Characterization of systolic intervals in healthy, conscious sheep

Objective-To characterize systolic intervals of the left ventricle and their relationship with heart rate in conscious sheep. Animals-11 healthy Romanov sheep (age range, 3 months to 10 years). Procedures-Systolic intervals and indices of myocardial contractility of the left ventricle were measured in conscious sheep by use of polycardiography. Results-The mean +/- SD pre-ejection period was 59 +/- 12 milliseconds, and the mean left ventricular ejection time was 194 +/- 34 milliseconds. The mean myocardial tension index was 0.22 +/- 0.05, and the mean ratio of the pre-ejection period to ejection time was 0.30 +/- 0.09. Total electromechanical systole, mechanical systole, and ejection time varied inversely with heart rate. The electromechanical delay and pre-ejection period were not correlated with heart rate, nor were the myocardial tension index and the ratio of the pre-ejection period to ejection time. The isovolumetric contraction index and isovolumetric contraction time were not significantly correlated with heart rate, although the values for the correlation coefficient were moderate (r = -0.561 and r = -0.482, respectively). Conclusions and Clinical Relevance-Although a larger study would be needed to provide reference intervals for healthy sheep, the results of the study reported here provided useful information for the cardiac evaluation of sheep. (Am J Vet Res 2009;70:330-333)