Catecholamine levels and pacing behavior of QT-driven pacemakers during exercise.

It is thought that increasing catecholamine levels in the heart are partly responsible for shortening of the repolarization time and so indirectly for the pacing behavior of the QT driven pacemaker. Adrenaline and noradrenaline (NA) plasma levels were determined at rest, during symptom-limited exercise, and during recovery more than 1 month after the implantation of a 919 or a Rhythmyx pacemaker (Vitatron, The Netherlands) in eight patients (age 54-85 yrs). Significant increases were detected in NA level (from 0.57 +/- 0.23 ng/mL to 2.15 +/- 0.76 ng/mL), but not in the circulating adrenaline level. The correlation coefficient of the mean pacing rate and the mean NA level during exercise and recovery was 0.963 (P less than 0.0001), the correlation coefficient with the mean oxygen consumption was 0.888 (P less than 0.01). No correlation with the adrenaline level was observed. The correlation coefficient of the changes of pacing rate and the changes of NA level during exercise and recovery was 0.882 (P less than 0.005). The pacing rate of the new generation of QT driven pacemakers is closely correlated with the noradrenaline spillover in the plasma, not with the adrenaline level. A short delay (less than 1 minute) is observed in the adaptation.