Bradycardia and AV Block — SAQ

Stem

A candidate is asked to manage a classic presentation of Bradycardia and AV Block in an exam setting. Use precise definitions, scores, doses, and decision thresholds.

Core knowledge (model answer backbone)

Bradyarrhythmia in adults means a resting heart rate below 60 bpm (the clinical threshold drops to below 50 bpm when truly symptomatic, and athletic resting bradycardia of 30 to 40 bpm is physiological). The two master categories are sinus node dysfunction (sinus bradycardia, sinus arrest, sinoatrial block, sick sinus syndrome) and atrioventricular (AV) block — 1st degree (PR over 200 ms, benign), 2nd degree Mobitz I (Wenckebach, usually benign, AV nodal, atropine-responsive), 2nd degree Mobitz II (infranodal, high risk of progression to complete block, Class I indication for pacing even when asymptomatic), and 3rd degree (complete heart block, AV dissociation, Class I pacing). Common aetiologies include age-related idiopathic fibrosis and calcification (Lev disease and Lenegre disease), inferior MI with right coronary artery occlusion supplying the AV node, iatrogenic drug toxicity (beta-blocker, calcium-channel blocker, digoxin), electrolyte disturbance (hyperkalaemia, hypermagnesaemia), post-cardiac surgery (aortic valve replacement, septal myectomy, TAVI, congenital repair), Lyme carditis, Chagas disease, sarcoidosis, amyloidosis, myocarditis, and high vagal tone (athletes, sle

Red flags

• Asystolic pause over 5 seconds (or any pause causing syncope) — Stokes-Adams attack; emergency pacing and permanent device work-up
• Complete heart block with wide-complex escape (ventricular rate under 40, unstable) — haemodynamic collapse imminent; emergency pacing (transcutaneous, isoprenaline, transvenous)
• Mobitz II 2nd-degree AV block — high risk of progression to complete block; admission and permanent pacing (Class I) even when asymptomatic
• Bradycardia in inferior MI — atrioventricular nodal block from right coronary occlusion; usually self-limiting but supportive pacing required for syncope or hypotension

High-yield structure examiners expect

Cover: Overview & Definition, Classification, Epidemiology & Risk Factors, Pathophysiology, Clinical Presentation, Differential Diagnosis.

Key doses / thresholds (from topic teaching)

• atropine 500 mcg IV bolus (max 3 mg)**, **isoprenaline 5
• adrenaline 1 mg IV** in arrest, **transcutaneous then t
• Repeat every 3 to 5 min to a maximum of 3 mg total" }
• typically above 6.5 mmol/L), hypermagnesaemia, severe **hypo
• atropine 500 mcg IV bolus**, repeat every 3 to 5 minutes
• titrated up to 20 mcg/min** OR **adrenaline (epinephrine) 2 t

Questions

a) Define the condition and give the most important classification or severity framework used in exams. (3 marks)

• Clear one-line definition matching standard teaching.
• Named classification / stages / types with discriminating features.
• One sentence on why classification changes management.

b) Outline pathophysiology in a mechanism chain that explains the main clinical features. (3 marks)

• Initiating insult → intermediate pathway → end-organ effect.
• Link at least two symptoms/signs to mechanism.
• Mention one complication pathway (e.g. shock, perforation, herniation, arrhythmia).

c) List discriminating clinical features and bedside assessment. (3 marks)

• Classic presentation plus one atypical group (elderly, pregnancy, child, immunocompromised).
• Named signs/manoeuvres if relevant.
• What must never be missed on exam/bedside (pregnancy test, airway, glucose, etc.).

d) Investigations with thresholds and one named score if applicable. (3 marks)

• First-line tests and what positive findings mean.
• Gold-standard or definitive investigation when needed.
• Score components reproduced exactly if a named score is standard for this topic.

e) Immediate resuscitation and definitive management with doses where standard. (3 marks)

• ABC / time-critical steps first.
• First-line drug(s) with agent + dose + route (or procedure steps).
• Escalation triggers (theatre, ICU, thrombolysis window, antidote, etc.).
• Disposition and safety-netting.

Marking tips

Full marks require specificity (numbers, names, doses) not generic "give antibiotics/fluids." Regional practice (ICMR / NICE / AHA) may be cited as alternative where relevant.