Electrocardiographical features in patients with bidirectional ventricular tachycardia

Abstract Background Electrocardiographical (ECG) features in patients with bidirectional ventricular tachycardia (BiVT), defined as a dual QRS morphologies alternating on a beat-to-beat basis in the inferior leads, has not been properly assessed to date. Purpose to sistematically describe the ECG characteristics during sinus rhythm and BiVT and its relationship with various etiologies. Methods we conducted an ambispective and multicentric registry on 13 hospitals, consisting on relevant clinical characteristics and ECG characteristics. Beat A was defined has having a net positive QRS in the inferior leads, whereas beat B had a net negative QRS in the inferior leads. Results A total of 19 patients were evaluated, with their ECG characteristics in sinus rhythm summarized in the Table 1 and BiVT features in Table 2. During sinus rhythm a high prevalence of U wave was observed (63.16% of the patients), which is consistent with the predominant underlying etiologies (50% of Andersen-Tawil and CPVT; the other etiologies were, mainly: digoxin intoxication [15.79%] and various cardiomyopathies). The BiVT exhibits a relatively narrow QRS for both beats, with an alternating axis between 114.8º for beat A and -76º for beat B and a similar slew rate (≈0.019 volts/sec) for both beats in sinus rhythm and BiVT. The predominant morphology in V1 was right bundle branch block (RBBB), which was greater than 80% for both beats. A non-statistically significant trend of slower HR during tachycardia was noted in channelopathies vs the rest of the etiologies (150.0±9.03ms vs 169.3±20.7, p=0.40). Conclusion Our study represents the largest population of BiVT described to date with structured ECG data collection. The absence of a predominant extreme axis (i.e. between -90 and -280º) and the relatively narrow QRS might be a reflect of the genesis of the arrhythmia within the His-Purkinje system via a "ping-pong" reciprocating bigeminy mechanism, as previously hypothesized.