Pediatric Atrial Ectopic Tachycardia Workup

During the arrhythmia in stable patients, 12-lead electrocardiography (ECG) is necessary. Laboratory testing is indicated for the exclusion of underlying systemic disorders. Echocardiography and Holter monitoring are also part of the standard workup. Electrophysiology testing may be useful in some patients. Exercise testing may occasionally unmask an intermittent atrial ectopic tachycardia (AET).

Go to Atrial Tachycardia and Multifocal Atrial Tachycardia for information on these topics.

Exclusion of systemic disorders

• Assess electrolyte levels, hematocrit levels, and thyroid function in patients with atrial ectopic tachycardia.
• Consider thyroid studies.
• Consider urine collections in some patients for assessment of possible pheochromocytoma.

Inspect the electrocardiogram (ECG) for P-wave axis and morphology, ventricular rate, and conduction block.

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.

The P-wave axis is usually abnormal, although a focus near the sinus node can be mistaken for sinus tachycardia. Similarly, the P-wave morphology may be abnormal. Onset of the tachycardia occurs with a P wave identical to the subsequent P waves. The tachycardia may exhibit a "warming up," which refers to a progressively shortening P-P interval for the first few beats of the arrhythmia. Similarly, a "cooling down" may be observed at its termination. First-degree atrioventricular (AV) block is typical and second-degree AV block is common. The tachycardia cycle length and degree of AV block are influenced by the autonomic tone.

Ectopic atrial tachycardia usually creates a P wave that is at least slightly different from sinus rhythm, first-degree atrioventricular (AV) block, and possible periods of second-degree AV block without termination of tachycardia.

To differentiate atrial ectopic tachycardia from sinus tachycardia secondary to cardiomyopathy, Gelb and Garson demonstrated that negative late terminal P-wave forces in lead V₂ occur more commonly in atrial ectopic tachycardia.^[4] The rate is also usually higher in atrial ectopic tachycardia.

Algorithms to determine the site of the ectopic focus based on P-wave morphology are known. A negative or biphasic (positive, then negative) P wave in lead V₁ indicated a right atrial tachycardia. A positive or biphasic (negative, then positive) P wave in ECG lead V₁ indicated a left atrial tachycardia.^[5]

Patients should undergo Holter monitoring to determine the time spent in tachycardia and the ventricular rates. Holter monitoring is particularly useful in identifying and analyzing onsets and offsets of tachycardia.

The Holter monitor findings often facilitate the diagnosis by revealing: (1) an elevated average heart rate over a 24-hour period, with reduced circadian variability; (2) a higher peak heart rate than normally encountered in sinus rhythm; or (3) periods of atrioventricular (AV) block, demonstrating 2 consecutive P waves at an elevated rate without an intervening QRS complex.

Perform echocardiography with a focus on cardiac function and dimensions to rule out cardiomyopathy and associated congenital heart disease. The earliest manifestation of cardiomyopathy may be ventricular dilatation. A decreased shortening fraction follows. Reversal of these findings after treatment follows a reciprocal pattern. Diastolic function abnormalities may also occur in tachycardia-induced cardiomyopathy, and they may be the last parameter to correct after therapy.

Atrial angiography may occasionally be helpful as a roadmap during radiofrequency (RF) catheter ablation.

Although invasive studies are not usually necessary to make a diagnosis of atrial ectopic tachycardia, in some patients, an esophageal electrophysiology recording may be useful to assist confirmation of the diagnosis; the response to overdrive pacing can also be assessed. Many automatic foci transiently suppress when overdrive pacing is performed.

An invasive electrophysiology study can also be performed for these indications, but this is usually performed in patients undergoing attempt at radiofrequency (RF) ablation.

In patients with ectopic atrial tachycardias arising from the pulmonary veins, an esophageal recording may also be helpful in localizing the site of tachycardia.

The response of atrial ectopic tachycardia to adenosine may be persistent in the setting of atrioventricular (AV) block or a transient slowing of the tachycardia; it rarely terminates. Direct current (DC) cardioversion usually does not terminate the arrhythmia.

Endomyocardial biopsy findings often reveal vacuolized myocytes in the setting of tachycardia-induced cardiomyopathy.