The Brugada Syndrome

During the past decade, the Brugada syndrome has gained increasing recognition as an important cause of ventricular fibrillation (VF) among patients with structurally normal hearts ("primary electrical disease," "idiopathic VF"). This disorder may account for as many as 40-60% of all cases of idiopathic VF in some regions, such as Southeast Asia and Japan (72). Recent evidence indicates that Brugada syndrome and congenital LQTS both represent primary disorders of cardiac ion channels (73). Animal models have yielded important clues regarding the mechanisms responsible for the cardinal ECG manifestation of Brugada syndrome and its relation to arrhythmogenesis. At the same time, sufficient worldwide clinical experience has been gained to develop preliminary recommendations for the diagnosis and treatment of this disorder.

Diagnostic Criteria

The diagnostic criteria for Brugada syndrome incorporate three key elements: 1) >1 mm of ST segment elevation in leads V1, V2, and V3, in the absence of QT prolongation; 2) no structural heart disease, despite extensive investigation; 3) a personal or family history of unexplained syncope or sudden cardiac death (74). When a family history is present, the mode of inheritance is consistent with autosomal dominant transmission with variable penetrance (73). Men appear to be disproportionately affected, for unclear reasons (>90% male predominance). In some individuals, particularly Southeast Asian men, a marked predisposition for nocturnal cardiac events has been described (72). This finding may be a manifestation of the deleterious influence of heightened vagal tone in this disorder.

Particular care is needed when attempting to distinguish the Brugada ECG from common normal variants. Right bundle-branch block (RBBB) has been described in association with ST segment elevation in Brugada syndrome; however, arrhythmic events appear to be related to the magnitude of ST-segment elevation and not to the presence or absence of RBBB (75). In many instances, the expanded S wave in the left lateral leads is absent, indicating that true RBBB is not present (Fig. 3). The morphology of the ST segment in Brugada syndrome has been classified as either "coved" or "saddle-back" (Fig. 4). These patterns can be differentiated from the benign early repolarization variant by the localization and morphology of the ST-segment changes. Patients with the early repolarization variant characteristically have elevated ST segments in leads V2-V4, with an upward concavity and positive T-wave polarity accompanied by a notched J point (Fig. 5). In contrast, the ST elevation of Brugada syndrome is limited to leads V1-V3, is slowly down-sloping, and is accompanied by a negative T wave. It is important to recognize that right precordial ST-segment elevation

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Brugada Syndrome Ecg
Fig. 3. Twelve-lead ECG of a patient with Brugada syndrome. (Reproduced with permission from Brugada et al. Right bundle-branch block (RBBB) and ST-segment elevation in leads V1 through V3: a marker for sudden death in patients without demonstrable structural heart disease. Circulation 1998;97:458.)

can be observed in a variety of other disorders (Table 5), which must be excluded before the diagnosis of Brugada syndrome is made (75).

Mechanism of ST Segment Elevation

The mechanism of the characteristic ST segment elevation of Brugada syndrome can be best understood with reference to the ionic currents that are active during phases 1 and 2 of the cardiac action potential (Fig. 6). In normal individuals, the ST segment is isoelectric. This is because the voltage during the early portion of phase 2 of the

Segment Changes

Fig. 4. Dynamic changes in the morphology of the ST segment in a patient with Brugada syndrome. (A) "Saddle-back" configuration of the ST segment in leads V1-V2. (B) "Coved" configuration of the ST segment in leads V1-V2. (Reproduced with permission fromMatsuo et al. Dynamic changes of 12-lead electrocardiograms in a patient with Brugada syndrome. JCE 1998;9[5]:510.)

Fig. 4. Dynamic changes in the morphology of the ST segment in a patient with Brugada syndrome. (A) "Saddle-back" configuration of the ST segment in leads V1-V2. (B) "Coved" configuration of the ST segment in leads V1-V2. (Reproduced with permission fromMatsuo et al. Dynamic changes of 12-lead electrocardiograms in a patient with Brugada syndrome. JCE 1998;9[5]:510.)

action potential is similar throughout the myocardium, because of the development of a prominent calcium current (ICa)-mediated action-potential plateau (75). The development of a normal plateau phase is critically dependent on the balance of ionic currents active at the end of phase 1—inward ICa and outward Ito (Fig. 6). It is noteworthy that the distribution of Ito is heterogeneous throughout the myocardium, with a greater concentration in the epicardium than the endocardium (76). In addition, the right ventricular epicardium appears to have a greater concentration of Ito than the left ventricular epicardium (77). Loss of the action-potential dome can occur when the net balance of current shifts outward at the end of phase 1. Conditions that can precipitate loss of the action-potential dome include genetic mutations in ion channels, such as SCN5A, ischemia, metabolic abnormalities, and pharmacologic interventions (INa and ICa blockers, IK-ATP activators). When these conditions are present, loss of the action-potential dome occurs preferentially in the epicardium because of the predominance of Ito in this layer, leading to a net flow of current from endocardium to epicardium and the ECG manifestation of ST-segment elevation. This phenomenon is most likely

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Brugada Syndrome

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  • marta siciliano
    How to read brugada syndrome on ecg?
    7 years ago

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