Junctional Ectopic Tachycardia Workup

Updated: Sep 13, 2016
  • Author: M Silvana Horenstein, MD; Chief Editor: Stuart Berger, MD  more...
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Workup

Laboratory Studies

In patients with postoperative junctional ectopic tachycardia (JET), assess serum magnesium levels, electrolyte levels, and lactate concentration.

In patients with other forms of JET, assess serum magnesium, electrolytes, and digoxin levels.

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Electrocardiography

Electrocardiography is the single most important test in all forms of JET (see image below).

Lead II rhythm strip of a surface ECG from a patie Lead II rhythm strip of a surface ECG from a patient with postoperative JET. Atrial activity (P) is marked with blue lines and ventricular depolarization (QRS) is marked in red. Note the narrow QRS complexes due to their origin at the AV junction. Also note the dissociation between atrial and ventricular depolarizations where some of the QRS complexes seem to "follow" the P waves. However, this is not possible because the PR intervals are exceedingly short to allow conduction. In addition, some of the P waves fall after the QRS.

Diagnosis of JET is based on the following:

  • QRS morphology is similar to sinus or atrial-conducted beats.

  • JET usually starts gradually (ie, has a "warm-up" pattern).

  • In junctional rhythm with 1:1 retrograde VA conduction, ventricular rate is equal to the atrial rate.

  • In junctional rhythm with retrograde VA dissociation, an irregular ventricular rate may be observed when appropriately timed atrial impulses conduct to the ventricles.

  • An exception to the last 2 patterns described above rarely occurs, when both JET and complete heart block are present.

The response to adenosine can also be used to identify whether the atrium or junction are driving the rhythm; however, this should be performed with care if the patient is severely ill. For example, in JET with 1:1 VA conduction, JET may be difficult to distinguish from other forms of supraventricular tachycardia with AV conduction. In this case, intravenous adenosine may be given to block VA conduction and, thus, help visualize atrial nonparticipation.

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Imaging Studies

Chest radiography

Chest radiography is used to assess for ventricular dilatation and dysfunction (when signs of pulmonary edema are present) in all patients with JET.

Echocardiography

Transthoracic echocardiography is also used to assess for ventricular dilatation and dysfunction in all patients with JET.

Transthoracic echocardiography and transesophageal echocardiography may be used to assess for significant postoperative residual hemodynamic abnormalities in patients with postoperative JET.

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Procedures

Rarely, cardiac catheterization is required in postoperative JET to assess for significant postoperative residual hemodynamic abnormalities.

Postoperatively, the use of atrial wire recordings to assess P-wave timing can facilitate determination of the diagnosis.

In some patients with 1:1 AV or VA association, whether the rhythm is being driven by the atrium or junction may be unclear. If this occurs, pacing the atrium faster than the intrinsic rhythm and then identifying the origin of the first escape beats following termination of pacing may be helpful.

In JET with 1:1 VA conduction, an atrial premature beat introduced immediately before the expected atrial depolarization does not conduct retrogradely because the origin of the intrinsic atrial depolarization is from retrograde conduction of the JET. However, if it were an atrial tachycardia with first-degree AV block (ie, with 1:1 AV association) a timed atrial premature beat would advance (ie, make it appear earlier in the electrogram) the next ventricular and atrial depolarizations. This would prove that ventricular depolarizations are being conducted from atrial depolarizations and not vice versa.

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Histologic Findings

Histologic studies have shown His bundle degeneration, Purkinje cell tumors, and fibroelastosis.

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