Effects of VNS FREQ on HR and heart period.

<p>Mean percent drop in HR for <b>(A)</b> P-VNS, <b>(B)</b> S-VNS (10%), and <b>(C)</b> S-VNS (20%) at different FREQ. Mean percent drop in Heart Period for <b>(D)</b> P-VNS, <b>(E)</b> S-VNS (10%), and <b>(F)</b> S-VNS (20%) at different FREQ. Note data reported here for P-VNS is the mean and SEM of the average of P-VNS #1 and P-VNS #2 protocols (n = 8). (*p < 0.05).</p

Effects of VNS on HRV using Poincaré analysis.

<p>Representative Poincaré plots of <b>(A)</b> P-VNS and <b>(B)</b> S-VNS (10%) during VNS stimulation (<b>ON</b>) at 10 Hz and 30 Hz demonstrating the elliptical fitting of the beat-distribution cloud and the standard deviation of short-term (SD1) and long-term (SD2) variability. <b>(C)</b> Mean SD1/SD2 ratio for <b>PRE</b>, <b>ON</b> and <b>POST</b> across different FREQ. (*p < 0.05).</p

Effects of STOCH on the chronotropic effects of VNS.

Mean percent drop in HR for (A) S-VNS (10%) and (B) S-VNS (20%) being compared to its immediate preceding P-VNS protocol at different FREQ. (C) Comparison of mean relative drop in HR between P-VNS protocols and (D) S-VNS (20%) and its subsequent P-VNS protocol at different FREQ. (*p < 0.05).</p

Stochastic vagus nerve stimulation affects acute heart rate dynamics in rats

<div><p>Vagus nerve stimulation (VNS) is an approved therapy for treatment of epilepsy and depression. While also shown to be promising in several preclinical and clinical studies to treat cardiovascular diseases, optimal therapeutic stimulation paradigms are still under investigation. Traditionally, parameters such as frequency, current, and duty cycle are used to adjust the efficacy of VNS therapy. This study explored the effect of novel stochastic VNS (S-VNS) on acute heart rate (HR) dynamics. The effect of S-VNS was evaluated in Sprague Dawley rats by comparing the acute HR and HR variability (HRV) responses to standard, periodic VNS (P-VNS) across different frequencies (FREQs, 10–30 Hz). Our results demonstrate that both S-VNS and P-VNS produced negative chronotropic effects in a FREQ-dependent manner with S-VNS inducing a significantly smaller drop in HR at 10 Hz and 20 Hz compared to P-VNS (p<0.05). S-VNS demonstrated a FREQ-dependent drop in the SD1/SD2 ratio, a measure of HRV, which was absent in P-VNS, suggesting that S-VNS may acutely modulate the nonlinear relationship between short- and long-term HRV. In conclusion, S-VNS is a novel stimulation procedure that may provide different physiological outcomes from standard P-VNS, as indicated by our analysis of HR dynamics. Our study provides a rationale for further detailed investigations into the therapeutic potential of S-VNS as a novel neuromodulation technique.</p></div

Detailed schematic of the experimental VNS protocol.

<p>Standard P-VNS or S-VNS with different degree of stochasticity (STOCH, 10% and 20%) was administered across different frequencies (FREQ, 20, 30, and 10 Hz) with stabilization times between protocols and conditions. P-VNS, periodic vagus nerve stimulation; S-VNS, stochastic vagus nerve stimulation; STOCH, stochasticity; <b>PRE</b>, baseline recording; <b>ON</b>, continuous VNS; <b>POST</b>, recovery.</p

The effect of GIRK4 and RGS6 ablation on APD heterogeneity, μ.

(A) Average APD heterogeneity, μ, as a function of BCL in WT, Girk4-/-, and Rgs6-/- hearts. (B-D) The effect of CCh on μ at different BCL in WT, Girk4-/-, and Rgs6-/- hearts. n = 8, 5, 8 for WT, Rgs6-/-, and Girk4-/- respectively. Statistics performed using 1-way ANOVA.</p

ECG recordings and corresponding HR responses.

<p>Representative segments of ECG recordings and corresponding heart rate (HR) response for an anesthetized rat for <b>PRE</b>, <b>ON</b>, and <b>POST</b> during <b>(A)</b> P-VNS, <b>(B)</b> S-VNS (10%), and <b>(C)</b> S-VNS (20%) of the right cervical vagus nerve. Zoomed-in snapshots of <b>PRE</b> (black), <b>ON</b> (red), and <b>POST</b> (yellow) highlights VNS artifacts during stimulation. Here, VNS was continuously delivered at 20 Hz, 500 µs pulse width, and 1.0 mA for 2 minutes.</p

Effects of VNS FREQ on HR recovery.

<p><b>(A)</b> Schematic representation of different scenarios of HR recovery based on the value of <i>HR</i>_{<i>POST Ratio</i>}. Mean <i>HR</i>_{<i>POST Ratio</i>} values for <b>(B)</b> P-VNS, <b>(C)</b> S-VNS (10%), and <b>(D)</b> S-VNS (20%) at different FREQ. # p<0.05 compared to a mean theoretical value of 1.</p

The effect of GIRK4 and RGS6 ablation on APD₈₀.

<p>(A) Change in average APD₈₀ with decreasing BCL in WT, <i>Girk4</i>^<i>-/-</i>, and <i>Rgs6</i>^<i>-/-</i> hearts. (‘#’ denotes statistical significance of p < 0.05 between WT and <i>Girk4</i>^<i>-/-</i>. ‘$’ denotes statistical significance of p < 0.05 between WT and <i>Rgs6</i>^<i>-/-</i>). (B) Representative 2D APD₈₀ maps from WT, <i>Girk4</i>^<i>-/-</i>, and <i>Rgs6</i>^<i>-/-</i> hearts, constructed at BCL = 120 ms both at baseline and post-CCh injection. Representative action potential traces are shown at baseline (top panel, pixels marked by *) and post-CCh (bottom panel, pixels marked by Δ). (C-E) The effect of CCh on APD₈₀ at decreasing BCL in WT, <i>Girk4</i>^<i>-/-</i>, and <i>Rgs6</i>^<i>-/-</i> hearts. (‘*’ denotes statistical significance of p < 0.05 between baseline and 300nM CCh; ‘&’ denotes statistical significance of p < 0.05 between baseline and 3uM CCh). n = 8, 5, 8 for WT, <i>Rgs6</i>^<i>-/-</i>, and <i>Girk4</i>^<i>-/-</i>_, respectively. All statistics performed using 1-way ANOVA.</p

The influence of M₂R-I_KACh signaling on in vivo HR and HRV.

<p>Summary of baseline and post-CCh (300nM CCh) in-vivo HR (A) and HRV (B) in WT, <i>Rgs6</i>^<i>-/-</i>, and <i>Girk4</i>^<i>-/-</i> mice. (‘*’ denotes statistical significance of p < 0.05 between baseline and CCh within the same genotype. ‘&’ denotes a statistically significant (p < 0.05) difference for both baseline and CCh when comparing between two genotypes). ‘#’ denotes statistical significance of p < 0.05 between WT and <i>Rgs6</i>^<i>-/-</i> mice post-CCh. ‘$’ denotes statistical significance of p < 0.05 between <i>Girk4</i>^<i>-/-</i> and <i>Rgs6</i>^<i>-/-</i> mice post-CCh. Statistics performed using 1-way ANOVA.) (C) Quantification of the total number of mice that exhibited arrhythmias post CCh. (‘*’ denotes statistical significance of p < 0.05 between <i>Girk4</i>^<i>-/-</i> and <i>Rgs6</i>^<i>-/-</i>. Statistics performed using Fisher’s exact test). (D) Representative examples of ECG data during control and demonstrating episodes of arrhythmia in WT and <i>Rgs6</i>^<i>-/-</i>, and no arrhythmia in <i>Girk4</i>^<i>-/-</i> mice post CCh. n = 8, 8, 6 for WT, <i>Rgs6</i>^<i>-/</i>-, and <i>Girk4</i>^<i>-/-</i>_, respectively.</p