Programmed ventricular stimulation in Brugada syndrome risk assessment

Brugada syndrome remains one of the more puzzling entities encountered in cardiac electrophysiology practice across Asia-Pacific referral centres, including those based in Sydney and Melbourne. The inherited sodium channelopathy can produce sudden cardiac death in otherwise healthy adults, yet many gene carriers never experience an arrhythmic event during a normal lifespan. That wide phenotypic gulf separating the asymptomatic carrier from the victim of nocturnal ventricular fibrillation drives the relentless search for reliable markers of individual susceptibility.

Programmed ventricular stimulation has occupied centre stage in this debate for more than two decades. By delivering carefully timed premature extrastimuli from the right ventricular apex and outflow tract, the technique attempts to provoke polymorphic VT or VF in the electrophysiology laboratory, with the assumption that inducibility translates into future spontaneous arrhythmic events. Australian electrophysiologists at institutions such as Royal Prince Alfred Hospital and the Alfred in Melbourne have long performed the protocol, sometimes booking it as a day-case procedure alongside ajmaline challenge testing.

Yet the prognostic weight of an inducible study remains fiercely contested. Meta-analyses disagree, guideline recommendations diverge between continents, and a single positive or negative result rarely settles management for an individual referred from a regional Queensland clinic or a Perth outreach service. Understanding where programmed stimulation genuinely adds value — and where it merely clouds decision-making — is now essential before committing a patient to an implantable defibrillator.

The genetic substrate and variable expressivity

Loss-of-function variants in SCN5A account for roughly a fifth of confirmed families, with additional contributions from GPD1L, SCN1B, CACNA1C, and a growing list of minor genes catalogued by Australian genetics services and international consortia. The penetrance is famously inconsistent: a 45-year-old cattle station manager from the Pilbara, his 22-year-old daughter studying physiotherapy in Brisbane, and their 70-year-old matriarch in Adelaide can all carry the same pathogenic variant yet present with entirely different ECG morphologies and clinical trajectories.

That expressivity reflects modifier genes, hormonal influences, and structural remodelling in the right ventricular outflow tract. Myocardial bridging, subtle fibrosis detected on cardiac MRI, and altered connexin distribution all modulate arrhythmic vulnerability. Recognising these layers helps explain why a single electrophysiology study in a fasting morning state may under-represent the arrhythmic substrate that a febrile illness or a heavy evening meal in a Sydney restaurant could unmask.

Clinicians therefore begin risk stratification with a detailed personal and family history: unexplained nocturnal syncope, documented seizures, agonal breathing during sleep, and any sudden death under 45 in first-degree relatives. Resuscitated cardiac arrest automatically places the patient in a high-risk category regardless of stimulation outcome, a point emphasised in the Journal's recent themed editions.

Non-invasive markers framing the PVS question

Before scheduling an invasive study, electrophysiologists rely on a constellation of clinical and electrocardiographic features. A spontaneous type 1 pattern — the coved ST elevation in V1 or V2 appearing on a baseline ECG or during fever — carries greater prognostic weight than a drug-induced pattern alone. Fragmented QRS complexes, prolonged peripheral S-wave upstroke, early repolarisation in inferolateral leads, and augmented right ventricular conduction delays all refine the pre-test probability.

Signal-averaged ECG, 24-hour ambulatory monitoring for nocturnal ST changes, and exercise testing may also identify higher-risk subgroups. Australian cardiac technicians in Townsville, Hobart, and Geelong frequently encounter the pattern incidentally during pre-employment medicals for mining, transport, or defence roles, prompting a cascade of investigations. Pharmacological provocation with flecainide, ajmaline, or procainamide unmasks concealed channels but requires resuscitation infrastructure and experienced staff.

When clinical features, ECG pattern, and family history point strongly toward high risk, some electrophysiologists skip programmed stimulation entirely and recommend an ICD based on shared decision-making. The procedure is then reserved for the grey zone: the asymptomatic middle-aged patient with a drug-induced type 1 pattern and an equivocal family history who arrives seeking clarity.

Anatomy of the stimulation protocol

Standard protocols derive largely from the work of Brugada himself, who popularised a minimum coupling interval of 200 ms and stimulation from at least two right ventricular sites. Most Australian laboratories in cities such as Newcastle, Wollongong, and the Gold Coast follow a stepwise approach: drive trains of 600 and 400 ms followed by up to three extrastimuli decremented to refractoriness or ventricular effective refractory period.

The endpoint is induction of polymorphic VT or ventricular fibrillation lasting more than 30 seconds or requiring termination. Monomorphic VT is generally not considered a positive endpoint in Brugada syndrome. Use of a quadripolar catheter at the right ventricular apex, with additional mapping at the outflow tract septum, increases sensitivity but also the rate of non-specific induction.

Aggressive short-coupled protocols can produce non-specific VF induction in structurally normal hearts, blurring the boundary between a clinically meaningful result and a laboratory artefact. This is one reason why current Heart Rhythm Society consensus statements recommend cautious interpretation and reproducibility checks before changing management.

Mixed evidence underpinning the test

Early observational studies suggested that inducibility powerfully predicted arrhythmic events, with reported hazard ratios above three. The 2015 BJP registry analysis tempered that enthusiasm, finding no significant association between induced VT/VF and subsequent appropriate ICD therapy after adjusting for baseline clinical variables. Subsequent meta-analyses produced conflicting summary estimates, partly because of protocol heterogeneity and inclusion of patients with cardiac arrest already destined for device implantation.

More recent work using contemporary ventricular stimulation protocols has revived moderate support for the technique in selected populations. A pooled individual-patient analysis published in a cardiology journal last year suggested that triple extrastimuli at the right ventricular outflow tract — combined with a spontaneous type 1 pattern — yielded a positive predictive value around 25 percent and a negative predictive value above 95 percent over medium-term follow-up.

A South-East Asian registry, particularly relevant given the regional prevalence of SCN5A founder variants in populations from Cambodia, the Philippines, and Thailand, has also reinforced the value of standardised protocols. Many cardiologists in Sydney and Melbourne treat patients from these backgrounds and witness the disproportionate burden of nocturnal sudden death in young Southeast Asian men. For them, refined use of PVS offers a tangible tool, though one that must be embedded within a broader risk assessment framework — a perspective elaborated on the journal's overview pages.

Translating evidence into Australian practice

Australian electrophysiologists increasingly approach Brugada risk stratification as a multimodal process. The decision tree commonly begins with the resting and provoked ECG, augmented by clinical history, family screening, and cardiac MRI where appropriate. Programmed stimulation finds its strongest role in asymptomatic patients with intermediate pre-test probability who seek additional clarity before accepting lifelong device therapy or lifestyle restrictions.

Reimbursement through the Medicare Benefits Schedule covers a substantial portion of the catheter study cost, and outpatient genetic counselling is increasingly available through services in Melbourne, Sydney, and Perth. Patients are counselled that a positive result roughly doubles the offer of an ICD, whereas a negative result reduces, but never eliminates, the lifetime arrhythmic risk. Fever management plans, avoidance of certain sodium channel-blocking agents, and targeted family screening remain essential regardless of stimulation outcome.

For clinicians managing overlapping structural and inherited conditions — such as patients requiring right-sided pacing across a tricuspid prosthesis — adjacent technological developments are reshaping practice. A recent feature on this platform covering leadless pacemaker therapy highlights how device miniaturisation is already intersecting with care for complex valve patients, and may eventually matter for some Brugada individuals who develop pacing indications after years of monitoring.

Readers are invited to explore the latest themed issues on inherited arrhythmia syndromes, sudden cardiac death, and ablation outcomes through the journal's open-access platform, and to submit original research, review proposals, and challenging case reports for editorial consideration. Open-access publication supports Australian and Asia-Pacific investigators in sharing findings promptly with colleagues across Wellington, Jakarta, and Tokyo without paywall barriers, accelerating the evidence base for one of the most debated tools in inherited arrhythmia care.