Student Presentation -- Ankur Shah
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Ph.D. Research Proposal, Friday June 14, 2019 -- Capture of His-Purkinje System during Sinus Rhythm and Ventricular Fibrillation

CVRTI 152, Canepa Conference Room, 2:30 pm

Speaker: Ankur Shah. Advisor: Dr. Derek Dosdall


Abstract:

Every month thousands of Americans at risk of cardiac arrest receive implantable cardioverter defibrillators (ICDs). ICDs automatically detect cardiac arrhythmias and send the appropriate kind of electrical pulses to terminate the arrhythmia. In case ventricular fibrillation (VF), which is a chaotic activation pattern of the myocardium, is detected, the ICD delivers a high energy shock. These high energy shocks are painful and can also cause electroporation, or tissue scarring. ICDs in patients, although life-saving reduces their quality of life. Therefore, a low energy shocking strategy is needed to prevent pain and heart damage.

The promising new idea is to use the conduction system to defibrillate the heart at a significantly lower energy level. The conduction system provides an efficient pathway to conduct electrical signals across the heart for its synchronous contraction to pump blood across the body. Critically timed pacing of ventricular myocardium (VM) during VF leads to the capture of the tissue around the electrode. The pacing of HB during VF should have a similar response with the excitation preferentially spreading in the conduction system. One hypothesis of this proposal is that HB pacing during VF captures the conduction system, which in turn influences the ventricular endocardial activation pattern to disrupt or entirely terminate VF. A real-time acquisition system will be developed to record and visualize the electrical signals and their spatial derivatives from a grid of electrodes placed in the vicinity of the HB. The real-time visualization and analysis will aid in identifying electrodes directly in contact with the HB. The system will also include an integrated pacing module which can deliver stimulation voltages to any of the electrodes. This system will then identify and pace the HB in VF induced perfused rabbit hearts and unperfused dog hearts. In the rabbit hearts, HB and nearby VM will be paced at rates faster than the intrinsic ventricular or HB rates during VF. The effect of different pacing rates and locations will be studied from the endocardial electrical activity recorded using a basket array inserted in the left ventricle. In dog hearts, the HB alone will be paced at a fixed rate faster than the intrinsic ventricular rate during unperfused VF. The influence of HB pacing with the changing time course of VF as global ischemia sets in will be studied from the endocardial activations recorded from a basket inserted in the left ventricles.

Selective HB sensing and pacing is challenging clinically in larger human hearts as the HB is about 1mm beneath the endocardial surface of the high septum in the right atrium. The Utah Electrode Array (UEA) has a multitude of ~1mm long closely spaced needle-like electrodes protruding from a plaque. Although the UEA is a good candidate to access the HB cells, it was initially designed for recording and stimulating neurons. Clinically relevant cardiac pacing current (high amplitude current) and pulse widths will be used to test the electrical stability of the UEA tips. Further, the mechanical stability will be investigated by deploying them in a dog and a rabbit heart to sense and pace the HB in sinus rhythm. Electrode impedance spectroscopy and scanning electron microscopy will be used to estimate electrode tip integrity.