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Ahead of the Bell: Thoratec slumps on study

NEW YORK (AP) -- Shares of Thoratec fell 11 percent in premarket trading Friday after a study found that the rate of blood clots in patients implanted with its HeartMate II pump is increasing.

A study by the Cleveland Clinic found that starting on March 1, 2011, 8.4 percent of patients who received a HeartMate II pump suffered a blood clot within three months of implantation. Before that date, 2.2 percent of patients experienced a blood clot within the first three months. Results from the study were taken from three medical centers, and the data were published Wednesday in the New England Journal of Medicine.

Thoratec Corp. did not immediately respond to a request for comment.

HeartMate pumps are used in patients who are waiting for a heart transplant or in those too sick for heart transplant surgery. In 2013 about 90 percent of Thoratec's revenue has come from sales of HeartMate products.

The company's shares lost $4.62 to $37.50 in premarket trading after closing at $42.12 on Wednesday.