[Posterobasal infarction and right bundle branch block: value of computerized vectorcardiography].

The object of this study was to determine the vectocardiographic criteria of posterobasal myocardial infarction associated with right bundle branch block. Seventeen patients were examined; all had clinical and enzymatic evidence of myocardial infarction, associated with the unusual appearances of right bundle branch block with an isolated R wave in V1 and V2. The Frank X, Y, and Z axes were treated by computer to obtain a detailed octonal study of the QRS and T loops. Vectors of special interest were determined: the maximum maximorum vector and the QRS half surface vector (module, azimuth, elevation, appearance time). The octonal and total surface are of the QRS and T loops and the spatial angle of the maximal vectors of the two loops were calculated. These cases were characterised by clockwise rotation of the QRS loop in the horizontal plane. The maximal QRS vector had a decrease module (1,29 mV +/- 0,49), an azimuth greater than 20 degrees (42,8 degree +2- 20,3) an appearance time of 55,7 +/- 12,1, and an elevation which was either positive or negative depending on the presence or absence of an associated left anterior hemiblock. The half-surface vector was superimposed on the maximal vector: module (1,09 mV +/- 0,39), azimuth (45,2 degrees 23,5(and appearance time (62,0 +/- 11,7 ms). The posterior surfaces were nil or negligible (less than 1 p. 100). The T loop had a clockwise rotation in the horizontal plane and its maximal vector projected anteriorly in 8 patients. The appearances observed in these 17 cases were different to those of isolated right bundle branch block. The classical causes of anterior ORS loops could be excluded easily: right ventricular hypertrophy, Wolff-Parkinson-White syndrome, intraventricular conduction defect. The following criteria were retained in the diagnosis of posterobasal infarction associated with right bundle branch block:--principally, clockwise rotation of the QRS loop in the horizontal plane;--anterior displacement of the maximal vector with an azimuth of over 20 degrees;--disappearance of the posterior forces;--associated with the usual criteria of right bundle branch block;--clockwise rotation of the T wave loop in the horizontal plane.