Page 112 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 111

BOX 11.1. Cardiac Necropsy Techniques in Cats Suspected of Dying from Heart Disease

In cats dying from possible cardiac disease, a comprehensive sequentially following the path of a red blood cell from
necropsy is done including both gross (preferably with photo- right atrium to aorta. With either method, a systematic
graphs for the medical record) and histopathologic analyses. assessment of all 4 chambers and 4 valves is essential,
Typically, the following postmortem examination procedure is including chamber content (i.e., identification of an
recommended: intracardiac thrombus), wall thickness and symmetry
between the septum and the free wall, valve
• The chest is opened laterally with transection of the dorsal structure, and integrity of endothelium and
and ventral extensions of all ribs on the left side, and all chamber walls.
the parasternal soft tissue attachments. The thoracic wall is • Samples for histologic analysis are obtained from the
reflected dorsally, exposing the entire thorax from the left interventricular septum, right and left ventricular free
side. Pleural and pericardial effusion are noted if present, and walls, and one or both atria, as well as visibly abnormal
samples obtained for analysis as clinically indicated. lesions. Full thickness tissue blocks from the ventricular Cardiomyopathies
• Before dissecting the pluck (lungs, trachea, heart, and associ- wall and septum should be taken in the transverse plane
ated vessels) from the esophagus and removing the pluck perpendicular to the long axis of the ventricle. Ideally,
from the body, attention should be paid to the cranial and several myocardial samples of the left ventricle are obtained
caudal mediastinum and the structure, location, and integrity including the basilar and mid-interventricular septum, the
of vascular connections, notably the aorta, cranial and caudal anterolateral left ventricular free wall, and the posterior
venae cavae, azygos vein, and thoracic duct. free wall between the papillary muscles, for evaluation of
• To remove the pluck after dissection from the esophagus, myocyte disarray, fibrosis, and small coronary artery disease
the cranial and caudal mediastina are removed, the trachea (Liu et al. 1993).
is transected at the thoracic inlet, and the cranial and caudal • Samples for histologic analysis are placed in 10% buffered
venae cavae, and azygos vein are transected 5–10 mm from formalin, fresh samples for DNA or RNA extraction should
their junction with the heart. The proximal descending sec- be deep frozen (−80°C) or preserved in a purpose-made
tion of the aorta is transected, and the brachiocephalic trunk medium (e.g., RNALater®), and samples for electron mi-
and left subclavian artery are also transected 3–5 mm distal croscopy (which should be harvested within 20 minutes of
to their branching from the aorta. death) are placed in glutaraldehyde.
• The lungs are removed from the pluck, paying special • Extracardiac examination typically includes the lungs for
attention to the pulmonary veins and arteries for size gross and histologic assessment for pulmonary edema or
(venous enlargement is expected with congestive heart noncardiac pulmonary parenchymal disease; the distal
failure), stenosis, and location (anomalous connections; aorta, renal arteries, and proximal femoral arteries to assess
rare). for arterial thromboembolism; the liver for evidence of
• The heart may be opened one of two ways: according to congestion; and the eyes, kidneys, and other organs as sug-
echocardiographic planes (single long-axis incision) or gested by clinical findings.

is less common than pulmonary edema in cats with arteriosclerosis, moderate to severe interstitial fibrosis,
HCM (20% of cats had pleural effusion versus >50% of and severe concentric hypertrophy of the papillary
cats having pulmonary edema on pathologic examina- muscles along with portions of the LV walls (Kittleson
tion) (Fox 2003a). This parallels the clinical observation et al. 1999). In a study comparing morphologic abnor-
that only 15% of cats with HCM and heart failure have malities of humans and cats with HCM, only 30% of
dyspnea due to pleural effusion; the majority of cats are cats had evidence of myofiber disarray of the septum,
dyspneic due to pulmonary edema (Rush et al. 2002). whereas the majority (92%) of people had disarray (Liu
Hallmark histopathologic myocardial lesions in cats et al. 1993). The majority of cats in this study were
with HCM include myofiber disarray, small coronary domestic shorthair, and only 1 Maine coon was included.
arteriosclerosis, and interstitial and replacement fibrosis It is possible that earlier pathologic studies were not as
(Figure 11.4) (Kittleson et al. 1999; Liu et al. 1993). thorough to search for myofiber disarray, or that Maine
Histopathologic abnormalities seen in the lungs of cats coon cats with HCM more often have myocyte disarray
with heart failure include presence of pulmonary edema than other breeds of cats. Abnormal intramural coro-
fluid within alveoli, thickened alveolar membranes, nary arteries are commonly found in people (66%) and
and ruptured alveoli. All eight Maine coon cats with cats (74%) with HCM and are mostly found within
severe HCM that died in one study had moderate to or at the margins of fibrous regions (Liu et al. 1993).
marked myofiber disarray of the LV wall and interven- In people with HCM, 13% of the septum and 10% of
tricular septum, moderate to severe intramural coronary the LV free wall consist of fibrosis, and the amount of