Pp.26.09: spike rate of multi-unit muscle sympathetic nerve fibers following catheter-based renal nerve ablation

Objective: Patients with treatment-resistant arterial hypertension exhibited profound reductions in single sympathetic vasoconstrictor fiber firing rates following renal nerve ablation. In contrast, integrated multi-unit muscle sympathetic nerve activity (MSNA) changed little or not at all. We hypothesized that conventional MSNA analysis may have missed single fiber discharges, thus, obscuring sympathetic inhibition following renal denervation. Design and method: We studied patients with difficult to control arterial hypertension (age 45–74 years) before, 6 (n = 11), and 12 months (n = 8) following renal nerve ablation. Electrocardiogram, respiration, brachial, and finger arterial blood pressure (BP), as well as the MSNA raw signal were analyzed. We detected MSNA action potential spikes using 2 stage kurtosis wavelet denoising techniques to assess mean, median, and maximum spike rates for each beat-to-beat interval. Results: Supine heart rate and systolic BP did not change at 6 (&dgr;HR: -2 ± 3 bpm; &dgr;SBP: 2 ± 9 mmHg) or at 12 months (&dgr;HR:-1 ± 3 mmHg, &dgr;SBP: -1 ± 9 mmHg) after renal nerve ablation. Mean burst frequency and mean spike frequency at baseline were 34 ± 3 bursts per minute and 8 ± 1 spikes per sec. Both measurements did not change at 6 months (-1.4 ± 3.6 bursts/minute; -0.6 ± 1.4 spikes per sec) or at 12 months (-2.5 ± 4.0 bursts/minute; -2.0 ± 1.6 spikes per sec) following renal nerve ablation. After renal nerve ablation, BP decreased in 3 out of 11 patients. BP and MSNA spike frequency changes were not correlated (slope = -0.06; p = 0.369). Conclusions: Spike rate analysis of multi-unit MSNA neurograms further suggests that profound sympathetic inhibition is not a consistent finding following renal nerve ablation.