Dysrhythmias: Recognition, ECG Assessment and Emergency Management

Learning objectives

• Describe normal conduction and the main categories of tachyarrhythmia, bradyarrhythmia and heart block.
• Use a systematic ECG approach including rate, rhythm, P waves, PR interval, QRS width and ST-T changes.
• Recognise instability, cardiac arrest rhythms and reversible causes.
• Outline emergency pathways for narrow-complex tachycardia, atrial fibrillation/flutter, wide-complex tachycardia, bradycardia, torsades, VF and heart block.
• Plan monitoring, medication safety, synchronized cardioversion, pacing, nursing care and discharge education.

Electrical pathway and terminology

The sinoatrial node normally initiates an impulse that travels through the atria, atrioventricular node, His bundle, bundle branches and Purkinje network. Dysrhythmias can arise from abnormal automaticity, re-entry, triggered activity or failure of conduction. A tachyarrhythmia is usually a rate above 100/min in an adult at rest, while clinically important bradyarrhythmia is commonly below 50/min with symptoms or poor perfusion. The number alone never replaces assessment of perfusion and the cause.

• Sinus tachycardia: a physiological response to pain, fever, hypoxia, dehydration, anaemia, shock or drugs; treat the cause.
• Supraventricular tachycardia: usually a regular narrow-complex re-entry rhythm with sudden onset and termination.
• Atrial fibrillation: absent organised P waves and an irregularly irregular ventricular response; raises thromboembolic stroke risk.
• Atrial flutter: organised atrial activity, often saw-tooth flutter waves, with variable AV block.
• Ventricular tachycardia: a broad-complex ventricular rhythm that may be stable, unstable or pulseless.
• Bradyarrhythmia/heart block: sinus-node disease, AV block, drug toxicity, ischaemia, electrolyte disturbance or increased vagal tone.

First contact and immediate safety

1. Check responsiveness, breathing and a central pulse. If pulseless or not breathing normally, start CPR, attach a defibrillator and follow the cardiac-arrest algorithm.
2. Call for help, bring the resuscitation trolley, apply ECG/SpO₂/BP monitoring and place defibrillator pads early when the rhythm is fast, broad or unstable.
3. Look at the patient before the screen: chest pain, dyspnoea, syncope, shock, confusion, seizure, pulmonary oedema and severe ongoing symptoms indicate instability.
4. Obtain IV access, a 12-lead ECG during the rhythm and a repeat ECG after treatment. Save and label rhythm strips.
5. Give oxygen only for hypoxaemia or respiratory distress; unnecessary hyperoxia is not a substitute for rhythm treatment.

ABCDE and instability assessment

Systematic ECG approach

1. Rate: calculate ventricular rate and note whether it is slow, normal or fast.
2. Rhythm: regular, regularly irregular or irregularly irregular; compare monitor and pulse for pulse deficit.
3. P waves: present and consistent, hidden, fluttering, fibrillatory or dissociated from QRS?
4. PR interval: constant, prolonged, progressively lengthening or unrelated to QRS?
5. QRS width: narrow suggests supraventricular origin; a wide complex may be ventricular, aberrant, pre-excited or due to hyperkalaemia. Treat an uncertain wide-complex tachycardia as VT until proven otherwise.
6. QT interval: prolonged QT increases torsades risk, especially with hypokalaemia, hypomagnesaemia and QT-prolonging medicines.
7. ST-T changes: look for ischaemia, infarction, hyperkalaemia or post-arrhythmia changes.
8. Compare: obtain previous ECGs and document onset, duration, symptoms and treatments.

Reversible causes

Stable versus unstable tachyarrhythmia

Stability is determined by perfusion and symptoms, not by a fixed heart-rate threshold. Unstable features include hypotension, shock, altered mental state, ischaemic chest pain and acute pulmonary oedema/heart failure.

• Unstable with a pulse: call for senior help, provide oxygen if hypoxaemic, sedate if feasible without delaying treatment and perform synchronized cardioversion using the local energy algorithm. If synchronization fails and the patient is crashing, follow the unsynchronized shock/ALS pathway.
• Stable narrow regular tachycardia: vagal manoeuvres may be attempted in a monitored patient; use adenosine only when the rhythm and contraindications have been checked and a trained prescriber is present.
• Stable irregular narrow rhythm: assess atrial fibrillation/flutter, rate, duration, anticoagulation status, heart failure and precipitating illness; involve a senior clinician for rate/rhythm and stroke-prevention decisions.
• Stable wide-complex tachycardia: treat as VT until proven otherwise, monitor continuously, obtain expert advice and use a local antiarrhythmic protocol.

Narrow-complex supraventricular tachycardia

• Usually sudden-onset, regular rhythm with narrow QRS and rates commonly 150–250/min.
• Assess for pre-excitation, asthma, heart failure, hypotension and irregularity before adenosine.
• In a cooperative stable adult, a monitored vagal manoeuvre may terminate AVNRT/AVRT; carotid sinus massage is avoided in carotid disease, bruit, prior stroke/TIA or uncertain diagnosis.
• Adenosine is a rapid IV medicine requiring ECG capture, resuscitation equipment and explanation of transient flushing or chest discomfort. Follow the local dose and contraindication protocol.
• If unsuccessful or contraindicated, obtain expert advice for an alternative agent or synchronized cardioversion.
• Investigate triggers such as infection, stimulant use, thyroid disease, anaemia and electrolyte abnormality after conversion.

Atrial fibrillation and atrial flutter

AF produces chaotic atrial activity and an irregular ventricular response; flutter commonly produces organised atrial activity with variable conduction. Emergency priorities are haemodynamic stability, ventricular rate, duration/onset, precipitating illness and embolic risk.

1. If unstable, perform synchronized cardioversion under senior guidance; manage airway, oxygenation and sedation safely.
2. If stable, treat fever, hypoxia, sepsis, electrolyte disturbance, ACS, heart failure and thyrotoxicosis.
3. Obtain duration of the rhythm, previous episodes, anticoagulant adherence, bleeding risk and stroke-risk factors before elective cardioversion.
4. Rate-control medicines require caution in hypotension, acute heart failure, pre-excitation and asthma; selection is a prescriber decision.
5. Anticoagulation and cardioversion timing follow current local/ESC guidance; never give or stop anticoagulants casually.
6. Document rhythm strips before and after treatment and arrange cardiology follow-up.

Wide-complex tachycardia and ventricular tachycardia

A broad-complex tachycardia may be VT, SVT with aberrancy, pre-excited AF or metabolic toxicity. Because misclassification can be fatal, an uncertain regular broad-complex rhythm is managed as VT.

• Check pulse and perfusion. Pulseless VT is a shockable cardiac-arrest rhythm: CPR, defibrillation and ALS medicines according to protocol.
• With a pulse but instability, perform synchronized cardioversion immediately.
• With a stable monomorphic VT, continuous monitoring, IV access, 12-lead ECG, senior consultation and a local antiarrhythmic pathway are required.
• Polymorphic VT or torsades requires urgent correction of QT-prolonging causes, magnesium according to protocol and immediate defibrillation if unstable or pulseless.
• Look for ACS, cardiomyopathy, hypokalaemia, hypomagnesaemia, drug toxicity and inherited channelopathy.
• Do not give AV-nodal blockers to an irregular wide-complex rhythm that could be pre-excited AF.

Bradycardia and heart block

Bradycardia may be physiological or a sign of infarction, hypoxia, hypothermia, drug toxicity, hyperkalaemia, raised intracranial pressure or conduction-system disease. Treat symptomatic bradycardia with poor perfusion rather than treating a number in isolation.

1. Assess airway, breathing, circulation, mental state, chest pain, syncope and shock; apply monitor, pads and obtain ECG.
2. Correct reversible causes, stop suspected causative medicines and check glucose/electrolytes.
3. For unstable symptomatic bradycardia, follow the local atropine and pacing algorithm. Prepare transcutaneous pacing early when high-grade AV block is suspected.
4. If atropine is ineffective or contraindicated, use chronotropic infusion and arrange transvenous pacing under senior critical-care/cardiology direction.
5. Mobitz II, complete heart block, alternating bundle-branch block, ventricular pauses and recurrent syncope require urgent specialist review and monitored admission.
6. Provide analgesia/sedation for pacing when safe, but never allow sedation to delay treatment of deteriorating perfusion.

Atrial and ventricular ectopics

Isolated premature beats are common and may be triggered by stress, caffeine, hypoxia, electrolyte abnormality or structural disease. Frequent, multifocal or repetitive ectopics, couplets, runs, syncope, chest pain or a family history of sudden death require ECG review, electrolytes and specialist assessment.

Investigations and disposition

• 12-lead ECG during symptoms and repeat after conversion; save rhythm strips.
• FBC, glucose, electrolytes including potassium/magnesium/calcium, renal function, troponin and pregnancy test where relevant.
• Chest imaging, blood gas, echocardiography or toxicology tests when guided by presentation.
• Admit unstable patients, those needing cardioversion/pacing, wide-complex rhythms, high-grade block, prolonged QT, ACS, heart failure or serious underlying disease.
• Discharge only after a senior review confirms a safe rhythm, corrected triggers, reliable follow-up and explicit return precautions.

Medication and procedure safety

• Attach ECG and defibrillator monitoring before IV antiarrhythmics or adenosine.
• Use synchronized mode for cardioversion when a pulse is present; confirm synchronization markers before delivering a shock.
• Ensure analgesia/sedation is titrated and airway equipment is available for electrical therapy.
• After a shock or medicine, reassess rhythm, perfusion, ECG intervals, electrolytes and neurological status.

Nursing interventions and monitoring

• Record symptoms, onset, rhythm, vital signs, consciousness, chest pain score, oxygen requirement and urine output.
• Maintain continuous ECG for unstable or treated patients; print and label rhythm strips before/after interventions.
• Check IV patency and flush adenosine rapidly through a proximal line as prescribed; document transient effects and conversion.
• Monitor for hypotension, bradycardia, bronchospasm, worsening heart failure, QT prolongation, sedation and recurrent dysrhythmia.
• For pacing, confirm electrical and mechanical capture, skin condition, comfort and battery/pad placement.
• Use SBAR handover with rhythm diagnosis, stability, treatment, response, pending tests and escalation plan.

Patient education and prevention

• Explain the rhythm in plain language and provide written medicine and follow-up instructions.
• Review stimulant use, alcohol, smoking, sleep, thyroid disease, medication adherence and electrolyte-loss illness.
• Teach return precautions: syncope, chest pain, breathlessness, new weakness, sustained palpitations, seizure or severe dizziness.
• Patients prescribed anticoagulants need adherence, bleeding precautions and review of interacting medicines.
• Patients with implanted devices need device-card information, wound care and urgent review for shocks, syncope or fever.

Clinical scenarios

Common errors to avoid

• Treating the monitor number without assessing perfusion or the underlying cause.
• Calling every fast rhythm SVT or every broad rhythm SVT with aberrancy.
• Giving AV-nodal blockers to possible pre-excited AF or unstable wide-complex tachycardia.
• Delaying cardioversion in shock, ischaemia, pulmonary oedema or altered consciousness.
• Ignoring electrolyte abnormalities, QT-prolonging medicines, ACS, sepsis or hypoxia.
• Failing to print an ECG, document onset or reassess after conversion.
• Discharging a patient with high-grade block, recurrent syncope or unexplained ventricular arrhythmia.

Revision questions

1. What features make a tachyarrhythmia unstable?
2. How do you systematically analyse a 12-lead ECG?
3. Why should an uncertain broad-complex tachycardia be treated as VT?
4. Describe the immediate care of pulseless VT/VF.
5. When is synchronized cardioversion indicated?
6. What reversible causes should be sought in bradycardia and tachycardia?
7. List the nursing observations required after adenosine, cardioversion or pacing.

Key takeaways

• Stability and perfusion determine urgency more than the heart rate alone.
• Obtain and interpret a 12-lead ECG while treating ABCDE threats.
• Unstable tachyarrhythmia needs synchronized cardioversion; pulseless VT/VF needs defibrillation and CPR.
• Symptomatic bradycardia may require atropine, pacing or chronotropic support.
• Correct hypoxia, ischaemia, sepsis, electrolyte disturbance and drug toxicity.
• Document rhythm strips, treatment response and a safe follow-up plan.

References for further study

• American Heart Association: 2025 ACLS algorithms
• Resuscitation Council UK: ABCDE approach
• European Society of Cardiology: 2024 atrial fibrillation guidance
• European Society of Cardiology: ventricular arrhythmias and sudden cardiac death
• NHS: Heart rhythm problems