Agreement between echocardiographic techniques in assessment of the left ventricular myocardial performance index in rabbits

Objective-To report reference values and examine the agreement in the myocardial performance (Tei) index of the left ventricle (LVTI) as measured by tissue Doppler imaging (TDI), pulsed-wave Doppler imaging (PWD), and M-mode echocardiography in clinically normal rabbits. Animals-26 clinically normal male New Zealand White rabbits. Procedures-Echocardiographic examinations that included TDI, PWD, and M-mode echocardiography were performed. Rabbits were sedated by SC administration of ketamine and midazolam. Intraclass correlation coefficients (ICCs) were used to measure absolute agreement among the 3 echocardiographic techniques. Intraclass correlation coefficients were computed for values a and b and for the equation (a - b)/b used to determine LVTI;, value a equals the sum of isovolumic contraction time, ejection time, and isovolumic relaxation time, and value b equals the left ventricular ejection time. Values of ICC > 0.75 indicated good agreement between 2 echocardiographic techniques. Results-For value a, Pearson correlation coefficients between pairs of techniques were all high (r >= 0.7). However, only the septal TDI and the lateral wall TDI had good agreement (ICC, 0.86). For value b, correlations were generally low with the exception of the correlation between the septal and the lateral wall TDI. For value b, TDI was the only technique with good agreement (ICC, 0.77). For LVTI, only TDI techniques had a significantly positive correlation. All the other correlations were close to zero with a paradoxic moderate negative correlation between PWD-determined LVTI and lateral wall TDI-determined LVTI. Conclusions and Clinical Relevance-For LVTI, the absolute agreement was poor between all pairs of techniques. (Am J Vet Res 2009;70:464-471)