- How can it be that these 2 ECGs are from the same patient?
- NOTE: All electrode leads were correctly positioned on the patient's extremities and chest (such that the change in appearance that we see in ECG #2 is not the result of lead reversal).
-USE.png) |
| Figure-1: Comparison between the 2 ECGs in today's case. |
===============================
- The rhythm in ECG #1 is sinus at a rate of ~70/minute. All intervals (PR, QRS, QTc) and the frontal plane axis are normal.
- Assuming the patient is over 35 years of age — LVH is probably present (deepest S in lead V2 + tallest R in lead V5 is very close to satisfying the 35 mm criterion, with an R wave in lead V4 that is extremely tall).
- The ST segment is coved in leads V3-thru-V6, with some ST depression and symmetric T wave inversion. There is nonspecific ST-T wave flattening in the limb leads.
- Impression: Sinus rhythm with probable LVH + ST coving and T wave inversion in leads V3-thru-V6 consistent with LV "strain" and/or ischemia. Clinical correlation is needed (and ideally finding a prior tracing for comparison).
- I wondered how much time had passed between the recording of ECG #1 and ECG #2?
- Seeing both tracings next to each other in Figure-1 — the differences between these 2 ECGs are striking! Not only is QRS amplitude increased in the repeat ECG — but the frontal plane axis has shifted dramatically to the right, and the QRS is now predominantly positive in lead V1 (whereas in the initial ECG — the QRS in V1 was predominantly negative).
- This is not the result of a conduction defect — because the QRS lacks the widening of RBBB or IVCD.
- Since lead I and lead V6 are both left-sided leads — these 2 leads normally bear some resemblance to each other. Yet lead I is now predominantly negative — and left-sided chest leads V4,V5,V6 are all markedly positive.
- Yet despite this bizarre and drastic change in QRST morphology that we see between the 2 tracings in Figure-1 in both limb and chest leads — we are told that all electrode leads are correctly positioned on the patient's extremities and chest (such that the change in appearance that we see in ECG #2 is not the result of lead reversal).
- Thinking "outside the box" and remembering that the reason ECG #2 was recorded was the sudden onset of CP — I wondered about physiologic events that might cause CP, and which have been known to produce bizarre positional shifts in relative cardiac anatomy (ie, abrupt onset of pneumothorax — or since this patient was admitted for abdominal pain, perhaps intestinal perforation?).
- OR — Could this still somehow be some manifestation of a technical misadventure?
- 2 hs-Troponins were negative — and another repeat ECG looked the same as ECG #2. Bedside Echo was normal, without any wall motion abnormality ==> the difference between ECG #1 and ECG #2 was not the result of acute infarction.
- Both ECGs are from the same patient.
- The 4 extremity electrodes were verified to all be on the correct extremities.
- The 6 precordial lead electrodes were all correctly placed on the chest.
- The connecting cables for unipolar lead V1 and the LL (Left Leg) electrode were swapped.
- As shown in Figure-2 — it's easy to understand how the technical misadventure of misconnecting the V1 and LL cables might happen since both cables are color-coded in RED.
- It turns out that the cable connectors were unplugged during room cleaning — and then misconnected when the cables were reattached.
-USE.png) |
| Figure-2: Magnified view of the ECG cable hub. |
===============================
-USE.png)
THE ANSWER:
In this case, the lead connections were incorrect at the cable hub: V1 and LL were swapped, as were V2 and LA. Note that both V1 and LL utilize red color-coding; errors can occur if the connectors are unplugged during room cleaning and subsequently reattached incorrectly. Based solely on the ECG, V1 and V2 showed tall R waves compared to the admission tracing. While a posterior MI was initially suspected clinically, this was ruled out following serial ECG follow-ups and an echocardiogram that showed no regional wall motion abnormalities (RWMA). Additionally, an abnormally tall R wave in aVR—a finding typically associated with sodium channel blocker toxicity—was observed; however, the patient was not tachycardic, the QRS complex was not widened, and a medication review ruled out toxicity. A shift in the QRS axis from normal to "right superior axis" (also known as "No-man’s land") was noted, raising suspicion of lead misplacement. Deep S waves in leads I, aVL, and II provided further clues that the leads were misplaced, altering the apparent QRS morphology. Combined with the suspicion of V1–V2 misplacement, it appeared that the V1 and V2 leads had been swapped with the limb leads. After confirming correct electrode placement and re-checking the setup, the error was traced back to incorrect connections at the cable hub.
I have unravelled the puzzle of this ECG , hope you enjory it. Never see this kind of misplacement before.
=================
MY REPLY:
Thanks for the explanation. The ECG is totally bizarre and does not look "anatomic". I should have mentioned that part of verifying that all was done correctly entails checking the cable connections. I "assumed" that was done — and that was my mistake. GREAT case — mystery solved!
PAUL MATERA Comment:
Ken Grauer , as you know we have discussed this issue a few times ie the old bad info in bad info out routine , patient position, lead placement, lead input, calibration all have to be “standard” .. supine (or notation that they were not able to) , leads and inputs correct , 10mm/mV , 25mm/sec (except for Nordic colleagues 50mm/sec) or a “standard” interpretation can’t be done . I have also had situations where the computer was reading something other than the ECG printout was showing .. because the paper feed was slipping making it look like bizarre dysrhythmia , my position is that a seasoned ECG interpreter can read through any non-standard ECG .. as long as the interpreter is aware of each lead positive and negative and which chest leads were misplaced , nod to Einthoven and Vector , great case
MY REPLY to Paul:
Paul Matera — Agree entirely with you Paul! The "hint" is how bizarre the change in these tracings is. Simple lead misplacement won't alter the chest leads (and certainly not like this). "Ya gotta be there" — but we need to routinely "add to the checklist" looking at the lead connectors.
林柏志 has kindly granted me permission to write this case up as an ECG Blog — which I will entitle, "The leads were not misplaced!" —
======================
Sukumaran and Selvaraj — Indian Pacing Electrophysiol J 24(2):119-121, 2024
https://pmc.ncbi.nlm.nih.gov/articles/PMC11010442/
Rudiger et al — Am J Emerg Med 25:174-178, 2007
https://www.sciencedirect.com/science/article/abs/pii/S0735675706003822?via%3Dihub
Lead reversals are surprisingly common in practice — estimated to make up between 0.4%-to-4% of all ECGs recorded. It is crucial to recognize electrocardiographic lead reversal because it can lead to a false diagnosis of myocardial ischemia or infarction. The most commonly encountered reversals involve misplacement of the limb electrodes, with right arm–left arm misplacement accounting for 20% of all lead reversals. ECG findings due to limb lead reversal produce characteristic patterns which can help identify them.
In contrast, when limb and precordial electrodes are interchanged (Fig. 4), the Wilson Central Terminal is altered, producing bizarre ECGs that are difficult to interpret. These are less common and usually happen because of the misconnection of the electrodes. Electrode misplacement due to faulty cable connections is much less common. Most modern ECG machines have a single cable attaching all the electrodes to the machine. However, a few machines have two separate cables with an identical attachment providing an opportunity for reversal of the cables.
======================
Paul and Jacob — Indian Pacing Electrophysiol 23(6):205-213, 2023
https://pmc.ncbi.nlm.nih.gov/articles/PMC10685096/
— This is an amazingly complete article that details virtually all possibilities of limb lead and precordial lead misplacements. In general — misplacements contained within limb leads (without interchange in any of the chest leads) — and those contained within the chest leads (without interchange in any of the limb leads) — are easier to recognize because the are likely to produce predictable lead reversal patterns (Reference my technical misadventure page). But reversals involving misplacement/interchange of limb and chest leads may produce any number of bizarre possibilities with a unique resultant ECG impossible to predict. The clinical implications are clear: #1) Realize that bizarre ECGs that seem impossible to explain by physiology do occur. When you see such a tracing in a patient in whom the clinical history does not suggest any medical condition likely to produce such a bizarre ECG — especially if other parameters (ie, CxR, Echo) look normal — then suspect some unusual “technical misadventure”. If limb lead electrodes are all on the correct extremity and chest lead electrodes seem appropriately placed — then look at the electrode lead hub connections!
Interchange of a precordial electrode with a limb electrode can occur due to the matching colours of the two electrodes [23], or the incorrect attachment of the cable connectors to the junction box of the ECG machine [24]. This distorts the Wilson's central terminal, and results in distortion of the tracings of multiple leads, with augmented precordial-like amplitudes in some of the limb leads and altered morphology in the concerned precordial leads. It could lead to ST elevation/depression in some of the leads, raising the possibility of erroneous diagnosis of myocardial ischaemia/infarction [24]. This distorts the Wilson's central terminal, and results in distortion of the tracings of multiple leads, with augmented precordial-like amplitudes in some of the limb leads and altered morphology in the concerned precordial leads. It could lead to ST elevation/depression in some of the leads, raising the possibility of erroneous diagnosis of myocardial ischaemia/infarction
=====================
I’ll close with this primer on terminology by “lub dub medical” on ECG Cables: The Complete Guide to Types, Connectors, Lead Configurations and Compatibility ( https://www.lubdub.com/ecg-cables-the-complete-guide-to-types-connectors-lead-configurations-and-compatibility/ ) that provides insight into the many ways the technical components of what goes into an ECG machine may vary. ECG machines are not all made the same. When you encounter a truly bizarre-looking ECG that does not comply with the usual predictable patterns of lead reversal — we need to put on our “detective hats” and look for unusual forms of technical misadventures.
-USE.png)
-labeled-USE.png)
-USE.png)
-USE.png)
-USE.png)
-USE.png)
-USE.png)
-USE.png)
-USE.png)
-USE.png)
.png){kind=link}