Heart Murmurs in Cats

What is a Heart Murmur?

The turbulence of blood flow in the heart results in an audible sound called a murmur. Before discussing murmurs, it is important to have a basic understanding of the different parts of the heart. 

Normal Heart Function and Blood Flow

Just like a human, a cat has a 4-chamber heart. The top chambers of the heart are called the atria (further classified into the left and right). 

The atria communicate with the bottom chambers called the ventricles (further classified as left and right). Between the atria and the ventricles, there are valves that help direct blood flow by opening or closing.  

The opening and closing of these valves and valves separating the chambers from large blood vessels are what cause the typical “lub” and “dub” sounds that are heard during auscultation of the heart using a stethoscope.

Oxygen-deprived blood is deposited into the right atrium through two large blood vessels. The blood then passes into the right ventricle when the valve (Tricuspid) is opened. 

The right ventricle then pumps the blood to the lungs where the blood becomes oxygenated. The oxygenated blood is then returned to the left atrium. When the valve (Mitral) dividing the left atrium from the ventricle is opened, blood enters the ventricle before being pumped out to the rest of the body.

A heart murmur is a sound that occurs secondary to turbulent blood flow through the heart. When a murmur is present, there is typically a “whooshing” sound that is appreciated in addition to the typical “lub” and “dub” sounds.

Classifying Heart Murmurs

The loudness of the heart murmur is described using a scale of 1-6.

• Grade 1: Minimally audible to the trained ear
• Grade 2: Slightly louder and easier to hear
• Grade 3: Can be easily noted with brief auscultation of the heart
• Grade 4: Murmur can be heard on both sides of the chest
• Grade 5: The murmur can be heard on all sides of the chest with brief and light auscultation. Loud
• Grade 6: A murmur can be palpated outside the chest and is very loud

What Causes Heart Murmurs in Cats?

The causes of heart murmurs are numerous. In some patients, the heart itself is functioning normally, but an abnormality outside of the heart leads to an audible murmur. Alternatively, in some patients, there are structural abnormalities in the heart itself.

Extracardiac

Murmurs that occur in cats with a normally functioning heart may have underlying processes occurring, leading to an audible change in blood flow.

 Examples of this can include:

• Anemia (blood becomes thin due to decreased amounts of red blood cells)
• Obesity or emaciation
• Fever/infection
• Hypoproteinemia (low protein levels in the blood)
• Hyperthyroidism leading to heart wall changes

Structural Abnormalities

Heart murmurs that occur due to cardiac abnormalities are referred to as structural murmurs. This can be further divided into congenital vs acquired.

Congenital Murmurs

Patients are born with structural abnormalities in the heart causing murmurs. These are often noted during initial kitten examinations. Examples include PDA (patent ductus arteriosus), and ventricular septal defect (VSD). 

Acquired Murmurs

These types of murmurs occur later in life and were not present at birth. Examples of this can include mitral/tricuspid valve degeneration.

Innocent Murmurs

These murmurs can occur in very young kittens without structural heart disease. Innocent murmurs are generally very quiet and will resolve by around 6 months of age.

Signs and Symptoms of Heart Murmurs in Cats

Signs of heart murmurs vary. Often cats and kittens do not exhibit signs until a significant disease is present.

Signs can include:

• Labored breathing
• Quick, shallow breaths
• Open mouth breathing
• Pain from/paralysis from clot formation
• Sudden death
• Listlessness
• Poor doing
• Decreased appetite
• Blue mucus membranes (cyanotic)

How is a Heart Murmur Diagnosed?

Heart murmurs are often initially noted on routine physical examinations. A veterinarian will closely auscultate your pet during the examination using a stethoscope and listen for an abnormal “whooshing” sound. 

Once the heart murmur is noted, underlying causes will likely be investigated through additional diagnostics.

Diagnostics

Blood Work

An important mechanism to screen for anemia or hyperthyroidism, two common causes of murmurs in cats

Echocardiograms

The echocardiogram (ultrasound of the heart) allows each valve and heart chamber to be closely evaluated. 

ECGs 

This is used to evaluate electrical impulses through the heart. 

proBNP Snap Test

This blood test allows evaluation of the stretch of the muscles making up the heart (myocardium). Elevated values can be suggestive of cardiac disease. This test often helps confirm the need for a patient to have additional diagnostics like an echocardiogram done.

Radiographs

Thoracic radiographs allow the size and shape of the heart to be evaluated. Additionally, this test will help determine if there is fluid accumulation occurring within the chest which can be seen in congestive heart failure patients. 

How are Heart Murmurs Treated in Cats?

The treatment of a heart murmur will be determined by the underlying cause or type of murmur that is present. In patients with heart murmurs secondary to other disease processes, treatment of the primary disease is necessary.