How should I auscultate a loud second heart sound (S2)?

How to Auscultate for a Loud S2

To auscultate a loud S2, position your stethoscope at the second left intercostal space (pulmonic area) and second right intercostal space (aortic area), listening specifically during expiration when left-sided sounds are loudest, and assess whether the loud component is A2 (suggesting systemic hypertension) or P2 (suggesting pulmonary hypertension). 1, 2

Optimal Auscultation Technique

Patient Positioning and Preparation

• Have the patient sit upright or lie supine with the back supported, relaxed for at least 5 minutes before auscultation 1
• Ensure the room is quiet—neither you nor the patient should talk during the examination 1
• Remove all clothing covering the chest wall to optimize sound transmission 1

Stethoscope Placement for S2

• Use either the diaphragm or bell of your stethoscope—both are acceptable for cardiac auscultation, though the diaphragm is typically preferred for higher-pitched sounds like S2 1
• Listen at the pulmonic area (second left intercostal space) to best hear P2, which becomes loud with pulmonary hypertension 2, 3
• Listen at the aortic area (second right intercostal space) to best hear A2, which becomes loud with systemic hypertension 1

Respiratory Maneuvers

• Have the patient breathe normally first, then ask them to take a deep breath and hold it briefly in expiration 2
• Left-sided heart sounds (including A2) are loudest during expiration because increased venous return to the left heart augments left ventricular stroke volume 1
• Right-sided sounds (including P2) increase with inspiration 1

Distinguishing the Components of a Loud S2

Identifying Which Component is Loud

A loud P2 (pulmonary component):

• Best heard at the second left intercostal space 2, 3
• Indicates pulmonary hypertension when P2 equals or exceeds A2 in intensity 2, 3
• May be accompanied by a right ventricular lift on palpation 2

A loud A2 (aortic component):

• Best heard at the second right intercostal space 1
• Suggests systemic hypertension or a hyperdynamic circulation 1

Assessing S2 Splitting Patterns

Normal physiologic splitting:

• S2 splits during inspiration (A2 followed by P2) and becomes single during expiration 2
• The presence of normal splitting reliably excludes severe aortic stenosis 4

Fixed splitting:

• S2 remains split throughout the respiratory cycle with no variation 2
• Classic finding in atrial septal defect—the split interval remains constant during both inspiration and expiration 1, 2

Reversed (paradoxical) splitting:

• S2 splits during expiration and becomes single during inspiration (P2 precedes A2) 2
• Occurs with delayed left ventricular systole, such as in left bundle branch block or severe aortic stenosis 2

Clinical Context and Associated Findings

When S2 is Abnormally Loud

• If accompanied by an ejection click, immediately consider pulmonary hypertension, bicuspid aortic valve, pulmonary stenosis, or atrial septal defect 3
• Order transthoracic echocardiography as the first-line diagnostic test when you detect an abnormally loud S2, especially with other abnormal findings 4, 3

When S2 is Soft or Absent

• A soft or absent A2 is highly specific for severe aortic stenosis and mandates immediate echocardiography 1, 4
• In severe aortic stenosis, valve calcification prevents normal forceful closure, progressively dampening the A2 sound 4
• This may result in a single S2 (only P2 audible) or reversed splitting 1, 2

Common Pitfalls to Avoid

• Do not assume a faint S2 is normal in elderly patients—it may indicate severe aortic stenosis even with a soft murmur 4
• Do not confuse a loud single S2 with normal S2—a single loud S2 may indicate pulmonary hypertension or congenital heart disease like L-transposition of the great arteries 3
• Do not rely solely on murmur intensity—severe aortic stenosis can present with a soft murmur and absent A2, particularly when cardiac output is reduced 4
• Always correlate auscultatory findings with other physical examination findings, such as carotid pulse character, jugular venous pressure, and precordial palpation 1

Dynamic Auscultation Techniques

• Use the Valsalva maneuver: Most murmurs decrease, but this helps assess changes in S2 splitting 1
• Use positional changes: Have the patient stand or squat to alter venous return and assess how S2 characteristics change 1
• Use handgrip exercise: Increases afterload and can accentuate certain findings 1