Atrial ectopic tachycardia (AET) is a rare arrhythmia; however, it is the most common form of incessant supraventricular tachycardia (SVT) in children. Atrial ectopic tachycardia is believed to be secondary to increased automaticity of a nonsinus atrial focus or foci. This arrhythmia, which is also known as ectopic atrial tachycardia or automatic atrial tachycardia, has a high association with tachycardia-induced cardiomyopathy. Atrial ectopic tachycardia is often refractory to medical therapy and is not usually responsive to direct current (DC) cardioversion.
The diagnosis of atrial ectopic tachycardia is based on the presence of a narrow complex tachycardia (in the absence of aberrancy or preexisting bundle branch block) with visible P waves at an inappropriately rapid rate. The rates range from 120 to 300 beats per minute (bpm) and are typically higher than 200 bpm, although physiologic rates may be observed (see Electrocardiography).
Patients with atrial ectopic tachycardia may present with circulat ory collapse similar to patients with cardiomyopathy. Immediate rate control is desired in these cases. Three options are available for long-term treatment of patients with atrial ectopic tachycardia: medication to suppress the arrhythmia or control the ventricular response, catheter ablation, or, uncommonly, surgery (see Treatment and Management).
Spontaneous depolarization is a phenomenon of automatic myocardium. The sinus node is usually the pacemaker of the heart, because it has the most rapid spontaneous rate of firing. A small cluster of cells with abnormal automaticity is presumed to be responsible for atrial ectopic tachycardia. The conduction spreads from this cluster to the surrounding atrium and to the ventricles via the atrioventricular (AV) node. A conduction delay from atrium to ventricle often occurs, with most patients demonstrating first-degree AV block and some showing second-degree block.
Because atrial ectopic tachycardia is often incessant, tachycardia-induced cardiomyopathy is commonly observed. Although the exact underlying mechanism of the development of cardiac dysfunction in the setting of chronic arrhythmias is unknown, numerous reports have documented improved cardiac function following ventricular rate control and treatment of the arrhythmia.
Atrial ectopic tachycardia is usually idiopathic. Occasionally, mycoplasmal or viral infections, such as respiratory syncytial virus, may trigger this arrhythmia, although more complex atrial tachycardias, such as chaotic atrial tachycardia, are more frequently found in this scenario. Atrial tumors have been reported to be associated with atrial ectopic tachycardia. Reports of familial cases with an autosomal dominant inheritance are present in the literature.  This arrhythmia is also observed in patients who have congenital heart disease and have undergone surgical treatment of this congenital heart disease.
The adult form of atrial ectopic tachycardia may have a different etiology and natural history than the pediatric form.
Although the exact incidence is unknown and few large series have been reported, atrial ectopic tachycardia reportedly comprises 5-10% of pediatric SVTs. Although estimates of the incidence of pediatric SVTs widely vary, atrial ectopic tachycardia likely occurs with an incidence of approximately 1 case per 10,000 children.
Atrial ectopic tachycardia is predominantly observed in infants and children; this accounts for a peak of 11-16% of tachycardias for which a mechanism is determined in young childhood.
Atrial ectopic tachycardia is generally well tolerated. Syncope is unusual, and cardiac arrest is rare, except when encountered as a complication of treatment. Tachycardia-induced cardiomyopathy is the most significant sequela of atrial ectopic tachycardia and may be insidious. The time to development depends on the rate and duration of the tachycardia; however, ventricular dilatation may be present on initial presentation. This can also be reversed with successful treatment of the arrhythmia.
Several reports have documented the spontaneous remission of atrial ectopic tachycardia in the pediatric population and in young adults.  This may occur in as many as one third of patients following withdrawal of medication. A review from Texas Children's Hospital suggests that children younger than 3 years have a better response to medication and a higher rate of spontaneous resolution of the arrhythmia. 
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