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The basic criteria for the vectorcardiographic diagnosis of right ventricular enlargement are discussed, in context with the course of myocardial activation. Right ventricular dilatation, secondary to isolated diastolic overloading (atrial septal defect) shows basically different degrees of dextrorotation. The ventricular curve starts to the left on the frontal and horizontal planes, and forward on the last one. Cases with right ventricular hypertrophy, produced by sustained systolic overload, are also evaluated. When the hypertrophy is generalized (pulmonary valvular stenosis), there is an increase in the manifestation of all the resulting vectors of activation of this ventricle: IIs, IIr, and IIIr. As a resultant of these changes, the ventricular curve presents a clockwise rotation in the three planes, and is oriented to the right and forward, with its terminal portions generally located above the E point. When the right ventricular hypertrophy is of the segmentary type, there is an increase of the manifestation of only some of the resulting vectors of the activation of this ventricle. For example, the vector IIr will be increased in cases of tetralogy of Fallot, while the IIIr will be increased in some cases of obstructive chronic pulmonary hypertensive cardiopathy. The T loop, of secondary type, generally opposes the vector IIr on the horizontal plane, and the IIIr on the frontal plane. When an important right ventricular dilatation is associated to a right bundle branch block of intermediate degree, owing to their proximity, the manifestation of the electromotive parietal forces is increased at the expense of the septal ones. This phenomenon produces a characteristic appearance of the SH loop, narrow and with a clockwise rotation.

Both, the vectorcardiographic changes produced by the various degrees of left bundle branch block and these observed with the different types of left distal block, are described. When a "wave jumping" phenomenon exists, the vectorcardiographic changes are more characteristic in the horizontal plane than in the frontal plane and can be interpreted satisfactorily in basis of the ventricular activation sequence. The normal counterclockwise rotation of the horizontal vectorcardiogram persists in the presence of left bundle branch block of slight and moderate degrees, since the electromotive forces of the free left ventricular wall are still predominant. In the majority of intermediate degree blocks, the middle portion of the RH loop develops with a clockwise rotation and general aspect with a clockwise rotation and the general aspect of the ventricular loop resembles an eight figure. This is due to the electromotive forces originated by the delayed depolarization of the left septal mass that starts to predominate. With advanced degrees of block, the largest portion of the RH loop shows a clockwise rotation, as well as marked notchings and slurrings. The initial anterior portion of the horizontal vectorcardiogram does not disappear, but is situated to the left of the anterior-posterior axis with a counterclockwise rotation (first right septal vector). Otherwise, the direct electrical sign of left distal block emphasized: evidence of delayed activation in a limited zone of the homolateral ventricle. This local delay gives rise to an asynchronism of the activation phenomenon between the upper and lower regions of the ventricle. The diagnosis of left bifascicular block is based essentially on the evidence of unequal delay of the activation sequence in the basal regions and in the inferior ones of the homolateral ventricle and also on the frequent persistence of the first left septal vector.

This is a report of the first four cases of left ventricle aneurysm of the posterior and inferior segments successfully treated surgically in the Hospital de Cardiología y Neumología del Centro Médico Nacional, México D. F., and represent the twelve per cent of all realized aneurysmectomies. The patients were all men with 57 years mean age, and a previous history of posteroinferior myocardial infarction, complicated in three of them with angor and severe ventricle arrythmias; chest X ray in lateral view showed a bump of the posteroinferior border of the cardiac silhouette; the echocardiography increase in the ventricular diameter below the mitral valve; the ventriculography made evident a diastolic bulging with systolic expansion of posterior and inferior segments of the left ventricle and no mitral regurgitation; selective coronary arteriography showed a dominant right pattern with 100 per cent proximal occlusion. Aneurysmectomy was done in all four cases and aortocoronary by-pass in two. The posteromedial papilar muscle was found respected in all cases and in two cases a mural thrombus was detected.

In the presence of low right atrial rhythms, the eight-shaped PF loop is located in the first quadrant, the PH loop is rotating in a counterclockwise direction and PS can rotate in either course. When the rhythm originates in high left atrial regions, PF and PH loop loops can be found in the third quadrant of both planes and should have a clockwise rotation. When the pacemaker is located in low left atrial regions, the PF loop rotates in a counterclockwise direction, or with its branches superposed, and located in the second quadrant; PH is rotating clockwise in the third quadrant; PS with either a clockwise or a counterclockwise rotation, is situated above and slightly ahead of the E point. In the presence of a nodal rhythm, the P loops show a counterclockwise rotation or an eight-shaped configuration. In the absence of atrial enlargements, the PF loop can be seen in the first quadrant and the PH in the first or the fourth quadrant.

The basic criteria for the vectorcardiographic diagnosis of left ventricular and biventricular enlargements are discussed on the basis of the myocardial activation sequence. Left ventricular dilatation, secondary to isolated diastolic overloading, increases the manifestation of all the vectors resulting of the activation of this ventricle. These changes reflect the proximity of the left ventricular walls to the exploring electrodes. The vectors above mentioned project themselves as wide ventricular curves with counterclockwise rotation on the three planes. The T loop, of secondary type, is concordant in its orientation with the R loop. Cases with left ventricular hypertrophy, produced by a sustained systolic overloading, are also described. In the presence of global left ventricular hypertrophy without LBBB, the manifestation of all the vectors resulting from the depolarization of this ventricle (I, IIl, IIIl), is increased. This is due to a prolonged duration of the corresponding activation fronts. These vectors are projected on the different segments of the ventricular curves and they show a counterclockwise rotation on the three planes. When LBBB is also present, the first septal vector is not evident. The T loop, of secondary type, opposes the R loop on the frontal and horizontal planes. The presence of left ventricular hypertrophy of the segmentary type, generally increases the manifestation of the vector I, and sometimes, also that of the vector IIIl. When both ventricles are hypertrophied, the electromotive forces of the chamber more severely affected predominate in the vectorcardiographic records.