Adjusted-MPI for the evaluation of right ventricular performance of the dog.

The Myocardial Performance Index (MPI) or Tei index is a non-invasive and reproducible Doppler index that allows to evaluate the ventricular systolic and diastolic performance. In human medicine, it has been demonstrated to be useful in estimating the prognosis in patients affected by pulmonary hypertension, dilated cardiomyopathy and heart failure. In veterinary medicine, the reports regarding the application of MPI in dogs for the evaluation of the right ventricular performance are scant. MPI is calculated based on the following equation: (TCO-ET)/ET, where TCO is the interval from the cessation to the onset of tricuspidal inflow, and ET is the ejection time of the right ventricular outflow. MPI is independent from heart rate when TCO and ET are obtained from cardiac cycles of equal duration. The aim of this study was therefore to normalize MPI (adjusted-MPI) for heart rate and to verify if this new index can be useful to better evaluate the ventricular performance in dogs with variations of heart rate. Doppler evaluation (using the echograph Esaote MyLab30-Vet equipped with ECG monitoring and a 1-4 MHz phased-array transducer) was performed on a group of 112 dogs. The dogs of, different breed, age, and sex were divided in two groups: group 1: healthy (29 dogs); group 2: with heart disease (83 dogs). Group 2 was divided into 2 sub-groups: A (without heart failure: 49 dogs) and B (with heart failure: 34 dogs). MPI was obtained calculating the mean value of three different TCO and ET for each dog. The mean values of TCO, ET and heart rate were used in the statistical analysis. In particular, with adjusted-Y method and the parallel regression lines test, used to obtain a common angular coefficient, it was possible to normalize TCO and ET to the same heart rate (128,04 bpm) and to calculate the adjusted-MPI (adj-MPI). MPI and adj-MPI values were subjected to the analysis of variance (ANOVA) in the three different groups of patients, and then, the Hocberg test allowed evaluation of a statistically significant difference between the three groups on the base of adj-MPI and non of MPI. We found that the adj-MPI in dogs with a heart rate between 59 and 213 bpm, was able to estimate more precisely the right ventricular performance compared to non-adjusted MPI, thus allowing a better distinction between healthy dogs and dogs affected by cardiac disease with or without heart failure.