Page 67 - Problem-Based Feline Medicine

5 – THE DYSPNEIC OR TACHYPNEIC CAT 59

Hypercoagulable states such as protein-losing When lesions are evident radiographically, lung pat-
nephropathies (i.e., glomerulonephritis, renal amyloi- terns range from focal areas of hyperlucency to alveo-
dosis, hypertension) or enteropathies (i.e., IBD, lym- lar infiltration, and mild to moderate pleural effusion.
phangiectasia), stasis of blood flow, exposure of
Pulmonary arterial angiography is the “gold stan-
vascular subendothelial tissue (i.e., vasculitis, right
dard” for evaluation of pulmonary thromboembolism
atrial dilation, post-stenotic “jet lesions”, trauma and in-
(PTE) in people. This requires catheterization of the
dwelling jugular catheters) all predispose to thrombus
right heart and injection of contrast material into the
formation.
pulmonary arterial tree. Areas of obstruction or
Pulmonary arterial obstruction causes ventilation/ decreased blood flow may be detected.
perfusion (V/Q) mismatch, resulting in hypoxemia and
Scintigraphic ventilation/perfusion studies utilize
dyspnea.
both aerosolized and injected radioisotopes to identify
● Increased pulmonary arterial pressure may induce
areas of V/Q mismatch. Special facilities and expertise
cor pulmonale, or right-sided heart failure.
are required, which are generally unavailable outside of
Feline heartworm disease frequently presents as teaching institutions.
severe peracute pulmonary inflammation, edema and
Echocardiography may reveal right atrial enlarge-
pulmonary thromboembolism resulting in acute respi-
ment with thrombus formation, pulmonary arterial
ratory failure and death.
dilation, right ventricular enlargement, pulmonary
hypertension on Doppler studies of the tricuspid and
pulmonic valves, or evidence of heartworm in the
Clinical signs
right heart or pulmonary arteries.
Severity of signs is proportional to the degree of arterial
Tall P waves on ECG may indicate right atrial
obstruction.
enlargement, and right axis shift supports right ventric-
Acute onset of severe dyspnea and tachypnea is typi- ular enlargement consistent with cor pulmonale.
cal. Cyanosis or collapse may also occur. Massive dis-
ease may result in sudden death. Differential diagnosis
Orthopnea (positional dyspnea), especially in lateral Severe dyspnea and cyanosis with normal thoracic radi-
recumbency, and reluctance to lie in lateral recum- ographs may accompany upper airway obstruction or
bency, may be an early sign. feline asthma.

Coughing may be evident, and ranges from mild to
Treatment
severe, and may involve hemoptysis.
Oxygen therapy during the respiratory crisis is impor-
Signs of right-sided heart failure may occur, such as
tant, but limited in efficacy if the blood delivery to the
tachycardia, jugular venous distension and split second
lung is compromised.
heart sounds.
The primary disease condition, if identified, should
Often presenting signs relating to the primary condition
be addressed as a priority.
are also evident, i.e., weight loss and diarrhea with pro-
tein-losing enteropathy. Thrombolytic therapy is controversial. The use of tis-
sue plasminogen activator (TPA) has been advocated,
but requires local delivery into the pulmonary arterial
Diagnosis circulation. This requires cardiac catheterization under
fluoroscopy. There are inherent risks involved with the
Thoracic radiographs may be totally normal, and in
procedure, and the risk of inducing a bleeding diathesis.
the presence of severe dyspnea, increase the index of
suspicion of pulmonary thromboembolism. Anti-thrombotic therapy using heparin has been
● Enlarged or truncated pulmonary arteries may be advocated to prevent further thrombin formation.
seen. Various protocols ranging from low (100 IU/kg SQ q 8