Ultra high density mapping and ablation biophysics of diseased human myocardium

Abstract

Atrial fibrillation (AF) is a cardiac arrhythmia with a prevalence in the United Kingdom of approximately 1.5 million people. Patients with AF can suffer debilitating symptoms including palpitations, breathlessness, and fatigue. Furthermore, they are at increased risk of other life changing conditions such as stroke, heart failure and dementia. Ventricular tachycardia (VT) is a life-threatening cardiac arrhythmia that most commonly occurs due to structural heart disease. During an episode of VT, patients can suffer with palpitations, pre-syncope, syncope, chest pains, breathlessness and ultimately may deteriorate into ventricular fibrillation and death.
When medical therapy fails for these arrhythmias, a treatment option is radiofrequency catheter ablation (RFCA). RFCA is an invasive procedure where a set of lesions applied to the myocardium using RF energy to inhibit recurrence of the arrhythmia. The procedure is aided by the creation of a 3D electroanatomical map (3D EAM), which integrates anatomy with electrophysiological parameters detailing the perceived underlying degree of fibrosis. During ablation itself, the development of the lesion can be monitored using biophysical feedback, that being either drops (Δ) in impedance (local [LI] or generator [GI]) or electrogram amplitude. Alternatively, an
accumulating scoring system known as Ablation Index (AI) based upon pre-determined ablation inputs known to affect lesion size such as power, duration and contact force can be used.
However, there are still several unknowns in RFCA. Firstly, as histology is not readily available, fibrosis is represented on 3D EAMs using an electrical surrogate, typically bipolar voltage amplitude. Despite widespread use of values representing dense scar and diseased tissue, these values have never been histologically validated. Secondly, novel ultra-high-density mapping systems have not yet been used to confirm the relationship of atrial fibrosis with progression of AF, between atria or cardiac rhythms (sinus rhythm vs AF) that have been described by lower density systems. Thirdly, pre-ablation factors that affect ΔLI and their relative importance have yet to be fully elucidated. Fourthly, the interaction of catheter contact force (CF) on tissue LI is unknown. Finally, the effect of ventricular tissue fibrosis on biophysical feedback during radiofrequency ablation in the human heart is uninvestigated.
In this thesis, I seek to shed some light onto these unknowns. In Chapter 3, I document a study where electrical surrogates of atrial fibrosis (bipolar voltage and LI) are assessed in a physiological manner using pacing thresholds. Based on this work, new thresholds for dense scar and diseased tissue are suggested. This is followed in Chapter 4, where the differences in tissue voltages and surface area of scar between rhythm, atria and AF type are explored using an ultra-high-density 3D EAM and these new scar thresholds. In Chapter 5, the interaction of catheter CF and resting tissue LI is studied using a catheter that integrates both technologies. Chapter 6 then proceeds to examine the effect and interactions of different ablation parameters that affect ΔLI for two different LI measuring catheters. Finally in Chapter 7, the effect of endocardial ventricular fibrosis on the relationship between GI and AI is investigated. Values of AI that do not provide additional biophysical changes on average are presented.
In conclusion, I find that current values used to determine atrial fibrosis can be improved. There is considerable interaction between CF and resting tissue LI, which alongside other ablation parameters can affect ΔLI. Lastly, endocardial ventricular fibrosis significantly effects biophysical feedback during RFCA. Ultimately, I hope these findings can be used by interventional electrophysiologists across the world to improve and guide their ablation procedures, enable them to optimise every ablation lesion they deliver and aid patients in being arrhythmia free for as long as possible.

More information

Identifiers

Catalogue record

Export record