Beat-to-beat morphologic variability of the electrocardiogram for the evaluation of chest pain in the emergency room.

The value of electrocardiographic, morphologic variability in the early diagnosis of acute myocardial infarction (AMI) and myocardial ischemia was evaluated in 49 nonselected patients presenting to the emergency room with chest pain. High-resolution electrocardiography was used to determine the morphologic variability of consecutive electrocardiographic complexes, and the ratio of the variance of the QRS onset to that of the entire electrocardiogram was calculated. A final diagnosis of AMI was confirmed in 8 patients, acute coronary insufficiency in 8, angina pectoris in 19, and a noncardiac origin for chest pain in 14. Patients with AMI had a significantly higher beat-to-beat electrocardiographic morphologic variability of the QRS onset (1.4 +/- 0.2) than did those with acute coronary insufficiency (1.1 +/- 0.2), angina pectoris (0.9 +/- 0.1) or noncardiac chest pain (0.8 +/- 0.1) (p < 0.05). The sensitivity of the clinical presentation, typical electrocardiographic changes and creatine phosphokinase levels for the diagnosis of an acute ischemic event on admission to the emergency room was 62, 25 and 37.5%, respectively. Relative variance of the QRS onset of > 0.86 had a sensitivity of 75% and a specificity of 61% for diagnosing an acute ischemic event. Logistic regression of these variables showed that the QRS onset relative variability is an independent predictor for an acute ischemic event. It is concluded that an increased beat-to-beat electrocardiographic variability in patients with AMI is present on admission to the emergency room and may assist in establishing the diagnosis in this setting.