Test Quickly Detects Heart Attacks

By William J. Cromie

Gazette Staff

Heartburn kept Charlie Kay awake for most of the night. At least he thought it was heartburn.

He felt dizzy when he got up. And despite gulping antacid pills, the tight pain in his chest wouldn't go away.

"Oh, my god," Charlie said to his wife, "I'm having a heart attack!"

While they drove to the hospital, a dozen thoughts -- none of them good -- revved up Charlie's mind.

He was sweating when he described his chest pains to the emergency-room doctor.

A nurse took some blood from Charlie's arm, and the doctor put seven drops of it onto a small plastic device, about the size of a stick of chewing gum.

In 20 minutes, the doctor was back, with a smile on his face.

"I don't think it's a heart attack Mr. Kay; heartburn is more likely."

It's not a true story, but Medical School researchers have successfully tested such a device on 100 people admitted to Brigham and Women's Hospital (BWH) with chest pain. A few drops of blood in a flat, four-inch-long gadget showed the presence or absence in their blood of a protein released from dying heart muscle.

"This rapid assay is a simple, efficient test that, for the first time, provides physicians with a bedside tool to evaluate patients with chest pain," said Elliott Antman, associate professor of medicine and director of coronary care at BWH. "The device not only reveals if a patient is suffering from heart damage, it also gives an indication of severity. Such information could help physicians caring for frightened and anxious patients, and, possibly, save millions in heart care costs each year."

Quicker, Surer Care

According to the American Heart Association, about 1.5 million Americans suffer heart attacks each year. That's a terrible toll, but it's only a fraction of the number of people who come to emergency rooms with chest pain. As things are now, most of these people are treated as heart attack victims. They go to intensive care units, where it usually takes two hours or more to get the results of laboratory blood tests.

Research to date indicates that the new handheld gauge can accurately determine in 20 minutes if a heart attack is under way. People who test negative can be given less intensive care. If the test is positive, aggressive, life-saving treatment can be started immediately.

Also, Antman points out, "about 5 percent of heart attacks are missed: that means tens of thousands of people who actually had heart attacks are discharged from hospitals without appropriate treatment."

When blood fails to nourish heart muscles because of a blocked coronary artery, muscle cells start to leak specific proteins. The presence of these proteins sounds a warning alarm that part of the heart is dying.

Until recently, cardiologists looked for a substance known as creatine kinase (CK), but this protein also leaks into the blood when other parts of the body are injured. High levels of CK might come from damage to a variety of different internal muscles.

"On the other hand, a minor heart injury might produce no increase in CK," Antman notes.

Researchers recently discovered a better alarm for heart injury, a group of proteins called cardiac-specific troponins. These proteins help heart muscles contract and relax, and when the muscle cells start to die, troponins leak into the blood.

Tests for troponin done in a hospital laboratory still involve a two-hour delay, however. To reduce that wait, Boehringer Mannheim, a German drug company, squeezed the test ingredients into a plastic device small enough to be carried in a shirt pocket. A tiny well holds drops of blood and chemicals (antibodies) that bind tightly to troponin. That binding produces a reddish-purple line that shows that the blood comes from someone having a heart attack. This test can be done at the patient's bedside in 20 minutes or less.

Working with BWH technician Christine Grudzien and pathologist David Sacks, Antman used the device to check the blood of 100 patients with suspected heart attacks. The gadget correctly identified attacks in progress in patients two to eight hours after their chest pain began.

TnT Spells Trouble

The particular protein the researchers used was a variety called troponin T, or TnT. Antman and his colleagues also studied another type, troponin I, as part of a larger study of blood samples from 1,473 suspected heart-attack victims in the U.S. and Canada.

They discovered that the more TnI present the higher the risk a person had of dying or having a second heart attack. Such results indicate that troponin tests not only provide a way of determining who is having a heart attack but how it should be treated.

"Patients with the highest TnI survived better when they underwent aggressive treatment shortly after hospital admission," Antman said. Such treatment included angioplasty, wherein cardiologists thread a small balloon into a heart artery, then open the blocked blood vessels by inflating the balloon.

Recently, the Food and Drug Administration approved troponin tests for quick identification of heart attack victims. The approval covers laboratory and bedside tests for TnT and laboratory tests only for TnI. A handheld TnI gauge is under evaluation in Canada.

The potential benefits have ignited what Antman calls "an explosion of interest by drug companies in both handheld and laboratory tests based on troponins."

BWH is setting up a study of troponin bedside detectors, as are other hospitals. "We're not yet using the handheld device as the sole criteria for quickly evaluating patients with chest pain," Antman cautions. "Further investigation is needed to determine how this tool should be integrated with other tests, and how it might impact the care of patients undergoing heart attacks."