ECG Blog #196: VT vs Aberrant? Adenosine?

The ECG in Figure-1 was obtained from a 55-year old man with a known history of coronary disease. He was hemodynamically stable at the time this tracing was recorded.

 

QUESTION: Which of the following choices provides the BEST answer regarding the rhythm shown in Figure-1?

 

Answers to Choose From:

• Choice A: The likelihood that the rhythm is VT (Ventricular Tachycardia) is approximately 50%.
• Choice B:  The likelihood that the rhythm is VT is approximately 70-80%.
• Choice C:  The likelihood that the rhythm is VT is over 95%.
• Choice D: The rhythm is more likely to be an SVT (SupraVentricular Tachycardia) with aberrant conduction.
• Choice E:  It is equally likely that the rhythm is any one of these 3 possibilities: i) an SVT with aberrant conduction; ii) AVRT (AtrioVentricular Reciprocating Tachycardia) in a patient with WPW; or iii) VT.

 

EXTRA Credit:

• Should you use Adenosine to treat the patient with this arrhythmia?

Figure-1: ECG obtained from a middle-aged man with coronary disease. What is the rhythm? (See text).

 

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NOTE #1: Some readers may prefer at this point to listen to the 13-minute ECG Audio before reading My Thoughts regarding the rhythm in Figure-1. Feel free at any time to review to My Thoughts (that appear below ECG MP-13).

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Today’s ECG Media PEARL #13a (12:20 minutes Audio) — reviews “My Take” on assessing the regular WCT (Wide-Complex Tachycardia), when sinus P waves are absent — with tips for distinguishing between VT vs SVT with either preexisting BBB or aberrant conduction.

NOTE: I did not talk about Fascicular VT in today's Audio Pearl (MP-13). This is an important exception to the appearance of VT, in which QRS morphology may resemble either RBBB/LAHB or RBBB/LPHB.

• I discuss Fascicular VT (and other Idiopathic VTs) in detail in ECG Blog #197.

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MY Approach to the Rhythm in Figure-1:

The “good news” about this case — is that the patient was hemodynamically stable at the time the rhythm was recorded. This means that synchronized cardioversion is not immediately needed — which provides a moment of time to better assess the rhythm.

 

As always — I find the most accurate and time-efficient process for arrhythmia interpretation is to use the Ps, Qs & 3R Approach. As I emphasized in ECG Blog #185 (and as I repeat in Figure-4 shown in the Addendum below) — it does not matter in what sequence the Ps, Qs and 3Rs are assessed — and, I altered the sequence below for today’s tracing, based on the easiest parameters to assess for the rhythm in Figure-1. So, — I noted the following:

• The rhythm in Figure-1 is fast and Regular. The ventricular Rate is ~170/minute.
• The QRS complex is wide.
• P waves are absent.
• The 5th parameter is the 3rd R, which stands for “Related”. But since no P waves are identified in Figure-1 — there is nothing to comment on regarding this 3rd R.

 

IMPRESSION of the Rhythm in Figure-1:

By the Ps, Qs, 3R Approach — We have described a regular WCT ( = Wide-Complex Tachycardia) Rhythm at ~170/minute, without clear sign of atrial activity.

• Unfortunately — there is no simultaneously-recorded long lead rhythm strip in Figure-1. That said — a long lead rhythm strip is really not needed for the diagnosis in today’s case.
• As emphasized in today's ECG Media PEARL #13 (above) — the differential diagnosis for a regular WCT rhythm without atrial activity includes: i) VT (Ventricular Tachycardia); ii) SVT (SupraVentricular Tachycardia) with preexisting BBB (Bundle Branch Block); iii) SVT with aberrant conduction; or, iv) Something Else? (ie, WPW).
• According to the literature — statistical odds that a regular WCT without evidence of atrial activity will turn out to be VT begin at ~80% — and, increase to ≥90% if the patient is of a “certain age” (ie, middle-aged and beyond) and has underlying heart disease. Therefore, even before looking at specific ECG findings in Figure-1, such as frontal plane axis and QRS morphology — the likelihood that this regular WCT will turn out to be VT in this 55-year-old man with coronary disease is at least 90%.

 

LOOKING Further — Clinical NOTES:

The clinical reality — is that emergency providers often have to begin treatment of tachyarrhythmias before being 100% certain of the specific rhythm diagnosis. In today’s case — it would be perfectly reasonable to accept the ≥90% likelihood of VT at this point in the case — and to treat the patient accordingly.

• As already noted — the fact that the patient in today’s case was hemodynamically stable with the rhythm in Figure-1 means that electrical cardioversion was not immediately needed, and that a trial of antiarrhythmic therapy would be reasonable. IF the patient were to deteriorate at any time during assessment and treatment — THEN cardioversion becomes immediately indicated.
• A number of antiarrhythmic treatment options could be tried, the most common of which include IV Amiodarone or Procainamide. Depending on provider preference, availability, and customs/protocol at one’s institution — either of these options could be selected.
• Although Adenosine has been recommended for empiric use as treatment of a regular WCT rhythm of uncertain etiology — this drug is unlikely to be effective if the rhythm is polymorphic VT or ischemic VT. So, while it would not necessarily be “wrong” to give Adenosine to the patient in today’s case — given the known history of coronary disease in this patient, and the overly wide and amorphous morphology (not resembling any known form of conduction defect) — an ischemic etiology for this patient’s VT is extremely likely. As a result — it might best not to try Adenosine in this patient (Summary of the pros and cons of using Adenosine appears below in Figure-5 and Figure-6 in the Addendum below).

 

Can We Increase Our Certainty that the Rhythm is VT?

While initiation of antiarrhythmic treatment for presumed, hemodynamically-stable VT would be reasonable at this point (given the ~90% likelihood that the WCT rhythm in Figure-1 is indeed VT) — Wouldn’t it be better to attain an even greater degree of certainty for the rhythm diagnosis? Realizing that there are numerous criteria in the literature for distinguishing between VT vs SVT rhythms — I wanted to present my approach that has served me well over the years in terms of time efficiency and accuracy.

• I begin with attention to the “3 Simple Rules” presented in Figure-2. Applying these rules to the regular WCT Rhythm in today’s case (that we saw in Figure-1) — there is extreme axis deviation (as determined by the all negative QRS in lead aVF) — the QRS in lead V6 is almost all negative (with no more than the tiniest r wave in this lead) — and, the QRS complex is both exceedingly wide and "ugly" in a number of leads (not resembling any known form of conduction defect — with a virtually amorphous QRS in lead V1).
• Conclusion: A positive response to any one of the 3 Simple Rules would have significantly increased the likelihood of VT from our starting estimation of ~90%. The fact that each of these 3 Rules are positive should place the likelihood of VT at well over 95%. 
• KEY Point: Once familiar with the rules — it should take no more than seconds for your “educated eye” to identify that the regular, fast WCT rhythm without P waves in Figure-1 has an extreme frontal plane axis — an almost totally negative QRS in lead V6 — and, an “ugly” QRS morphology in multiple leads.

 

Figure-2: Use of the “3 Simple Rules” for distinction between SVT vs VT (excerpted from my ACLS-2013-ePub).

Beyond the Core:

The “beauty” of the 3 Rules that I illustrate in Figure-2 (and in today’s ECG Media PEARL #13) — is their simplicity and the speed with which these rules can be applied at the bedside. As a more advanced concept — I’ll add 2 additional ECG features to consider that are relevant to today’s case.

• The finding of an all-positive monophasic R wave in lead aVR during a regular WCT rhythm is virtually 100% specific for the diagnosis of VT. The reason for this — is that a monophasic R wave in lead aVR during a WCT rhythm indicates that the electrical impulse must be originating from a site in the ventricular apex, and traveling upward toward the base (ie, in the direction of lead aVR). SVT rhythms do not originate from the apex. Unfortunately — sensitivity of this finding is not high (ie, it won’t be often that you see a monophasic R wave in lead aVR during a WCT rhythm). That said — when found (as seen by the all-upright QRS in lead aVR of Figure-1) — the diagnosis of VT is confirmed!
• Assessment of QRS morphology may help! As I noted in Figure-2 — aberrant conduction almost always manifests some form of conduction defect (ie, RBBB, LBBB, LAHB, LPHB — or some combination thereof). IF a typical RBBB morphology for the QRS complex in lead V1 during a WCT rhythm can be demonstrated — then a supraventricular etiology becomes much more likely (Figure-3). In today’s case — the opposite was found regarding QRS morphology in lead V1. Thus, the nearly amorphous QRS morphology in lead V1 of Figure-1 provides further support that the rhythm here is VT.

Figure-3: Use of lead V1 for assessing QRS morphology during a WCT rhythm (excerpted from my ACLS-2013-ePub).

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Relevant ECG Blog Posts to Today’s Case:

• ECG Blog #220 — Walking Step-by-Step through a detailed Case Study of a regular WCT rhythm (Audio Pearl on what is Hemodynamic Stability?).
• ECG Blog #42 — Comprehensive review of criteria for distinguishing VT vs Aberration.
• 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. 
• ECG Blog #38 and Blog #85 — Review of Fascicular VT.
• ECG Blog #35 — Review of RVOT VT
• 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.

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ADDENDUM (2/20/2021):

• I like to frequently emphasize my systematic approach to rhythm interpretation. Relevant links to audio — video — and pdf review of this topic are found on my ECG Blog #185. I reproduce the 5 KEY elements to my approach below in Figure-4.
• Adenosine is a wonderful drug for emergency treatment of reentry SVTs. It is also effective for a selected number of adenosine-responsive VT rhythms (primarily in younger adults who do not have underlying heart disease). Because of its ultra-short half-life following IV administration — it is usually safe when given empirically to patients in whom the etiology of a WCT rhythm is unknown. That said — side effects can occur, and these are not uniformly short-lived. Therefore — the drug is probably best avoided for WCT rhythms for which it has little to no chance of being effective (ie, polymorphic VT; ischemic-etiology VTs). In Figure-5 and Figure-6 — I reproduce the section on these pros and cons for use of Adenosine (excerpted from my ACLS-2013-ePub).

Figure-4: Review of the 5 KEY elements in the Ps, Qs & 3R Approach to systematic rhythm interpretation (See text).

Figure-5: Pages 1 and 2 on use of Adenosine (excerpted from my ACLS-2013-ePub).

 

Figure-6: Pages 3 and 4 on use of Adenosine (excerpted from my ACLS-2013-ePub).