The effects of rate and irregularity on sympathetic nerve activity in human subjects

Segerson, Nathan M.; Sharma, Niraj; Smith, Michael L.; Wasmund, Stephen L.; Kowal, Robert C.; Abedin, Moeen; MacGregor, John F.; Pai, Rakesh K.; Freedman, Roger A.; Klein, Richard C.; Wall, T. Scott; Stoddard, Gregory; Hamdan, Mohamed H.

doi:10.1016/j.hrthm.2006.09.017

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Volume 4, Issue 1 , Pages 20-26, January 2007

The effects of rate and irregularity on sympathetic nerve activity in human subjects

Nathan M. Segerson, MD
- University of Utah, Salt Lake City, Utah
Niraj Sharma, MD
- University of Utah, Salt Lake City, Utah
Michael L. Smith, PhD
- University of North Texas Health Sciences Center, Fort Worth, Texas.
Stephen L. Wasmund, PhD
- University of Utah, Salt Lake City, Utah
Robert C. Kowal, MD, PhD
- University of Utah, Salt Lake City, Utah
Moeen Abedin, MD
- University of Utah, Salt Lake City, Utah
John F. MacGregor, MD
- University of Utah, Salt Lake City, Utah
Rakesh K. Pai, MD
- University of Utah, Salt Lake City, Utah
Roger A. Freedman, MD
- University of Utah, Salt Lake City, Utah
Richard C. Klein, MD
- University of Utah, Salt Lake City, Utah
T. Scott Wall, MD
- University of Utah, Salt Lake City, Utah
Gregory Stoddard, PhD
- University of Utah, Salt Lake City, Utah
Mohamed H. Hamdan, MD
- University of Utah, Salt Lake City, Utah
- Address reprint requests and correspondence: Mohamed H. Hamdan, M.D., Division of Cardiology, Department of Internal Medicine, University of Utah Hospitals and Clinics, Room 4A100, 30 N. 1900 E., Salt Lake City, UT 84132.

Received 13 July 2006; accepted 11 September 2006. published online 18 September 2006.

Background

We have recently shown that atrial fibrillation is associated with an increase in sympathetic nerve activity (SNA) compared with sinus rhythm. It remains unclear, however, whether these findings are true at various rates and whether the magnitude of sympathoexcitation is related to the degree of irregularity.

Objective

To determine the role of irregularity in mediating the SNA changes at various pacing rates. Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P <.001) but that MAP and DBP did not change significantly.

Methods

Using custom-made software, atrioventricular sequential pacing with predetermined rates (100, 120, and 140 bpm) and irregularities (standard deviation = 0%, 5%, 15%, and 25% of mean cycle length) was performed in 23 patients referred for electrophysiologic evaluation. Pacing at each rate/irregularity was performed for 2 minutes, with 2 minutes of recovery in between. Systolic, diastolic, and mean arterial blood pressure (SBP, DBP, and MAP), central venous pressure (CVP), and SNA were measured at baseline and during pacing.

Results

Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P <.001 but that MAP and DBP did not change significantly. A significant correlation was found between the pacing irregularity and SNA, with greater sympathoexcitation noted at greater degrees of irregularity (r = 0.2, P = .04). A five-variable linear model using DBP, MAP, CVP, and degree of pacing irregularity to predict SNA was highly statistically significant (r = 0.46, P <.001). After controlling for hemodynamic changes, for every 1% increase in irregularity, there was a 6.1% increase in SNA.

Conclusion

We have shown that greater degrees of irregularity cause greater sympathoexcitation and that the effects of irregular pacing on SNA are independent of the hemodynamic changes.

Keywords: Arrhythmia, Fibrillation, Sympathetic nervous system