US EPA

2609683 

Journal Article 

Equine myocardial right ventricular ouflow tract function in horses with RAO 

Stahl, AH; Gehlen, H 

2010 

0 

Pferdeheilkunde
ISSN: 0177-7726 

26 

3 

335-343 

WOS:000278934600002 

RAO is one of the most common equine airways diseases. In former studies conventional echocardiography was only in rare cases able to reveal cardiac hypertrophy or dilatation of the right ventricle, cor pulmonale, in terms of RAO, although in right heart catheterization pressure changes were often evident. By Doppler myocardial imaging already subtle changes of myocardial movement con be detected. This pilot study was aimed to show how and to what extent pulmonary and systemic hypoxia as well as higher pulmonary resistance may influence right ventricular myocardial outflow tract function. In a first step normal values for right ventricular myocardial outflow tract parameters were determined and in a second step these values were compared to those of RAO subjects. The study population consisted of 12 warm-blood horses (age 6 - 13 years). All horses underwent physical and further clinical pulmonary examination, as well as conventional echocardiography (standard two-dimensional, M-Mode and colour-flow doppler echocardiography) and simultaneously obtained electrocardiogram. 6 horses (mean weight 559 +/- 51 kg; height 170 +/- 7 cm) were diagnosed with RAO by history (coughing, dust and exercise intolerance for more than 3 months), clinical signs (coughing, nasal discharge, exaggerated abdominal effort at rest), endoscopy (excessive mucus production and thickened tracheal bifurcation), cytological evaluation of tracheobronchial secretions (> 25% neutrophiles, Curshmann Spirals) thoracic radiography (peribronchial infiltrations) and arterial blood gas analyses (alveolo-arterial oxygen difference, AaDO(2) > 14 mmHg). 6 horses (mean weight 574 +/- 33 kg; height 169 +/- 4 cm) were considered to be cardiopulmonary healthy based upon previous examination. Doppler myocardial imaging of the right ventricular outflow tract was obtained from right parasternal cardiac window. Three consecutive cardiac cycles were stored for off-line analysis. By Tissue velocity imaging the myocardium was colour coded and the region of interest was placed at the base of the pulmonary valve and tracked throughout the cardiac cycle. By 2 dimensional strain imaging (2 DS / speckle tracking) the right ventricular outflow tract myocardium was equally subdivided in three segments: basal (near the tricuspid valve), mid (between basal and apical segment) and apical (near the pulmonary valve). Systolic, early diastolic filling and late diastolic filling / atrial contraction velocities, as well as deformation (strain and strain rate) and displacement parameters were measured. Tissue velocity imaging at the pulmonary valve based myocardium showed a significantly increased atrial contraction velocity (p < 0.05) in RAO horses. Angle-independent 2 DS imaging revealed significant differences between RAO and control horses at the basal and mid segment of the right ventricular outflow tract in strain, strain rote (p < 0.005) and velocity (p < 0.05) parameters. Doppler myocardial imaging objectively quantifies RAO's impact on right ventricular myocardial function. This study gives a non-invasive insight on right ventricular myocardial outflow tract function and measures myocardial changes due to RAO. These results point out cardiopulmonary interaction and the necessity of early RAO treatment. Otherwise the right ventricle might be a powerful contributor to performance insufficiency in terms of RAO. 

Cardiology; RAO; right ventricular myocardial function; tissue Doppler imaging; tissue velocity imaging