Cardiovascular - Heartworm Flashcards by Bianca Ferlisi

Heart worm species

Dirofilaria immitis

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Life span of heart worm in dogs

6-7m, 184-210d

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Life cycle of HW in dogs dependent on

ambient temperature ad Wolbachia

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Life cycle of HW in dogs

adult worms live in PA
after mating female worms release microfilaria (mf) into circulation
mf ingested by female mosquitos - become L1
2 melts over 8-17d period to L3
L3 transmitted from mosquito to dog
L3 to L4 in Sc tissue over 1-12d, then final molt to immature adult (S5)
S5 migrates to vasculature then to PA to complete maturation

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T/F: prevalence of HW disease in dogs is increasing

true

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heart worm infection = heart worm disease?

no, heart worm disease occurs when heart worm infection is prolonged or severe

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Features of heart worm disease in dogs

pulmonary artery and pulmonary parenchyma injury, pulmonary hypertension, R sided cardiac dysfunction, glomerulonephritis, anemia, thrombocytopenia, canal syndrome, DIC

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What is considered the onset of heart worm disease in dogs?

damage to the pulmonary artery

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What occurs in the pulmonary aa in dogs as a result of adult worms living there?

inflammation, endothelial damage, myointimal proliferation, disruption of vascular integrity, fibrosis, pulmonary hypertension

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Living worms in dogs can create

mechanical obstruction within the pulmonary arteries

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Dead worms in dogs induce

thrombosis and inflammation

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Outcome of pathophysiology of HWD in dogs

decreased return to left artery and ventricle (preload) = low systemic pressure

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What type of hypertrophy occurs in right ventricle in dogs?

concentric

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2 things that result in increased pulmonary vascular resistance in dogs

structural changes causing narrowed pulmonary lumen

vasoactive substance from worms, endothelium, and platelets cause vasoconstriction

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What sided heart failure may you see as a result of HW disease in dogs

right sided CHF

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Which is FALSE regarding pulmonary parenchymal disease resulting from HWD?
A) decreased vascular permeability into surrounding tissue
B) eosinophilic granulomatosis as result from host response
C) pulmonary thromboembolism (PTE) seen
D) post PTE lung consolidation

A - increased vascular permeability to tissue (fluids, cells, toxins)

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Wolbachia pipientis

intracellular, gram -, live in D. immitis
endotoxins and surface proteins have been implicated in pathogenesis and adverse reactions associated wth HWD
Doxy effective attracting Wolbachia

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T/F: doxycycline is effective at reducing/eliminating wolbachia and reduces larval and adult stages of D. immitis in dogs

true

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Heartworm disease and glomerulonephtitis in dogs

secondary to antigen-antibody deposition, results in albuminuria (and potentially hypoalbuminemia)

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What is caval syndrome in dogs?

mechanical obstruction by worms of blood flow to R side of heart and vena cava, only occurs if worm burden is heavy
hemolytic anemia and cariogenic shock result (rare but lifethreatning)

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T/F: aberrant migration of worms to other tissues (neuro, muscular, ocular, systemic aa.) more common in dogs than cats

false, more common in cats

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Clinical signs of HWD in dogs

most dogs asymptomatic
exercise intolerance, weight loss, lethargy, cough, tachypnea, dyspnea, hemoptysis, abdominal distension, syncope or collapse, hematuria

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PE findings on HWD dog

may be normal
weight loss and poor BCS
split S2
murmur due to tricuspid regurgitation (right apical systolic)
gallop
abnormal lung sounds
tachypnea, dyspnea
R sided CHF

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T/F: thoracic rads are helpful to diagnose HWDin dogs

True! Look for large, dilated, tortuous pulmonary aa
look at lung parenchyma for interstitial infiltrates
look for R sided cardiac enlargement

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CBC abnormalities associated with HWDin dogs

neutrophilic, eosinophilia, basophilia, anemia, thrombocytopenia

Why may you see elevated liver enzymes in a HWD dog?

hepatic congestion from R sided CHF

urinalysis of a dog w HWD may reveal

albuminuria

When is an echo indicated in a HW patient?

if there is concern for pulmonary hypertension and/or canal syndrome

What is the test of choice if an arrhythmia is ausculted on a HWD patient (dogs)?

echo

Best treatment for HWD in dogs?

macrocyclic lactone preventative Doxycycline Exercise restriction adulticide therapy with melarsomine dihydrochloride

Macrocyclic lactone preventative in dogs

``` prevents further infection reduces or eliminates microfilaria destroys developing L3 and L4 started day HWI is diagnosed ivermectin, salamectin, moxidectin ```

``` Which would you NOT give to a microfilaremic dog? Why? A) ivermectin B) Milbemycin C) Moxidectin D) Selamectin ```

B - milbemycin | is a potent microfilaricide, death of too many worms at once can cause anaphylaxis

Two uses of doxycycline in dogs

reduce/eliminate Wolbachia | reduce Mf and other stages of D. immitis

Why is exercise restriction imperative in HWD dogs?

reduce risk of thromboembolic complications

3 dose "split dose" protocol in dogs

highly effective at eliminating adult worms reduces risk of post-adulticidal complications use melarsomine dihydrochloride, organic arsenical rapidly absorbed after IM injection dogs with intra-cardiac worms/caval syndrome should not be treated with adulticide until worms. have been extracted

"slow kill" of adults with macrocyclic lactones in dogs

ongoing damage to pulmonary artery and lungs | method not recommended, could be used for a patient in which 3 dose with melarsomine is not an option

Adulticide drug of choice in canines with HWD

melarsomine dihydrochloride

Adjunct Tx for canines

analgesia for melarsomine injections (opioids, corticosteroids or NSAIDs) corticosteroid therapy - prevent/tx adverse reactions to microfilaricides

What could you give a dog to treat pneumonitis, pulmonary granulomas, and pulmonary thromboembolism associated with HWD?

corticosteroids

Treatment of anaphylaxis associated with microfilaricidal therapy in dogs

uncommon except with milbemycin oxide monitor dogs after preventative consider pretreatment with corticosteroid and diphenhydramine avoid milbemycin

Treatment of eiosinophilic pneumonitis or granulomatosis in dogs

corticosteroids (prednisone or prednisoloe) | often occurs early in disease course

treatment of pulmonary thrombosis or thromboembolism in dogs

supplemental O2, corticosteroid therapy, sildenafil if pulmonary hypertension severe can cause sudden death

Treatment of pulmonary hypertension in dogs

sildenafil, supplemental O2

Treatment of congestive heart failure in dogs

(R sided) - furosemide, sildenafil +/- pimobendan, ACE inhibitor if not hypotensive or dehydrated abdominocentesis if ascites delay adulticide therapy until CHF stabilized

Treatment of caval syndrome in dogs?

emergency worm extraction via jugular vein | delay adulticide therapy (at least 30 days)

Prognosis for dogs with HWD

good with asymptomatic infection good in dogs w/ mild-moderate disease guarded for severe HWD Patients that develop CS, DIC, CHF, PTE, eosinophilic granulomatosis, PA disease = worse prognosis

prevention of HWD?

educate clients

T/F: cats are more resistant to heart worm infections than dogs

True, cats are unnatural host

T/F: aberrant migration of worms more common in cats

True

T/F: pulmonary disease can develop in cats even if mature adult worms never exist

true

Key differences of HWD in cats

not preferred target for mosquito mosquito must have fed on infected dog first unnatural host - resistant to HWI (no or few adults, often amicrofilaremic) longer life cycle (7-8m) aberrant migration more common mature adults not needed for pulmonary disease to develop

If prevalence of HWI low in cats, why is it important we protect cats from D. immitis?

cats get HARD

What is HARD

Heartworm-associated respiratory disease

General info about HARD

inflammatory and proliferative disease of pulmonary aa, bronchioles and pulmonary parenchyma in cats without mature infections

Which is FALSE regarding HARD? A) ~50% cats with immature infections develop HARD B) HARD produces asthma like symptoms C) HARD is a diagnosis of exclusion D) HARD requires cats to have mature infections

D - HARD occurs in cats without mature infections

Role of PIMs in HARD?

pulmonary intravascular macrophages contribute to profound inflammatory reaction to immature and dead worms

Signalment of cats with HARD

male, 4-6y, exposure to outdoors

Acute signs of HARD

due to dead worm embolization anaphylaxis, resp distress, dyspnea, coughing, shock, ptylism, vomiting and diarrhea, altered mentation, ataxia, vision loss, seizure, sudden death

Chronic signs of HARD

coughing, wheezing, dyspnea, lethargy, hyporexia, weight loss, exercise intolerance, vomiting, R sided CHF

PE on a HARD cat

may be normal | abnormal lung sounds, tachypnea/dyspnea, murmur, gallop, weight loss, ascites

Why is antigen test not ideal diagnostic for cat HWI?

because the antigen detected is in reproductive tract of adult female which is likely not in the cat

What diagnostic test is ideal to test cats for HWI?

antibody test

Treatment of HWI in cats

microfilaricidal not indicated because low #sadulticide therapy not recommended - high risk of mortality and morbidity cats should receive short term corticosteroid therapy for HARD supplemental O2, parenteral corticosteroid and bronchodilator if embolic/anaphylactic emergency consider doxy for wolbachia and clopidogrel for PTE prevention