C. Roger Smith

CATEGORIZATION OF COMMON DOMESTIC MAMMALS BASED UPON THEIR VENTRICULAR ACTIVATION PROCESS

According to their time-order of ventricular activation, various mammalian species may be divided into two categories. In category A, with the dog as prototype and including also man, monkey, cat, and rat, the ventricles are excited with three general “fronts” of depolarization:‘ ’ (1) Initial depolarization (during the first 5 to 10 msec. of QRS) of an endocardia1 shell surrounding the apex of the left ventricle (although simultaneously the interventricular septum is excited from right ventricular endocardium toward the left) (FIGURES 1A and 1B). (2) Depolarization of both ventricular free walls (during the next 15 msec. of QRS) from subendocardial terminations of the Purkinje fibers toward the epicardium (FIGURE 2A). (3) Terminal depolarization of the bases of both ventricles and of the interventricular septum (during the last 5 msec. of QRS) in a general apicobasilar direction (FIGURE 3A). I n category B, with the goat as prototype and containing also the horse, cow, pig, and sheep, ventricular activation proceeds with only two general “fronts” of dep~lar iza t ion :~ .~ (1) Initial activation almost identical with “front” 1 of category A (FIGURES 1A and B). (2) Terminal depolarization of the middle and basilar thirds of the interventricular septum (during the final 40 msec. of QRS) in a general apicobasilar direction (although during activation of the middle third, a small volume of myocardium comprising the extreme epicardial base [and one near the apex], of the left ventricle is activated simultaneously in a subepicardial to epicardial direction (FIGURE 2B). At a time confluent with the ending of “front” 1 and the beginning of “front” 2 (approximately 15 msec. after onset of QRS), the major masses of both ventricles are excited with a single “burst” of depolarization “permitted” by more general penetration of the Purkinje fibers into the epicardium of species comprising this category.6 Since this activation occurs without spread in any particular direction (many polarity reversals exist within the free walls of the ventricles), it contributes little, if a t all, to the

Fractional Distribution of Right Ventricular Output in the Lungs of Dogs

Microspheres, approximately 50 μ in diameter and labeled with scandium46, were injected into the jugular vein of seven anesthetized dogs. Each lobe of lung contained nearly equal counts per minute per gram of tissue. This suggests that the indicator was completely mixed with the blood by the time it arrived in the pulmonary artery, and that the perfusion rate of blood per gram of lung is nearly identical for all lobes.

Alterations in QRS during ischemia of the left ventricular free-wall in goats

Summary X, Y , and Z axis electrocardiograms, spatial magnitude and spatial velocity electrocardiograms and QRS loops in three planes were recorded from goats before and during ischemia of the left ventricular free-wall produced by injection of ceramic microspheres into branches of the left circumflex coronary artery. Epicardial electrograms were recorded from ischemic and nonischemic regions of the left ventricle to determine time of arrival of depolarization at epicardial sites subjacent. Ischemia produced tardy and unopposed activation of the left ventricular free-wall and oriented major vectors caudad and dorsad, as opposed to their craniad and dorsad orientation in the control state. Peak magnitude of QRS portion of the spatial magnitude electrocardiogram increased markedly, and duration of QRS doubled. Epicardium in the ischemic zone depolarized tardily, whereas in the control state, epicardium from all areas on the left ventricle was activated early during QRS and nearly simultaneously.

QRS component of the orthogonal lead, spatial magnitude and spatial velocity electrocardiograms, and vectorcardiograms of turkeys

Summary Using the Wilson equilateral tetrahedral reference system, electrocardiograms were recorded from turkeys, and analysis of orthogonal characteristics was performed by digital computation. QRS was 59 msec. Initial activity, lasting for approximately 15 msec, and produced presumably by endocardial to subendocardial activation of a zone around the apex of the left ventricle, was oriented ventrad and slightly craniad but occasionally caudad. Remaining activity, produced presumably by apico-basilar activation of the middle and basilar thirds of the interventricular septum, was oriented markedly craniad and dorsad. The peak of the QRS portion of the spatial magnitude electrocardiogram was 0.88 mV. Two peaks of the QRS portion of the spatial velocity electrocardiogram were 115 and 66 mV./msec. and occurred during the rising and falling portions, respectively, of QRS in the spatial magnitude electrocardiogram. Pathways of ventricular depolarization in the turkey are presumed to be similar to those of ungulates and different from those of carnivores and primates. These differences stem apparently from the more complete penetration of Purkinje fibers to the epicardium of turkeys.

Electrocardiographic and vectorcardiographic response to right ventricular hypertrophy in the goat.

Basic differences were observed in the elctrocardiographic and vectorcardiogrpahic response to RVH in goats when compared to man and dogs. Instead of RVH inducing a redistribution of major fronts of electrical activity which result in profound QRS complex alterations as in man and dogs, it appears to produce no significant alteration of the QRS complex or major vector orientation in goats. Although slight reorientation of sagittal and horizontal vector forces occurred during development of RVH, no statistically significant changes could be detected.

CONTRACTILITY OF THE NORMAL CANINE VENTRICLE

Although the kidneys, the adrenal cortex, the autonomic nervous system and the heart have been incriminated in the pathogenesis of congestive heart failure 1-5 and although criteria pathognomonic of congestive heart failure do not exist, nonetheless we may indict reduction in ventricular contractility as an event most likely to lead t o development of congestive heart failure. Others will describe the pat hophysiology of the ventricles in congestive heart failure. The purposes of this paper are t o define contractility, to review briefly and historically methods for studying contractility. and t o demonstrate clinical application of one method.