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Retired NBME Step 2 CK Form 6 Answers

step2ck_form6/Block 4/Question#9 (reveal difficulty score)
A 4-week-old newborn is brought to the ...
High pulmonary vascular resistance ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: Pulm heart_sounds inc Cardio

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 +4  upvote downvote
submitted by โˆ—keyseph(99)
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Gonna write another answer to this since the other answer is so long.

Basically, holosystolic murmur over lower left sternal border in a newborn is most likely a VSD. The murmur from a VSD is due to left-to-right shunt from LV to RV.

In utero and early after birth, pulmonary arterial pressure is high, so the pressure gradient between LV and RV is low. The left-to-right shunt is therefore not that substantial.

As pulmonary growth progresses, the pulmonary arterial pressure decreases, which increases left-to-right shunting and increases the murmur.

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 +2  upvote downvote
submitted by โˆ—qfever(67)
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Got this question wrong and googled an explanation: (All credit goes to http://www.usmleforum.com/files/forum/2013/2/746009.php)

This pt most likely got " VSD " :

-In order for a murmur to be present Blood has to flow across the defect from Higher Pressure Chamber to Lower Pressure Chamber.

-If the Pressure b/w two chambers is equal or nearly equal then there will be NO Flow across the defect ------ Hence NO Murmur.

-At Birth "Pulmonary Vascular Resistance is High" due to the

"Hypertrophy of Pulmonary Arterioles" during Fetal life keeping the pulmonary arterial pressure higher than normal that produce RV Hypertrophy.

*and cz of this High Pulmonary Vascular Resistance which transmit high pressure back to RV, result in "NO Shunting Across VSD"------ and this is the reason NO Murmur is detected on initial examination.

-Following birth "Involution Of Pulmonary Vasculature" start and Pulmonary Vascular Resistance start to decline as the arteriolar muscular hypertrophy regress----- and Resistance Falls to it's lowest point by the 6th wk of life

-and it is then (in a few wks after birth) when there is more shunting of blood across VSD producing a Holosystolic Murmur.

-This is the reason VSD detected in a few wks after the birth frequently on the first pediatrician's visit.

An infant with a large VSD will fail to thrive and become sweaty and tachypnoeic (breathe faster) with feeds.

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 +0  upvote downvote
submitted by โˆ—charcot_bouchard(574)
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First, I guess everyone was correct to diagnose it was a TOF case with VSD.

All murmur follows V shape relation to flow and intensity. TOo much flow (for eg, Such a big VSD that equalize pressure) - Weak murmur.

Too little flow (like severe stenosis, right after birth hish pulmonary resistance) - Weak murmur.

If you decide ur murmur is VSD ans option comes down to A & C. C is not realistic.

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