ASD Murmur Mechanism?

[AlexRusso]

I had a Q-bank question today describing a midsystolic ejection murmur heard in the pulmonic region with right atrial and ventricular hypertrophy and a split s2. I figured this was pulmonary stenosis but the answer was Atrial Septal Defect. FA didn'd have anything about ASD murmurs, so I looked in pathophys for the boards and wards and yes there is a systolic ejection murmur. I don't undertand how you get a systolic murmur when the defect is in the atria. Intuition says it should be a late diastolic murmur when the atria contract right before the end of diastole. Apparently not. Anyone know how ASD's cause SYSTOLIC murmurs? Can someone reason this out for me?

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[Idiopathic]

When do the atria fill? Systole...Hence, the ASD would present with a systolic murmur. We had this come up in Path class this year and had to work through it. I think the 'ejection' murmur might be a little harsh, if anything there would be increased SBP which could increase atrial filling pressure and cause turbulent blood flow through the defect, but I know that ASD presents in systole...that is how I remember it.

 

[mpp]

The extra volume in the right ventricle (from the blood coming through the ASD and through the Tricuspid valve) causes the ejection murmur through the pulmonic valve.

Murmurs are typically caused by blood under pressure...the ventricles are usually the cause of the murmur (the atria don't contract with enough force to cause this murmur) since they have blood under presssure.

 

[mpp]

I should also add, that's why you get the widely split S2, lots of volume through the pulmonic valve leads to delayed closing (although I've also heard that's not 'the real reason' but how it's often explain...good enough for me since it works).

 

[BrooklynDO]

I had a Q-bank question today describing a midsystolic ejection murmur heard in the pulmonic region with right atrial and ventricular hypertrophy and a split s2. I figured this was pulmonary stenosis but the answer was Atrial Septal Defect. FA didn'd have anything about ASD murmurs, so I looked in pathophys for the boards and wards and yes there is a systolic ejection murmur. I don't undertand how you get a systolic murmur when the defect is in the atria. Intuition says it should be a late diastolic murmur when the atria contract right before the end of diastole. Apparently not. Anyone know how ASD's cause SYSTOLIC murmurs? Can someone reason this out for me?

is the the one with the "blue kid"? I got it right but more from the fact of the murmer than this fun fact from FA : blue kid with above murmer= asd, blue kid without this precise murmer is vsd (mcc ) also If i remember correctly the hypertophy was specifically right ventricle, and I didnt think vsd's would have a specific hypertrophy because blood would be bouncing back and forth... i dunno if that makes sense but it kinda worked for me

 

[AlexRusso]

is the the one with the "blue kid"? I got it right but more from the fact of the murmer than this fun fact from FA : blue kid with above murmer= asd, blue kid without this precise murmer is vsd (mcc ) also If i remember correctly the hypertophy was specifically right ventricle, and I didnt think vsd's would have a specific hypertrophy because blood would be bouncing back and forth... i dunno if that makes sense but it kinda worked for me

No the pt in this question was a 35 y/o female in for a routine check-up. Besides the murmur and the split S2 she also had a right axis deviation on EKG a prominent right vetricular cardiac impulse, and enlarged rt. atrium and ventricle on CXR. I didn't think it was a VSD but I did think it was pulmonic stenosis, which happened to be one of the choices. Especially b/c the stem mentioned the split s2, which is a feature of pulmonic stenosis. Actually, had they not mentioned that the right atrium was hypertrophied this could have very well been a pulmonic stenosis. The explanation said that this was the only feature distinguishing the ASD and PS. mpp thanks for the explanation..i kinda understand now. More blood on the right side of the heart due to the ASD would cause there to be more turbulent flow through the pulmonic valvue, explaining the murmur. Thanks for the help guys.