S4 is absent during which rhythm?

S4 is absent during which rhythm?

• A. Atrial fibrillation
• B. Normal sinus rhythm
• C. Ventricular tachycardia
• D. Second-degree AV block

Answer: (A)

S4 is an atrial gallop produced by the atria contracting against a stiff, noncompliant ventricle late in diastole. It relies on organized atrial contraction to generate that extra heart sound just before S1. In atrial fibrillation, the atria beat in a chaotic, uncoordinated way and there is no effective atrial kick. Without that organized atrial contraction against a stiff ventricle, the S4 sound cannot be produced, so S4 is absent. In other rhythms, where atrial contraction remains organized or diastolic dysfunction allows the atrial kick to contribute to ventricular filling, an S4 may still be heard if the ventricle is stiff.

S4 is an atrial gallop produced by the atria contracting against a stiff, noncompliant ventricle late in diastole. It relies on organized atrial contraction to generate that extra heart sound just before S1. In atrial fibrillation, the atria beat in a chaotic, uncoordinated way and there is no effective atrial kick. Without that organized atrial contraction against a stiff ventricle, the S4 sound cannot be produced, so S4 is absent. In other rhythms, where atrial contraction remains organized or diastolic dysfunction allows the atrial kick to contribute to ventricular filling, an S4 may still be heard if the ventricle is stiff.