Which cardiac murmur is heard most loudly beneath the left pectoral region (left lower sternal border)?

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Tricuspid Regurgitation

The murmur heard most loudly beneath the left pectoral region (left lower sternal border) is tricuspid regurgitation (TR). 1, 2

Key Diagnostic Features

The left lower sternal border is the classic location for right-sided heart murmurs, particularly TR. According to ACC/AHA guidelines, a right heart murmur in early to midsystole at the lower left sternal border likely represents TR without pulmonary hypertension 1. This location distinguishes it from other cardiac murmurs based on anatomic positioning.

Supporting Evidence from Physical Examination

Research specifically examining systolic murmur patterns confirms that the "left lower sternal" murmur pattern indicates significant tricuspid regurgitation with a likelihood ratio of 8.4 2. This makes it highly specific for TR when heard in this location.

Distinguishing Characteristics

Respiratory Variation

  • TR murmurs increase with inspiration (Carvallo's sign) 1
  • This occurs because inspiration increases venous return to the right heart, augmenting the regurgitant flow
  • Left-sided murmurs typically become louder during expiration

Timing and Quality

  • TR without pulmonary hypertension produces an early systolic murmur that begins with S1 and ends in midsystole 1
  • The murmur may be holosystolic if pulmonary hypertension is present
  • Often accompanied by regurgitant cv waves in the jugular venous pulse 1

Clinical Context Matters

When TR is Present Without Audible Murmur

Regurgitant cv waves may be present in the jugular veins even without an audible murmur 1. This is an important pitfall—absence of a murmur does not exclude TR.

Associated Findings

In injection drug users presenting with fever, petechiae, Osler's nodes, and Janeway lesions, a murmur at the lower left sternal border strongly suggests TR from infective endocarditis 1.

Differential Considerations

While the left lower sternal border is most characteristic of TR, other conditions occasionally heard in this region include:

  • Ventricular septal defects (though these are typically holosystolic and louder)
  • Still's murmur in children (innocent murmur best heard at lower left sternal border) 3

However, in adults with pathologic murmurs, TR remains the primary diagnosis for murmurs loudest at the left lower sternal border.

References

2
Research

Etiology and diagnosis of systolic murmurs in adults.

The American journal of medicine, 2010

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