ECG Blog #356 — Multiple Wavelets ...

The ECG in Figure-1 — was obtained from a patient with fatigue and an "irregular pulse". What is the rhythm?

Figure-1: 12-lead ECG and long lead II rhythm strip — obtained from a patient with fatigue and an "irregular pulse". (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on the ECG in Figure-1:

I thought today's tracing would be interesting to share — in that I have never seen atrial activity looking quite like this.

• My approach to this tracing is the same as always — which is to start by assessing the rhythm in the long lead II rhythm strip. The QRS is narrow. The ventricular rhythm is fast and irregularly irregular. Sinus P waves are absent. Therefore the rhythm is AFib (Atrial Fibrillation) with a rapid ventricular response.
• Looking at the rest of the 12-lead ECG — overall QRS amplitude is reduced. The frontal plane axis appears to be leftward — but not enough to qualify as a hemiblock (ie, the QRS is not predominantly negative in lead II). There is no chamber enlargement. Although difficult to assess given baseline atrial activity — ST-T wave changes look nonspecific, and do not appear to be acute.

What About the Atrial Activity?

The aspect of this tracing that I had not seen before — regards the appearance of atrial activity. The leads are on correctly. The reason for the unusual-looking atrial activity is neither baseline artifact nor tremor. Instead — it is all atrial activity.

• Atrial activity is multi-directional. An observer described this activity in Figure-1 as "atrial torsades" — in that atrial deflections are clearly all positive (ie, between beats #3-thru-6) — then all negative (between beats #8-9) — flat (beween beats #9-thru-11) — negative again (between beats #12-13) — and then all positive a final time toward the end of the tracing.
• Although we think of AFib as a completely irregularly irregular rhythm without design — on occasion, AFib may temporarily organize (ie, into "wavelets" of electrical activity). When it does — the rhythm may resemble AFlutter in lead V1 (often only in this lead) — until the wavelets deteriorate, and clear AFib activity resumes.
• An example of this temporarily "organized" atrial activity is seen in Figure-2. Although tempting to interpret this activity in lead V1 as AFlutter — the rhythm does not qualify as "atrial flutter" — because atrial activity is too fast (ie, well over 350/minute in parts); irregular; and not consistent in atrial morphology.
• Descriptively — the term "AFib-Flutter" has sometimes been used to describe the atrial activity seen in Figure-2. The point to emphasize is that in the absence of consistent regular flutter activity throughout the rhythm strip — the rhythm  seen in Figure-2 behaves clinically as if it was AFib.

Why Today's Rhythm is Different:

The picture of transient "organization" of atrial activity seen in lead V1 of Figure-2 is common. 

• What is different about today's rhythm in Figure-1 — is the distinctly directional atrial waves of similar morphology that so clearly alternate in direction.

Figure-2: AFib with temporary "organization" of atrial activity. The rhythm resembles atrial flutter.

Mechanisms that Maintain AFib:

Advances in our understanding of the pathophysiology responsible for maintaining AFib suggests a number of ways in which this arrhythmia may be sustained. These include: i) Local ectopic discharge from one or more atrial pacemakers; ii) A single localized reentry circuit; and/or, iii) The presence of multiple functional reentry circuits that alternate control of the arrhythmia (Iwasaki et al — Circulation 124:2264-2274, 2011).

• The most logical explanation for the distinctly directional atrial activity in Figure-1 — is the 3rd mechanism cited above, in which there are multiple functional reentry circuits that continually alternate control, with changing direction of atrial activity as they do.

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Acknowledgment: My appreciation to Arron Pearce (from Manchester, UK) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my systematic approach to 12-lead ECG Interpretation.
• ECG Blog #185 — My systematic approach to Rhythm Interpretation.