By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
I was asked to interpret the ECG in the figure below without the benefit of any history. The rhythm obviously is irregular. Is this likely to be a problem?
My Thoughts: Interpreting ECGs without the benefit of any history always is challenging. Such is the case with this tracing, which manifests significant irregularity.
• I favor beginning my interpretation of any 12-lead ECG with an initial quick glance at the rhythm. Seeing the simultaneously recorded two-lead rhythm strip shown in the figure facilitates this task.
• As noted, the rhythm is irregular, without any particular pattern (i.e., there is no group beating). The QRS is narrow in each of the 12 leads on this tracing, so the rhythm is supraventricular.
• P waves are present in front of each QRS complex in the long lead rhythm strip (best seen in the long lead II). The interesting feature of these P waves is that P wave morphology changes. The first three QRS complexes in the long lead II rhythm strip are upright sinus P waves, with a constant and normal PR interval.
• P wave morphology changes dramatically beginning with the fourth QRS complex, to a double-negative-notched morphology with a short PR interval. Whether this represents a low atrial or junctional ectopic focus is uncertain, but it represents displacement of the site of impulse formation away from the sinoatrial node. P wave morphology changes again with the seventh beat; that suggests a return to sinus rhythm at a slightly faster rate.
• The rhythm ends with a slowing heart rate and a return to the double-negative-notched P wave morphology.
Impression: This rhythm is most consistent with a wandering atrial pacemaker. Unlike multifocal atrial tachycardia, the change in the site of the supraventricular pacemaker is gradual with a wandering pacemaker.
• Technically, the diagnosis of a wandering atrial pacemaker requires gradual shift between at least three different supraventricular sites. I suspect we might have seen a shift to one or more additional sites in this rhythm if the monitoring period had been longer.
• Interpreting the rest of the 12-lead ECG in this case — benign. A wandering atrial pacemaker often is a benign variant in an otherwise healthy young adult. If clinical correlation of this rhythm was that it was recorded because of its irregularity in an otherwise healthy and asymptomatic young adult, then no further evaluation would be needed.
Note: For more information about and further discussion of this case, please visit here.
Interpreting ECGs without the benefit of any history always is challenging. Such is the case with the figure in this article, which manifests significant irregularity.
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