- A) AFib with a rapid ventricular response.
- B) SVT with RBBB aberration.
- C) The rhythm could be VT.
- D) The rhythm is VT.
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| Figure-1: Which of the above choices is the best answer? = = = = = = = [ Abbreviations: AFib (Atrial Fibrillation) — SVT (SupraVentricular Tachycardia) — RBBB (Right Bundle Branch Block) — VT (Ventricular Tachycardia)]. |
- Take another LOOK at today's tracing in Figure-2. For clarity — I've numbered the beats in the long lead II rhythm strip.
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| Figure-2: I've numbered the beats in today's tracing. |
- The overall rhythm appears to be Regular. This is best assessed in simultaneously recorded leads I and III, in which it is easier to see the consistency in the R-R interval (and more difficult to appreciate in lead II — where there is more artifact distortion).
- The Rate of the rhythm is slightly more than 150/minute (ie, with an R-R interval of slightly less than 2 large boxes in duration).
- The QRS is wide (at least 3 small boxes in duration — therefore ≥0.12 second).
- Are there P waves?
- The fact that the R-R interval in Figure-2 is regular effectively rules out AFib (and if we can confirm that P waves are truly present — this would definitively rule out AFib).
- The rhythm in Figure-2 is a regular WCT (Wide Complex Tachycardia).
- The rate of the rhythm is slightly more than 150/minute.
- There is no clear sign of sinus P waves (ie, There is no consistent upright P wave with constant PR interval preceding each QRS complex in the long lead II rhythm strip).
- The above said — a number of small upright deflections in the baseline do appear to be present throughout the long lead II. These could be P waves.
- PEARL #1: Assuming today's patient is an adult — by far, the most common cause of a regular WCT rhythm without clear sign of sinus P waves is VT. Therefore — We need to assume VT until proven otherwise!
- Although the predominantly upright QRS complex in lead V1, in association with wide terminal S waves in lateral lead V6 could be consistent with RBBB conduction — you should virtually never see an all negative QRS complex in lead I with a supraventricular rhythm.
- Based on QRS morphology then — this strongly suggests that the rhythm in Figure-2 is VT (which means we can effectively rule out SVT with RBBB aberration).
- But — Are we 100% certain that today's rhythm is VT?
- To Emphasize: IF we were at the bedside with this patient — the 1st thing we would do is determine if the patient is hemodynamically stable! That's because if the patient is not stable with this rhythm — then it would no longer matter what the rhythm is, because synchronized cardioversion would then be immediately indicated.
- But assuming that this patient is hemodynamically stable — we would then have a moment in time to quickly look a little closer.
- Please NOTE: I have described my above thoughts in slow motion. With practice and experience — You should be able to arrive at this point in the process in no more than 10-to-15 seconds!
- Is there an EASY way to determine with certainty whether P waves are (or are not) present in today’s ECG?
- PEARL #3: As I have often emphasized in this ECG Blog — the simple step of labeling P waves is incredibly helpful for determining the presence and nature of underlying atrial activity.
- In Figure-3 — I’ve labeled with RED arrows those small upright deflections in the long lead II rhythm strip that look like they may represent P waves.
- If these RED arrows in Figure-3 are in fact highlighting the presence of underlying P waves — Does this suggest what the P-P interval might be?
- PEARL #4: If we can demonstrate that the small upright deflections in Figure-3 remain consistently regular throughout the long lead II — this would prove that these small upright deflections do represent an underlying rhythm of regular P waves.
- To do this — I look to see what the shortest distance between 2 consecutive RED arrows might be. Doesn't it look like this shortest distance repeats between the 4th and 5th RED arrows — and between the 7th and 8th RED arrows?
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| Figure-3: I've highlighted with RED arrows the small upright deflections in the long lead II rhythm strip that I can clearly see. |
- To Emphasize: I am not encouraging the use of calipers if your patient is unstable. A hemodynamically unstable patient in a WCT rhythm should be immediately cardioverted!
- But IF the patient whose rhythm is shown in Figure-3 is hemodynamically stable — it takes no more than seconds to walk out the rhythm that I've highlighted with colored arrows in Figure-4.
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| Figure-4: I've added WHITE and PINK arrows to Figure-3. |
- Although on-time regular wide QRS complexes prevent us from seeing P waves under the WHITE arrows that I've added to Figure-4 — a definite underlying upright deflection can be seen under each of the 2 PINK arrows!
- This tells us that the colored arrows in Figure-4 represent an underlying rhythm of regular P waves occurring at an atrial rate of ~90/minute!
- In my experience — AV dissociation is greatly overdiagnosed! This is because of the tendency to assume there is AV dissociation whenever clinicians see any suggestion of underlying baseline deflections. In my decades of following up on regular WCT rhythms — most cases of WCT rhythms labeled as showing "AV dissociation" do not truly represent this finding.
- It is because true AV dissociation proves that a WCT rhythm is VT — that I feel it best to avoid the diagnosis of AV dissociation unless you can clearly demonstrate the presence of underlying regular P waves throughout a significant portion of the rhythm. Doing so can only be done by use of calipers.
- Unfortunately — the clinical reality is that it is rare to see AV dissociation in faster WCT rhythms. This is because when a WCT occurs at a faster rate — the wide QRS complexes and often large-sized ST-T waves are highly efficient at "hiding" underlying P waves.
- BOTTOM Line: The colored arrows in Figure-4 do demonstrate AV dissociation. This proves beyond doubt that today's WCT rhythm is VT!
- Additional examples of "My Take" on assessing the regular WCT rhythm can be found in ECG Blog #196 — Blog #220 — Blog #263 — and Blog #283 — among many others.
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| Figure-5: XXX |
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| Figure-6: XXX |
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| Figure-7: XXX |
ADDENDUM (2/XXX/2026):
I refer the reader to my ECG Blog #196 — in which I walk through a similar problem-solving process for another regular WCT rhythm.
- I've excerpted from that post my Audio PEARL on assessing the regular WCT — as well as Figures on my "3 Simple Rules" and on QRS morphology in lead V1.
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| Figure-8: Use of the “3 Simple Rules” for distinction between SVT vs VT (excerpted from my ACLS-2013-ePub). |
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| Figure-9: Use of lead V1 for assessing QRS morphology during a WCT rhythm (excerpted from my ACLS-2013-ePub). |
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Константин Тихонов <dropattack03@icloud.com> (2/11/2026)
I had a patient on call today. This is a 45-year-old man with a history of hypertrophic cardiomyopathy (without obstruction of the outflow tract of the left ventricle) and thyrotoxicosis. In January of this year, he had two similar episodes, and he was hospitalized twice by an ambulance team. Both times, the rhythm was restored with the help of electric pulse therapy. The diagnosis was ventricular tachycardia. He called an ambulance for a rapid heartbeat. During our examination, the patient was not pale, and there was no diaphoresis. His blood pressure was 125/70, compared to his normal blood pressure of 130/80. His oxygen saturation was 97%. His respiratory rate was 16.
ECG No. 1 was recorded first. After that, there was a short episode of sinus rhythm recovery with premature ventricular complexes, after which the tachycardia with wide QRS complexes recurred (ECG No. 2).
ECG No. 3 was recorded after 150 mg of amiodarone, after which the patient felt a significant improvement in his well-being.
My opinion:
I believe that ECG No. 1 shows ventricular tachycardia.
1. There is an almost regular rhythm with small differences in RR intervals in some places. (Black lines)
2. The electrical axis on ECG No. 1, in my opinion, is approximately +120 degrees, while on ECG No. 3 it is about +60 degrees.
3. I have marked with red arrows on ECG No. 1 the possible presence of atrioventricular dissociation, which I believe is present.
4. The R nadir time in lead II is more than 50 ms.
5. The QRS complexes in tachycardia are similar in morphology to the premature ventricular complexes on ECG No. 3.
ECG No. 3 raises special questions. It seems to me that there are regular P waves, the first of which are conducted, while the second are not and are hidden in the ST-T of the ventricular extrasystoles. These P waves are very similar in morphology to the sinus waves, as can be seen by comparing their morphology, which I have indicated with blue arrows on ECG No. 3. Also, these possible P's are not premature, so they are probably not blocked atrial extrasystoles. Is it possible that after a sinus contraction, a ventricular extrasystole occurs that retrogradely depolarizes the AV node, but the next sinus P finds the AV node in the absolute refractory period and is not conducted to the ventricles?
MY REPLY:
Hi Konstantin.Yes — VERY interesting case. I would like to do an ECG Blog on this case. Because the tracings are so long, I will need to reduce them — and I probably will only show the 1st and 3rd tracings together with the laddergram that I’ve drawn below. If OK by you — I will acknowledge you — and I’ll let you know when I publish this (it may be a little while — as I have other cases to go before this).
MUCH better to show this tracing when you ask the question about retrograde P waves — because I can now directly refer to this ECG.
- There are NO retrograde P waves. You did a GREAT job highlighting the P waves. There is often some underlying sinus arrhythmia — which is the reason for slight change in P-P intervals.
- You PROVE beyond doubt (100%) that this rhytm is VT. Assuming no lead misplacement — you virtually NEVER see an all negative QRS in lead I.
- You very nicely highlight the on-time sinus P waves. This establishes AV dissociation, which especially given the abnormal QRS morphology tells us 100% that this rhythm is VT.
- Your ECG #3 shows ventricular bigeminy. The attached laddergram shows what is happening = on-time sinus P waves that are unable to conduct because the ventricular beats do conduct retrograde and therefore prevent every-other on-time P wave from being conducted down to the ventricles.
- This is a NICE PEARL — the fact that on-time sinus P waves continue throughout the tracing proves that beats #2,4,6,8,10,12 can not possibly be supraventricular (because if they were supraventricular, they would have reset the SA node)
I hope this makes sense. You did a GREAT job mapping out the P waves and the AV dissociation — and this PROVES this rhythm is VT.
Do you have any more follow-up on this patient!
Take care.
: ) Ken
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KONSTANTIN Reply:
Thanks a lot, Ken. I am very glad that my version turned out to be correct, because I am now trying to learn to understand complex rhythms in more detail.
On account of this patient. Later that night, the patient called an ambulance twice more and had two more recurrences of ventricular tachycardia. As a result, he was admitted to the hospital. He has been assigned to conduct an electrophysiological examination and the issue of installing a cardioverter-defibrillator will be considered.
