Machinery heart murmur

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