Obstructive HCM: the rise of new septal ablation techniques

LVOT obstruction in HCM: towards a new interventional paradigm

Hypertrophic obstructive cardiomyopathy (HOCM), with an estimated prevalence of 0.5% in the general population, presents the practitioner with a complex equation: relieving left ventricular outflow tract (LVOT) obstruction while minimising therapeutic morbidity. Although surgical septal myectomy (SSM) and alcohol septal ablation (ASA) are the pillars of septal reduction therapy (SRT), their limitations are well-documented: major invasiveness for SSM and risks of permanent conduction blocks for ASA, the latter also showing efficacy variability related to coronary anatomical heterogeneity.

This review synthesises recent advances in emerging image-guided interventional techniques for the treatment of HCM. The objective is to evaluate the feasibility and clinical outcomes of new modalities such as endocardial radiofrequency ablation (PESA) or intramyocardial radiofrequency ablation (PIMSRA), stereotactic body radiotherapy (SBRT), and technologies in the validation phase such as pulsed field ablation (PFA).

The central hypothesis of this work suggests that these minimally invasive approaches can match the hemodynamic efficacy of conventional methods while significantly reducing complications, particularly conduction system injuries and risks associated with extracorporeal circulation. This analysis explores whether these innovations can transform the management of refractory patients, especially those deemed ineligible for gold-standard treatments.

Methodological approach and data sources

This summary review compiles the results of several clinical and experimental studies on the treatment of obstructive hypertrophic cardiomyopathy (HCM). The authors rely on a multi-level data structure to evaluate the efficacy of septal interventions:

• Large-scale analysis: A meta-analysis including 15,968 patients was used to compare the 5-year outcomes of surgical septal myectomy (SSM) versus alcohol septal ablation (ASA).
• Clinical follow-up studies: The evaluation of percutaneous intramyocardial septal radiofrequency ablation (PIMSRA) is based on a cohort of 27 patients followed over a 5-year period to measure the stability of hemodynamic results.
• Interventional protocols and gradient measurements: Reported data include precise measurements of the left ventricular outflow tract gradient (LVOTG). For example, the TA-BSM technique (beating-heart septal myectomy) was evaluated on its ability to reduce the LVOTG from 86 mmHg to 19 mmHg, while stereotactic body radiation therapy (SBRT) showed a reduction from 88 mmHg to 52 mmHg.
• Preclinical models: The efficacy of transcoronary radiofrequency ablation (TCRFA) was initially validated in a canine model, demonstrating a reduction in LVOTG of more than 50%.

The primary analysis criteria focus on the reduction of septal thickness, improvement in NYHA classification, and the rate of major complications, such as complete atrioventricular block requiring permanent pacemaker implantation.

Comparative analysis of the performance of septal reduction therapies (SRT)

This synthesis of clinical and experimental data evaluates the efficacy of traditional interventions versus emerging technologies for the treatment of obstructive hypertrophic cardiomyopathy (HCM).

Clinical efficacy and safety profiles

The results highlight a diversification of options for patients presenting a resting or provoked gradient ≥50 mmHg. Percutaneous intramyocardial septal radiofrequency ablation (PIMSRA) stands out with a significantly lower permanent pacemaker implantation rate compared to ASA, thanks to the bypassing of the conduction bundle.

• Transcoronary radiofrequency ablation (TCRFA): Canine models show a reduction in LVOTG >50% without rhythmic complications, an efficacy judged comparable in the first human trials.
• PESA: Although reducing LVOTG, this technique reports higher complication rates in small samples, with a risk of transient exacerbation of obstruction due to post-ablation oedema.
• Mavacamten: This first-in-class cardiac myosin inhibitor demonstrates a reduction in symptomatic burden and dependence on invasive SRT procedures.

Sur le plan chirurgical, la myectomie septale transapicale à cœur battant (TA-BSM) permet une réduction drastique du gradient (de 86 à 19 mmHg) sous guidage échocardiographique continu, bien qu'elle exige une courbe d'apprentissage technique élevée pour l'opérateur.

Analysis of New Frontiers in Septal Reduction

The data reported in this review highlight a major transition in the management of obstructive HCM: the shift from invasive surgery (SSM) toward increasingly precise image-guided interventions. Clinically, the rise of PIMSRA (percutaneous intramyocardial septal radiofrequency ablation) is particularly notable. By bypassing the conduction bundles, this technique significantly reduces the need for permanent pacemakers compared to ASA, while maintaining a durable reduction in the left ventricular outflow tract gradient (LVOTG) and septal thickness at 5 years.

However, this study highlights significant structural limitations. Most new techniques, such as PESA or TCRFA, suffer from a lack of standardized protocols and limited sample sizes. For instance, the long-term follow-up for PIMSRA is based on a cohort of only 27 patients. Furthermore, innovative approaches like SBRT (radiotherapy) raise concerns regarding late radiation-induced fibrosis and arrhythmogenic risk, limiting their current use to inoperable patients.

While SSM remains the gold standard for hemodynamic improvement of pressure gradients, the heterogeneity of coronary anatomy directly impacts the efficacy of ASA, which presents a higher reintervention rate. The emergence of cardiac myosin inhibitors, such as mavacamten, is also redefining the timing of intervention by reducing the initial dependence on invasive septal reduction.

Summary of clinical results

This analysis highlights an equivalent 5-year survival rate between surgical myectomy and alcohol ablation (n=15,968 patients), despite a more pronounced inter-individual efficacy variability for the latter. Innovations such as TA-BSM (gradient reduction from 86 to 19 mmHg) and PIMSRA are emerging as promising alternatives, with PIMSRA offering increased safety for the conduction system. However, vigilance is required with PESA: acute post-ablation septal edema can transiently worsen the outflow tract obstruction.

In concrete terms, for the practitioner:

• Electrical safety: Prioritize PIMSRA in patients at high risk of heart block, as its precision preserves conduction bundles better than alcohol ablation.
• Post-ablation follow-up: Closely monitor the LVOT gradient immediately after PESA to identify any paradoxical obstructive exacerbation related to acute tissue inflammation.
• Pre-operative strategy: Consider the introduction of mavacamten to reduce dependence on invasive interventions in your refractory symptomatic patients.

Technical Lexicon of the Study

SAM (Systolic Anterior Motion): Systolic anterior motion of the anterior mitral leaflet, a key mechanism of left ventricular outflow tract (LVOT) obstruction in hypertrophic cardiomyopathy (HCM).

ASA (Alcohol Septal Ablation): Technique consisting of inducing a controlled septal infarction by infusing ethanol into a septal perforating artery in order to reduce obstructive hypertrophy.

PESA (Percutaneous Endocardial Septal Radiofrequency Ablation): Endocardial radiofrequency ablation performed via a transcatheter approach under 3D electroanatomical mapping guidance and intracardiac echocardiography.

PIMSRA (Percutaneous Intramyocardial Septal Radiofrequency Ablation): Procedure involving the insertion of a radiofrequency needle via a transapical approach under echocardiographic guidance for the direct ablation of hypertrophic myocardium.

SBRT (Stereotactic Body Radiotherapy): Stereotactic body radiotherapy delivering high doses of radiation to the septum via image-guided linear accelerators for inoperable patients.

SESAME (Septal scoring along the midline endocardium): Transcatheter electrosurgical technique mimicking surgical myotomy to facilitate valve implantation or relieve LVOT obstruction.

PFA (Pulsed Field Ablation): Ablation technology using microsecond electrical pulses to induce apoptosis of cardiomyocytes while preserving the extracellular matrix and conduction tissues.

TA-BSM (Transapical Beating-Heart Septal Myectomy): Septal myectomy performed on a beating heart via a transapical approach, without extracorporeal circulation, allowing for real-time hemodynamic assessment.

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