The acute effect of atrioventricular pacing on sympathetic nerve activity in patients with normal and depressed left ventricular function

Abstract

Although modest elevations in pacing rate improve cardiac output and induce reflex sympathoinhibition, the threshold rate above which hemodynamic perturbations induce reflex sympathoexcitation remains unknown. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressures (MAP) and sympathetic nerve activity (SNA) were measured during normal sinus rhythm (NSR) and atrioventricular (AV) sequential pacing in 25 patients. Pacing was performed at 100, 120, and 140 beats/min with an AV interval of 100 ms. Patients were divided into two groups based on normal or abnormal left ventricular ejection fraction (LVEF): group 1 (n = 11; mean LVEF, 55%) and group 2 (n = 14; mean LVEF, 31%). In group 1, relative to NSR, SBP decreased an average of 2%, 3%, and 8% at 100, 120, and 140 beats/min (P < 0.001), respectively. DBP and MAP increased 9%, 15%, and 15% (P = 0.001) and 3%, 6%, and 5% [P = not significant (NS)], respectively. In group 2, SBP reductions were even greater, with an average decrease of 4%, 8%, and 16% (P < 0.001). Whereas DBP increased 9%, 9%, and 8% at 100, 120, and 140 beats/min (P = NS), MAP increased 3% and 2% at 100 and 120 beats/min but decreased 3% at 140 beats/min (P = 0.001). SNA recordings were obtained in 11 patients (6 in group 1 and 5 in group 2). In group 1, SNA decreased during all rates, with a mean 21% reduction. In group 2, however, SNA decreased at 100 and 120 beats/min (49% and 38%) but increased 24% at 140 beats/min. Patients with depressed LVEF exhibited altered hemodynamic and sympathetic responses to rapid sequential pacing. The implications of these findings in device programming and arrhythmia rate control await future studies.

Fig. 1.

The mean changes in blood pressure (BP) parameters in group 1 (A) and group 2 (B). The reference point (0%) for each measurement is the BP during sinus rhythm before pacing. Multivariable models showed rate effected an increase in systolic BP (SBP; P < 0.001) and a decrease in diastolic BP (DBP; P < 0.001) in group 1, with mean arterial pressure (MAP) not significantly effected. In group 2, rate exhibited even greater effects on SBP but had less effect on DBP [P = not significant (NS)]. MAP increased 3% and 2% at 100 and 120 beats/min (bpm) but decreased 3% at 140 beats/min (P = 0.001). LVEF, left ventricular ejection fraction.

Fig. 2.

Sample tracings of sympathetic nerve activity (SNA) at baseline and during pacing at 100, 120, and 140 beats/min from a patient with a normal LVEF (group 1). EF, ejection fraction.

Fig. 3.

Sample tracings of SNA at baseline and during pacing at 100, 120, and 140 beats/min from a patient with a depressed LVEF (group 2).

Fig. 4.

The mean changes in SNA in both groups. The reference point (0%) for each measurement is the SNA during sinus rhythm before pacing. SE estimates are indicated with whisker bars. In a multivariable model, the combined effect of pacing at 140 beats/min and left ventricular dysfunction (group 2) increased SNA by 67% (95% confidence interval 4.0, 131%), P = 0.04, relative to all other observations.