Abstract 10597: Epidural Sympathetic Afferent Blockade by Resiniferatoxin Reverses Vagal Dysfunction Following Myocardial Infarction

Abstract

Introduction: Myocardial infarction (MI) induces sympathovagal imbalance, predisposing for ventricular tachyarrhythmias (VT). Thoracic epidural anesthesia reduces VT burden through sympathetic blockade. However, it is unknown if sympathetic afferent activation may cause vagal dysfunction, and if blockade of these spinal afferents can improve vagal function and reduce VT burden. Methods: Chronic MI was percutaneously created in Yorkshire pigs (n=8). In terminal experiments 6 to 8 weeks post MI, an epidural catheter was placed at the C7-T1 epidural space. After sternotomy, a 56 electrode sock was placed over the ventricles to record activation recovery intervals (ARI, surrogate of action potential duration). Effective refractory periods (ERP) were assessed via extra-stimulus pacing and left ventricular (LV) pressure monitored via a pressure catheter. Vagal function was assessed by baroreflex sensitivity (BRS) after phenylephrine (3 μg/kg, IV). ARIs, ERP, LV function, and BRS were checked before and after epidural RTX (0.6 μg/kg/ml). VT inducibility was assessed by endocardial extra-stimulus pacing from the right ventricular apex. Results: Epidural RTX led to a modest hemodynamic response peaking at 10.2 ± 4.2 min post-RTX with stabilization by 118 ± 15 min, characterized by increased LV systolic pressure (121±5.6 to 133±9.7 mmHg; p =ns) and contractility (1411±74 to 1514±163 mmHg/s; p =ns). While ARI and atrial/ventricular ERP did not change significantly, BRS was significantly augmented by 2 hrs (2.1±0.6 to 4.3±0.8 ms/mmHg, p <0.01). 9/9 animals in our chronic MI model were inducible for VT by extra-stimulus pacing whereas only 1/6 were inducible for VT after epidural RTX ( p <0.001). Conclusion: Blockade of nociceptive spinal sympathetic afferents by RTX augments reflexive vagal function without altering basal cardiac function. Blockade of nociceptive afferents and restoration of parasympathetic function alone may be sufficient to suppress VT.