Effect of ventricular ectopic beats on ventricular repolarisation measurements

The influence of premature ventricular ectopic beats on ventricular repolarisation measurements in patients undergoing chronic haemodialysis was investigated. The ECGs from five patients were recorded during kidney dialysis treatment. Recordings were made on a 12-lead Mortara H-12 recorder and transferred to a personal computer for analysis. 12-lead sections containing five consecutive beats were extracted at intervals of approximately 20 minutes, providing 13 rhythm sections from each recording. All sections contained four sinus beats and one centrally-positioned premature ventricular beat. The QT interval was measured manually using an interactive computer display. The end of the QT interval was defined as the point at which the T-wave returned to the TP baseline, and it was assessed separately for each beat. The aim of the study was to investigate changes in ventricular repolarisation due to ventricular ectopic beats and dialysis therapy. It was not possible to measure the QT interval in all ECGs because of noise or low-amplitude T-waves, but measurements were available from 82.1%. The QT interval did not change significantly over the time course of the treatment. In all five patient recordings, the ectopic beats had a significantly greater QT interval (mean±SD = 416±38 ms) than the initial sinus beat (371±20 ms, p<0.05) in all patients. In three recordings, the sinus beat after the ectopic beat also had an elevated QT interval compared with the initial sinus beat. The final sinus beat had returned to the initial QT in all patients. These results indicate that the presence of ectopic beats needs to be considered when presenting repolarisation measurements