When to Worry About Murmurs

Jul 7, 2020 / Practitioner Updates

Drs. Kadotani and Fries Exam a dog

The hospital’s cardiology service is comprised of three board-certified cardiologists: Dr. Saki Kadotani (seated above), Dr. Ryan Fries (standing), and Dr. Jordan Vitt (not shown). Current cardiology residents are Drs. Gabrielle Wallace, Leah Kruckman, and Lindsey Humphries. Our full-time technicians are Katie McConnell and Candice Simpson.

 

A heart murmur is caused by turbu­lent blood flow within the heart. The flow disturbances are most often related to valvular incompetence, valvular stenosis, or the presence of a shunt. However, a heart murmur can also be created by other physiologic or pathological processes.

The first step in determining the significance of a heart murmur is to ascertain whether the murmur is functional or pathologic. To do this, the murmur needs to be evaluated within the context of the patient being examined.

The causes of physiologic murmurs include:

  • Innocent flow murmur
  • Decreased blood viscosity (moderate to severe anemia)
  • Fever
  • Hypertension
  • Pregnancy
  • Hyperthyroidism
  • High sympathetic tone
  • Hypoproteinemia

The Seven S’s of Innocent Murmurs

  • Systolic – Occurs only during systole
  • Sweet – Not harsh in sound
  • Soft – Grade II or less
  • Small – Murmur is focal and limited to one area
  • Single – No other associated abnormalities
  • Short – Does not take up all of systole
  • Sensitive – Changes with respiration or heart rate

Summary of Common Congenital Heart Disease

Congenital Abnormality Murmur Timing Murmur PMI Femoral Pulses Signalment Sequelae
PDAContinuousLeft basilarHyperkineticFemale, small breed, any breedLeft sided CHF
Pulmonic stenosisSystolicLeft basilarNormalSmall to medium breedsRight sided CHF, arrhyth­mias, syncope, sudden death (uncommon)
Subaortic stenosisSystolicLeft basilarHypokineticLarger breeds; GSD, Golden, Newfie, Rottweiler, BoxerLeft sided CHF, arrhyth­mias, syncope, sudden death, endocarditis
VSDSystolicRight sidedNormalAnyLeft sided CHF if hemody­namically significant

Heart Murmurs in Puppies

It is not uncommon for young puppies, especially large breed dogs, to develop an innocent heart murmur. The murmur may first appear at 6 to 8 weeks of age, and usually goes away by age 4 to 5 months. This type of murmur is benign.

A heart murmur that does not fit the criteria of seven S’s (see box) should be considered pathologic. A heart murmur that is grade III or higher, continuous, still present at 6 months, heard best on the right, or getting worse should be evaluated. Generally, puppies and juvenile patients with non-physiologic murmurs should undergo echocardiographic evaluation.

The timing and location of some cardiac murmurs is notably characteristic of certain lesions. Murmurs of pulmonic and subaortic stenosis will be systolic and best heard at the heart base, whereas patent ductus arteriosus will be continuous. Right-sided heart murmurs can be caused by ventricular septal defect or tricuspid valve dysplasia.

Heart Murmurs in Adult Dogs

Generally, all murmurs in adult dogs are indicative of structural heart disease. The cause of a murmur can often be determined or strongly suspected based on auscultation and the signalment of the patient.

Left apical systolic heart murmurs: Left apical systolic heart murmurs indicate mitral regurgitation. The most common cause of mitral regurgitation is myxomatous mitral valve disease (MMVD). MMVD should be suspected in middle-aged or older dogs, generally weighing <20 kg. Although there is not an exact correlation, the louder the heart murmur in a dog with suspected MMVD, the more persuasive to be with diagnostics.

If a left apical systolic heart murmur is heard in large or giant breed dogs, both MMVD and dilated cardiomyopathy (DCM) should be considered. Murmurs caused by DCM are generally soft. Mitral regurgitation in this case is caused by valvular annular dilation.

Right apical systolic heart murmurs: Right apical systolic heart murmurs indicate tricuspid regurgitation. The most common cause of tricuspid regurgitation is chronic valvular disease. Approximately 30% of dogs with MMVD will also have tricuspid valve involvement. Another cause of tricuspid regurgitation is pulmonary hypertension.

Diastolic murmurs: Diastolic murmurs are rare in dogs. The most common condition associated with diastolic murmurs is aortic insufficiency secondary to aortic endocarditis. All diastolic or to-and-fro murmurs should be evaluated.

Heart Murmurs in Kittens

Kittens can also have innocent flow heart murmurs. It is important not to squeeze the chest too hard which might create a murmur. As with puppies, a heart murmur that is grade III or higher, continuous, still present at 6 months, heard best on the right, or that it is getting worse should be evaluated.

Heart Murmurs in Adult Cats

A new onset of heart murmur in adult cats should be evaluated. Left sided systolic heart murmur is the most common. Hypertrophic cardiomyopathy (HCM) is the most likely cause; other possibilities include other cardiomyopathy and a physiologic heart murmur caused by dynamic right ventricular outflow tract obstruction (DRVOTO).

When to Evaluate

Should all heart murmurs undergo comprehensive evaluation? Not necessarily. It requires consideration of the animal’s use. In some cases, sufficient information can be obtained from the physical examination to educate clients and provide guidance without further evaluation.

On the other hand, breeding animals should be screened more aggressively for diseases that could be passed on. Animals that need to go under general anesthesia, such as for a dental procedure, may require further evaluation.

Lastly, the ability, cost, and utility of available diagnostic tests as well as the client’s desire to know what the underlying cause may play a role.

Patient

Differentials

Recommended Diagnostics

Puppy/kitten with a soft systolic murmur
  • Innocent flow murmur
  • Congenital heart disease
    • Subaortic stenosis
    • Pulmonic stenosis
    • Ventricular septal defect
    • Tricuspid valve dysplasia
    • Mitral valve dysplasia (kitten)
  • Monitor with serial auscultation
  • If the murmur gets louder or is still present at 5-6 months of age, an echocardiogram is recommended
  • If the murmur goes away, no further evaluation needed
  • +/- Bloodwork
Puppy/kitten with a loud systolic or continuous murmur
  • A loud murmur is more worrisome for congenital heart disease (see above for common congenital heart disease)
  • Echocardiogram is recommended
  • For suspected PDA, thoracic radiographs are also recommended
Young to mid-adult dog with new onset murmur
  • Either acquired or previously undetected congenital heart disease
  • If large breed dog or at-risk breed, concerning for DCM
  • Certain breeds may get “flow” murmurs from elevated transaortic velocity
  • CKCS and Dachshunds can get early onset of MMVD
  • Echocardiogram
  • +/- thoracic radiographs
  • +/- bloodwork to rule out systemic conditions
Young to mid adult cat with new onset murmur
  • HCM is the most likely cause
  • Other possibilities include DRVOTO, mitral regurgitation, other cardiomyopathy
  • Echocardiogram
  • +/- NT pro-BNP
  • Bloodwork
Older small breed dog with left sided systolic murmur
  • MMVD most likely
  • Thoracic radiographs
  • Blood pressure
  • +/- Echocardiogram
Older large breed with left sided systolic murmur
  • Could be either MMVD or DCM
  • DCM murmurs are generally softer
  • Echocardiogram
  • Thoracic radiographs
  • Blood pressure
  • +/- NT pro-BNP
Older cat with new left sided systolic murmur
  • HCM
  • Hyperthyroidism
  • Systemic hypertension
  • Other cardiomyopathy
  • DRVOTO
  • Blood pressure
  • Bloodwork including T4
  • NT pro-BNP
  • Echocardiogram

If you have questions about heart murmurs or any heart related questions, please do not hesitate to contact the cardiology service at the Veterinary Teaching Hospital for more information.

217-300-1643
vthcariology@vetmed.illinois.edu

By Saki Kadotani, DVM, DACVIM (Cardiology)