New Test Speeds Diagnosis of Heart Attack
An inexpensive new blood test developed by Texas researchers could improve the treatment of heart attacks and save as much as $4 billion in medical costs each year by quickly identifying which patients who show up at emergency rooms with symptoms are actually having an attack.
The test, which is already available to hospitals, could speed the treatment of heart attack patients and reduce the use of potentially hazardous clot-busting drugs on patients who have symptoms but turn out not to be having an attack.
Now, only 10% of the 5 million patients who enter U.S. emergency rooms each year with symptoms are having a heart attack. Nonetheless, a majority of them are admitted to expensive intensive care units as a safety measure. Determining whether they are having an attack can require 12 to 24 hours, by which time the damage from the attack is complete.
In contrast, the new test, developed at Baylor College of Medicine, can identify actual victims in less than two hours, leaving time to minimize permanent damage to heart tissues, the team reports today in the New England Journal of Medicine.
“Had this test been used as a screening test, we could have reduced our coronary care admission rate by 70%,” said Dr. Peter R. Puleo, a Baylor cardiologist.
“If this turns out to be as good as they say it is, it will give an enormous economic and patientcare benefit,” said Dr. Pravin Shah of Loma Linda Medical Center, a member of the American Heart Assn.’s Council on Clinical Cardiology. “At the present time, emergency room physicians tend to play it extra safe, largely for medico-legal reasons.”
The new test meshes well with the current debate about minimizing health care costs, said Dr. George Sopko, a cardiologist at the National Heart, Lung and Blood Institute. “With the test, one can eliminate quite a few unnecessary hospitalizations, and therefore reduce the cost, as well as using existing health care facilities more appropriately.
“What I like about the test is that it can be used in just about every hospital . . . it’s fairly simple, it can be done fast and it should be helpful for physicians.”
Heart attack is the single largest killer of both men and women in the United States. Every year, about 1.5 million Americans have a heart attack--more correctly called myocardial infarction--and an estimated 481,000 die of it. Fully 250,000 of those die before reaching a hospital--in large part because half of all heart attack victims wait more than two hours before seeking help.
Television and movies tell us that physicians diagnose a heart attack by hooking up an electrocardiogram, or EKG, which measures electrical activity in the heart. That can be true, but only part of the time. About half of all heart attack victims display a peculiar wiggle, called a Q wave, in their EKG that is unique to heart attack victims.
In other heart attack cases, the EKG reveals little. In that case, physicians must rely on a detailed clinical history and blood tests. The most useful test looks for the presence of an enzyme called CK-MB that leaks into blood from damaged heart tissues. Existing tests for CK-MB take five to six hours and are about 50% accurate in diagnosing heart attacks.
Because of this lag in diagnosis, many patients with chest pain are admitted to intensive care by physicians practicing what Loma Linda’s Shah calls “defensive medicine.” No more than 30% of those admitted are having heart attacks. Studies have shown that the cost of this excess hospitalization is about $4 billion a year.
Dr. Robert Roberts and his colleagues at Baylor have developed a new, 25-minute test that can detect an unusual form of CK-MB produced in heart attacks at the extremely low concentrations present shortly after an attack. The test is manufactured by Helena Laboratories Inc. of Beaumont, Tex., and has been approved by the Food and Drug Administration for monitoring the progress of heart attack victims.
Roberts, Puleo and their colleagues studied 1,110 patients who came to the emergency room of Ben Taub General Hospital in Houston with heart symptoms, testing blood for CK-MB every 30 to 60 minutes for at least six hours. They found that it was 93.9% accurate in identifying those patients who had heart attacks, compared to only 48% for the conventional CK-MB test. It was 96.2% accurate in identifying those who did not have a heart attack.
“Until now,” Roberts said, “we had no great reason to make a diagnosis in two to four hours because we didn’t have treatments. Now we know that time is muscle and we have clot-busters to save (heart) muscle, so we have a greater impetus for early diagnosis. This allows us to do it.”
