Heart disease accounts for around 15% of medical cases vets see. It’s a broad term for conditions of the heart, blood vessels or valves. Both congenital heart disease (present at birth) and acquired heart disease (occurs in adulthood) are largely hereditary in nature, although in some cases environmental factors are also important.
Only around 5% of cases are congenital so in this blog we focus on the acquired heart disease. There are different types of acquired heart disease; the type and stage of discovery will change the treatment options.
What causes heart disease?
The two principal causes of acquired heart disease are:
Chronic degenerative valve disease (DVD). The valves inside the heart, which create a seal preventing blood from flowing the wrong way, degenerate over time. Initially there may be no signs but as the heart is working harder to pump, it can become enlarged. Valve disease accounts for about 75% of canine heart disease. Cavalier King Charles spaniels, chihuahuas, miniature poodles, miniature pinschers, fox terriers, Boston terriers, and miniature schnauzers are all more prone.
The second most common cause of heart disease is dilated cardiomyopathy (DCM, also known as dilated heart). Over time, diseased heart muscle leads to thinning and enlargement of the chamber walls. Changes to the heart wall can also commonly cause disturbances to the rhythm of the heart which may lead to fainting or even sudden death. It occurs in giant breeds such as Newfoundlands, dobermanns (45% of this breed suffer with DCM), and great danes. The exception is the cocker spaniel and they can suffer both types of heart disease. Boxers can suffer a specific cardiomyopathy – arrhythmogenic right ventricular cardiomyopathy (or boxer cardiomyopathy), which usually presents with severe arrhythmias (abnormal heartbeats).
In both situations, the result of this poorly-pumping, inefficient heart is usually congestive heart failure (CHF), where blood dams up in the organs, most commonly the lungs, and these organs then won’t function normally or will become swollen with fluid, or both.
Clinical signs may include rapid breathing at rest, shortness of breath, coughing, blue gums, difficulty exercising, or even fainting or collapse.
What is the outlook?
Heart disease can be split into ‘stages’ which helps us direct treatment options and prognosis:
Stage A includes high risk breeds such as the cavalier King Charles spaniel, but currently with no signs.
Stage B1: murmur but no clinical signs, or signs on x-ray or heart scan (echocardiography).
Stage B2: signs of enlargement of the heart on x-ray or echocardiography.
Stage C: symptoms that require treatment.
Stage D: symptoms becoming unresponsive to management.
Valve disease is often picked up at health checks, when the vet detects a heart murmur, before symptoms are shown. Dilated heart cases are often only diagnosed at the symptomatic stage, as murmurs can be subtle or absent so are not found on examinations. Screening programs in prone breeds may find cases earlier.
Sadly, once dogs with valve disease are showing signs they usually don’t survive longer than a year. With dilated heart disease, survival times are worse, ranging from 4-6 months, although cocker spaniels may survive up to 2 years. The poor outlook, quality of life, financial and time commitments that care brings must be considered when deciding the right path.
So what are the options?
Cardiology is a very specialist field. While GP vets are often skilled in the area, they may discuss referring your dog to a specialist for further tests, monitoring and treatment. This may lead to significant financial and time commitments.
Heart disease, once symptomatic, is progressive and fatal. Treatment depends on the severity of the signs and the cause of the heart failure and aims to improve quality of life for as long as possible.
In emergency situations, oxygen, intensive care and stabilisation are required. If non-responsive, euthanasia may sadly be the only option.
With less severe signs or after stabilisation, long-term medication and monitoring by your GP or cardiologist will usually be the first option considered.
Valve surgery or replacement is standard in humans. While feasible for dogs in specialist units, it’s still being developed and tested so it’s not widely available in the UK.
Most commercial diets have adequate levels of taurine (a building block of protein) which is important as deficiency may be linked to heart disease. Diets rich in omega-3-fatty acids are known to help and once in heart failure, sodium may be restricted, but not before.
What medications are there?
There are many mixtures, dosages and frequencies of medication to ease signs, depending on the cause and severity of the heart failure. The common ones are listed below but there are others that cardiologists may recommend to you or your GP vet:
Diuretics help manage fluid overload in animals. Furosemide is most commonly used. Torasemide is similar but more potent, with a longer duration of action. Other diuretics may be added at a later stage in severe cases. Another diuretic, spironolactone, may also reduce heart scarring. These medications can cause dehydration and renal issues. The dose and effect must be balanced with these risks.
Pimobendan improves heart muscle contraction, dilates blood vessels, increases cardiac function, and helps manage blood pressures in patients with heart failure.
Dogs with dilated hearts often have arrhythmias. There are different types of arrhythmias so diagnosis by ECG (electrocardiograph) is imperative as antiarrhythmic therapies can have unwanted side effects. Digoxin and calcium channel blockers (such as diltiazem) are examples of drugs used to treat certain arrhythmias.
ACE inhibitors (ACEi) widen blood vessels, improving blood flow so decreasing the amount of work for the heart. They block a blood substance called angiotensin which is a powerful blood vessel narrower made as a result of heart failure. Common drugs include benazepril and enalapril.
Using medication in dogs with no symptoms has until recently been controversial. However, recent studies show that dogs with enlarged hearts may benefit from early medication. Ace inhibitors given in the preclinical dobermans with dilated hearts showed prolonged survival times but this is not the case with valve disease.
A more recent study showed using pimobendan in dobermanns in the early stages of dilated heart disease slowed down the progression of the disease, both to heart failure, and to death. Another very recent study in dogs with stage B2 valve disease (enlarged heart but no other symptoms) showed that using pimobendan delayed signs and increased lifespan.
This demonstrates how important monitoring, pre-screening and early detection are in breeds susceptible to heart disease. The earlier these conditions are diagnosed, the more effective treatment is likely to be!