ECG Blog #175 (Lead Reversal – Lateral MI – Dextrocardia)

You are asked to interpret the 12 lead ECG with the simultaneously-obtained long lead II rhythm strip shown in Figure-1. This tracing was obtained from a man in his 60s — who presented to the ED for sudden onset of palpitations.

• What is the likely cause of this patient’s symptoms?
• WHAT ELSE is going on in this ECG?

Figure-1: 12-lead ECG with lead II rhythm strip from a man in his 60s, who presented with new-onset palpitations. What is going on?

COMMENT: Looking at the long lead II rhythm strip — the rhythm is rapid and irregularly irregular. No P waves are seen in any of the 12 leads. Therefore, the rhythm is AFib (Atrial Fibrillation) with a rapid ventricular response — and this is the probable cause of this patient’s sudden development of palpitations.

• WHAT ELSE is going on?
• HINT #1: HOW OFTEN have you seen Q waves this deep in lead I?
• HINT #2: What do you think about R wave progression in the chest leads?

ANSWER: It is highly unusual for there to be predominant Q waves in lead I. Even when there has been lateral infarction — the presence of a predominant initial negative deflection in lead I is not commonly seen.

• PEARL: The finding of a predominant Q wave in lead I should raise the question of lead misplacement vs dextrocardia. This is especially true IF there is global negativity (ie, of the P wave, QRS complex, and T wave) in lead I.
• If neither lead misplacement nor dextrocardia turn out to be present in ECG #1 — then the Q waves in high lateral leads I and aVL (as well as in lead II) + the abnormal ST-T waves we see in a number of other leads in this tracing should suggest the possibility of myocardial infarction that could be recent or acute.

NOTE: Assessment of the ECG in Figure-1 for possible lead misplacement or dextrocardia is clearly made more difficult — because the rhythm is AFib, and no P waves are seen.

• I have on several occasions reviewed ECG findings with LA-RA (Left Arm-Right Arm) Lead Reversal (See My Comment at the bottom of the page in the February 11, 2020 post in Dr. Smith’s ECG Blog — and especially See the case and discussion of LA-RA lead reversal with an acute MI in ECG Blog #264).
• 
  
• It appears that at least some of the beats in lead I of ECG #1 manifest inverted T waves, as well as deep initial Q waves. In addition, there is a prominent positive component to the R wave in lead aVR. These findings are consistent with either LA-RA lead reversal or dextrocardia.
• DID YOU NOTICE that there is Reverse R Wave Progression in the chest leads of ECG #1? That is, the tallest R wave is seen in lead V1 — after which there is progressive decrease in R wave amplitude as one moves across the chest leads. Other than in lead V1 — QRS amplitude in the chest leads of ECG #1 is tiny, and represented by a most unusual rSr’ pattern in leads V3-thru-V6.

QUESTION: What’s the easiest way to distinguish between LA-RA lead reversal vs dextrocardia in ECG #1?

ANSWER: There are several easy things one can do:

• Listen to the patient’s chest to determine if heart sounds are heard on the left or the right?
• Get a chest X-ray (Figure-2).
• Verify lead placement — and repeat the ECG. IF LA-RA lead reversal is suspected — do one more ECG with right-sided chest leads. IF dextrocardia is suspected — one might also another ECG with both limb leads and chest leads reversed.

Figure-2: A chest x-ray of this patient (See text).

FIGURE-2: The chest x-ray on this patient confirms Dextrocardia!

• The aortic knob and heart shadow is a virtual mirror-image of normal position.

About DEXTROCARDIA: There is a distinct terminology associated with the numerous potential variations of dextrocardia. I summarize some of the BASICS regarding this clinical entity in Figure-3:

• As noted in Figure-3 — Situs Inversus Totalis is the most common form of dextrocardia, with an incidence of ~1 per 15,000 in the general population. Although I do not clearly see a stomach bubble in this x-ray — thoracic structures appear to be a mirror-image of normal.

Figure-3: Summary of some basic concepts about Dextrocardia — adapted from Maldjian & Saric’s Review in AJR (See text). NOTE — Another good reference on ECG findings with Dextrocardia is this article by Mozayan & Levis.

QUESTION: This patient’s ECG was repeated after switching both limb leads and chest leads (Figure-4). The rhythm is still AFib with a rapid ventricular response.

• WHAT do you now see?

Figure-4: The ECG has been repeated after switching limb leads and chest leads. (See text).

ANSWER: ECG #2 was obtained after switching polarity of the limb leads and placing precordial leads at comparable positions on the right side of the chest.

• Note that the overly large Q wave that was seen in lead I of ECG #1 (as well as T wave inversion in this lead) is no longer seen.
• Predominant negativity of both the QRS and T wave now is seen in lead aVR (as is normally expected).
• R wave progression in the chest leads now is appropriate (with no more than slightly delayed transition, that occurs between leads V4-to-V5). Compared to ECG #1 — QRS amplitude in ECG #2 has increased greatly in the chest leads, and now manifests appropriate QRS morphology in the precordial leads.
• Although nonspecific ST-T wave changes persist — there is no longer suggestion of recent infarction. The intermittent Q waves in leads III and aVF of ECG #2 are most likely not an abnormal finding in this patient with rapid AFib.

-----------------------------------------------------------------------

Acknowledgment: My appreciation to 유영준 (from Seoul, South Korea) for the case and this tracing.

-----------------------------------------------------------------------

================================== 

Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• 
  
• ECG Blog #264 — Reviews a case of LA-RA Lead Reversal + an Acute MI (with Audio Pearl and complete discussion on how to recognize lead reversal).
• 
  
• The November 19, 2020 post in Dr. Smith's ECG Blog — in which I present an easy-to-overlook but important case in which LA-LL lead reversal was missed (with the "tip-off" being recognition of a taller P wave in lead I > lead II).
• The August 28, 2020 post in Dr. Smith's ECG Blog — My Comment (in my Addendum, at the very bottom of the page) reviews expected findings when there is LA-LL lead reversal (Tipoff = the P in lead I is larger than the P in lead II).
• 
  
• The July 29, 2018 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) reviews this case in which there were 2 technical errors that multiple physicians failed to recognize ( = LA-RA lead reversal and too high placement of leads V1, V2 on the chest). 
• The February 11, 2020 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) reviews this case in which there was LA-RA lead reversal.

ECG Blog #174 (AV block – PACs – group beating)

The 2 lead II rhythm strips shown in Figure-1 were obtained from the same patient, just a few minutes apart. Unfortunately — no history is available.

• Note that there is group beating in both tracings. Is this Wenckebach? (ie, Is the rhythm in this figure 2nd-degree AV block, Mobitz Type I?).
• How certain are you of your answer?
• HINT: Find a pair of calipers — and USE them to figure out your answer!

Figure-1: Two lead II rhythm strips obtained minutes apart from the same patient. Is this 2nd-degree AV block of the Mobitz I type ( = AV Wenckebach)? 

COMMENT: The presence of group beating should be immediately noticed in Figure-1. That is, there are 2 groups of 3 beats (ie, in rhythm A — beats #3,4,5 and beats #6,7,8) — and multiple groups of 2 beats (ie, beats #11,12 in A — and in B, beats #2,3; 4,5; 6,7; 8,9, 10,11). Recognition of group beating can prove invaluable — because this finding instantly tells you: i) that some kind of repetitive pattern is present in the rhythm; and, ii) that you should strongly consider the possibility of some type of Wenckebach conduction.

• IF the rhythm in Figure-1 was AV Wenckebach — then at least several of the “FOOTPRINTS” of Wenckebach should be present. (This is a direct link to 32:20 in our ECG Video on the Basics of AV Block, and takes you to the part in which we discuss the “Footprints of Wenckebach”. If you click on SHOW MORE, below this video on the YouTube page — You’ll see a detailed linked Contents of all in this video!).
• Use of calipers instantly tells us that the rhythm in Figure-1 is not AV Wenckebach because: i) the P-P interval is definitely not regular (Usually the P-P interval is at least fairly regular when there is AV block); and, ii) the PR interval is not reliably increasing within groups of beats (We should see PR interval prolongation when there is AV Wenckebach) — SEE Figure-2!

Figure-2: We’ve labeled the P waves that were seen in Figure-1 (See text).

FIGURE-2: In Figure-2 — We’ve labeled sinus P waves with RED arrows. Additional P waves are highlighted by BLUE arrows. Note that the T waves under each of the BLUE arrows in Figure-2 are deformed (usually be a notch), compared to the T waves that are not hiding P waves within them (ie, NO P waves are hiding within the T waves of beats #3, 6, 9, 11 in A; and beats #2, 4, 6, 8 and 10 in B).

• Therefore — the BLUE arrows in tracings A and B in Figure-2 represent P waves. Compared to the P-P interval between 2 sinus P waves (ie, between 2 RED arrows) — each of the P waves highlighted by BLUE arrows occurs much earlier-than-expected, which means the P waves highlighted by BLUE arrows are PACs (Premature Atrial Contractions).
• Taking another look at the 2 rhythm strips shown in Figure-2 — we see that every 3rd P wave (ie, each of the BLUE arrows) — is a PAC. Therefore, the underlying rhythm in Figure-2 is Atrial Trigeminy (which is the term we use to describe an underlying sinus rhythm, in which every 3rd beat is a PAC).
• The PACs preceding beats #2, 5 and 8 are conducted. However, none of the other PACs in Figure-2 are conducted. Instead, the PACs following beats #10 and 12 in A — and following beats #1, 3, 5, 7 and 9 in B are all “blocked” (ie, non-conducted), and followed by a short pause.
• BOTTOM LINE: The underlying rhythm in Figure-1 is atrial trigeminy (ie, every 3rd P wave is a PAC). Some of these PACs are conducted. Others are “blocked”. All of the PACs in B are blocked — and this produces a form of group beating that simulates AV Wenckebach — BUT — there is no AV block in Figure-2, for the reasons we state above.
• P.S. — Use of calipers allows you to rule out AV block within seconds! It should take no more than a few seconds to determine that every 3rd P wave in Figure-2 occurs far too early to be a sinus rhythm (as would be expected when there is AV block).

BEYOND-the-CORE: As is often the case in “real life” — there is a final “twist” to the rhythm in Figure-2. Do you see it?

• HINT: Is P wave morphology for all of the P waves highlighted by RED arrows the same?
• NOTE: My answer below is complex. It is not meant to confuse — but rather to illustrate the challenges faced by the astute clinician when confronted with a truly complex “real life” tracing. Less experienced interpreters may want to ignore what I write below. My hope is that what I write below proves insightful, especially for more experienced interpreters.

ANSWER: Perhaps the greatest challenge the astute clinician faces when interpreting a complex arrhythmia that is less-than-perfect technically — is distinguishing between deflections that are due to artifact vs the slight variation in P wave, QRS and/or ST-T wave morphology that may normally occur in “real life”.

• Because rhythm strips A and B in Figure-2 were obtained just seconds apart — I would expect moment-to-moment fluctuations in P wave and/or QRS morphology to be minimal. Yet despite virtually no change in QRS morphology between tracings A and B — I thought the P waves under the RED arrows of beats #3,4; 6,7; 9,10; and 12 in A, were in general taller and more pointed than almost all of the other P waves. This made me wonder IF those smaller and rounder P waves in these 2 tracings might not reflect P waves arising from an alternate atrial site?
• That said — strongly against this possibility, is that fact that the R-R intervals between beats with successful RED-arrow P waves are virtually identical! I definitely would not expect this, if ectopic site atrial P waves were mixed in with sinus P wave activity.
• BOTTOM LINE: I suspect all P waves in tracings A and B of Figure-2, that are highlighted by RED arrows — are of sinus origin. I suspect there is just a lot of moment-to-moment variation in sinus P wave morphology. That said — I cannot prove this based only on these 2 tracings ...

===================================
For MORE on PACs vs Wenckebach:

• Please see ECG Blog #66 and Blog #164 —

ECG Blog #173 (VT - AFib - Polymorphic - WPW)

-----------------------------------------------------------

NOTE: My complete write-up of this case is found on the March 11, 2020 post on Dr. Smith's ECG Blog — CLICK HERE — 

-----------------------------------------------------------

The Case: A young adult presented to the ED for with "heart awareness" and the ECG shown in Figure-1 — but with no more than slight shortness of breath. BP ~130/70.

Questions:

• What is the cardiac rhythm in Figure-1?
• How certain are you of your diagnosis?
• Is the clinical scenario consistent with what you might expect for this rhythm?

Figure-1: The initial ECG in this case.

-----------------------------------------------------------

NOTE: My complete write-up of this case is found on the March 11, 2020 post on Dr. Smith's ECG Blog — CLICK HERE — 

-----------------------------------------------------------