Differences in QT interval determined from multi-lead ambulatory ECG during rest and physical exercise

BackgroundMulti-lead ambulatory ECG recording offers recognised advantages for ventricular depolarisation–repolarisation (QT) interval analysis, especially during physical exercise. However, data are usually reported for a single lead and do not quantify between-lead variability, leading to possible misinterpretation. The aim of this study was to quantify between-lead agreement for QT recorded during rest and exercise.MethodNine males and eight females of similar age and aerobic fitness undertook progressive sub-maximal bicycle exercise. A three-lead ECG was recorded continuously during pre-exercise, exercise and recovery. Beat-to-beat cardiac cycle (RR) and QT data were measured for each sinus beat. Bland–Altman analysis was used to quantify between-lead agreement for RR and QT intervals, and the influence of gender was assessed.ResultsMean between-lead bias was significantly (p < 10−6) greater for QT compared with RR, and in males the limits of agreement (LOA) for QT was significantly (p < 10−6) greater than for RR. Relative to mean parameter values the between-lead LOA for RR was low, with maximal values (% of mean) of 0.1% (male) and 0.3% (female). Paired-lead bias for RR was also relatively low (5.0% and 6.7%), but paired-lead bias for QT (8.3% and 6.9%) and paired-lead LOA for QT (13.1% and 12.8%) were notably larger.ConclusionThe RR interval can be measured with equivalent accuracy and reliability from any ECG lead that demonstrate good signal quality. However, the between-lead bias and LOA for QT interval data should be quantified when reporting results from a multi-lead ambulatory ECG. Interpretation of the results of such studies should take account of between-lead and between-gender QT differences, and should note the physiological conditions during recording.