Heart sounds are understood to be produced by the closure of heart valves. Abnormal heart sounds can arise from a variety of causes while murmurs arise from turbulent blood flow. Good examination technique is crucial in diagnosing abnormal heart sounds and murmurs.

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Cardiology – Abnormal Heart Sounds and Murmurs: What you need to know
Whiteboard Animation Transcript
with Michael Froeschl, MD
https://medskl.com/module/index/abnor...


Abnormal heart sounds and murmurs often reflect important underlying structural heart disease, a term that refers to problems with either the heart valves or the heart muscle (or sometimes both).

But before we tackle abnormal heart sounds and murmurs, we should first review briefly the normal heart sounds. Recall that it is closure of heart valves that produces the normal heart sounds: mitral and tricuspid valve closure produces the first heart sound (“S1”), and aortic and pulmonic valve closure produces the second heart sound (“S2”). Heart valve opening does not normally produce a sound. Also, flow of blood from one cardiac structure to another is usually laminar and therefore silent under normal conditions.

Abnormal heart sounds can result from any of three general mechanisms.

1. First, a normally silent event in the heart becomes audible. For example, opening of an abnormal valve may be heard as an “ejection sound” (as in bicuspid aortic valve) or an “opening snap” (as in mitral stenosis). Two other common examples of this first mechanism for abnormal heart sounds occur when ventricular filling becomes abnormal. A third heart sound (“S3”) in early diastole results from the impact of inflowing blood against a distended ventricle. And a fourth heart sound (“S4”) results from atrial contraction forcing blood into a stiff ventricle in late diastole.

2. A second mechanism accounting for abnormal heart sounds is when a new abnormal event happens in the heart. The “systolic click” that results from a floppy mitral valve prolapsing backward into the left atrium during systole is a good example.

3. A third mechanism causing an abnormal heart sound is incorrect timing of otherwise normal cardiac events, for example, abnormal splitting of the second heart sound as seen in an ASD.

Murmurs are caused by turbulent blood flow between cardiac chambers. Murmurs can result from one of three mechanisms (or any combination thereof).

1. First, increased flow through a normal conduit, for example increased stroke volume across the aortic or pulmonic valves in a pregnant woman.

2. Second, murmurs can result from normal flow through an abnormal conduit, for example in aortic sclerosis or aortic stenosis.

3. Third, murmurs are produced when there is abnormal flow between two structures, as in mitral regurgitation or a ventricular septal defect.