see also: [[Left Bundle Branch Block|LBBB]], [[Right Bundle Branch Block|RBBB]], [[Transcutaneous pacing]], [[Pacemaker issues]]. [Bear - AV blocks](bear://x-callback-url/open-note?id=E7022034-3BC9-49C1-B0BC-B49AF92190EF-22242-000010BC4F03A554), [Bear - Bigeminy or 2nd deg heart block](bear://x-callback-url/open-note?id=142683ED-4EB2-45D0-9AF2-510A291454EF-2780-000001D0EB393650), [Hayes' - bifasicular block](x-devonthink-item://B678C4E3-A138-403F-8AD8-E40A0619381D) > [!key points] > - *heart block* describes the AV conduction > - "escape" describes any ventricular activity > - *junctional escape* = rate 40-60, usually narrow complex. no relationship btwn QRS and any atrial activity > - *ventricular escape* = rate 20-40 with broad complex. also called idioventricular escape. from bundle of His or purkinge > - not everyone with AV dissociation has 3rd degree heart block, but 3rd deg usually has AV dissociation (p-to-p regular, PR randomly changing) # Types of AV block - blocked PACs → non-conducted ps are early - if p-to-p interval is NOT regular, then the rhythm is not an AV block, likely PACs or hyper-K - 2nd degree heart block - mobitz I (Wenckebach)→ regular p-to-p, PR increasing - generally respond to atropine, rarely need PPM - often due to *excessive vagal tone* - mobitz II → regular p-to-p, pr unchanged - usually infranodal below AV node, hence *wide QRS*. usually need PPM - High grade AV block - conduction ratio of p:qrs is 3:1 or higher - can be type 1 (at level of AV node) or type 2 (infranodal) - usually needs PPM - 3rd deg HB (complete heart block) - p-p constant, QRS-QRS constant - pr intervals vary - if narrow QRS usually junctional escape rhythm → usually vagal, decent prognosis - if wide QRS, usually ventricular escape rhythm → infranodal, likely needs PPM # Causes of AV block - ↑ vagal tone - idiopathic progressive conduction system disease (eg Lenegres disease) - ischaemic heart disease - cardiac surgery - inhereted familial AV block - drugs: - [[Calcium channel blocker overdose|Verapamil]] - [[Digoxin toxicity|digoxin]] - [[Amiodarone]] - adenosine - [[beta blocker overdose|beta blockers]] - quinidine - procainamide # Examples ## PACs sinus bradycardia with PACs ![[Pasted image 20241024191716.png]] p-to-p interval NOT constant. not mobitz or CHB; just premature atrial complexes: ![[Pasted image 20241024193039.png]] ## Mobitz I > - Generally respond well to atropine; rarely require permanent pacemaker > - Generally due to excessive vagal tone 2nd Deg AV block, type I p-to-p constant pr interval gradually increases ![[Pasted image 20241024191846.png]] Mobitz I with 3:2 conduction (clumps). 3 ps for every 2 QRS ![[Pasted image 20241024192008.png]] Mobitz I with variable conduction ratios: ![[Pasted image 20241024192053.png]] ## Mobitz II 2nd deg AV block type I p-to-p constant > unlike mobiz I, QRS complex are usually wide - pr interval constant, but with non-conducted p waves - at least 2 consecutive p-QRS complex that demonstrate constant pr before unconducted p wave Look at end of pacing strip to see the two consecutive p-qrs (three in below case) before blocked p wave. If you only saw the 2:1 seen earlier in rhythm strip, wouldn’t be able to call it mobitz II; would be called “==2nd degree AV block with 2:1 conduction==” (likely if wide QRS treated as mobitz 2, if narrow QRS treated as mobitz 1) ![[Pasted image 20241024192339.png]] Mobitz II with 3:2 conduction (clumps). regularly irregular. ![[Pasted image 20241024192430.png]] 2nd deg block 2:1. is *easy to miss* because p waves burried in the T waves (recall morphology of T wave from "Bix rule" for atrial flutter) ![[Pasted image 20241024192521.png]] ## High grade AV block / advanced HB High grade AV block: ![[Pasted image 20241024192731.png]] Advanced AVB, RBBB/LAFB ![[Pasted image 20241024192813.png]] ## Complete heart block - complete AV dissociation, independent atrial and ventricular rates ![[Pasted image 20241024190515.png]] CHB with junctional escape rhythm: ![[Pasted image 20241024192949.png]] CHB with ventricular escape rhythm: ![[Pasted image 20241024193013.png]] ## Hyper-k (NOT a mobitz) has clumps, but not regular; irregular p-to-p interval so NOT AV block. bizarre ∴ consider ↑K. ![[Pasted image 20241024193158.png]] ## junctional escape rhythm - rate 40-60 - narrow complex ![[Pasted image 20241024190540.png]] ## ventricular escape rhythm - rate 20 - 40 with broad complex - aka idioventricular escape rhythm - bundle of his or purkinge ![[Pasted image 20241024190649.png]] Complete heart block with ventricular escape rhythm: ![[Pasted image 20241024190920.png]] ## putting it together Atrial fibrillation with 3rd degree AV block and a junctional escape rhythm (“regularised AF”): ![[Pasted image 20241024190819.png]] inferior STEMI + RV stemi (STE in III>II, STD v2) + complete heart block and junctional escape: ![[Pasted image 20241024190850.png]] # bifasicular and trifasicular block | type | description | | ------------------ | --------------------------------------------------------------------- | | Bifasicular block | RBBB + hemiblock | | trifasicular block | block of both L and R bundles OR 1st deg AV block + bifasicular block | # Left anterior fasicular block, left posterior fasicular block | | LAFB | LPFB | | ------- | ---- | ---- | | Axis | LAD | RAD | | I, aVL | qR | rS | | II, III | rS | qR |