Medical Student University of British Columbia, British Columbia, Canada
Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare inherited arrhythmia syndrome characterized by adrenergically mediated ventricular tachyarrhythmias, leading to syncope or sudden cardiac death. Diagnosis and treatment surveillance rely on exercise-stress testing (EST), which unmasks characteristic arrhythmias during increased workloads. The conventional Bruce protocol, designed for ischemia evaluation, raises workload gradually and may be insensitive in detecting life-threatening arrhythmias given that abrupt, high-intensity adrenergic stress is a classic trigger for CPVT events. To address this gap, a novel “Burst” EST was developed to induce a sudden increase in sympathetic tone via sprint-based exertion. This study aims to understand the yield of the Burst protocol in detecting increased ventricular ectopy in a larger population.
METHODS AND RESULTS: This retrospective cohort study assessed 17 genetically confirmed or clinically diagnosed CPVT patients (12 probands, 5 identified through family screening) followed at the BC Inherited Arrhythmia Clinic. Each patient underwent both the standard Bruce and Burst EST, with all tracings independently reinterpreted by a cardiologist. Patients completed a median of 3 Bruce (range 1–7) and 2 Burst ESTs (1–4; p = 0.17). The median age at first Bruce was 26 years (IQR 19–38) versus 33 years (IQR 21–43) at first Burst EST, a median within-subject difference of 3 years (p < 0.001). Burst EST elicited a higher ventricular arrhythmia score (VAS) than Bruce; median VAS 3.0 (IQR 2.0–4.0) versus 1.0 (IQR 1.0–3.0), with a median within-subject difference 1.0 point (p = 0.005). In 12 cases (71%), Burst EST provoked more complex ectopy that led to therapeutic escalation (β-blockers or flecainide). In four cases (24%), the Burst protocol revealed increased arrhythmic burden without a change in therapy, often due to an overall mild phenotype or a low arrhythmic burden. In one case (6%), both protocols showed comparable arrhythmias.
Conclusion: The Burst EST may unmask a more severe arrhythmic phenotype in select CPVT patients, potentially due to a: (1) sudden surge of catecholamines early in exercise, (2) greater psychological stress induced by burst exertion; and/or (3) protective effect of gradual exercise derived by a slow increase in RyR2 leakiness. These observations have the potential to improve diagnosis and monitoring in CPVT patients, who face a high risk of death if under-recognized and/or treated. Indirectly, these results may also shed light on safer forms of physical activity in CPVT, such as sports that focus on endurance rather than short burst aerobics.
