Page 95 - Clinical Pearls in Cardiology

Auscultation of the Precordium 83

somewhat fainter and is heard at the tricuspid area. The
clinician should pay close attention to the intensity of S1.
Most clinically significant abnormalities of S1 are related
to its intensity or loudness rather than its split (i.e M1-T1
split). When compared to the second heart sound, the
first heart sound is longer in duration but it is lower in
pitch. The important factors that influence the intensity
of the first heart sound are the following:
• Duration of the PR interval: Short PR interval causes
loud S1, whereas long PR interval (e.g. first degree
heart block) produces soft S1.
• Atrioventricular pressure gradient: A large atrio-
ventricular pressure gradient (e.g. mitral stenosis)
produces loud S1.
• Rate of rise of ventricular pressure during systole: A
rapid rate of rise in ventricular pressure due to the
increased force of ventricular contraction (e.g. in
hyperdynamic circulatory states) produces loud S1.
A slow rate of rise in left ventricular pressure (e.g. left
ventricular dysfunction) produces soft S1.
• Mobility and thickening of the valve cusp: A mobile
and thickened valve cusp produces loud S1 (e.g. early
mitral stenosis with uncalcified valve cusps).
• Factors that decrease the conduction of the sound
like thick chest wall, pericardial effusion, emphysema
etc. are associated with soft S1.
Table 2: Difference between loud and soft S1
Loud SI Soft S1
Short PR interval Long PR interval
Large AV pressure gradient Small AV pressure gradient
Rapid rise in ventricular Slow rise in ventricular
pressure pressure
Contd...