Endocardial pacing site affects left ventricular end-diastolic volume and performance in the intact anesthetized dog.

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Abstract
We investigated how pacing from different endocardial sites affects the left ventricular three-dimensional contraction pattern and performance in intact anesthetized dogs. We used data from the motion of radiopaque markers implanted in the left ventricular endocardium in an analysis based on the polar decomposition theorem to determine the left ventricle's three-dimensional principal directions and magnitudes of deformation, and its axis and angle of rotation during the cardiac cycle. This paper also derives a new procedure that permits statistical comparison of different left ventricular cavity deformation patterns. During normal sinus rhythm and pacing from the right atrium, left ventricular septum, left ventricular apex, and right ventricular apex, the principal directions of left ventricular deformation remained relatively fixed with respect to the left ventricle's anatomy, independent of heart rate and pacing site. These directions were oriented in septum-free wall, anterior-posterior, and apex-base directions. End-systolic pressure and volume did not vary significantly among pacing sites. End-diastolic volume varied significantly among pacing sites, with right ventricular apical pacing producing the smallest end-diastolic and stroke volume. These results reveal that beats produced by right ventricular apical pacing eject less blood compared with beats produced by right atrial, left ventricular septal, or left ventricular apical pacing.