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Cardiology Notes

Veterinary Medicine Notes > Small Animal Internal Disease - Cardiology Notes

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Q18. Congenital heart diseases Congenital heart diseases are morphological and functional abnormalities of the heart and adjacent large vessels that are present at birth. Can have environmental and genetic causes. Ones to talk about;

* Patent Ductus Arteriosus

* Atrial and Ventricular Septal Defects

* Pulmonary and Aortic Valve Insufficiency

* Tricuspid and Mitral (Atrioventricular) Valve Insufficiency

* Aortic Stenosis

* Tetralogy of Fallot

Type of defect


Congenital heart defects in cats

Siamese, Burmese, Asian short haired breeds

Patent Ductus Arteriosis

Maltese, Bischon Frise, GS, Collie

Atrial Septal Defects

Boxer, Pincher

Ventricular Septal Defects


Aortic Stenosis

Large Breeds

There are others, but this is impossible to remember

* Most defects are detected soon after birth, but can be later

* PDA is more common in females. Apart from that, there is no gender predisposition. Male cats are more likely to have congenital heart defects.

Typical Clinical Presentation Heart murmers - can be physiological in young animals up to 6 months old, but these are usually of low intensity. Congenital heart disease murmurs are of high intensity. Atrial Pulse - A very strong pulse (hyperkinetic) indicates low diastolic pressure, which occurs in Patent Ductus Arteriosis or Aortic Regurgitation. A very weak pulse (hypokinetic) suggests low cardiac output, which would happen in Stenosis (also shock). Jugular Distension - Indicates there is elevated venous pressure which would occur due to a righ sided defect such as Tricuspid Valve Dysplasia or Pulmonary Stenosis Mucous Membranes - Cyanosis occurs when arterial blood oxygen is <45mm Hg Exhaustion, Exercise Intolerance, Lethargy, Syncope Diagnostic Measures ECG - Any abnormalities such as a wide QRS complex could indicate disease causing hypertrophy USG - 2D, M Mode or Doppler can show the direction and velocity of blood flow and allow visualisation of structure.. X Ray - Thoracic view to evaluate heart size and shape, look for any vessel enlargement or pleural effusion. CT, MRI, Cardiac Catherisation, Angiography - Also possible by specialists

Patent ductus arteriosus Ductus arteriosis is a connection between the pulmonary artery and the aorta that should close at birth due to breathing, and be securely closed by 7 - 10 days old. Patent ductus arteriosis occurs when it doesnt close fully. This is the most common congenital heart defect in dogs and also common in cats. Et:

Blood mixing occurs between the aorta and pulmonary artery, usually blood flows from the aorta to pulmonary artery


Causes reduced oxygenation and left ventricle hypertrophy and also overloading of pulmonary circulation, causing pulmonary edema.


Usually only older that 6 weeks. Pale mucous membranes, strong pulse and murmers. An ECG will show left ventricular enlargement (as a very high R wave), and left atrial enlargement (a wide P wave). X rays and USG would also show an enlarged heart.


You can also get a "reversed PDA" when blood flows from the pulmonary artery to the aorta. These dogs instead have right ventricle hypertrophy and reduced pulmonary blood flow (exhausted). Also murmurs are not present.


Surgery. Furosemide and ACE inhibitors to reduce pulmonary edema. Surgery needs a left thoracotomy and suturing of the PDA. A newer method id to block the duct with metal covered with Dacron, which is very effective.

Atrial and Ventricular Septal Defects * Patent Foramen Ovale is a type of atrial septal defect Are caused by defects in the walls between the two atria or the two ventricles. Pressure is higher on the left side of the heart, so blood flows from left to right. Atrial Septal Defects - blood flowing into the right atrium (in diastole) causes dilation of the right atrium and hypertrophy of the left atrium. In large defects, signs of right sided heart failure can be seen. Ventricular Septal Defects - blood flowing into the right ventricle (in systole) causes hypertrophy of the right ventricle, or the formation of a common pumping chamber. Murmers will depend on the size and location of the defect Dx:

Clinical signs indicated heart problem, Xray showing hypertrophy, ECG with abnormalities, USG can show defect.


Surgery, but not usually performed in small animal practice. So supportive Tx only: vasodilators and exercise restriction.

Pulmonary and Aortic Valve Insufficiency Quite rare. Occurs due to abnormal formation of values or dilation of the annulus. Pulmonary insufficiency cayses regurgitation and volume overload in the right ventricle (hypertrophy) and can lead to right sided heart failure. Aortic insufficiency causes regurgitation and volume overload of the left ventricle (hypertrophy), and can lead to left sided heart failure. CS:

Clinical signs indicated heart disease. Murmers, systolic and/or diastolic


Breed, X ray showing hypertrophy, Abnormal ECG, USG showing defect


None. If heart failure happens then you can try and treat that (later question)

Atrioventricular Valve (tricuspid/mitral) Insufficiency Congenital malformations of the tricuspid or mitral valves have been reported. Malformation of the valve can result in regurgitation or stenosis. Reguritation or stenosis can result in hypertrophy of the volume overloaded chamber. Valvular

stenosis can lead to the development of CHF, and it can also cause a low cardiac output, so syncope is common. Mitral stenosis can cause left sided heart failure (pulmonary hypertension), but remember that right sided heart failure will be a natural progression of this, giving different signs depending on when you catch it. Dx:

As above. Murmers can be heard over the affected valve. Jugular distension and ECG abnormalities indicating hypertrophy. X ray. USG.


Surgerical replacement of the affected valve - whether this is actually done....?

Pulmonary Stenosis Common in dogs and occasionally found in cats. Narrowing of the pulmonary artery causes an increase in pressure of the right ventricle, leading to right sided hypertrophy and heart failure. Its mainly due to dysplasia of the pulmonary valve. CS:

Of heart problems. Right sided heart failure. Murmers


Breed. ECG. X ray. USG.


Surgery, but probably medical treatment for HF

Aortic Stenosis The most common congenital heart defect in large breeds. Causes increased pressure in the left ventricle and hypertrophy, also the lack of blood flow to coronary arteries increases the risk of myocardial infarction. Results in the development of left sided heart failure, which will progress to right sided heart failure. CS:

As before, but sudden syncope or sudden death are common.


Breed. As before


Medical Tx for heart failure

Tetralogy of Fallot A congenital defect that includes 4 deferent features:


Pulmonary stenosis


Right ventricle hypertrophy (secondary to the pulmonic stenosis)


Ventricular Septal Defect (subaortic)


Dextra-rotated aorta (rightward-positioned aorta)

Tetraology of Fallot is a cyanotic congenital heart disease. Mixing of venous and arterial blood causes cyanosis.


As before


Can live for many years if mild. Surgery is technically possible

Q19. Diseases of the pericardium and myocardium (cardiomyopathy) Pericardial diseases Congenital pericardial disorders Pericardio-peritoneal Diaphragmatic Hernia (PPDH) Et:

A PPHD exists when a defect in the diaphragm and the pericardium allows abdominal contents to enter the pericardial space. Rare.


Dyspnoe, tachycardia, GIT signs


Xray, USG



Acquired pericardial disorders Percarditis Bacterial (Mycobacterium, Nocardia/Pasteurella from lungs, Actinomyces), fungal (Cocciodiomycosis immitis) and viral (FIP) infections are occasionally associated with pericardial effusion. Et:

Infection results in inflammation and resulting infiltration of exudate and immune cells. The formation of fibrinous adhesions can result in constrictive pericarditis.


As pericardial effusion - Weakness, respiratory distress, coughing, collapse, muffled heart sounds, weak pulse, pale mucous membranes


Pericardiocentesis with culture/viral assays/fungal assays/neoplastic cell count. USG. Abnormal ECG.


Pericardiocentesis then depends on cause

Pericardial effusion Pericardial effusion is fluid within the pericardial sac. This compression causes cardiac tamponade causing reduced CO which can resemble right side heart failure. Et:

Neoplasia is most common (haemangiosarcoma and heart base tumours in dogs, lymphoma in cats). Can also be caused by pericarditis (etiologies above), trauma, and secondary to chronic heart failure.


Weakness, respiratory distress, coughing, collapse, muffled heart sounds, weak pulse, pale mucous membranes


X ray, ECG showing ventricular arrhythmias, paricardiocentesis with fluid testing, USG (effusion is a black space surrounding the heart)


Pericardiocentesis. Pericardectomy if recurring - Give ATB with surgery. Most tumours that cause effusions do not respond to chemotherapy.

Cardiomyopathies Dilated Cariomyopathy Breeds: Doberman pinscher, Boxer, Giant Breeds, Cocker Spaniel (90% is dobermans and boxers)


A decrease in myocardial contractility results in a decrease in stroke volume. However, this loss of contractility also affects the mitral value - resulting in regurgitation. The heart muscle gradually becomes fibrous and fatty, with many inflammatory cells and microfibre necrosis. The end result is a heart muscle that cannot contract. The initial decrease in stroke volume is slightly compensated for - heart rate increases and the kidneys retain salt and water (influenced by aldosterone release). This helps to return stroke volume towards normal allowing the animal to continue for a while.


In boxers and dobermans, sometimes the only sign is sudden death. Also possible - syncope, arrhythmias, ventricular premature complexes and ventricular tachycardia. Also signs of congestive heart failure - lethargy, exercise intolerance coughing, tachypnoe etc. Some animals show no abnormalities, but arrhythmias can often be heard, including a soft systolic murmer, decreased arterial pulses.


X ray - an enlarged round heart may be seen, but in deep chested dogs it can still look normal. Left ventricle and left atrial enlargement, pulmonary congestion and edema (due to heart failure), pleural effusion, hepatosplenomegaly and ascites occur rarely. ECG - Ventricular premature complexes are most common sign, esp in predisposed breeds. Atrial fibrillation. USG - Gives a definative diagnosis. Dilated Cardiomyopathy is characterised by increased end-diastolic diameter.


Treat any arrhythmias. Digoxin is used to increase contractility and slow the heart rate. Furosemide is given to reduce congestion. ACE Inhibitors (Benazepril) can also alleviate congestion (Angiotensin converting enzyme - when active allowes aldosterone to be produced, increasing water reabsorption - we want to stop this to reduce congestion). L-Carnitine is an amino acid that helps the heart. Taurine is another muscle amino acid that can be supplemented if levels are low.

Cat Cardiomyopathies = Hypertrophic Cardiomyopathy, Restrictive Cardiomyopathy, Dilated Cardiomyopathy Unlike dogs, where valvular disease is the most common form of cardiac disease, in cats myocardial disease is the most common form of cardiac disease. Primary myocardial diseases are those due to intrinsic abnormalities in the myocardium (the three listed above). Cats also develop myocardial disease secondary to systemic conditions such as hypertension and hyperthyriodism Hypertrophic Cardiomyopathy Breeds: British Shorthair and Maine Coon - can be hereditary, so consider problems of breeders. Et:

Caused by a genetic sarcomere mutation which produces some dysfunctional muscle fibres, some muscle fibres are however, normal, and increase in size to compensate causing hypertrophy. Abnormal muscle fibres degenerate and are replaced by scar tissue, resulting in a thickened ventricle, which can contract well, but cannot relax properly. This deformation often results in the development of mitral regurgitation and aortic outflow obstruction.


Most cats present with acute heart failure (but in actual fact disease may have been going on for years). The cardiac disease develops slowly, so owners don't notice anything until pulmonary edema and pleural effusion develop, causing dyspnoe. Thromboembolism involving one or more limbs may also be the first clinical sign that occurs in some cases (paralysis, pain, cold, lacks pulse, blue from lack of blood). Murmur - systolic murmur is common on the left or right sternal region.


X ray (atrial enlargement, pulmonary edema or pleural effusion), ECG is usually needed for definative diagnosis. USG (thickening of the left ventricular wall of > 6mm indicates hypertrophic cardiomyopathy). Rule out hyperthyroidism with T4 levels.


Furosemide, ACE Inhibitors. B Blockers/Ca Channel Blockers to decrease HR and give the heart more time to reach diastole.

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