Effects of mental and physical stress on central haemodynamics and cardiac sympathetic nerve activity during QT interval-sensing rate-responsive and fixed rate ventricular inhibited pacing.

The effects of mental stress and dynamic exercise on central haemodynamic variables and cardiac sympathetic nerve activity were studied in 15 patients during both fixed rate ventricular-inhibited (VVI) and QT interval-sensing rate-responsive (TX) pacing. Haemodynamic measurements were made at rest, during a mental stress test and during supine exercise at 30 W. Cardiac sympathetic nerve activity was assessed by measuring the arterial and coronary sinus plasma concentrations of noradrenaline (NA) and adrenaline (ADR), the NA kinetics in arterial plasma (radiotracer infusion) and the overflow of NA into the coronary sinus. During exercise the paced ventricular rate increased by 47% with TX. TX provided a higher cardiac output than VVI despite a similar myocardial oxygen consumption and a lower level of cardiac sympathetic activity. Cardiac NA overflow based on 3H-NA extraction over the heart increased from 182 to 1046 pmol min-1 in the VVI mode (P less than 0.01) and from 178 to 793 pmol min-1 in the TX mode (P less than 0.001). The difference in cardiac NA overflow in response to exercise (P less than 0.05 by ANOVA) was not reflected in similar differences in arterial NA concentrations or spill over rates. During mental stress the ventricular rate increased in 12/14 patients. Noradrenaline overflow increased similarly in the two modes. Changes in cardiac NA overflow during mental stress and exercise were correlated with increases in TX pacing rate. This study confirms that both mental and physical stress cause significant changes in cardiac sympathetic nerve activity and central haemodynamic variables, and that the TX pacemaker responds by increasing its pacing rate in a physiological manner.