Page 234 - Small Animal Internal Medicine, 6th Edition

206 PART I Cardiovascular System Disorders

HW-associated pneumonitis and PTE result in pulmo- Treatment of Cats With Heartworm Disease
nary infiltrates. Focal perivascular and interstitial opacities MEDICAL THERAPY AND
VetBooks.ir are more common than diffuse infiltrates but are nonspecific. COMPLICATIONS
Radiographs tend to be normal in cats without clinical signs.
ECHOCARDIOGRAPHY Adulticide therapy is not recommended in most cases
because the likelihood of severe complications in this species
Echocardiographic findings can be normal unless worms are is high. Also, spontaneous cure can occur in cats because of
located in the heart, main pulmonary artery segment, or the shorter HW life span, and cats do not act as reservoirs
proximal left and right pulmonary arteries. Echocardiogra- for HWD transmission to other animals.
phy is more sensitive for HW screening in cats versus dogs The recommended approach for infected cats is to initiate
because worms are physically larger compared with the cat’s monthly HW preventative (if not already begun) and to use
body size; worms are therefore more likely to extend into the prednisone as needed for respiratory signs and radiographi-
main PA or RV from their preferred location in the distal cally evident pulmonary interstitial infiltrates. Clinical utility
PAs. On two-dimensional echocardiograms, HWs appear as of doxycycline in cats with HWD is not yet established;
bright, double-line (parallel) echodensities; they are visible however, given the effects of doxycycline on HW viability
in up to 75% of infected cats. Higher numbers of worms and reproductive capacity in dogs, it is reasonable to treat
increase the likelihood of identification with echocardiogra- cats with doxycycline in the same manner (10 mg/kg PO
phy. Because worms are seen more often in the pulmonary q12h for 4 weeks beginning at time of diagnosis). If cats
arteries than in right heart chambers, an index of suspicion develop GI adverse effects at this dose, the dose can be
and careful interrogation of these structures are important. lowered to 5 mg/kg q12h. Serologic tests (for HW Ab and
Ag in tandem) are obtained every 6 to 12 months to monitor
ELECTROCARDIOGRAPHY infection status. Ag-positive cats usually become negative
ECG findings are often normal. Severely affected cats with within 4 to 5 months of worm death; Ab tests can remain
HW-induced CHF can have changes suggesting RV enlarge- positive at least 6 to 12 months. Serial thoracic radiographs
ment and axis deviation. Arrhythmias appear to be uncom- and echocardiograms also can be useful for monitoring cats
mon, although advanced pulmonary arterial disease and that have had abnormal findings. Interstitial pulmonary
CHF are more likely to cause ventricular tachyarrhythmias. infiltrates usually respond to prednisone (e.g., 1-2 mg/kg PO
q24h, reduced gradually over 2 weeks to 0.5 mg/kg q48h,
OTHER TESTS then discontinued after 2 more weeks). Prednisone therapy
Between one and two thirds of infected cats have peripheral could be repeated periodically if respiratory signs recur.
eosinophilia, usually from 4 to 7 months after infection. The possibility of severe respiratory distress and death
Otherwise the eosinophil count often is normal; basophilia is always present, especially after worm death. PTE is
is uncommon. About one third of the cases have mild non- more likely to produce a fatal outcome in cats than dogs.
regenerative anemia. Advanced pulmonary arterial disease Clinical findings with PTE include fever, cough, dyspnea,
and thromboembolism might be accompanied by neutro- hemoptysis, pallor, pulmonary crackles, tachycardia, and
philia (sometimes with a left shift), monocytosis, thrombo- hypotension. Radiographic signs include poorly defined,
cytopenia, or DIC. Hyperglobulinemia, the most common rounded or wedge-shaped interstitial opacities that obscure
biochemical abnormality, occurs inconsistently. The preva- associated pulmonary vessels. Alveolar infiltrates are seen
lence of glomerulopathies in cats with HWD is unknown, in some cases. Cats with acute disease are given support-
but it does not appear to be high. ive care, including supplemental oxygen, a glucocorticoid
Tracheal wash or bronchoalveolar lavage specimens can (dexamethasone at 0.2 mg/kg IM or IV), a bronchodilator
show an eosinophilic exudate that suggests allergic or para- (such as terbutaline), and fluid support as needed. Silde-
sitic disease, similar to that found with feline asthma or nafil (1-2 mg/kg PO q8-12h) is indicated if severe PAH is
pulmonary parasites. This finding usually occurs between 4 documented. Antiplatelet drugs (clopidogrel or aspirin) or
and 8 months after infection. Later in the disease, tracheal anticoagulants (heparins) can be considered in cats with
wash findings can be unremarkable or indicate nonspecific PTE. Diuretics are not indicated unless right-sided CHF
chronic inflammation. Pleural effusion resulting from HW- is present.
induced CHF generally is a modified transudate, although Right-sided CHF develops occasionally in cats with severe
chylothorax occasionally develops. pulmonary arterial disease and PAH. Dyspnea (caused by
At around 6.5 to 7 months after infection, a transient (1-2 pleural effusion) and jugular venous distention or pulsation
months in duration), low-grade microfilaremia occurs in are common. Radiographic and ECG findings usually suggest
about half of cats with mature infections. Therefore microfi- RV enlargement. Therapy is directed at decreasing pulmo-
laria concentration tests usually are negative. Nevertheless, a nary arterial pressure and controlling the signs of heart
concentration test could still prove valuable in some indi- failure. This includes thoracocentesis as needed, cage rest,
vidual cats. Between 3 and 5 mL, rather than 1 mL, of blood sildenafil, furosemide, an ACEI, and pimobendan. The cat’s
should be used to increase the probability of detecting clinical progress and clinicopathologic abnormalities are
microfilariae. used to guide supportive therapy.