Multi-beat averaging reveals u waves are ubiquitous and standing tall at elevated heart rates following exercise

The reporting of U wave abnormalities is clinically important, but the measurement of this small electrocardiographic (ECG) feature is extremely difficult, especially in challenging recording conditions, such as stress exercise, due to contaminating noise. Furthermore, it is widely stated that ECG U waves are rarely observable at heart rates greater than 90 bpm. The aims of the study were (i) to assess the ability of multi-beat averaging to reveal the presence of U waves in ECGs contaminated by noise following exercise and (ii) to quantify the effect of exercise on U wave amplitude. The multi-beat averaging algorithm was applied to recover U waves in 20 healthy subjects in pre- and post-exercise recordings. Average beats were generated from 30 beat epochs. The prevalence of U waves and their amplitudes were measured in pre- and post-exercise recordings and changes in amplitude due to exercise were quantified. U waves were present in all subjects in pre-exercise recordings. Following exercise, U waves could not be seen in standard ECG but were observable in all 20 subjects by multi-beat averaging and despite significantly increased mean (±SD) heart rate (63 ± 8 bpm vs. 100 ± 9 bpm, p < 0.0001). Furthermore, U waves were observable in all subjects with heart rates greater than 90 bpm. U waves significantly increased in amplitude following exercise (38 ± 15 μV vs. 80 ± 48 μV, p = 0.0005). Multi-beat averaging is effective at recovering U waves contaminated by noise due to exercise. U waves were measurable in all subjects, dispelling the myth that U waves are rarely seen at elevated heart rates. U waves exhibit increased amplitudes at elevated heart rates following exercise

The effect of beat interval on ventricular repolarisation in atrial fibrillation

© 2018 Creative Commons Attribution. Atrial fibrillation (AF) is characterised by rapid beat interval changes. The aim of the study was to investigate the effect of such changes on ECG ventricular repolarisation characteristics. In 10 AF recordings beat averaging of lead V4 was used to generate averaged T waves where the preceding beat interval (R-R) was either short (625+/-25 ms) or long (1075+/-25 ms). The amplitudes of T wave (T amp) and T wave end, defined as the TU nadir, (TUn amp), and the intervals for R wave to T wave peak (R-T) and R wave to T wave end (R-TUn) where measured from these average beats. Difference in measured T wave characteristics between short and long beat intervals were quantified. All measurements increased significantly for long preceding beat intervals compared to short: T amp (mean±SD) 0.31±0.17 mV (short) vs 0.35±0.20 mV (long) (p = 0.04); TUn amp 0.00±0.02 mV (short) vs 0.03±0.03 mV (long) (p = 0.009); R-T 251.7±13.5 ms (short) vs 264.2±12 ms (long) (p = 0.002) and R-TUn 376.5±31 ms (short) vs 392±26.5 ms (long) (p=0.027). ECG T wave characteristics are significantly affected by preceding ventricular beat interval in AF