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Is There a Grouping?
By Ken Grauer, MD, Professor, Department of Community Health and Family Medicine, University of Florida. Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.
Scenario: The ECG shown above was obtained from an 88-year-old woman who refused treatment. What is the rhythm? Is there a grouping? Is anything else going on?
Interpretation: Determination of the rhythm in this 12-lead ECG is made challenging by the lack of a lead II rhythm strip. This makes it decidedly more difficult to track atrial activity throughout the tracing. The key to determining the cause of irregularity in this ECG lies with identifying P waves in at least one of the simultaneously recorded leads in each lead set.
We start with a lead in which no doubt exists about the presence of P waves. This is lead V1 (with regular atrial activity also seen well in leads V2 and V3, which are the other two leads simultaneously recorded with lead V1). It can be seen that a similar looking P wave regularly occurs in lead V1 at a rate of about 80 beats/min (i.e., with a P-P interval of just under 4 large boxes). Setting our calipers at this P-to-P interval distance allows us to consistently map out small amplitude, but nevertheless regular, atrial activity in leads II (and III), aVF, V3, and V6. We now note "groupings" of QRS complexes (of 3 beats with similar R-R intervals in leads aVF and V3, and of the two beats seen in lead V6 that occur just before the tracing ends). Each of these beat groupings are separated by a brief pause of similar duration (of just under 7 large boxes) that occurs just before the lead change from lead III to lead aVF, during the lead change between leads aVF and V3, and during the lead change between leads V3 and V6.
Recognition of group beating (i.e., "groupings") as described for this tracing strongly suggests Wenckebach conduction. Confirmation that the rhythm is in fact 2nd degree AV block, Mobitz Type I (i.e., AV Wenckebach), is forthcoming from the observation of progressive PR interval lengthening for the 3 beats seen in lead V1, followed by a dropped beat, brief pause, and shortening of the PR interval as the rhythm resumes with the first QRS complex seen in lead V4.
Other findings of note on this tracing include LVH and symmetric T wave inversion in all lateral leads, consistent with ischemia and/or "strain." Clinical decision-making is simplified for this elderly patient who is refusing treatment. One would otherwise want to rule out ischemic heart disease as the cause of her conduction disturbance, while assessing potential need for cardiac pacing, which most often is not needed for 2nd degree AV block, Mobitz Type I, when the overall rate is adequate, as seen here.