Fourth (4th) heart sound

The fourth heart sound is due to atrial contraction inducing ventricular filling towards the end of diastole. They are never audible in normal subjects. A fourth heart sound is the result of powerful atrial contraction filling an abnormally stiff ventricle.

Left atrial heart sound is maximal at the apex, with possible causes including:

• left ventricular hypertrophy
• fibrotic left ventricle
• hypertrophic cardiomyopathy

Right atrial heart sound is maximal at the lower left sternal edge and on inspiration. This may occur in right ventricular hypertrophy.

Evidence base:

• in patients referred for non-emergency left sided heart catherisation, third and fourth heart sounds detected by phonocardiography (1)
  • neither the phonocardiographic S3 nor the S4 is a sensitive marker of left ventricular dysfunction
  • the phonocardiographic S3 is specific for left ventricular dysfunction and appears to be superior to the moderate specificity of the phonocardiographic S4
• thus the absence of a gallop rhythm should not be used to indicate the absence of left ventricular dysfunction and certainly cannot replace other diagnostic testing when screening for left ventricular dysfunction (2)

Reference:

1. Marcus GM et al. Association between phonocardiographic third and fourth heart sounds and objective measures of left ventricular dysfunction. JAMA 2005; 293:2238-44.
2. Commentary. Evidence-Based Medicine 2005;10:182.