Preventing Sudden Cardiac Death in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is the most common inherited cardiac disorder, affecting roughly one in every 500 adults. While many people live their entire lives without symptoms, a small but tragic fraction experience sudden cardiac death, often as the first clinical manifestation of the disease. The unpredictable nature of these events has driven decades of research into identifying at-risk individuals and protecting them before tragedy strikes.

Over the past three decades, the implantable cardioverter-defibrillator has emerged as the only therapy proven to abort lethal ventricular arrhythmias and prolong life in hypertrophic cardiomyopathy. Its ability to detect and terminate ventricular tachycardia or fibrillation within seconds has transformed the outlook for high-risk patients. Yet implanting a device also carries costs: lifelong complications, psychological burden, and decisions about driving, sport, and employment.

For clinicians in Australia and across the Asia-Pacific region, the practical challenge is selecting the right patient for the right therapy at the right time. This review summarises current evidence on sudden cardiac death risk stratification, examines the role of cardiac defibrillators in primary and secondary prevention, and discusses how Australian guidelines, registries, and access pathways shape real-world care.

Hypertrophic cardiomyopathy and the burden of sudden cardiac death

Hypertrophic cardiomyopathy is characterised by unexplained left ventricular hypertrophy, myocyte disarray, and interstitial fibrosis, all of which create a substrate for malignant ventricular arrhythmias. The annual incidence of sudden cardiac death in unselected HCM cohorts is around 0.5 to 1 percent, but rises sharply in the presence of established risk markers. Autopsy series from Australian forensic institutes have repeatedly identified HCM as one of the leading structural causes of unexpected death in young adults, particularly among athletes and first responders.

The tragedy of a sudden collapse during sport, often broadcast widely on television, has shaped public perception of the disease. Beyond high-profile cases, however, sudden cardiac death occurs across the lifespan, including in middle-aged adults whose diagnosis was previously unknown. Population studies from Melbourne and Perth suggest that more than half of HCM-related deaths occur in individuals outside the highest-risk profile groups, underscoring the limitations of any single risk factor.

The cost of these events extends beyond the individual. Families, workplaces, and communities bear the long shadow of a preventable death. This reality has motivated aggressive screening programmes, including pre-participation electrocardiogram screening advocated by some sporting bodies in New South Wales and Victoria, although the cost-effectiveness of such programmes remains debated. Identifying those at highest risk remains the central goal of contemporary HCM management.

Risk stratification models and their application

The 2014 European Society of Cardiology risk calculator and the more recent 2022 American Heart Association and American College of Cardiology guidelines provide the dominant frameworks for estimating five-year sudden cardiac death risk. Variables include maximal wall thickness, left atrial size, family history of sudden death, non-sustained ventricular tachycardia on ambulatory monitoring, unexplained syncope, and apical aneurysm. Each carries different weight, and subtle shifts in any variable can move a patient across the threshold for intervention.

Magnetic resonance imaging with late gadolinium enhancement has added powerful prognostic information. Extensive fibrosis, involving more than 15 percent of left ventricular mass, has been associated with a doubling of sudden cardiac death risk independent of conventional markers. Australian imaging centres in Sydney, Brisbane, and Adelaide routinely incorporate cardiac MRI into risk assessment, although access in rural and remote regions remains uneven.

Cardiac myosin inhibitors such as mavacamten have recently entered Australian practice through the Pharmaceutical Benefits Scheme, offering a disease-modifying option for symptomatic obstructive disease. While their primary endpoint is symptom and gradient reduction, long-term registries will need to evaluate whether reducing hypertrophy also translates into lower arrhythmic mortality. For now, the risk calculator, augmented by imaging biomarkers, remains the cornerstone of decision-making.

How the implantable cardioverter-defibrillator saves lives

The implantable cardioverter-defibrillator continuously monitors cardiac rhythm and delivers tiered therapy: antitachycardia pacing for slower ventricular tachycardias, followed by shock therapy for faster or disorganised rhythms. In hypertrophic cardiomyopathy, the predominant arrhythmia at the time of sudden cardiac death is ventricular fibrillation, often degenerating from rapid monomorphic ventricular tachycardia. Devices typically terminate such events within 10 to 15 seconds, restoring sinus rhythm before irreversible organ damage occurs.

Long-term outcome data are reassuring. Pooled cohort studies report appropriate intervention rates of 4 to 5 percent per year in primary prevention and 10 to 12 percent per year in secondary prevention, figures substantially higher than in ischaemic cardiomyopathy. Conversely, inappropriate shocks occur in around 3 to 4 percent of patients annually, driven largely by atrial fibrillation with rapid ventricular response, lead noise, or T-wave oversensing. Modern programming strategies, including longer detection windows and morphology discrimination, have substantially reduced these numbers.

The procedure is well established in Australian centres. Cardiologists at the Royal Melbourne Hospital, Westmead Hospital, and the Prince Charles Hospital in Brisbane have published extensive experience with transvenous and, increasingly, subcutaneous systems. For younger patients with HCM, who may require decades of device therapy, the choice between transvenous and extravascular approaches is a topic of active investigation.

Patient selection in contemporary practice

Selecting patients for implantation requires balancing absolute risk against the lifetime burden of device therapy. Current consensus recommends an ICD when the estimated five-year sudden cardiac death risk exceeds 6 percent, with consideration of patient age, comorbidities, and preferences. In those with prior ventricular arrhythmia or cardiac arrest, secondary prevention implantation is almost universal unless life expectancy is severely limited by another condition.

Shared decision-making has become the standard of care. Patients should understand that the device does not prevent arrhythmias but terminates them, that shocks may be uncomfortable, and that driving restrictions apply for periods ranging from weeks to several months following an intervention. Discussions led by heart rhythm nurses and genetic counsellors, often coordinated through specialised clinics, support informed choices and improve adherence to follow-up.

A growing recognition of genotype-positive, phenotype-negative individuals is reshaping these conversations. Carriers of pathogenic sarcomere mutations without overt hypertrophy face a low absolute risk of sudden cardiac death, and routine implantation is not currently justified. Emerging data on subtle imaging phenotypes and blood biomarkers may refine this position in coming years.

Long-term outcomes, complications, and quality of life

Survival benefit is the most important outcome, but it is not the only one. Device-related complications accumulate over time, particularly in younger recipients. Lead failure, infection, venous occlusion, and the need for reoperation affect a meaningful proportion of patients followed for more than a decade. Australian registries, including those supported by the Cardiac Society of Australia and New Zealand, have documented complication rates broadly consistent with international experience.

Psychological outcomes deserve attention. Anxiety, depression, and post-traumatic stress can follow appropriate or inappropriate shocks, and rates of driving cessation contribute to loss of independence, particularly for those in regional areas without alternative transport. Cardiac rehabilitation programmes adapted for ICD recipients, such as those offered through the Baker Institute in Melbourne, integrate exercise prescription with psychological support.

Atrial fibrillation is the most common sustained arrhythmia in HCM, occurring in more than 20 percent of patients over a lifetime. Management often requires collaboration between ablation specialists and device implanters, particularly when atrial arrhythmia triggers inappropriate shocks. Practical resources on cavotricuspid isthmus ablation and atrial tachycardia mapping provide useful procedural guidance for electrophysiologists managing these complex substrates in HCM patients with coexisting devices.

Special considerations for Australian patients and equity of access

Geography shapes the experience of HCM care in Australia. Although tertiary electrophysiology centres in Melbourne, Sydney, Perth, and Brisbane provide comprehensive device implantation and follow-up, patients in the Northern Territory, Far North Queensland, and parts of Western Australia often travel thousands of kilometres for routine checks. Telemedicine-enabled remote monitoring, supported by Medicare rebates since 2018, has narrowed this gap but has not eliminated it. First Nations Australians also face disparities in cardiovascular outcomes, a concern now prioritised in national heart disease strategies.

Reimbursement pathways influence device choice. Private health insurers cover the majority of defibrillator implantations, while public hospital systems provide access for uninsured patients through state-funded programmes. The cost of newer extravascular devices, which may reduce long-term lead complications, remains higher than conventional transvenous systems, and equity of access is an ongoing point of discussion among clinicians and policy makers.

Climate, sport, and culture intersect with HCM management in distinctive ways. Australia's passion for competitive swimming, surf lifesaving, and community football means that screening, restriction, and return-to-play decisions carry particular weight. National guidelines from the National Heart Foundation of Australia and Sport Australia provide a framework, but local interpretation remains a clinical and ethical responsibility for treating physicians.

The evidence supporting defibrillator therapy in hypertrophic cardiomyopathy is stronger than for almost any other inherited arrhythmia syndrome. Readers interested in contributing original research, case series, or thematic reviews on this and related electrophysiology topics are invited to consult the for-authors page for submission requirements, editorial scope, and the journal's commitment to rigorous, timely peer review.