Changing murmurs in infective endocarditis

Heart murmurs are invariably present in infective endocarditis and changing murmurs are characteristic. The valve lesion is always destructive producing progressive incompetence. Two events are common:

• acute aortic incompetence caused by fenestration or inversion of an aortic valve cusp - produces a fall in cardiac output and a shock-like state. Tachycardia occurs with a small pulse volume. The first heart sound is lost owing to premature closure of the mitral valve caused by the very high end-diastolic pressure in the left ventricle. A third heart sound or a mitral diastolic murmur is common because of the brief time available for ventricular filling through the mitral valve.
  
  
• acute mitral incompetence caused by rupture of damaged chordae tendinae - produces a systolic murmur which peaks in mid-systole and is best heard at the base of the heart. The patient usually remains in sinus rhythm with little left atrial enlargement.