What is the definition of a loud 2nd heart sound?

Definition of a Loud Second Heart Sound

A loud second heart sound (S2) is characterized by increased intensity of the aortic component (A2) and/or pulmonary component (P2), most commonly caused by elevated pressure in the aorta or pulmonary artery, with pulmonary hypertension being the primary pathologic cause to consider when encountering this finding. 1

Physiologic Mechanism

The second heart sound results from deceleration of blood columns following semilunar valve closure, which throws the cardiohemic system into vibration rather than from the valve closure itself. 2, 3

• The aortic valve closure occurs approximately 12 milliseconds (range 5-25 ms) before the audible A2 component. 2
• The pulmonary valve closure precedes the audible P2 component by approximately 60 milliseconds (range 30-75 ms). 2
• The closed valve acts as an elastic membrane that generates compression and expansion of blood, producing transient pressure changes that manifest as sound. 3
• The amplitude of the closure sound varies directly with diastolic pressure in the respective great vessel, explaining why elevated arterial or pulmonary pressures produce louder sounds. 3

Primary Causes of Loud S2

Pulmonary Hypertension

• When a loud second heart sound is heard, pulmonary hypertension must be the primary diagnostic consideration, as elevated pulmonary artery pressure increases the intensity of P2. 1
• The increased diastolic pressure in the pulmonary artery creates greater stretch of the pulmonary valve leaflets, amplifying the sound transient. 3

Anatomic Considerations

• Congenitally corrected transposition produces a loud S2 due to the anterior position of the aortic valve, which brings the sound source closer to the chest wall. 1
• This anatomic variant creates a diagnostic challenge, as it can be difficult to distinguish from true pulmonary hypertension based on auscultation alone. 1

Clinical Context and Normal Variants

Pregnancy

• A louder than normal first heart sound with prominent splitting can occur in normal pregnancy due to a 50% increase in circulating blood volume and increased cardiac output. 4
• The second heart sound may widen and appear fixed during later stages of pregnancy as a normal physiologic finding. 5, 4

Tetralogy of Fallot

• In repaired tetralogy of Fallot, a mostly widely split second heart sound is the typical clinical finding rather than a loud S2. 6

Diagnostic Approach

When encountering a loud S2, systematically assess:

• Location of maximal intensity: A loud P2 is best heard at the upper left sternal border (pulmonic area), while a loud A2 is best heard at the upper right sternal border (aortic area). 7
• Respiratory variation: Listen during normal and deep breathing to assess for splitting patterns that may indicate underlying pathology. 7
• Associated findings: Look for signs of right ventricular hypertrophy (right ventricular lift, right axis deviation on ECG) if pulmonary hypertension is suspected. 7

Common Pitfall

Do not confuse a loud S2 with abnormal splitting patterns. A loud S2 refers to increased intensity of one or both components, while splitting abnormalities (fixed, paradoxical, or wide) refer to the timing relationship between A2 and P2. 7, 8 These are distinct physical examination findings that may coexist but represent different pathophysiologic processes.