Which statement accurately represents a characteristic of the third or fourth heart sound?

Systolic sounds include the following:

• 1st heart sound (S1)

• Clicks

S1 and the 2nd heart sound (S2, a diastolic heart sound) are normal components of the cardiac cycle, the familiar “lub-dub” sounds.

Clicks occur only during systole; they are distinguished from S1 and S2 by their higher pitch and briefer duration. Some clicks occur at different times during systole as hemodynamics change. Clicks may be single or multiple.

Clicks due to myxomatous degeneration of valves may occur any time during systole but move toward S1 during maneuvers that transiently decrease ventricular filling volume (eg, standing, Valsalva maneuver). If ventricular filling volume is increased (eg, by lying supine), clicks move toward S2, particularly in mitral valve prolapse. For unknown reasons, characteristics of the clicks may vary greatly between examinations, and clicks may come and go.

Diastolic sounds include the following:

• 2nd, 3rd, and 4th heart sounds (S2, S3, and S4)

• Diastolic knocks

• Mitral valve sounds

Unlike systolic sounds, diastolic sounds are low-pitched; they are softer in intensity and longer in duration. Except for S2, these sounds are usually abnormal in adults, although an S3 may be physiologic up to age 40 and during pregnancy.

S3 occurs in early diastole, when the ventricle is dilated and noncompliant. It occurs during passive diastolic ventricular filling and usually indicates serious ventricular dysfunction in adults; in children, it can be normal, sometimes persisting even to age 40. S3 also may be normal during pregnancy. Right ventricular S3 is heard best (sometimes only) during inspiration (because negative intrathoracic pressure augments right ventricular filling volume) with the patient supine. Left ventricular S3 is best heard during expiration (because the heart is nearer the chest wall) with the patient in the left lateral decubitus position.

S3, with or without S4, is usual in significant systolic left ventricular dysfunction; S4 without S3 is usual in diastolic left ventricular dysfunction.

A summation gallop occurs when S3 and S4 are present in a patient with tachycardia, which shortens diastole so that the 2 sounds merge. Loud S3 and S4 may be palpable at the apex when the patient is in the left lateral decubitus position.

A diastolic knock occurs at the same time as S3, in early diastole. It is not accompanied by S4 and is a louder, thudding sound, which indicates abrupt arrest of ventricular filling by a noncompliant, constricting pericardium.

An opening snap (OS) may occur in early diastole in mitral stenosis Mitral Stenosis Mitral stenosis is narrowing of the mitral orifice that impedes blood flow from the left atrium to the left ventricle. The usual cause is rheumatic fever. Common complications are pulmonary... read more or, rarely, in tricuspid stenosis Tricuspid Stenosis Tricuspid stenosis (TS) is narrowing of the tricuspid orifice that obstructs blood flow from the right atrium to the right ventricle. Almost all cases result from rheumatic fever. Symptoms include... read more . Mitral opening snap is very high pitched, brief, and heard best with the diaphragm of the stethoscope. The more severe mitral stenosis is (ie, the higher the left atrial pressure), the closer the opening snap is to the pulmonic component of S2. Intensity is related to the compliance of the valve leaflets: The snap sounds loud when leaflets remain elastic, but it gradually softens and ultimately disappears as sclerosis, fibrosis, and calcification of the valve develop. Mitral opening snap, although sometimes heard at the apex, is often heard best or only at the lower left sternal border.

Systolic murmurs may be normal or abnormal. They may be early, mid, or late systolic, or holosystolic (pansystolic). Systolic murmurs may be divided into ejection, regurgitant, and shunt murmurs.

Systolic ejection murmurs may occur without hemodynamically significant outflow tract obstruction and thus do not necessarily indicate a disorder. In normal infants and children, flow is often mildly turbulent, producing soft ejection murmurs. Older patients often have ejection murmurs due to valve and vessel sclerosis.

During pregnancy, many women have soft ejection murmurs at the 2nd intercostal space to the left or right of the sternum. The murmurs occur because a physiologic increase in blood volume and cardiac output increases flow velocity through normal structures. The murmurs may be greatly exaggerated if severe anemia complicates the pregnancy. These murmurs are distinct from the venous hum sometimes caused by engorged breast vessels during pregnancy (mammary souffle).

A mitral or tricuspid murmur due to an atrial tumor or thrombus may be evanescent and may vary with position and from one examination to the next because the position of the intracardiac mass changes.

Pearls & Pitfalls

• Systolic murmurs may be normal or abnormal but diastolic murmurs are always abnormal.

Continuous murmurs occur throughout the cardiac cycle. They are always abnormal, indicating a constant shunt flow throughout systole and diastole. They may be due to various cardiac defects (see table Etiology of Murmurs by Timing Etiology of Murmurs by Timing

When circulation is increased, as occurs during pregnancy, anemia, and hyperthyroidism Hyperthyroidism Hyperthyroidism is characterized by hypermetabolism and elevated serum levels of free thyroid hormones. Symptoms include palpitations, fatigue, weight loss, heat intolerance, anxiety, and tremor... read more

A pericardial friction rub is caused by movement of inflammatory adhesions between visceral and parietal pericardial layers. It is a high-pitched or squeaking sound; it may be systolic, diastolic and systolic, or triphasic (when atrial contraction accentuates the diastolic component during late diastole). The rub sounds like pieces of leather squeaking as they are rubbed together. Rubs are best heard with the patient leaning forward or on hands and knees with breath held in expiration.