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).
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• 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.

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Acknowledgment: My appreciation to 유영준 (from Seoul, South Korea) 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.
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• 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).
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• 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).
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• 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.