Automated QT interval measurement in Holter ECGs recorded at 180 and 1000 samples/second

To study the effect of sampling rate on automated QT measurements, Holter ECGs were recorded at 180 and 1000 samples/second (s/s) using 2 recorders; 30 ECG snapshots were extracted at varying heart rates from 16 healthy subjects and re-sampled to 180, 500 or 1000s/s using the Antares software. QT interval by CalECG algorithm was longer (5.0±6.3 ms, p<;0.001) in 180s/s ECGs than in 1000s/s ECGs. It decreased to 2.1±5.8ms when 180s/s ECGs were re-sampled to 500s/s, and to 2.6±6.2ms at 1000s/s. It also decreased progressively on resampling both sets of ECGs to 1000s/s (2.6±6.2ms), 500s/s (1.8±5.5ms) and 180s/s (0.4±5.9ms). Differences in QT interval were independent of the QT measurement algorithm used: University of Glasgow (Uni-G) program and CalECG for 500s/s ECGs; Veritas and CalECG for 1000s/s ECGs. Thus, QT interval is longer in ECGs with lower sampling rates; resampling them to a higher resolution partially compensates for this.