Novel mapping and ablation approaches within myocardial scar

The arrhythmogenic substrate within myocardial scar contains regions of slow conduction that support reentry, characterized by low amplitude and fractionated electrograms (EGMs). Ablation therapy to prevent arrhythmias associated with such scar needs both accurate identification and interpretation of these EGMs and effective delivery of radiofrequency energy. This thesis explored new clinical approaches to the mapping and ablation of these EGMs within scar based arrhythmia. Previous studies from our institution have shown how robotically controlled catheters offer increased stability to achieve deeper lesions. At the start of this thesis, we demonstrated the feasibility of using the Hansen Robotic System within ventricular scar during post-infarct Ventricular Tachycardia (VT) ablation to reduce future implantable cardiac defibrillator (ICD) therapies. This included patients with advanced substrates having already incurred multiple previous ICD therapies. Having proven the possibility of robotic VT ablation, we investigated, as a randomised study, whether earlier substrate ablation after the first ICD therapy may improve outcomes. Earlier ablation delayed the time to VT recurrence compared to a non-ablative approach, though this did not reach statistical significance. In patients with LV ejection fraction >30%, ablation did significantly delay time to recurrence. In these studies, the substrate was broadly characterized by EGMs with bipolar voltage <1.5mV. Inaccurate delineation of the arrhythmogenic substrate may have been responsible for future VT recurrence. We analysed the effectiveness of increasing EGM resolution within scar using the ultra-high density Rhythmia system. This was preliminarily tested during post-AF ablation Atrial Tachycardia (AT) procedures, a more common and stable reentrant model than VT, but also involving complex circuits between scar and conductive tissue. Improving EGM/mapping resolution using the Rhythmia system was not entirely useful, as we were mis-lead by small rotational activations observed on most of the maps, the majority of which were pseudo-reentrant, often related to mis-annotation of EGM local activation time (LAT) and inaccurate interpolation of activation within regions of low voltage. An alternative means of displaying activation within scar without the need to reduce EGMs to a single LAT was required. Ripple Mapping (RM) was previously developed in our institution to provide this alternative means, and displays an EGM in its entirety as a moving bar on the map. We prospectively tested the feasibility of Ripple mapping within scar; we first developed a method of using RM to differentiate regions of ablation related scar from low voltage but functional tissue in iatrogenic ATs, and observed very high ablation success. This was reproducible during multi-centre studies. Within post-infarct ventricular scar, mapping in sinus rhythm/controlled pacing, RM helped us to differentiate local from far-field activation, especially with small tip and narrowly spaced electrodes, and visualise channels of delayed conduction through scar that collocated with the diastolic pathway mapped in VT, ablation of which reduced future VT recurrence. However, ablation within these ventricular channels did not eliminate future VT recurrence. We considered whether the lines of block bordering these channels may be functional by comparing the scar locations under different cycle lengths and activation directions. Remapping post ablation atrial scars under different cycle lengths and activation directions using RM demonstrated a generally fixed scar distribution. Within ventricular scars, where the diastolic pathway could be mapped in VT, in certain areas, it was formed of functional block during tachycardia with preserved EGMs in sinus rhythm; further studies within ventricular scar under different pacing rates and activation directions may better our understanding of the ventricular substrate. In conclusion, this thesis proposes that RM be considered the gold standard approach to mapping EGMs to determine the arrhythmogenic substrate in post ablation ATs. In post-infarct VT, undertaking ablation using robotic navigation after the first ICD therapy, specifically in patients with EF >30%, and using RM based approach to define this arrythmogenic substrate can help to improve outcomes.Open Acces

Controlled regional hypoperfusion in Langendorff heart preparations

We describe a new approach that combines several techniques to allow abnormal electrical and calcium activity to be visualized within hypoperfused myocardial tissue. A flexible microcannula was inserted into the left anterior descending artery of Langendorff perfused rat hearts, an air-tight seal between the coronary artery and the cannula was created, and an HPLC pump was used to deliver a specified flowrate through the microcannula. High resolution optical mapping of NADH/calcium, NADH/voltage or calcium/voltage was then conducted using a dual camera system. The ECG was acquired using surface electrodes. This perfusion technique is superior to occluding a vessel by either a tie or a clamp because it allows precise control of the composition and amount of flow to a defined ischemic bed. Another advantage is that flow can be stopped and resumed remotely, without touching the heart. This allows ectopic beats, or other arrhythmogenic activity, such as alternans, to be recorded immediately after changes in flow are imposed. Altogether, the described method provides a powerful new tool to assess how coronary flow rate affects the degree of local ischemia by the ability to record abnormal patterns of electrical activity and associated intracellular calcium transients with high spatiotemporal resolution from epicardial areas as small as 100 × 100 μm

An approach to help differentiate postinfarct scar from borderzone tissue using Ripple Mapping during ventricular tachycardia ablation

BackgroundVentricular scar is traditionally highlighted on a bipolar voltage (BiVolt) map in areas of myocardium MethodsFifteen consecutive patients (left ventricular ejection fraction 30 ± 7%) underwent endocardial left ventricle pentaray mapping (median 5148 points) and ablation targeting areas of late Ripple activation. BiVolt maps were studied offline at initial voltage of 0.50-0.50 mV to binarize the color display (red and purple). RMs were superimposed, and the BiVolt limits were sequentially reduced until only areas devoid of Ripple bars appeared red, defined as RM-scar. The surrounding area supporting conducting Ripple wavefronts in tissue ResultsRM-scar was significantly smaller than the traditional 0.50 mV cutoff (median 4% vs. 12% shell area, p ConclusionPostinfarct scars appear significantly smaller than traditional 0.50 mV cut-offs suggest, with voltage thresholds unique to each patient

Impact of COVID-19 on patients awaiting ablation for atrial fibrillation

ObjectiveAtrial fibrillation (AF) ablation services were significantly affected by the COVID-19 pandemic. We aimed to evaluate a symptom-based clinician prioritisation scheme for waiting list management compared with patient-completed quality of life (QoL) scores. We also sought to understand factors influencing QoL, particularly the impact of COVID-19, on patients awaiting AF ablation, via a bespoke questionnaire.MethodsPatients awaiting AF ablation were sent two QoL questionnaires (Atrial Fibrillation Effect on QualiTy of Life (AFEQT) and EuroQol 5D (EQ5D-5L)) and the bespoke questionnaire. At a separate time point, patients were categorised as C1-urgent, C2-priority or C3-routine by their cardiologist based on review of clinic letters.ResultsThere were 118 patients included with priority categorisation available for 86 patients. Median AFEQT scores were lower in C2 (30.4; 17.2-51.9) vs C3 patients (56.5; 32.1-74.1; pConclusionThe QoL of patients awaiting AF ablation is impaired and AFEQT helps to identify patients at risk of admission, over and above physician assessment. COVID-19 influenced patients seeking medical attention with symptomatic AF when they normally would. Regular exercise is associated with better QoL in patients awaiting AF ablation

Delineating postinfarct ventricular tachycardia substrate with dynamic voltage mapping in areas of omnipolar vector disarray

BackgroundDefining postinfarct ventricular arrhythmic substrate is challenging with voltage mapping alone, though it may be improved in combination with an activation map. Omnipolar technology on the EnSite X system displays activation as vectors that can be superimposed onto a voltage map.ObjectiveThe study sought to optimize voltage map settings during ventricular tachycardia (VT) ablation, adjusting them dynamically using omnipolar vectors.MethodsConsecutive patients undergoing substrate mapping were retrospectively studied. We categorized omnipolar vectors as uniform when pointing in one direction, or in disarray when pointing in multiple directions. We superimposed vectors onto voltage maps colored purple in tissue >1.5 mV, and the voltage settings were adjusted so that uniform vectors appeared within purple voltages, a process termed dynamic voltage mapping (DVM). Vectors in disarray appeared within red-blue lower voltages.ResultsA total of 17 substrate maps were studied in 14 patients (mean age 63 ± 13 years; mean left ventricular ejection fraction 35 ± 6%, median 4 [interquartile range 2-8.5] recent VT episodes). The DVM mean voltage threshold that differentiated tissue supporting uniform vectors from disarray was 0.27 mV, ranging between patients from 0.18 to 0.50 mV, with good interobserver agreement (median difference: 0.00 mV). We found that VT isthmus components, as well as sites of latest activation, isochronal crowding, and excellent pace maps colocated with tissue along the DVM border zone surrounding areas of disarray.ConclusionDVM, guided by areas of omnipolar vector disarray, allows for individualized postinfarct ventricular substrate characterization. Tissue bordering areas of disarray may harbor greater arrhythmogenic potential