Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 53
Fig. 2-21 Graphs showing the normal
values (predicted value ±95%
confidence interval) of the normal
left ventricular wall thickness during
diastole (A) and systole (B). (From
Bonagura JD, O’Grady MR, Herring
DS: Echocardiography: Principles of
interpretation. Vet Clin North Am
1985; 15:1189.)
A
B
valve, the sample volume is positioned in the left ventricle, just distal to the mitral valve
annulus at the point of maximal opening of the mitral valve. 25,67 Normal studies at heart
rates less than approximately 125 beats per minute will clearly reveal separate flows during
passive (E wave) and active (A wave) filling of the ventricle (Fig. 2-34). With very slow
rates, a separate L wave associated with pulmonary vein inflow may be seen between the
E wave and A wave. During systole, a fourth wave (S wave) is seen, which is a low-velocity,
positive turbulent flow signal and occurs after the A wave. In heart rates greater than
approximately 125 beats per minute, these flow phases begin to coalesce, and at rates
greater than 200 beats per minute the E and A waves are no longer distinguishable. 25
Similar information may be obtained at the tricuspid valve (Fig. 2-35).
AO RTA
The aortic arch and branches of the ascending aorta are obscured by the fluid density of
the cranial mediastinum. On the lateral radiograph, the descending aorta can be identified
crossing the trachea cranial to the tracheal bifurcation and continuing caudally and dorsally
from that point. If a good inspiratory radiograph is obtained, the aorta may be traced
to the diaphragm. However, in most normal animals, its smooth margin (especially the