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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) [ABSTRACT FROM AUTHOR]

Abstract: The avian cardiovascular system is of special interest because avian hearts are relatively larger than mammalian hearts, and activation of ventricular myocardium in birds has a “flash” pattern. Systolic time intervals and indices of myocardial contractility were examined in anaesthetized open-chest chickens by polycardiography, including synchronous recordings of electrocardiogram, phonocardiogram, and apex cardiogram. The asynchronous contraction time, isometric contraction time, pre-ejection period and ejection time were 26±3 (Mean±SD), 21±9, 47±12, and 83±23 ms, respectively, for heart rates of 260±57 bpm. The myocardial tension index, isometric contraction index and the pre-ejection period/ejection time ratio were 0.39±0.11, 0.42±0.10, and 0.54±0.14, respectively. A “flash” pattern of ventricular myocardial depolarization causes more rapid excitation and as a consequence shorter asynchronous contraction time of relatively larger chicken hearts compared with rabbit hearts. Inverse relation (P <0.05) of the asynchronous contraction time to the heart rate in chickens is probably associated with the specific activation pattern of avian ventricles. Establishment of the values of systolic time intervals will facilitate a better understanding of cardiac function in birds. The obtained results are discussed in comparison with the rabbit. The indices calculated from the systolic time intervals show disadvantageous contractile function of chicken heart compared to rabbit heart. [Copyright &y& Elsevier]

The present study is the first attempt to examine the effect of left ventricular hypertrophy (LVH) on the excitation pattern of the ventricular epicardium in experimental hypertensive rats. The left renal artery was clipped in Wistar rats ( n= 8; 6–8 months old; weight, 174–295 g) to produce two-kidney one-clip (2K1C) hypertension. After 4 weeks, blood pressure was measured, and epicardial potential mapping was performed under sinus rhythm from 64 unipolar electrodes regularly distributed over the ventricular epicardium. Systolic blood pressure was ∼40% higher in the rats with a clipped renal artery (162 ± 14 mmHg, mean ± s.d.) than in the normotensive rats (115 ± 3 mmHg). LVH (∼23% increase in the ratio of the left ventricular weight to the body weight, P < 0.05) was observed in the 2K1C hypertensive rats. The depolarization pattern of the ventricular epicardium in the normotensive rats was similar to that in the rats with 2K1C hypertensive LVH. The duration of ventricular epicardial activation was shown to increase (∼35%, P < 0.05) in the hypertensive rats as compared to the normotensive animals. This study provides an explanation for alterations of the body surface potential distribution in hypertensive patients with LVH. [ABSTRACT FROM AUTHOR]