Use of a phase-locked loop to correct heart rate variability artifacts in data from human cardiac transplant recipients

Although human cardiac transplant recipients exhibit very low levels of heart-rate variability, the study of this variability may be clinically applicable in detecting graft rejection. However, when Holter recorders are used to gather ECG data, tape speed variations during recording or playback may introduce heart-rate artifacts. The authors show that these artifacts are significant (relative to the level of heart-rate variability observed in transplant patients) and that the use of a phase-locked loop during data sampling eliminates them. Without the phase-locked loop, the artifactural heat-rate standard deviation for tape speed fluctuations on the order of 1% is 0.58 BPM², whereas with the phase-locked loop this figure is reduced by 95% to 0.029 BPM²