A nurse is performing a cardiac assessment on a child. Which characteristic would indicate a diagnosis of a grade 1 heart murmur?

Cardiac assessment is a systematic evaluation of the heart and circulation that combines history-taking, physical examination, and diagnostic techniques to identify cardiovascular health, risks, or disease. It focuses on vital signs, inspection, palpation, auscultation, and sometimes point-of-care imaging to detect abnormalities in heart function and blood flow.

Rationale for correct answer:

D. Fifth intercostal space, left midclavicular line: The first heart sound (S1) is produced by the closure of the atrioventricular (AV) valves, the mitral and tricuspid valves, at the beginning of ventricular systole. S1 is loudest at the apical area. In clinical testing, the apex is classically identified as the 5th intercostal space at the left midclavicular line, which is considered the standard landmark for auscultating SA. The diaphragm of the stethoscope is preferred because S1 is a high-pitched sound.

Rationale for incorrect answers:

A. Third or fourth intercostal space: These locations are closer to the base of the heart, where S2, the closure of aortic and pulmonic valves is louder than SA.

B. The apex with the stethoscope bell: Using the bell is better for low-pitched sounds, like S3 or S4, not the high-pitched SA.

C. Second intercostal space, midclavicular line: The second intercostal space corresponds to the aortic and pulmonic areas, where S2 is best heard, not SA.

Test-taking strategy:

• For heart sounds, exams often prefer precise anatomical landmarks over general descriptions.
• Remember S1 is caused by AV valve closure (mitral/tricuspid) best heard at the apex of the heart.
• Remember S2 is caused by semilunar valve closure (aortic/pulmonic).
• Use the diaphragm for high-pitched sounds (S1, S2), and bell for low-pitched sounds (S3, S4, murmurs).

Take home points

• S1 results from mitral and tricuspid valve closure and is best at apex (5th ICS, left midclavicular line).
• S2 is caused by aortic and pulmonic valve closure and is best at base (2nd ICS, right and left).
• Correct auscultation location is essential for identifying murmurs, rhythm abnormalities, and cardiac function in children.

Heart sounds are produced by valve closure and changes in blood flow within the heart. Correct interpretation of heart sounds requires understanding the cardiac cycle, specifically the relationship between atrial contraction, ventricular contraction, and valve movement.

Rationale for correct answer:

C. S1 is directly caused by AV valve closure. It signifies the beginning of ventricular systole. This sound is best heard at the apex of the heart, where the mitral valve is located. Clinically, S1 coincides with the carotid pulse, ventricular contraction, and rising ventricular pressure.

Rationale for incorrect answers:

A. Late diastole is characterized by atrial contraction and ventricular filling. The AV valves are still open at this time, so no S1 occurs yet.

B. Early diastole begins after ventricular relaxation, when the semilunar valves close (aortic and pulmonic valves), producing S2, not SA.

D. Closure of the aortic and pulmonic (semilunar) valves generates the second heart sound (S2), which marks the end of systole and beginning of diastole.

Test-taking strategy:

• Always match valve type to heart sound:
  • AV valves closure (mitral, tricuspid) causes SA.
  • Semilunar valves closure (aortic, pulmonic) causes SB.
• Use timing clues:
  • Systole begins with S1
  • Diastole begins with S2

Take home points

• S1 (“lub”) occurs with closure of the mitral and tricuspid valves and marks the beginning of ventricular systole.
• S1 is best heard at the apex and coincides with the carotid pulse.
• S2 (“dub”) results from semilunar valves closure and marks the start of diastole.
• Understanding heart sounds requires linking valve movement, pressure changes, and the cardiac cycle.