Analysis of QRS complex recorded through a semiorthogonal lead system in the horse

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Abstract
A semiorthogonal lead system for recording electrocardiograms from horses was designed. The X, Y, and Z axes of the body were monitored by leads I, aVF, and V10 (the unipolar lead taken from the dorsal spinous process of the seventh thoracic vertebra), respectively. Records were taken from 15 standing horses. Ventricular premature beats were elicited by pricking foci on the right and left ventricular epicardium. For normally conducted beats, two major vectors represented forces generating the QRS complex. Vector 1, probably representing excitation of the apical third of the interventricular septum from left to right, was relatively low in magnitude, and was oriented dextrad, ventrad, and craniad. Vector 2, probably representing depolarization of the basilar third of the interventricular septum from left to right and in an apicobasilar direction, was of greater magnitude and was oriented ventrad, sinistrad, and craniad. Occasionally a vector intermediate between vectors 1 and 2 was oriented caudad and dorsad. The origin of this vector is equivocal. Left ventricular premature beats generated vectors of great magnitude oriented dextrad and craniad. Right ventricular premature beats generated vectors of magnitude between those of sinus or left ventricular origin, and directed predominantly sinistrad.