Beyond wall thickness in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a heterogeneous inherited myocardial disorder in which prevention of sudden cardiac death in hypertrophic cardiomyopathy remains a central clinical challenge. Although care has improved, fatal ventricular tachyarrhythmia—including ventricular tachycardia degenerating into ventricular fibrillation—can occur in patients whose conventional markers appear reassuring. Wall thickness, symptoms, ventricular function, arrhythmia burden, myocardial fibrosis and family history each contribute, but none is sufficiently precise alone. The task is to estimate individual risk, identify reversible triggers and match surveillance or device therapy to the patient rather than the disease label.

Left ventricular maximal wall thickness remains an established risk factor, especially when hypertrophy is extensive. Used as a simple threshold, however, it can miss dangerous combinations of moderate hypertrophy and other high-risk features, while provoking premature anxiety in people with marked thickening but no adverse substrate. Risk assessment should combine clinical history, ambulatory electrocardiography, echocardiography, exercise testing and cardiac magnetic resonance, with uncertainty made explicit during shared decision-making.

Why wall thickness alone is insufficient

Wall thickness is readily available from echocardiography and describes phenotypic severity, yet the biological meaning of a millimetre measurement is limited. Septal thickness may be underestimated in some phenotypes, and measurements vary with loading, blood pressure and image quality. Apical hypertrophy can be overlooked when attention focuses on the septum. A 30 mm threshold is not an automatic indication for an implantable cardioverter-defibrillator, and a lower value does not confer reassurance when other markers are concerning.

The same wall thickness can accompany very different prognoses. Unexplained syncope, extensive nonsustained ventricular tachycardia, reduced left ventricular ejection fraction, an apical aneurysm, a large left atrium, conduction disease and a family history of premature sudden death may all increase concern. Conversely, older age, controlled symptoms and a low arrhythmia burden can modify the interpretation of a single finding. Contemporary guideline risk calculators standardise these variables, yet their value depends on the population in which they were derived and on how complete the source data are.

Everyday Australian activities shape how risk appears. A patient may first report presyncope during an AFL match, cricket training, lap swimming, gym work or a bush walk rather than during a clinic walk. Heat, dehydration and abrupt changes in volume status can alter symptoms and haemodynamics. Stimulant-rich energy drinks, pre-workout products and some over-the-counter medicines may provoke palpitations or tachycardia. Exertion-related symptoms demand review, even when an episode occurred in an apparently healthy person, while events at rest or during sleep must not be dismissed.

Building a multidimensional risk profile

The history should begin with the event, not merely the diagnosis. For presyncope or syncope, establish whether exertion was present, whether there was a prodrome, whether injury occurred, and whether a relative died suddenly before age 50. Palpitations, angina, dyspnoea and exercise intolerance may reveal ischaemia, outflow obstruction or arrhythmia. Family screening and genetic counselling can uncover clinically affected relatives; a pathogenic sarcomeric variant strengthens the familial context, while a variant of uncertain significance should not be used alone to predict death.

Investigations should map phenotype and substrate. Twelve-lead electrocardiography identifies conduction and repolarisation abnormalities; echocardiography measures wall thickness and distribution, left ventricular outflow tract gradient, ejection fraction, left atrial size, right ventricular function and apical morphology. Ambulatory monitoring establishes the frequency and complexity of premature ventricular contractions and nonsustained ventricular tachycardia. Exercise testing can reveal ischaemia, an abnormal blood-pressure response or exercise-induced arrhythmia, while cardiac magnetic resonance assesses myocardium and scar. One reassuring ambulatory recording cannot exclude intermittent risk.

Interpretation should be longitudinal. A changing ventricular function, growing scar, persistent ventricular ectopy or new conduction abnormality may matter more than a stable score. International risk calculators can support communication and referral, but they should not override a coherent clinical pattern, particularly in apical disease or where key variables are missing. In Australia, multidisciplinary assessment is concentrated in tertiary services in Sydney, Melbourne and other capitals, so regional clinicians should transfer images and reports early, document the limited pathway and use tele-cardiology where available rather than treating distance as a reason to delay.

Imaging fibrosis and hidden electrical substrate

Late gadolinium enhancement cardiac magnetic resonance provides evidence of replacement fibrosis, which may create an arrhythmogenic substrate capable of sustaining ventricular tachycardia. The presence and extent of LGE, its distribution and associated regional wall abnormalities can refine assessment when conventional markers are equivocal. Extensive fibrosis is increasingly recognised as a risk modifier, but prognostic thresholds are not interchangeable across scanners and protocols, and LGE should not be a stand-alone rule for implanting or excluding a defibrillator.

Imaging must look beyond the most visible scar. Apical aneurysm and outflow-tract fibrosis may be missed without dedicated views; right ventricular insertion-point fibrosis can be relevant in advanced hypertrophy. T1 and T2 mapping may add information about diffuse disease, and coronary imaging can clarify suspected ischaemia when symptoms warrant it. Electrophysiology studies can identify inducible ventricular arrhythmias in selected patients, although their routine predictive value remains limited. Even a negative magnetic resonance scan cannot exclude genetically mediated electrical instability.

Practical interpretation depends on quality and access. HCM protocols require accurate wall-thickness measurement, contrast timing and ventricular coverage, so an abbreviated scan may understate disease. Metropolitan hospitals generally offer advanced imaging, while patients in regional and remote Australia may need travel, sometimes with substantial costs and delays. Shared protocols, structured image transfer and remote review can reduce variation. Recording whether a scan was technically adequate, and which sequences were acquired, allows later clinicians to judge the strength of the conclusion.

Prevention devices and shared decisions

Risk assessment becomes actionable through prevention. Beta-blockers are commonly used for angina, dyspnoea and ventricular ectopy, with treatment individualised to haemodynamics. Verapamil or diltiazem may help selected patients with preserved systolic function and mild obstruction, but can be harmful in severe left ventricular outflow obstruction or systolic dysfunction. Rhythm-control drugs and anticoagulation require specialist review; atrial fibrillation in HCM increases heart-failure and embolic risk, and anticoagulation decisions require an appropriate stroke-risk assessment rather than rhythm diagnosis alone.

For sudden-death prevention, an implantable cardioverter-defibrillator may be considered when estimated risk is high and meaningful survival time is expected. Implantation is difficult to justify solely because wall thickness crosses a threshold. Counselling should cover shocks, device infection, lead complications, replacement procedures, anxiety and future lead or generator changes. Selected patients may be considered for a wearable cardioverter-defibrillator as a temporary bridge, but it is not a permanent substitute for an implanted device. The Australian Therapeutic Goods Administration regulates these products, and local follow-up capacity should be discussed before implantation.

Atrial fibrillation adds another layer of management because HCM can limit cardiac reserve and reduce output during tachycardia. When ablation is considered, prior surgery, ventricular hypertrophy and altered anatomy can complicate mapping and anticoagulation planning. Although the journal's prior surgery ablation considerations focus on a broader post-surgical population, their perioperative and electrophysiological principles are useful when HCM teams coordinate surgical and rhythm-control care. Local anaesthetic, anticoagulation and surgical pathways should be planned together.

Once a plan is chosen, consistency matters. Review beta-blocker dose and adherence, eliminate unnecessary stimulants, assess hydration during hot weather, and establish safe exercise limits through shared decision-making. High-intensity or competitive activity generally requires specialist assessment before participation; low-intensity recreation may be appropriate after review. Families should receive written instructions for emergency care, including calling 000, recognising sudden collapse and locating an automated external defibrillator at sporting clubs, gyms and community venues. Remote monitoring can support early detection of arrhythmia or device problems, provided alerts have an assigned clinical response.

Australian practice and research priorities

Access shapes prevention in Australia. Medicare rebates help with GP and specialist consultations and many diagnostic investigations, while the Pharmaceutical Benefits Scheme covers many relevant medicines, although out-of-pocket costs remain for some families. Community pharmacies can support titration and adherence checks, yet treatment decisions still belong within specialist HCM care. Practice nurses, remote monitoring and tele-cardiology can extend follow-up beyond major cities, but emergency and device services remain unevenly distributed. Local pathways should identify a named cardiologist, an escalation plan and a route to advanced imaging.

Genetic information adds ethical and legal responsibilities. Under the Privacy Act 1988 and the Australian Privacy Principles, consent and data governance matter when HCM results, family histories and genomic information are stored or shared with relatives and researchers. Genetic counselling should separate diagnostic testing, predictive testing and family screening, explain uncertain findings, and discuss implications for insurance and employment without discouraging appropriate care. Digital referral systems should use secure transfer, minimum necessary access and clear consent when reports move between regional clinics and metropolitan centres.

Research priorities include representative Australian cohorts, sex-specific analyses, long-term scar evolution, apical phenotypes and outcomes after contemporary device therapy. Registries should record background, medications, exercise exposure, ambulatory arrhythmia, imaging quality and device complications rather than wall thickness alone. The Journal of Arrhythmia offers open access to original research, reviews, clinical guidance and themed collections, providing a route for clinicians and trainees to update practice and for investigators to submit work addressing these gaps. Better multicentre data can make risk pathways more accurate and equitable.

Clinicians can act immediately by treating each HCM assessment as a combined risk review. Document wall thickness and distribution, symptoms and family history, ambulatory arrhythmia, ventricular function, outflow obstruction and cardiac magnetic resonance findings; state which data are missing and how they will be resolved. Patients should leave with a clear medication plan, exercise advice, device rationale if relevant, and written instructions for emergencies and family screening.

Families can use that written plan to support timely care, while researchers can contribute standardised, longitudinal data to the evidence base. Read current guidance, share difficult cases with specialist colleagues and support publication of multicentre studies: every additional well-characterised patient helps distinguish a high-risk phenotype from a misleading wall-thickness measurement and moves prevention closer to the individual.