I was sent the ECG in Figure-1 — told only that it was from a middle-aged man who presented for acute CP (Chest Pain).
QUESTIONS:
- What is going on?
- How to approach interpreting this ECG?
- What is the rhythm?
-USE.png) |
| Figure-1: The initial ECG in today's case. (To improve visualization — I've digitized the original ECG using PMcardio). |
==============================
My Approach:
As always (assuming your patient is stable and not in need of immediately cardioversion) — I favor a systematic approach, beginning with a quick look at the rhythm ==> "Watch your Ps,Qs, and the 3Rs" (as reviewed in ECG Blog #185).
- I vary which of these 5 KEY parameters I look at first — depending on particularities of the rhythm.
- In today's case, as I looked at the long lead II rhythm strip — I was struck by the almost beat-to-beat variability in QRS morphology. That said — many of the beats look to be narrow, suggesting the underlying rhythm is supraventricular.
- P waves are present!
PEARL #1: The simple step of labeling P waves is often surprisingly helpful in figuring out what is going on. I have done this in Figure-2 (RED arrows highlighting those P waves that I can definitely identify).
- What do we learn from Figure-2?
-USE-P%20waves.png) |
| Figure-2: I've labeled those P waves that I can definitely identify. |
==============================
What We Learn from Figure-2:
- The underlying rhythm in today's tracing appears to be sinus — as upright P waves with a constant and normal PR interval are seen in front of beats #1,3,4,6,8,11,13 and 15.
- We see 2 sinus-conducted beats in a row = beats #3 and 4. The R-R interval between beats #3 and 4 is just over 3 large boxes — suggesting an underlying sinus rhythm at ~90/minute.
- Although we do not clearly see P waves throughout the entire tracing — the constant P-P interval between consecutive RED arrow P waves that we do definitely see suggests that there probably is a regular underlying P wave rhythm.
- The underlying atrial rhythm is regular.
- In addition to the RED arrow P waves that we definitely see — the PINK arrows in Figure-3 highlight "on time" sinus P waves that partially deform some part of the QRS.
- Even though we do not see any deformation of beat #10 — it makes sense that another "on time" sinus P wave is hidden entirely within this beat ( = the WHITE arrow drawn over beat #10).
- PEARL #3: The PR interval for all of the "on time" PINK arrow P waves is too short to conduct normally. This establishes the presence of intermittent AV dissociation — and this proves that beats #2,5,7,14 and 16 must all be ventricular beats.
- The reason for slight variation in QRS morphology for these ventricular beats — is that there most probably is some fusion of conduction between sinus P waves and the ventricular beats that follow soon thereafter (See ECG Blog #128 — for more on fusion beats).
- Fusion is unlikely for beat #10 — because the "on time" WHITE arrow P wave occurs too late to be able to penetrate the ventricles in time to conduct. This provides insight as to what PVCs look like in simultaneously-occurring leads V1,V2,V3- START HERE !!! More PEARLS — Note only 1 normal sinus-conducted beat in V1,2,3 = beat #11! - simplify this in Figure-4 !!!!
XXXXX
-USE-All%20P%20waves.png) |
| Figure-3: XXXX |
XXXXX
-USE-All%20P%20waves-Focus.png) |
| Figure-4: XXXX |
XXXXX
-USE-All%20P%20waves-Focus-shade.png) |
| Figure-5: XXXX |
XXXXX
%20ECG-1%20(9-21.25-2026)-USE-All%20P%20waves.png) |
| Figure-6: XXXX |
XXXXX
==================================
Acknowledgment: My appreciation for the anonymous contribution of today's case.
================================== 
=============
mohammad dalirian <mdalirian1380@gmail.com> (2/25/2026)
From: mohammad dalirian <mdalirian1380@gmail.com>
Subject: ECG - February 25, 2026 at 2:40:57 PM EST
Hello Professor - Do Anonymous
Middle aged man with chest pain — What's the Rhythm & Culprit?
MY REPLY:
— Are there “Normal” Beats? —
I was sent this tracing = Middle-aged man with CP — How to approach?
Hi. This is a VERY challenging tracing!
- Is this YOUR patient? OR — Did you find this case on the internet? If on the internet — please give me the exact LINK to where it was posted.
- If you could get me some follow-up as to what happened? Perhaps a follow-up ECG? If cardiac cath was done — or if thrombolytics were given — then I’d LOVE to do an ECG Blog on this case IF you would give me permission?
- As you can see in the long lead II rhythm strip — QRS morphology continually changes! But the underlying atrial rhythm is regular! (RED arrows).
- Beats #1,3,4,6,8,11,13,15 are all sinus-conducted beats.
- The other beats are PVCs. Those PVCs with a P wave in front of them ( = beats #2,5,9,12,) are FUSION beats ( = the on-time sinus P wave was able to partially conduct until it encountered the ventricular beats.
- Note that there is a ventricular couplet (2 PVCs in a row) for beats #9,10. The distance between these 2 beats = 2.6 large boxes, which corresponds to a ventricular rate of ~115/minute, which is slower than the rate for VT (Ventricular Tachycardia). Therefore — rather than VT — this is AIVR (an Accelerated IdioVentricular Rhythm) — and AIVR in the setting of an acute MI is often a “reperfusion” arrhythmia. I don’t know WHEN this ECG occurred with respect to the onset and duration of this patient’s CP ???? But reperfusion ( = reopening) of the acutely occluded coronary artery, which we call the “culprit” artery — can occur following cath with PCI — or — following thrombolytics — or — occur spontaneously. In any case — if this is a reperfusion arrhythmia, then the patient’s CP shoud have decreased!
- Note that the PVCs change the QRST morphology! — so it’s best to look at the sinus-conducted beats in each of the 12 leads to assess for ST-T wave changes. Within the dotted BLUE rectangles, are sinus-conducted beats in each of the 12 leads!
- In leads I,II,III (ie, for beats #1,2,3,4) — there is a large Q, ST coving and shallow T wave inversion for sinus-conducted beats #3,4. There is ST depression in leads I and II.
- In leads aVR,L,F (ie, for beats #5,6,7,8) — the ST segment of beat #6 looks a bit elevated (if not altered by some artifact). There is reciprocal ST dep in lead aVL for beat #6 — so I think there has been an inferior MI at some point in time. But it is hard to determine the acuity of this without knowing specific details about the history ( = When did CP begin with respect to this tracing? Was the patient still having CP at the time this ECG was recorded? Is there any prior history of a previous MI?
- In the chest leads — beat #11 is sinus-conducted — and it shows ST elevation in leads V1,V2,V3 (with the most ST elevation in lead V3 !!!!)
- In leads V4,V5,V6 for beat #13 — there is ST flattening and dep in leads V5,V6.
BOTTOM LINE — My guess is that this ECG represents an acute STEMI from proximal LAD occlusion (producing a “Precordial Swirl” pattern in the chest leads = See ECG Blog #380 — for more on Precordial “Swirl”). The evidence of inferior MI could either be acute (from an LAD with “wraparound” that also supplies the inferor wall) — or more likely from a prior inferior MI. History, prior tracings, cath results etc would be needed figure this out ...
So — What happened? I hope the above is helpful — :) Ken
