3. Fourth Heart Sound
Fourth heart sound (S4) occurs as a result of forceful atrial contraction ("atrial
kick"). It is a low-pitched sound heard in pre-systole (late diastole; before first
heart sound). It is absent in atrial fibrillation
S4 may be confused with spilt S1. Firm pressure by the diaphragm of
stethoscope eliminates S4 but not split S1.
S4 is always abnormal.
A fourth heart sound arising from the left side is known as "left-sided fourth
heart sound" and the one arising from right side as "right-sided fourth heart
sound".
Left-sided S4 is best heard during expiration with the patient in the left lateral
position.
Right-sided S4 is best heard during inspiration.
4. Causes of Fourth Heart Sound
Left-sided S4 Right-sided S4
• Systemic hypertension
• Hypertrophic cardiomyopathy
• ischemic heart disease
(especially acute myocardial
infarction)
• Acute mitral regurgitation
• Anemia, thyrotoxicosis and
AV fistulae
• Right ventricular hypertrophy
due to
• Pulmonary hypertension
• Pulmonary stenosis