Percussion of the heart

Physical principles and dullness zones

The heart is a dense muscular organ, which is why tapping over it produces a dull sound. The surrounding lungs contain air and yield a clear pulmonary resonance. Thanks to this contrast, we can outline the cardiac borders.

In clinical practice, two key zones are distinguished:

• Relative cardiac dullness. These are the areas of the organ whose periphery is covered by the edges of the lungs. The sound here is muffled (quieter than pulmonary resonance, but not completely dull). It is this zone that reflects the true borders of the heart.
• Absolute cardiac dullness. The central area that is not covered by lung tissue at all and is directly adjacent to the anterior chest wall. The sound over it is absolutely dull (femoral dullness). This zone is formed exclusively by the right ventricle.

Anatomic formation of the borders

Percussion borders reflect the projection of specific heart chambers and major blood vessels onto the thorax.

Left border of relative dullness (when examined from top to bottom) is formed by four structures:

1. Aortic arch.
2. Pulmonary artery.
3. Auricle of the left atrium (projected at the level of the 3rd rib).
4. Left ventricle (identified as a narrow band).

Right border is formed differently: its upper part (starting from the 2nd intercostal space) is formed by the superior vena cava (v. cava superior), and the lower part by the right atrium (atrium dextrum).

Methodology for determining relative dullness borders

There is a strict algorithm for each border to avoid diagnostic errors.

Determining the right border The main task here is to exclude the influence of the liver, which also produces a dull sound.

1. First, the upper border of the liver is located: the pleximeter finger is placed parallel to the intercostal spaces and percussed from top to bottom. Normally, the border is located in the 5th intercostal space.
2. Then, move up by one intercostal space (usually the 4th intercostal space).
3. The finger is turned parallel to the right sternal border and light percussion is performed from outside inward (from the lungs toward the heart) until dullness appears.

Determining the left border This step is inextricably linked to the localization of the apex beat.

1. Palpate the apex beat beforehand. Percussion is performed strictly in the same intercostal space (most often the 5th).
2. If the apex beat is not palpable, the examination by default starts in the 5th intercostal space.
3. Percuss from the anterior axillary line (linea axillaris anterior) toward the sternum. To map out the complete left border, similar actions are repeated in the overlying intercostal spaces.

Normative values in a healthy individual

With correct percussion technique, the following borders of relative dullness are determined in a healthy individual:

• Right: located in the 4th intercostal space, running along the right sternal border or protruding outward from it by no more than 1 cm.
• Left: located in the 5th intercostal space (or at the level of the found apex beat), 1 cm medial to the left midclavicular line (linea medioclavicularis sinistra).
• Upper: percussed from the 2nd rib downward along the left parasternal line. Normally, it corresponds to the lower edge of the 3rd rib (or the 3rd intercostal space). If the border is shifted to the upper edge of the 3rd rib or into the 2nd intercostal space, this indicates pathology — enlargement of the left atrium.

Vascular bundle is measured in the 2nd intercostal space using quiet percussion perpendicular to the sternum. Normally, its borders exactly coincide with the edges of the sternum.

Examination of absolute dullness

Since absolute dullness reveals the area not covered by the lungs, its determination requires a special technique — threshold (sub-threshold/quietest) percussion.

Striking with the percussion hammer must be as quiet as possible, and complete silence must be ensured in the room. The border is considered to be the moment when the sound completely disappears. There is also an alternative approach: percussing from the center of the absolute dullness zone outward until pulmonary resonance appears.

Normal borders of absolute dullness:

• Right: left sternal border at the level of the 4th intercostal space.
• Left: 1–2 cm medial to the previously found left border of relative dullness.
• Upper: 4th intercostal space.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Technique of quiet and threshold percussion
• Anatomic projection of heart chambers onto the anterior chest wall
• Causes of the upper border of relative dullness shifting
• Rules for percussing the vascular bundle in the 2nd intercostal space

Other topics in the "Cardiovascular system" section

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