machinery heart murmur

Last reviewed 01/2018

These occur when there is a communication in the circulation with a continuous pressure gradient throughout the cardiac cycle. Continuous murmurs are often maximal in late systole. This fact helps to discriminate a continuous murmur from an ejection murmur accompanied by an early diastolic murmur. Possible causes of a continuous murmur include:

  • aorta to pulmonary artery communication such as patent ductus arteriosus - maximal below the left clavicle

  • systemic arteriovenous communication: - congenital e.g. aortic sinus of Valsalva aneurysm rupturing into the right heart - acquired as the result of trauma e.g. knife wound

  • pulmonary arteriovenous communications

  • bronchial artery anastomosis in pulmonary atresia

  • artificial ducts (Waterson or Blalock shunt)

  • prosthetic valve

  • venous hum