Cardiovascular Diseases in Small Animals

Cardiovascular Diseases in Small Animals

• Diseases discussed include cardiomyopathies, valvular disease, diseases of the peripheral vasculature, and systemic hypertension.
• Learning objectives for each section focus on creating differential diagnosis lists, determining appropriate medical/surgical interventions, and prognosis.

Cardiomyopathies

• Cardiomyopathy is defined as "disease of the myocardium."
• Cardiomyopathies should be differentiated from heart disease with known causes like hypertension, ischemia (coronary heart disease), viral myocarditis, septic myocarditis, hyperthyroidism, and neoplastic infiltrative disease of the myocardium.
• Four types of cardiomyopathy discussed are: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), and arrhythmogenic right ventricular cardiomyopathy (ARVC).
• DCM is common in dogs and characterized by ventricular dilation and a thin, hypomotile ventricular wall.
• HCM is prevalent in cats, marked by ventricular wall hypertrophy and a restricted ventricular lumen.
• RCM results in a stiff ventricular wall with atrial dilation.
• ARVC, prevalent in boxers, is characterized by a fibrofatty infiltrate primarily affecting the right ventricle.
• The cause of DCM is often multifactorial, with potential contributing factors like taurine deficiency, carnitine deficiency, toxic agents (like doxorubicin), and potentially grain-free or lamb-based/vegan diets. Some breeds show high prevalence.
• HCM can be familial, often exhibiting mutation A31P in the cardiac myosin binding protein C gene, especially amongst Maine Coon cats. The prevalence of this in this breed is significantly high (up to about 42% in Europe and 46% in Australia) and increases with age. Some cats with HCM do not have the mutation.
• Ragdoll cats are also affected by another mutation that is associated with HCM.
• Most cases of HCM are in domestic short-hair cats, and the genetic aspect is still under research.
• Physical findings and clinical presentations, including murmur, gallop rhythm, pulse deficits, diastolic gallop, and jugular vein distension, are discussed.
• Radiography and echocardiography are detailed as crucial diagnostic tools. Echocardiography is the standard for diagnosis of DCM.
• Treatment approaches for cardiomyopathies are mentioned in general terms, with a promise to cover them in future lectures.

Valvular Disease (Myxomatous Mitral Valve Disease - MMVD)

• MMVD is the most common form of heart disease in dogs, accounting for at least 75% of cases.
• It predominantly affects small breeds (<20 kg) and large breeds, with larger breeds experiencing quicker progression.
• The disease mainly affects the left atrioventricular valve, although tricuspid involvement is observed in some cases (30% in some studies).
• The cause is unknown but may have a genetic component affecting affected breeds.
• Pathophysiology focuses on mitral valve leaflet damage (expansion from ECM, proteoglycans, GAGs, fibrosis, degradation of endothelium).
• Increased cardiac workload leads to volume overload and eccentric hypertrophy of the left ventricle.
• The condition often progresses to congestive heart failure.
• Diagnosis uses clinical signs, auscultation, blood pressure, thoracic radiography, and echocardiography.
• Stage-dependent medical management (including Pimobendan and furosemide; or ACE inhibitors with pimobendan) is detailed.
• Echocardiography is crucial for diagnosis and measuring LA:Ao ratio to confirm the condition and for evaluating severity.
• Prognosis is connected to the target organ damage; treatment is generally life-long.

Diseases of Peripheral Vasculature (Dirofilariasis, Aortic Thromboembolism, Systemic Hypertension)

• Dirofilariasis (heartworm) is caused by the nematode Dirofilaria immitis, transmitted by mosquitos.
• Clinical signs of dirofilariasis in dogs and cats often only manifest several months after infection as L5 larvae migrate to the lungs where adult worms cause damage.
• Diagnosis methods include blood tests (eosinophilia, microfilaria, antigen tests) and radiography (enlarged main pulmonary artery, right ventricular enlargement, and enlarged tortuous caudal lobar pulmonary arteries).
• Recommended prevention methods involve ivermectin, selamectin, milbemycin oxime, and moxidectin.
• Aortic thromboembolism (ATE) can be catastrophic in cats, often caused by underlying heart disease, particularly HCM and left atrial enlargement.
• The condition presents with bilateral leg dysfunction (paresis, paralysis) accompanied by other symptoms like pain, pulselessness, pallor (or cyanosis), and poikilothermia (cold limbs).
• Understanding cardiac conditions, including heart rate and rhythm, murmur, and hypothermia is required for appropriate diagnosis and treatment recommendations.
• Echocardiography is key to assessing left atrial enlargement.
• The 5Ps are common symptoms: Posterior paresis/paralysis, Pain, Pulselessness, Pallor, Poikilothermia.
• Systemic hypertension is a sustained elevation in systolic blood pressure, and can be primary or secondary.
• Secondary hypertension can arise from complications from various diseases like kidney disease, hyperadrenocorticism, adrenal tumors, hyperthyroidism, diabetes mellitus, and cardiovascular diseases.
• Diagnosis involves identifying the presence and severity of hypertension and associated cardiac conditions alongside the use of dopler and oscillometric methods for measuring blood pressure.

Further Reading

• Recommended references for cardiovascular diseases include Ettinger's Textbook of Veterinary Internal Medicine and Small Animal Cardiovascular Medicine (Kittleson and Kienle).
• The American Heartworm Society (https://www.heartwormsociety.org) is also recommended for additional information.

Case Studies

Two specific cases, Flynn and others, were presented. These cases involved clinical findings, differentials, and subsequent diagnosis or treatment considerations.