to a registry study of almost 50,000 patients.
• The study, published Aug. 11 in JAMA Cardiology, found women are more likely to suffer major adverse events because of bleeding or pericardial effusion requiring drainage. More women died, too, but the difference was small and deaths were rare in both cohorts.
• Publication of the study comes as Boston Scientific prepares to fend off competition from Abbott Laboratories' rival left atrial appendage occluder, which one analyst forecasts to win around 20% of the market by 2023.

Dive Insight:

Around 70% of participants were male in the PREVAIL and PROTECT AF clinical trials Boston Scientific ran to support FDA approval of Watchman. The gender imbalance in the two clinical trials limited the amount of evidence on the effect of the device in women. The authors of the JAMA Cardiology paper said sex-specific subanalyses are limited, too.

To better understand how women respond to Watchman, the researchers analyzed outcomes from almost 50,000 people in the National Cardiovascular Data Registry LAAO Registry treated with the Boston Scientific device from 2016 to 2019. The analysis uncovered gender differences. 

Women were more likely to experience adverse events, with 6.3% suffering side effects compared to 3.9% of men. The researchers also found a difference in major adverse events, 4.1% versus 2.0%, and adverse events linked to major bleeding or pericardial effusion requiring drainage. More women, 16.0% versus 11.6% of men, spent more than one day in the hospital.

The mortality rate was higher in women, although the authors caution that "death was rare and absolute differences were minimal." The death rate in women was 0.3%, compared to 0.1% in men.

Women were sicker than men in some regards before treatment with Watchman. The female cohort was on average older than the male group and had higher rates of paroxysmal atrial fibrillation, prior stroke and uncontrolled hypertension. However, congestive heart failure, diabetes and coronary artery disease were more common in men.

Having concluded that "women have a significantly higher risk of in-hospital adverse events," the authors called for more research into how to reduce gender-specific risks. The authors particularly want to see more research into potential strategies for reducing the risk of major bleeding and pericardial effusion requiring drainage in women.

Safety and efficacy in women could emerge as a front in the fight for market share between Boston Scientific's Watchman, which has enjoyed a monopoly for several years, and Abbott's recently FDA-approved Amplatzer Amulet. The U.S. introduction of Amulet poses a threat to Watchman, which is tipped to account for almost 10% of Boston Scientific sales by 2023 and is a key growth driver.