Effect of premature ventricular beats on manual and automatic repolarization measurements

Abstract

Objective: To compare QT interval and QT dispersion in ventricular ectopic beats with measurements from the preceding and the immediately following sinus beats, and investigate differences between manual and automatic measurements. Patients: Eleven chronic uremic patients. Main outcome measures: ECGs were recorded during hemodialysis treatment and 12-lead sections containing five consecutive beats were extracted, each containing four sinus beats and one centrally-positioned premature ventricular beat. QT measurements were performed both manually and with a computer-automated technique. Results: T wave amplitude was greater in the ectopic beats compared to the sinus beats (0.61 ± 0.18 vs. 0.23 ± 0.06 mV, P <.001). The ectopic beats had a greater QT than the sinus beats when measured manually (415 ± 35 ms vs. 386 ± 28 ms, P <.001), or automatically (375 ± 30 vs. 366 ± 27 ms, P<.01). The sinus beats following the ectopics had a greater QT than the preceding sinus beats (400 ± 27 vs. 386 ± 28 ms, P<.001, manual; 382 ± 24 vs. 366 ± 27 ms, P<.001, automatic). Differences in QT dispersion were seen only between the ectopic and sinus beats (91 ± 31 vs. 58 ± 27 ms, P <.001, manual; 68 ± 33 vs. 49 ± 35 ms, P <.001, automatic). Conclusions: Manual measurement resulted in greater QT values than automatic measurement. Both techniques identified differences between sinus and ectopic beats. The ventricular ectopic beats resulted in an increase in the QT of the immediately following sinus beats. These results confirm the need to interpret QT measurements with care in the presence of ectopic beats.