Page 347 - Feline Cardiology

360 Section K: Heartworm Disease

interstitial lung lesions caused by the death of immature • Canine data suggests that doxycycline treatment
worms has been termed HARD (heartworm-associated reduces damage associated with eventual worm death
respiratory disease) (Dillon 2007). (due to a reduction in Wolbachia antigens). Although
efficacy in cats remains unclear many clinicians recom-
mend a course of doxycycline at the time of diagnosis.
TREATMENT
• The monthly use of ivermectin at the prophylactic
Retrospective studies suggest that 10–20% of cats with dose (24 mcg/kg) for 2 years has been reported to
adult heartworm infections die secondary to death of reduce worm burdens by 65% as compared to
the worm (Nelson 2008b), but adulticide treatment untreated cats (Nelson et al. 2005). Therefore, in
itself is associated with significant risk in cats, as well. In cats suspected to have heartworm infection, prophy-
addition to the toxicity and reported lack of efficacy of lactic ivermectin therapy is recommended to both
heartworm adulticide agents, killing of the heartworm(s) prevent superinfection and to slowly kill the current
in a cat results in significant risk of fatal pulmonary infection. However, the inflammatory response to
thromboembolism and necrosis (McIntosh and Daniel worm death is likely to occur with ivermectin-treated
1999). For these reasons, and because the disease is often worm death as well, and therefore owner education is
self limiting in cats, infected cats are usually managed important.
with supportive treatment. Lifelong treatment for
chronic bronchial disease may be necessary even after Acute crisis due to a dying worm(s) may require emer-
death of all heartworms in some cats due to residual, gent therapy with supportive therapy for treating shock.
chronic pulmonary disease. Unfortunately, sudden Depending on the individual case, this may include
death may still occur without premonitory signs until
all adult worms have died. Some authors suggest provid-
ing the owner with injectable dexamethasone sodium • Intravenous corticosteroids (dexamethasone sodium
phosphate so that the owner may administer it in a crisis phosphate, up to 2.2 mg/kg IV or IM)
(Nelson 2008b). Similarly a bronchodilator (i.e., inject- • Fluid therapy. The typical shock rate of crystalloid
able aminophylline, albuterol inhaler) may also be ben- fluids is 60 ml/kg in cats; however, it is important to
eficial to dispense in case acute dyspnea occurs. recognize that each animal is unique and will have
a different response to fluid therapy. Generally,
Heartworm Disease montelukast, 2 mg/day) may prevent fatal lung injury calculated shock dose given rapidly. The patient
There is anecdotal evidence that antileukotrienes (i.e.,
fluid therapy should be started at 1/3 to 1/4 of the
when adult worms die, although thorough investigation
should then be reassessed and fluid rate can be reduced
of this drug and use has not been performed in the cat
if there is clinical improvement or continued at a
(Nelson 2008b). Similarly, it is possible that therapy with
doxycycline will reduce lesions associated with eventual
taline, 0.01 mg/kg IV; or aminophylline, 4–6 mg/kg
worm death (due to a reduction in Wolbachia antigens), high rate. Bronchodilator therapy is indicated (terbu-
but studies in cats are still lacking. These treatment IV—inject slowly; or albuterol sulfate inhaler, 1
options may be useful to consider at the time of diag- actuation). Intravenous medications would be prefer-
nosis (prior to a crisis). able in a dyspneic cat; however, in a crisis the owner
The following are general treatment recommenda- can administer albuterol with an inhaler while en
tions for heartworm disease in cats: route for emergency care.
• Oxygen supplementation
• Treat asthmalike signs with prednisolone (2 mg/kg, • Diuretics and nonsteroidal anti-inflammatory drugs
daily for 10 days; gradually tapering to 0.5 mg/kg every such as aspirin are not recommended. Studies in cats
other day by 2 weeks and discontinue in another 2 with heartworm disease have shown only limited
weeks). Repeat treatment as needed if recurrent clini- benefit to aspirin therapy at a dose that approached
cal signs occur. Prednisolone is also warranted in cats the feline toxic range (Rawlings 1990; Rawlings et al.
without clinical signs if there is radiographic evidence 1990).
of lung disease.
• Consider the addition of a bronchodilator if clinical Use of injectable arsenicals has been associated with
signs persist despite anti-inflammatory treatment fatal thromboembolism or acute lung injury in cats, and
with corticosteroids (i.e., terbutaline, 0.625–1.25 mg/ is not recommended (Small et al. 2008). However, surgi-
cat PO q 8–12 h; aminophylline, 4–6 mg/kg PO cal removal of heartworms is feasible and effective in
q 8–12 h; theophylline, 25 mg/kg PO q 24 h; albuterol cats with echocardiographically visible worms in the
sulfate inhaler, 1 actuation q 12 h). right heart and/or main pulmonary arteries (when the