[Vectorcardiogram in experimental infarct of the right posterior ventricular wall]

In 20 dogs a chemical necrosis was produced by infiltration of 80% phenol solution within the posterior right ventricular wall and the neighboring interventricular septum. Vectorcardiographic loops were obtained by the cube system in vertical and horizontal heart positions under control conditions, 90 minutes after the necrosis was produced and also after RBB was severed. In 15 dogs the RBB was injured after the necrosis was produced and in 5 previously. In all dogs direct unipolar leads (epicardial and intraventricular), thoracic and abdominal unipolar leads (MD, ME, MI) as well as standard leads were also obtained following the experimental protocol outlined above. Analysis of the changes caused by necrosis in the location rotation and voltage of the initial, intermediate and preterminal portions of the vectorcardiographic curve in the three planes (F, H and left S) permits the formulation of the following conclusions: 1) The most significant alterations were observed in the frontal and sagital planes, particularly in RF and RS loops. In most of the cases, RF and RS loops were displaced upwardly, to the left on the frontal view and slightly anterior on the sagital. The rotation changed to counterclockwise direction on the frontal view and to clockwise on the sagittal one. In a few cases, the clockwise rotation of RF loop was conserved but it was displaced above the mean value of RF curl in horizontal hearts (+ 3 degrees 30'). 2. RH loop shifted posteriorly in both vertical and horizontal heart positions. The area enclosed by centripetal anterior branch RH loop was reduced and its apex was frequently delayed by 3 msec. 3) In presence of RBBB, the alterations described above on the frontal and sagittal views were conserved in both heart positions. The only distinct behaviour was observed in the horizontal loop, in which RH loop is posteriorly located with counterclockwise rotation in the vertical hearts and anteriorly in the horizontal one. Nevertheless, the voltage of R loops increased in both positions when the necrosis was produced after the RBBB. 4) In spite of differences in thickness of the right ventricular wall between dog and man (it is thicker in the dog), we propose that alterations of RF and RS loops could be extrapolated to the human V.C.G. in order to evaluate the involvement of the right ventricle by myocardial necrosis. 5) Similar alterations of RF and RS loops were observed in the presence of necrosis of the left posterior ventricular wall. The only clue to establish a differential diagnosis is based on the characteristics of RH loop, which is more anteriorly displaced with an "8" aspect or clockwise rotation in the presence of left side necrosis. Both VCG and ECG appear to be helpful on the topographic diagnosis and evaluation of injured myocardium in the right ventricle.