St. Jude Medical Inc. has launched a large U.S. clinical study with a heart defibrillator that can give doctors and patients warning signals of a possible heart attack.

The company's Fortify device has a mechanism to monitor the ST segment -- or the electrical changes between heartbeats -- which it can transmit to health care professionals. These changes can serve as an early warning to doctors that a patient may be at risk of suffering a heart attack, said Dr. Mark Carlson, St. Jude's chief medical officer.

As the $12 billion market for implantable cardioverter defibrillators (ICDs) slows, medical technology companies have added new features as a way of trying to boost sluggish sales, said Aaron Vaughn, an analyst with Edward Jones.

ICDs are stopwatch-sized devices that shock an errantly beating heart back into rhythm. The biggest players, Medtronic Inc., Boston Scientific Corp. and St. Jude, are either based or have major operations in the Twin Cities.

The Fortify device will be implanted in up to 5,228 patients at 200 hospitals across the country, a large study for med tech. Results will be used to seek Food and Drug Administration (FDA) approval for use in the United States; the Fortify defibrillator is already available in Europe.

It's unclear whether any centers in Minnesota will be included in the study.

Early warning of a heart attack is especially critical because many patients who suffer one never experience symptoms, and more than half of patients experiencing a heart attack die before reaching the hospital, Carlson said.

Two-thirds of patients who have been treated with an ICD experience obstructed blood flow and oxygen to the heart muscle, often a precursor to a heart attack. If the ST segment shifts, the ICD records high-resolution electrograms that can be transmitted over the Internet to doctors.

The first U.S. implant in the St. Jude study occurred at Huntsville Hospital in Alabama. A St. Jude spokeswoman said the study will take "several years," given its large size.

The new features on the Fortify device, along with others marketed by St. Jude's competitors are "incremental improvements," Vaughn said. Medtronic, for instance, recently won FDA approval for a pacemaker that is compatible with MRI scans.

In addition, St. Jude markets the Fortify ICD as one of the smaller ICDs in the industry, meaning the surgery to implant the device is less invasive. The company did not release the cost of the Fortify device, but typically ICDs cost about $30,000.

"The entire ICD market is slowing, if not declining," so companies have to do something to boost sales, Vaughn said.

The ICD market has slowed in the past year following the publication of a study in a major medical journal suggesting the device is overused. In addition, the U.S. Department of Justice has launched an investigation into the way the device is used.

Janet Moore • 612-673-7752