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Murmurs are additional vibrations of the heart that are caused due to some disturbance in the flow of blood. Such a disturbance is enough to produce noises which are audible. Heart murmur in dogs includes a number of definitive factors such as the timing, which assist in the classification of different types of heart murmurs. For example, systolic murmurs are caused due to contraction of the cardiac muscles; diastolic murmurs result from the relaxation of cardiac muscles between heart beats and continuous and to and fro murmurs usually occurs in almost all or most of the heart cycle.

Heart murmur is prevalent in dogs as well as in cats.

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Symptoms of heart murmur in dogs

  • The signs and symptoms that accompany heart murmur in dogs are dependent on a number of factors such as their location, configuration and grade.
  • In case, heart murmur is caused due to the presence of a structural cardiac condition, then the dog may experience additional symptoms of congestive cardiac failure such as weakness, intolerance to exercise and coughing.

Grading scale for heart murmur in dogs

  • Grade 1: The heart murmur is just audible
  • Grade 2: It is faint but can be easily heard via a stethoscope
  • Grade 3: The loudness is intermediate. Heart murmur in dogs caused due to blood circulation mechanics are of minimum grade 3 category.
  • Grade 4: The murmur is loud and it reverberates widely which may often include the other side of chest.
  • Grade 5: It is very loud and is audible via a stethoscope that barely touches the chest. One can distinctly feel the strong vibrations through the chest wall of the affected dog.
  • Grade 6: It is extremely loud and is clearly audible via a stethoscope that barely touches the chest. One can distinctly feel the strong vibrations through the chest wall of the affected dog.

Configuration of heart murmur in dogs

  • Crescendo-decrescendo murmurs become louder and then duller. They are representative of ejection murmurs that result from unstable forward flow.
  • Plateau murmurs are uniformly loud and are representative of regurgitation of blood through an irregular valvular opening.
  • Decrescendo murmurs commence loud and then become softer. They are representative of diastolic murmurs.

Causes of heart murmur in dogs

Some of the causes of heart murmur in dogs are as follows:

  • Disturbances in flow caused due to obstruction of outflow or due to flow into an expanded great vessel or due to forward flow via diseased valves.
  • Blood flow disturbances that result from high flow through abnormal or normal vessels or from parts that vibrate in the flow of blood.
  • Disturbances in flow caused due to regurgitant flow that results from patent ductus arteriosus, from an abnormal valve or from a defect present in the septum

Mentioned below are some of the medical conditions that can result in heart murmur in dogs:

Systolic Murmurs

  • Anemia
  • Heartworm infection
  • Hyperthyroidism
  • Tricuspid and mitral valve cardiac failure
  • Tricuspid and mitral valve dysplasia
  • Aortic valve insufficiency and cardiomyopathy
  • Tricuspid and mitral valve endocarditis, i.e. inner cardiac regions inflammation
  • Systolic anterior mitral motion  or SAM
  • Dynamic subaortic stenosis
  • Dynamic right ventricular outflow obstruction
  • Aortic stenosis
  • Ventricular and atrial septal defect
  • Pulmonic stenosis
  • Tetralogy of Fallot

Continuous or To-and-Fro Murmurs

  • Patent ductus arteriosus
  • Aortic stenosis with aortic regurgitation
  • Ventricular septal defect with aortic regurgitation

Diastolic Murmurs

  • Pulmonic and aortic valve endocarditis, i.e.  inflammation of inner cardiac layer
  • Tricuspid and mitral valve stenosis

Diagnosis of heart murmur in dogs

In the diagnosis for heart murmur in dogs, the veterinarian first determines the exact cause of the symptoms by differentiating between a number of irregular cardiac sounds, such as ejection sounds, clicks, split sounds and gallop rhythms.  The vet must also distinguish between irregular heart and lung sounds, by listening to the timing of the sounds and correlating them to either the heartbeat or respiration.

The underlying cause can also be identified by factors such as radiation and location of the heart murmur in dogs as well as the timing during a heart cycle. The vet may accomplish this by carrying out a number of tests such as Doppler studies, chest X-rays, echocardiography, etc. Anemic murmurs can be diagnosed and confirmed via the preferred method of a complete blood count.

Treatment of heart murmur in dogs

  • Most cases of heart murmur in dogs are treated as any regular, non-urgent conditions that affect dogs. In case, the vet detects a risk to heart failure, then emergency care may be required.
  • The signs and symptoms that accompany heart murmur in dogs determine the method of treatment. For example, puppies that are affected by low grade heart murmurs need little or no medical attention, as such cases usually resolve themselves with a period of 6 months.  The life expectancy of dogs with loud heart murmurs and no medication cannot be more than 3 years.
  • Dogs affected by heart murmurs are recommended to get checkups and diagnostic imaging done on a regular basis.
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