ECG Blog #384 — Why So Fast?

The ECG in Figure-1 was obtained from a young man with a history of rheumatic heart disease — who presented with “palpitations”. He was hemodynamically stable at the time this tracing was recorded.

• How would YOU interpret the ECG in Figure-1?
• How would you treat the patient?

Figure-1: The initial ECG in today’s case. What is the rhythm? How would you treat the patient? (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on the ECG in Figure-1:

The “good news” about today’s case — is that the patient was hemodynamically stable at the time the initial ECG in Figure-1 was recorded. By definition, this means that despite the fast heart rate — providers had at least “a moment in time” to contemplate the etiology of the rhythm before initiating treatment. By the Ps, Qs, 3R Approach (See ECG Blog #185):

• The rhythm in Figure-1 is fast and Regular.
• By the Every-Other-Beat (or in this case Every-3rd-Beat) Method (See ECG Blog #210) — the Rate of the rhythm is ~250-260/minute (ie, As shown in Figure-2 —  the R-R interval of every 3rd beat is 3.6 large boxes — which means 1/3 the rate = ~85/minute X 3 ~250-260/minute).
• The QRS complex is wide (ie, ~0.13-0.14 second).
• There is no clear sign of P waves (and therefore no indication of any Relation between atrial activity and neighboring QRS complexes).

Putting It All Together: The rhythm in Figure-1 is an extremely fast (ie, ~250-260/minute) — and regular WCT (Wide-Complex Tachycardia) rhythm, without clear sign of atrial activity.

• The KEY determination to make for ECG #1 — is between VT (Ventricular Tachycardia) — vs some form of SVT (SupraVentricular Tachycardia).
• Statistically, in an unselected adult population — VT is much more common than an SVT rhythm, especially in a patient such as the one in today’s case who has underlying heart disease. That said — since today’s patient is a “young man” — and the rate of today’s rhythm is extremely fast (ie, 250-260/minute — which is faster than is usually seen in a VT rhythm that maintains a well-defined QRS morphology) — we clearly can not discount the possibility of an SVT rhythm.
• IF today’s rhythm was an SVT — a rate of 250-260/minute is clearly too fast to be sinus tachycardia. While AFlutter (with 1:1 AV conduction) and ATach are possibilities — a reentry SVT rhythm (either AVNRT or AVRT) would seem far more likely. The extremely rapid rate increases the chance of an AP (Accessory Pathway)-dependent reentry circuit (ie, of AVRT).
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• BOTTOM Line: To Emphasize — The above “thought process” should take no more than seconds to complete! That said — I could not be sure of the etiology of today’s rhythm on the basis of my analysis thus far. KEY Point: It is common for even the most experienced clinician not to be 100% certain of the etiology of a regular WCT rhythm at the time that they need to begin treatment.

Figure-2: I've labeled the ECG in Figure-1 — to illustrate use of the Every-Other-Beat Method for accurate estimation of the heart rate.

Does QRS Morphology Help?

Take another look at the regular WCT rhythm in Figure-2:

• Does QRS morphology in ECG #1 favor VT? — or — an SVT with either preexisting BBB (Bundle Branch Block) or aberrant conduction?

ANSWER: Does QRS Morphology Help?

QRS morphology in Figure-2 could be consistent with supraventricular conduction (ie, from either preexisting BBB — and/or — from aberrant conduction):

• The RsR’ triphasic QRS complex seen in lead V1 of ECG #1 (with S wave that descends below the baseline — and taller right “rabbit ear”, together with wide, terminal S waves in lateral leads I, V6) — is consistent with rbbb conduction.
• The predominant S wave in lead I, with steep downslope — in association with predominant positivity of the QRS in lead iII — is consistent with lphb conduction.
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• BOTTOM Line: Use of QRS morphology is not perfect for distinguishing VT from an SVT rhythm. Sometimes it helps. At other times — it does not help. Most of the time — QRS morphology provides clues that “move the likelihood” of VT vs an SVT rhythm in one direction or the other, albeit without 100% certainty. QRS morphology is most helpful when either: i) A completely typical RBBB morphology is seen (ie, an rsR’ in lead V1, with S wave that descends below the baseline and taller, slender R’ = “right rabbit ear” in this lead V1 — with wide terminal S waves in lateral leads I and V6); or, ii) An ill-defined QRS morphology is seen that is not consistent with any known form of conduction defect.
• The “Long” ANSWER: In today's case — QRS morphology in ECG #1 clearly could be consistent with supraventricular conduction showing RBBB/LPHB. That said — I thought there were a few slightly atypical features for expected QRS morphology with LPHB — including: i) Absence of a typical qR pattern in both leads II and III (ie, the QRS complex is nearly equiphasic in lead II — and there is no clear initial q wave preceding the upright R wave in lead III); and, ii) The QRS is all negative in lead aVL (whereas typically lead aVL would show a similar rS complex, as we see here in lead I). Given statistical prevalence of VT in patients with a regular WCT rhythm — I suspected fascicular VT for the rhythm in today's case. That said — I was not at all certain about the diagnosis (See ECG Blog #197 — as well as other references listed below for more on this topic).
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• The “Short” ANSWER: The patient in today’s case presents in a regular WCT rhythm, without clear sign of atrial activity. Although I initially suspected fascicular VT — there is no way to be certain that the rhythm is not a reentry SVT from the single tracing shown in Figure-2. Since the patient was initially stable hemodynamically — a trial of IV Verapamil could be the initial treatment of choice, given that IV Verapamil is often effective for both fascicular VT and reentry SVT rhythms (AVNRT, AVRT). Alternatively (and equally appropriate given the extremely rapid ventricular rate) — one might opt for sedation and immediate synchronized cardioversion.

CASE Follow-Up:

An initial trial of low-dose IV Verapamil was given — but was not successful. At this point, the decision was made for synchronized cardioversion — which converted to the rhythm shown in ECG #2. 

QUESTIONS:

• How would you interpret the repeat ECG shown in Figure-3?
• Does ECG #2 help to tell us what the rhythm in ECG #1 was?

Figure-3: Comparison between the initial ECG — and the repeat tracing obtained following synchronized cardioversion. (To improve visualization — I've digitized the original ECG using PMcardio).

Case CONCLUSION:

The repeat ECG in Figure-3 shows conversion of the rhythm in ECG #1 to sinus tachycardia (restoration of upright sinus P waves in lead II — at a rate of ~110/minute).

• Comparison of QRS morphology between the 2 tracings shown in Figure-3 (ie, during and after the WCT rhythm) — reveals remarkable similarity in virtually all 12 leads! Especially remarkable — is the virtually identical initial deflection in all leads (ie, small, thin initial r wave in lead I — similar shape and slope of the biphasic R wave in lead II; identical-looking initial r waves in leads V1,V2 — and more of the same in the other 8 leads).
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• BOTTOM Line: The finding of near-identical QRS morphology during and after the WCT rhythm — confirms that the etiology of the WCT rhythm in ECG #1 was supraventricular, here with preexisting RBBB/LPHB. The very rapid ventricular rate attained (ie, ~250-260/minute) — with need for synchronized cardioversion suggests: i) That the rhythm in ECG #1 was probably orthodromic AVRT; and, ii) That this young man with established rheumatic heart disease and underlying bifascicular block (RBBB/LPHB) will probably best be served by referral to EP Cardiology for ablation. 

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Acknowledgment: My appreciation to Mubarak Al-Hatemi (from Qatar) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #185 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.
• ECG Blog #210 — reviews the Every-Other-Beat Method for rapid estimation of heart rate.
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• ECG Blog #220 — reviews the approach to a Regular WCT (Wide-Complex Tachycardia).
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• ECG Blog #323 — WCT with RBBB Morphology = Fascicular VT.
• ECG Blog #196 — Reviews another Case with a Regular WCT Rhythm.
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• 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?
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• ECG Blog #197 — Review of Fascicular VT.
• ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).
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• 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 — Comprehensive review of criteria for distinguishing VT vs Aberration.
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• See ECG Blog #240 — for Review on the ECG assessment of the patient with a regular SVT rhythm (including distinction between the various types of SVT reentry). 

• See ECG Blog #250 — for Review of another case of regular SVT with ST depression.
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• ECG Blog #220 — reviews my LIST #1: Causes of a Regular WCT and — HOW to assess Hemodynamic Stability.
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• González-Torrecilla et al: Ann Noninvasive Electrocardiol 16(1):85-95, 2011 — Reviews distinction between AVNRT vs AVRT and other regular SVT rhythms in patients without WPW.
• Please check out the November 12, 2019 post in Dr. Smith's ECG Blog — in which I reviewed the case of a different kind of regular SVT Rhythm (AFlutter).