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NBME 21 Answers

nbme21/Block 2/Question#16

A 34-year-old woman comes to the physician because ...

Atrioventricular bundle

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submitted by hayayah(422),

This pt has an ASD which is a "hole" between the LA and RA. Fixing it could damage the AV bundles.

sahusema  the atrioventricular bundle is also called the bundle of his +  

TLDR: last sentence summarizes it

The exact mechanism underlying AVB following ASD closure remains speculative. We can hypothesize that the possible mechanism of AVB is an inflammatory response and subsequent edema as a correlative result of mechanical rubbing of the occluder against the proximal conduction system. The margins of the secundum atrial septal defect include Bachmann’s bundle, the primary path for electrical conduction from the sinoatrial node to the atrioventricular node. The atrioventricular conduction bundle, which emerges from Bachmann’s bundle in the atrioventricular node area to conduct electrical impulses to the Purkinje fibers, is especially prone to damage.

Atrioventricular Block Subsequent to Intraoperative Device Closure Atrial Septal Defect with Transthoracic Minimal Invasion; A Rare and Serious Complication https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3532427/

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submitted by hello(69),

Please help

Mid-systolic ejection click = pulmonic stenosis

How is pulmonic stenosis related to the patient's ASD -- does ASD cause pulmonic stenosis??

burak  ASD has typically 3 associated sounds according to UW, they are all about increased blood in RA. Increased blood in RA causes more blood do ejected from tricuspid (dşastolic rumble), and more blood to be ejected to pulmonary circulation which cause pulmonary flow murmur (midsystolic murmur in pulmonary region). It even can cause pulmonary regurgitaion like murmur, but most important murmur in ASD is typically midsystolic murmur. You can check it out on FA 2018 page 284 +1  
hello  Ok, what I learned: Extra blood in the right heart (due to ASD) doesn't lead to pulmonic stenosis? Instead, it's that pulmonic stenosis = most common comorbid heart association with ASD +1  
burak  No it's not pulmonic stenosis, it doesn't lead. Murmur associated with ASD is pulmonic stenosis-like murmur, because it's caused by excess RA and RV volume ejecting to the pulmonary arteries. So it's same location with pulmonic stenosis, and it's systolic. You get it? +1  
hello  @burak Yep! +  

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submitted by burak(8),

Isn't it dependent on the location? I answered it coronary sinus because av node is located in Koch triangle; which composed of CSinus, Tendon of Todaro, Tricuspid annulus?

hello  The correct answer was atrioventricular BUNDLE-- it's also known as the Bundle of His. AV Bundle ≠ AV Node. +1  
burak  Now it's more confusing to me:) because av bundle is more inferior to the av node. +  
hello  Patient has ASD --> need to repair interatrial septum. AV bundle aka bundle of His is located neart interatrial septum. Coronary sinus opens into atria but is not located near the interatrial septum +2