Article by Dr. Thomas Burnell and Dr. Bethany Turner
Next Lesson - Special Circulations
Core
In valve stenosis, there is narrowing of the affected valve. This causes a decreased flow of blood through the valve which results in blood backing up behind the valve, on the side it came from.
In valve regurgitation, the valve cannot properly close. This causes some backflow of blood through the valve in the reverse direction when, or after, the heart contracts.
Valve stenosis and regurgitation have different effects depending on which valve they affect. The different pathologies will also have differing sounds and patterns on auscultation.
When auscultating a heart murmur, the sound produced is caused by turbulent blood flow (swirling, uneven flow) generated by the pathology affecting the heart valve.
Mitral valve stenosis is narrowing of the mitral valve. This most commonly occurs due to rheumatic fever (an inflammatory illness that can follow a bacterial throat infection and damage the heart valves), which causes commissural fusion (the edges, or commissures, of the valve leaflets stick together). The leaflets are the flaps of the valve. In high-income countries, where rheumatic fever has become less common, degenerative calcification of the mitral valve (gradual calcium build-up with age) is an increasingly common cause, especially in older adults.
The effects of this are:
- Backing up of blood into the pulmonary circulation causes damage and fibrosis of the blood vessels (the vasculature) which leads to increased resistance to blood flow.
- The increased resistance to flow results in pulmonary hypertension (raised blood pressure in the blood vessels of the lungs).
- The higher pressures within the pulmonary circulation force fluid out of the capillaries causing pulmonary oedema.
- Left atrial dilatation (stretching and widening of the left atrium) occurs as the left atrium has to pump harder against the stenosed valve to move blood through it.
- Left atrial dilatation leads to fibrosis and remodelling of the atria to repair damaged tissue caused by stretching of the atria.
- Fibrosis interrupts electrical pathways leading to ectopic beats (extra heartbeats that start outside the heart's normal pacemaker) which can cause atrial fibrillation (an irregular, often fast, heart rhythm).
- Left atrial dilatation can rarely compress the oesophagus (the gullet), causing dysphagia (difficulty swallowing).
- Left atrial dilatation can also, rarely, compress the left recurrent laryngeal nerve (the nerve to the voice box), which runs close to the oesophagus. This can cause the patient to present with a hoarse voice (Ortner's syndrome).
Mitral valve stenosis is heard as a diastolic rumble murmur (a low-pitched rumbling sound heard while the ventricles fill) between the second heart sound (S2, the sound of the aortic and pulmonary valves closing) and the first heart sound (S1, the sound of the mitral and tricuspid valves closing).
Diagram: Mitral valve stenosis and how it affects blood flow through the valve
SimpleMed original by Dr. Bethany Turner
Aortic valve stenosis is narrowing of the aortic valve. There are several causes of this:
- Degeneration of the valve, e.g. due to calcification (calcium build-up) or fibrosis (scarring) with age
- Congenital bicuspid valve (a valve born with two cusps instead of three)
- Chronic rheumatic fever which causes commissural fusion of the valve leaflets
The effects of an aortic valve stenosis are:
- Left ventricular hypertrophy as the ventricle must pump harder to force the blood through the narrowed valve.
- This can lead to left sided heart failure.
- Haemolytic anaemia (anaemia caused by breakdown of red blood cells). It is uncommon in native aortic valve stenosis. The high shear forces (stretching and tearing forces) as blood is forced through the narrowed valve can damage red blood cells (RBCs). It is better recognised with prosthetic (replacement) valves.
Aortic valve stenosis is heard as a crescendo-decrescendo murmur (a murmur that gets louder, then quieter) between S1 and S2.
Diagram: How aortic stenosis affects blood flow
SimpleMed original by Dr. Bethany Turner
Mitral valve regurgitation is pathology affecting the mitral valve resulting in blood flowing backwards through it on ventricular contraction. There are several causes:
- Myxomatous degeneration: the valve tissue becomes floppy and weak, and the leaflets can prolapse (flop back) into the left atrium. It is often idiopathic (of unknown cause).
- Damage to the papillary muscle (one of the small muscles inside the left ventricle that tether the valve flaps) after a myocardial infarction (heart attack). Damage to the papillary muscle means it is less effective at anchoring the chordae tendineae (the thin cords that hold the valve flaps in place) and therefore less effective at preventing the valve from prolapsing. This allows blood to flow backwards through the prolapsed mitral valve. If the muscle ruptures, the result is sudden, severe regurgitation that can cause pulmonary oedema and cardiogenic shock (the heart cannot pump enough blood to the body), which is a medical emergency.
- Left sided heart failure which causes left ventricular dilatation (widening of the ventricle). This dilatation causes stretching of the valve so it no longer forms a tight seal, allowing blood to leak through.
- Rheumatic fever causes fibrosis of the valve which disrupts the seal of the valve, allowing blood to leak through.
Mitral valve regurgitation allows blood to leak back into the left atrium. This increases the preload of the ventricle (the stretch on the ventricle wall from the blood filling it before it contracts) as more blood enters the ventricle on diastole. The left ventricle hypertrophies to cope with the increased volume of blood which can lead to left sided heart failure.
Mitral valve regurgitation is heard as a holosystolic murmur (a murmur heard throughout the whole of systole) between S1 and S2.
Diagram: The flow of blood in mitral regurgitation
SimpleMed original by Dr. Bethany Turner
Aortic valve regurgitation is pathology affecting the aortic valve resulting in blood flowing backwards through it after ventricular contraction. There are several causes:
- Aortic root dilatation (widening of the first part of the aorta, where it leaves the heart) which causes the leaflets to be pulled apart so they no longer form a tight seal.
- Valve damage caused by endocarditis (infection of the inner lining of the heart and valves) or rheumatic fever.
- Connective tissue disorder, e.g. Marfan syndrome (an inherited condition affecting connective tissue).
The effects of aortic valve regurgitation are:
- Blood flows back into the left ventricle during diastole causing a reduced diastolic pressure. The systolic pressure is often increased due to the increased stroke volume.
- The decreased diastolic pressure increases the pulse pressure (the gap between the systolic and diastolic pressures), and this can be felt as a bounding pulse (a strong, forceful pulse that rises and falls quickly, also called a water-hammer or collapsing pulse).
- Blood flows back into the left ventricle which increases the stroke volume. The heart hypertrophies to cope with the increased stroke volume. This can result in left sided heart failure.
Aortic valve regurgitation is heard as a decrescendo early diastolic murmur (a murmur that starts loud just after the second heart sound and fades away) between S2 and S1.
Diagram: The flow of blood in aortic regurgitation
SimpleMed original by Dr. Bethany Turner
Heart murmurs are often caused by pathology affecting the heart valves, although some murmurs can occur in structurally normal hearts. In order to locate which valve is affected, you must auscultate each of the valves individually with a stethoscope.
The aortic valve can be auscultated on the right side in the 2nd intercostal space (the gap between the 2nd and 3rd ribs) on the sternal edge.
The pulmonary valve can be auscultated on the left side in the 2nd intercostal space on the sternal edge.
The tricuspid valve can be auscultated on the left side in the 4th intercostal space on the lower left sternal border.
The mitral valve can be auscultated on the left side in the 5th intercostal space, in the midclavicular line (an imaginary vertical line down from the middle of the collarbone).
Right sided heart murmurs are louder in inspiration as there is decreased pressure in the chest. This increases cardiac return (the blood returning to the heart) to the right atrium, so more blood arrives there. Increased volume of blood being pumped means the effect of stenosis or regurgitation is increased so can be heard louder.
Left sided heart murmurs are louder in expiration as there is increased pressure in the chest. In inspiration the left ventricle pumps less blood with each beat. The usual explanation is that blood pools in the lungs, so less returns to the left atrium, although the exact mechanism is still debated. In expiration this reverses, so more blood returns to the left atrium. The volume of blood being pumped from the left atrium is increased, so the stenosis or regurgitation can be heard louder.
This can be remembered using the mnemonic RILE: Right Inspiration, Left Expiration.
Edited by: Dr. Ben Appleby
Reviewed by: Dr. Marcus Judge
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