ECG Blog #315 — Bradycardia and Abdominal Pain

The ECG in Figure-1 — was obtained from a 65-year old woman who presented to the ED (Emergency Department) for abdominal pain. No chest pain. She was hemodynamically stable at the time the ECG in Figure-1 was recorded.

• How would YOU interpret the ECG in Figure-1?
• What is the rhythm?

Figure-1: 12-lead ECG and long lead II rhythm strip obtained from a 65-year old woman with abdominal pain. What is the rhythm?

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NOTE: The ECG in today's case was reproduced from a smart phone photo. As a result — the tracing is angled and slightly distorted. That said — the advantage of transmitting smart phone tracings is that within seconds — consultation from anywhere in the world with an internet connection becomes possible.

• Despite some distortion — accurate interpretation of the rhythm in Figure-1 still is possible!
• Please Also NOTE: Recording of the long lead II rhythm strip from this smart phone photo was not entirely simultaneous with the 12-lead ECG above it. This adds to the challenge of interpreting this tracing — since we lose the ability to directly compare changes in QRS morphology for each beat in the rhythm strip — to morphology changes in the 12-lead. Are YOU up to the challenge?

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MY Approach to the ECG in Figure-1:

As always — I favor beginning with the long lead rhythm strip at the bottom of the tracing before concentrating on the 12-lead. My systematic approach to every arrhythmia that I encounter is encompassed by the memory aid, "Watch Your Ps, Qs and the 3Rs" (See ECG Blog #185):

• The overall rhythm is slow. The rhythm is not regular. That said — there does appear to be a "pattern" to the rhythm, in that there are coupled beats that are spaced at a similar distance to the preceding QRS complex (ie, the coupling interval of beats #2, 5 and 8 in the long lead rhythm strip looks to be equal).
• Realizing that there is some distortion of this tracing — many of the R-R intervals appear to repeat! That is — the R-R interval between beats #2-3; 5-6 and 8-9 looks to be the same! (ie, just under 6 large boxes in duration).
• The slightly longer R-R intervals that are seen between beats #3-4; 6-7; 9-10 and 10-11 also appear to be equal! (ie, about 7 large boxes in duration). This repetition of intervals is not due to chance!

Continuing with the Ps, Qs & 3Rs:

• The QRS complex of the underlying rhythm is narrow. That is — the 1st beat in each grouping (ie, beats #1, 3, 4, 6, 7, 9, 10 and 11) is narrow and not preceded by any P wave! Each of these beats must therefore be a junctional "escape" beat (at a junctional escape rate here, set at an appropriate junctional rate of between 40-60/minute).
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• I next looked for P waves. There are some P waves on this tracing! For clarity in Figure-2 — I have added colored arrows to highlight the P waves that I believe to be present.

Figure-2: There are some P waves on this tracing! (See text).

PEARL #1: How to Find P Waves ...

The KEY to interpreting today's rhythm lies with identifying the P waves that are present. This is challenging! — because most of the P waves on this tracing are partially (or totally) hidden within preceding T waves.

• Begin by identifying those deflections that you know represent P waves (RED arrows).
• At this point I thought to myself: "IF there was an underlying regular sinus rhythm — what would the P-P interval have to be?" I contemplated my answer based on knowing that the 2 RED arrows in Figure-2 definitely represented 2 P waves.
• Working backward from the 2nd RED arrow — it is clear that there is no P wave within the R-R interval between beats #8-9. Looking carefully at each of the T waves for beats #1, 4, 6, 7 and 10 — I thought the T wave of beat #7 looked different (ie, with a smaller peak — as suggested by the PINK arrow).
• IF this PINK arrow is truly highlighting a partially hidden P wave — then the P-P interval in this tracing could be the distance between this PINK arrow — and the RED arrow that occurs just after beat #9.
• IF this was true — then the remaining P waves in Figure-2 might be hiding (and slightly deforming) the T waves of beats #1, 4, 6 and 10 (as highlighted by the WHITE arrows).

PEARL #2: It is Essential to Use Calipers!

As I have emphasized on multiple occasions in this ECG Blog — many complex rhythms defy interpretation unless you use calipers.

• Accounting for the slight distortion we have noted in the rhythm strip, as well as for some degree of sinus arrhythmia (that so often accompanies sinus bradycardia) — it literally took me no more than seconds to postulate the probable location of underlying sinus P waves that I highlight with the colored arrows in Figure-2. I simply could not have identified these P waves without calipers.

PEARL #3: It Helps When You Know What You Are Looking For!

Solving complex arrhythmias is similar to solving a mystery in a detective story. Most of the time — there are a limited number of possibilities. In today's case — the "pattern" of the rhythm is bradycardia with intermittent coupled beats (ie, there is an intermittent bigeminal rhythm).

• As discussed in ECG Blog #243 — the differential diagnosis for a bigeminal rhythm is limited. Once you are aware of the possibilities for a bigeminal rhythm (that I summarize in Figure-3) — recognition of the slow rate with junctional escape at the end of each of the longer R-R intervals in Figure-2 — should immediately suggest "escape-capture" as the most likely mechanism. None of the other entities in Figure-3 make sense. Therefore — I immediately suspected (and looked for) an escape-capture mechanism for today's rhythm.

Figure-3: Causes of a Bigeminal Rhythm (See text).

The LADDERGRAM:

A picture is worth 1,000 words! It's easiest to illustrate the mechanism in today's case with a laddergram (Figure-4).

Figure-4: Since the QRS complex of beats #1,3,4,6,7,9,10,11 is narrow and not preceded by any P wave — we established that these are junctional "escape" beats, here with an appropriate junctional "escape" rate in the low 40s (ie, with an R-R interval between successive junctional beats of ~7 large boxes). Because the sinus bradycardia rate is even slower than the junctional rate — most beats on this tracing are junctional except for the on-time P waves that occur before beats #2, 5 and 8 (which occur at a point in the cardiac cycle in which they are able to "capture" the ventricles).

Final Observations:

As noted earlier — recording of the long lead II rhythm strip in today's tracing was not entirely simultaneous with the 12-lead ECG above it.

• PEARL #4: There are numerous ECG recording systems in use across the world. The one in use for today's tracing was different than the recording systems that I am accustomed to. The first 3 beats in the long lead II rhythm strip are recorded simultaneous with the recording of the 3 beats seen leads I, II and III of the 12-lead ECG. 
• The 12-lead ECG then shows the appearance of these first 3 beats in the long lead rhythm strip in each of the 3 remaining lead groupings (ie, in leads aVR,aVL,aVF — in leads V1,V2,V3 — and finally in leads V4,V5,V6).
• For example — the 2nd beat in lead V1 manifests an RBBB pattern. This corresponds to beat #2 in the long lead rhythm strip.
• Note that this beat #2 in the long lead II rhythm strip — corresponds to the 2nd beat that is recorded in the lead grouping that shows leads I, II and III. The wide terminal S wave in lead I for this beat #2 is consistent with RBBB conduction.
• Finally — Note that QRS morphology for this beat #2 shows a very deep S wave in lead I — and a qR in leads II and III — which is consistent with LPHB conduction.
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• PEARL #5: Each of the coupled beats in the long lead II rhythm strip (ie, beats #2, 5 and 8) look similar — in that they are each slightly wider than beats #1,3,4,6,7,9,10,11 (because they have a terminal S wave). Since QRS morphology of beats #5 and 8 looks identical to that of beat #2 in the long lead rhythm strip — all 3 of these beats must be conducting with RBBB/LPHB aberrancy!
• It is completely understandable that these conducted "capture" beats (ie, beats #2,5,8) might conduct with aberration — since they each occur early in the cycle, at a time when these P waves may fall within the relative refractory period.

In CONCLUSION: 

The primary problem in today's case is marked sinus bradycardia. Perhaps this is simply a result of increased vasovagal tone brought about as a pain response to this patient's abdominal discomfort?

• Since the rate of this patient's sinus bradycardia is slower than her junctional "escape" rate — the principal rhythm that we see is junctional escape.
• There is no evidence of any AV block in Figure-4 — because the P waves occurring right after the QRS complexes of beats #3, 6, 9 and 10 all occur so early in the cycle, that they would not be expected to conduct. And when on-time P waves occur just a little bit later in the cycle — they do conduct (ie, "capture" the ventricles) with a reasonable PR interval.
• Because sinus bradycardia is often the 1st rhythm disturbance seen with SSS (Sick Sinus Syndrome) — clinical correlation will be needed to determine IF the marked sinus bradycardia in today's case is simply a vasovagal response to pain — or something more significant (ie, drug or electrolyte effect, sleep apnea, hypothyroidism, SSS, etc.).

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Acknowlegment: My thanks to Rafi Mohd (from Jammu-Kashmir, India) for allowing me to use this tracing and clinical case.

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Relevant ECG Blogs to Today's Audio Pearl:

• ECG Blog #185 — Reviews the Ps, Qs & 3R Approach to Systematic Rhythm Interpretation. 
• ECG Blog #188 — Reviews how to understand (and how to draw) Laddergrams! 
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• ECG Blog #256 — Escape-Capture Bigeminy (with junctional escape and "capture" from retrograde conduction — with AUDIO Pearls on "Escape-Capture" and on "Sick Sinus Syndrome" plus Step-by-Step Laddergram).
• ECG Blog #163 — Escape-Capture Bigeminy (with sinus bradycardia and resultant junctional escape — and possibly also with SA block).
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• ECG Blog #239 — Reviews the concept of Echo Beats, and its clinical applications (showing an unusual bigeminal rhythm case of AV Wenckebach over dual AV nodal pathways, terminated by Echo beats).
• ECG Blog #232 — For review of a bigeminal rhythm due to subtle 3:2 AV Wenckebach. (NOTE: The Audio Pearl in this post is devoted to the concept of Bigeminal Rhythms). 
• ECG Blog #243 — For review of a bigeminal rhythm due to AFlutter with dual-level Wenckebach conduction out of the AV node.
• ECG Blog #252 — For review of a bigeminal rhythm due to atrial trigeminy with blocked PACs. 
• ECG Blog #206 — For review of a fascinating case of a bigeminal rhythm due to 3:2 AV Wenckebach with alternating Hemiblock.
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• ECG Blog #70 — Reviews the Ashman Phenomenon (as a reason for aberrant conduction).