Diseases of the cardiovascular system IV Flashcards
Name three common peripheral vascular diseases
- Dirofilariasis
- Aortic thromboembolism
- Systemic hypertension
What kind of worm is dirofilaria and where does it reside?
Large, whitish worm
* Females - ~30 cm long
* Males - ~23 cm long
* Adults reside in the pulmonary arterial system – cause
damage to pulmonary vessels and lungs
What is the distribution of dirofilaria?
Worldwide distribution of D. immitis –
though limited to regions with suitable
mosquito intermediate hosts
» Some regions have seasonal periods
of susceptibility
» Not currently in the UK – but beware
of travelling dogs and future potential
with climate change!
When do dirofilaria clinical signs develop in dogs?
Most dogs with low heartworm burden have no clinical signs
» Clinical signs seen in dogs if they have a severe allergic responses to the adult worms and/or microfilariae, or have high worm burdens
» Signs may develop 3-6 months after infection as L5 larvae reach the lungs. Signs may occur acutely with worm death
What are the clinical signs of dirofilaria in dogs?
- Coughing
- Exercise intolerance
- Syncope
- Weight loss
- Tachypnoea, dyspnoea, abnormal respiratory sounds
- Abnormal heart sounds
- Congestive heart failure (ascites, hepatomegaly, jugular distension) * Pulmonary thromboembolism
- Multi-organ involvement * Death
What are the hyper-acute clinical signs of dirofilaria in cats?
Sudden death
What are the chronic clinical signs of dirofilaria in cats?
- Coughing
- Dyspnoea
- Asthma-like attacks
- Vomiting
- Inappetence/weight loss
- Lethargy
- Chylothorax
How would you diagnose dirofilaria on radiography?
» Enlarged main
pulmonary artery
» Right ventricular
enlargement
» Enlarged tortuous
caudal lobar
pulmonary arteries
What does mild dirofilaria look like on echocardiography?
Usually looks normal
What does moderate dirofilaria look like on echocardiography?
RV often dilated +/- free wall thickening
What does severe dirofilaria look like on echocardiography?
Moderate to severe RV distension
Where might heartworms be estimated?
Doppler evidence of pulmonary hypertension
can be estimated if tricuspid or pulmonic
regurgitation is identified
Where may heartworms be found?
Heartworms may be identified in the main
pulmonary artery and branches, and in the right
heart chambers and vena cavae in some cases
What is the specific test used for heartworms?
Heartworm antigen test
How does a heartworm antigen test work?
- Heartworms must mature before either antigen or
microfilaria tests become positive (6-7 months
after infection) * Sensitivity is proportional to worm burden and
specificity is nearly 100% - Detect female worms only (detects an antigen
most abundant in the uteri of gravid females and
eggs) * False negative results occur in cases of light
infections, immature females, male-only infections,
antigen-antibody complex-related interference, test
malfunction, and by not following the manufacturer
instructions!
What are the two specific tests for microfilaria?
- Fresh blood direct smear
- Modified Knott’s Test
What are the two main treatments for dirofilaria?
- Surgical removal (caval syndrome)
- Supportive therapy (doxycycline, amcrocyclic lactones, exercise restrcition)
Name 4 medicines that can be used to help prevent dirofilaria
- Ivermectin
- Selamectin
- Milbemycin oxime
- Moxidectin
What is a feline aortic thromboembolism also known as?
Saddle thrombus
Usually caused by heart disease
How do saddle thrombi occur?
Occurs when thrombo-emboli (usually
from LA) lodge in the distal aortic
bifurcation (most common), or in
brachial, visceral or cerebral arteries
» ATE is rare in dogs
What is the pathophysiology of saddle thrombi?
» Virchow’s Triad
* Damage to vascular endothelium of
LA
* Sluggish blood flow (typically due to
LA enlargement with spontaneous
echo contrast of blood in the LA
* Hypercoagulability (more difficult to
identify but inflammation and altered
platelet function play a role)
» Clot forms in LA and washes down
the arterial tree
What are the 5 main clinical signs of a feline aortic thromboembolism?
- Posterior paresis
- Pain
- Pulselessness
- Pallor
- Poikilothermia
What specific therapy can be used for a cat with a saddle thrombus?
- Prevent continued thrombus formation
- Clopidogrel 18.75 mg/kg PO q24hr * Improving flow to infarcted organ(s) * Monitor for reperfusion injury
- But…while it can buy some time, ATEs can and do still occur
1. and long-term survival is poor
What is the usual prognosis for a saddle thrombus?
Poor to grave (25-30% can recover completely) * Depends on presenting signs
* Single pelvic limb infarctions do much better compared to bilateral * Non-survival has been associated with hypothermia, bradycardia and absence of motor function
What is systemic hypertension?
A sustained elevation in systolic BP
» There is a balance between sympathetic and
parasympathetic tone.
» Influenced by the R-R interval, inotropism and
peripheral resistance
What are the two categories of systemic hypertension?
- Secondary hypertension – more common
- Primary (idiopathic) hypertension
What animal is systemic hypertension more common in?
It is more common in older male dogs rather than females
What conditions are most commonly associated with secondary hypertension?
» Kidney disease – most common
» Hyperadrenocorticism
» Adrenal tumours
» Hyperthyroidism
» Diabetes mellitus
» Cardiovascular disease
Why would you focus on the cats eye when looking at hypertension?
Only part of the cats body where blood vessels are visible
What are the main clinical manifestations of hypertension?
- Renal manifestations
- Neurological manifestations
- Epistaxis
What is the prognosis for hypertension?
- Dependent on target organ damage
- Treatment usually life-long
- When well managed further complications are
minimised
