Microvolt T-Wave Alternans Is Modulated by Acute Low-Level Tragus Stimulation in Patients With Ischemic Cardiomyopathy and Heart Failure.

Kanchan Kulkarni,Kimberly A Parks,Jagmeet P Singh,Khaled Elkholey,Antonis A Armoundas,Stavros Stavrakis

doi:10.3389/fphys.2021.707724

Abstract

Aims: Microvolt T-wave alternans (TWA), an oscillation in T-wave morphology of the electrocardiogram (ECG), has been associated with increased susceptibility to ventricular tachy-arrhythmias, while vagus nerve stimulation has shown promising anti-arrhythmic effects in in vivo and ex vivo animal studies. We aimed to examine the effect of non-invasive, acute low-level tragus stimulation (LLTS) on TWA in patients with ischemic cardiomyopathy and heart failure.Methods: 26 patients with ischemic cardiomyopathy (left ventricular ejection fraction <35%) and chronic stable heart failure, previously implanted with an automatic implantable cardioverter defibrillator (ICD) device with an atrial lead (dual chamber ICD or cardiac resynchronization therapy defibrillator), were enrolled in the study. Each patient sequentially received, (1) Sham LLTS (electrode on tragus, but no stimulation delivered) for 5 min; (2) Active LLTS at two different frequencies (5 and 20 Hz, 15 min each); and (3) Active LLTS, during concomitant atrial pacing at 100 bpm at two different frequencies (5 and 20 Hz, 15 min each). LLTS was delivered through a transcutaneous electrical nerve stimulation device (pulse width 200 μs, frequency 5/20 Hz, amplitude 1 mA lower than the discomfort threshold). TWA burden was assessed using continuous ECG monitoring during sham and active LLTS in sinus rhythm, as well as during atrial pacing.Results: Right atrial pacing at 100 bpm led to significantly heightened TWA burden compared to sinus rhythm, with or without LLTS. Acute LLTS at both 5 and 20 Hz, during sinus rhythm led to a significant rise in TWA burden in the precordial leads (p < 0.05).Conclusion: Acute LLTS results in a heart-rate dependent increase in TWA burden.

Highlights

Heightened sympathetic activity has been associated with the generation of ventricular tachy-arrhythmias
The most common cause of death in patients with ischemic cardiomyopathy (ICM) is sudden cardiac death (SCD), here, the objective of this study is to examine the effect of level transcutaneous vagus nerve stimulation (LLTS) on T-wave alternans (TWA), in patients with ICM and heart failure (HF) (New York Heart Association, NYHA, class II), which are known to have the highest risk of SCD (Myerburg and Junttila, 2012)
Higher levels of TWA burden were observed during atrial pacing compared to sinus rhythm, during all five interventions, demonstrating the dependency of alternans onset on the underlying heart rates (HRs) and subsequently the effect of LLTS on modulation of TWA

Summary

Introduction

Heightened sympathetic activity has been associated with the generation of ventricular tachy-arrhythmias. The effect of the sympathetic nervous system stimulation on the heart is complex and is governed by the state of the myocardium, interventions that reduce cardiac sympathetic activity have been shown to protect against arrhythmias (Schwartz and Zipes, 2000; Rubart and Zipes, 2005), whereas those that enhance sympathetic activity provoke them (Rubart and Zipes, 2005; Billman, 2006). TWA has been observed to occur at significantly lower heart rates (HRs), with peak alternans level increasing with sympathetic stimulation compared to baseline, in basic science studies (Ng et al, 2007)

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Conclusion