Diving deeper: Essential role of advanced ventricular tachycardia ablation techniques in hypertrophic cardiomyopathy

It is well described that ventricular tachycardia (VT) ablation in those with non-ischemic cardiomyopathy (NICM) tend to be more complex and have worse outcomes than those with ischemic cardiomyopathy. The culprit? The presence of heterogenous scar distribution often involving epicardial and midmyocardial regions, demanding the use of advanced ablation techniques to achieve success. While areas such as the LV basal annulus, periaortic region, and septum are often implicated as critical sites for VT in those with NICM, we also know that the etiology influences the underlying substrate. Indeed, as compared to arrhythmogenic right ventricular dysplasia, myocarditis, and dilated cardiomyopathy, those with hypertrophic cardiomyopathy are often more difficult and associated with poor outcomes following VT ablation [1]. Therefore, further understanding of the underlying HCM substrate may lead to improved ablation outcomes.

With that background, Subramanian et al. report short and long-term outcomes of 14 patients with hypertrophic cardiomyopathy undergoing catheter ablation for VT from a single institution between 2012 and 2023 [2]. The mean age of the cohort was relatively young (48 years), 86 % male, mean ejection fraction of 42 %, 35 % had LV obstruction, 29 % had a left ventricular apical aneurysm, and mean maximal left ventricular thickness was 20.2 mm. All patients were on prior antiarrhythmic drug. Cardiac magnetic resonance imaging (CMR) was obtained in 10/14 patients with all 10 demonstrating extensive late gadolinium enhancement, including within interventricular septum (n = 7), lateral wall (n = 5), anterior wall (n = 4), and apical segments (n = 4). Eleven (79 %) demonstrated scar-related VT, 3 (21 %) had bundle-branch reentrant VT (BBRVT), and half of the patients required epicardial ablation. At a mean follow-up of 28 months (±5 months), VT recurrence was observed in slightly over a third of the patients and two required repeat VT ablation.

Subramanian et al. should be congratulated on this important addition to the limited literature on outcomes of VT ablation in those with HCM. Although only 14 patients were included, these findings emphasize four important key factors in managing and performing VT ablation in this challenging cohort. 1.) Scar-related or re-entry is the most common mechanism of VT in those with HCM. As re-entry typical involves area of scar and conduction delays, pre-procedural planning with CT or CMR becomes valuable in identifying targeted areas. Mapping techniques including bipolar and unipolar voltage mapping, pace-match mapping, and activation mapping all can serve a purpose in identifying critical substrates. Newer techniques utilizing high-definition mapping catheters, particularly strategic activation mapping for even a brief period or isochronal late activation mapping during sinus or paced-rhythm may improve the success and efficiency of targeted ablation of the functional substrate [3]. 2.) The authors report BBRVT as the mechanism in VT in nearly a quarter of the patients. Commonly observed in those with His-Purkinje disease and prior aortic valve replacements, myotonic dystrophy, or non-ischemic dilated cardiomyopathy, those afflicted become susceptible to this potentially fatal arrhythmia [4]. This finding alone supports the required use of dedicated catheter to either sense a His or right bundle potential during VT induction. 3.) Those with HCM and concomitant LV aneurysm are not only at higher mortality risk and progressive heart failure but are also at risk of VT arising from the border zone or within the aneurysm [5]. Exclusion of LV apical thrombus prior to ablation and caution with catheter manipulation and ablation at the thinned apical myocardium should be encouraged. These areas are particularly challenging, where multiple procedures are often required, and an endocardial-only approach often leads to failure. This leads to the last key point. 4.) Those with HCM have a high prevalence of epicardial VT. Due to the epicardial and midmyocardial scar within this population, epicardial mapping and ablation is often required. In this cohort, the epicardium was identified as the critical site in half of the patients with epicardial mapping performed in 11/14 patients, a similar experience to a previously reported cohort of patients with HCM undergoing VT ablation [6]. Taken together, this finding suggests that VT ablation of those with HCM should only be done experienced centers with epicardial access and mapping expertise. Given the improved safety of epicardial access specifically with the use of a long micropuncture needle, these along with prior published experiences should strongly lower the threshold for upfront epicardial access [7].

VT ablation in those with HCM is undoubtedly challenging, although a significant reduction in VT recurrence can be achieved by experienced operators as shown in the present study. Still, these outcomes have largely remained similar in the past decade. In a recent meta-analysis of 68 patients with drug-refractory VT and HCM, long-term follow-up of an average 1.5 years, freedom from VT was achieved in 70 % of patients [8]. The use of advanced ablation techniques including high-resolution mapping catheters, epicardial ablation, bipolar ablation, needle catheter ablation, ethanol ablation, or remote magnetic catheter navigation for difficult to reach areas, along with mechanical circulatory support, should strongly be considered in most patients [[9], [10], [11], [12], [13]]. Additionally, exclusion of BBRVT should also be required to successfully treat and may even avoid an unnecessarily higher risk procedure. Given the complexity, the findings in the current study will not be generalizable to institutions who lack this experience. Next, integration of advanced imaging pre-procedurally to target substrate, including CMR or high-resolution cardiac computed tomography, may improve procedural efficiency and efficacy [14,15]. Pre-procedural VT localization can further be streamlined by the use of non-invasive 3D imaging systems using a standard 12-lead ECG and CMR, such as Vivo [16]. Overlap of etiologies should not be ignored. For example, use of CMR and cardiac positron emission tomography to evaluate for concomitant sarcoidosis or myocarditis should strongly be encouraged as immunosuppressive therapy may slow the progression of scar formation and reduce ventricular arrhythmias [17]. Although VT ablation can safely and effectively be performed in those with HCM, we must remember that these patients often suffer from end-stage heart failure. While ablation undoubtedly improves quality of life and reduces VT recurrence, a multidisciplinary team approach with advanced heart failure care for this relatively young population should simultaneously be ongoing to best improve outcomes. Bringing together expertise, advanced techniques, and thorough care sets a promising path in the evolving landscape of managing HCM.