Initial assessment
Patient with tachycardia and a palpable pulse. The first step is the A-B-C-D-E assessment: airway patency, breathing, circulation, level of consciousness and skin assessment. Signs of clinical instability should be identified, including hypotension, altered mental status, ischaemic chest pain, acute heart failure with dyspnoea/fatigue/oedema or syncope. In the presence of instability, specialist support should be contacted immediately.
Reversible causes
Reversible causes should be identified and treated: electrolyte abnormalities, anaemia, fever, hyperthyroidism, hypoglycaemia, anxiety, excessive intake of caffeine, alcohol, cocaine, cannabis or amphetamines; adverse drug effects, including tricyclic antidepressants, methylphenidate, digoxin and antiarrhythmics; and pacemaker-mediated stimulation. Early correction improves symptoms and may resolve the tachycardia.
ECG and QRS
A 12-lead ECG should be performed. Classification is based on QRS width: narrow (<120 ms) suggests supraventricular origin; wide (≥120 ms) requires ventricular tachycardia to be considered the main diagnosis.
Regular narrow QRS
Typically AVNRT/AVRT, meaning atrioventricular nodal or atrioventricular re-entry. Initial management consists of vagal manoeuvres: Valsalva, carotid sinus massage, cold stimulus to the face or cough reflex. The carotid artery should be auscultated beforehand; massage should be unilateral for 5–10 s with firm pressure. Possible adverse effects include dizziness, syncope and transient ventricular arrhythmias.
Adenosine
If there is no reversion with manoeuvres, administer adenosine as a rapid bolus: 6 mg IV; if necessary, repeat with 12 mg. Use continuous ECG monitoring because of its very short half-life. Adverse effects are usually self-limiting, including chest discomfort, dyspnoea and flushing. If sinus rhythm is restored, arrange outpatient investigation, including thyroid function, echocardiogram, ECG/Holter monitoring and cardiology assessment.
Alternatives
If adenosine is contraindicated or unsuccessful, consider IV verapamil or metoprolol, respecting contraindications: avoid beta-blockers in bronchospasm; verapamil is contraindicated in decompensated heart failure or second-/third-degree AV block. Diltiazem is a valid alternative, 15–20 mg IV, with repeat dosing after 15 min if needed.
Irregular narrow QRS
Suggests atrial fibrillation, with differentials including flutter with variable conduction and multifocal atrial tachycardia. Prioritise ventricular rate control with a beta-blocker or calcium-channel blocker, according to contraindications. For recurrent symptoms or refractory cases, consider catheter ablation.
Regular wide QRS
Differentiate monomorphic VT from SVT with bundle branch block. If in doubt, treat as VT. Administer IV amiodarone 150–300 mg over 20–60 min, diluted in dextrose, followed by a maintenance infusion over the next 24 h. Response to adenosine may suggest SVT with bundle branch block.
Specialist support
Consider early contact with specialist support in the presence of instability, unsatisfactory response, diagnostic uncertainty or pharmacological contraindications.
Maintenance plan
After stabilisation, define maintenance treatment according to the type of tachycardia: oral medication, rhythm clinic follow-up and, when indicated, electrophysiological study and catheter ablation.
