Updated from 8:54 a.m. EDT

Possis Medical

(POSS)

lost a huge chunk of market value Tuesday after a catheter it sells as a treatment for blood clots in coronary arteries failed to show clinical superiority in heart attack patients.

Shares were recently down $11.76, or 38%, to $19. The company lowered its 2005 earnings and revenue guidance and saw its shares lowered to neutral from buy at First Albany after the results were publicized.

Possis was conducting a post-marketing study on its AngioJet XMI catheter, which has already been cleared by the FDA for treating blood clots in coronary arteries and leg veins. In the heart study, Possis measured the device's effectiveness by looking at the amount of traumatized heart tissue, which is known as "infarct," one month after a heart attack.

Among patients studied, 197 who got the AngioJet had a mean final infarct size of 12.5%, while 205 patients in the control arm had a mean final infarct size of 9.8%. Secondary endpoints like improved blood flow and avoidance of procedural complications saw no statistically significant difference.

"While the study showed that the AngioJet was safe to use in heart attack patients and effectively removes angiographically visible thrombus, the AiMI study, based on a nuclear endpoint, did not provide a basis for concluding that the AngioJet device should be routinely used for all heart attack patients to reduce final infarct size," the company said in a release.

As a result of the failure, the company dropped its guidance for the year that began Aug. 1 to earnings of 70 cents to 82 cents a share on revenue of $85 million to $90 million, down from its old estimate of earnings of 83 cents to 96 cents a share on revenue of $92 million to $98 million.