Heart disease in dogs & cats 1: Congestive heart failure

As our pets live longer the number of animals with heart disease will continue to increase. Happily our ability to manage and treat heart disease in dogs & cats has improved radically over the last two decades.

Heart disease in our pets is rather different to in ourselves. The vascular diseases such as arteriosclerosis don’t occur as dogs and cats metabolise fat far more effectively than we do (dogs use fat as an energy source in preference to carbohydrate. People are the other way around). Dogs and cats can also get heartworm infections, which cause heart disease. By treating the underlying parasitic infection, a lot of the clinical signs will resolve.

Congestive heart failure means that the heart is no longer pumping enough blood around the body, to deliver oxygen to tissues without the body making some changes.

The earliest change we see is increased respiratory rate (breathing more quickly) at rest. This is an easy thing to check at home. Watch your dogs breathing when they are fast asleep. If they take less than 30 breaths per minute their heart function is probably normal. If they take more than 30 breaths per minute their heart function may be compromised.

The most common cause of congestive heart failure is a heart murmur, or leaky valve. Heart valves ensure blood moves around the body in one direction. If the valves leak there is some back flow and some efficiency is lost. Many animals (and people) have heart murmurs with no degree of congestive heart failure. A heart murmur can be detected with a stethoscope during a consult. If a heart murmur is detected an increased vigilance for other signs of heart disease is warranted, and we may recommend a cardiac ultrasound (echocardiogram) to further localize and assess the severity of the problem.

Signs of congestive heart failure

At home you may notice weakness, lethargy and exercise intolerance. Dogs will often cough in the later stages of the disease, particularly at night. Sitting rather than lying down can often relieve the cough. You may also notice rapid breathing and, if you look, a pale or blue tinge to the gums. In some cases fluid will accumulate in other areas. Sometimes in the abdomen giving a pot bellied appearance, and sometimes in the legs and feet.

Diagnostic tests

A lot of the information we need we can obtain by clinical examination in the consult room. Depending on the circumstances some or all of the following procedures can also be useful.

• Heartworm test
• Chest x-rays
• General blood screen
• Electrocardiogram
• Cardiac ultrasound

Treatment

A number of treatment options are available, but some general issues also need to be addressed.

Overweight animals should be dieted as soon as quickly as possible. In the early stages of the disease dietary salt reduction can be useful.

Animals with heart disease need restricted but regular exercise. Regular short walks are safer than longer walks. If any time during exercise your pet shows signs of distress you need to stop and let them rest until their breathing returns to normal. Over exercise and consequent oxygen deficit is very damaging to the heart, and dangerous.

Many medications may be used for your pet. Some of the most common ones are outlined below.

Diuretics
The most common, but by no means only, diuretic used is furosemide. This is commonly used to clear pulmonary oedema. This is a condition where fluid collects in the lungs due to back pressure from the faulty heart. Pulmonary oedema causes the coughing seen in patients with this disease, and furosemide is used to relieve it.

ACE inhibitors (fortekor, Vetace)
These drugs are used to treat high blood pressure in people. In our pets they dilate the aorta, the major blood vessel coming out of the heart. This means there is less back pressure on the heart and blood travels out more easily. This is analogous to taking a kink out of a hose, and letting the water flow more freely.

Positive inotropes (Pimobendon, Vetmedin,)
These drugs have a blood vessel dilating effect, but also increase the force with which the heart contracts. Best results are usually achieved by using these drugs in conjunction with ACE inhibitors, and using diuretics as necessary.

Essential fatty acids
It is thought that high doses of essential fatty acids can slow the progression of heart disease, especially if given early in the course of the disease, by decreasing the formation of scar tissue in the damaged heart.