What is the significance of a slight murmur heard at the 2nd sternal border?

Murmur at the 2nd Sternal Border: Clinical Significance

A slight murmur at the 2nd sternal border most commonly represents either an innocent pulmonary flow murmur or pathologic aortic/pulmonic valve disease, and the key to differentiation lies in the murmur's characteristics, associated cardiac findings, and response to dynamic maneuvers. 1

Anatomic Localization

The 2nd sternal border corresponds to two critical auscultatory areas:

• Right 2nd intercostal space (right upper sternal border): Aortic valve area 1
• Left 2nd intercostal space (left upper sternal border): Pulmonic valve area 1

Differential Diagnosis by Murmur Type

Innocent (Benign) Murmurs at This Location

Innocent pulmonary systolic murmur is the most common benign cause:

• Medium-pitched, harsh character heard at left middle and upper sternal border 1
• Disappears with upright position 1
• Grade ≤2/6, crescendo-decrescendo, mid-systolic without radiation 2
• No further workup needed in asymptomatic patients with normal exercise capacity 2

Venous hum (if continuous with diastolic accentuation):

• Medium-pitched, blowing character at right or left upper sternal border 1
• Disappears with jugular venous compression or supine position 1

Carotid bruit (if radiating from neck):

• Medium-pitched, harsh character at upper sternal border or supraclavicular region 1
• Disappears with bilateral shoulder hyperextension 1

Pathologic Murmurs Requiring Further Evaluation

Aortic stenosis (right 2nd intercostal space):

• Midsystolic crescendo-decrescendo murmur from outflow obstruction 1
• Associated findings: soft or absent A2, reversed splitting of S2 indicating severe disease 1
• Early aortic systolic ejection sound (heard during both inspiration and expiration) suggests bicuspid aortic valve 1

Pulmonic stenosis (left 2nd intercostal space):

• Midsystolic murmur at pulmonic area and left sternal border 1
• Ejection sound heard only during expiration at pulmonic area 1

Atrial septal defect:

• Grade 2/6 midsystolic murmur in pulmonic area and left sternal border 1
• Fixed splitting of S2 during both inspiration and expiration is pathognomonic 1

Aortic regurgitation (often presents with systolic murmur):

• Systolic murmur is more common than diastolic murmur on routine screening 3
• 86% of patients with moderate aortic regurgitation have a systolic murmur 3
• Diastolic murmurs are rare (only 14% with moderate AR) 3

Critical Red Flags Requiring Echocardiography

Immediate referral to cardiology is warranted for: 4

• Holosystolic or diastolic murmur (almost always pathologic) 2, 4
• Grade ≥3/6 intensity 4
• Harsh quality 4
• Abnormal S2 (fixed splitting, reversed splitting, soft/absent A2) 1, 4
• Systolic click 4
• Increased intensity when standing (suggests hypertrophic cardiomyopathy) 4
• Radiation to carotids or apex 3

Diagnostic Approach Using Dynamic Auscultation

Positional changes are critical for differentiation: 1

• Standing/upright position: Innocent murmurs typically disappear or decrease 1, 2
• Supine position: Venous hum disappears 1
• Respiratory variation: Right-sided murmurs increase with inspiration; left-sided with expiration 1

Specific maneuvers: 1

• Jugular venous compression eliminates venous hum 1
• Bilateral shoulder hyperextension eliminates carotid bruit 1

When to Order Echocardiography

Echocardiography is indicated when: 1, 2, 4

• Any red flag features are present 4
• A specific innocent murmur cannot be confidently identified 4
• Patient has symptoms (dyspnea, chest pain, syncope, decreased exercise tolerance) 2, 4
• Patient is at risk for valve disease (prior rheumatic fever, Kawasaki disease, family history of sudden cardiac death, congenital heart disease) 4
• Grade 3 or higher murmur requires echocardiography to distinguish benign from pathologic causes 1

Echocardiography is NOT needed for: 2

• Grade 1-2/6 mid-systolic murmur 2
• Crescendo-decrescendo pattern 2
• Position-dependent (disappears when standing) 2
• No radiation 2
• Asymptomatic patient with normal physical capacity 2

Common Pitfalls to Avoid

• Do not dismiss systolic murmurs in patients at risk for aortic regurgitation: 78% of mild AR and 67% of moderate AR present with "benign-appearing" systolic murmurs 3
• Always assess S2 splitting: Fixed splitting indicates ASD; reversed splitting indicates severe AS 1
• Listen through complete respiratory cycle: Respiratory variation provides crucial diagnostic information 1
• Neonatal murmurs require different approach: More likely to represent structural heart disease and warrant echocardiography 4
• ECG and chest X-ray rarely assist in diagnosis and should not delay echocardiography when indicated 4