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Basics ⬇

Basics

Definition

Vibrations caused by disturbed blood flow

Timing of Murmurs

  • Systolic murmurs occur between S1 and S2 (systole).
  • Diastolic murmurs occur between S2 and S1 (diastole).
  • Continuous and to-and-fro murmurs occur throughout all or most of the cardiac cycle.
  • Continuous murmurs are usually accentuated near S2 and to-and-fro murmurs are usually absent near S2.

Grading Scale for Murmurs

  • Grade I-barely audible.
  • Grade II-soft, but easily auscultated. Doesn't radiate far from point of maximal intensity.
  • Grade III-intermediate loudness; heard easily some distance from PMI, but not to opposite side of chest; most hemodynamically important murmurs are at least grade III.
  • Grade IV-loud murmur radiating widely, often including opposite side of chest.
  • Grade V-very loud, audible with stethoscope barely touching the chest; palpable thrill.
  • Grade VI-very loud, audible without the stethoscope touching the chest; palpable thrill.

Configuration

  • Plateau murmurs have uniform loudness and are typical of regurgitant murmurs such as mitral and tricuspid insufficiency and ventricular septal defect.
  • Crescendo-decrescendo murmurs get louder and then softer and are typical of ejection murmurs such as pulmonic and aortic stenosis and atrial septal defect.
  • Decrescendo murmurs start loud and then get softer and are typical of diastolic murmurs such as aortic or pulmonic insufficiency and mitral or tricuspid stenosis.

Location

Dogs

  • Mitral area-left fifth intercostal space at costochondral junction.
  • Aortic area-left fourth intercostal space above costochondral junction.
  • Pulmonic area-left second to fourth intercostal space at sternal border.
  • Tricuspid area-right third to fifth intercostal space near costochondral junction.

Cats

  • Mitral area-left fifth to sixth intercostal space one-fourth ventrodorsal distance from sternum.
  • Aortic area-left second to third intercostal space just above the pulmonic area.
  • Pulmonic area-left second to third intercostal space one-third to one-half ventrodorsal distance from sternum.
  • Tricuspid area-right fourth to fifth intercostal space one-fourth ventrodorsal distance from sternum.

Pathophysiology

  • Disturbed blood flow associated with high flow through normal or abnormal valves or with structures vibrating in the blood flow.
  • Flow disturbances associated with outflow obstruction or forward flow through stenosed valves or into a dilated great vessel.
  • Flow disturbances associated with regurgitant flow through an incompetent valve, septal defect, or patent ductus arteriosus.

Systems Affected

Cardiovascular

Signalment

Dog and cat

Signs

Relate to cause of the murmur

Causes

Systolic Murmurs

  • Mitral and tricuspid valve endocardiosis
  • Cardiomyopathy and AV valve insufficiency
  • Physiologic flow murmurs
  • Anemia
  • Mitral and tricuspid valve dysplasia
  • Systolic anterior mitral motion
  • Dynamic right ventricular outflow obstruction
  • Dynamic subaortic stenosis
  • Atrial septal defect
  • Ventricular septal defect
  • Pulmonic stenosis
  • Aortic stenosis
  • Tetralogy of Fallot
  • Mitral and tricuspid valve endocarditis
  • Hyperthyroidism
  • Heartworm disease

Continuous or To-and-Fro Murmurs

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

Diastolic Murmurs

  • Mitral and tricuspid valve stenosis
  • Aortic and pulmonic valve endocarditis

Risk Factors

Cardiac disease

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Differential Signs

  • Must differentiate from other abnormal heart sounds-split sounds, ejection sounds, gallop rhythms, and clicks.
  • Must differentiate from abnormal lung sounds and pleural rubs; listen to see if timing of abnormal sound is correlated with respiration or heartbeat.

Differential Causes

  • Pale mucous membranes support diagnosis of anemic murmur.
  • Location and radiation of murmur and timing during cardiac cycle can help determine cause; see algorithm.

CBC/Biochemistry/Urinalysis

  • Anemia in animals with anemic murmurs
  • Polycythemia in animals with right-to-left shunting congenital defects
  • Leukocytosis with left-shift in animals with endocarditis

Other Laboratory Tests

N/A

Imaging

  • Thoracic radiography-useful for evaluating heart size and pulmonary vasculature in hopes of determining cause and significance of murmur.
  • Echocardiography-recommended when a cardiac cause is suspected and the nature of the defect is unknown.
  • Doppler studies sometimes required to confirm cause of murmur.

Diagnostic Procedures

  • Electrocardiography may be useful in assessing heart enlargement patterns in animals with murmurs.
  • Blood cultures and serology for Bartonella if suspect endocarditis.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s)

N/A

Contraindications

N/A

Precautions

N/A

Possible Interactions

N/A

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

Low-grade systolic ejection murmurs in puppies may be physiologic; most resolve by 6 months of age. If murmur still present after 6 months, include diagnostic imaging.

Possible Complications

If murmur is associated with structural heart disease, may see signs of congestive heart failure (e.g., coughing, dyspnea, and ascites) or exercise intolerance.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

N/A

Age-Related Factors

  • Murmurs present since birth generally associated with a congenital defect or physiologic flow murmur.
  • Acquired murmurs in geriatric, small-breed dogs usually associated with degenerative valve disease.
  • Acquired murmurs in large-breed dogs usually associated with dilated cardiomyopathy.
  • Acquired murmurs in geriatric cats usually associated with cardiomyopathy or hyperthyroidism.

Zoonotic Potential

None

Pregnancy/Fertility/Breeding

Murmurs in puppies and kittens may reflect a congenital defect and thereby influence decisions on breeding that animal or repeating the mating.

See Also

See “Causes”

Abbreviations

  • AV = atrioventricular
  • PMI = point of maximal intensity
  • S1 = first heart sound
  • S2 = second heart sound
  • VSD = ventricular septal defect

Author Francis W.K. Smith, Jr.

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Suggested Reading

Gompf RE. The history and physical examination. In: Smith FWK, Tilley LP, Oyama MA, Sleeper MM, eds., Manual of Canine and Feline Cardiology, 5th ed. St. Louis, MO: Saunders Elsevier, 2015 (in press).

Keene B, Smith FWK, Tilley LP, Hansen B. Rapid Interpretation of Heart Sounds, Murmurs, Arrhythmias, and Lung Sounds: A Guide to Cardiac Auscultation in Dogs and Cats, 3rd ed. CD-ROM and Manual. Philadelphia: Elsevier, 2015.