News Release

Certain Heart Attack Patients Are Under-Treated

Peer-Reviewed Publication

University of California - San Francisco

The most common test for heart attacks, the electrocardiogram, is highly inaccurate for patients with a condition known as left bundle-branch block (LBBB), according to the results of a new study by researchers at the San Francisco Veterans Affairs Medical Center and the University of California San Francisco. Because of the electro-cardiogram's inability to diagnose LBBB patients, they are consistently under-treated say the researchers.

Approximately 100,000 Americans with LBBB experience myocardial infarction (heart attacks) every year. Patients with LBBB account for six percent of all myocardial infarction (MI) victims in the US. Results of the study are published in today's (February 24) issue of the Journal of the American Medical Society (JAMA).

For years physicians have considered the electrocardiogram (ECG) to be the gold standard for diagnosing myocardial infarction. The ECG measures heart function by calculating how tiny amounts of electricity travel through the muscles of the heart. However for LBBB patients, ECG results can be fatally misleading.

Left bundle-branch block occurs when a small area of damaged heart tissue doesn't allow an electrical current to pass through in a normal manner. Because of this anomaly, LBBB patients will always have abnormal ECG readings. These skewed results make it extremely difficult, if not impossible, to accurately diagnose a heart attack.

Several years ago a group of physicians in the US developed a mathematical formula or algorithm based on the ECG to determine whether a patient with LBBB and symptoms of a heart attack was actually experiencing an MI. The numerical results of the ECG are plugged into the algorithm and a simple computation is done. The 'answer' to the math problem is supposed to indicate whether the patient is really experiencing a heart attack.

In February 1996, the authors of the study, led by Dr. E.B. Sgarbossa, published their findings supporting the use of this ECG algorithm in the New England Journal of Medicine. The study found the test to have a 73 percent detection rate for MIs in LBBB patients, with a ten percent occurrence of false positive results. The ECG algorithm was quickly adopted by many physicians across the country.

Suspicious of the test's accuracy, the SFVAMC-UCSF investigators reviewed the records of 83 LBBB patients with suspected MIs who were treated at UCSF Medical Center between 1994 and 1997. Their results indicated that the ECG algorithm had a detection rate of only ten percent -- far worse than the findings published in 1996.

"We suspect there are several reasons for the discrepancies between the findings," says Michael Shlipak, MD, MPH, SFVAMC general medicine physician and UCSF clinical research fellow. "Because the LBBB patients in the earlier study were enrolled in a research trial, they are different from the typical patients who come to the ER with severe chest pain. Also, the control patients in that study (healthy outpatients), may not have been an appropriate group for comparison because they had no symptoms of MI."

Once the investigators determined the ECG algorithm was inaccurate, they set out to develop an optimal treatment plan with a "decision tree" or blueprint for physicians to follow when treating LBBB patients.

A standard treatment for heart attacks is called thrombolytic therapy, where a drug to thin the blood is administered. Thrombolysis is used to dissolve the blood clot that caused the MI and thereby reduce the patient's risk of death. However, thrombolysis can be dangerous if a patient is not actually experiencing MI. Because of the difficulty in correctly identifying heart attacks in LBBB patients, many physicians do not use thrombolytic therapy. In fact, only five percent of these patients are given the therapy, yet they have the highest mortality rate among MI patients.

The refusal to use thrombolysis is a mistake according to Shlipak. "We have shown that providing thrombolysis to LBBB patients with suspected heart attack will lead to greater survival for this high-risk group," says Shlipak. "The inevitable risk of treating patients who are not suffering a heart attack is far outweighed by the benefits to LBBB patients who do have MI."

Co-investigators on the study were William L. Lyons, MD, SFVAMC general medicine physician; Alan S. Go, MD; Tony M. Chou, MD, UCSF assistant professor of medicine; G. Thomas Evans, MD, UCSF associate clinical professor of medicine and director of electrocardiography at UCSF Medical Center, part of UCSF Stanford Health Care; and Warren S. Browner, MD, MPH, SFVAMC chief of general internal medicine and UCSF professor of medicine and anesthesia. Go is now physician research scientist with Kaiser Permanente Medical Care Program. ###

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