What are the borders of the cardiac box?

Borders of the Cardiac Box

The cardiac box is anatomically defined by the sternal notch superiorly, the xiphoid process inferiorly, and the nipples laterally. 1

Anatomical Landmarks

The traditional cardiac box boundaries are:

• Superior border: Sternal notch 1
• Inferior border: Xiphoid process 1
• Lateral borders: Nipples bilaterally 1

These landmarks define a rectangular region on the anterior chest wall that overlies the heart and pericardium. 1

Clinical Context and Anatomical Reference Points

The anatomical structures that define these borders include:

• Sternum: The sternal notch (superior) and xiphoid process (inferior) are fixed bony landmarks located in the midline of the anterior thoracic wall 1
• Sternal borders: The lateral edges of the sternum serve as medial reference points 1
• Intercostal spaces: The cardiac box typically spans from approximately the 2nd intercostal space superiorly to the 5th-6th intercostal space inferiorly 1

Important Clinical Caveats

The cardiac box concept has significant limitations in predicting cardiac injury, particularly for gunshot wounds. 2, 3

Mechanism-Dependent Relevance

• For stab wounds: Injuries within the cardiac box demonstrate significantly higher rates of cardiac injury (14.3% vs 2.4% outside the box, p=0.001) 3
• For gunshot wounds: The cardiac box is a poor predictor of cardiac injury, with no significant difference between injuries inside versus outside the box (9.1% vs 3%, p=0.328) 3
• High-energy missiles can cause cardiac injury regardless of entrance site location 2

Alternative Risk Assessment

Research suggests that entrance wounds from the anterior to posterior midline of the left thorax provide the highest positive predictive value (41%) with high sensitivity (90%) for cardiac injury, making this region more clinically relevant than the traditional cardiac box for gunshot wounds. 2

For penetrating trauma evaluation, clinicians should "think outside the box" and not rely solely on cardiac box boundaries to determine risk of cardiac injury, especially for ballistic trauma. 2