Which of the following cardiac conditions does a fourth heart sound (S4) indicate?
A. Dilated aorta.
B. Normally functioning heart.
C. Decreased myocardial contractility.
D. Failure of the ventricle to eject all of the blood during systole.
Correct Answer: D. Failure of the ventricle to eject all of the blood during systole.
An S4 occurs as a result of increased resistance to ventricular filling after atrial contraction. The increased resistance is related to decreased compliance of the ventricle. Commonly, its presence indicates increased resistance to filling of the left or right ventricle because of a reduction in ventricular wall compliance, and it is accompanied by a disproportionate rise in ventricular end-diastolic pressure.
Option A: A dilated aorta doesn’t cause an extra heart sound, though it does cause a murmur. Aortic regurgitation, also known as aortic insufficiency, is a decrescendo blowing diastolic murmur heard best at the left lower sternal border, heard when blood flows retrograde into the left ventricle. This is most commonly seen in aortic root dilation and as sequelae of aortic stenosis.
Option B: An S4 isn’t heard in a normally functioning heart. Heart sounds are created from blood flowing through the heart chambers as the cardiac valves open and close during the cardiac cycle. Vibrations of these structures from the blood flow create audible sounds — the more turbulent the blood flow, the more vibrations that get created.
Option C: Decreased myocardial contractility is heard as a third heart sound. The third heart sound (S3) is a low-frequency, brief vibration occurring in early diastole at the end of the rapid diastolic filling period of the right or left ventricle. Recent studies have shown that the third heart sound is loudest external to the left ventricular cavity, implying that the sound is not radiating from an intracardiac source.
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