QT dispersion (QTd, equals maximal minus minimal QT interval) on a standard ECG has been shown to reflect regional variations in ventricular repolarization and is significantly greater in patients with than in those without arrhythmic events.Methods and ResultsTo assess the effect of thrombolytic therapy on QTd, we studied 244 patients (196 men; mean age, 57±10 years) with acute myocardial infarction (AMI) who were treated with streptokinase (n= 115) or anistreplase (n=129) at an average of 2.6 hours after symptom onset. Angiograms at 2.4±1 hours after thrombolytic therapy showed reperfusion (TIMI grade ≥ 2) in 75% of patients. QT was measured in 10±2 leads at 9±5 days after AMI by using a computerized analysis program interfaced with a digitizer. QTd, QRSd, JT (QT minus QRS), and JT dispersion (JTd, equals maximal minus minimal JT interval) were calculated with a computer. There were significant differences in QTd(96±31, 88±25, 60±22, and 52±19 milliseconds;P< .0001) and in JTd(97±32, 88±31, 63±23, and 58±21 milliseconds;P= .0001) but not in QRSd(25±10, 22±7, 28±9, and 24±9 milliseconds;P= .24) among perfusion grades 0, 1, 2, and 3, respectively. Similar results were obtained comparing TIMI grades 0/1 with 2/3 and 0/1/2 with 3. Patients with left anterior descending (versus right and left circumflex) coronary artery occlusion showed significantly greater QTd(70±29 versus 59±27 milliseconds,P= .003) and JTd(74±30 versus 63±27 milliseconds,P= .004). Similarly, patients with anterior (versus inferior/lateral) AMI showed significantly greater QTd(69±30 versus 59±27 milliseconds,P= .006) and JTd(73±30 versus 63±27 milliseconds,P= .007). Results did not change when Bazett's QTc, or JTc, was substituted for QT or JT or when ANOVA included adjustments for age, sex, drug assignment, infarct site, infarct vessel, and number of measurable leads. On ANCOVA, the relation of QTdor JTdand perfusion grade was not influenced by heart rate.ConclusionsSuccessful thrombolysis is associated with less QTdand JTdin post-AMI patients. The results are equally significant when either QT or JT is used for analysis. These data support the hypothesis that QTdafter AMI depends on reperfusion status as well as infarct site and size. Reduction in QTdand its corresponding risk of ventricular arrhythmia may be mechanisms of benefit of thrombolytic therapy.