Multifocal Atrial Tachycardia

Multifocal atrial tachycardia (MAT) is an irregular atrial rhythm at a rate over 100/min with at least three different P wave morphologies in the same lead, variable PP, PR and RR intervals, an isoelectric baseline between P waves, and no single dominant atrial pacemaker.

When the rate is under 100/min the rhythm is called a wandering atrial pacemaker. It is found in 0.05 to 0.3% of hospital ECGs, mostly in people over 60 years. Between 60 and 80% have chronic lung disease, especially chronic obstructive pulmonary disease with hypoxaemia and hypercapnia.

Other causes are pulmonary hypertension, pulmonary embolism, sepsis, heart failure, coronary disease, valve disease, hypomagnesaemia, hypokalaemia, theophylline toxicity, beta agonist excess and postoperative states. In hospital mortality is high (30 to 60%) because of the underlying illness and not the rhythm.

A substantial share of patients later develop atrial fibrillation.

Pathophysiology. Triggered activity from raised intracellular calcium and delayed afterdepolarisations, promoted by hypoxia, hypercapnia, acidosis, catecholamines, methylxanthines, electrolyte depletion and atrial stretch from raised right atrial pressure. Several atrial foci fire in turn, giving the irregular rhythm.

• Symptoms of the underlying disease: dyspnoea, wheeze, cough, fever, leg swelling. Palpitations may be absent.
• Irregularly irregular pulse that mimics atrial fibrillation.
• Examination: features of chronic lung disease, cor pulmonale, heart failure or sepsis.
• Theophylline toxicity: nausea, vomiting, tremor, agitation, seizures.

Red flags.

• Hypoxaemia or hypercapnic respiratory failure
• Haemodynamic compromise
• Serum theophylline level over 20 mg/L
• Potassium under 3.5 mmol/L or magnesium under 0.7 mmol/L
• Suspected pulmonary embolism or sepsis
• Heart rate over 150/min

• 12-lead ECG and rhythm strip: rate over 100/min, three or more P wave morphologies, variable PR intervals, some P waves blocked, isoelectric baseline between P waves.
• Arterial blood gases, oxygen saturation, chest X-ray.
• Laboratory: potassium, magnesium, calcium, glucose, creatinine, troponin, natriuretic peptide, thyroid function, theophylline and digoxin levels, inflammatory markers, cultures.
• Echocardiography for ventricular function, pulmonary pressure and valve disease.
• CT pulmonary angiography when pulmonary embolism is suspected.

Differential diagnosis.

• Atrial fibrillation (no discrete P waves, completely irregular)
• Atrial flutter with variable block
• Sinus tachycardia with frequent atrial premature beats
• Wandering atrial pacemaker (rate under 100/min)
• Focal atrial tachycardia
• Junctional tachycardia
• Digoxin toxicity (atrial tachycardia with block)
• Sinus arrhythmia

Treat the cause first; the rhythm often settles within days.

• Oxygen to a saturation of 88 to 92% in hypercapnic lung disease, and 94 to 98% otherwise. Non-invasive ventilation for hypercapnic respiratory failure. Treat infection, heart failure and pulmonary embolism.
• Reduce or withdraw theophylline and minimise beta agonist doses where possible. Use ipratropium for bronchodilation.
• Magnesium sulphate 2 g (8 mmol) intravenously over 20 minutes, repeated once after 4 to 6 hours if needed, aiming for serum magnesium of 1.0 mmol/L or more. Monitor reflexes, respiratory rate and blood pressure. Reduce the dose at creatinine clearance under 30 mL/min.
• Potassium to 4.0 to 5.0 mmol/L: potassium chloride intravenously 10 mmol/h (maximum 20 mmol/h through a central line with ECG monitoring), or oral potassium chloride 40 to 80 mmol daily in divided doses, rechecking at 24 hours. Reduce or avoid in renal impairment.

Rate control for persistent symptomatic MAT after correction.

• Verapamil 5 mg intravenously over 2 minutes (3 minutes in older adults), repeated once after 10 minutes, maximum 10 mg. Oral 40 to 120 mg every 8 hours (usual 80 mg), maximum 480 mg daily. Contraindicated in reduced ejection fraction, hypotension, high grade atrioventricular block and with a beta blocker. Start low and reduce in severe liver impairment.
• Bisoprolol 1.25 mg orally once daily, increased every 1 to 2 weeks to 2.5 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. Cardioselective beta blockers are usually tolerated in chronic obstructive pulmonary disease without active bronchospasm. Avoid in severe or unstable airway disease.
• Amiodarone 300 mg intravenously over 1 hour (central line when possible), then 900 mg over 23 hours, maximum 1.2 g in 24 hours, as a short course for refractory cases. Contraindicated in severe sinus node disease and high grade atrioventricular block. Monitor thyroid and liver function.
• Avoid digoxin (ineffective, and toxic with hypoxia and hypokalaemia) and DC cardioversion (ineffective).
• Atrioventricular node ablation with pacing is reserved for rare, refractory symptomatic cases.

Atrial fibrillation or flutter coexisting: anticoagulation directed by stroke risk. 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. Neonates and children with MAT usually have lung disease, and the rhythm resolves with treatment of the underlying illness.

Monitoring. Continuous ECG during acute illness. Potassium and magnesium every 12 to 24 hours until stable. Oxygen saturation and blood gases. Theophylline level when used (usual range 10 to 20 mg/L). ECG when the respiratory illness settles, since rhythm usually returns to sinus.

Referral and escalation. Respiratory and cardiology review for persistent MAT, ventricular dysfunction or recurrent episodes. Urgent for hypoxaemic respiratory failure, haemodynamic compromise or suspected pulmonary embolism.