Tuesday, March 31, 2020

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? NOTE — Enlarge by clicking on the Figure.



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 previously reviewed ECG findings with LA-RA (Left Arm-Right ArmLead Reversal (See My Comment at the bottom of the page in the February 11, 2020 post in Dr. Smith’s ECG Blog).
  • 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).



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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