Diagnosis of Heart Disease in Dogs

There are quite a number of methods available to a veterinarian when it comes to diagnosing a heart disease. These include reviewing the animal’s medical history, analysing the symptoms, performing a physical exam, and analysing the outcome of particular tests or imaging processes.

A majority of Heart diseases can be detected from physical examination and x-rays. The physical examination takes a two-pronged approach. It involves the use of a stethoscope in order to listen to the sounds made by the dog’s internal organs, mainly the heart, lungs, and abdominal organs. It also involves investigating the status of parts of the body by feeling with hands and fingers, in order to make a distinction between firm and fluid-filled swellings.

Imaging Techniques Used in Diagnosis Of Heart Disease In Dogs

Imaging techniques that can be used are x-rays, electrocardiography i.e. measuring cardiac electrical activity, and echocardiography i.e. a form of ultra-sonography. There are also situations that necessitate the use of more specialized tests such as cardiac catheterization (inserting a slender flexible tube via an artery into the heart) or nuclear studies (x-ray tests involving injection of radioactive isotopes). One of the best ways of diagnosing heartworm disease is by conducting a blood test to discover the existence of female heartworms.

X-rays

Chest x-rays, or radiographs, are commonly used to diagnose heart disease in dogs. Any form of enlargement of the heart or certain chambers within the heart is usually indicative of heart disease. The x-rays may also help to identify the exact disease the animal is suffering from e.g. fluid in the lungs is correlated to congestive heart failure. While chest x-rays help to identify heart disease, they have some drawbacks. It does not confirm the precise origin of a particular symptom or exclude another origin e.g. it doesn’t tell whether fluid in the lungs is due to a heart or lung disease. It is also not as precise as echocardiography when it comes to assessing heart and chamber size.

Electrocardiography

This is the measuring and recording of cardiac electrical activity from the body surface, by using electrodes. Electrocardiography is specifically used to diagnose arrhythmias such as bradycardia (unusually slow rhythm), tachycardia (unusually rapid rhythm), sinus arrhythmia, or sinus arrest. It can also be useful in identifying conduction anomalies, failure of electrical signal to pass through the heart tissue, and atrioventricular blocks i.e. first, second and third degree blocks.

Another benefit of electrocardiography is that it can be used to detect enlargement of the heart chambers. This anomaly is indicated by irregular waveforms that are picked up on the electrocardiogram recording. Varied readings mean that the different chambers of the heart are enlarged. A key point to be noted is that while the electrocardiogram might give an indication of chamber enlargement, other methods are much more sensitive, e.g. echocardiography and chest x-rays.

Echocardiography

Echocardiography is a form of ultrasonography that is used to assess the aorta, heart, and pulmonary artery. It is suited for verifying uncertain diagnoses, for identifying heart tumours, or for spotting pericardial disease. It is used in tandem with alternative diagnostic techniques to evaluate and display images of the heart as it works inside the chest. It provides numerous advantages, such as:

  1. It enables calculation of the heart chamber and wall dimensions.
  2. It displays clear images of the physical structure and movement of the heart valves.
  3. It makes it possible to calculate and analyse the differences in pressure, volumes of blood flow, and measurements of heart function.

Types of Echocardiography

There are three distinct classes of echocardiography:

Two-dimensional echocardiography produces a 2-D, wedge-shaped picture of the heart as it moves.

M-mode echocardiography is a result of a 1-D ray of ultrasound that goes through the heart, generating an ‘ice-pick image.’ The ray travels through cardiac tissue which it then begins to plot on a screen. This method of assessment is generally used to determine thickness of the chamber wall, chamber dimensions, dimensions of the aorta, dimensions of the pulmonary artery, and motion of heart valves.

Doppler echocardiography is used to locate heart murmurs. It achieves this through a system of varying the frequency of an ultrasonic beam after it hits a mobile red blood cell, thus enabling measurement of blood flow rates and identifying high-speed or unstable flow.

Cardiac Catheterization

This is the insertion of specialized tubes (catheters) into the heart, aorta, or pulmonary artery. This procedure is resorted to when others diagnostic tests are unable to determine specific cardiac irregularities, or are insufficient in assessing the severity of a lesion. Cardiac catheterisation can also be used to gather data for medical research, to evaluate the heart prior to surgery, and also during treatment. However, analytical and pre-surgical cardiac catheterisation has mostly been substituted by echocardiography.

Heart Disease Versus The Breed

Most heart disorders out there are specific to particular breeds of dogs. For example, mitral regurgitation is prevalent in Cavalier King Charles Spaniels and older, male Cocker Spaniels. Adult Miniature Schnauzers are prone to specific types of arrhythmias, and young Wirehaired Fox Terriers frequently suffer from tetralogy of Fallot. Such knowledge of dog breeds and their associated heart disease can prove invaluable to your veterinarian when it comes to making a diagnosis.

Symptoms And Signs of Heart  Disease

Dogs displaying symptoms of heart disease may have a previous record of intolerance to exercise, loss of energy, coughing, breathing problems, rapid breathing rate, abdominal inflammation due to fluid build up in the abdomen, fainting due to deficit of blood flow to the brain, a bluish hue to skin and membranes because of oxygen deficit in the blood, poor appetite and loss of weight. Some uncommon symptoms include the legs swelling, yellowing of the eyes, skin, or membranes, or coughing up blood, and bloody mucous.

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