6.3.3 Further diagnostic aids
Although mild-moderate TR may not be associated with any clinical signs, it can be significant in some individuals and therefore further investigation may be justified. Echocardiography is the best method to assess whether TR is resulting in significant volume overload. Unfortunately, accurate measurement of the RV or RA size from either M-mode echocardiography or 2DE is difficult because of the absence of good landmarks and the trabeculations of the RV surface. However, a subjective assessment of the size of the structures is useful. The RA and RV should be examined from the right parasternal location in long-axis and short-axis views, and at angles between the two. Familiarity with these views will allow a subjective assessment of the size of the atrium and ventricle. The aorta acts as a reference point. A thick chest wall can give the appearance of a large RV because more of the free-wall is visible. Prolapse of the TV is most often seen in the long-axis view. Using pulsed-wave Doppler, a jet of regurgitant blood is most frequently detected in the long-axis view running along the side of the atrium where it borders the aorta. Jets which can be detected over a much wider area of the RA are more likely to be associated with clinically significant disease. If RV volume and pressure are particularly high, the interventricular septum (IVS) will be flaftened, i.e. it is pushed towards the LV, and in extreme cases, the motion of the IVS will be paradoxical (see section 4.2.6).
Contrast echocardiography can be a useful technique in animals with loud pansystolic murmurs on the right side of the chest, particularly when Doppler equipment is not available. Contrast may be seen regurgitating back into the RA in cases of TR. Some animals with TR may have increased amounts of sponcontrast within the RA and RV. When TR is present this may be seen moving back into the RA during systole. The echocardiographic features of TR were summarised in Table 4.10.
Electrocardiography is indicated in horses with arrhythmias, but is not helpful for assessing the degree of volume overload in individual animals with TR.
Clinical pathology may be helpful in animals with suspected endocarditis; however, this is very uncommon.