How to Differentiate Opening Snap from S3 Heart Sound Clinically

In this video we are going to discuss four major points by which you can differentiate opening snap (OS) sound of mitral stenosis (MS) from third heart sound (S3) clinically. And the examples of these two sounds.

1. First major difference is that opening snap is associated with loud first heart sound (S1).

2. Secondly opening snap is short sharp click best heard at left lower sternal border with diaphragm of the stethoscope, whereas third heart sound is best heard at apex with the bell of stethoscope.

3. Third difference is that on standing opening snap moves further away from A2, whereas S3 doesn't change its position on dynamic auscultation.

4. And the last difference is measuring the distance of S2 from opening snap with phonocardiography, as its difficult to appreciate clinically. S2 to opening snap distance is usually less than 100 msec whereas the distance of S3 from S2 is more than 100 msec.

These are the major differences between these two sounds. Example sound of opening snap and third heart sound (S3) with illustration is given in the end of video. You can further clarify the concept by slowing down the speed of video to listen murmurs accurately. Listen to these two example sounds and practice on your patients. Hope you enjoyed learning.

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