CHICAGO - Some heart attack patients have electrocardiograms (ECGs) that are normal or non-specific when they first seek treatment at a hospital.  While these patients have a lower risk of death than patients with ECG results indicating a heart attack, the combined rate of death and life-threatening adverse events among patients with normal or non-specific initial ECGs is unexpectedly high, according to an article in the October 24/31 issue of The Journal of the American Medical Association (JAMA).

Robert D. Welch, M.D., of Wayne State University School of Medicine, Detroit, and colleagues analyzed data on hospitalized patients with acute myocardial infarction (AMI, heart attack) who have normal or non-specific ECGs, and those who have ECGs resulting in a diagnosis of heart attack, to determine the predictive value of the initial ECG for in-hospital mortality.  The multi-hospital study included 391,208 patients enrolled in the National Registry of Myocardial Infarction (NRMI) 2 and 3 databases between June 1994 and June 2000.

According to background information cited in the article, previous studies have suggested that normal and non-specific initial ECGs are associated with a favorable prognosis for patients with AMI.  But the mortality rate of patients with proven AMI and a normal initial ECG has not been well described, and may be quite high.  To date, there has been no large multi-hospital study of AMI patients addressing the independent prognostic value of a normal or non-specific initial ECG.

The authors compared in-hospital mortality, and the composite outcome of in-hospital death and life-threatening adverse events for three groups of hospitalized patients with confirmed AMI.  There were 30,759 (7.9 percent) patients with normal ECG results on initial testing, 137,574 (35.1 percent) with non-specific ECGs, and 222,875 (57.0 percent) with ECGs indicating the patient suffered a heart attack. 

"The overall in-hospital mortality rates for the final study population were 5.7 percent with normal, 8.7 percent with non-specific, and 11.5 percent with diagnostic initial ECGs, and the composites of death and serious cardiac event rates were 19.2 percent, 27.5 percent, and 34.9 percent, respectively," the authors report.

The authors adjusted for other predictor variables, including demographics, medical history, diagnostic procedures, and therapy.  They found that a normal initial ECG remained a strong predictor of a lower mortality rate.

"For patients with AMI, a normal initial ECG was associated with a 41 percent lower risk of in-hospital death," the authors write.  Patients with non-specific ECG results had a 30 percent lower risk of in-hospital death, compared with the diagnostic ECG group.

"The unexpected finding of this study was that patients with an initially normal ECG had a substantial mortality rate, one that approximates the 30-day risk for patients with ST-segment elevation [a diagnostic ECG finding] treated in recent trials of reperfusion therapies [using drugs (thrombolysis), balloon angioplasty or surgery]," the authors report.

The authors cite statistics indicating that more than 5.3 million patients sought emergency care for chest pain or related symptoms in 1998.  They suggest their findings have implications for the approximately 2 percent to 4 percent of patients with AMI who are inadvertently discharged from the emergency department.

"The initial ECG is the first and most effective tool used for risk-stratification of patients with symptoms suggestive of AMI," the authors write.  "It is therefore important to understand its prognostic value and to be aware of the actual and absolute risks for those patients with proven AMI."

"Our results underscore the finding that the favorable prognosis of a normal ECG in chest pain patients is not conferred to those with confirmed AMI, though patients with AMI and a normal or non-specific initial ECG are at lower risk for in-hospital death or serious complications than those with diagnostic ECGs," they write. 

"Future work will be needed to define optimal management strategies for patients with AMI who present with initially normal or non-specific ECGs," the authors conclude.

(JAMA.  2001; 286:1977-1984; available post-embargo at jama.com)

Editor's Note:  The National Registry of Myocardial Infarction is supported by Genentech, Inc., South San Francisco, Calif.  Study co-author Robert J. Zalenski, M.D., is a paid consultant to Genentech, Inc. 

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