Mapping hidden scar in nonischemic cardiomyopathy VT ablation

Ventricular tachycardia arising in the setting of nonischemic cardiomyopathy presents one of the more demanding challenges in interventional electrophysiology. Unlike patients with prior myocardial infarction, where dense endocardial scar follows the territory of a culprit coronary artery, those with dilated, inflammatory, or genetically mediated cardiomyopathies harbour scar that is often patchy, mid-wall, or predominantly epicardial. The arrhythmia substrate can lurk between layers of seemingly viable myocardium, defying the conventions that govern post-infarct mapping.

Ablation strategies that depend purely on induction and activation mapping frequently fall short in this population. Haemodynamic intolerance during tachycardia, multiple unstable reentrant circuits, and the inability to reproducibly trigger the clinical arrhythmia all push operators toward a substrate-based approach. Pre-procedural characterisation of the abnormal myocardial regions, combined with high-density mapping during sinus rhythm, has therefore become the cornerstone of contemporary management.

For Australian cardiologists managing these patients across vast distances and varied referral pathways, the move toward substrate-guided ablation has practical consequences. From tertiary centres in Sydney, Melbourne, and Adelaide to outreach services reaching the Top End and the Pilbara, the technique influences referral patterns, procedural planning, and follow-up infrastructure across the country.

What defines the substrate in nonischemic cardiomyopathy

The electrophysiological substrate in nonischemic cardiomyopathy differs qualitatively from ischaemic scar. Fibrosis tends to cluster around the basal segments, particularly the perivalvular regions of the mitral and tricuspid annuli, with frequent involvement of the subepicardial layer. In arrhythmogenic right ventricular cardiomyopathy, fibro-fatty replacement characterises the so-called triangle of dysplasia, while in lamin or phospholamban mutation carriers, scar distribution can be diffuse and progressive, sometimes appearing normal on conventional imaging.

Bipolar voltage mapping performed with multielectrode catheters reliably identifies regions where local electrograms fall below standard thresholds, typically under 1.5 mV for dense scar and 1.5 to 0.5 mV for border zone. Yet in nonischemic hearts, normal bipolar voltage can mask disease because the catheter may sit on healthy epicardium while the diseased tissue lies deeper. This is where unipolar mapping proves its worth, as it samples a wider electrical field and can flag mid-wall or epicardial abnormality even when endocardial bipolar signals appear preserved.

Late potentials, fractionated electrograms, and local abnormal ventricular activities serve as functional markers of the channels and slow-conduction zones that perpetuate reentry. Identifying these signals during sinus rhythm, rather than chasing them during tachycardia, allows operators to construct an anatomical blueprint of the arrhythmogenic terrain before any ablation is delivered.

Mapping tools: from voltage to functional activation patterns

High-density multielectrode mapping systems have transformed substrate characterisation. Pentarray and small basket catheters, used routinely at Australian centres such as Royal Prince Alfred and The Alfred, allow rapid acquisition of thousands of points with minimal motion artefact. The resulting maps blend anatomical detail with electrogram timing, and modern software overlays highlight regions of late activation, fractionation, and decrement on a single colour-coded surface.

Isochronal late activation mapping refines this further by displaying the latest activated regions as a timing isochrone layer. Within these isochrones, the transition zones, where crowding of lines indicates steep conduction gradients, often harbour the critical isthmuses of reentry. Operators increasingly target these crowded isthmuses rather than the entire scar, which improves lesion specificity and reduces unnecessary tissue destruction.

Decrement-evoking pacing, in which extrastimuli reveal concealed but defined lateness, can unmask channels invisible on standard substrate maps. This technique is particularly valuable in nonischemic cardiomyopathy, where circuit geometry is unpredictable and conventional pacing protocols may miss critical sites. Combined with omnipolar mapping and directional catheter technology, the modern lab offers tools that were largely aspirational a decade ago. For clinicians seeking parallel progress in atrial fibrillation, high-power short-duration strategies have followed a similar trajectory toward more efficient, contact-force guided lesion delivery.

Imaging integration and pre-procedural planning

Cardiac MRI with late gadolinium enhancement has become the dominant pre-procedural imaging modality for nonischemic cardiomyopathy VT ablation. Distribution of enhancement in the mid-wall or epicardial layer strongly predicts the location of arrhythmia substrate and informs whether an endocardial, epicardial, or combined approach is appropriate. Centres in Australia have responded by embedding cardiac MRI review into their pre-ablation multidisciplinary meetings, often combining radiology, heart failure, and electrophysiology input in a single session.

When MRI is contraindicated because of renal impairment, device artefacts, or patient intolerance, CT with iodine contrast or intracardiac echocardiography offers alternative anatomical surrogates. Integration of these images with electroanatomical maps allows registration of scar geometry onto the live mapping field. This is particularly useful when targeting low-voltage corridors that may otherwise be missed on voltage mapping alone, or when confirming epicardial involvement suggested by unipolar abnormalities.

The Asia Pacific Heart Rhythm Society, jointly publishing this journal, has fostered cross-regional consensus documents encouraging image integration as a standard of care. Within Australia, adherence to these recommendations varies between metropolitan quaternary centres and regional hubs, but the gradual adoption of cloud-based image sharing is narrowing that gap and improving pre-procedural confidence for operators flying in from satellite outreach sites.

Epicardial access and practical workflows in Australian labs

Epicardial access via the subxiphoid approach remains a critical component of the substrate-based toolkit for nonischemic cardiomyopathy VT. Where endocardial voltage is unremarkable but clinical arrhythmia suggests an epicardial origin, dry taps and pericardial mapping can reveal the full extent of scar. Australian operators have accumulated substantial experience with this technique, and serious complications such as right ventricular puncture, hepatic injury, and coronary laceration remain uncommon in experienced hands.

Pre-procedural coronary angiography or CT is essential to avoid thermal injury to epicardial vessels during ablation. The proximity of the left phrenic nerve and the recurrent laryngeal branch adds further anatomical complexity. Adjunctive strategies including fluid or air inflation, balloon isolation, or simply choosing a different ablation site are deployed routinely to protect adjacent structures.

Distance imposes unique workflow considerations in Australia. Patients referred from Perth, Darwin, or far-north Queensland often arrive with limited prior electrophysiology data, and the procedural team must construct the entire mapping and ablation plan within a single hospital admission. This reality reinforces the value of substrate-based strategies, since reliance on tachycardia induction, which can be time-consuming and unreliable, becomes impractical. Integrated electrophysiology and heart failure clinics in Brisbane and Adelaide have pioneered streamlined admission pathways that combine device interrogation, imaging review, and ablation in one episode of care. For those seeking context on how substrate thinking was originally codified in ischaemic disease, the journal's coverage of post-infarction VT ablation offers a useful point of comparison, even though the anatomical substrate differs.

Outcomes, recurrence, and long-term follow-up

Acute procedural success in nonischemic cardiomyopathy VT ablation, defined as non-inducibility of the clinical arrhythmia at the end of the case, now exceeds 70 percent in most contemporary series. Long-term freedom from ventricular arrhythmia, however, is more variable, with single-procedure freedom from VT recurrence ranging from 50 to 70 percent at three years. Repeat procedures, often performed after a 12-month interval, remain the norm rather than the exception in this challenging population.

Predictors of recurrence include extensive epicardial scar, advanced NYHA class, and the presence of additional non-clinical VTs inducible at the index procedure. The growing use of stereotactic body radiotherapy for refractory VT, available at selected Australian centres, has expanded the therapeutic options when catheter ablation fails and is being investigated in local prospective registries.

Follow-up infrastructure relies heavily on remote monitoring of implantable cardioverter-defibrillators, which is well reimbursed through Australia's Medicare Benefits Schedule. Device-transmitted arrhythmia episodes can be triaged from rural and remote clinics, alerting electrophysiologists in tertiary centres to early recurrence before symptoms develop. This integration of device data, telehealth consultations, and selective re-referral reflects an Australian model of care that may serve as a template for other geographically dispersed populations.

Aboriginal and Torres Strait Islander patients face a higher burden of cardiomyopathy and reduced access to tertiary electrophysiology services. Outreach programs in the Northern Territory and Western Australia, supported by visiting cardiologists and telehealth links, are working to close this gap, and culturally safe education around device therapy and ablation is gaining momentum across primary health networks.

Substrate mapping continues to evolve as imaging, catheter technology, and artificial intelligence converge. The next wave of evidence will clarify whether earlier intervention, before extensive scar develops, alters the natural history of arrhythmia in inherited cardiomyopathies. For now, the technique offers Australian clinicians a reproducible framework to ablate scar that often hides in plain sight.

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