Orientation and configuration of vectorcardiographic QRS loops from normal cats

The orientations (angles) of mean QRS vectors were manually calculated from scaler orthogonal leads (I, aVf, V10; X, Y, Z) and from X-Y oscilloscope recordings from cats injected with ketamine and acetylpromazine. Those angles calculated from individually recorded leads (I, aVf, and V10) were from cats in right lateral and sternal recumbency. Leads, X, Y, and Z were recorded simultaneously from cats in the sternal recumbency. The oscilloscope recordings were derived from the X, Y, and Z leads. Arithmetic and maximal measurements from ECG scaler leads and maximal and half-area measurements from oscilloscopic recordings were used for calculations. Recordings from 15 cats and from 1 cat 15 times. Based on visual inspection of scattergrams, the X, Y, and Z vectors were not different in orientation from I, aVf, and V10 vectors. Orientation of oscilloscopic vectors were more variable than orientations of vectors calculated from scaler leads. Body position of the cat during recording did not affect mean values of angles derived from leads I, aVf, and V10. Type of measurements did not affect mean values. Variation of orientation was greater among cats than for the intraindividual vector orientations. Configuration and direction of QRS loops from 27 normal cats were also recorded. The greatest variation in loop configuration was in the frontal plane.