Abstract
No systematic correlation is available regarding the effect of heart rate on cardiac size and performance in man. Thus echocardiograms were performed in 25 normal subjects at 10 beat increments of heart rate from 50 to 150 beats/min during atrial pacing. Blood pressure as obtained with sphygmomanometer did not change significantly during pacing (group mean systolic 125, diastolic 81 and mean 96 mm Hg). Left ventricular end-diastolic dimension and end-systolic dimension decreased with increasing heart rate from a group mean of 4.8 and 3.0 cm, respectively, at a rate of 70/min to 3.0 and 2.3 cm at a rate of 150/min. The percent reduction in left ventricular dimensions was linear and was related to heart rate as end-diastolic dimension = −0.0027 heart rate + 1.26, r = 0.90 and end-systolic dimension = −0.0026 heart rate + 1.24, r = 0.72. Mean fiber shortening velocity increased with a greater heart rate from 1.09 at a rate of 70/min to 1.63 circumference/sec at a rate of 150 beats/min, and the percent increase was also linearly related to rate as velocity = 0.0047 heart rate + 0.56, r = 0.67. Echocardiographic shortening fraction did not change during pacing (mean 0.38). Interventricular septal and posterobasal wall thickness measured at end-diastole increased with accelerated pacing rates from 9.2 and 8.7 mm, respectively, at a rate of 70/min to 11.3 and 10.2 mm at a rate of 150/min. The percent increase in septal and posterobasal wall thickness was linearly related to rate as septal thickness = 0.0036 heart rate + 0.66, r = 0.82 and posterobasal thickness = 0.0027 heart rate + 0.75, r = 0.70, respectively. Left atrial dimension diminished with increased pacing rate to a rate of 120/min but reached a plateau at rates of greater than 120/min.These data indicate that cardiac size is significantly affected by alterations in heart rate. Although velocity of circumferential fiber shortening is augmented by accelerated heart rate, shortening fraction is not influenced by changes in heart rate. These data provide guidelines by which to account for alterations in heart rate in the measurement of echocardiographic variables of cardiac size and performance.
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