From the Research
Yes, you can hear an S3 heart sound in a patient with atrial fibrillation. An S3 (third heart sound) occurs during early diastole when blood rapidly flows into the ventricle, causing vibrations of the ventricular wall. This sound is independent of the atrial rhythm and instead relates to ventricular filling dynamics. In atrial fibrillation, despite the irregular atrial activity, the ventricles still undergo filling phases, and if ventricular compliance is decreased or there is volume overload, an S3 may be present. In fact, an S3 in atrial fibrillation often indicates underlying heart failure or volume overload, making it an important clinical finding, as noted in a study published in the American Journal of Medicine 1.
When auscultating a patient with atrial fibrillation, listen carefully during early diastole, just after S2, using the bell of the stethoscope at the apex with the patient in the left lateral position to best detect an S3. The sound is low-pitched and may be described as a "Kentucky" in the "Ken-tuck-y" cadence of heart sounds. A study published in JACC: Heart Failure found that an S3 was associated with increased mortality in patients with heart failure and atrial fibrillation, although it was not an independent predictor in multivariate analysis 2.
Key points to consider when evaluating a patient with atrial fibrillation and a potential S3 include:
- The presence of an S3 may indicate underlying heart failure or volume overload
- Careful auscultation is necessary to detect the S3, which is a low-pitched sound
- The S3 is independent of the atrial rhythm and relates to ventricular filling dynamics
- An S3 in atrial fibrillation is an important clinical finding that may indicate increased mortality, as suggested by studies such as the one published in the American Journal of Medicine 1 and JACC: Heart Failure 2.
It is also worth noting that while older studies, such as one published in Circulation in 1976 3, have explored the mechanism of atrial sounds in atrial fibrillation, the most relevant and recent evidence supports the idea that an S3 can be heard in patients with atrial fibrillation and is an important clinical finding. However, the most recent and highest quality study on this topic, published in 2024 in the American Family Physician 4, does not specifically address the question of hearing an S3 in atrial fibrillation, but it does provide general guidance on the diagnosis and treatment of atrial fibrillation.