An automated algorithm minimising ATP failure: re-initiation to enhance anti-tachycardia pacing efficacy
Authors: Qian S , Connolly A , Mendonca-Costa C , Campos F , Rodero C , Whitaker J , Rinaldi C , Bishop M 
Published: May 2022

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Medical Research Council, UK

Background
Re-initiation is an important mechanism of anti-tachycardia pacing (ATP) failure, whereby VT is first terminated by the initial ATP application, before being re-initiated by successive pulses. Current ICD designs are able to measure and store electrograms (EGMs) for detecting and classifying arrhythmias, which contain information that may also be used during ATP application. Developing an algorithm that automatically processes EGMs during ATP, with the goal of detecting the initial VT termination and truncating subsequent ATP pulses (which has the potential to re-initiate), may thus increase ATP efficacy.

Purpose
To develop a proof-of-concept ATP detection algorithm: Early Termination Detection Algorithm (ETDA), to automatically sense the signs of early VT termination and cease further ATP pulses based on real-time sensed EGMs from implanted devices.

Methods
A cohort of 7 porcine infarcted ventricular computational models were subject to virtual induction protocols to induce sustained VTs. Functional model properties were adjusted to provide 73 unique VT episodes (260≤VT cycle length (CL)≤480ms). For each episode, burst ATP was delivered from typical pacing sites near the right ventricle (RV) septum to evaluate its efficacy. The ATP failures and their failure mechanisms were identified, accordingly. During ATP application, five common sensing EGM vectors from implanted devices were recovered from simulations including can-to-Superior vena cava (SVC) coil, can-to-RV ring, SVC coil-to-RV coil ring, RV coil tip-to-RV coil ring and LV coil at the lateral base-to-RV tip. Our proposed ETDA utilises those EGMs for VT termination detection. Specifically, correlation coefficients (CCs) of the EGMs between two successive ATP pulses were calculated and averaged to identify sudden changes in EGM morphology that indicate VT termination (Fig A). A discriminating threshold on the CCs was chosen by comparing all re-initiation cases with detailed analysis of the actual VT termination time observed from simulation results. ETDA was then applied to all cases to identify initial termination and improvement in efficacy.

Results
Before ETDA application, ATP terminated 42 cases (58%, Fig C), with re-initiation attributing to 11 (35%) of ATP failures. Application of ETDA accurately detected VT termination in 91% of re-initiated cases, 90% of terminated cases and 81% of not-terminated cases (Fig B), which enhanced the overall ATP efficacy to 71% (P=0.08) (Fig C).

Conclusions
The real-time EGMs measured from standard ICD/CRT-D devices may be used to improve ATP efficacy through an approach such as ETDA. ETDA detects signs of early termination automatically in real time which enables identification of successful VT termination, truncating subsequent pulses that may re-initiate the VT, which enhances overall ATP efficacy.