QRS component of the spatial vectorcardiogram and of the spatial magnitude and velocity electrocardiograms of the normal dog

The ventricular activation process (QRS) of forty healthy dogs was studied by means of vectorcardiograms using Wilson's equilateraltetrahedral reference system, scalar electrocardiograms, and by constructing spatial magnitude electrocardiograms and spatial velocity electrocardiograms. These data were correlated with anatomic cross sections through corresponding planes of the frozen animal. An attempt was made to correlate the electrical activity, as measured by electrodes placed on the body surface, with the ventricular activation process.

The typical QRSsÊ loop was roughly heartshaped, and was almost coplanar with the median sagittal plane. Good correlation existed between the actual circumferential thoracic leads and the derived scalar electrocardiograms. Apparent variations between the actual electrocardiogram and those derived from the QRSsÊ loops in the horizontal plane projection were explained on the basis of spatial orientation of the exploring electrode.

The electrical activity of the dog's heart has been presented in three divisions based on time and the areas of the ventricles activated. Activation of the interventricular septum from left-to-right constitutes the 6 milliseconds vector which is directed cephalad, ventrad and slightly dextrad. The spatial magnitude electrocardiogram of the QRS complex reaches its first peak during this period, while the spatial velocity electrocardiogram of the QRS complex reaches its first peak and following dip. Simultaneous activation of the apex and free wall of the left ventricle constitutes the 22 milliseconds vector which is directed caudad with little ventral and sinistral orientation. The spatial magnitude electrocardiogram reaches its second and maximal peak during this period, while the spatial velocity electrocardiogram reaches its second peak, a brief dip and its third and maximal peak.

Activation of the basilar areas of both ventricles and the interventricular septum constitutes the 32 milliseconds vector which is directed cephalad and dorsad, with slight dextral orientation. The spatial magnitude electrocardiogram reaches its third and minimal peak during this period, while the spatial velocity electrocardiogram continues to decline.