From the Guidelines
The fourth heart sound (S4) is an abnormal heart sound that occurs just before the first heart sound (S1) during late diastole, when the atria contract, and is often associated with conditions such as hypertension, aortic stenosis, hypertrophic cardiomyopathy, coronary artery disease, and advanced age. This sound is caused by vibrations from blood being forced into a stiff or non-compliant left ventricle during atrial contraction, indicating that the ventricle is resistant to filling and requiring an unusually forceful atrial contraction to complete ventricular filling 1.
Clinical Significance of S4
The presence of an S4 should prompt further cardiac evaluation, as it often indicates increased left ventricular pressure or decreased ventricular compliance. While not always pathological in elderly patients, an S4 in younger individuals typically suggests underlying cardiac pathology that requires investigation. According to the 2020 AHA/ACC guideline for the diagnosis and treatment of patients with hypertrophic cardiomyopathy, a fourth heart sound (S4) is a common physical finding in patients with HCM, along with a systolic murmur, prominent apical point of maximal impulse, and abnormal carotid pulse 1.
Key Points to Consider
- S4 is a low-pitched "lub-dub-dub" sound that can be heard best with the bell of the stethoscope at the apex of the heart while the patient lies in the left lateral position.
- Conditions associated with S4 include hypertension, aortic stenosis, hypertrophic cardiomyopathy, coronary artery disease, and advanced age.
- The presence of an S4 should prompt further cardiac evaluation to investigate underlying cardiac pathology.
- In patients with HCM, S4 is often accompanied by other physical findings such as a systolic murmur, prominent apical point of maximal impulse, and abnormal carotid pulse 1.
From the Research
Definition of Cardiac Sound S4
- The fourth heart sound (S4) is a cardiac sound that is associated with a stiff left ventricle 2.
- It is generated from an abnormally stiff left ventricle, supporting the concept that the S4 is a pathologic finding in older patients 2.
Association with Diastolic Dysfunction
- The presence and intensity of S4 is associated with diastolic stiffness, as measured by the end-diastolic pressure volume relationship (EDPVR) 2.
- However, another study found that S4 is neither sensitive nor specific for discriminating normal from abnormal diastolic function, and may be absent in severe diastolic dysfunction 3.
- The correlation between S4 and diastolic dysfunction is not straightforward, as S4 can be present in individuals with normal diastolic function and absent in those with severe diastolic dysfunction 3.