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CARDIOLOGY

BLOCKS + BRADYCARDIA

PromptECG’s - 3rd degree heart block***, PR prolongation, Bifascicular block 
Response
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PromptBlock types
ResponseYou know this
1st = Discharge
2nd type 1 = Discharge
2nd type 2 = Admission/telemetry/correct underlying cause/pacing or PPM
3rd deg AV block = Oh Fuck. Resus.
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PromptBifascicular block – ECG findings and significance
ResponseEITHER
RBBB + LAFB (manifested as LAD)
RBBB + LPFB (manifested as RAD)
(in the absence of other causes)

Significance:
Bifascicular block can turn into 3rd degree heart block (may be intermittent >> Syncope, badness, etc)
In the context of chest pain bisfascicular block is highly associated with proximal LAD occlusion, even without ST changes.

Investigations:
Test for ischeamia – Stress echo, angiogram
Test for arrhythmias – Halter, Electrophysiology studies
Test for underlying structural heart disease and function – Echo
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PromptLeft anterior fascicular block (LAFB) Criteria
ResponseLAD
qR complexes in I + aVL (ie: tiny Q, Big tall R)
rS compexes in II, III, aVF
Prolonged R wave peak itime in aVL >45 mS
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PromptLeft Posterior Fascicular block (LPFB) Criteria
ResponseRAD
rS complexes in I+ aVL
qR complexes in II, III, aVF
prolonged R awave peak time in aVF
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PromptTifascicular block
ResponseConduction delay in all 3 fascicles below the AV node (RBBB, LAFB, LPFB)
Manifests as bifascicular block + 3rd degree AV block
EITHER
  • 3rd degree AV block + RBBB + LAFB (= LAD)
  • 3rd degree AV block + RBBB + LPFB (= RAD)
  • My notes from somewhere
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PromptLBBB ECG findings
ResponseQRS duration ≥ 120ms
Dominant S wave in V1
Broad monophasic R wave in lateral leads (I, aVL, V5-6) (V6: broad, notched (‘M’-shaped) R wave)
Absence of Q waves in lateral leads
Prolonged R wave peak time > 60ms in leads V5-6
Ischaemia = Sgarbossa Criteria
  • LITLF
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PromptRBBB ECG findings
ResponseQRS duration > 120ms
RSR’ pattern in V1-3 (“M-shaped” QRS complex)
Wide, slurred S wave in lateral leads (I, aVL, V5-6)
  • LITFL
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PromptCauses of heart block
(and bradycardia)
ResponseDrugs
  • Ca channel blockers, Beta blockers, Digoxin, amiodarone, organophosphages
  • PR prolongation – cholinergic agents, macrolides, Psychotropics
Electrolytes – Hyperkalaemia,

Ischaemia/Infarction
  • RCA in particular but any
Structural
  • Degenerative disease in conductive system, cardiac fibrosis
  • Infiltrative disorders eg: sarcoid, amyloid, SLE, systemic sclerosis
Hypothyroidism
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Prompt3rd degree HB management (Or symptomatic bradycardia)
ResponsePlace patient on 15L O2 via NRB – aim saturations >94%
Atropine 600 mics IV every 3-5 mins total dose 3mg. Aim HR >60 and SBP>90 or MAP >65

Haemodynamic resuscitation – IV fluids + endpoint
2nd line drug therapy – adrenaline or Isoprenaline:
Adrenaline 25-50 mic bolus at beside
Isoprenaline or adrenaline infusion + dose
  • Isoprenaline 2mg in 500 mL 5% dextrose (40 mics/mL) – star 0.05 mics/kg/min ~3mL/h and titrate to HR
Electrical management – failure to respond to pharmacotherapy will require external cardiac pacing at 70 BPM aiming for both electrical and mechanical capture at BP >90 or MAP >65
Analgesia with pacing – Fentanyl 15 mic IV aliquots Q5 min titrated to comfort. Sedation IV midazolam 1mg aliquots q5 min titrated to comfort
Seek and treat precipitant – Eg: calcium gluconate for hyperkalaemia

Disposition – ICU/Cath lab etc.
Endpoints – SBP>90, Pulse >50

Note: Atropine likely to fail in 3rd degree heart block (works on AV node which is often ischaemic) – poor answer. 600microg aliquots to 3mg
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PromptPros/cons different options
Response
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PromptCauses of bradycardia
ResponsePretty much the same as causes of heart block. Not repeated
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PromptBradycardia management
ResponsePretty much the same as treatment of heart block. Not repeated. Atropine probably more likely to work if nodal brady
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PromptExternal Pacing *** (maybe move to pacing?)
ResponseSee pacing.
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PromptBifascicular block importance and causes
ResponseSee above
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PromptInvestigations for Bifascicular block
ResponseSee above
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PromptMobitz 2 ECG
ResponseSame as 3rd deg
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PromptMobitz management
ResponseSame as 3rd deg
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PromptChemical pacing agents
ResponseIsoprenaline (B1 Agnoist) – 2mg in 500 mL D5W – 0.05 mics/kg/min – start 15 mL/hg
Adrenaline – 4mg/100 mL D5W – start 0.05 mics/kg/min = 3 mL/h
Dopamine
Dobutamine
??Insulin (HIET) if Beta blocker/CCB overdose and no response to above
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