- Confirmed JET: a) tachycardia with a QRS complex similar to the basal tracing or to a tracing obtained by atrial stimulation, together with b) AVD with slower atrial rate than ventricular rate. Only patients with confirmed or probable JET who were treated with hypothermia were included in this study. Standard electrocardiograms were examined, as were atrial electrograms recorded during episodes of arrhythmia with the atrial electrodes placed during surgery or with esophageal electrodes. We reviewed the clinical records of patients operated on for congenital heart defects between September 1999 and October 2001 at the Área Infantil del Corazón (Pediatric Heart Service) of the Juan Canalejo Hospital Complex in A Coruña, northwestern Spain. 2 This treatment, first described in 1987, 3 has been reported in the literature infrequently, and all reports involve low numbers of patients.
The poor response to pharmacological treatment has led to a search for other treatment options, including moderate hypothermia. Although it is self-limiting within 48-72 h, mortality in the absence of prompt treatment is 40% 1 because of elevated heart rate (HR) and atrioventricular dissociation (AVD). Because the tracing shows an irregular pattern of irregularity, all entities in the differential diagnosis are still viable.Acute junctional ectopic tachycardia (JET) can appear after surgery for congenital heart defects. If it were regularly irregular, several ECG diagnoses would move up in the differential diagnosis: namely, normal sinus rhythm (NSR) with a regular bigeminal, trigeminal, or quadrigeminal pattern, and second-degree atrioventricular (AV) block in a fixed pattern (eg, 2-to-1, 3-to-1, and so forth). The rhythm in this tracing (shown in Figure 1 with the ventricular beats/ QRS complexes numbered on the lead II rhythm strip at the bottom) appears to be irregularly irregular. 1 To narrow the differential, first determine whether the rhythm is irregularly irregular or regularly irregular. "Regularly irregular" versus "irregularly irregular." An irregular, narrow-QRS-complex rhythm evokes a wide differential diagnosis ( Table). Normal standardization is reflected by a plateau-shaped waveform that is 2 large boxes in amplitude (or 20 small squares, as in these tracings) "double standard" shows a waveform 4 large boxes (or 40 small squares) in amplitude. Increasing the calibration to double standard results in the doubling in size of all cardiac waveforms, as well as of the plateau-shaped waveform at the extreme left of each row of waveforms on the tracing. This is referred to as increasing the "standardization," or calibration, of the tracing to "double standard" (ie, 20 mm/mV, rather than the default of 10 mm/mV). Lastly, the ECG machine may be manipulated to increase the size of all the complexes, thus making minute P waves larger. A previous ECG will demonstrate what the patient's P waves normally look like and thus help determine whether minor, difficult-to-classify "atrial" deflections are indeed artifact or coarse atrial fibrillation rather than P waves. This strategy is frequently used to evaluate T-wave patterns in patients with possible cardiac ischemia, but it is underutilized in settings such as this. It is also often helpful to obtain a previous ECG for comparison. Here, these would include leads II and V 5. If the rhythm diagnosis remains obscure after reviewing the 12-lead tracing, it is best to generate a rhythm strip using the 12-lead ECG machine, incorporating the leads that best demonstrate atrial activity in that patient.
Imagine trying to determine in this patient whether P waves were present if you were given only a single-lead rhythm strip from lead III or lead V 1!
The first step in deciphering a tricky narrow-QRS-complex rhythm is to ask for a 12-lead ECG, if patient stability allows, since atrial activity may be obscure in certain leads. Beats 5 and 8 have P-like deflections immediately preceding the QRS complexes, but these are too close to the QRS complexes to conduct.
There appear to be P waves preceding some, but not all, beats (all except 5 and 8). The ECG shows an irregularly irregular rhythm that is slightly bradycardic but nearly normal in rate ( Figure 1). Answer: Normal sinus rhythm with junctional escape beats
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