The ECG in Figure-1 was obtained from a middle-aged woman — who presented to the ED (Emergency Department) with palpitations. She was hemodynamically stable at the time ECG #1 was recorded. The patient had been started on propafenone several days before.
QUESTION: What is the cardiac rhythm?
- — a) Sinus rhythm with intermittent LBBB aberrancy.
- — b) Sinus rhythm with intermittent RBBB aberrancy.
- — c) Sinus rhythm with runs of NSVT.
- — d) Atrial Fibrillation with aberrant beats.
- — e) Atrial Fibrillation with lots of PVCs.
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| Figure-1: The initial ECG in today's case — obtained from a middle-aged woman with palpitations. (To improve visualization — I've digitized the original ECG using PMcardio). |
MY Approach to the Rhythm in Figure-1:
This is a challenging tracing. The “good news” — is that this patient is hemodynamically stable — which means that you have a moment of time to contemplate your answer.
- PEARL #1: When faced with a complex arrhythmia, in which there is more than a single element in the tracing — I look first to see if there is an underlying rhythm. Looking at the 3 simultaneously-recorded long lead rhythm strips in Figure-1 — We can see that this arrhythmia has wider beats, and narrow beats.
Take a LOOK at Figure-2 — in which I've enclosed some of the wider beats in each of the 12 leads (within the dotted BLUE rectangles).
QUESTION:
- How would you describe QRS morphology of the wider beats?
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| Figure-2: QRS morphology of the wider beats? |
QRS Morphology of the Wider Beats:
Looking at the QRS complexes within the dotted BLUE rectangles — the wider beats in Figure-2 appear to manifest LBBB (Left Bundle Branch Block) conduction:
- The QRS of wider beats in left-sided leads I, aVL and V6 — all manifest a monophasic R wave.
- Anterior leads V1,V2,V3 — manifest a predominantly negative QRS (See ECG Blog #293 — for review of QRS morphology expected with RBBB and LBBB conduction).
- Most of the time with LBBB conduction — transition to predominant QRS positivity occurs slightly later than is seen in Figure-2. Even accounting for potential superposition of hidden P waves on the initial part of the QRS in lead V3 — We usually don't see as wide of an initial R wave with LBBB as appears in lead V3 — nor do we see predominant positivity of the QRS already by lead V4 (Blue arrow in this lead).
- To Emphasize: Distinction between the QRS morphology of VT (Ventricular Tachycardia) — vs that of a supraventricular rhythm with aberrant conduction, is often not clear cut. The advanced point that I am highlighting here — is that although QRS morphology of the wider beats in Figure-2 could be consistent with LBBB aberrancy — I was not yet convinced.
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Is there an Underlying Rhythm?
P waves are present in today's tracing.
- I limit my initial search for atrial activity to those P waves I am certain of. Armed with the knowledge that leads II and V1 are most often the best leads for detecting P waves — I began my search for atrial activity in lead V1 (RED arrows in Figure-3).
- NOTE: The last colored arrow in Figure-3 is PINK — because I was not initially sure that the abbreviated negative deflection seen just before the QRS of beat #21 was a P wave.
- PEARL #3: While emphasizing that I do not advocate for the use of calipers when the patient in front of you is "crashing" — Today's patient was hemodynamically stable at the time this tracing was recorded. When you have a moment of time — use of calipers expedites detection of P waves.
- Setting my calipers to the P-P interval suggested by the 2 negative deflections that we clearly see in lead V1 before beats #14 and 15 — allows us to confirm that the PINK arrow P wave in front of beat #21 (that manifests this same P-P interval) — is definitely also a P wave.
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| Figure-3: Beginning my search for atrial activity in the long lead V1 — RED arrows highlight those P waves I am certain of. |
Use of Other Leads:
The "beauty" of having several simultaneously-recorded long lead rhythm strips — is that this allows us to amplify our assessment by using more than a single lead. Whereas left-sided lead V5 adds little to our search for atrial activity — lead II provides invaluable assistance!
- Note in Figure-4 how the dotted RED timelines precisely correlate the pointed upright deflections in lead II — with the negative RED arrow P waves in lead V1.
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| Figure-4: I've added dotted RED timelines to highlight the appearance of sinus P waves in simultaneously-recorded lead II. |
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Now LOOK in Figure-5 — which illustrates how we can go back-and-forth between simultaneously-recorded leads V1 and II — sometimes seeing atrial activity better in one of these leads — and sometimes seeing atrial activity better in the other lead.
QUESTION:
- Do you see indication of more P waves in lead II than those that we highlight with RED arrows in Figure-5?
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| Figure-5: Looking at lead II — Are there more P waves than those that are marked by the RED arrows in this lead? |
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In Figure-6 — I've added more colored arrows to highlight the presence of a fairly regular underlying atrial rhythm throughout the entire long lead rhythm strip.
- RED arrows in Figure-6 illustrate those sinus P waves that we most readily identified because of the distinct negative P waves that we seen in lead V1.
- Using the P-P interval defined earlier in Figure-3 by the distance between the 2 consecutive RED arrow P waves that we definitely see before beats #14 and 15 — PINK arrows in Figure-6 correspond to sinus P waves that produce "on-time" notching in the lead II baseline.
- Although not seen in Figure-6 — the WHITE arrows highlight where additional "on-time" sinus P waves are virtually certain to be hiding.
- BOTTOM Line: An underlying rhythm of fairly regular sinus P waves appears to be present in today's ECG. Given the constantly changing PR interval between these sinus P waves and the neighboring wide QRS complexes — this establishes the presence of AV Dissociation!
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| Figure-6: Colored arrows highlight the presence of an underlying rhythm of fairly regular sinus P waves. |
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- If you are able to establish the presence of true AV Dissociation during a regular WCT rhythm — this essentially confirms that the rhythm is VT (Ventricular Tachycardia).
- As emphasized in ECG Blog #468 — Most of the time, AV dissociation will not be seen unless the rate of VT is relatively slow. This means that the ECG finding of AV dissociation will rarely be helpful to distinguish between the faster VT rhythms vs SVT rhythms with either preexisting bundle branch block or aberrant conduction (and it is the faster VT rhythms that are the most difficult to identify). The rate of the wide beats in today's rhythm is ~135/minute.
- Many providers "think" they are seeing AV dissociation when in fact it is not present. Unless you can walk out regular underlying P waves through much (most) of the tracing — it us unlikely that AV dissociation is present (See ECG Blog #133 — and — ECG Blog #151 for examples of true AV dissociation with VT).
- Although the WHITE arrow P waves in Figure-6 are hidden (because they occur within the QRS complex of beats #4,5; 10,11; 16 and 22) — there are enough "on-time" sinus P waves occurring in today's rhythm to establish that true AV Dissociation is present.
PEARL #5: Of similar diagnostic assistance in the assessment of regular WCT rhythms — is the finding of fusion beats ("F" ) and/or capture beats ("C" ).
- Fusion Beats — may be seen when one or more supraventricular impulses occur at the same time as ventricular beats are occurring. The result is a QRS complex of intermediate morphology that will look more like either the supraventricular or ventricular complex, depending on how far through the ventricules the sinus-conducted impulse is able to penetrate before meeting the ventricular beat (See ECG Blog #128 for illustrated explanation of this concept).
- Capture Beats — occur when a normally conducted (narrow QRS) beat appears within a WCT rhythm (such as VT). This can happen if a sinus-conducted beat occurs at just the right moment, such that normal conduction is not prevented by the VT rhythm.
A Picture is Worth 1,000 Words ...
Take a LOOK at Figure-7.
- RED arrows in Figure-7 highlight the underlying sinus P wave rhythm that continues "on-time" throughout the long lead rhythm strips.
- Beat #14 is a capture beat ("C"). Note that the QRS complex of this beat is narrower than any other QRS complex in this tracing — and that beat #14 is preceded by a RED arrow P wave with a normal PR interval (it therefore being plausible that the timing of this P wave might be fortuitous enough to be conducted normally to the ventricles).
- Beats #2,3; 9, and 20 are all fusion beats ("F") — which manifest different degrees of fusion, depending on where in the cycle the preceding P wave falls. For example, beat #2 manifests a greater degree of fusion (and therefore looks more like a supraventricular beat — because its longer preceding PR interval allows sinus conduction to penetrate further into the ventricles before fusion occurs). In contrast — the shorter PR interval before beat #20 results in less fusion, and a QRS that bears closer resemblance to ventricular beats.
- BOTTOM Line: The presence of AV dissociation and/or fusion or capture beats during a WCT rhythm proves that the wide beats are of ventricular etiology (such that the correct answer to today's initial question is that the rhythm is sinus with runs of NSVT).
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| Figure-7: I've labeled the fusion and capture beats that prove today's rhythm is sinus with runs of NSVT. |
Today's Patient was Started on Propafenone ...
Propafenone is a Type 1C antiarrhythmic agent — with indications for treatment of AFib, reentry SVT rhythms (including those with an Accessory Pathway), and ventricular rhythms (Kim et al — Acta Cardiol Sin 37:100-103, 2021 — and — Do — Cardiovasc Prev Pharmacother 5(1):1-14, 2023).
- The patient in today's case was started on Propafenone several days prior to her presentation in the ED, presumably for frequent PVCs that rendered her symptomatic with severe palpitations.
- The concern regarding the use of Propafenone — is the risk of proarrhythmia, in which use of a drug to treat arrhythmias paradoxically worsens the original arrhythmia.
- The risk of proarrhythmia is significantly increased in patients with underlying ischemic or structural heart disease (albeit today's patient was previously healthy).
- Among the manifestations of Propafenone-induced Proarrhythmia include: i) Aggravation of the particular arrhythmia being treated; ii) Alteration of cardiac conduction properties (including PR interval prolongation and potential for marked QRS widening) — iii) Slowing the rate of AFlutter — with potential to allow 1:1 AV conduction with an accelerated ventricular rate; iv) Precipitation of VT/VFib/Torsades de Pointes; and, v) Unmasking Brugada Syndrome (by the drug's sodium-channel-blocking effect).
- NOTE: Proarrhythmic events in patients on Propafenone most often occur during the 1st week of treatment — which is precisely the timing associated with the recording of today's ECG!
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Acknowledgment: My appreciation to Mubarak Al-Hatemi (from Qatar) for allowing me to use this case and these tracings.
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Additional Relevant ECG Blog Posts to Today’s Case:
- ECG Blog #185 — Reviews my System for Rhythm Interpretation, using the Ps, Qs, 3R Approach.
- ECG Blog #210 — Reviews the Every-Other-Beat (or Every-Third-Beat) Method for estimation of fast heart rates — and discusses another case of a regular WCT rhythm.
- ECG Blog #220 — Review of the approach to the Regular WCT (Wide-Complex Tachycardia).
- ECG Blog #489 — in which the initial ECG looks similar to that in today's case (but for which the answer is different).
- ECG Blog #196 — Reviews another regular WCT.
- ECG Blog #263 and Blog #283 — Blog #361 — Blog #384 — and Blog #460 — and Blog #468 — and Blog #491 — More WCT Rhythms ...
- ECG Blog #197 — Reviews the concept of Idiopathic VT, of which Fascicular VT is one of the 2 most common types.
- ECG Blog #346 — Reviews a case of LVOT VT (a less common idiopathic form of VT).
- ECG Blog #204 — Reviews the ECG diagnosis of the Bundle Branch Blocks (RBBB/LBBB/IVCD).
- ECG Blog #203 — Reviews ECG diagnosis of Axis and the Hemiblocks. For review of QRS morphology with the Bifascicular Blocks (RBBB/LAHB; RBBB/LPHB) — See the Video Pearl in this blog post.
- ECG Blog #211 — WHY does aberrant Conduction occur?
- ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).
- ECG Blog #445 and Blog #361 — more regular WCTs.
- ECG Blog #475 — Aberrant SVT?
- ECG Blog #323 — Review of fascicular VT.
- ECG Blog #38 and Blog #85 — Review of Fascicular VT.
- ECG Blog #278 — Another case of a regular WCT rhythm in a younger adult.
- ECG Blog #35 — Review of RVOT VT.
- ECG Blog #42 — Criteria to distinguish VT vs Aberration.
- ECG Blog #133 and ECG Blog #151— for examples in which AV dissociation confirmed the diagnosis of VT.
- Working through a case of a regular WCT Rhythm in this 80-something woman — See My Comment in the May 5, 2020 post on Dr. Smith’s ECG Blog.
- Another case of a regular WCT Rhythm in a 60-something woman — See My Comment at the bottom of the page in the April 15, 2020 post on Dr. Smith’s ECG Blog.
- A series of 3 challenging tracings with QRS widening (See My Comment at the bottom of the page in the March 6, 2025 post on Dr. Smith's ECG Blog).
- Review of the Idiopathic VTs (ie, Fascicular VT; RVOT and LVOT VT) — See My Comment at the bottom of the page in the September 7, 2020 post on Dr. Smith’s ECG Blog.
- Review of a different kind of VT (Pleomorphic VT) — See My Comment in the June 1, 2020 post on Dr. Smith’s ECG Blog.
