Echocardiographic determination of stroke volume during rapid atrial pacing and volume loading in normal rats

Objective: The aim was to validate echocardiographic assessment of acute changes of left ventricular stroke volume in normal rats. Methods: By transthoracic use of a 7.5 MHz ultrasonic transducer, the left ventricular dimensions were determined before and during rapid atrial pacing and saline infusion in seven Wistar rats weighing 310-470 g. Left ventricular volume was calculated from short axis dimensions according to a cube function formula. Echo stroke volume (SVE) was then compared with that obtained simultaneously using a pulsed Doppler flow meter placed around the ascending aorta (SVF). Results: The SVE (ml) was decreased from 0.30(SD 0.12) to 0.13(0.06) by rapid pacing and increased from 0.27(0.12) to 0.63(0.16) by volume loading. Regression analysis showed high correlations between SVE and SVF during both pacing (r=0.84) and infusion (r=0.91) studies. Furthermore, correlations between SVE and SVF in individual animals were very close (r=0.87-0.99 in the pacing study and 0.92-0.99 in the volume study). Interobserver and intraobserver variances were small, with close correlations (r=0.96-0.99) and modest standard errors of the estimate (0.02-0.04 ml) between the two measurements. Conclusions: Echocardiography allows reliable in vivo measurement of cavity dimensions and assessment of acute alterations in stroke volume in normal rats.