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

Systole (medicine)

Systole is the contraction of the heart. Used alone, it usually means the contraction of the left ventricle.In all mammals, the heart has 4 chambers. The left and right ventricles pump together. The atria and ventricles pump in sequence...

 S₁. It is best conceptualized as hearing a "split S1." This produces a rhythm classically compared to the cadence of the word "Tennessee

Tennessee

Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...

" with the first syllable ("Ten-") representing S₄.

Physiology

The normal heart sounds, S₁ and S₂, are produced by closing of the atrioventricular valves and semilunar valves 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 their left-hand side, or with the patient holding expiration

Exhalation

Exhalation is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing....

. 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

Inhalation

Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....

.

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

Gallop rhythm

A gallop rhythm refers to a rhythm of the heart on auscultation. It includes three or four sounds, thus resembling the sounds of a gallop....

 by virtue of having an extra sound; the other gallop rhythm is called S₃

Third heart sound

The third heart sound or S3 is a rare extra heart sound that occurs soon after the normal two "lub-dub" heart sounds .-Physiology:It occurs at the beginning of diastole approximately 0.12 to 0.18 seconds after S2...

. The two are quite different, but they may sometimes occur together forming a quadruple gallop. If the heart rate

Heart rate

Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

 is also very fast (tachycardia

Tachycardia

Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

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

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

Stethoscope

The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

.

Associations

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

• hypertrophy of the ventricle
• long-standing hypertension
  Hypertension
  Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
  
   (causes ventricular hypertrophy)
• aortic stenosis (causes ventricular hypertrophy)
• overloading of the ventricle (causes ventricular hypertrophy)
• fibrosis
  Fibrosis
  Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
  
   of the ventricle (eg. post-MI
  Myocardial infarction
  Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
  
  )
• Congestive Heart Failure

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.