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  • br Cardiac imaging br Head

    2019-05-07


    Cardiac imaging
    Head-up tilt testing Head-up tilt (HUT) testing is recommended to judge an episode of syncope to be likely caused by VF by excluding neurally mediated syncope (NMS). However, NMS may coexist with Brugada syndrome [42]. We conducted HUT testing in 46 patients with type-1 Brugada ECG, 20 healthy control subjects, and 15 patients with suspected NMS [43]. HUT testing was positive in 35% of Brugada patients (16/46), 10% of control subjects (2/20), and 67% of suspected NMS patients (10/15). The HUT-positive rate was significantly higher in Brugada patients with VF (7/14; 50%) than that in control subjects (10%) (P<0.05). Augmentation of ST-segment amplitude (≥0.05mV) in leads V1 through V3 was observed in 69% of the HUT-positive Brugada patients (11/16) during vasovagal responses and was associated with augmentation of parasympathetic tone following sympathetic withdrawal, which was evaluated by the hoechst 33342 manufacturer rate variability. These data suggested that some Brugada patients have an impaired balance of the autonomic nervous system, which may relate to their syncopal episodes.
    Conflict of interest
    Acknowledgments Dr. Shimizu was supported in part by the Research Grant for the Cardiovascular Diseases (H24-033) from the Ministry of Health, Labour and Welfare, Japan.
    Introduction Brugada syndrome (hereafter referred to as BrS) is characterized by a peculiar ST segment (J point) elevation in the right precordial leads of the electrocardiogram (ECG) as well as idiopathic ventricular fibrillation, occurring particularly during sleep, which often results in nocturnal sudden death. There is a definite male predominance in BrS-related morbidity, and men are ∼10-times more affected than women. Approximately 20% of the phenotype-positive probands have a family history of syncope or sudden death. These clinical features are partially similar to those previously described as “Pokkuri” disease in Japan [1,2] and “Lai Tai” in Thailand [3]. Indeed, its prevalence is higher in Japan and Southeastern Asia, which may be partially related to an Asian-specific sequence in the promoter region of SCN5A[4]. The disease was named after the report in 1992 by the Brugada brothers [5], but several case reports on similar ECG findings and clinical phenotypes from Italy and Japan were published previously [1,2,6]. Some of these reports described an associated structural abnormality, especially in the right-side of the heart, suggesting the coexistence of subclinical arrhythmogenic right ventricular cardiomyopathy [7]. Patients with BrS have been shown to carry SCN5A mutations, which raises the possibility that the specific structural change is caused by SCN5A mutations [8,9]. The inheritance pattern of BrS shows an autosomal dominant mode of transmission. Candidate gene analysis showed that mutations in SCN5A were responsible for the phenotype of BrS in 3 families, and over 300 SCN5A mutations have been reported to date [10]. SCN5A encodes for the α subunit of the cardiac sodium channel, and SCN5A mutations are found in 11–28% of clinically diagnosed BrS patients [11]. Since 1998, genetic variants in over 10 genes have been reported in patients with BrS. Table 1 lists these genes, the mutation locations, and the functional changes in each ion channel current induced by these mutations. In all genotypes, either the decrease in inward sodium or calcium currents (INa or ICa) or the increase in outward potassium currents is thought to be responsible for the BrS phenotype. BrS is, therefore, a very heterogeneous disease entity from the perspective of its genetic background. In addition, it is notable that the genotypes of over two-thirds of BrS patients have not yet been determined despite extensive genetic testing, which limits the prognostic value of the genetic tests. Indeed, except for SCN5A-related BrS, the genotype–phenotype correlation of other BrS-associated genetic changes is relatively not well studied. The paucity of genetic studies of BrS is mainly due to the small number of families with a history of BrS that have been genotyped. Presently, genetic testing is only diagnostic; however, once the proband is successfully genotyped, for example as a carrier of SCN5A mutation, the mutation-specific genetic test would be highly recommended for family members because it can determine the relatives that are at a potential risk for BrS and BrS-related death. In this review, we summarize the genetic basis of BrS, with a particular focus on recent reports.