Bifascicular Block A block of two of the
Bifascicular Block A block of two of the three conducting fascicles in the bundle of His. The resultant changes in heart muscle contraction coordination will influence the ECG. Right Bundle Branch Block (RBBB) and either a Left Anterior Fascicle Block (LAFB) Most commonly affected as thin and only supplied by LAD coronary artery (left axis deviation and conduction delay) or a Left Posterior Fascicle Block (LPFB) Dual blood supply so rarer (right axis deviation and conduction delay) ECG – RBBB + right or left axis deviation
Trifascicular Block Incomplete Fixed block of two fascicles and a delay in the third Bifascicular block + 1 st degree AV block Bifascicular block + 2 nd degree AV block RBBB + alternating LA/LP FB Causes IHD, hypertension, Aortic stenois, hyperkalaemia, Digoxin toxicity and primary degenerative disease (Lev’s/Legenere’s disease) Consequences Complete heart block Asystole Complete All three fascicles 3 rd degree AV block + ventricular escape rhythm (eg LAFB/LPFB + 3 rd degree AV block) Treatment Transcutaneous/venous pacing if unstable Permanent Pacemaker • Class I indication if symptomatic (syncope) • Class II indication with 2 nd degree AV block Atropine unlikely to work as block is below the AV node Avoid/stop medication affecting the AV node (Beta blockers, calcium channel blockers and digoxin)
Bi-fascicular block, left axis deviation + RBBB Incomplete tri-fascicular block – T 1 heart block + RBBB + left axis deviation Complete Tri-fascicular block – complete heart block + left axis deviation + RBBB Ref: LITFL FOAMed
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