Focal Atrial Tachycardia

Focal atrial tachycardia is a regular atrial rhythm arising from a discrete site with centrifugal spread, at an atrial rate of 100 to 250/min, with an isoelectric baseline between P waves.

It accounts for about 5 to 15% of adults referred for ablation of supraventricular tachycardia and is a leading cause of incessant tachycardia in children. Mechanisms are enhanced automaticity, triggered activity and micro-reentry.

Common sites are the crista terminalis (most frequent in the right atrium), tricuspid annulus, right atrial appendage, coronary sinus ostium, atrial septum, pulmonary veins (most frequent in the left atrium), left atrial appendage, mitral annulus and aortic cusps.

Causes are structural heart disease, atrial scars after surgery or ablation, digoxin toxicity (atrial tachycardia with block), chronic lung disease, hypokalaemia, hypomagnesaemia, alcohol, stimulants, theophylline and acute illness. Many cases are idiopathic.

Pathophysiology. Automatic foci show warm up and cool down of rate, and are not terminated by pacing or cardioversion. Triggered and re-entrant foci start and stop abruptly, and triggered foci are usually terminated by adenosine.

Sustained or incessant tachycardia causes left ventricular dilatation and failure (tachycardia induced cardiomyopathy), which usually recovers when the rhythm is controlled.

• Palpitations, dyspnoea, chest discomfort, presyncope and fatigue. Paroxysmal, persistent or incessant.
• Incessant forms may be asymptomatic until left ventricular failure appears.
• Digoxin toxicity: atrial tachycardia with variable atrioventricular block, nausea, visual disturbance, confusion.
• Examination: regular rapid pulse, possibly with variable block.
• ECG: P waves with a morphology different from sinus rhythm (except high crista terminalis foci). A long RP interval is typical, and the tachycardia persists with atrioventricular block.

Red flags.

• Incessant tachycardia with falling ejection fraction
• Haemodynamic instability or syncope
• Digoxin toxicity with block, hyperkalaemia or acute kidney injury
• Underlying structural heart disease or recent cardiac surgery
• Infant or young child with persistent tachycardia and heart failure

• 12-lead ECG with P-wave morphology for origin. A negative or biphasic P wave in V1 suggests a right atrial origin. A positive P wave in V1 suggests a left atrial or septal origin. Negative P waves in the inferior leads suggest an inferior focus, and positive inferior P waves a superior focus.
• Adenosine response: termination suggests a triggered focus. Transient atrioventricular block that unmasks continued atrial activity establishes atrial tachycardia and excludes atrioventricular reentry, which terminates.
• Ambulatory ECG for burden, warm up pattern and incessant behaviour. Echocardiography for ventricular function and structural disease.
• Laboratory: potassium, magnesium, digoxin level, thyroid function, creatinine.
• Electrophysiology study: activation mapping to find the earliest atrial activation, with ablation in the same session.

Differential diagnosis.

• Sinus tachycardia and inappropriate sinus tachycardia (gradual change in rate, P wave like sinus)
• Sinus node reentry (P wave identical to sinus, abrupt onset and offset)
• Atrial flutter (continuous flutter waves at 250 to 350/min)
• Atrioventricular nodal reentry and AVRT (adenosine terminates)
• Permanent junctional reciprocating tachycardia
• Multifocal atrial tachycardia
• Atrial fibrillation
• Junctional tachycardia

Acute, stable.

• Treat the cause: stop digoxin, correct potassium to 4.0 to 5.0 mmol/L and magnesium to the normal range, and stop stimulants.
• Adenosine 6 mg rapid intravenous bolus with a 20 mL saline flush, then 12 mg after 1 to 2 minutes if needed, then 12 mg once more, maximum total 30 mg. Use 3 mg through a central line or with dipyridamole, carbamazepine and in heart transplant recipients. Contraindicated in asthma and second or third degree atrioventricular block without a pacemaker. It terminates triggered foci and shows the diagnosis in the others.
• Metoprolol 2.5 to 5 mg intravenously over 2 minutes, repeated every 5 minutes to a maximum of 15 mg. Hold for heart rate under 50/min or systolic blood pressure under 100 mm Hg. Contraindicated in decompensated heart failure, atrioventricular block over first degree, severe asthma and shock.
• Verapamil 5 mg intravenously over 2 minutes (3 minutes in older adults), repeated once after 10 minutes, maximum 10 mg. Contraindicated in reduced ejection fraction, hypotension and recent intravenous beta blocker.
• Amiodarone 300 mg intravenously over 1 hour (central line when possible), then 900 mg over 23 hours. Maximum 1.2 g in 24 hours. Use for refractory tachycardia or structural disease. It interacts with warfarin and digoxin, and is contraindicated in severe sinus node disease, high grade atrioventricular block and thyroid disease. Avoid when QTc is prolonged.
• Unstable: synchronised cardioversion at 70 to 120 J biphasic, which often fails with automatic foci because they restart at once. Avoid cardioversion in digoxin toxicity because of the risk of ventricular fibrillation.

Digoxin toxicity with life threatening arrhythmia. Digoxin specific antibody fragments. Vials = serum digoxin (ng/mL) multiplied by weight (kg), divided by 100, where each 40 mg vial binds about 0.5 mg of digoxin. Empirical dosing is 10 vials for acute ingestion of unknown amount and 3 to 6 vials for chronic toxicity. Recheck potassium, which can fall sharply after treatment.

Chronic therapy.

• Catheter ablation is first line for symptomatic, recurrent or incessant tachycardia and for tachycardia induced cardiomyopathy. Acute success is 80 to 95%, with recurrence 10 to 20%.
• Bisoprolol 2.5 mg orally once daily, increased every 1 to 2 weeks to 5 to 10 mg once daily, maximum 20 mg daily. Do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment.
• Verapamil 40 to 120 mg orally every 8 hours (usual 80 mg), maximum 480 mg daily, long term. Start low and reduce in severe liver impairment.
• Flecainide 50 mg orally twice daily, increased to 100 mg twice daily, maximum 300 mg daily, only without structural or ischaemic heart disease and combined with a beta blocker or verapamil to prevent 1:1 conduction if flutter develops. Reduce the dose when QRS widens by over 25%. At creatinine clearance of 35 mL/min or less start at 50 mg twice daily with level monitoring.
• Amiodarone orally 200 mg three times daily for 1 week, 200 mg twice daily for 1 week, then 200 mg once daily (maintenance 100 to 200 mg once daily), maximum 600 mg daily during loading. Thyroid and liver function every 6 months, with baseline chest X-ray and lung function. Halve digoxin and reduce warfarin by 30 to 50%.
• Tachycardia induced cardiomyopathy: rate or rhythm control plus heart failure therapy, with recovery of ejection fraction usually over 3 to 6 months.
• Anticoagulation is not needed for focal atrial tachycardia alone. When atrial fibrillation or flutter also occurs, apixaban 5 mg orally twice daily, reduced to 2.5 mg twice daily when at least two of age 80 years or over, weight 60 kg or under and serum creatinine 133 micromol/L or over are present. Also 2.5 mg twice daily at creatinine clearance 15 to 29 mL/min, and avoided under 15 mL/min. Maximum 10 mg daily. Long term.

Special groups.

• Infants and children: many infant tachycardias resolve in the first 1 to 2 years. Treat incessant tachycardia with ventricular dysfunction promptly under paediatric electrophysiology.
• Pregnancy: adenosine 6 mg and cardioversion are safe. Maintenance with metoprolol tartrate 25 to 100 mg orally twice daily, maximum 200 mg daily in this setting, or verapamil. Flecainide is reserved for refractory cases. Avoid amiodarone because of foetal thyroid and growth effects.

Monitoring. ECG and ambulatory ECG at 1 to 3 months after starting a drug or ablation. Echocardiography at 3 to 6 months when ejection fraction was reduced. Potassium and magnesium on diuretics. Drug specific monitoring for flecainide (QRS width) and amiodarone (thyroid and liver function every 6 months).

Referral and escalation. Refer to electrophysiology for ablation assessment. Urgent for incessant tachycardia with falling ejection fraction, digoxin toxicity or haemodynamic compromise.