Junctional Ectopic Tachycardia Workup
- Author: M Silvana Horenstein, MD; Chief Editor: Stuart Berger, MD more...
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.
Electrocardiography is the single most important test in all forms of JET (see image below).
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.
Chest radiography is used to assess for ventricular dilatation and dysfunction (when signs of pulmonary edema are present) in all patients with JET.
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.
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.
Histologic studies have shown His bundle degeneration, Purkinje cell tumors, and fibroelastosis.
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