By Susan Kelly

CHICAGO (Reuters) - Two studies on implanted cardiac rhythm devices presented at a major medical meeting showed mixed results for patients whose heart conditions are not normally treated with the products, researchers said.

Companies such as Medtronic Inc and Boston Scientific Corp that make the devices are studying whether the products can help more patients with different forms of heart disease live longer in hopes of expanding the market.

In one study, defibrillators implanted soon after a heart attack reduced patients' risk of sudden cardiac death due to an abnormal heart rhythm, but non-sudden deaths rose.

The clinical trial, called Iris, compared outcomes for patients who received an implantable cardioverter defibrillator, or ICD, within a month of a heart attack to patients treated with standard medical therapy alone.

There were fewer sudden cardiac deaths in patients who got an ICD in the days following a heart attack, but that was counterbalanced by an increase in non-sudden cardiac deaths, according to authors of the study, which was presented on Tuesday at the American College of Cardiology meeting in Orlando, Florida.

"Based on these findings, routine ICD implantation after (a heart attack) cannot be recommended at this time," study author Dr. Adnan Chhatriwalla of the Cleveland Clinic said in a summary of the trial.

ICDs, which are used to shock a racing heart back to its normal rhythm, are not approved for implantation in patients who have just suffered a heart attack.

Patients who received an ICD in the Iris study were at high risk for sudden cardiac death, which can result from the onset of an abnormal heart rhythm. But the results for about 900 patients treated in European hospitals found no difference in the primary endpoint of all-cause mortality between groups at three years.

"During the first month after myocardial infarction, in an optimally treated high-risk patient population, ICD implantation does not offer a survival benefit," Dr. Gerhard Steinbeck, a paid adviser to Medtronic, said in a slide presentation on the study.

A significant percentage of people who survive a heart attack will ultimately die from a dangerous heart rhythm originating in the lower chambers of the heart, Medtronic said. About 15 percent will die in the first weeks, and an additional 10 percent during the first year.

HEART FAILURE HELPED IN REVERSE STUDY

In a second study presented at the meeting called Reverse, two-year data from a European arm of the trial showed patients with mild heart failure who received cardiac resynchronization therapy combined with drug therapy saw their disease worsen less than those on medicine alone.

CRT devices, which synchronize the heart's contractions, are typically implanted in patients diagnosed with severe heart failure, where the heart cannot pump enough blood through the body.

The Reverse trial, also sponsored by Medtronic, missed its primary endpoint on a measure of disease progression in one-year data presented at the ACC meeting last year.

Leerink Swann analyst Rick Wise, in a note to clients on Monday, said positive trends on secondary goals in the Reverse study alone won't alter the market but may set the stage for a larger study under way called MADIT-CRT that, if successful, could drive greater use of the higher-priced CRT-D devices.

Boston Scientific is sponsoring the MADIT-CRT trial.

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