Tachycardia

Tachycardia is a heart rate over 100 beats/minute at rest in adults. It is a sign, not a diagnosis: it can be a normal physiological response (exertion, anxiety, pain, fever), a compensatory response to systemic illness (hypovolaemia, sepsis, hypoxia, anaemia, pulmonary embolism, heart failure), or a primary rhythm disorder (supraventricular and ventricular tachyarrhythmias). The first decisions are whether the patient is unstable and whether the rhythm is sinus.

Clinical relevance. Sinus tachycardia is the commonest, and treatment of the cause is treatment of the tachycardia. Slowing a compensatory sinus tachycardia (for example with a beta blocker in hypovolaemia or sepsis) can cause collapse. In contrast, tachyarrhythmias with haemodynamic compromise need immediate cardioversion.

Classification by ECG.

• Narrow complex (QRS under 120 ms): sinus tachycardia, atrial fibrillation, atrial flutter, atrial tachycardia, atrioventricular nodal re-entrant tachycardia, atrioventricular re-entrant tachycardia.
• Broad complex (QRS 120 ms or more): ventricular tachycardia, supraventricular tachycardia with aberrancy or bundle branch block, pre-excited tachycardia, paced rhythm, hyperkalaemia, sodium channel blocker toxicity. Treat broad complex tachycardia as ventricular tachycardia until proven otherwise.
• Regular or irregular.

Classification by cause.

• Physiological: exertion, emotion, pain, fear, caffeine, heat.
• Pathological sinus: fever, sepsis, hypovolaemia, haemorrhage, anaemia, hypoxia, pulmonary embolism, heart failure, thyrotoxicosis, phaeochromocytoma, drugs and withdrawal, pregnancy, anxiety.
• Primary arrhythmia.

History.

• Onset (abrupt or gradual), duration, triggers, associated symptoms (chest pain, breathlessness, dizziness, syncope, palpitations).
• Features of systemic illness: fever, cough, diarrhoea, vomiting, bleeding, trauma, abdominal pain, urinary symptoms, rash.
• Cardiac history: ischaemic heart disease, valve disease, heart failure, previous arrhythmia, family history of sudden death.
• Thyroid, anaemia, pregnancy, diabetes, alcohol, withdrawal.
• Drugs: salbutamol, theophylline, thyroid hormone, decongestants, caffeine, nicotine, cocaine, amphetamines, atropine and anticholinergics, tricyclics, vasodilators, withdrawal from beta blockers, benzodiazepines, alcohol, opioids.
• Psychological: anxiety, panic.

Examination.

• Rate (manual count for full minute), rhythm, volume, character; blood pressure lying and standing; temperature; respiratory rate; oxygen saturation; capillary glucose; capillary refill; mental state.
• Look for shock (cool peripheries, delayed refill, oliguria), heart failure (raised jugular venous pressure, crackles, oedema), anaemia (pallor), thyroid, infection, dehydration, abdominal or pelvic source, calf swelling, tremor.
• Cardiac: murmurs, rubs, third heart sound.

Red flags (adverse features indicating instability).

• Systolic blood pressure under 90 mmHg, shock.
• Chest pain, acute heart failure, syncope or altered consciousness.
• Heart rate over 150.
• Broad complex tachycardia.
• Pre-excited atrial fibrillation (irregular broad complex tachycardia, rate over 200).
• Hypoxia, sepsis, haemorrhage, pulmonary embolism features.
• Heart rate that does not respond to treatment of the cause.

Sinus tachycardia (rate usually under 150). Physiological, anxiety and pain, fever and infection, sepsis, haemorrhage, dehydration, anaemia, hypoxia, pulmonary embolism, heart failure, myocardial infarction, cardiac tamponade, thyrotoxicosis, phaeochromocytoma, pregnancy, drugs and withdrawal, postural orthostatic tachycardia syndrome, inappropriate sinus tachycardia.

Atrial arrhythmias. Atrial fibrillation, atrial flutter (rate about 150 with 2 to 1 block), atrial tachycardia, multifocal atrial tachycardia (chronic obstructive pulmonary disease).

Re-entrant supraventricular tachycardias. Atrioventricular nodal re-entrant tachycardia, atrioventricular re-entrant tachycardia (Wolff-Parkinson-White).

Ventricular arrhythmias. Monomorphic ventricular tachycardia (scar, cardiomyopathy, idiopathic outflow tract), polymorphic ventricular tachycardia and torsades de pointes, ventricular fibrillation, accelerated idioventricular rhythm.

Mimics. Artefact, paced rhythm, supraventricular tachycardia with bundle branch block.

1. Assess stability and ABCDE; attach monitor; 12 lead ECG at once; intravenous access; oxygen if saturation under 94%.
2. Classify the rhythm: regular or irregular, QRS width. Look for P waves, delta waves, flutter waves, and long QT. A rhythm strip during vagal manoeuvre or adenosine can unmask flutter waves.
3. Sinus tachycardia: look for the cause with blood tests (full blood count, C reactive protein, lactate, glucose, urea, creatinine, electrolytes, thyroid stimulating hormone, troponin, D-dimer, arterial or venous gas, blood cultures, urine dipstick, pregnancy test), chest radiograph, and imaging as indicated. Echocardiography for effusion, ventricular function.
4. Tachyarrhythmia: electrolytes (potassium, magnesium, calcium), thyroid function, troponin, digoxin level, drug screen, echocardiography.
5. Broad complex: use criteria for ventricular tachycardia (atrioventricular dissociation, capture or fusion beats, QRS over 160 ms, concordance across the chest leads, Brugada algorithm, Vereckei aVR criteria).
6. Holter or event monitor later if intermittent; exercise test; electrophysiology study.

Limits. Sinus tachycardia over 150 is unusual in adults; a fixed rate near 150 suggests flutter. Adenosine is diagnostic but not therapeutic in flutter and atrial tachycardia. Aberrancy can mimic ventricular tachycardia; presume ventricular tachycardia if uncertain.

Unstable tachycardia (adverse features). Synchronised direct current cardioversion under sedation (propofol or midazolam with analgesia): broad complex or atrial fibrillation 120 to 150 J biphasic, escalating; regular narrow complex 70 to 120 J; flutter 70 to 120 J. If ineffective after 3 shocks, give amiodarone 300 mg intravenously over 10 to 20 minutes, then repeat the shock, followed by amiodarone 900 mg over 24 hours.

Sinus tachycardia. Treat the cause: fluids and blood for hypovolaemia, antibiotics and source control for sepsis, oxygen for hypoxia, anticoagulation for pulmonary embolism, analgesia for pain, antipyretic for fever, treatment of anxiety, and thyroid or anaemia treatment. Do not give rate lowering drugs to compensatory tachycardia. Inappropriate sinus tachycardia or postural orthostatic tachycardia syndrome: ivabradine 5 mg twice daily (titrate to 7.5 mg twice daily), propranolol 10 to 40 mg twice daily, fluids and exercise.

Regular narrow complex tachycardia. Vagal manoeuvres, then adenosine 6 mg then 12 mg, then a further 12 mg by rapid intravenous bolus with a 20 mL saline flush (3 mg through a central line); verapamil 2.5 to 5 mg intravenously if adenosine fails; synchronised cardioversion if unstable or refractory. Atrial flutter: rate control with bisoprolol, diltiazem or digoxin, cardioversion, and anticoagulation by CHA2DS2-VASc (men 2 or more, women 3 or more); ablation of the cavotricuspid isthmus.

Irregular narrow complex tachycardia (atrial fibrillation). Rate control (bisoprolol 2.5 to 10 mg daily, diltiazem 60 to 120 mg three times daily, or digoxin 0.125 to 0.25 mg daily) or rhythm control, and anticoagulation with apixaban 5 mg twice daily (2.5 mg twice daily if two of age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more); treat precipitants; cardioversion within 48 hours of onset after immediate anticoagulation; amiodarone for heart failure.

Pre-excited atrial fibrillation. Avoid atrioventricular nodal blockers (adenosine, verapamil, diltiazem, beta blockers, digoxin); use synchronised cardioversion or intravenous procainamide 10 to 17 mg/kg at 20 to 50 mg/minute, or flecainide; ablation of the accessory conduction tissue.

Broad complex tachycardia, stable. Amiodarone 300 mg intravenously over 20 to 60 minutes then 900 mg over 24 hours; or procainamide; or lidocaine 1 to 1.5 mg/kg intravenously (maximum 3 mg/kg) then 1 to 4 mg/minute in ischaemia; magnesium 2 g for torsades; correct potassium and magnesium; electrical cardioversion if drug therapy fails. Known supraventricular tachycardia with bundle branch block can be treated with adenosine. Avoid verapamil in broad complex tachycardia.

Torsades de pointes. Magnesium sulphate 2 g intravenously over 10 minutes (repeat once), potassium over 4.5 mmol/L, remove QT prolonging drugs, isoprenaline or overdrive pacing for pause dependent tachycardia, defibrillation if pulseless or unstable.

Pulseless ventricular tachycardia or ventricular fibrillation. Defibrillation (200 J biphasic), cardiopulmonary resuscitation, adrenaline 1 mg after the third shock then every 3 to 5 minutes, amiodarone 300 mg after the third shock then 150 mg after the fifth, reversible causes (hypoxia, hypovolaemia, hypo and hyperkalaemia, hypothermia, tension pneumothorax, tamponade, toxins, thrombosis).

Specific causes.

• Thyrotoxicosis: propranolol 20 to 80 mg every 6 hours (or 1 mg intravenously every 5 minutes up to 5 mg) and antithyroid drugs; thyroid storm needs hydrocortisone 100 mg every 8 hours, potassium iodide, and intensive care.
• Digoxin toxicity: stop digoxin, correct potassium, digoxin-specific antibody fragments (800 mg for life threatening arrhythmia).
• Tricyclic antidepressant or sodium channel blocker toxicity: sodium bicarbonate 50 to 100 mmol (8.4% solution 50 to 100 mL) intravenously for QRS over 100 ms.
• Cocaine or sympathomimetic toxicity: benzodiazepines (lorazepam 2 to 4 mg intravenously), cooling, and avoid unopposed beta blockade.
• Anaemia: transfusion for haemoglobin under 70 g/L (or under 80 with cardiac disease).
• Pulmonary embolism: anticoagulation.
• Pericardial tamponade: pericardiocentesis.
• Phaeochromocytoma: alpha blockade first.

Lifestyle and prevention. Avoid triggers; treat heart failure, hypertension, sleep apnoea; limit alcohol; weight reduction.

Monitoring. Continuous ECG monitoring until stable; electrolytes every 12 to 24 hours; repeat ECG after drug administration; QTc monitoring during amiodarone infusion.

Referral and escalation. Cardiology for persistent arrhythmia, ventricular tachycardia, pre-excitation, and cardioverter defibrillator consideration. Critical care for shock. Endocrinology for thyroid storm.

Admission. Unstable or recurrent tachycardia, broad complex tachycardia, new atrial fibrillation with comorbidity, ventricular arrhythmia, drug toxicity, and sinus tachycardia from serious illness.

Safety netting. Return for a heart rate over 150, fainting, chest pain, breathlessness, or lasting palpitations.

Special groups. Children: normal heart rate declines with age (infants up to 160, school age up to 120), and supraventricular tachycardia is common. Pregnancy: physiological sinus rate rise 10 to 20 beats/minute; adenosine and electrical cardioversion are safe; avoid atenolol and amiodarone. Older adults: atrial fibrillation, sepsis, and drug effects. Athletes: pre-excitation screening. Endemic regions: sepsis, malaria, anaemia, rheumatic heart disease and thyrotoxicosis.