Shares of Abiomed (ABMD) - Get Report sprang a leak Monday after a pair of studies raised questions about the effectiveness of the medical device maker's Impella heart pump.

Abiomed's stock price plunged in the wake of new research unveiled at an American Heart Association meeting in Philadelphia on Sunday showed a higher risk of "adverse events and costs" associated with the use of the Impella compared to the lower-tech, intra-aortic balloon often used.

The studies found 45% of patients died when Impella was used to keep the blood flowing, compared with 34% who died when an intra-aortic balloon was used.

The Impella heart pump, at $15,000, is also expensive to use, the researchers said.

More than twice as many patients undergoing cardiogenic shock had major bleeding compared with those who were treated with the balloon, or 34% to 16%.

"The associated clinical outcomes did not show any substantial improvement, while costs of hospitalization rose," said Dr. Amit Amin, the lead researcher on one of the two studies and an assistant professor at the Washington University School of Medicine in St. Louis, as reported by HealthDay.

Executives at Abiomed have argued Impella's safety has been vetted over the course of many studies, with the company pointing to another study that the company contends shows a nearly 30% drop in serious heart complications compared to the use of the balloon.

The stock declined 10.89% to $198.93 in trading Monday.