Diagram of the heart.

The fourth heart sound or S₄ is a rare extra heart sound that occurs immediately before the normal two "lub-dub" heart sounds (S₁ and S₂). It occurs just after atrial contraction and immediately before the systolic S₁. This produces a rhythm classically compared to the cadence of the word "Tennessee" with the first syllable ("Ten-") representing S₄.

[edit] Physiology

S₄ is sometimes audible in the elderly due to a more rigid ventricle. When loud, it is a sign of a pathologic state,^[1] usually a failing left ventricle. If the problem lies with the left ventricle, the gallop rhythm will be heard best at the cardiac apex. It will become more apparent with exercise, with the patient lying on their left-hand side, or with the patient holding expiration. If the culprit is the right ventricle, the abnormal rhythm will be most evident on the lower left hand side of the sternum and will get louder with exercise and quick, deep inspiration ^[2].

S₄ has also been termed an atrial gallop or a presystolic gallop because of its occurrence late in the heart cycle. It is a type of gallop rhythm by virtue of having an extra sound; the other gallop rhythm is called S₃. The two are quite different, but they may sometimes occur together forming a quadruple gallop. If the heart rate is also very fast (tachycardia), it can become difficult to distinguish between S₃ and S₄ thus producing a single sound called a summation gallop.

[edit] Causes

S₄ is caused by the atria contracting forcefully in an effort to overcome an abnormally stiff or hypertrophic ventricle. This causes abnormal turbulence in the flow of blood that can be detected by a stethoscope.

[edit] Associations

The S₄ heart sound is associated with any process that increases the stiffness of the ventricle,^[3] including:

• hypertrophy of the ventricle
• long-standing hypertension (causes ventricular hypertrophy)
• aortic stenosis^[4] (causes ventricular hypertrophy)
• overloading of the ventricle (causes ventricular hypertrophy)
• fibrosis of the ventricle (eg. post-MI)
• Congestive Heart Failure

[edit] Treatment

The S4 heart sound itself does not require treatment; rather plans should be laid to stop the progression of whatever causes the underlying ventricular dysfunction. The S4 heart sound is a secondary manifestation of a primary disease process and treatment should be focused on treating the underlying, primary disease.

[edit] References

[edit] External links

• KUO PT, SCHNABEL TG, BLAKEMORE WS, WHEREAT AF (1957). "Diastolic gallop sounds, the mechanism of production". J. Clin. Invest. 36 (7): 1035–42. doi:10.1172/JCI103499. PMID 13449156. http://www.pubmedcentral.gov/articlerender.fcgi?artid=1072690.