Exercise Testing in the Workup of Catecholaminergic Polymorphic VT

Catecholaminergic polymorphic ventricular tachycardia sits among the most deceptive of the inherited arrhythmia syndromes. Patients typically present in childhood or adolescence with palpitations, syncope triggered by exertion or emotional surge, or, tragically, with sudden cardiac death as the first manifestation. The resting 12-lead ECG looks reassuringly normal, which is precisely why provocative manoeuvres have shaped the diagnostic landscape since the original descriptions of Coumel and Leenhardt in the 1990s. For Australian clinicians working at quaternary centres such as the Royal Melbourne Hospital or the Sydney Children's Hospitals Network, integrating treadmill exercise testing into the evaluation pathway has become a near-mandatory step whenever a young patient presents with exertional syncope or a family history of unexplained sudden death.

An exercise challenge does more than provoke an arrhythmia. It allows clinicians to characterise the pattern, gauge adrenergic dependency, establish a baseline PVC burden, and re-examine the patient after therapy is started. With genomic testing now reimbursable through Medicare for many inherited cardiac conditions, exercise testing pairs naturally with cascade family screening, particularly where RYR2 or CASQ2 variants have been confirmed in a proband. The test is cheap, widely available, and reproducible, yet its interpretation requires a clear understanding of what catecholaminergic polymorphic ventricular tachycardia actually is at a cellular level.

The cellular substrate driving adrenergic arrhythmias

CPVT arises from defects in intracellular calcium handling, predominantly in the cardiac ryanodine receptor (RYR2) or its modulatory proteins such as calsequestrin (CASQ2) and triadin. Under sympathetic stimulation, phosphorylated RyR2 channels leak calcium from the sarcoplasmic reticulum during diastole. The resulting delayed afterdepolarisations trigger ventricular ectopy that can degenerate into polymorphic or bidirectional tachycardia. Because the structural heart is normal, imaging studies show nothing, and the disease hides behind a quiet resting ECG.

The clinical correlate of this biology is straightforward: any situation that floods the patient with catecholamines can unmask the phenotype. A treadmill ramp, sustained handgrip, or the adrenaline surge of competitive sport is all capable of provoking the arrhythmia. Australian paediatric electrophysiologists at the Royal Children's Hospital in Parkville have long stressed that an exercise test should not be limited to the treadmill — an adrenaline infusion protocol or mental stress challenge may also be considered, particularly in children whose arrhythmias are inconsistent.

Why resting studies fall short in CPVT

A resting ECG, ambulatory monitor, or even an echocardiogram provides essentially no diagnostic yield in an untreated CPVT patient. Sinus rhythm looks normal, QT intervals are normal, and there is no epsilon wave, no Brugada pattern, no sign of structural disease. It is only when catecholamine levels climb that the arrhythmogenic substrate reveals itself. This explains why so many families first come to attention after an episode at Saturday-morning footy or a swim carnival, where exertion combined with emotion drives the sympathetic surge.

Exercise testing addresses this blind spot elegantly. The standard Bruce or modified Bruce protocol ramps heart rate and circulating catecholamines in a controlled, monitored setting. Telemetry recordings capture a characteristic signature of progressively worsening ventricular ectopy, beginning with isolated premature ventricular complexes, advancing through bigeminy, and culminating in non-sustained polymorphic or bidirectional ventricular tachycardia if the patient is untreated. The threshold heart rate at which ectopy appears carries prognostic information: an earlier onset tends to correlate with a higher future risk of cardiac arrest despite beta-blocker therapy. Differential diagnosis matters here, since reflex syncope can mimic CPVT, and a tilt-table-guided investigation is occasionally part of the broader workup when the clinical picture is mixed.

Designing a stress test for children and adults

In adult cardiology practices across Australia, treadmill exercise testing follows a familiar pattern, although paediatric application requires adjustments that adult laboratories sometimes miss. Most laboratories use a ramped Bruce protocol, with a modified Bruce or a low-level Naughton-style protocol for children who cannot sustain standard adult workloads. The aim is not maximal aerobic capacity; the aim is a heart rate rise to roughly 85–90% of age-predicted maximum, sustained for several minutes to allow catecholamine accumulation. Frequent blood pressure and rhythm checks are mandatory, and a defibrillator must be at the bedside throughout. Some Australian centres affiliated with the Baker Heart and Diabetes Institute advocate telemetry capture throughout recovery as well, since arrhythmias in CPVT often emerge as the heart rate falls and adrenergic tone remains elevated.

Practical preparation matters more than the choice of protocol. Patients should avoid strenuous exercise the day before, abstain from caffeine, and hold any rate-limiting drug under explicit clinician instruction. Beta-blockers, if already prescribed, are sometimes withheld for 24–48 hours to allow a diagnostic yield, but this must be balanced against the risk of precipitating breakthrough arrhythmia in a high-risk patient. Pre-test counselling should make clear that the team may need to terminate the challenge, and that intravenous beta-blockade or flecainide will be administered if sustained arrhythmia develops.

Reading the exercise tracing: hallmark patterns

The hallmark finding is bidirectional ventricular tachycardia, in which the QRS axis flips beat-to-beat, producing an alternating morphology that reflects alternating exit sites from a focus near the Purkinje network. Polymorphic VT, polymorphic PVCs with progressive shortening of the coupling interval, and ventricular bigeminy that emerges at a reproducible heart rate threshold are all diagnostic clues. Not every patient with CPVT will show the textbook bidirectional pattern; many show polymorphic non-sustained runs or even isolated couplets that worsen as workload increases.

Quantifying the response also matters. A reproducible threshold heart rate for the first PVC, an absolute PVC count at peak exertion, and the suppression of ectopy during recovery can each be used to monitor therapy. A repeat study after starting nadolol or propranolol, or after adding flecainide, often shows abolition of polymorphic runs even if isolated PVCs persist. Persistent non-sustained VT at the same threshold despite therapy should prompt reconsideration of the drug regimen, dosing, or the diagnosis itself.

Distinguishing CPVT from related arrhythmia syndromes

Distinguishing CPVT from other inherited arrhythmia syndromes is critical, because management diverges sharply. Overlapping inherited arrhythmia syndromes such as early repolarisation syndrome and Brugada syndrome can produce polymorphic VT during exertion or recovery, but their resting signatures, response to sodium channel blockers, and genetic substrates differ. Experienced electrophysiologists recognise that the two diagnoses can coexist or be confused, and that exercise testing often resolves the ambiguity when the history alone cannot.

The diagnostic picture also benefits from repeat testing on therapy. Once nadolol or flecainide has been started, a follow-up treadmill study shows whether ventricular ectopy has been suppressed, and whether residual PVCs retain the CPVT signature. Cascade genetic testing in the proband, combined with exercise testing of first-degree relatives when a pathogenic RYR2 or CASQ2 variant has been identified, helps the team give the family a clear answer rather than a list of possibilities.

From positive test to long-term management

A confirmed diagnosis reshapes the patient's trajectory. First-line therapy is a non-selective beta-blocker such as nadolol, titrated to a target dose based on heart rate response, exercise testing, and tolerability. Flecainide is added when breakthrough ectopy persists or when the genotype predicts a less robust beta-blocker response. Lifestyle modification is non-negotiable: competitive sport, high-adrenaline activities, and unsupervised intense exercise are restricted, and Australian adolescents and their families often need clear written guidance, especially when school sport, swimming lessons, or weekend cricket matches form a regular part of life.

For patients with recurrent syncope or cardiac arrest despite maximal medical therapy, left cardiac sympathetic denervation offers a procedural next step, and a small subset with refractory polymorphic VT may be considered for an ICD. Some of the broader mechanical and pharmacologic strategies for managing recalcitrant ventricular arrhythmias are explored in the discussion of LVAD-associated arrhythmia management, and although CPVT patients rarely require mechanical circulatory support, the lessons on antiarrhythmic escalation translate across clinical contexts.

Family screening completes the picture. Exercise testing of first-degree relatives, cascade genetic testing where a pathogenic variant is known, and referral to a cardiac genetics service — whether through the Australian Genetic Heart Disease Registry or a state-based clinic at Royal Prince Alfred — all flow naturally from a positive treadmill study in the proband. Once the family is sorted out, ongoing surveillance keeps the team ahead of breakthrough events.

Catecholaminergic polymorphic ventricular tachycardia rewards clinicians who pursue provocation. A carefully performed treadmill study, read with an understanding of calcium-handling biology and interpreted in the context of the patient's age, genotype, and clinical history, will deliver the diagnosis in the majority of cases. Browse the latest themed collections and submit your work to the Journal of Arrhythmia to keep this conversation moving forward across the Asia Pacific electrophysiology community.