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Tachyarrhythmias: AFib, VT, and SVT — High-Yield for MRCP Part 1

TL;DR

For MRCP Part 1, tachyarrhythmias are tested through rapid ECG pattern recognition and safe first-line management. Atrial fibrillation is irregularly irregular, supraventricular tachycardia is a regular narrow-complex tachycardia, and ventricular tachycardia is a broad-complex tachycardia until proven otherwise. Exam success depends on identifying rhythm regularity, QRS width, and haemodynamic stability.


Why this topic matters for MRCP Part 1

Tachyarrhythmias are among the most frequently examined cardiology themes in MRCP Part 1. Questions typically combine a short clinical stem with an ECG description and ask for the most appropriate next step. Candidates are not expected to demonstrate advanced electrophysiology knowledge; instead, the exam rewards safe, guideline-aligned decision-making and avoidance of dangerous assumptions.

This article supports revision within the broader MRCP Part 1 curriculum and should be read alongside systematic ECG practice and question-bank exposure.

For an overview of the full exam structure, see the MRCP Part 1 overview:👉 https://crackmedicine.com/mrcp-part-1/


Scope of tachyarrhythmias in the exam

In MRCP Part 1, tachyarrhythmias are broadly approached using two questions:

  1. Is the rhythm narrow-complex or broad-complex?

  2. Is the patient haemodynamically stable?

From these, most answers follow logically.


Core differences at a glance

Feature

Atrial Fibrillation (AF)

Supraventricular Tachycardia (SVT)

Ventricular Tachycardia (VT)

Rhythm

Irregularly irregular

Regular

Usually regular

P waves

Absent

Hidden or retrograde

Absent / AV dissociation

QRS width

Narrow (unless BBB)

Narrow

Broad

Typical rate

110–180 bpm

150–250 bpm

120–250 bpm

Hallmark clue

Irregular pulse

Sudden onset/offset

Broad-complex rhythm

Exam principle

Rate control first

Vagal → adenosine

VT until proven otherwise

The 5 most tested subtopics

1. Atrial fibrillation: rate vs rhythm control

AF is the commonest arrhythmia tested. The exam focuses on recognition and safe initial management.

Key points:

  • No discrete P waves

  • Irregular R–R intervals

  • Ventricular rate often >120 bpm

In stable patients, rate control is first-line (beta-blockers or rate-limiting calcium channel blockers). Rhythm control and cardioversion are reserved for specific indications such as haemodynamic compromise or very recent onset.

Stroke prevention is often tested conceptually using CHA₂DS₂-VASc rather than detailed scoring.

Authoritative guidance:

2. Supraventricular tachycardia (SVT): think re-entry

SVT in MRCP questions usually refers to AV nodal re-entry tachycardia.

Classic exam stem:

  • Young patient

  • Sudden palpitations

  • Regular narrow-complex tachycardia at ~180–220 bpm

Management sequence:

  1. Vagal manoeuvres

  2. Adenosine, if vagal manoeuvres fail and no contraindication exists

Understanding this sequence is far more important than naming the exact re-entry circuit.

3. Ventricular tachycardia: default diagnosis

A core exam rule:

Any broad-complex tachycardia in an older patient or someone with structural heart disease is VT until proven otherwise.

Clues favouring VT:

  • Previous myocardial infarction

  • Cardiomyopathy

  • Capture or fusion beats

AV nodal blocking agents (e.g. verapamil) are dangerous if the rhythm is VT.

ESC reference:

4. Haemodynamic instability overrides rhythm classification

Across AF, SVT, and VT, the presence of instability changes management.

Signs of instability:

  • Hypotension

  • Chest pain

  • Acute pulmonary oedema

  • Syncope or shock

In these scenarios, synchronised DC cardioversion is the correct answer regardless of rhythm subtype.

5. ECG interpretation: what examiners really expect

MRCP Part 1 ECG questions are deliberately simplified.

High-yield approach:

  • Irregular rhythm → AF

  • Regular narrow-complex tachycardia → SVT

  • Broad-complex tachycardia → VT until proven otherwise

Subtle ECG features rarely determine the correct answer.


Concept: Candidate reviewing ECG printouts with notes and laptop

Mini-case (MRCP-style SBA)

Question A 72-year-old man with a history of anterior myocardial infarction presents with dizziness and palpitations. ECG shows a regular broad-complex tachycardia at 150 bpm. Blood pressure is 105/65 mmHg. What is the most appropriate next step?

Correct answer Treat as ventricular tachycardia.

Explanation In MRCP Part 1, a broad-complex tachycardia in a patient with ischaemic heart disease should always be assumed to be VT. Even if relatively stable, management must prioritise safety and avoid AV nodal blockers.


Common pitfalls (exam traps)

  • Assuming all regular tachycardias are SVT

  • Using adenosine in undifferentiated broad-complex tachycardia

  • Forgetting AF can present with a fast narrow-complex rhythm

  • Over-interpreting rare ECG signs

  • Ignoring haemodynamic instability

Practical study checklist

Use this during revision:

  1. Can I classify tachycardia by QRS width within 10 seconds?

  2. Do I default to VT when the rhythm is broad-complex?

  3. Can I identify AF purely from rhythm regularity?

  4. Do I know first-line management for stable patients?

  5. Can I recognise when cardioversion is required?

Reinforce these skills with timed ECG-based questions from the MRCP question bank:👉 https://crackmedicine.com/qbank/

Then test exam readiness using full-length practice papers:👉 https://crackmedicine.com/mock-tests/


FAQs

Is atrial fibrillation always a narrow-complex tachycardia?

Usually, but AF with bundle branch block or pre-excitation can appear broad. Irregularity remains the key diagnostic clue.

Can adenosine be used in all SVTs?

No. It is appropriate for regular narrow-complex tachycardias but should be avoided in irregular or broad-complex rhythms.

How often is ventricular tachycardia tested in MRCP Part 1?Very frequently, often indirectly as a “broad-complex tachycardia” scenario requiring safe management.

Do I need to memorise antiarrhythmic drug doses?

No. MRCP Part 1 tests choice of therapy rather than dosing details.


Ready to start?

If you want to convert ECG recognition into guaranteed exam marks, reinforce this topic with active practice:


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