Measurements of right ventricular internal dimensions and their relationships to severity of tricuspid valve regurgitation in national hunt thoroughbreds.

The effect of tricuspid valve regurgitation (TR) in right ventricular (RV) chamber size has not been reported. An echocardiographic and auscultation study was conducted on 394 race-fit National Hunt Thoroughbreds (TBs) in 4 training yards. Auscultation was performed on each horse and audible murmurs of TR graded using a 1-6 scale. Echocardiography was also performed and standard, 2-dimensional (2D), short (SA) and long axis (LA) images of the RV obtained from a right parasternal location. An m-mode image was recorded from an SA view of the RV just below the level of the tricuspid valve. Colour flow Doppler (CFD) echocardiography was used to interrogate the tricuspid valve and right atrium. If retrograde flow was visible, representative recordings were also acquired. Severity of TR by CFD was graded using a subjective 1-9 scale. Measurements of RV chamber size in systole and diastole were made from archived 2D, LA, SA and m-mode images by a single observer unaware of the auscultation and CFD findings. To determine day-to-day repeatability of RV measurements from each imaging plane and of TR by CFD, 5 horses were examined on 5 consecutive days using an identical echocardiographic protocol. Images from 30 horses in the original dataset were also measured on a second occasion to determine the intra-observer repeatability. There were significant positive correlations between the severity of TR by CFD and RV internal diameter from each image plane. In contrast, there were no significant associations between grade of TR by auscultation and any RV dimension. Data also showed that only RV measurements derived from M-mode images have acceptable intraobserver repeatability and similarly the M-mode measurements had the best overall day-to-day repeatability. Data showed that TR assessed by CFD was positively associated with the diastolic and systolic dimensions of the RV, but failed to demonstrate a positive association between the presence of a murmur of TR and RV chamber size. M-mode and 2D echocardiography provided moderately reliable and repeatable methods for obtaining measurements of RV internal dimensions. M-mode images provide the most reliable and repeatable measurements, particularly for less experienced operators.