Alpha and beta angles of r’ wave to differentiate between Brugada syndrome and incomplete RBBB

It is a common problem to differentiate between types 2 and 3 of Brugada ECG pattern and incomplete right bundle branch block (IRBBB). Chevallier S and colleagues [New Electrocardiographic Criteria for Discriminating Between Brugada Types 2 and 3 Patterns and Incomplete Right Bundle Branch Block. J Am Coll Cardiol, 2011; 58:2290-2298] have come out simple measurements on surface ECG to differentiate these two. This article was accompanied by an editorial by Prof. Pedro Brugada himself [On the Intriguing Phenotypic Manifestations of Brugada Syndrome and the Diagnostic Value of the Electrocardiogram. J. Am. Coll. Cardiol. 2011; 58(22): 2299 – 2300], one of the three Brugada brothers who described the syndrome. Alpha and beta angles were measured as follows: Alpha is the angle between the vertical and the downslope of the r’ wave. Beta is the angle between the upslope of the S wave and the downslope of the r’ prime wave. Both are measured in the lead V2. The authors compared the angles in those in whom the type 2 and 3 Brugada patterns got converted to type 1 pattern with ajmaline infusion and those which did not. Those which got converted were designated as true Brugada syndrome while others were considered as incomplete RBBB. The beta angle was smaller in those with IRBBB than in those with Brugada syndrome. The alpha angle also had a similar but less sensitive and specific role. Prof. Brugada commented that alpha angle is purely dependent on repolarization while beta angle depends on both terminal depolarization and initial repolarization. He explained it in the context of three hypothesis on the pathophysiologic mechanisms of Brugada syndrome, which he termed as Amsterdam, New York, and Buenos Aires hypotheses.

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