Beat-to-beat QRS amplitude variability after acute myocardial infarction and coronary artery bypass grafting

Ischemic myocardial injury has been demonstrated to be associated with increased beat-to-beat electrical variability of the depolarization phase. This can be quantified by electrocardiographic (ECG) signal variance analysis, a technique that has proven its diagnostic value in the detection of coronary artery disease (CAD). This study evaluates QRS amplitude variability during a 6-month follow-up period in 73 patients with acute myocardial infarction (AMI) and in 56 patients subjected to coronary artery bypass grafting (CABG). The beat-to-beat QRS amplitude variability was quantified with variance electrocardiography. The equipment allows computerized time domain analysis of high-fidelity ECG signals from 24 leads, and the detected electrical heterogeneity is then expressed as a nondimensional index ranging from 0 to 150, with values > 90 being indicative of ischemic myocardial involvement. One week after AMI 55% of the patients presented with an abnormal QRS variability index > 90. A significant (p < 0.01) increase in the index values occurred during the followup period, but only in the patients with an initial index < 70. In the CABG group 44% of the patients had a preoperative QRS variability index > 90. The values increased (p < 0.05) in all patients after surgery; the increase was transient in patients with an initial index < 70 (p < 0.01). The results demonstrate that the myocardial injury in patients with CAD is often associated with increased electrical variability of myocardial depolarization. The QRS amplitude variability index can be used as a marker of such an injury, and analysis of its changes in the course of ischemic cardiac events may provide new insights into the dynamics of ischemic heart disease and the myocardial healing process.