Congenital heart conditions
There are a number of defects in heart structure that may occur as a foetal (unborn) kitten undergoes development. These defects include ventricular septal defects, atrioventricular (AV) valvular dysplasia, aortic stenosis, patent ductus arteriosus (PDA) and the Tetralogy of Fallot. It has been suggested that the Siamese breed and male kittens may be more at risk of developing these conditions.

Detecting a cardiac problem may include a number of different procedures. Listening to the sounds of the heart with a stethoscope can detect a heart murmur which indicates the heart valves are not closing properly or the the presence of a septal defect (hole). Radiology (x-rays) is a useful to identify an enlarged heart or blood vessel. Electrocardiography (ECG) which involves attaching electrodes to the skin to measure small electrical currents travelling through the heart. Echocardiography is the examination of the heart using an ultrasound

Normal Heart
The heart acts as a pump to move blood around the body. It is divided into two halves, the left half pumps blood at high pressure around the whole body whilst the right half only needs to pump blood through the lung and back to the left side of the heart therefore it can function at relatively lower pressure. Each side of heart is further divided into two chambers. Blood returning to the heart from the body or the lung enters the first chamber called the atrium. Contraction of the atrium pushes the blood into the second chamber called the ventricle which then contracts to pump the blood out of the heart. Between these two chambers are valves that close when the ventricle contracts to ensure blood doesn’t flow backwards into the atrium.

Ventricular Septal Defects
A ventral septal defect is a hole that exists between the left ventricle and the right ventricle. Defects allow blood to escape from the left ventricle wihch operates at a higher pressure into the right ventricle. This results in a blood overload in the lungs and the left side of the heart.
The size of the hole determines the extent of the problem. Most cats have small defects that never produce a problem and they live a normal life. Moderate defects cause left sided heart failure as this side of the heart is doing more work. Large defects will cause the right ventricle to stretch as a result of the increase pressure of blood coming through from the left ventricle. Those with a significant defect may show signs of dyspnoea (problems breathing) exercise intolerance, syncope (temporary loss of consciousness) and a cough.
Definitive diagnosis generally requires doppler echocardiograms

Medical management will aim to decrease the volume overload on the heart and to remove fluid build up in the lungs. Decreasing the salt in the diet is generally recommended. The drugs currently recommended may include enalapril (ACE inhibitor) which reduces the load against which the heart is pushing by acting on the blood vessels; furosemide (diuretic) wihch stimulates the kidney to remove fluid build up on the body (hence the lungs) and digoxin which increase the performance of the heart muscle. Potential complications from the use of these drugs may arise if the kidneys are damaged. Cats showing significant clincial signs have an estimated life expectancy of 6-18 months with medical treatment. Surgical treatment to close the defect may be appropriate for some cats, however this is a very specialised procedure.

Atrioventricular Valvular Dysplasia
The valves responsible for preventing back-flow from the ventricle to the atrium are called the tricuspid in the right side and and mitral valves in the left side of the heart. Some cats can have a valve dysplasia (malformed valve), the result of which allows some blood to leak back into the atrium from the ventricle when it contracts. This restricts flow back to the heart and increases the pressure in the blood vessels returning to the heart resulting in an accumulation of fluid in the body tissues

The signs seen depend on which valve is malformed. If the mitral valve (left) is affected then the back flow will occur towards the left atrium and will subsequently effect the lungs. The signs seen will generally include a cough, exercise intolerance, dyspnoea and syncope. If the tricuspid valve is affected then the back flow will occur into the right atrium and thus restrict blood from returning from the body. The signs seen may include peripheral oedema (swelling due to fluid, usually most noticeable in the lower limbs) and ascites (swollen abdomen due to fluid accumulation). Although these signs can be evident at an early age in affected cats, there may be a delayed until they are mature before the condition is apparent.
ECG and xray may indicate the secondary changes to the heart. The malformed valves may be apparent on echocardiographs

The prognosis for this condition is poor and medical management is the only option. Decreasing the salt in the diet is generally recommended. The drugs currently recommended may include enalapril, furosemide and digoxin (see septal defect).

Aortic Stenosis
The aorta is the vessel responsible for carrying blood from the left ventricle out into the body. Stenosis is a narrowing of the vessel which resluts in a restriction to blood flow. This places back-pressure on the pumping heart as it attempts to force the blood through the restriction wihch can lead to enlargement and thickening of the left ventricle. As a result blood flow in the vessels supplying the myocardium (heart muscle) itself can be compromised producing ischemia and infarction (not enough blood flow and area of dead muscle. This is similar to the human “heart attack”. Other secondary conditions include valve failure and arrythmias (incorrect pattern of beating).

Generally a heart murmur can be heard in moderate to severe cases. The left side of the heart may be enlarged on radiographs (xray). ECG trace may also indicate an enlarged heart and ventricular arrhythmias. Echocardiagraphs may show the stenosis of the aorta

The signs of aortic stenosis depend on the severity of the obstruction and may include syncope, dyspnoea, exercise intolerance and a cough. Effective management of this condition is not yet possible, there are many different opinions on which treatments are appropriate. Beta-adrenergic blocking agents are indicated where arrhythmias and syncope (fainting) are apparent. Signs of congestive heart failure due to valve damage can be treated symptomatically with diuretics and digoxin. Sudden death is a possibility outcome for any cat that is affected by aortic stenosis and the prognosis is generally poor.

Patent Ductus Arteriosus
The ductus arteriosus is a blood vessel present in unborn animals which runs from the pulmonary artery to the aorta allowing blood to bypass the lungs. At birth muscles in the ductus are stimulated to contract, decreasing the size of the bypass, and directing blood to the newly inflated lungs. Over the first week of life the ductus normally closes completely.

In some kittnes the ductus arteriosis fails to close (patent ductus arteriosis- PDA) due to the muscles which should contract to close the ductus being abnormal. Some of the blood returning from the body to the heart fails to pass through the lungs before returning to the circulation. Not only is this oxygen level in the blood reduced but the bypass causes increased pressure in the left side of the heart leading to dilation and eventually left sided heart failure.

PDA kittens may only show poor growth and poor tolerance to exercise in the early stages. As left sided heart failure develops coughing and panting may become more pronounced.

The most prominent clinical finding is a heart murmur (rushing sound) and possibly a vibration (thrill) which can be felt on the lower left chest wall. These due to the turbulence created by the blood rushing through the PDA. Xray and ultasound are used to confirm the diagnosis.

Recommended treatment is surgical closure of the PDA. This is generally carried out between 2 and 4 months of age. Although there is a small risk of death associated with the surgery treated cats have a good long term outlook compared with untreated cats.


Tetralogy of Fallot
This is a serious problem that is actually a combination of conditions:
1. ventricular septal defect
2. pulmonic stenosis (stenosis of the vessel leading from the right ventricle to the lungs)
3. over-riding aorta (where blood enters the aorta not only from the left ventricle but also from the right ventricle)
4. right ventricle hypertrophy (the right side of the heart wall becomes thicker)

The dynamics of blood flow will vary with the severity of the various problems. Generally most cats will tend to show signs of cyanosis (blue color gums), weakness, syncope and dyspnoea.

Diagnosis is generally confirmed using echocardiography

Most cats with this condition live less than 1 year once signs become apparent. Surgical correction may be possible in some cases, but a specialist institution capable of heart bypasses will be required. Medical management is limited, exercise restriction is advised and periodic phlebotomy (draining of some blood) may be required in some cases. Propranolol (beta-blocking agent) may greatly reduce the clincial signs in some cases.

Overall it is important to realise that although these problems do exist the relative importance of each has yet to be fully determined in a particular sex or breed. It is suspected that the problems are inherited, but there is not currently enough information to establish either whether this is true or in what manner the genetics are passed on. It is probably wise not to breed with animals affected by any of these conditions.