# Bradyarrhythmias and Pacemakers

> Bradyarrhythmias and pacemakers for NEET-SS Cardiology: block localisation, pacing indications, NBG codes and post-implant care in exam notes.

- Canonical URL: https://prepelephant.com/topics/neet-ss/cardiology/bradyarrhythmias-and-pacemakers
- Exam / course: NEET-SS · Subject: Cardiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Bradyarrhythmias and Pacemakers", PrepElephant, https://prepelephant.com/topics/neet-ss/cardiology/bradyarrhythmias-and-pacemakers

## Direct answer

Bradyarrhythmias arise from sinus node dysfunction or atrioventricular conduction disease, and the first task is localisation: Mobitz I (Wenckebach) block with a narrow QRS is usually AV-nodal, often transient and managed conservatively, whereas Mobitz II and third-degree block with a wide QRS are infranodal, carry Stokes-Adams risk and need pacing. Exclude reversible causes first — rate-limiting drugs, hyperkalaemia, ischaemia (AV-nodal in inferior infarction, infranodal with poor prognosis in anterior infarction), hypothyroidism and Lyme disease. Pacemaker nomenclature (NBG code) describes the chamber paced, sensed, the response and rate modulation.

## What you must remember

- **ECG localisation:** Mobitz I shows progressive PR prolongation before a dropped beat (usually AV-nodal, benign); Mobitz II shows sudden dropped beats without PR change (infranodal, dangerous); complete heart block shows AV dissociation with a narrow junctional escape of 40–50 beats per minute (often congenital, better tolerated) or a wide ventricular escape of 20–40 (syncope-prone).
- **Pacing indications:** symptomatic sinus node dysfunction including tachy-brady syndrome; Mobitz II and third-degree atrioventricular block regardless of symptoms; alternating bundle branch block; symptomatic pauses.
- **Reversible causes and their acute care:** withhold offending drugs (beta-blockers, calcium channel blockers, digoxin, amiodarone); intravenous atropine 1 mg repeated — unreliable below the AV node and in transplanted hearts; transcutaneous pacing as a bridge; chronotropic infusions; glucagon for beta-blocker toxicity; calcium and insulin-dextrose for hyperkalaemia.
- **Infarction context:** inferior infarction causes AV-nodal block that is usually transient (atropine, temporary wire if needed); anterior infarction causes infranodal block with wide complexes — temporary pacing, frequently progressing to permanent implantation.
- **NBG code:** first letter — chamber paced (A, V, D); second — chamber sensed; third — response; fourth — rate modulation; in practice VVI for atrial fibrillation with slow rates, DDD for sinus rhythm, biventricular for resynchronisation.
- **Device follow-up and complications:** regular threshold, sensing and impedance checks; pneumothorax, lead dislodgement and pocket infection; pacemaker syndrome from VVI pacing in sinus rhythm; MRI-conditional protocols; leadless pacemakers in selected patients.

## Common confusion

Physiological bradycardia is over-treated: asymptomatic pauses in trained athletes and sleep-related slowing need no device. Candidates mislabel Wenckebach as dangerous — with a narrow QRS it rarely is — while under-calling Mobitz II, which is paced regardless of symptoms. Atropine is another trap: it can worsen infranodal block by accelerating the sinus rate against a fixed distal substrate; below the node, pacing is the answer.

## Exam-focused takeaway

Stems pair an ECG with a symptom and ask for disposition: asymptomatic Wenckebach (observe), syncope with wide-complex complete block (permanent pacemaker), bradycardia after inferior infarction (atropine and observation), or beta-blocker toxicity with a potassium of 7 (calcium first). NBG-code questions ask you to expand VVIR or DDD. Anchor each block type to its escape rhythm and prognosis.

## Frequently asked questions

### How are Mobitz I and Mobitz II blocks managed differently?

Mobitz I with a narrow QRS is usually AV-nodal and observed if asymptomatic; Mobitz II and third-degree block are infranodal and merit pacemaker implantation regardless of symptoms.

### Why does atropine sometimes fail in complete heart block?

Atropine acts at the AV node; infranodal block with a wide ventricular escape does not respond and may worsen — transcutaneous or transvenous pacing is required.

### What does the NBG pacemaker code describe?

Chamber paced, chamber sensed, sensing response, and rate modulation — for example, DDDR paces and senses both chambers with dual response and rate adaptation.

### Which bradycardic patterns need no pacemaker?

Asymptomatic sinus bradycardia in athletes, sleep-related pauses, and asymptomatic Mobitz I with a narrow QRS.

### How does infarct location predict block behaviour?

Inferior infarction produces transient AV-nodal block; anterior infarction produces infranodal, wide-complex block needing temporary then often permanent pacing.