Page 46 - Feline Cardiology

40 Section B: Diagnostic Testing

Diagnostic Testing

Figure 6.2. Lateral (A) radiograph from a cat with a “lazy” (cranioventrally rotated) heart position. Also note the tortuous course of the
aorta (arrows).

had primary heart disease, while all cats with a VHS >9.3 the falciform ligament and subcutaneous fat can assist
had heart disease (Sleeper, in press). Therefore, the in subjectively determining the contribution of pericar-
echocardiogram yielded the most useful information dial fat to heart size. Also, the margin of the cardiac
in cats where heart enlargement was questionable silhouette appears less well-defined than normal if a
(8 V < VHS < 9.3). Excluding pericardial disease cases, substantial amount of pericardial fat is present, and the
cats with a VHS >9.5 were likely to have heart disease, border near the right atrium often has an angular
and definitive diagnosis of the underlying heart disease appearance (squared border as opposed to the normal
could be pursued once the patient was stabilized. In cats egg-shaped feline heart) (Figure 6.4). Finally, in some
with VHS = 8–9.3 V, an echocardiogram was valuable to obese cats, altering the exposure by increasing mAs and
determine whether heart disease was, or was not, present. decreasing kVp enhances radiographic differentiation of
In obese cats, excessive pericardial fat can make the fat and heart (Litster and Buchanan 2000b).
cardiac silhouette appear enlarged, obscure the cranial In the lateral projection, the cranial pulmonary arter-
margin of the heart, and/or cause tracheal elevation. It ies are dorsal to the bronchus and the cranial pulmonary
is sometimes difficult to identify the true cardiac silhou- veins are ventral to the bronchus. The cranial lobar
ette, which can cause overestimation of heart size. vessels are usually seen as pairs of vessels, each pair with
Although the separation of two soft tissue structures a bronchus (artery-bronchus-vein from dorsal to
from each other can be accentuated by the presence of ventral). The more cranial pair of vessels generally cor-
fat, pericardial fat represents an intermediate opacity responds to the side on which the cat was recumbent
between myocardium and air-filled lung, which compli- when the lateral projection was made. The normal pul-
cates identification of the cardiac margins. Additionally, monary arteries and veins should be equal in size, and
concurrent subcutaneous fat may be substantial, and their width where they cross the 4th rib should not
together these factors may make it difficult to identify exceed the width of the narrowest portion of that rib
the true cardiac silhouette in many obese cats, leading (Hayward et al. 2004).
to inaccurate estimation of heart size. Recognizing this In the DV or VD projection, the cardiac axis is most
possibility usually allows the astute clinician to avoid the commonly on or close to midline, and the width of the
pitfall. Examination of the degree of abdominal fat in cardiac silhouette does not usually exceed 50% of the