Page 367 - Feline Cardiology

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Pulmonary Thromboembolism and Pulmonary

Hypertension

Key Points

• Pulmonary thromboembolism (PTE) affects cats without sex, age, or breed predisposition, including several cases in cats <2
years old.
• A variety of associated disorders are thought to contribute to PTE, notably heart disease and neoplasia. It is rare for PTE to
occur without a concurrent or predisposing disorder. Clinical signs are most commonly constitutional (e.g., lethargy, anorexia)
or respiratory (e.g., dyspnea) and are subtle or nonspecific, because in virtually all feline cases, pulmonary thromboembolism
was not suspected at admission or during treatment.
• Pulmonary hypertension is a rare disorder in cats, and when it occurs, it is typically associated with (and likely caused by)
congenital heart disease, heartworm disease, pulmonary thromboembolism, or pleural effusion of any cause.
• Management of cats with pulmonary hypertension revolves around identification and treatment of the associated/inciting
cause.

PULMONARY THROMBOEMBOLISM diagnostic imaging or thorough diagnostic testing to
exclude other causes of dyspnea (pulmonary thrombo-
Introduction embolism often is a clinical diagnosis of exclusion); and
In both human and veterinary medicine, pulmonary third, effective treatment requires therapy directed at
thromboembolism is an underrecognized, potentially both the clot and the underlying process that almost
life-threatening disorder. It is characterized by in situ always accompanies it and likely predisposed to its
formation of a thrombus (a clump of red and white formation.
blood cells, platelets, fibrin, and possibly foreign mate-
rial, bacteria, fungi, or neoplastic cells; or air, fat, or Etiology and Pathophysiology
amniotic fluid) within a pulmonary artery, embolization In pulmonary thromboembolism cases, pulmonary
(detachment of a distant thrombus from the venous arterial or arteriolar obstruction is caused by a clot of
system to a pulmonary artery); or a combination of the blood and possibly other substances. Pulmonary arterial
two. resistance is increased due to this mechanical obstruc-
Pulmonary thromboembolism is an uncommon dis- tion of blood flow and also due to reflex vasoconstric-
order in cats, but it is likely underrecognized. One nec- tion from release of vasoactive mediators (serotonin,
ropsy survey identified a prevalence rate of 0.06% in the thromboxane) from the thrombus. Low output
feline population of accessions to a university pathology (“forward”) heart failure and shock may occur with
service (Schermerhorn et al. 2004). acute, massive pulmonary thromboembolism (Whitley
There are three crucial elements that dominate the and Stepien 2001). Factors that cause hypoxemia in cases
diagnosis and treatment of pulmonary thromboembo- of pulmonary thromboembolism include ventila-
lism. First, there is a need for early suspicion of the tion : perfusion mismatch, alveolar dead space, intrapul-
diagnosis; second, there must be confirmation through monary or intracardiac right-to-left shunting, pulmonary

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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