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).

ECG Blog #395 — No Simple Explanation ...

The tracing in Figure-1 was sent to me for my interpretation. As per the title of today's Blog post — There is no simple explanation for all that is happening in this challenging tracing. Are YOU up for the challenge?

• I found that the most challenging part of today's tracing is determining the etiology of beat "X". As I explain below — I think it unlikely that beat "X" represents a single, slightly accelerated junctional beat.
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• Can YOU come up with a more likely explanation? 

Figure-1: How would YOU interpret this challenging tracing? 

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NOTE:  Although determining the etiology of beat "X" involves a number of advanced concepts — today's case also reviews KEY points in the assessment of any arrhythmia — so, regardless of your level of experience interpreting arrhythmias — I hope you'll stick with me!

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HOW to Begin?

Regular followers of my ECG Blog know I routinely emphasize a series of user-friendly points to facilitate the interpretation of any rhythm. These include the following:

• IF there is more than a single feature in a given arrhythmia (ie, When the tracing is not a simple sinus rhythm) — then LOOK to see if there is an underlying rhythm?
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• IF there are easier elements of the rhythm to interpret, as well as more difficult elements — Start with the EASIER elements (and save the more difficult elements for last). You'll often be pleasantly surprised that explanation of the more difficult elements becomes evident once you've interpreted some of the less difficult elements.
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• Number the beats. This way you and your colleagues can be certain you are all talking about the same part(s) of the tracing. (This also saves YOU time — because you have a numbered reference point to quickly locate that part of the tracing you were looking at).
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• Label the obvious P waves.

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Take another LOOK at today's tracing in Figure-2 — in which I have numbered the beats and labeled the obvious sinus P waves with RED arrows.

• Is there an underlying rhythm in Figure-2?
• What is the "easiest" part of today's tracing to interpret?

Figure-2: I have numbered the beats and labeled (with RED arrows) the obvious sinus P waves. 

The Underlying Rhythm:

The simple step of labeling those P waves that are obvious in Figure-2 — allows us to quickly recognize that the underlying rhythm in today's tracing is sinus.

• That the underlying rhythm is sinus — is established by the RED arrows in Figure-2 that appear before beats #1,2; 4,5; 8; 10,11; and 13 — with each of these P waves manifesting a similar shape and the same normal PR interval in front of the QRS complex that follows each of these P waves.
• The 1 RED-arrow P wave in Figure-2 that is not followed by a QRS complex — is the P wave distinguished by the extra little "hump" that peaks through the ST segment of beat #7 (ie, This is the 5th RED arrow in Figure-2). 
• We know that this extra "hump" in the ST segment of beat #7 is a sinus P wave — because the distance from this little "hump" until the next sinus P wave — is virtually the same as the distance between the P waves that precede beats #1-2; beats #4-5; and beats #10-11.

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Helpful Reminder: Using calipers greatly facilitates (and speeds up) the interpretation of any complex arrhythmia! In particular — use of calipers will make it much easier to answer this next Question:

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QUESTION:

• As you take another LOOK at Figure-2 — Do you see any indication of additional P waves?

ANSWER:

• In Figure-3 — I've added BLUE arrows to today's rhythm, to show how using calipers facilitates visualization of an underlying regular atrial rhythm (ie, on-time P-wave-induced deflections that deform the ST-T waves of beats #3,6,9 and 12 are seen under each of the BLUE arrows).

Figure-3: I've added BLUE arrows to today's rhythm — to show that the underlying atrial rhythm continues throughout the entire rhythm.

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NOTE: The P-P interval between each of the colored arrows is not precisely regular. As is often the case — there may be slight sinus arrhythmia. That said — it should be apparent that the "theme" of the P waves in Figure-3 is that of an underlying almost regular sinus rhythm.

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What About the Wide Beats in Figure-3?

At this point — it's worthwhile considering those parts of today's tracing that we've established.

• The underlying rhythm in Figure-3 is sinus (ie, Beats #1,2; 4,5; 8; 10,11; and 13 are all clearly sinus-conducted).
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• Beats #3,6,9 and 12 are wide, very different in morphology from sinus-conducted beats — and not preceded by P waves. This defines beats #3,6,9 and 12 as PVCs (Premature Ventricular Contractions) — until proven otherwise.
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• PEARL #1: PVCs may or may not conduct retrograde back to the atria. When PVCs do conduct retrograde — they will depolarize the atria, thereby resetting the SA node. As a result — there will be a delay before the next sinus P wave appears.
• In contrast, when PVCs do not conduct retrograde — the next sinus P wave will usually occur on time! This is precisely what we see with the BLUE arrows in Figure-3 — namely that on-time sinus P waves continue throughout the entire tracing!
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• PEARL #2: The fact the early-occurring wide beats in Figure-3 do not reset the SA node proves that beats #3,6,9 and 12 are PVCs! This is because if these early beats were PACs or PJCs conducted with aberrancy — these premature supraventricular beats would have reset the SA node!

Putting It All Together:

We have explained almost everything in today's rhythm — except beat #7, which is a narrow QRS complex that is not preceded by any P wave.

• To Emphasize: IF this is as far as you got — namely, that the rhythm in today's tracing is sinus with frequent PVCs — this clearly would be sufficient for appropriate clinical management of this patient.
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• BUT — If you are intellectually curious as to what I feel is the most likely explanation for beat #7 — Read on!

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The CHALLENGE in Today's Rhythm:

What follows is the advanced part of today's arrhythmia. For clarity in Figure-4 — I've labeled each of the P waves in this tracing.

• At first glance — the absence of any P wave in front of beat #7 suggests that this narrow QRS complex (with identical QRS morphology as is seen for other sinus-conducted beats) would be a junctional beat.
• However, if beat #7 represented a slightly accelerated junctional escape focus — I would have expected beats #4, 10 and 13 (which are preceded by longer R-R intervals) — to also be junctional escape beats instead of sinus-conducted.

Figure-4: I've labeled each of the P waves in today's rhythm.

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Laddergram Illustration:

Academically — I was fascinated by today's rhythm. But at this point, since I could not yet explain all ECG features — I needed to draw a laddergram. I'll emphasize that I am almost always able to quickly and accurately recognize the likely mechanism of most complex rhythms without need for a laddergram. Today's tracing is an exception, in that I needed to see IF with assistance of a laddergram, I could work out a plausible mechanism to explain this unusual rhythm. 

• Sequential legends over the next 8 Figures illustrate my thought process as I derived this laddergram. (See ECG Blog #188 for review on how to read and/or draw Laddergrams).
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• To EMPHASIZE — This laddergram was challenging to draw, as I explain below. That said — my hope is that even readers with limited experience with laddergrams will be able to follow my rationale for deriving the most plausible explanation for beat #7.

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Figure-5: It is usually easiest to begin a laddergram by marking the path of sinus P waves through the Atrial Tier (as per the RED lines drawn directly below the onset of each of the P waves — as shown here by the large BLUE arrows). Note that these RED lines in the Atrial Tier are nearly vertical — since conduction of sinus P waves through the atria is rapid. Note also that the P-P interval between successive P waves (vertical RED lines) is similar, albeit not quite equal (ie,There is slight sinus arrhythmia).

Figure-6: The most challenging part of most laddergrams is construction of the AV Nodal Tier — so I typically save that for last. Therefore, after drawing in all P waves into the Atrial Tier — It's easiest to next add indication of all narrow (ie, conducting) QRS complexes into the Ventricular Tier. The large BLUE arrows show that I use the onset of each QRS as my landmark. Note that the RED lines in the Ventricular Tier are also nearly vertical — since conduction of these narrow QRS complexes through the ventricles is rapid.

Figure-7: It's time to begin "solving" what we can in the laddergram. I start by connecting those sinus P waves in the Atrial Tier that I know are conducting to narrow QRS complexes in the Ventricular Tier (slanted BLUE lines that I've drawn connecting P waves a,b; d,e; h; j,k; and m to beats #1,2; 4,5; 8; 10,11; and 13 in the Ventricular Tier).

Figure-8: The next element in today's tracing that I am certain about — is that beats #3,6,9 and 12 are PVCs (since these beats are wide — very different in morphology from sinus-conducted beats — and not preceded by P waves). I've drawn these PVCs in BLUE, as originating from the ventricles — and conducting back toward the atria.

Figure-9: How far back into the AV Nodal Tier these 4 PVCs conduct is uncertain — but given that RED-arrow sinus P waves continue at a fairly regular rate throughout the entire rhythm strip — we can surmise that retrograde activity from these PVCs does not reach the Atrial Tier (the dotted BLUE lines suggesting retrograde conduction from these PVCs stops within the AV Nodal Tier). NOTE: I added a question mark ( ? ) within the AV Nodal Tier to indicate my uncertainty about how far down P wave "g" is able to conduct.

Figure-10: We know that P waves "c", "i" and "l" do not conduct down to the ventricles (because P waves "d", "j" and "m" are all clearly sinus-conducted). As a result — I added in BLUE butt-ends to show P waves c,i,l are all stopped within the AV Nodal Tier.
—  —  —  — 
KEY Point: I also added a BLUE butt-end for P wave "g". Since P wave "h" is clearly sinus-conducted — P wave "g" can not possibly be conducting, since there is no QRS complex after P wave "g" that could be conducted. For this reason — I added a question mark ( ? ) under P wave "f ", since this is the only P wave left to be accounted for.

Figure-11: Since P wave "f " is the only unaccounted for P wave — and beat #7 is the only unaccounted for QRS complex — P wave "f " must be conducting to produce beat #7. This could occur (as per the slanted BLUE line connecting P wave f with beat #7) — IF retrograde conduction from PVC #6 delayed forward conduction of "f".

Figure-12: The logical completion of today's laddergram is that passage of P wave "f" through the AV Nodal Tier blocks forward conduction of P wave "g" (as per the dotted BLUE line).
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KEY Question: Why is P wave "f" able to make it through the AV Nodal Tier — when P waves "c", "i" and "l" are blocked by retrograde conduction from PVCs #3,9 and 12?
—  —  —  —
ANSWER: The fact that there is an underlying sinus arrhythmia affects the point within the Refractory Period that P waves c,f,i and l occur. Note that the longest P-P interval of 880 msec. occurs between P waves "e" and "f " — which allows a little bit more time for recovery of conduction properties, which is why P wave "f" is able to conduct to produce beat #7, albeit with a very long PR interval.

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NOTE: Learning to draw Laddergrams is challenging. I fully acknowledge that it took me many years until I felt comfortable with this skill. That said — learning to read laddergrams is not difficult! Hopefully, even readers with minimal experience in this area were able to understand my reasoning in design of the laddergram for today's complex arrhythmia.

• I review the basics for reading and drawing laddergrams in my ECG Blog #188. I also add links to more than 90 step-by-step laddergrams that I have added over the years to my ECG Blog — so that anyone wanting practice reading and/or drawing laddergrams has a wealth of material to practice with.
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• As always — I welcome questions and/or comments on today's ECG Blog post! THANK YOU for your interest! 

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Acknowledgment: My appreciation to Mayan Kain (from Tel Aviv, Israel) 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 #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 90 laddergram cases — many with step-by-step sequential illustration).

 

ECG Blog #394 — Is QRS Morphology Disguised?

The ECG in Figure-1 — was obtained from an older man with a history of prior infarction and coronary bypass surgery.

• How would you interpret this tracing?
• Clinical implications?

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

MY Thoughts on the ECG in Figure-1:

The rhythm in ECG #1 is sinus at ~65/minute — with an upright P wave in lead II, and a constant and normal PR interval (ie, not more than 0.21 second in duration). The QTc appears to be normal. There is no ECG indication of chamber enlargement — ST-T wave changes do not look acute.

• The QRS complex is obviously wide (ie, to at least 0.15 second in some leads).
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• In the Chest Leads — The RsR' complex in lead V1, with wide terminal S wave in lead V6 is consistent with an RBBB (Right Bundle Branch Block) pattern.
• In the Limb Leads — The predominantly positive QRS complex in high-lateral leads I and aVL suggests a LBBB (Left Bundle Branch Block) pattern, albeit with a tiny terminal s wave in lead I — and a small, narrow q wave in lead aVL.
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• Clinical IMPRESSION: Today's ECG shows sinus rhythm with QRS widening in a pattern that is not consistent in all 12 leads with either RBBB or LBBB. Instead — QRS morphology in today's tracing suggests masquerading BBB. 

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What is MBBB? (Masquerading Bundle Branch Block)?

I review my user-friendly approach to the ECG diagnosis of the Bundle Branch Blocks in ECG Blog #282 — and to Hemiblocks and Bifascicular Blocks in ECG Blog #203. In brief — the 3 KEY leads that allow accurate diagnosis of RBBB and LBBB within seconds (!) — are right-sided lead V1 and left-sided leads I and V6.

• Supraventricular conduction defects not consistent with either RBBB or LBBB in all 3 of these key leads are most easily classified as IVCD (IntraVentricular Conduction Defect) — with this category representing the "end result" of a number of different pathophysiologic processes.
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• MBBB is a special type of IVCD that although uncommon, is important to recognize because it identifies a group of patients with: i) Very severe underlying heart disease; ii) A much higher predisposition for developing complete AV block (and needing a pacemaker); and, iii) An extremely poor longterm prognosis.

ECG Criteria for the diagnosis of MBBB are described by Dhanse et al (J Clin Diag Research: 10(9), 2016) — and Buttner and Cadogan (LITFL, 2021) — and include the following: 

• An ECG pattern consistent with RBBB in the chest leads (ie, with a widened, predominantly positive QRS in lead V1).
• An ECG pattern consistent with LBBB in the limb leads (ie, with a widened, monophasic QRS in leads I and aVL).
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• NOTE: Variations on this above "theme" of MBBB are common. Thus, the S wave that is typically associated with RBBB patterns in lateral chest leads V5,V6 may or may not be present. In the limb leads, rather than a strict LBBB pattern — more of an extreme LAHB (Left Anterior HemiBlock) pattern may be seen (ie, with wide and predominantly [if not totally] negative QRS complexes in the inferior leads — and with a smaller [blunted] terminal s wave in leads I and aVL).
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• BOTTOM Line: Knowing the clinical history may aid in recognition of IVCD patterns that are consistent with MBBB (ie, if the patient has a known history of severe, underlying heart disease). Distinction from simple bifascicular block (ie, with RBBB/LAHB) — may be facilitated by seeing one or more of the following: i) More of a monomorphic upright QRS in lead V1 (which lacks the neatly defined, triphasic rsR' with taller right "rabbit ear" seen with typical RBBB); ii) Lack of a wide terminal S wave in lateral chest lead V6; iii) Seeing an all-positive (or at least predominantly positive) widened QRS in leads I and/or aVL, with no more than a tiny, narrow s wave in these leads; and/or, iv) Seeing widened, all-negative (or almost all-negative) QRS complexes in the inferior leads.

What About Today's ECG?

Today's patient has a known history of significant underlying heart disease (ie, he is an older adult with a prior infarction, who underwent coronary bypass surgery). His ECG in Figure-1 shows the following:

• Sinus rhythm with marked QRS widening.
• An ECG pattern consistent with RBBB in the chest leads (ie, with an RsR' complex in lead V1 — and wide terminal S waves in lateral chest leads).
• An ECG pattern consistent with LBBB in the limb leads (ie, with predominantly positive QRS in leads I and aVL, albeit with atypical lbbb features of a narrow, terminal s wave in lead I and an initial q wave in lead aVL).
• A QRS morphology in the inferior leads that would otherwise suggest an extreme LAHB pattern — if it weren't for the very wide, predominant R waves suggesting lbbb in leads I and aVL.
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• Taken Together: Today's ECG suggests masquerading BBB. It will be important to correlate this tracing clinically — taking into account the increased chance of needing a pacemaker and the poor longterm prognosis.

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Acknowledgment: My appreciation to Andrea Röschl (from Neumarkt, Germany) 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 #282 — reviews a user-friendly approach to the ECG diagnosis of the Bundle Branch Blocks (RBBB, LBBB and IVCD).
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• ECG Blog #203 — reviews ECG diagnosis of Axis, Hemiblocks and Bifascicular Blocks.