Influence of alterations in heart rate on echocardiographic measurements in the dog.

M-mode echocardiograms were recorded from 10 conscious, clinically normal dogs at various heart rates during atrial pacing. Heart rate was recorded as cycle length (seconds), and measurements were made only during sustained 1:1 atrial-to-ventricular conduction. In all dogs studied, there was a significant (P less than 0.01) positive correlation of left ventricular internal chamber dimension in diastole and systole to cycle length. Also, there was positive correlation between these left ventricular dimensions and the square root of cycle length, which predicted a plateau in dimensional changes as cycle length increased. Echocardiographic shortening fraction and left ventricular and septal wall thickness measurements did not change consistently during pacing. We concluded that left ventricular chamber dimensions in the dog may be significantly affected by alterations in heart rate.