RESUMO
BACKGROUND: Changes in U-wave amplitude after premature ventricular contractions (PVC) are known as prognostic markers in the long QT syndrome dependent on bradycardia. The purpose of the study was to find correlation between postextrasystolic ST-U segment changes and a history of sustained ventricular tachycardia or ventricular fibrillation (VT/VF). METHODS: The ST-U segment configurations were taken from the 24-hour ambulatory ECG. The comparison of the morphology of these segments was performed between sinus beats preceding PVC's and first postextrasystolic beats. POPULATION: Two groups of patients were evaluated: 1) 32 patients with VT/VF history (VT/VF group), and 2) 36 patients with potentially malignant arrhythmia (structural heart disease with frequent PVCs and/or nonsustained VT- nsVT) (non-VT/VF group). RESULTS: We found T-wave changes in 8 patients (25%) from the VT/VF group and in 12 patients (33.3%) from the nonVT/VF group (P = NS) and U-wave changes in 13 patients (40.6%) and 3 patients (8.3%), respectively (P < 0.05). Other ECG indexes related to PVC's were also considered: RR interval, coupling interval (CI), prematurity index (PI), and postextrasystolic pause (PP). The analysis of these ECG indices revealed, when compared with patients without T-U-wave changes, that the occurrence of U-wave changes was significantly related to longer RR interval of the sinus rhythm preceding PVC: 1025 +/- 211 vs 918 +/- 200 ms (P < 0.05). The prematurity index was lowest in patients with U-wave changes: 0.54 +/- 0.12 vs 0.65 +/- 0.16 (P < 0.01) while postextrasystolic pauses leading to the postextrasystolic U-wave changes were significantly longer: 1383 +/- 223 vs 1130 +/- 247 ms (P < 0.001). CI did not differentiate patients: 556 +/- 108 vs 584 +/- 117 ms (P = NS). CONCLUSIONS: Postextrasystolic changes in ST-U segment configuration are dependent on bradycardia, low prematurity index of the PVC, and the lengthening of the postextrasystolic pause. U-wave changes more frequently appeared in patients with malignant arrhythmias. Follow-up study is needed to assess if they might be predictive for the occurrence or reoccurrence of arrhythmic episodes.