QT dispersion and early arrhythmic risk during acute myocardial infarction.

It has been suggested that QT dispersion (maximal minus minimal QT interval calculated on a standard 12-lead electrocardiogram) could reflect regional variations of ventricular repolarization and could provide a substrate for reentry ventricular arrhythmias. The present study evaluates QT dispersion in patients with acute myocardial infarction, assessing its relation with early severe ventricular arrhythmias and some clinical features. Three hundred three patients with acute myocardial infarction and a control group of 297 healthy subjects were studied. QT and QTc dispersion were determined on the electrocardiogram taken after 12 hours and on days 3 and 10 after symptoms onset and on the electrocardiogram taken in the control group. The average values of QT and QTc dispersions (ms) were as follows: 70.5 +/- 42.5-87 +/- 45.6 (12th hour), 66.7 +/- 37.6-76.8 +/- 43.6 (day 3), 68.8 +/- 42.7-76.8 +/- 42.8 (day 10), versus 43 +/- 13.2-53.9 +/- 16.2 (control group). There were statistically significant differences between QT and QTc dispersion recorded in normal subjects and in each of the three electrocardiograms taken in patients with infarction. A greater QT dispersion was recorded in patients with anterior infarction (78.9 +/- 38.5 vs 64.9 +/- 42.8 in inferior/lateral infarction). In the first 3 days QT dispersion was not different in patients treated and untreated with thrombolysis, whereas on day 10 it was greater in untreated patients (74.9 +/- 45.3 vs 60.5 +/- 37.2). Creatine kinase peak level did not influence QT dispersion. In the first 72 hours of infarction, 37 patients developed ventricular fibrillation or sustained ventricular tachycardia. Higher early values of QT and QTc dispersion were found in patients who developed severe ventricular arrhythmias (107.8 +/- 62 and 124.8 +/- 67.5 ms) than in patients without serious arrhythmias (62.9 +/- 32.2 and 80.1 +/- 37.9 ms). These data suggest that: (1) QT dispersion increased during acute myocardial infarction. (2) The values were higher in the early hours and fell late after infarction with thrombolysis. (3) Greater QT dispersion is associated with severe ventricular arrhythmias.

[Correlations between the efficacy of thrombolytic therapy and appearance of abnormal Q waves in the early stages of acute myocardial infarction]. / Correlazione tra efficacia della terapia trombolitica e comparsa di onde Q patologiche nella fase precoce dell'infarto miocardico acuto.

BACKGROUND: The purpose of this study was to determine the time course of the appearance of abnormal Q waves on the electrocardiogram (ECG) over the first 6 hrs of the symptoms of acute myocardial infarction (AMI) and to determine what implications, if any, such Q waves have for the efficacy of thrombolytic therapy. Severe myocardial ischemia can produce early QRS changes in the absence of infarction. Abnormal Q waves on the baseline ECG may not be an accurate marker or irreversibly injured myocardium. METHODS: A study of 232 patients with AMI consecutively admitted to our coronary care units was carried out. Patients with previous AMI were not included. The presence and number of abnormal Q waves, as defined by Selvester, on the initial ECG was determined for each patient. The presence or absence and magnitude of ST segment elevation and depression were recorded and these data were used to estimate the left ventricular infarct size should thrombolytic therapy not be given (Aldrich score). Quantitative thallium-201 tomographic imaging was performed after a mean of 42 +/- 40 days from hospital discharge in 145 patients. RESULTS: In patients admitted within 1 hr of symptoms, 53% had abnormal Q waves on the initial ECG independent of the duration of symptoms before therapy (p < 0.001). Despite this finding, the presence of abnormal Q waves on the admission ECG did not eliminate the effect of thrombolytic therapy on reducing final infarct size (p < 0.001). CONCLUSIONS: Abnormal Q waves are a common finding early in the course of AMI. However, there is no evidence that abnormal Q waves are associated with less benefit in terms of reduction of infarct size after thrombolytic therapy.