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  • Consequently in asymptomatic individuals multiple and repeat

    2019-05-15

    Consequently, in asymptomatic individuals, multiple and repeated ECG recordings rather than drug testing are recommended for detecting the transient appearance of a spontaneous type 1 ECG, which may indicate the future development of arrhythmic events. Moreover, in addition recording at higher lead positions, other provocation tests such as exercise testing, glucose tolerance testing, and full-stomach testing, which provoke similar conditions to those of the spontaneous appearance of a type 1 ECG, may be useful in asymptomatic patients showing only a non-type 1 ECG [30,32,53].
    Conflict of interest
    Introduction Brugada syndrome is characterized by specific ST-segment changes in the right precordial electrocardiographic leads, known as the type-1 or coved-type Brugada electrocardiogram (ECG). In addition, Brugada syndrome is associated with a high risk of sudden cardiac death due to ventricular fibrillation (VF) without structural heart diseases. Since Brugada and Brugada first described 8 patients with a history of aborted sudden cardiac death due to VF and type-1 ECG in 1992, Brugada syndrome has become a distinct clinical entity [1–8].
    Epidemiology The worldwide prevalence of Brugada syndrome [8] is estimated to be 1 in 10,000, but it is much higher in Asian and Southeast Asian countries, especially Japan, the Philippines, and Thailand, reaching 5–10 in 10,000, while it is much lower in some Eastern European countries like Denmark, with an estimated prevalence of 1.1 in 100,000. Brugada syndrome, also known as pokkuri (Japan), bangungot (the Philippines), and lai tai (Thailand), seems to be the most common cause of natural death in Asian men younger than 50 years. The reason for this higher prevalence in Asia may be in part related to an Asian-specific sequence in the promoter region of SCN5A[9]. Brugada syndrome usually manifests during adulthood, with a mean age of sudden death of 41±15 years; however, cases in children are rare [8]. A family history of unexplained sudden death is present in 20–40% of cases in Western countries and 15–20% of cases in Japan [5,8,10,11]. Male predominance in patients with Brugada syndrome is also well known. Since all of the mutations identified in patients with Brugada syndrome display an autosomal A-366 mode of transmission, men and women are genetically expected to equally inherit the defective gene. However, the clinical phenotype is 8–10 times more prevalent in men than in women [8]. Experimental studies in dogs have suggested that the presence of a more prominent transient outward current (Ito) in males may contribute to the male predominance of the syndrome [12]. Some clinical studies have suggested that higher testosterone levels in men than in women may also have a significant role in the male predominance [13]. Episodes of VF occur more frequently at night or during sleep (2000–0800) than during the daytime as a form of sudden unexplained nocturnal death, syncope, or agonal respiration in approximately 70–80% of patients with Brugada syndrome [8,14,15]. Some authors speculate that this circadian pattern is related to increased vagal tone [16]. Our data detected by implantable cardioverter defibrillator (ICD) have shown that about half of the VF episodes are preceded by ventricular premature complex (VPC) with a similar morphology to initiating VPC of VF [15]. Atrial fibrillation is associated with 10–20% of Brugada cases in Western countries and 20–30% of Brugada cases in Japan [17]. The association of atrioventricular nodal reentrant tachycardia or Wolff-Parkinson-White (WPW) syndrome has also been reported.[18]
    Electrocardiographic characteristics The fist Brugada Consensus Report in 2002 suggested 3 types of ST-segment elevation patterns in the right precordial leads of the ECG (Fig. 1) [6]. Type-1 or coved-type ST-segment elevation is characterized by a J-point elevation of ≥2mm (0.2mV) followed by a negative or isoelectric T-wave (Fig. 1A). Type-2 ST-segment elevation shows a saddleback appearance with a J-point elevation of ≥2mm followed by a trough displaying a ≥1-mm ST elevation with either a positive or biphasic T-wave (Fig. 1B). Type-3 ST-segment elevation has a saddleback appearance with a J-point elevation of <1mm. The morphology and level of the ST-segment elevation are often accentuated; however, the type-1 or coved-type Brugada ECG is more frequently recognized just before and after episodes of VF [19,20] and is linked to a higher incidence of VF and sudden cardiac death [21]. Although the original report by Brugada and Brugada described the presence of right bundle branch block (RBBB), the RBBB was revealed to be nonessential for the diagnosis of Brugada syndrome [6]. Mild depolarization abnormalities, such as widening of the P wave and QRS duration, and prolongation of the PQ interval are observed in patients with Brugada syndrome, more often in those with SCN5A mutations than in those without SCN5A mutations [22].