The fourth heart sound or S₄ is an extra

heart sound Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stet ...

that occurs during late diastole, immediately before the normal two "lub-dub" heart sounds (S₁ and S₂). It occurs just after atrial contraction and immediately before the

systolic Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun ...

S₁ and is caused by the atria contracting forcefully in an effort to overcome an abnormally stiff or hypertrophic ventricle. This produces a rhythm classically compared to the cadence of the word "

Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...

." One can also use the phrase "A-stiff-wall" to help with the cadence (a S₄, stiff S₁, wall S₂), as well as the pathology of the S₄ sound.

Physiology

The normal heart sounds, S₁ and S₂, are produced during the closing of the

atrioventricular valves A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart v ...

and

semilunar valves A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart v ...

, respectively. The closing of these valves produces a brief period of turbulent flow, which produces sound. The S₄ sound occurs, by definition, immediately before S₁, while the atria of the heart are vigorously contracting. It is manifest as a vibration of 20 to 30 Hz within the ventricle. While the mechanism is not absolutely certain, it is generally accepted that S₄ is caused by stiffening of the walls of the ventricles (usually the left), which produces abnormally turbulent flow as the atria contract to force blood into the ventricle. S₄ is sometimes audible in the elderly due to a more rigid ventricle. When loud, it is a sign of a pathologic state, 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 the left-hand side, or with the patient holding

expiration Expiration or expiration date may refer to: Expiration Expiration may refer to: *Death *Exhalation of breath, breathing out *Expiration (options), the legal termination of an option to take an action *Shelf life, or the time after which a product ...

. If the problem is in the right ventricle, the abnormal sound will be most evident on the lower left hand side of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

and will get louder with exercise and quick, deep

inspiration Inspiration, inspire, or inspired often refers to: * Artistic inspiration, sudden creativity in artistic production * Biblical inspiration, the doctrine in Judeo-Christian theology concerned with the divine origin of the Bible * Creative inspirat ...

. 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 A gallop rhythm refers to a (usually abnormal) rhythm of the heart on auscultation. It includes three or four sounds, thus resembling the sounds of a Horse gait#Gallop, gallop. The normal heart rhythm contains two audible heart sounds called S1 ...

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 Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

is also very fast (

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...

), it can become difficult to distinguish between S₃ and S₄ thus producing a single sound called a summation gallop.

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.

References

External links

* {{DEFAULTSORT:Fourth Heart Sound Cardiology