ECG Blog #303 (EQC) — The Patient Fainted

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Today’s tracing is another ECG “Quick Case” ( = EQC) — in which I’ll provide a more “time-efficient” account of my thought process (with goal toward expediting your interpretation within seconds rather than minutes)! Relevant links are at the bottom of the page.

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Today's CASE: 

The 12-lead ECG and long lead II rhythm strip in Figure-1 — was obtained from an older woman who “suddenly fainted”. No chest pain.

QUESTIONS:

• How would YOU interpret the rhythm and the 12-lead?
• What do you think may have happened?

Figure-1: ECG from an older woman who fainted. No chest pain.

MY Thoughts on the Initial ECG in Figure-1:

The rhythm is regular at ~50-55/minute. The QRS is wide. Looking at the long lead II rhythm strip — a P wave does precede each QRS complex with a fixed (and normal) PR interval — so there is at least some conduction.

• In general — the best lead for identifying atrial activity is lead II. Lead II provides the extra advantage of telling us if there is or is not sinus rhythm. The P wave should always be upright in lead II if there is a sinus rhythm. The only exceptions to this general rule — is if there is dextrocardia or lead reversal.
• That said — there are times when atrial activity is seen better in other leads. In my experience — the 2nd-best lead for viewing atrial activity is lead V1. This is followed by leads III, aVR, aVF — and then taking a quick look at the remaining 7 leads.
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• What did YOU see in lead V1?

Additional Atrial Activity:

Although it would be easy to overlook additional atrial activity if one only looked at the long lead II rhythm strip — Lead V1 clearly tells us that there are 2 equally-spaced P waves for each QRS complex (RED arrows in Figure-2).

• The fact that these P waves in lead V1 are equally spaced (RED arrows) — tells us that the underlying sinus rhythm continues throughout the tracing. There is 2:1 AV block (ie, 2 P waves for each QRS) — which defines the rhythm as some form of 2nd-Degree AV Block.
• Since the ventricular rate is 54/minute — the atrial rate is twice this, or 108/minute.
• The reason the 2nd P wave may not have initially be seen in the long lead II rhythm strip — is that it was hidden within the preceding T wave (WHITE arrows in the long lead II).
• Although the 2nd P wave within each R-R interval is easiest to recognize in lead V1 — other leads also suggest this (ie, RED & WHITE arrows in lead V5).
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• PEARL #1: Use of calipers makes it easy to confirm regularity of the underlying atrial rhythm. Thus rules out entities such as atrial bigeminy (in which every-other-P-wave is a PAC). That said — it is common to see slight variation in the P-P interval in patients with 2nd- or 3rd-degree AV block. This is called a “ventriculophasic” sinus arrhythmia. Most of the time this entity can be recognized by the fact that the P-P interval that “sandwiches” a QRS complex tends to be slightly shorter than the P-P interval that does not contain a QRS complex within it (thought to be due to slightly improved circulation from the cardiac output generated by the QRS within the 2 P waves that initiates mechanical contraction).

Figure-2: I've added RED and WHITE arrows to indicate the location of regular atrial activity (See text).

What About Your Interpretation of the 12-Lead ECG?

Now that we have defined the rhythm in Figure-2 as sinus with 2nd-Degree AV Block and 2:1 AV Conduction — there remains the question of how to interpret the rest of the 12-lead ECG.

• As stated — the QRS complex is wide (probably ~0.12 second in Figure-2). QRS morphology is consistent with complete RBBB (ie, RBBB “Equivalent” Pattern in the form of a QR in lead I — and wide terminal S waves in both leads I and V6).
• There is also LAHB, based on the predominantly negative QRS complexes in each of the inferior leads. Therefore, there is bifascicular block ( = RBBB/LAHB).
• There is also evidence of prior infarctions. The lack of an initial r wave in lead III (ie, Qr pattern) — is not the result of simple LAHB, and indicates prior inferior infarction at some point in time.
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• PEARL #2: It is often difficult to distinguish between LAHB with or without prior inferior infarction. This is because the initial depolarization vector with each of these entities is “opposing” — such that the initial r wave with LAHB may prevent inscription of the Q wave of inferior infarction — and — the Q wave of inferior infarction may prevent inscription of the initial positive deflection (r wave) with the hemiblock. That said, in today’s case — the CLUES that tell us that both LAHB and prior inferior infarction have occurred at some point in time are: i) The wide initial Q wave in lead III (which should not be there with simple LAHB); ii) Fragmentation of the QRS in both leads II and aVF (ie, the extra “notching” on the upslope of the S wave) — and the r’ that we see in lead III (ie, normally with simple LAHB, there is an rS pattern in all 3 inferior leads — and not a Qr as we see here).
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• PEARL #3: There has also been anteroseptal infarction at some point in time — as seen by the large Q waves in numerous chest leads. With simple RBBB — there should be a triphasic (rsR’ or rSR’) complex in lead V1. The deep, wide Q wave we see here in lead V1 tells us that there has definitely been previous anteroseptal infarction.
• Large Q waves, as well as additional fragmentation (notching) is also seen in leads V2, V3 and V4. In addition to extensive prior anteroseptal infarction — this patient clearly has significant coronary disease (ie, fragmentation in this clinical setting suggests extensive “scar”, from infarction and/or cardiomyopathy).
• As to assessment of ST-T wave abnormalities — nothing looks to be acute! Instead, there is nonspecific ST-T wave flattening — with slight-but-real ST elevation in leads V2, V3, V4. 
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• PEARL #4: Note that the ST segment in lead V1 is isoelectric. Normally with simple RBBB — the ST-T wave should be “oppositely-directed” to the last QRS deflection in the 3 KEY leads (ie, Since the last deflection in lead V1 is a positive R wave — there should normally be some ST-T wave depression in lead V1 when there is simple RBBB without any complicating factors). The fact that the ST-T wave in lead V1 is isoelectric instead of being at least slightly depressed is not "normal" with RBBB.

BOTTOM LINE: In addition to 2nd-Degree AV Block with 2:1 AV conduction — there has been inferior and anteroseptal infarction at some point in time. Although there is some ST elevation in leads V2,V3,V4 (and some inappropriate ST segment flattening in lead V1) — this is minimal. Other leads show nonspecific ST-T wave flattening and shallow T inversion in V5,V6 — so none of this looks acute. Instead — the slight ST elevation may reflect a left ventricular aneursym. 

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The CASE Continues:

ECG #2 was obtained 15 minutes after ECG #1 (See Figure-3).

QUESTIONS:

• What has happened in the 15 minutes since ECG #1?
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• Has the “degree” of AV block improved?
•     HINT: WHY did I calculate the atrial rate in each tracing?

Figure-3: ECG #2 was obtained 15 minutes after ECG #1. What has happened during these 15 minutes?

ANSWERS:

There is no longer 2:1 AV conduction in ECG #2. Instead — there is sinus rhythm with 1:1 AV conduction (RED arrows) — and a PVC ( = beat #6).

• I suspect that an on-time sinus P wave is hidden within the ST-T wave of beat #6 in ECG #2.
• There has been essentially no change in QRS morphology or in ST-T wave appearance between the 2 tracings.
• The atrial rate has slowed slightly in ECG #2 (ie, from 108/minute — to 95/minute).

PEARL #5: Often ignored is the potential effect that the atrial rate may have on AV conduction. In today’s case — it is likely that the “degree” of AV block was not “worse” in ECG #1. Instead — it may simply be that the diseased AV node (in this older patient who obviously has severe underlying heart disease) may be able to conduct 1:1 at a sinus rate of 95/minute — but when the atrial rate speeds up a little (ie, to 108/minute) — it is only able to conduct 1 out of every 2 sinus impulses to the ventricles.

• Given the history of syncope in this older patient — and the presence of bifascicular block (RBBB/LAHB) with prior infarctions — and periods of 2:1 AV Block — a permanent pacemaker may be needed. 
• Ongoing ECG monitoring may facilitate documenting the need for a pacemaker. 
• Echocardiography and cardiac catheterization may be indicated looking for LV aneurysm — determining LV function — and to clarify the anatomy in the event that there may be “fixable” coronary disease that might improve the patient’s conduction system disease.

Final PEARL: We can not distinguish with certainty between the Mobitz I and Mobitz II types of 2nd-Degree AV Block when there is 2:1 AV conduction. This is because we never see 2 consecutively conducted beats in a row — which means that we never get to see whether the PR interval would increase prior to dropping a beat IF given a chance to do so (as would be typical for the Mobitz I form of 2nd-degree AV block).

• Mobitz I is far more common than Mobitz II. That said — when the QRS complex is wide — the PR interval of conducted beats is normal — and the patient clearly has significant underlying structural heart disease (as is seen in today's case) — then the chance that the conduction defect is Mobitz II increases. That said, regardless of whether the block is Mobitz I or Mobitz II — permanent pacing may still be needed in this patient for all of the reasons mentioned earlier.

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Acknowledgment: My appreciation to 유영준 (from Seoul, Korea) for making me aware of this case and allowing me to use this tracing.

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Relevant ECG Blog Posts to Today's Post:

• ECG Blog #204 — Reviews the ECG diagnosis of BBB (reviewed in the Video Pearl).
• ECG Blog #203 — Reviews a user-friendly approach to the Hemiblocks and to Bifascicular Block.
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• ECG Blog #236 — Reviews the 3 types of 2nd-Degree AV Block.
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• ECG Blog #271 — Reviews the concept of diffuse subendocardial ischemia.
• ECG Blog #162 — Reviews a case of LBBB with acute STEMI.
• ECG Blog #221 — How to diagnose acute MI when there is RBBB (reviewed in the Audio Pearl).
• ECG Blog #298 — Reviews a case of RBBB/LAHB + Post. MI.