Arrhythmia outcomes following alcohol septal ablation for HOCM

Hypertrophic obstructive cardiomyopathy remains one of the more demanding conditions encountered in adult cardiology practice. When symptoms persist despite optimal medical therapy, alcohol septal ablation has become an established percutaneous alternative to surgical myectomy, particularly for patients deemed at higher operative risk. As uptake of the procedure has grown across Australian tertiary centres, careful attention has turned to the rhythm complications that accompany the technique, both in the immediate post-procedural period and over years of follow-up.

Cardiologists in Sydney, Melbourne, Brisbane, and Perth now manage sizeable cohorts of patients who have undergone the procedure, and Australian electrophysiology labs have contributed meaningfully to the international literature on arrhythmic sequelae. Understanding these outcomes is essential for counselling, surveillance, and shared decision-making between operators, general cardiologists, and patients.

Procedure background and Australian practice patterns

Alcohol septal ablation was first described in the mid-1990s and has since been adopted by most large Australian cardiology services with a structural heart and adult congenital disease program. The technique involves selective catheterisation of a septal perforator branch of the left anterior descending artery, followed by slow injection of absolute ethanol to create a localised infarction within the basal septum. The resulting scar thins the bulging septum and reduces the dynamic left ventricular outflow tract gradient.

Australian practice has generally aligned with European and North American consensus documents, modified locally by the availability of cardiac surgical backup and by case-volume considerations in regional centres. Major metropolitan hospitals such as Royal Prince Alfred in Sydney, The Royal Melbourne, and The Prince Charles in Brisbane perform the procedure regularly, while smaller centres typically refer complex cases outward. Patient selection follows the standard criteria: symptomatic obstructive hypertrophic cardiomyopathy with a resting or provocable gradient of 50 mmHg or greater, refractory to beta-blockade, verapamil, or disopyramide, and with anatomy suitable for selective targeting of the perforator supplying the area of systolic anterior motion contact.

The procedural endpoint is a significant reduction in gradient, ideally with symptomatic improvement. Echocardiographic guidance, often with intracoronary myocardial contrast, helps confirm that the correct territory is being targeted and minimises collateral necrosis of remote myocardium. Both transthoracic and transoesophageal echocardiography are routinely used in Australian catheter labs for this purpose, with cardiology advanced trainees frequently rotating through these procedures as part of their interventional exposure.

Acute conduction disturbances and pacemaker dependency

The most predictable arrhythmic consequence of alcohol septal ablation is injury to the conduction system. Because the targeted septal territory frequently encompasses branches of the right bundle and the left posterior fascicle, conduction abnormalities are expected rather than incidental. Transient or persistent complete atrioventricular block occurs in a substantial minority of patients, and historically between 7 and 20 per cent of those treated have required permanent pacemaker implantation during the index admission.

Right bundle branch block develops in the majority of patients, while new left bundle branch block is less common but clinically significant when it occurs, particularly in those with pre-existing right bundle branch block who then become pacemaker dependent. Temporary pacing wires are routinely placed during the procedure in Australian labs and are typically left in situ for 24 to 48 hours, with a low threshold for upgrading to permanent systems if high-grade conduction disease persists beyond this window.

Operators at high-volume Australian centres have refined their techniques to reduce the territory of infarction and the consequent conduction injury, using smaller ethanol volumes and more selective cannulation. A non-trivial rate of pacemaker implantation persists despite these refinements, and patients should be counselled accordingly. The decision to implant is influenced by the local availability of device follow-up, particularly for patients living in rural and remote communities where access to a pacemaker clinic may involve long travel and where remote monitoring technologies have become increasingly important.

Long-term ventricular arrhythmia risk and the procedural scar

Beyond the immediate post-procedural window, there is ongoing interest in the long-term arrhythmogenic potential of the iatrogenic septal scar. Because ventricular tachyarrhythmia is a recognised mechanism of sudden cardiac death in hypertrophic cardiomyopathy generally, any intervention that adds scar to a substrate already prone to arrhythmia deserves careful scrutiny. Late ventricular tachycardia and ventricular fibrillation have been documented after alcohol septal ablation, with the scar border zone implicated as the likely re-entry substrate.

Registry data and meta-analyses have produced somewhat inconsistent estimates, partly because of heterogeneous patient populations and differing definitions of arrhythmic endpoints. Some series suggest a small absolute increase in ventricular arrhythmia risk compared with surgical myectomy, while others show equivalent long-term rates when matched for baseline risk. Australian electrophysiologists have generally adopted a pragmatic approach, recognising the small but real late risk and integrating it into individualised sudden cardiac death risk stratification using the conventional HCM risk calculator alongside procedural factors.

For patients deemed at elevated risk, prophylactic implantation of a cardioverter-defibrillator may be considered independently of the ablation itself. Where uncertainty exists about the contribution of the ablation scar to overall risk, cardiac MRI with late gadolinium enhancement can help quantify the burden of fibrosis, although interpretation in the post-ablation population requires familiarity with expected appearances to avoid over- or under-calling scar. Researchers interested in contributing original data or review articles on this evolving area may consult the journal's author guidelines when preparing submissions.

Atrial fibrillation and supraventricular arrhythmias

Atrial arrhythmias are common in hypertrophic cardiomyopathy regardless of treatment strategy, reflecting diastolic dysfunction, left atrial enlargement, and underlying myocyte disarray. Alcohol septal ablation can influence atrial arrhythmia burden through several mechanisms. Reduction in outflow obstruction and improvement in diastolic function may lower left atrial pressures and reduce atrial stretch, while conversely the procedural insult and pericardial inflammation can transiently provoke atrial fibrillation in the early recovery phase.

Reported new-onset atrial fibrillation rates in the first month after the procedure range from 5 to 15 per cent across published series. Longer term, atrial fibrillation remains a frequent comorbidity, and many Australian patients who have undergone the procedure are eventually managed with anticoagulation and rate or rhythm control according to standard Heart Rhythm Society and Cardiac Society of Australia and New Zealand recommendations. Pulmonary vein isolation is offered in selected patients at high-volume Australian electrophysiology centres when atrial fibrillation becomes symptomatic and refractory, with outcomes broadly comparable to those seen in non-ischaemic substrates.

Both amiodarone and sotalol are used in the Australian setting, with consideration given to the longer half-life of amiodarone, thyroid and hepatic surveillance requirements, and the QT-prolonging effects of sotalol. Drug therapy is increasingly complemented by catheter ablation as first-line strategy in selected cases, reflecting the maturation of Australian atrial fibrillation ablation programmes over the past decade. Direct oral anticoagulants, listed on the Pharmaceutical Benefits Scheme, are the usual choice for stroke prevention in this group.

Risk stratification, follow-up, and comparison with surgical myectomy

Pre-procedural risk assessment in 2025 increasingly incorporates cardiac MRI, genetic testing results, and ambulatory rhythm monitoring alongside standard echocardiographic parameters. After the procedure, Australian centres typically schedule clinical review at one month with an ECG and echocardiogram, then at six months, and annually thereafter, with implantable loop recorders used selectively in patients with palpitations or unexplained syncope. Device interrogation and remote monitoring are routinely offered to patients with pacemakers and defibrillators, and access to these services is supported by Medicare funding for device checks.

Comparison with surgical septal myectomy remains central to patient counselling. Myectomy is associated with a lower rate of permanent pacemaker implantation and, in many series, a lower long-term burden of ventricular tachycardia, while alcohol septal ablation offers a less invasive route with shorter recovery. Australian practice increasingly individualises the choice on the basis of anatomy, age, comorbidity, patient preference, and surgeon or operator experience. Patients with extensive septal hypertrophy, concomitant cardiac surgical needs, or marked right ventricular involvement may be steered toward myectomy, while older patients with suitable anatomy and higher surgical risk are commonly directed to alcohol septal ablation.

Ongoing ANZ and international collaboration continues to refine the evidence base. Clinicians managing these complex patients should ensure arrhythmia surveillance is embedded in long-term care plans, with clear pathways for device follow-up, anticoagulation review, and access to specialist electrophysiology input when symptoms recur or new rhythm disturbances emerge.

Share your research, contribute invited reviews, and engage with the international arrhythmia community through the journal's open-access platform. For questions regarding submissions, letters to the editor, or general editorial matters, please contact the editorial office directly.