Assessment of the Dynamic Response of Cardiac Depolarization During Stress Test Recovery Evaluated in Patients with Brugada Syndrome

Abstract

Brugada syndrome is a genetic disease that may cause sudden cardiac death in patients with structurally normal heart. This study aims to assess dynamic response of cardiac depolarization to physical exercise, and particularlly, during recovery phase. Several ECG depolarization features were studied including the R and S waves amplitude (Ra and Sa), the up-stroke and down-stroke of the R and S waves (S U , S D and S S ) and their respective angles (α R and α S ). Standard 12-lead ECG recordings were acquired during physical exercise test in 23 Brugada patients (11 symptomatic). By using a three-constant S-shaped function, we assessed the dynamics of the ECG markers by modeling their response during the recovery period. Brugada syndrome patients who were asymptomatic presented higher change values and faster change speed than symptomatic patients in several evaluated markers, especially in left precordial leads. On the other hand, symptomatic patients presented larger lag values as compared with asymptomatic patients. We concluded that dynamics of depolarization features, assessed during periods of increased parasympathetic tone, seems to be linked with the presence of symptoms in Brugada patients. IntroductionBrugada syndrome (BrS) is a genetic pathology, firstly described more than 20 years ago, and associated with a high risk of sudden cardiac death (SCD) in patients with an apparently normal structural heart. The coved type-1 ECG pattern (ST elevation ≥ 2mm, negative symmetric T wave) in ≥ 1 lead of the precordial leads V1-V3 is the main electrophysiological diagnostic marker in BrS [1].The major challenges today regarding the management of BrS patients are related to risk stratification and the definition of the best treatment approach. The implantation of a cardioverter defibrillator (ICD) is the only validated treatment, recommended for symptomatic patients who have experienced syncope, ventricular fibrillation or an aborted SCD. However, therapeutic strategies are more complex on asymptomatic patients, representing about 60% of BrS patients. The difficulty is thus to identify asymptomatic patients that may benefit from an ICD implantation.Depolarization disorders have been one of the two main hypotheses underlying the pathophysiology of BrS, associated with slowing conduction within the right ventricular outflow tract (RVOT) [2]. Moreover, the role of the autonomic modulation seems to have an important component in this pathology. In this study, we investigate the cardiac depolarization response to exercise in BrS. A set classical and more refined features extracted from the ECG within the depolarization phase are analyzed, in order to assess potential differences between symptomatic and asymptomatic BrS patients. Both the original ECG features and their heart rate corrected versions were analyzed for this purpose.