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Chapter 25: Pulmonary Thromboembolism and Hypertension 387

pulmonary scintigraphy (perfusion scan with Chapter 20). The heparins require adequate plasma
technetium-99m-labeled macroaggregated albumin) antithrombin (AT) levels to be effective, and for this
demonstrated perfusion defects consistent with pulmo- reason, significantly hypoproteinemic patients (particu-
nary thromboembolism, and although a ventilation scan larly those that are hypoalbuminemic, since albumin
was not performed concurrently, the diagnosis was and AT are similar in molecular weight) should be anti-
supported because a thrombus had been visualized coagulated with drugs other than heparin or low molec-
echocardiographically in the right pulmonary artery ular weight heparin. Anticoagulant treatment approaches
(Pouchelon et al. 1997). Presence of a perfusion defect and options are identical to those for aortic thrombo-
on nuclear scintigraphy in the absence of radiographic embolism, and the reader is referred to Chapter 20 for
pulmonary abnormalities of that lung segment are this information.
highly suggestive of pulmonary thromboembolism.
However, for most cats with pulmonary thromboembo- Outcome and Prognosis
lism, the standard of care for diagnostic imaging at the
present time should include thoracic radiography, echo- The prognosis for cats with pulmonary thromboembo-
cardiography, and arterial blood gas analysis. lism varies depending on cause, extent, and response to
Plasma D-dimer is a breakdown product of cross-linked treatment. Subjective experience and extrapolation from
fibrin, which is produced when fibrin is degraded by other species suggest that a better prognosis exists when
plasmin. Measurement of plasma D-dimer concentra- respiratory signs are minimal or absent, when a precipi-
tions in humans with pulmonary thromboembolism is tating cause can be identified and treated, and when
a highly sensitive (approaching 100%), poorly specific hypoxemia is mild (e.g., A-a gradient <20 mm Hg). In
test, meaning that a negative result rules out pulmonary turn, these elements likely depend mainly on the
thromboembolism in most cases, but a positive result promptness of suspicion of pulmonary thromboembo-
may or may not be the result of pulmonary thrombo- lism and initiation of tests and treatment based on rea-
embolism (Fedullo and Tapson 2003). D-dimer mea- sonable clinical suspicion. The late onset of clinical signs
surement for assessment of thrombotic states in cats is and lack of specificity of signs for pulmonary thrombo-
not routinely done, but results of a study of cats suffer- embolism translate to typically a guarded to poor prog-
ing from arterial thromboembolism indicate that nosis of this disease in cats.
D-dimers are not effective at detecting the disorder
(poor sensitivity). D-dimer concentration was elevated
in only half of cats with arterial thromboembolism, and PULMONARY ARTERIAL HYPERTENSION
there was no difference in D-dimer concentration
between normal cats and cats suffering from arterial Introduction
thromboembolism (Stokol et al. 2008). No studies have Pulmonary hypertension is an uncommon, poorly
evaluated the utility of D-dimer to screen for pulmonary described disease in cats. It is defined as an elevated
thromboembolism in cats. pulmonary artery systolic, diastolic, or mean arterial
pressure. In order to define an abnormally elevated pul- Pulmonary Arterial Disorders
Treatment monary artery pressure, normal pressures must first be
Optimal management of pulmonary thromboembolism defined. The normal systolic and mean pulmonary arte-
involves three aspects of treatment: identification and rial pressures in healthy cats are 15–22 mm Hg
correction of the underlying cause whenever possible, (average = 18; right ventricular pressure) [Lord et al.
anticoagulation to prevent growth of the thrombus and 1974] and 15.1 ± 4.29 mm Hg [Nadeau and Colebatch
formation of additional thrombi, and supportive care. 1965] in cats anesthetized with surital/nitrous oxide/
Thrombolysis is controversial, and active dissolution of halothane, and chloralose, respectively. Systolic right
thrombi is currently reserved for patients with severe ventricular—and therefore, pulmonary arterial—
clinical signs (hypotension, cardiogenic shock, and pressures of 36 ± 10 mm Hg have been reported in
severe dyspnea) and a high index of suspicion (if not healthy cats anesthetized with surital when evaluations
confirmation) of pulmonary thrombosis. took place at 5200 feet (1600 m) altitude (Reeves et al.
Anticoagulation can be achieved with heparin or low 1963). Systolic, diastolic, and mean pulmonary arterial
molecular weight heparin in hospital, followed by low pressures for cats and dogs under pentobarbital anesthe-
molecular weight heparin daily injections, oral clopido- sia are reported as 25 ± 5, 10 ± 3, and 15 ± 5 mm Hg,
grel (18.75 mg PO q 24 hr with food), oral warfarin respectively (Thomas and Sisson 1999) and 15–30, 5–15,
(0.25–0.6 mg PO q 24h), or oral aspirin (5–81 mg PO q and 8–20 mmHg for “cats and dogs under general anes-
3 days) if the inciting cause has not been eliminated (see thesia” (Kittleson and Kienle 1998). A mean pulmonary