Bradycardia-Dependent ECG Changes in Brugada Syndrome

Abstract

rugada syndrome (BS), a distinct subtype of idiopathic ventricular fibrillation (VF), is characterized by a distinctive ST segment elevation in the right precordial leads. [1][2][3] The mechanism responsible for this ST segment elevation and genesis of VF is still under investigation. Several possible mechanisms have been proposed for the ST segment elevation in BS. Among them are conduction delay, accentuation of the action potential notch and loss of the action potential dome in the right ventricular outflow epicardium. 3,4 In BS, unlike other diseases, VF and sudden death mainly occur in the resting state, predominantly during sleep. 5,6 The typical ECG changes are variable over time and are modulated by exercise or pharmacological interventions that interact with autonomic nervous activities. 5,[7][8][9] We recently reported an inadequate prolongation of the QT interval (short QT interval) at longer RR intervals 10 and an augmentation of the ST elevation through vagal activity in patients with BS. 11 The nighttime onset of VF episodes may be related to both a shorter QT interval and an enhanced ST elevation during bradycardia at night. This could be because of a slow recovery from the inactivation of prominent Ito. 12 However, it is still unclear how the RR intervals affect the ECG changes in BS and whether rate dependent changes in the ECG would be different between symptomatic and asymptomatic patients. The present study was therefore designed to examine the effects of the RR intervals on ECG changes during an electrophysiologic study (EPS) in both symptomatic and asymptomatic patients. Methods Study PopulationTwenty-one consecutive male patients with BS were studied: 9 were symptomatic with either documented VF or episodes of unexplained syncope, and the other 12 were asymptomatic without either spontaneous VF or inducible VF during the EPS. The study protocol was approved by the institutional review board and written informed consent was given by all patients before participation. We diagnosed BS in accordance with recently established ECG criteria. 3 Patients with coved-type ST elevation accompanied by Jwave amplitude ≥2 mm in one of the leads V1-3 were included. 3 For patients with saddle-back-type ST elevation (type 2 or 3), coved-type ST elevation ≥2 mm induced by pilsicainide, a class Ic antiarrhythmic drug, was required. 3 In all patients, physical examination, chest X-ray, 2-dimensional-echocardiography, exercise test and thallium or 99m Tc-tetrofosmin myocardial single photon emission computed tomography failed to disclose apparent evidence of organic heart disease. Patients with diabetes mellitus, long QT syndrome or electrolyte abnormality and patients taking any drugs were excluded from the present study. EPS and Analysis of ECGsEPS was performed in all 21 patients after all antiarrhythmic drugs had been discontinued for at least 5 halflives of the drug. A steerable 6F octapolar catheter with Background In patients with Brugada syndrome (BS), ventricular fibrillation (VF) occurs mainly during ...

Exercise-Induced ECG Changes in Brugada Syndrome

“…This confirms reports of QRS widening during exercise in patients using therapeutic doses of flecainide 12,23 and in BrS patients at fast pacing rates during EPS. 32 These data suggest further I Na reduction in BrS patients during exercise. In BrS SCN5Aϩ further I Na reduction may be attributed to accumulation of mutant Na ϩ channels in the slow inactivated state during tachycardia.…”

National Russian Guidelines on Application of the Methods of Holter Monitoring in Clinical Practice

“…В ряде наблюдений отмечено укорочение интер-вала QT [459] или недостаточное удлинение интер-вала QT на брадикардии в ночное время с индуци-руемой ФЖ [461] и "гипоадапатция" интервала QT в ночное время при оценке "QT динамики" при ХМ дром удлиненного интервала QT (установленного на основании критериев Шварца): оценка среднесу-точных значений интервалов QT и QTс, максималь-ного QT и QTс, частотной адаптации интервала QT, "QT динамики", максимального уровня микровольт-ной альтернации зубца Т временным методом (С); 2. Сибсы больных с синдром удлиненного интер-вала QT (С).…”

Risk Stratification of Asymptomatic Patients With Brugada Type or J-Wave Type ECG

“…At rest, an increase in Ito may limit the prolongation of the APD, especially at slower heart rates and also produce a prominent J wave on the ECG. 12 During exercise, both a faster heart rate and an increase in adrenergic tone may offset the excessive Ito and make the difference in the ECG insignificant.…”