Overview — Arrhythmias Are a Symptom, Not the Disease
"New-onset atrial fibrillation in the critically ill is rarely a primary cardiac event — it is most often a marker of an underlying physiological insult: sepsis, hypovolaemia, hypoxia, electrolyte derangement, pain, or catecholamine excess. The first therapeutic question is never 'which antiarrhythmic?' but 'what is driving this rhythm?'. Correcting the precipitant frequently restores sinus rhythm without any rhythm-specific drug."
Washington Manual of Critical Care, 4th Ed. Wolters Kluwer 2023. Chapter: Cardiac Arrhythmias.The First Branch Point — Stable or Unstable?
Every tachyarrhythmia is triaged by the same question: is the patient haemodynamically unstable because of the rhythm? The four signs of instability are:
- Hypotension / shock — poor perfusion, mottling, lactate
- Acute altered mental status — reduced cerebral perfusion
- Ischaemic chest pain — rate-related demand ischaemia
- Acute heart failure / pulmonary oedema
If instability is caused by the arrhythmia → immediate synchronised DC cardioversion (for tachyarrhythmias with a pulse). If the patient is stable → there is time to identify the rhythm and treat pharmacologically.
Before and alongside rhythm treatment, correct: hypoxia, hypovolaemia, electrolytes (K⁺, Mg²⁺, Ca²⁺), acidosis, sepsis/fever, pain & agitation, anaemia, hyperthyroidism, drug effects (inotropes, aminophylline), PE, and myocardial ischaemia. Magnesium is the most commonly under-replaced — keep Mg²⁺ >1.0 mmol/L (ideally >1.0–1.2) in any ICU arrhythmia.
Marino Physiology — Rate, Filling & the Cost of Losing Atrial Kick
"Two consequences of a sustained tachyarrhythmia threaten the critically ill heart. First, diastole shortens disproportionately as heart rate rises, curtailing both ventricular filling and coronary perfusion — which occurs almost entirely in diastole. Second, the loss of organised atrial contraction removes the atrial 'kick', which contributes up to 25–30% of ventricular filling in a stiff or poorly compliant ventricle. In the patient who depends on preload, this combination can precipitate abrupt cardiovascular collapse."
Marino PL. The ICU Book, 5th Ed. Tachyarrhythmias. Wolters Kluwer; 2025.In rapid AF, the very fast ventricular rate is often counter-productive: shortened diastole means each beat fills less, so stroke volume falls and cardiac output can drop despite the high rate. Slowing the rate (target initially <110/min, "lenient" control) lengthens diastole, improves filling, restores coronary perfusion, and frequently raises blood pressure. This is why a rate-controlling agent — not a pressor — is often the correct first move in a hypotensive patient whose hypotension is rate-driven.
Magnesium suppresses triggered activity and is first-line for torsades de pointes (2 g IV over 1–2 min, even when serum Mg is normal). It also slows AV nodal conduction (useful adjunct in rapid AF) and reduces post-operative AF. Hypomagnesaemia is common in the ICU (diuretics, GI losses, alcohol, refeeding) and frequently coexists with hypokalaemia — replacing K⁺ without Mg²⁺ often fails because hypomagnesaemia drives renal K⁺ wasting.
- Irregularly irregular, no P waves → atrial fibrillation
- Regular, narrow, rate ~150 → think atrial flutter with 2:1 block (flutter rate ~300) or AVNRT/AVRT
- Regular, narrow, rate 100–160 with visible P of varying morphology → sinus tachycardia or (multifocal) atrial tachycardia — MAT is classic in decompensated COPD; do NOT cardiovert, treat the lung disease
- Regular, WIDE complex → assume VT until proven otherwise, especially with structural heart disease
Synchronised Cardioversion — When the Rhythm Is Killing the Patient
⚡ Unstable Tachycardia WITH a Pulse (ACLS)
Synchronise for organised rhythms with a pulse (AF, flutter, SVT, monomorphic VT) — the shock is timed to the R wave to avoid the vulnerable T-wave period (R-on-T → VF). Do NOT synchronise for pulseless VT/VF or polymorphic VT — the defibrillator may fail to find an R wave and never discharge; deliver an immediate high-energy unsynchronised shock instead.
The Stable Patient in Rapid AF
🔵 Rate Control (usual first choice)
- Target: <110/min lenient (RACE II); tighter if symptomatic
- Beta-blocker: metoprolol 2.5–5 mg IV q5min, or esmolol infusion (titratable, short-acting)
- Non-DHP CCB: diltiazem 0.25 mg/kg IV — avoid in HFrEF / hypotension
- Digoxin: add-on in heart failure / hypotension (works at rest, weak in high-catecholamine states)
- Amiodarone: rate control when others contraindicated (sepsis, shock) — also a "soft" rhythm agent
🟠 Rhythm Control (selected cases)
- When: AF clearly driving instability, recent onset, reversible trigger treated, or fails rate control
- Electrical: synchronised DCCV (most effective)
- Chemical: amiodarone (safe in structural disease / low EF); flecainide/propafenone ONLY if structurally normal heart
- Timing & clot risk: if AF >48h (or unknown), cardioversion risks thromboembolism — anticoagulate or exclude LA thrombus on TOE first (unless unstable)
New AF complicates ~10–15% of severe sepsis. It is usually driven by the septic state (catecholamines, inflammation, volume shifts, hypomagnesaemia). Priorities: treat the sepsis, optimise volume, replace K⁺ and Mg²⁺. If pharmacological rate control is needed in a vasoplegic patient, amiodarone is often preferred (less hypotension than beta-blockers/diltiazem). Many patients revert spontaneously as the sepsis resolves. Cardioversion has a high early recurrence rate while the driver persists.
Other Tachyarrhythmias You Will Meet
2. Adenosine 6 mg rapid IV push + 20 mL flush → 12 mg → 12 mg. Warn the patient (brief chest tightness, impending-doom feeling, transient asystole). Continuous ECG/rhythm strip — diagnostic if it unmasks flutter waves.
3. If recurs/refractory: diltiazem or beta-blocker. Avoid adenosine in severe asthma → bronchospasm
Stable: amiodarone 300 mg IV over 20–60 min (or procainamide). Unstable: synchronised DCCV.
Never give an AV-nodal blocker (verapamil/diltiazem) to a WCT you cannot confidently call SVT — it can precipitate haemodynamic collapse in VT and in pre-excited AF.
Multifocal atrial tachycardia (MAT) is common in our large burden of decompensated COPD/cor pulmonale — recognise it (≥3 distinct P-wave morphologies, irregular), do NOT cardiovert; treat hypoxia, theophylline toxicity and electrolytes; verapamil or metoprolol if rate control needed (beta-blocker cautious in bronchospasm).
Drug availability: esmolol may be limited in smaller centres — metoprolol IV and diltiazem are widely available. Amiodarone is the ICU workhorse. Streptokinase-era allergy notes do not apply here. Ensure magnesium sulphate (widely stocked for eclampsia) is used proactively.
Drug Reference — ICU Tachyarrhythmias
| Drug | Indication | Dose | Cautions |
|---|---|---|---|
| Metoprolol IV | Rate control AF/flutter, SVT | 2.5–5 mg IV over 2 min, repeat q5min up to 15 mg | Avoid in decompensated HF, severe bronchospasm, hypotension |
| Esmolol | Titratable rate control | 500 µg/kg bolus → 50–200 µg/kg/min infusion | Ultra-short acting — ideal if unsure of tolerance |
| Diltiazem | Rate control AF (preserved EF) | 0.25 mg/kg IV over 2 min → 5–15 mg/h infusion | Avoid in HFrEF, hypotension, WPW-AF |
| Amiodarone | AF/VT, rate & rhythm in shock/HF | 300 mg IV over 20–60 min → 900 mg/24h; arrest VT/VF: 300 mg bolus | Phlebitis (central line for infusion); dilute in D5W; hypotension if pushed fast |
| Digoxin | Rate control add-on (HF/hypotension) | 500 µg IV → 250 µg q6h ×2 (load ~1 mg/24h) | Weak in high-catecholamine states; toxicity in renal failure / hypokalaemia |
| Adenosine | Regular narrow SVT (diagnose/treat) | 6 mg rapid IV push + flush → 12 mg → 12 mg | Avoid in asthma; warn patient; transient asystole expected |
| Magnesium sulphate | Torsades; AF adjunct; post-op AF | 2 g IV over 1–2 min (torsades); 2 g over 20 min (AF) | Monitor reflexes; caution in renal failure |
| Flecainide / Propafenone | Pharmacological cardioversion AF | Flecainide 2 mg/kg IV (max 150 mg) over 10 min | ONLY structurally normal heart — proarrhythmic in ischaemia/HF |
Narrow regular (SVT): 50–100 J · Atrial flutter: 50 J · Atrial fibrillation: 120–200 J · Monomorphic VT (with pulse): 100 J · Polymorphic VT / pulseless: max-energy UNsynchronised. Always sedate the conscious patient; ensure the SYNC button is re-armed before each shock (most defibrillators drop out of sync mode after a discharge).
Thromboembolic Risk in AF
Anticoagulate if score ≥2 (men) / ≥3 (women) AHA/ACC 2023, ESC 2024. DOAC preferred over warfarin (except mechanical valve or moderate–severe mitral stenosis → warfarin). Assess bleeding with HAS-BLED (modifiable factors), but a high HAS-BLED is NOT a reason to withhold anticoagulation.
ICU caveat: Critically ill patients frequently have competing high bleeding risk (post-op, thrombocytopenia, planned procedures). Anticoagulation decisions for new ICU AF are individualised and often deferred until the acute bleeding risk settles — but document the plan and reassess daily so it is not forgotten at discharge.
Common Mistakes in ICU Arrhythmia Management
Cardioverting sinus tachycardia or MAT because the number is high is harmful. Sinus tachycardia is a compensatory response (hypovolaemia, sepsis, pain, PE) — slowing it removes a needed compensation and can cause collapse. Always confirm the rhythm and ask what is driving it before treating.
In AF with WPW (irregular, wide, very fast — often >250/min), verapamil, diltiazem, digoxin and adenosine block the AV node and accelerate conduction down the accessory pathway → VF. Use synchronised DCCV (or procainamide if stable). The same "assume VT" caution applies to any wide irregular tachycardia.
Most defibrillators revert to unsynchronised mode after each synchronised shock. If a second cardioversion is needed, the SYNC button must be pressed again — otherwise either the shock lands on the T wave (R-on-T → VF) or, if you intended sync, the machine waits for an R wave it cannot find and never fires.
Hypomagnesaemia causes renal potassium wasting, so hypokalaemia is refractory until Mg²⁺ is corrected. In any ICU arrhythmia, replace both — and keep K⁺ 4.5–5.0 and Mg²⁺ >1.0 mmol/L. This single habit prevents a large fraction of ICU tachyarrhythmias and torsades.
Rapid amiodarone bolus causes hypotension (vasodilatory solvent effect). Outside cardiac arrest, give the loading dose over 20–60 minutes and use a central line for ongoing infusion (peripheral phlebitis). Dilute in 5% dextrose — it precipitates in saline.
Restoring sinus rhythm in AF of >48 h (or unknown duration) without prior anticoagulation or TOE risks dislodging a left atrial appendage thrombus → embolic stroke. Unless the patient is unstable, exclude thrombus (TOE) or anticoagulate for 3 weeks first, and anticoagulate ≥4 weeks afterwards.
References
- Joglar JA, Chung MK, Armbruster AL et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation. Circulation 2024;149:e1–e156.
- Van Gelder IC, Rienstra M, Bunting KV et al. 2024 ESC Guidelines for the management of atrial fibrillation. Eur Heart J 2024;45:3314–3414.
- Panchal AR, Bartos JA, Cabañas JG et al. Part 3: Adult Basic and Advanced Life Support: 2020 AHA Guidelines for CPR and ECC. Circulation 2020;142(suppl 2):S366–S468.
- Van Gelder IC, Groenveld HF, Crijns HJ et al. (RACE II). Lenient versus strict rate control in patients with atrial fibrillation. N Engl J Med 2010;362:1363–1373.
- Appelboam A, Reuben A, Mann C et al. (REVERT). Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias. Lancet 2015;386:1747–1753.
- Marino PL. The ICU Book, 5th Ed. Tachyarrhythmias. Wolters Kluwer; 2025.
- Irwin RS, Rippe JM. Irwin and Rippe's Intensive Care Medicine, 8th Ed. Supraventricular & Ventricular Arrhythmias. Wolters Kluwer; 2018.
- Washington Manual of Critical Care, 4th Ed. Chapter: Cardiac Arrhythmias. Wolters Kluwer 2023.