Page 569 - The Veterinary Laboratory and Field Manual 3rd Edition

506 Samuel Sharpe

SaMPLInG
Formalin:

• A 0.5–1 cm thick transverse section from
each lung.
• Bronchial lymph node.

Fresh-frozen:

• Larger piece of lung for bacterial culture/
ancillary testing.
Figure A2.1 Bovine left ventricular papillary muscle.
Note the multifocal to coalescing areas of reddening
Heart on the cut surface of the papillary muscle corre-

• Leave the heart attached to the lungs to facili- sponding to areas of ischaemic infarction as a result
tate examination of great vessels. of bacterial vasculitis caused by Histophilus somni
• Make a transverse incision across the ven- infection. See also Online figure 1. Photo: courtesy
tricles just below the level of the papillary of C. MacGowan, University of Calgary, Canada.
muscle.
• This allows measurement of the thickness of necrotizing myocarditis caused by Histophilus
the left and right ventricular (LV and RV) free somni infection (Figure A2.1).
walls and the interventricular septum. The LV
free wall and interventricular septum should tHInGS to notE
be of similar thickness. Ratio of LV : RV thick- Examination of the heart should encompass the
ness should be 2 : 1 to 3 : 1. myocardium, endocardium, heart valves, and
• Open the proximal pulmonary artery to check great vessels. In overview, the left ventricle is thick
for thromboemboli. walled and forms a point at the apex of the heart.
• Complete heart examination by dissecting Note if the silhouette of the heart is rounded as
the heart in the direction of blood flow. this may indicate myocardial remodelling.
• Begin at the right auricle and open the auri-
cle and atrium parallel to the atrioventricular • Myocardium: The heart is a muscle and as
valves. such should be diffusely soft to firm, dark
• Dissect the right ventricular free wall by care- red with an intact, shiny epicardial surface.
fully incising around the coronary groove up Areas of reddening, pallor, excessive softness
and out of the pulmonary outflow tract. or firmness should be noted and sampled.
• Open the left auricle and atrium in the same • Valves: In health both the atrioventricular and
way as the right. semilunar valves have a fibrous core covered
• Make a single cut in the left ventricular free by shiny, intact endocardium and are deli-
wall down through the mitral valve. cate, translucent structures with a sharp free
• Open the aortic outflow tract by cutting up edge. Disruption of the endocardium usually
through the septal leaflet of the mitral valve. by bacterial infection (vegetative valvular
• In cattle, it is often useful to make a trans- endocarditis, see Figure A2.6) with result in
verse incision through the papillary muscle of accumulation of fibrin and clotted blood on
the left ventricle as this is a common site for the valvular surface.

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