ECG Blog #436 — Bigeminy or Alternans?

The ECG in Figure-1 — was obtained from an older man with known coronary disease. He was on a number of medications — including antiplatelet agents, a statin drug and Digoxin.

• The patient presented to the ED (Emergency Department) for an episode of syncope. He developed cardiac arrest shortly after the ECG in Figure-1 was recorded.

QUESTIONS:

• How would YOU interpret the ECG in Figure-1?
•   What is the most likely cause of this arrhythmia?

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

MY Thoughts on the ECG in Figure-1:

A repetitive bigeminal pattern is seen in Figure-1 — in which QRS morphology alternates with each beat. 

• There are 2 different QRS morphologies — both of which clearly manifest a wide QRS complex when this rhythm is viewed in certain leads. Thus, although one of these QRS morphologies looks narrow in lead V3 — a glance at leads III, aVR, aVL, V1 and V2 confirms that the QRS is wide!
• NOTE: Although QRS morphology from one-beat-to-the-next looks similar in certain leads (ie, in leads aVR, V4,V5,V6) — there can be no doubt about the presence of 2 distinct QRS morphologies when one looks at leads I, III, aVL, aVF — and leads V1,V2,V3.
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• The overall rate of the rhythm in Figure-1 is fast (at least 150/minute).
• There are no P waves.
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• And, the patient is older (ie, prone to reduced renal function) — and he is taking Digoxin.

IMPRESSION: Given the presence of a wide tachycardia — with 2 distinct QRS morphologies, and no sign of P waves — a presumed diagnosis of BiDirectional Ventricular Tachycardia has to be made.

• As discussed in ECG Blog #231 — Bidirectional VT is a special form of VT, in which there is beat-to-beat alternation of the QRS axis. This unique and very uncommon form of VT is distinguished from PMVT (PolyMorphic VT) and from pleomorphic VT — because a consistent pattern (ie, alternating long-short cycles) is usually seen throughout the VT episode. As implied in its name, there are 2 QRS morphologies in bidirectional VT — and they alternate every-other-beat (CLICK HERE — for this case report Review by Femenia et al on Bidirectional VT in a patient with CPVT = Catecholaminergic Polymorphic VT).
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• KEY Point: There are a limited number of causes of Bidirectional VT — with the 2 most common causes being Digoxin toxicity and CPVT. Given that today's patient was taking Digoxin — Digoxin Toxicity was immediately suspected as the most likely cause. 
• Since Digoxin is primarily renally excreted — older age, that is commonly associated with reduced renal function, would predispose to developing Digoxin toxicity.

As reviewed by Almarzuqi et al (Vasc Health Risk Mgmt 18:397-406, 2022) — Potential Causes of Bidirectional VT include:

• Digitalis toxicity.
• CPVT (Catecholaminergic PolyMorphic VT).
• Acute myocardial ischemia.
• Familial hypokalemic periodic paralysis.
• Cardiac Sarcoidosis.
• Primary Cardiac Tumors and/or Cardiac Metastasis.
• Andersen-Tawil Syndrome ( = Long QT Syndrome, Type 7).
• Acute Myocarditis.
• Certain drug overdoses (Aconitine poisoning, severe caffeine poisoning).

To Emphasize: Bidirectional VT is rare. That said, it does occur — and awareness of the entities associated with this diagnosis may be important in evaluation and treatment.

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CASE Conclusion:

As noted above — today's patient developed cardiac arrest shortly after arrival in the ED. Despite prolonged resuscitation with multiple defibrillation attempts — the patient could not be saved.

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Acknowledgment: My appreciation to Hafiz Abdul Mannan Shahid (from Lahore, Pakistan) for the case and these tracings.

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Related ECG Blog Posts to Today’s Case: 

• ECG Blog #36 — Reviews irregular wide tachycardias (with distinction between Torsades de Pointes vs Polymorphic VT discussed in Figure-3 in this post). 
• See My Comment in the June 1, 2020 post in Dr. Smith's ECG Blog — for review of Pleomorphic VT.
• ECG Blog #231 — for review on the types of VT (including monomorphic — polymorphic — pleomorphic — and bidirectional VT).
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• Bidirectional VT: Challenges and Solutions (Almarzuqi et al — Vasc Health Risk Mgmt 18:3997-406, 2022). 
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• Pleomorphic VT and Sudden Cardiac Death — Editorial by Liu and Josephson on potential mechanisms to explain the ECG appearance of Pleomorphic VT. 
• Case Report on BiDirectional VT — by Femenia et al on this patient with BiDirectional VT from CPVT (Catecholaminergic Polymorphic VT).
• ECG Blog #197 — Reviews the concept of Idiopathic VT (including recognition and treatment of Fascicular VT and RVOT VT).
• Multifocal vs Polymorphic VT — September 23, 2011 post from Dr. S. Venkatesan's insightful and user-friendly Cardiology Blog (from which I adapted his figures to derive my Figure-3).

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ADDENDUM (7/22/2024):

H.S.Cho (조현석 — from Seoul, South Korea) — wrote me regarding his observation that there actually is atrial activity in today's tracing. I did not initially see this — but on review of this ECG — I agree with Dr. Cho's astute observation (Figure-2):

• RED arrows occurring at a fairly regular rate in first part of lead II suggest that there is an underlying atrial rhythm — and that there is AV dissociation. 
• I suspect a P wave is hidden under the BLUE arrow. Thereafter we lose indication of atrial activity on this tracing.
• I do not see atrial activity in other leads — but the arrows in lead II clearly suggest that an underlying atrial rhythm is present.

Among the reference links above — I found the article by Almarzuqi et al (Bidirectional VT: Challenges and Solutions) fascinating in review of potential mechanisms for Bidirectional VT, depending on etiology. Almarzuqi et al emphasize that by definition — bidirectional VT requires 2 morphologically distinct foci or circuits that alternate and are stable — since if these circuits were to degenerate, then bidirectional VT would degenerate into polymorphic VT.

• The finding of an underlying atrial rhythm with AV dissociation would not alter that theory.

My THANKS again to Dr. Cho for his astute observation of AV dissociation in today's tracing! 

Figure-2: I've labeled today's tracing — as per the email I received from H.S.Cho.