NBME 21 Atrioventricular bundle (NBME Answers)

Retired NBME 21 Answers

nbme21/Block 2/Question#16 (reveal difficulty score)
A 34-year-old woman comes to the physician ...
Atrioventricular bundle 🔍 / 📺 / 🌳 / 📖
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submitted by ∗hayayah(1212)

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

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sahusema the atrioventricular bundle is also called the bundle of his +6

bbr What if it had said "AV node", that's in the interaatrial septum as well, right? I'm wondering, that could be answer as well. (FA 2019 pg291) +1

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submitted by ∗chandlerbas(118)

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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 ∗burak(71)

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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?

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hello The correct answer was atrioventricular BUNDLE-- it's also known as the Bundle of His. AV Bundle ≠ AV Node. +3

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 +6

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submitted by ∗hello(429)

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Please help

Mid-systolic ejection click = pulmonic stenosis

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

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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 +3

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? +2

hello @burak Yep! +

peachespeaches Fixed split= ASD Wide Split= something like pulm stenosis. The questions ays "fixed split" +

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