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Tachyarrhythmias
Is the patient unstable? Then the rhythm can wait — the shock can't. Check for adverse features first. If present, synchronised DC cardioversion. If not, sort the rhythm into four boxes — broad or narrow, regular or irregular — and treat accordingly. Built for revision, not live patient decisions.
Settle them, and check the basics
stable or unstable?Red flags — what each should make you think
Sinus tachycardia is not an arrhythmia to treat; it's a sign. Sepsis, bleeding, PE, pain, hypovolaemia and thyrotoxicosis all cause it. Never cardiovert or rate-control a sinus tachycardia; find the cause.
If adverse features are present (Resus Council UK)
- ⚡Synchronised DC cardioversion
- AmIf unsuccessful: amiodarone
- ∞Then amiodarone infusion
- O₂Oxygen if hypoxic, IV access
- K/MgCorrect electrolytes
- ☎Senior + anaesthetics
Understand the patient — the four boxes
stable patientBroad complex (QRS ≥0.12 s)
- Regular — assume VT: amiodarone 300 mg IV over 10–60 min, then 900 mg over 24 h. If previously confirmed SVT with bundle branch block, treat as narrow complex.
- Irregular — AF with bundle branch block (treat as AF); pre-excited AF (WPW: very fast, varying wide bizarre complexes) — avoid adenosine, digoxin, verapamil, diltiazem; seek expert help, consider cardioversion; torsades — magnesium 2 g IV over 10 min.
Narrow complex (QRS under 0.12 s)
- Regular — vagal manoeuvres first (modified Valsalva: strain, then lie flat with legs raised). Then adenosine 6 mg rapid IV bolus with flush, then 12 mg, then 18 mg, with ECG running. If adenosine reveals flutter waves → rate control.
- Irregular — probably AF: rate control with a beta-blocker (or diltiazem/verapamil if no heart failure; digoxin or amiodarone if heart failure); assess for anticoagulation. See the AF page.
Before adenosine: warn the patient (a brief sense of impending doom), use a large proximal vein, and avoid it in severe asthma. Reduce the dose if on dipyridamole or after heart transplant.
Work A–E — assess and act as you go
The diagnoses you must not miss
tap to open eachWhat points toward it, what would rule it in, and how to manage it.
Broad complex regular tachycardia, especially with IHD/cardiomyopathy. AV dissociation, capture or fusion beats, very wide QRS, concordance.
12-lead ECG; if in doubt, treat as VT.
Unstable → synchronised shock. Stable → amiodarone. Pulseless → ALS (unsynchronised defibrillation).
Irregularly irregular, very fast (can exceed 250/min), QRS width varying beat to beat. Delta wave on old ECG.
12-lead ECG; expert review.
Avoid AV-node blockers (adenosine, verapamil, diltiazem, digoxin, beta-blockers) — they can trigger VF. Cardioversion if unstable; expert advice for drugs.
Polymorphic VT with twisting axis; long QT, low K/Mg, QT-prolonging drugs.
ECG, K, Mg.
Magnesium sulfate 2 g IV over 10 min, correct K, stop culprit drugs; defibrillate if pulseless.
Sinus tachycardia or fast AF driven by sepsis, hypovolaemia, PE, thyrotoxicosis, pain.
Clinical + targeted tests.
Treat the cause. Rate-controlling a compensatory tachycardia can cause collapse.
Investigate — what to order, when, and what it tells you
test with a question in mind12-lead ECG
Bloods
Other
How the plan comes together
disposition · handoverhome
Terminated SVT with normal ECG, no structural heart disease, no adverse features. Teach vagal manoeuvres; refer to cardiology/arrhythmia clinic.
admit / CCU
VT, pre-excited AF, adverse features, recurrent episodes, abnormal echo, or any ischaemia.
Hand over: rhythm (with ECG), drugs/shocks given, electrolytes, current rhythm.
Unstable? Shock. Stable? Four boxes: broad or narrow, regular or irregular. And treat broad complex regular tachycardia as VT until proven otherwise. Nicely done getting here.
Clerking template
copy or downloadTachyarrhythmias — documentation structure
A structure and prompt list to help you document and think systematically. It is not a completeness check and cannot guarantee nothing is missed — use your trust's own proforma, your seniors, and your clinical judgement.
Test yourself
active recallCover the answer, say it out loud, then reveal. Retrieval beats re-reading.
0 / 11 knownFrequently asked questions
quick answersWhat are the red flags for a tachyarrhythmia?
- Shock (SBP below 90, cold, confused) — think adverse feature — cardiovert
- Syncope — think adverse feature
- Chest pain / ischaemic ECG — think adverse feature
- Heart failure — think adverse feature
- Broad complex regular — think VT until proven otherwise
- Irregular, very fast, broad, bizarre — think pre-excited AF — avoid AV-node blockers
- Polymorphic twisting VT — think torsades — magnesium
What is the initial management of a tachyarrhythmia?
- Synchronised DC cardioversion — up to 3 attempts, under sedation or general anaesthesia
- If unsuccessful: amiodarone — 300 mg IV over 10–20 min, then repeat the shock
- Then amiodarone infusion — 900 mg over 24 h
- Oxygen if hypoxic, IV access — monitor, 12-lead ECG when possible
- Correct electrolytes — potassium, magnesium, calcium
- Senior + anaesthetics — for sedation and airway
Always alongside senior support and your local guideline.
What diagnoses must you not miss in a tachyarrhythmia?
- Ventricular tachycardia — broad · regular
- Pre-excited AF (WPW) — irregular · very fast · bizarre
- Torsades de pointes — polymorphic · long QT
- Secondary tachycardia — sepsis · bleed · PE
Open each one in the must-not-miss section for what points toward it, how to rule it in, and how to manage it.
What investigations should a junior doctor order for a tachyarrhythmia?
- 12-lead ECG — QRS width, regularity, P waves, delta wave, QT, ischaemia.
- Bloods — K, Mg, Ca.
- Other — Structural heart disease.
Admit or discharge: how is the plan decided for a tachyarrhythmia?
- Home — Terminated SVT with normal ECG, no structural heart disease, no adverse features. Teach vagal manoeuvres; refer to cardiology/arrhythmia clinic.
- Admit / ccu — VT, pre-excited AF, adverse features, recurrent episodes, abnormal echo, or any ischaemia.
Is there a clerking template for a tachyarrhythmia?
Yes — there is a free clerking template for a tachyarrhythmia on this page, structured as presenting complaint, red flags asked, history, examination (A–E), investigations, differentials, plan and escalation. You can copy it or download it as a Word document. Jump to the template.
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