Cardiac MRI in ventricular tachycardia ablation planning

Ventricular tachycardia remains a leading cause of sudden cardiac death in patients with ischaemic and non-ischaemic cardiomyopathies, and recurrent arrhythmia continues to drive hospital admissions, device shocks, and impaired quality of life across the Asia-Pacific region. Although catheter ablation has matured into a cornerstone therapy over the past two decades, recurrence rates after VT ablation in structural heart disease remain frustratingly high in many published series. The introduction of cardiac magnetic resonance as a routine planning tool has begun to reshape how electrophysiology teams approach these complex procedures, shifting some of the decision-making upstream of the catheter laboratory.

By offering high-resolution three-dimensional views of dense scar, border zone, and residual viable myocardium, CMR provides a non-invasive roadmap that complements intraprocedural electroanatomical mapping. For Australian operators balancing metropolitan quaternary workloads with the realities of regional referrals and long patient journeys, integrating CMR into the ablation strategy translates into more focused procedures, fewer repeat hospitalisations, and clearer conversations with patients about likely outcomes. The technology is no longer experimental; it is steadily becoming part of standard workflow in larger Australian centres.

Why pre-procedural substrate visualisation matters

Ventricular tachycardia circuits in structural heart disease typically depend on narrow corridors of surviving myocytes embedded within heterogeneous scar. Endocardial voltage mapping alone can substantially underestimate the true extent of the substrate, particularly when circuits are intramural, epicardial, or located in regions where catheter contact is technically difficult to achieve. A pre-procedural CMR identifies the full thickness and distribution of fibrosis before any catheters enter the heart, allowing the operator to anticipate where critical isthmuses are likely to reside and how best to access them.

This planning step also informs practical decisions such as whether epicardial access is required, whether general anaesthesia or even extracorporeal membrane oxygenation support should be on standby, and how long the procedure is likely to run. For Australian patients who travel from regional centres such as Townsville, Cairns, or Hobart to a tertiary electrophysiology service in Brisbane, Sydney, or Melbourne, a well-prepared single procedure reduces the financial, logistical, and emotional cost of repeat admissions. It also helps align patient expectations with realistic procedural goals, an important consideration in shared decision-making.

CMR sequences that reveal the arrhythmogenic substrate

Late gadolinium enhancement is the workhorse sequence, providing high-contrast images of dense fibrosis that correspond well with low-voltage regions identified during electroanatomical mapping. T1 and T2 mapping add further layers of information by quantifying interstitial expansion and myocardial oedema, which can identify acute inflammatory substrates such as those seen in myocarditis-associated VT or in the early post-infarct period. Feature-tracking strain imaging highlights mechanical dyssynchrony that often colocalises with electrical re-entry circuits and may reveal subtle regions of dysfunction not yet visible on LGE.

More recent work has applied machine-learning algorithms to automatically quantify the border zone, the grey region between dense scar and healthy myocardium where most VT channels reside. In older Australian cohorts where renal function may limit gadolinium use, native T1 mapping offers a contrast-free alternative that still captures interstitial disease. Each sequence adds a small but meaningful piece to the substrate puzzle, and most Australian imaging laboratories with cardiac MRI capability now offer at least LGE and T1 mapping for VT planning studies. The trend is toward standardised protocols that allow reproducible post-processing across sites.

Integrating CMR with electroanatomical mapping

Once the CMR is acquired, the images are segmented and exported as DICOM files into electroanatomical mapping systems such as CARTO, Ensite X, or the Rhythmia platform. Registration algorithms align the pre-procedural anatomy with the real-time electroanatomical map created during the study, allowing the operator to see voltage data overlaid on the scar geometry. This fusion helps distinguish scar that is electrically silent from scar that still conducts, narrowing the ablation target and reducing unnecessary radiofrequency delivery.

Practical challenges remain. Patients with frequent VT often cannot lie flat, tolerate breath-holds, or maintain a stable rhythm during CMR acquisition, leading to motion artefact that degrades image quality. Implanted devices, common in this population, create local signal voids that distort adjacent myocardium, although wideband sequences and device-specific protocols are steadily improving this. At Royal Melbourne Hospital and Westmead in western Sydney, multidisciplinary teams routinely merge CMR with mapping data, and the workflow has become embedded in local protocols endorsed through the Cardiac Society of Australia and New Zealand. Similar pathways are being adopted at other tertiary centres as experience accumulates.

Targeting VT circuits and critical isthmuses

Critical isthmuses for re-entrant VT are usually thin strips of viable myocardium traversing dense scar, often only a few millimetres wide. On CMR, these appear as corridors of intermediate signal intensity bridging regions of late gadolinium enhancement, sometimes described as channels or peninsulas of border zone. When these corridors are registered onto the electroanatomical map, ablation lesions delivered across them interrupt the circuit and reduce inducibility at programmed stimulation. The strategy has shown particular benefit in patients with extensive infarction, where multiple VT morphologies can be abolished by targeting a small number of channels rather than chasing each individual morphology.

The channel-based approach has proven especially valuable in non-ischaemic cardiomyopathies such as arrhythmogenic right ventricular cardiomyopathy and dilated cardiomyopathy, where the substrate is patchy and easily missed by point-by-point mapping alone. Outflow tract and idiopathic VT, by contrast, usually have a normal CMR, and imaging is reserved for ruling out structural disease rather than guiding ablation. For patients with scar-mediated VT, however, the integration of CMR-defined channels with intraprocedural mapping has become a defining feature of contemporary planning.

Clinical outcomes and the evidence base

A growing body of literature supports CMR-guided VT ablation. Meta-analyses of observational series have consistently shown higher freedom from recurrent VT when pre-procedural CMR is incorporated, with reductions in arrhythmia burden that translate into fewer implantable cardioverter defibrillator shocks and shorter hospital stays. Randomised data remain limited, partly because blinding the operator to imaging is impractical and partly because imaging protocols and ablation strategies vary between centres. The balance of evidence nevertheless favours routine CMR in patients with structural heart disease undergoing either a first or redo VT ablation, particularly when the substrate is expected to be complex.

Cost-effectiveness analyses from comparable healthcare systems suggest that the upfront expense of CMR is offset by reductions in redo procedures, hospital days, and long-term device therapy. Within Australia, where the Medicare Benefits Schedule funds cardiac MRI for accepted indications including cardiomyopathy assessment, the marginal cost of adding a planning scan is small relative to the overall ablation admission. The remaining uncertainty around optimal imaging protocols, post-processing standards, and long-term follow-up is an active area of investigation, and registries such as those coordinated through the Asia Pacific Heart Rhythm Society are beginning to provide the kind of multi-centre data needed to refine current practice.

Alongside substrate-based ablation, parallel work on autonomic modulation is reshaping how clinicians think about arrhythmia triggers and recurrence, and several groups are now exploring its role as an adjunct to imaging-guided ablation in patients with refractory VT.

Implementing CMR-guided VT ablation across Australia

Delivering CMR-guided VT ablation at a national scale requires more than scanner availability. Workflows must accommodate outpatient referral, image acquisition with adequate arrhythmia suppression, post-processing, multidisciplinary review, and finally registration into the electrophysiology laboratory. In metropolitan centres such as the Royal Prince Alfred in Sydney, The Prince Charles Hospital in Brisbane, the Royal Melbourne, and Fiona Stanley in Perth, these steps are largely embedded and supported by dedicated cardiac radiologists. In regional and remote areas, access remains uneven, and patients often travel long distances for both imaging and treatment, sometimes crossing state borders to reach the nearest tertiary service.

Telehealth-based heart team meetings have partially bridged this gap, allowing regional cardiologists to present cases to quaternary electrophysiologists and radiologists without the patient leaving home. Indigenous health services in northern Australia have also developed partnership models that coordinate transport, accommodation, and cultural support for patients referred from communities in the Top End and the Kimberley. Embedding CMR planning into these pathways offers a tangible way to reduce procedure-related travel and to ensure that the benefits of contemporary ablation reach beyond the largest cities, supporting more equitable care for Australians living outside the metropolitan footprint.

As CMR continues to influence how VT ablation is planned and delivered, the Journal of Arrhythmia remains a valuable resource for clinicians seeking to stay current with these developments. The journal's combination of original research, themed collections, and society-supported guidelines makes it well suited to translating imaging advances into everyday electrophysiology practice across diverse healthcare settings. For trainees and established electrophysiologists alike, details about submissions, special issues, and society partnerships can be found at the journal's about page, making it straightforward to engage further with the field.