Atrial tachycardia (AT) is a tachycardia originating from the atria that does not require the atrioventricular (AV) node for maintenance. The mechanisms include increased automaticity, reentry, and triggered activity. It is classified into focal atrial tachycardia and multifocal atrial tachycardia, and the latter is also known as chaotic atrial tachycardia, which is a common arrhythmia in severe pulmonary diseases and may eventually progress to atrial fibrillation.
Etiology
Coronary artery disease, chronic lung diseases, digitalis toxicity, excessive alcohol consumption, and various metabolic disorders can be causative factors. Surgical scars from cardiac surgery or catheter ablation can also lead to atrial tachycardia, and it can occur in some patients with structurally normal hearts.
Clinical manifestations
Symptoms often include palpitations, dizziness, thoracodynia, tachypnea, and malaise, though some patients may be asymptomatic. Patients with organic heart disease may experience syncope, myocardial ischemia, or pulmonary edema. Symptoms can be transient, intermittent, or persistent. When the atrioventricular conduction ratio changes, auscultation reveals an irregular heart rhythm with varying intensity of the first heart sound.
Electrocardiogram features
Focal atrial tachycardia ECG features include:
- Atrial rate is usually 150 - 200 bpm
- P wave is different from sinus P wave in morphology
- Second-degree type I or II AV block may occur as the atrial rate increases, with 2:1 AV conduction, but tachycardia remains unaffected
- The isoelectric line between P waves persists (unlike in atrial flutter where it disappears)
- Vagal stimulation cannot terminate the tachycardia, only exacerbating AV block
- Heart rate gradually accelerates at onset
Figure 1 Focal atrial tachycardia
In lead II, the atrial rate is 187 bpm with 1:1 AV conduction; in lead III, the atrial rate is 167 bpm with 2:1 AV conduction.
Multifocal atrial tachycardia ECG features include:
- Usually three or more different P wave morphologies are with varying PR intervals
- Atrial rate is 100 - 130 bpm
- Most P waves are conducted to the ventricles, but some occur prematurely and are blocked, resulting in an irregular ventricular rate
Figure 2 Multifocal atrial tachycardia
In leads II, aVF, and V1, P waves show multiple morphologies with variable 2:1 to 1:1 AV conduction.
Treatment
The management of atrial tachycardia primarily depends on the ventricular rate and the hemodynamic status. If the ventricular rate is not very fast and there are no severe hemodynamic disturbances, oral β-blockers can be chosen. In the absence of structural heart disease, non-dihydropyridine calcium channel blockers and class Ic antiarrhythmic drugs (propafenone) may be used. If the ventricular rate exceeds 140 bpm, or if there are signs of digitalis toxicity, severe congestive heart failure, or shock, emergency treatment is required.
Treatment of etiologies and triggers
Focus should be on treating the underlying disease. Patients with lung disease should have hypoxemia corrected and infections controlled. In case of digitalis toxicity, the drug should be discontinued immediately, and any accompanying electrolyte disturbances, especially hypokalemia, should be corrected.
Control of ventricular rate
In the acute phase, if patients are hemodynamically stable and without decompensated heart failure, intravenous β-blockers or non-dihydropyridine calcium channel blockers can be used. If medication fails to control the ventricular rate, synchronized direct current cardioversion may be considered. In patients with recurrent multifocal atrial tachycardia and left ventricular dysfunction unresponsive to medication, AV node ablation in combination with permanent pacemaker implantation may be considered.
Restoration of sinus rhythm
Adenosine is preferred for cardioversion. If ineffective, class Ic (propafenone) or class III (amiodarone, ibutilide) antiarrhythmic drugs can be used. Patients who are hemodynamically unstable should undergo immediate synchronized direct current cardioversion. For recurrent focal atrial tachycardia or focal atrial tachycardia causing tachycardia-induced cardiomyopathy, catheter ablation is the first-line treatment.