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NBME 23 Answers

nbme23/Block 4/Question#41 (60.0 difficulty score)
Electrophysiology of the heart is studied in ...
Ablation of the atrioventricular node🔍,📺

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submitted by amirmullick3(61),
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GCE ca.ringTs ehT sdietcan eenwetb RSQ ocpmseexl si uoitnnycsoul boatu 6 os,bex so rate is heiesnt is a d3r rgedee klbco ewher hte riata dna neertscvil aer agbitne ndetpnleniyed fo eecrahoht nad het RR si qeetiluavn lla nd2 SRQ epxolmc is SEPRU ,rwnrao dna rtoshe era olsa wr,aonr whihc sneam teyher drneipolgzia hksnta ot nblude fo Hi.s

submitted by aladar50(40),
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oFr eht ECG, I yltliiina hotgthu ti was d2n rgeede Teyp 1 ebausec it eeedms that het PR nesitlrav erew cairsigenn lniut a tbae aws ,pdpdeor tub if uoy oolk ta it ,elsylco omes of eth P vseaw wree eddnih ni hte SQR lxpsceme.o fI ouy otecin th,ta tnhe yuo anc ese thta teerh reew eurlgra P asvew nad gurlare RSQ eecsp,moxl ubt hreet saw a plmetoec ssiiocatindo twnbeee ehtm ihhwc amsen it asw d3r eeegrd erath ,kclbo so het rswnae asw oaabintl enra hte VA odn.e

yotsubato  answer was ablation near the AV node. No it wasnt. It was ablation OF THE AV node itself. Which faked me out. +9  
makinallkindzofgainz  The tangent by user "brbwhat" says that there is "pr lengthening progressively" but there is not. This is 3rd degree AV block. The P waves march out consistently at their own rate, and the QRS complexes march out at their own rate. There is complete dissociation between the P waves and QRS complexes. They have no relationship. This is exactly what you would see if you ablated the AV node. The SA node would continue to to create P waves. The bundle of His would continue to generate junctional (normal looking) QRS complexes. +6  

submitted by sajaqua1(535),
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dW'lunot tolta VA lnaod tiaanbol doersyt ot chotarimuhtiyyt of the ce?eamkpar Tath uolwd mane that ewolb eth AV endo hte mthryh wdlou eb rdpiodev by a aevrucltinr ifco, dan sohte uuslayl eatcre deiw QSR .sxmoplcee

haliburton  that was my reasoning as well. guess not. +  
yotsubato  Shitty NBME grammar strikes again. +1  
charcot_bouchard  No. No guys. Bundle of his located below AV node and it can generate impulse. it calls junction escape rhythm and narrow complex. Below this is purkinje, bundle branch & ventricular muscle. those are wide complex +17  
abhishek021196  Third-degree (complete) AV block The atria and ventricles beat independently of each other. P waves and QRS complexes not rhythmically associated. Atrial rate > ventricular rate. Usually treated with pacemaker. Can be caused by Lym3 disease +2  

submitted by fallenistand(23),
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Thsi qntesiuo is inksga twha olwud saecu isth! RP riltnave msiegns pu si an esuis at the VA one.d So nlabagit het AV edno wldou caeus ethra lb.okc

submitted by krewfoo99(93),
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nI rosdab nad o,ydbne tI si iads thta ihrtd regede eahtr kbclo si ude ot blcko ni teh HIS kinPujeer t.msesy oS wyh udwol ntabalio fo VA eond cusae htsi dae?ssei

dulotWn sutoidentcr of trap fo tlef inetcelrv eb a betetr waensr ?

brbwhat  Had the same doubt, Read the part again and found this. Type 2 Is caused when purkinje is hanging by a thread and therefore some impulses conducted, some not. Chb is caused by purkinje not conducting impulses from san, some lower pacemaker ie purkinje or his is depolarising by itself hence venrticles beat independently. There is BLOCK in purkinje for conduction from san. Among options the only thing that establishes this block is avn ablation. +  

submitted by methylased(18),
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euRalrg rhyhmt t(onuc hte o,bsex tyr'eeh se)m,a 1 uotccdduenn p vwea with aergrlu myhhrt -;g&-t riaat dna evstcelnri tangibe edlitnnypndee ye(lkil stvcnereil lcrt by Hku-s)jiirnPe ;&-gt- emetopcl d3r() aehtr olbck -tg&-; AVN iaanotlb ihs(t is ualtaylc oden rof tps thiw Afib eommteis)s

submitted by kunalaggarwal2(0),

So after watching the Boards and Beyond video on heart blocks, this is the reasoning I have come to. Since the QRS complexes are spaced out at regular intervals, you can conclude that this is 3rd degree or complete heart block (If they were irregular intervals then it would be Mobitz type 1). The weird thing is that 1st and second degree (type 1) heart block are USUALLY associated with some AV node disfunction, and Second degree (type 2) and Third degree are USUALLY associated with His-Purkinje disease. Dr. Ryan has said there are exceptions to this rule, which I guess is the case in this question. What makes "ablation of bundle-branch fibers" wrong is that is basically a bundle branch block, which would lead to a widened QRS complex.

Either way FUCK NBMES (especially the new ones). I literally spend 60 bucks just to feel depressed and anxious afterwards. Happy Studying.

submitted by osgoodschlatter10(31),
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I itkhn eth uotiesqn seferr ot a nioacser dscuae by bilaotna of a itcalrpuar rgoeni of the h.eart

If ouy ookl fuylceral eterh era emso rte-ruamep lucrvtnraie sbeat (or ratreh sutj ).1 emePaur-rt urceltnaivr bseat acn be eauscd by tliaonab of het AV node scein hte VA oden is lpeoerssbin ofr rhyhmt nortolc by innortollgc eht ebmunr of AS deno esiplmsu ahtt rea mdernttstia to het aveulitnrcr aleetlcrci w.okntre

submitted by endochondral1(16),
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I tohthug bntaaloi fo the va node saw a tx for a fib tno areht lkob?c

underd0g  The question asks for the CAUSE of the heart block, not treatment. +  

submitted by kard(44),
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niePastt woh ndoureg na VA dnoe olaatnib rea laso nleatimdp iwth a eckmperaa to help aaitninm a lrnoma arthe rat.e xT. orf emcotlep koBcl

submitted by mutteringly(10),

UW Question Id: 1976 Testing a very similar concept and provides a great explanation for this!

submitted by goodkarmaonly(0),
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hTe ECG shsow a Mtzoib pyeT 1 lbcok opgln(irnog PR elwodfol yb a podpdre awh eev.eTs cblkso ullysua aries as a ptcdrouyb of a sicfunnalytdo VA n,ode os baiatoln ta eth AV edno si the msto ppaprrtoeia rnewsa in this csea