Late potentials and computerized averaging electrocardiogram in acute myocardial infarct: evaluation of myocardial reperfusion

Myocardial reperfusion after thrombolytic therapy in acute myocardial infarction can be directly demonstrated with coronary angiography or it can be assessed thanks to indirect markers of reperfusion, such as modifications in the "averaged" QRS complex. We assessed the presence of late potentials in 37 patients within 5 hours of acute myocardial infarction onset and evaluated their disappearance or modification after reperfusion. Signal-averaged electrocardiogram, obtained computerizing QRS complexes filtered through Simson's bidirectional filter (25-250 Hz), was serially recorded in each patient: at admission, as well as 12 hours, 3 and 10 days following urokinase and/or heparin therapy. Other indirect markers of reperfusion (incidence of ventricular arrhythmias, serum CK-MB level, ST elevation) were contemporaneously evaluated. All patients underwent coronary angiography between 6 and 83 days after acute myocardial infarction. Late potentials (Total QRS greater than 115 ms; Under 40 microV greater than 39 ms; RMS Last 40 ms less than 25 microV) were present only in 25% of patients, and they always disappeared after successful thrombolysis. On the contrary if ischemia-related vessel occlusion persisted, late potentials persisted as well or else were first recorded on the 3rd or 10th day following acute myocardial infarction. Quantitative analysis of the "averaged" QRS complex showed a statistically significant reduction in QRS duration (-9.1 +/- 12.7 ms) 3 days after acute myocardial infarction in reperfused patients (group A, n = 24), while no significant reduction in the total QRS (-1 +/- 6.7 ms) was observed in non-reperfused cases (group B, n = 13), (p less than 0.05 group A vs group B). So, 10 ms reduction in total QRS duration was a good marker of reperfusion, with specificity = 92% and sensitivity = 54%; marker sensitivity was even higher (= 79%) when coupled with serum CK-MB peak within 12 hours of therapy (diagnostic accuracy = 84%). In conclusion, even if late potentials have a low prevalence in acute myocardial infarction (25%) their disappearance correlates with myocardial reperfusion. Furthermore, a reduction in total QRS duration greater than or equal to 10 ms can itself be a good marker of successful thrombolysis.