Heart Murmurs: Focus on the Mitral Valve

Heart Murmurs: Focus on the Mitral Valve

# Origin of Heart Murmurs

A heart murmur occurs when blood flows abnormally through the heart valves, producing characteristic sounds. Factors that increase blood turbulence will create a murmur, including:

• High blood velocity through a vessel with a constant diameter.

• Blood flow through a narrowed opening or from a narrow opening to a wider opening, or vice versa.

• Communication between two blood vessels or two chambers of the heart.

• Reduced blood viscosity.

# Classification of Murmurs

By Nature:

• Ejection murmur: caused by the ejection of blood through a narrowed opening.

• Regurgitant murmur: caused by the backflow of blood against the direction of flow through a narrowed opening.

By Timing:

• Systolic murmur: occurs during the contraction phase of the heart.

• Diastolic murmur: occurs during the relaxation phase of the heart.

• Continuous murmur: lasts throughout the cardiac cycle.

By Clinical Significance:

• Functional (innocent) murmur: does not reflect structural damage to the heart valve, chordae tendineae, or papillary muscles; it is only due to changes in the ventricular wall that secondarily alter the valve rings or increase blood volume.

• Organic murmur: reflects structural damage to the heart valve, chordae tendineae, papillary muscles, or the presence of an abnormal opening.

# Describing a Heart Murmur

When listening to a heart murmur, the following information should be noted:

1. Location: the location on the chest where the murmur is loudest.

2. Timing: whether the murmur occurs during systole, diastole, or continuously.

3. Pitch: whether the murmur is high or low pitched.

4. Quality: whether the murmur is soft or harsh. (Note: a low pitch and harsh quality may indicate a diastolic rumble in mitral stenosis).

5. Intensity: from 1/6 to 6/6 (see details below).

6. Effect of respiration: how the murmur changes when the patient inhales and exhales.

7. Radiation: to which locations the murmur radiates.

8. Significance: functional or organic.

Assessing Murmur Intensity:

• 1/6: very faint, heard only in a quiet room, using a good stethoscope.

• 2/6: audible but faint, not radiating.

• 3/6: readily audible with the stethoscope in place, radiating, no thrill.

• 4/6: loud, with clear radiation, thrill present.

• 5/6: as loud as 4/6, audible with the stethoscope slightly off the chest or with the hand on the auscultation point and the stethoscope on the hand.

• 6/6: as loud as 5/6, audible even when the stethoscope is lifted from the chest or with the hand on the auscultation point and listening at the wrist.

# Systolic Murmur at the Mitral Valve Area

Characteristics of a systolic ejection murmur:

• Auscultation: starts immediately after S1 (first heart sound) and ends before S2 (second heart sound).

• Shape on a phonocardiogram: a diamond shape, where the murmur starts after S1, increases in intensity to a peak, and then decreases before S2.

Explanation of the Diamond Shape:

• Significance: The murmur starts after S1 because the pressure in the left ventricle exceeds the pressure in the aorta, opening the aortic valve. The increasing left ventricular pressure, combined with the resistance of the blood that was “held back” in the aorta during diastole, results in a delayed increase in blood velocity. This delayed increase is why the ejection murmur begins weakly and then gets louder. As the left ventricular pressure decreases, the velocity of the blood flow decreases, causing the murmur to decrease in intensity. When the aortic valve is about to close, the velocity of the blood flow is not sufficient to produce a murmur, so the murmur ends before S2.

Characteristics of a systolic regurgitant murmur:

• Auscultation: starts simultaneously with S1, remains constant in intensity, and ends simultaneously with S2.

• Shape on a phonocardiogram: a rectangular shape.

• Found in mitral regurgitation and ventricular septal defect.

When a systolic murmur is heard at the mitral valve area, consider:

• Mitral regurgitation:

• Location: loudest at the apex.

• Timing: throughout systole.

• Pitch and Quality: harsh, soft if left ventricular failure is present.

• Intensity: variable, not correlated with the degree of regurgitation.

• Change with respiration: not clear.

• Radiation: radiates to the axilla, possibly to the back, and does not change with posture.

• Other heart sounds:

• Third heart sound (S3): a gallop sound.

• Loud, split S2: a sign of pulmonary hypertension.

Mitral valve prolapse:

• One or both valve leaflets prolapse into the left atrium during systole.

• Auscultation:

• Mid-systolic click (sharp, brief).

• Immediately after the click, a systolic murmur.

Differentiating the murmurs of mitral valve prolapse and mitral regurgitation:

• Mid-systolic click: present only in mitral valve prolapse, absent in mitral regurgitation.

• The systolic murmur in mitral valve prolapse: occurs later than in mitral regurgitation (after the click).

• With the Valsalva maneuver or standing: the sounds in mitral valve prolapse are louder, while the sounds in mitral regurgitation are quieter.

# Advice

• This article only explains some common murmurs, and less common murmurs are only briefly discussed.

• If you hear a heart murmur, consult your doctor for a proper diagnosis and appropriate treatment.