QRS width in right bundle branch block. Accuracy and reproducibility of manual measurement

Background: The QRS prolongation acid its relation to malignant ventricular arrhythmias are topics of interest. Controversies exist about the methodol ogy of measuring the QRS. The aim of this study was to assess the accuracy and reproducibility of manual measurement of the QRS in standard electrocar diograms in patients with right bundle branch block and compare results wit h computer reading. Methods and Results: Five experienced cardiologists at different levels of training were required to measure QRS duration in 30 el ectrocardiograms with different degrees of right bundle branch block collec ted from 24 randomly selected patients who had had radical repairs of tetra logy of Fallot. In each set of electrocardiograms there were six records wh ich had been duplicated. The observers were neither told the purpose of the study nor how the electrocardiograms had been obtained, nor informed that some of the electrocardiograms were duplicates. photocopies were identified by number, covering the patient's name and computerised measurement. Signi ficant differences were found in the measurement of QRS in the same ECG cal culated twice by the same observer (with an absolute variation up to 50 ms) , within different observers (P=0.037) and measured manually or by computer (P=0.019). The width of the QRS did not influence the measurements as the biggest intra-observer variation (50 ms) was observed for relatively wide c omplex (median value between the two measurements 155 ms) and the biggest i nter-observer (60 ms) for narrow complex (median value between the five mea surements 110 ms). The QRS morphology appeared to influence the measurement s, as the intra- and inter-observer variations were more consistent in the presence of obvious notching, slurrings and terminal slow vectors. Conclusi ons: Measurement of QRS is difficult, can be operator dependent and influen ced by the presence of conduction abnormalities which reduce its accuracy a nd reproducibility. (C) 2000 Elsevier Science Ireland Ltd. All rights reser ved.