PassFinals
Cardiovascular

Tachyarrhythmias

For an abnormal-origin tachyarrhythmia, first decide whether there is a pulse, then whether life-threatening adverse signs make the patient unstable; only a stable patient proceeds to classification by QRS width and regularity, while sinus tachycardia is treated by correcting its cause.

In a nutshell

Use a sequence, not a favourite drug: pulse first, then stability, then ECG classification. Pulseless VT or VF follows cardiac-arrest ALS; an unstable tachyarrhythmia with a pulse receives synchronised cardioversion; only a stable abnormal-origin rhythm branches by narrow or broad QRS and regular or irregular rhythm. Sinus tachycardia is treated by correcting its cause.

Core rule1,2

Pulse → stability → width → regularity. Never reverse that order, and do not use this antiarrhythmic pathway for sinus tachycardia.

First decisions

  1. Check for a pulse

    If absent, start CPR and use the ALS cardiac-arrest pathway; VF or pulseless VT requires unsynchronised defibrillation.2

  2. Start ABCDE care

    With a pulse, monitor ECG, blood pressure and SpO2, record a 12-lead ECG, obtain IV access, give oxygen only below 94% saturation and identify reversible causes.1

  3. Decide stability

    Any life-threatening adverse sign moves directly to synchronised cardioversion; reassess because a stable patient can deteriorate.1,2

  4. Classify only if stable

    Use QRS width under or at least 0.12 seconds, then regularity, to select the safe rhythm branch; seek expert help for uncertainty or persistence.1

Unstable tachyarrhythmia with a pulse

Synchronised cardioversion is the treatment when the tachyarrhythmia is causing life-threatening compromise.

  • Adverse signs: shock; syncope with severe or ongoing hypotension; myocardial ischaemia; severe heart failure with pulmonary oedema; or immediately post-ROSC.1
  • Give up to three synchronised shocks, checking R-wave synchronisation before each; use appropriate sedation or anaesthesia if conscious without delaying a life-saving shock.1,2
  • Initial energy: maximum defibrillator output for AF; 70–120 J for atrial flutter or paroxysmal SVT; 120–150 J for VT with a pulse, then increase as the RCUK pathway specifies.2
  • If still unstable after three attempts, give amiodarone 300 mg (see BNF) IV over 10–20 minutes or procainamide 10–15 mg/kg (see BNF), maximum 1 g (see BNF), IV over 20 minutes according to protocol, then repeat the synchronised shock.1,2

Stable rhythm branches1,2,6,4,3,7,8

ECG patternLikely rhythmImmediate pathwaySafety trap
Narrow + regularAVNRT, orthodromic AVRT; fixed-block flutter or atrial tachycardia may mimicModified Valsalva; if the tachycardia is not itself pre-excited, rapid IV adenosine 6 mg, then 12 mg, then 18 mg (see BNF), each with an immediate flush and under the locally authorised protocol; if ineffective seek expert help, then IV verapamil or an IV beta blocker, then synchronised shockAdenosine may reveal rather than terminate flutter or atrial tachycardia. A delta wave on the resting ECG does not by itself bar adenosine here, but keep a defibrillator to hand. Give verapamil or an IV beta blocker, never both
Narrow + irregularProbable AF; variable-block flutter or multifocal atrial tachycardiaConfirm the rhythm, then rate control by ejection fraction: above 40%, a beta blocker, verapamil, diltiazem or digoxin; below 40%, a beta blocker or digoxin, aiming in a stable patient for a rate below 110 per minute. Use the AF-specific anticoagulation and cardioversion pathwayDo not use the regular SVT adenosine pathway; avoid rate-limiting calcium-channel blockers below 40% ejection fraction and in acute decompensated heart failure
Broad + regularVT until a secure alternative is established; SVT with aberrancy is possibleTreat as VT with synchronised shock(s); when sedation or anaesthesia risk is too high, use the current RCUK procainamide or amiodarone route with expert help (see BNF). A rhythm securely known to be SVT with pre-existing aberrant conduction may use the narrow regular pathwayThe current RCUK V3 branch no longer presents amiodarone as the automatic first action for every stable regular broad-complex rhythm. If adenosine is trialled for suspected aberrancy and fails, revert to treating as VT
Broad + irregularPre-excited AF or polymorphic VT, including torsades with prolonged QTImmediate expert help; pre-excited AF: IV procainamide (see BNF) or cardioversion; prolonged-QT polymorphic VT: magnesium 8 mmol (see BNF) IV over 10 minutes and correct causesAvoid AV-nodal blockers in pre-excited AF and avoid amiodarone in prolonged-QT polymorphic VT

Medication traps

A drug that is appropriate for one stable branch may be dangerous in another.

  • Do not give adenosine, verapamil, diltiazem, beta blockers or digoxin in pre-excited AF; ESC also advises against IV amiodarone in this setting.3,1
  • What bars adenosine is a pre-excited tachycardia, meaning one that is broad and/or irregular, not a delta wave on the resting ECG. Adenosine can itself provoke atrial fibrillation, so have a defibrillator available when a manifest pathway is known.3,7
  • Verapamil and an IV beta blocker are alternatives, never a combination: simultaneous IV beta blockade is a listed contraindication to IV verapamil and can cause profound bradycardia or asystole.8,1
  • Before adenosine, check asthma or other bronchospastic lung disease, conduction disease, long-QT syndrome, hypotension, decompensated heart failure, dipyridamole or methylxanthine use and recent heart transplantation against the current BNF and product information.6,7
  • For probable AF with acute decompensated heart failure, obtain senior specialist advice on beta blockers and do not use verapamil or diltiazem.4
  • In prolonged-QT polymorphic VT, correct precipitants, use magnesium and expert rate acceleration where indicated, and avoid amiodarone.1

After conversion or stabilisation

  • Repeat and save the 12-lead ECG, all rhythm strips and the response to each intervention; the post-conversion tracing may reveal pre-excitation, QT abnormality, ischaemia or conduction disease.1,5,3
  • Continue monitored care after instability, post-ROSC rhythm, broad-complex tachycardia, recurrent episodes, ischaemia, heart failure, important electrolyte disturbance or unresolved diagnosis.2,1
  • Arrange rhythm-specific follow-up: electrophysiology for recurrent re-entrant SVT or flutter, an AF stroke-prevention and rate/rhythm plan, and ventricular-arrhythmia or inherited-cardiac-disease assessment where indicated.4,3,2
  • Arrhythmic syncope, an abnormal ECG, heart failure, exertional loss of consciousness or a family history of young sudden cardiac death requires the urgent cardiovascular-assessment pathway.5
  • Driving: no driving while waiting for specialist assessment after transient loss of consciousness, and the DVLA Group 1 standard is at least 4 weeks off driving with notification where an arrhythmia has caused or is likely to cause incapacity, or at least 2 days after uncomplicated catheter ablation without notification.5,9

Exam traps

  • Synchronised cardioversion is for a tachyarrhythmia with a pulse; VF or pulseless VT requires unsynchronised defibrillation through the cardiac-arrest algorithm.
  • A single past faint is clinically important, but the current immediate RCUK adverse sign is syncope with severe or ongoing hypotension.
  • Do not cardiovert or give an antiarrhythmic merely to normalise sinus tachycardia; find and treat the driver.
  • A broad-complex tachycardia is not safely relabelled SVT with aberrancy because the patient looks well; manage uncertainty as VT.
  • Adenosine can expose atrial flutter without terminating it, so a transiently slower ventricular rate is not successful rhythm conversion.
  • Pre-excited AF is irregular and broad: AV-nodal blockers can accelerate accessory-pathway conduction and provoke ventricular fibrillation.

Illustrations

Monomorphic ventricular tachycardia on ECGTwelve-lead ECG showing a rapid regular broad-complex monomorphic tachycardia. In an uncertain case, use the ventricular-tachycardia pathway unless a secure alternative diagnosis is established.Ksheka, Wikimedia Commons · CC-BY-SA-2.5

Key sources

  1. Resuscitation Council UK, Adult tachyarrhythmia algorithm V3 (updated March 2026) (RCUK Guidelines 2025, algorithm V3)
  2. Resuscitation Council UK, Adult advanced life support Guidelines (Resuscitation Council UK Guidelines 2025)Published 27 Oct 2025
  3. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia (doi:10.1093/eurheartj/ehz467)Published 31 Aug 2019
  4. NICE, Atrial fibrillation: diagnosis and management (NG196)Published 27 Apr 2021 | Updated 30 Jun 2021
  5. NICE, Transient loss of consciousness ('blackouts') in over 16s (CG109)Published 25 Aug 2010 | Updated 21 Nov 2023
  6. BNF, Adenosine
  7. Adenosine 3 mg/ml solution for injection, Summary of Product Characteristics (emc 11530)Updated 27 Nov 2025
  8. Verapamil 2.5 mg/ml Solution for injection, Summary of Product Characteristics (emc 979)
  9. DVLA, Assessing fitness to drive: cardiovascular disorders (DVLA Assessing fitness to drive)Updated 7 Nov 2025

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.