CONGRESS ABSTRACT

Background The ECG is useful in the differential diagnosis of a “paraphysiological” or pathological condition, especially in asymptomatic patients in whom findings are doubtful for a correct diagnosis.   Clinical case Forty-year-old, normotype, without cardiovascular risk factors, asymptomatic. Diagnosis of anterior fascicular block due to electrocardiographic evidence of marked left axis deviation. A careful analysis shows that in reality it is a slight delay in right intraventricular conduction without anteriorization of terminal forces that simulates a left anterior hemiblock. ECG: sinus rhythm, electrical axis extremely deviated to the left (-60°), with clockwise rotation on the longitudinal axis due to a probable prevalence of the right ventricle, normal P wave axis, normal atrioventricular conduction, slight delay of right intraventricular conduction, no ventricular repolarization abnormalities, corrected QT interval 391 msec. The ECG suggests a left anterior hemiblock. Upon further analysis, the ECG shows an incomplete right bundle branch block, without anterior deviation of the terminal forces; in fact: 1) although there is a marked left axial deviation and negative complexes in DII and DIII, the S wave is > in DII than in DIII; this is not compatible with an isolated anterior fascicular block, in which the S wave is wider in DIII than in DII; 2) the QRS in aVL is of low voltage, while in the left anterior hemiblock aVL shows a high R wave, expression of forces directed upwards and to the left; therefore, the mid-terminal ventricular forces are directed upward and to the right; 3) lead V1 shows polyphasic low voltage rsr’s’ complexes, suggestive of incomplete right bundle branch block; 4) large and broad terminal R wave in aVR; 5) no secondary ST-T changes in DI and aVL; 6) non-delayed intrinsicoid deflection in aVL < 0.05 seconds.   Conclusions The diagnosis of right bundle branch block, without anteriorization of terminal forces, simulating a left anterior hemiblock, is based on: 1) marked left axis deviation with negative complexes in the inferior leads; 2) qRs complexes in DI and aVL; 3) larger S wave in DII than in DIII; 4) rSr’ complexes in DIII or aVF; 5) low QRS voltage in lead aVL; 6) absence of secondary ST-T changes in DI and aVL; 7) non-delayed intrinsicoid deflection in aVL <0.05 seconds.