Evaluation of three-dimensional acceleration signals for rate adaptation in cardiac pacemakers

The aim of this study was to determine which of the one-dimensional acceler ation signals best correlates with the heart rate under the conditions of d aily activities, or whether such correlation is shown by three-dimensional acceleration signals. A commercially available biosignal system (ZAK, Germa ny) was used to record electrographic data and acceleration caused by body movements in the three directions vertical, sagittal and lateral. The evalu ation was performed on 12 young healthy volunteers and 4 elderly volunteers with cardiovascular disorders but adequate chronotropic function. Informed consent was given by all participants. Activity signals and heart rate wer e recorded while walking under two different conditions. For analysis, the pathways were divided into segments with different gradients. All the accel eration signals were analysed statistically and temporally with regard to p eak-to-peak value, root mean square value, and step frequency by means of c ross correlation. Both statistical and temporal analysis showed that the co rrelation of heart rate and all one-dimensional acceleration signals and th e three-dimensional acceleration signal was relatively low (r less than or equal to 0.6). Walking uphill even showed a negative correlation between ac celeration signals and heart rate. Despite the widespread use of activity-c ontrolled pacemakers, the correlation between heart rate and acceleration s ignals is not satisfactory.