This Health Focus is on Heart Disease in Animals.
Heart disease in animals is more common than most people think and it is one of the leading causes of death in geriatric dogs. The heart basically works as a pump that moves blood round the body. It collects freshly oxygenated blood from the lungs and then sends it out to the rest of the body because the body needs oxygen to survive. It then collects all the used blood from the body that has no oxygen in it, and pumps it off to the lungs for a fresh supply. While the blood is being circulated through the body, it passes through the intestines, where proteins, fats and carbohydrates are absorbed. These feed all the organs that the blood subsequently passes through. It also passes through the kidneys, which remove wastes from the blood, by forming urine to get rid of them. When it passes through the liver, poisons are drawn out and detoxified and sugar levels are normalized by the liver and pancreas. So without a healthy heart, everything else in the body becomes unhealthy too, because all the organs depend on the heart for oxygen and nourishment.
The heart has 4 chambers or compartments. The top two chambers are inlet chambers that collect the blood, and they are known as atria. The bottom two chambers are outlet chambers that pump the blood out to the body and the lungs and they are called ventricles. The heart has a left and right side, each with its own atrium and ventricle. The left side of the heart receives blood with oxygen from the lungs and sends it off to the body and the right side of the heart receives blood without oxygen from the body and sends it to the lungs. There are one way valves inside the heart between the atria and ventricles and also going out of the ventricles as the blood leaves the heart. Any blood vessel that enters the heart at the atria is called a vein and any blood vessel leaving the heart is called an artery. The heart has its own little arteries and veins that supply it’s muscle with oxygen and food; these are called coronary arteries. In humans, when a person has a heart attack it is sometimes called a coronary because it is the coronary artery that gets blocked.
Heart disease in animals occurs when 1 or more parts that make up the heart get damaged or stop working properly.
The most common heart problem seen is heart disease of the valves of the heart. These are often picked up by your vet on the table when your pet’s heart is listened to. A leaking valve or one that doesn’t open makes a noise that can be heard with a stethoscope. These are known as heart murmurs and are graded from 1 to 6, with one being the softest and 6 the loudest type of murmur. Dogs with very bad heart murmurs can often be picked up by an observant owner who sees the heart beating through the chest wall or felt with their hands when their pet is being stroked.
There are two types of valve disease – inborn valve disease and valve disease due to damage and disease. With valve disease, the valve either does not open or does not close properly. Valves that do not open properly (stenosis) are more common with inborn valve disease. The main problem is that blood can’t get through the valve to where it needs to go. This causes it to build up in the ventricle below the valve and can cause the ventricle to enlarge because of this. The most common valves affected are the pulmonic valve and the aortic valve, which are the valves at the exit from the heart.
With valves that do not close properly, the blood which is supposed to go one way, ends up leaking back the wrong way (insufficiency). This causes blood to accumulate on the wrong side of the valve. This blood then dams back out the heart, into the veins of the body, where it lies in pools. These pools of blood increase pressure in the veins, which makes water leak out the veins (as normal veins have many tiny pores in them) into the closest organs. The result is that water builds up in the lungs, the liver and the abdominal cavity. The most common leaky valve problem occurs due to degeneration and old age of the heart valve in elderly small breed dogs and the most common valve affected is the mitral valve, which lies between the atrium and the ventricle on the left side of the heart. Infections can also lodge in heart valves, damaging them and causing them to crumple and become leaky.
Heart disease can also affect the muscle. If there is something stopping blood leaving a ventricle the way it is supposed to, such as a valve that won’t open, the heart muscle can become diseased. It can get thicker and thicker (hypertrophy) from all the effort of trying to push the blood out the heart. If it gets too thick it becomes a problem as the heart thickens to the inside and thus the chamber becomes smaller and smaller over time, so less and less blood can get in. In the end, not enough blood is sent to the body per pump because there simply isn’t enough space for blood to get in in the first place. Sometimes the heart muscle can also dilate, i.e. become thinner and thinner over time as too much blood fills as heart chamber. This thin enlarged heart muscle is too weak to send enough blood to the body per pump and the body becomes starved of oxygen and nutrition. Some large breed dogs such as Irish Wolfhounds, have a genetic tendency to develop these dilated hearts, in a condition known as dilated cardiomyopathy (DCM).
Cats with Hyperthyroidism can get changes in their heart muscles – they are prone to hypertrophic cardiomyopathy, but dilated cardiomyopathy is also seen. Some viruses such as the Parvo virus can affect heart muscle, leading to sudden death in these already very ill puppies. Infection of the heart muscle or lining of the heart (endocarditis) can heal but leave scarring. This can lead to problems because scar tissue does not move and thus the heart cannot expand enough to take in blood and ends up supplying too little blood per pump.
Arrhythmias are a problem of the electrical system of nerves lying deep within the heart muscle, that control how fast the heart beats, and if they become faulty, the heart beats either too slowly, which means not enough blood is sent out to the body per minute, or too fast, which strains the heart and makes it go into heart failure as it doesn’t get a chance to rest. This problem in people is solved by implanting a pacemaker to regulate how fast the heart beats. Some diseases of the body, such as Addison’s disease (Hypoadrenocorticism) and acute kidney failure can cause changes in the blood potassium levels which can lead to a slowing down of the heart and eventual death. To diagnose an arrhythmia, a vet will typically do a blood test and and ECG, if the facilities are available.
The pericardium is a sac around the heart. If there is a bleed into it, or water builds up inside it due to right sided heart failure, or there is a tumour inside it at the heart base, it can fill with fluid or blood. This effectively stops the heart beating properly and leads to heart disease in animals, as the heart cannot expend as it is being squashed from the inside. This is an emergency, as the fluid needs to be drained out quickly or the animal may die. Your vet will typically hear a muffled heart sound and on X ray the heart shadow is huge, round and balloon shaped.
Heart failure occurs when the heart disease has become bad enough that the heart no longer sends enough blood, and thus enough oxygen and nutrition to the internal organs, and they start to take strain and not function properly. Or, if the fluid pooling in the veins has accumulated in the lungs to the extent that an animal is not able to get enough oxygen in because the lungs, which are normally filled with air, are filled with water. If the fluid pooling in the liver and abdominal cavity accumulates to the point where the liver can’t function well and the animal doesn’t eat this also is classed as severe heart failure.
Signs of Heart Failure
There are 2 sides to every heart and thus 2 types of heart failure – left and right, although sometimes both types are seen
Left Sided Heart Failure
Coughing, especially at night
Gums are pale and tongue has a bluish tinge
Sudden collapse and fainting spells
Drops of moisture round nostrils
Animal won’t settle and sits up and struggles to breathe
Right Sided Heart Failure
Cats that show difficulty in breathing with a heaving chest, sitting up and not settling and bluish tinged tongue
Diagnosis of Heart Failure
Heart failure can be picked up by your veterinarian on the table, using the signs listed above. It is recommended, though, that your vet does further tests to assess how bad the heart failure is and where the problem lies. Chest X rays should be done, and at least 2 views (one from the side, one from the top or bottom of the animal) should be taken to assess heart size, look for fluid build up in the lungs and check for growths at the base of the heart that could cause heart failure. Echocardiography or ultrasound of the heart is also useful. This will pick up the strength of each contraction of the heart as well as how much leakage is occurring through damaged heart valves. Any inborn or congenital heart defects will also be picked up at the same time, the thickness of the heart muscle will be assessed, the size of each chamber of the heart will be measured and any tumours or masses inside the heart can be seen at the same time. ECG or electrocardiogram is useful if an arrhythmia is suspected. Your vet should also check for Heartworm, if you live in an area where Heartworm is found, and treat for it.
Treatment of heart failure
Heart failure is treated most commonly in 3 ways:
1. By getting rid of all the extra water on the chest and in the belly.
Diuretics are usually used for this. These drugs make the kidneys lose water, by drawing more water out of the blood, which makes the blood thicker. This thick blood attracts water by osmosis, and this draws water out of the lungs and abdominal cavity back into the blood to replace the water lost. The most common two drugs used to this are Furosemide or “Lasix” and Spironolactone or “Spiractin”. These drugs take a few hours to work if given orally. Furosemide can be injected into a vein or under the skin for a more rapid effect. If an animal is really struggling to breathe or is really bloated and distended, fluid may be drawn directly out of the chest or abdominal cavity with a needle to save it’s life.
2. By giving drugs that allow the heart to function more effectively.
ACE inhibitors, such as Enalapril, Benazepril and Captopril, of which the common trade names include “Renitec”, “Enacard” and “Fortekor”, act by reducing the blood pressure slightly. This slightly lowered blood pressure allows the heart to ease up a little and not work as hard to pump blood out. This saves the sick heart muscle from overworking and extends it’s life. These drugs also have a mild diuretic effect. They stop the kidneys producing an enzyme that would increase blood pressure and cause the body to retain water and thus lower blood pressure and cause mild water loss from the body.
Drugs such as Digoxin have been used to treat heart failure since ancient times. Digoxin, which goes by the trade name “Lanoxin” increases the strength of the contractions of the heart muscle, enabling the heart to push harder with every beat. Digoxin should only be used if there is no obstruction, such as a valve that won’t open and should not be used if there is thickening of the heart muscle, or hypertrophy. For these reasons, it should not be used as the first choice of drug, and then only after a heart scan.
Beta blockers and Calcium channel blockers can also be used to treat some cases of heart failure. Beta blockers slow the heart down, and thus stop it from over working. Calcium channel blockers reduce blood pressure by reducing the force of the heart muscle’s contraction. Aminophylline or “Millophyline” is sometimes still prescribed to control the coughing that occurs with heart failure as it opens the airways. It does, however, tend to increase the rate of the heart at the same time, as it is a caffeine derivative, so should only be used in certain cases.
3. By modifying the diet
Diets that are low in salt are recommended for heart failure such as the Hills H/D diet. Also if a patient is very fat, he may be put on a reduced calorie diet such as the Eukanuba Restricted Calorie in order to lose weight so that the heart doesn’t take any unnecessary strain.