ECG Blog #396 — Why the Flat Line?

The ECG in Figure-1 — was obtained from a middle-aged man with palpitations and shortness of breath. He was hemodynamically stable at the time this tracing was recorded.

• How would YOU interpret the ECG in Figure-1?
• Is there evidence of a recent or ongoing acute MI?
• What might you do first? 

Figure-1: The initial ECG in today's case. (To improve visualization — I've digitized the original ECG using PMcardio).

PEARL #1:  Since today’s patient is hemodynamically stable — there is at least a “moment of time” for you to better contemplate the situation before having to initiate management decisions.

• KEY Point: Although true that patients with longstanding, severe pulmonary disease may manifest a QRST complex in standard lead I with marked overall reduction in QRST amplitude (See ECG Blog #65 — regarding Schamroth’s Sign) — you should never normally see a completely flat line in any of the standard limb leads. IF ever you do see a completely flat line in lead I, lead II or lead III — it is almost certain that there is some type of lead misplacement. Repeat the ECG!

PEARL #2: YES — I did see what looks like a large acute or reperfused inferior MI (QS complexes and deep T wave inversion in leads II,III,aVF) — but since this patient is stable and some type of lead reversal is almost certain (See PEARL #1) — I would repeat the ECG after verifying electrode lead placement to see whatever ECG changes might be real.

• Note also that the P wave is negative in standard lead II in Figure-1 (as well as in leads III and aVF, which are the other 2 inferior leads). It is well to remember that IF the P wave in lead II is negative — then by definition — You do not have sinus rhythm (unless there is lead misplacement or dextrocardia).
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• Again, since today’s patient is hemodynamically stable — there is no urgency. Verify lead placement. — Then repeat the ECG. 

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The CASE Continues:

The treating clinician immediately recognized the likelihood of some type of lead misplacement. As a result — he immediately repeated the ECG after verifying lead placement.

• How would you interpret the repeat ECG in Figure-2?
• What KIND of lead reversal was present in ECG #1?

Figure-2: The repeat ECG in today's case — recorded as soon as the treating clinician recognized the lead misplacement. (To improve visualization — I've digitized the original ECG using PMcardio).

MY Interpretation of ECG #2:

The repeat ECG in Figure-2 — appears to be technically appropriate. The rhythm is sinus bradycardia at a rate just over 50/minute. All intervals (PR,QRS,QTc) are normal. The frontal plane axis is normal at +70 degrees.

• Although difficult to measure (because of marked overlap of the QRS in multiple chest leads) — there appears to be greatly increased QRS amplitude, consistent with voltage for LVH.
• R wave progression is probably normal (again — difficult to assess given marked QRS overlap in multiple chest leads). That said — the R wave is unexpectedly tall already by lead V2 (~15 mm in height).
• T waves are prominently peaked in multiple leads — with 1-2 mm of gradually upsloping ST elevation in leads V1-thru-V4. There is no reciprocal ST depression.
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• KEY Point: Once all electrode leads were properly placed for ECG #2 — the negative inferior lead P waves disappeared (and the normal upright P waves in lead II of a sinus rhythm were then seen) — and the inferior lead QS waves with deep T wave inversion disappeared.
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• Impression: In this middle-aged man with palpitations and dyspnea, but no chest pain — I suspect that the T wave peaking and slight, upward-sloping chest lead ST elevation represent a repolarization variant. Especially given the unexpectedly tall R wave by lead V2, with greatly increased and overlapping chest lead QRS amplitudes — I did not think any of these findings represented an acute process. In view of the increased QRS amplitudes — I'd favor an Echo.
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• Follow-Up: Nothing acute was found on further evaluation.

What Happens with Lead Reversal?

My favorite on-line “Quick GO-TO” reference for the most common types of lead misplacement comes from LITFL ( = Life-In-The-Fast-Lane). I have used the superb web page they post in their web site on this subject for years. It’s EASY to find — Simply put in, “LITFL Lead Reversal” in the Search bar — and the link comes up instantly.

• This LITFL web page describes the 7 most common lead reversals. There are other possibilities (ie, in which there may be misplacement of multiple leads) — but these are less common and more difficult to predict.
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• By far (!) — the most common lead reversal is mix-up of the LA (Left Arm) and RA (Right Arm) electrodes. This lead reversal is usually EASY to spot — because it typically produces global negativity of the P wave, QRS and T wave in lead I — which is something that is virtually never normally seen (See ECG Blog #264 — for an example of LA-RA lead reversal).
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• In contrast — it is EASY to overlook what is probably the 2nd-most frequent form of lead misplacement, which is LA-LL reversal. This is because the ECG picture seen with LA-LL reversal does not immediately stand out as physiologically “off” (See Figure-3 — in which I summarize KEY points that help me most in recognizing lead reversals — with LINKS in my References below to over 15 Blog post examples of various forms of lead misplacement).

Figure-3: Tips for recognizing lead reversal (See text).

What about the Type of Lead Reversal in Today's Case?

The technical misadventure in today's case is unique from other Blog post examples I have published — in that there is bilateral arm-leg reversal (LA-LL plus RA-RL — with summarizing features in Figure-4).

• Note how each of the abnormal findings in ECG #1 — are corrected in ECG #2 after proper electrode lead placement.
• Note again that the KEY to facilitating immediate recognition of this technical misadventure — is seeing the flat line in lead I.

Figure-4: Comparison between limb lead appearance in ECG #1 with ECG #2 (These distinguishing features summarized from the LITFL web site that I referred to above).

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Acknowledgment: My appreciation to H.S. Cho = 조현석 (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.
• ECG Blog #185 — Review of the Ps, Qs, 3R Approach for systematic rhythm interpretation.
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• ECG Blog #264 — Review of limb lead reversal (ie, LA-RA lead reversal in a patient with an acute MI).
• ECG Blog #375 — LA-LL Lead Reversal.

OTHER Examples of Lead Reversal (from Dr. Smith's ECG Blog):

Technical errors featuring a variety of lead reversal placements remain a surprisingly common “mishap” of everyday practice. As a result — it's important to familiarize ourselves with how best to recognize the various forms of these "misadventures". For review — Check out My Comment — at the bottom of the page in the following posts on Dr. Smith's ECG Blog:

• The June 4, 2018 post (LA-LL reversal).
• The July 29, 2018 post (LA-RA reversal).
• The November 4, 2018 post (Leads V1,V2 misplacement).
• The February 11, 2020 post (LA-RA reversal).
• The March 18, 2020 post (LA-RA reversal).
• The July 28, 2020 post (RA-LL reversal).
• The August 28, 2020 post (LA-LL reversal).
• The November 19, 2020 post (LA-LL reversal).
• The November 27, 2021 post (LA-RA reversal).
• The April 17, 2022 post (Leads V1,V2 misplacement).
• The May 5, 2022 post (LA-RA reversal).
• The May 24, 2022 post (LA-LL reversal).
• The May 26, 2022 post (LA-LL reversal).
• The August 17, 2022 post (LA-RA reversal).
• The May 13, 2023 post (LA-RA reversal).
• The May 30, 2023 post (LA-RA reversal).