Effects of changes in ventricular size on regional and surface QRS amplitude in the conscious dog. Circulation 62: 174

SUMMARY Eight conscious dogs instrumented with wall thickness sonomicrometers and 11 subcutaneous electrodes in a modified McFee vectorcardiographic array were studied during changes in ventricular volume. Simultaneous measurements were made of QRS amplitudes of the endocardial and epicardial ECG, QRS spatial vector magnitudes (SVM), end-diastolic wall thickness (EDT), end-systolic wall thickness (EST) and the amount of systolic thickening (zAWT). Ventricular size was decreased by atropine and infulsion of 0.02 gg/kg/min of isoproterenol to increase the mean heart rate from 81 ± 5 beats/min (mean ± SEM) to 174 10 beats/min (p < 0.001), and was reflected by an increased mean EDT (9.06 ± 0.64 mm to 9.94 i 0.61 mm, p < 0.005). The endocardial QRS amplitude increased in each dog (mean increase 21.55 ± 1.36 mV to 25.13 ± 1.35 mV, p < 0.001), whereas the SVM decreased from 7.69 ± 0.75 mV to 6.18 ± 0.48 mV (p < 0.02). Ventricular size was then increased by rapid saline infusion and was reflected by a decrease of EDT from 9.65 ± 0.66 mm to 9.09 ± 0.66 mm (p < 0.001), while heart rate remained unchanged. Endocardial amplitude decreased in each dog (average decrease 3.59 ± 0.25 mV, p < 0.001), while the SVM increased in each dog (average increase 0.81 ± 0.18 mV, p < 0.005). The mean epicardial amplitudes did not change significantly during either increases or decreases in ventricular volume. In each dog, there was a linear relation between EDT and endocardial amplitudes (r values> 0.88) and an inverse linear relation betwee