Background: Since its first description, Brugada Syndrome is characterized by definite ECG abnormalities (J wave, elevated ST segment) restricted in right precordial leads. The most recent Consensus distinguished 2 electrocardiographic patterns: type 1 with a coved ST-segment elevation ?2 mm followed by a negative T wave in at least 1 right precordial lead and type 2 characterized by a saddle-back ST elevation followed by a positive T wave. Brugada Pattern (BP) could be found in one or more right precordial leads, at conventional or higher intercostal spaces. A recent study , conducted by our group, reported that slightly less than one half of patients with type 1 BP show a definite ST segment depression (? 0.1 mV with duration ? 0.08 s) in the inferior leads. Thus, 4 distinct ST abnormalities phenotypes were recognized in Type 1 BP: Phenotype A) Type 1 BP diagnosis in V1-V2 at 4th ics, no ST segment depression in inferior leads (Fig. 1A); Phenotype B) Type 1 BP diagnosis in V1-V2 at 4th ics, ST segment depression in inferior leads ( ? 0.1 mV with duration ? 0.08 s) (Fig. 1B); Phenotype C) Type 1 BP diagnosis at high ics (3rd or 2nd), no ST segment depression in inferior leads (Fig. 1C); Phenotype D) Type 1 BP diagnosis at high ics (3rd or 2nd), ST segment depression in inferior leads ( ? 0.1 mV with duration ? 0.08 s) (Fig. 1D). Several studies found a correlation between the right ventricular outflow tract (RVOT) anatomical location and the leads in which a diagnostic type 1 Brugada pattern could be observed. , We hypothesized the key role of orientation of right ventricular outflow tract in the chest, particularly the inclination of anterior wall compared to the sternum, contributing to the determination of these various ECG phenotypes.
Methods: In order to assess our hypothesis we used an interactive simulation program able to assess the relationship between the electric current sources of the heart and the resulting electrocardiographic signals on the body surface (ECGSIM vers. 3.0.0 ). , Our aim was to create “areas of injury”, with various size, reproducing the endo-epicardial transmural gradient (Fig. 2) described by Antzelevitch , typical of BP, in two heart’s 3D model: one with a vertical RVOT orientation (Figure 3, Model 1), the other one with an horizontal heart and, thus, an horizontal RVOT (Figure 3, Model 2), as commonly found in obesity, pregnancy, low height and other conditions.
Results:Model 1 (Vertical RVOT) First of all, an “area of injury” was localized in the lower part of a vertical RVOT (Fig. 4A). In this case the simulated ECG showed a clear type 1 BP both in V1 and V2 recorded at the 4th ics. In fact, due to the vertical orientation of RVOT, the abnormal BP vector was directed mainly anteriorly (Fig. 5a). Thus, despite of a great ST segment elevation in the right precordial leads no significant ST segment depression in inferior leads was found (phenotype A, Fig. 6A). On the contrary, if an “area of injury” was created in the upper part of a vertical RVOT (Fig. 4C) V1 and V2 recorded at the 4th ics didn’t show type 1 BP (an isolated ST segment elevation of 2 mm is observed in V2) and no significant ST segment depression in inferior leads was found. Only evaluation of the 3rd ics revealed a typical type 1 BP (phenotype C, Fig. 6C). In this case, the upper “area of injury” within RVOT impaired BP recognition at 4th ics; again, due to the vertical orientation of RVOT, the abnormal BP vector was directed anteriorly, giving no ST segment abnormalities in the peripheral leads. Model 2 (Horizontal RVOT) An “area of injury” involving the lower part of an horizontal RVOT (Fig. 4B) showed an ECG compatible with phenotype B. Due to the horizontal orientation of RVOT, abnormal BP vector was directed both superiorly and anteriorly (Fig. 5b). This appeared as a concomitant clear BP recorded in V1 and V2 at 4th ics and a significant ascending ST depression in the inferior leads (Fig. 6B). Contrariwise, if an “area of injury” was reproduced in the middle-upper part of an horizontal RVOT (Fig. 4D), the simulated ECG showed a clear ST segment depression ( ? 0.1 mV with duration ? 0.08 s) in all inferior leads accompanied only by a mild ST segment elevation in lead V2 recorded at 4th ics. Only evalution of 3rd and 2nd ics allowed type 1 BP diagnosis (phenotype D, Fig. 6D).
Conclusions: This computed model supports the strict relationship between ST segment depression in the inferior leads and the ST segment elevation in right precordial leads, typical of type 1 BP. A horizontal RVOT, in fact, gives raise to abnormal BP vector directed both superiorly and anteriorly, explaining, at the same time, typical BP appearance in right precordial leads and ST segment depression in the inferior leads. Analysis of the inferior leads could be useful especially in patients with no clear type 1 BP with V1-V2 at the 4th ics suggesting the need to record upper right precordial leads. Cardiac imaging, such as computed tomography and magnetic resonance, or perhaps echocardiography, could find a further validation of this hypothesis. Further studies needs to assess a possible prognostic role of various ECG phenotypes of type 1 BP.