The plasma catecholamine responses to ventricular pacing: implications for rate responsive pacing.

Many patients with VVI and VVIR pacemakers will alternate between periods of sinus rhythm and ventricular pacing. These rhythm shifts may be poorly tolerated by some patients. Changes in plasma catecholamine levels during these rhythm shifts may contribute to these patients' symptoms. We measured blood pressure, ejection fraction and plasma norepinephrine, epinephrine, and dopamine serially in nine patients with normal left ventricular ejection fractions and VVI pacemakers during sinus rhythm and at paced rates of 10 beats per minute (bpm) above sinus rates (10 + NSR), 100 bpm, and 130 bpm. The mean norepinephrine level at baseline was 143 +/- 16 pg/mL and increased to 166 +/- 36 pg/mL at 10 + NSR, 204 +/- 47 pg/mL at 100 bpm, and 182 +/- 34 pg/mL at 130 bpm. These increases corresponded to mean percent changes from baseline of 17% (P = 0.02), 33% (P = 0.002), and 24% (P = 0.07), respectively. The magnitude of the norepinephrine response was not correlated with the pacing rate. The mean plasma epinephrine level at baseline was 57 +/- 6 pg/mL and peaked at 51 +/- 12 pg/mL at 10 + NSR, 89 +/- 31 pg/mL at 100 bpm and 101 +/- 28 pg/mL at 130 bpm. These increases corresponded to mean percent changes from baseline of -10% (P = NS), 30% (P = 0.07), and 89% (P = 0.02), respectively. No trends in the dopamine response to pacing were noted. During ventricular pacing there were no significant changes in mean blood pressure and only slight changes in ejection fraction. The individual percent changes in plasma norepinephrine and epinephrine at 100 bpm were inversely correlated to the changes in systolic blood pressure (R = -0.68, P = 0.06, and R = -0.81, P = 0.03, respectively). These results suggest that plasma norepinephrine and epinephrine increase acutely in response to ventricular pacing at rates commonly seen during rate responsive ventricular pacing.