Gallop rhythm

A gallop rhythm refers to a (usually abnormal) rhythm of the heart on auscultation. The normal heart rhythm contains two audible sounds, called S₁ and S₂, giving the well-known "lub-dub" rhythm. They are caused by the closing of valves in the heart. A gallop rhythm contains another sound, called S₃ or S₄, dependent upon where in the cycle this added sound comes; it can also contain both of these sounds.

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S₃

S₃ (or third heart sound) is the name of the vibration which occurs during early diastole, shortly after the second heart sound S₂, giving a rhythm much like the cadence in the word 'Kentucky'. It can be a normal finding in people under 40 years of age, but over this age is usually a sign of heart failure. It is usually low-pitched and difficult to hear, and is best heard with the bell of the stethoscope. An S₃ rhythm is also known as ventricular gallop.

Causes

It is caused by the sudden slowing of blood rushing in from the atrium into the ventricle as it is relaxing.

Associations

It is associated with heart failure, caused by conditions which have:

Rapid ventricular filling

• Mitral regurgitation - this is when one of the heart valves that usually stops blood going from the left ventricle to the left atria fails, allowing blood into the atria during systole. This means they will be overfilled when they come to contract, leading to the rapid ventricular filling.
• Elevated left atrial and left ventricular filling pressures, usually a result of a stiffened and dilated left ventricle
• Ventricular septal defect - this is a hole in the wall between the two ventricles, which allows rapid filling from the other ventricle.

Poor Left Ventricular Function

• Post-MI - the death of tissue in the ventricular wall due to loss of blood supply causes areas which do not move as well, if at all (hypokinetic and akinetic), meaning they do not relax quickly enough so the ventricular filling is relatively too quick.
• Dilated cardiomyopathy - the ventricular walls are abnormal for a variety of reasons, and become thin and stiff so do not relax well.

In conditions affecting the pericardium or diseases that primarily affect the heart muscle (restrictive cardiomyopathies) a similar sound can be heard, but is usually more high-pitched and is called a 'pericardial knock'.

The S3 can also be confused with a widely split S2, or a mitral opening snap, but these sounds are typically of much higher pitch and occur closer to the onset of S2.

Treatment

The gallop rhythm itself does not need to be treated; the underlying cause requires correction; depending on the aetiology the gallop rhythm may resolve.

S₄

S₄ (or fourth heart sound) occurs just before S₁ (thus right at the end of one whole cycle), giving a cadence like the word 'Tennessee'. It is never normal. If the problem lies with the left ventricle, the gallop rhythm will be heard best at the cardiac apex (the point of the two ventricles). 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 ^[1]. .

Causes

It is caused by the atria contracting forcefully in an effort to overcome an abnormally-stiff ventricle.

Associations

The S₄ rhythm is associated with anything that increases the stiffness of the ventricle, including:

• long-standing hypertension
• aortic stenosis
• overloading of the ventricle
• fibrosis of the ventricle
• hypertrophy of the ventricle

Treatment

Again, the rhythm itself does not require treatment; rather plans should be laid to stop the progression of whatever cause of ventricular dysfunction there is.

Summation Gallop

If a fast heart rate (tachycardia) is present along and S₃ and S₄ both occur, the rate may become high enough so that the distinction between the two sounds is lost, and they summate into a single sound.

References

1. ^ Tavel ME. The appearance of gallop rhythm after exercise stress testing. 'Clin Cardiol'. 1996 Nov;19(11):887-91