Which of the following is true about fourth heart sound `S4′
**Core Concept**
The fourth heart sound (S4) is a low-frequency heart sound that occurs during late diastole, just before the first heart sound (S1). It is associated with atrial contraction and is often heard in conditions where there is increased stiffness of the ventricles.
**Why the Correct Answer is Right**
The S4 sound is caused by the atria contracting against a stiff or non-compliant ventricle. This can be seen in conditions such as left ventricular hypertrophy, coronary artery disease, or cardiomyopathies. The S4 sound is thought to be mediated by the atrioventricular (AV) valves, particularly the mitral valve, which is subjected to increased pressure and tension during atrial contraction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the S4 sound is not related to the tricuspid valve, but rather the mitral valve.
* **Option B:** This option is incorrect because the S4 sound is not a normal finding in children, but rather a pathological finding that occurs in adults with certain cardiac conditions.
* **Option C:** This option is incorrect because the S4 sound is not related to the aortic valve, but rather the AV valves.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the S4 sound is often associated with conditions that lead to increased stiffness of the ventricles, such as hypertension or coronary artery disease. This can be remembered using the mnemonic "S4 = Stiff ventricles".
**Correct Answer:** C.