ECG Interpretation: ECG Blog #284 — Diagnose this WCT in Seconds?

The ECG in Figure-1 is from a 50-year old man who presented to the ED (Emergency Department) with palpitations.

QUESTIONS:

What is the diagnosis?
How certain are you of your answer?

Figure-1: Initial ECG from a 50-year old man who presented to the ED with palpitations.

My Approach to Today's Case:

My immediate impression of the ECG in Figure-1 (formed within the first 2-3 seconds of seeing this tracing) — is that the rhythm is very fast, and that the QRS is obviously wide.

Clinically — The 1st priority is to determine hemodynamic status. For the purpose of discussion — Let's assume that this patient was hemodynamically stable in association with this rhythm.

As usual — My thought process for assessing this rhythm is based on the Ps, Qs, 3R Approach (See ECG Blog #185):

The rhythm in Figure-1 is fast, but not Regular. Taking a close look at the long lead II rhythm strip (Figure-2) — the rhythm is irregularly irregular (ie, R-R intervals vary from one beat to the next).
P waves are absent.
Since P waves are absent — there is no Relationship between P waves and neighboring QRS complexes.
The QRS is obviously Wide (ie, Looking at those leads in which the QRS looks widest — there should be no doubt that QRS duration is at least 3 little boxes in duration = more than 0.12 second).

PEARL #1: It's obvious that the Rate of this irregular tachycardia is very fast. It is relevant (as we'll see momentarily) to determine how fast the rhythm is at its most rapid point.

The shortest R-R intervals are between beats #7-8; 12-13; and #21-22 — being just over 1 large box in duration for these 3 intervals. This corresponds to a maximum ventricular rate of over 250/minute!
We can calculate the average rate for this irregular tachycardia — by noting that there are 30 beats in this 9-second rhythm strip (ie, The rhythm strip is 45 large boxes ÷ 5 = 9 seconds). This corresponds to an average ventricular rate of ~200/minute!

Figure-2: I've numbered the beats in the long lead II rhythm strip.

Putting It All Together:

The rhythm in Figure-2 is extremely rapid and irregularly irregular. No atrial activity is seen. Although the QRS complex is clearly widened, the gross irregularity of the rhythm makes ventricular tachycardia unlikely. This leaves AFib (Atrial Fibrillation) as the probable diagnosis. That said — the rate of the rhythm at certain points in the tracing is much faster than is usually seen with atrial fibrillation.

Under normal conditions with AFib — the refractory period of the AV node does not allow more than 150-to-200 impulses/minute to be conducted to the ventricles. A ventricular response that at times exceeds a rate of 250/minute is simply too fast for atrial impulses to be transmitted over the normal (AV nodal) conduction pathway.

PEARL #2: Recognition that AFib with a wide QRS complex attains a ventricular response that often exceeds 220/minute (and at times exceeds 250/minute) — instantly tells you that the patient must have WPW (Wolff-Parkinson-White) Syndrome, in which AFib impulses are by-passing the AV node, and are being conducted to the ventricles over an AP (Accessory Pathway).

PEARL #3: In addition to an excessively rapid ventricular response — 2 other characteristic ECG findings of AFib in a patient with WPW are seen in Figure-2. These are: i) There is surprising variation in R-R intervals, in which some of the longer R-R intervals are more than twice as long as the shortest R-R intervals (ie, as occurs for the last R-R interval on the tracing between beats #29-30); and, ii) Unlike monomorphic VT — QRS morphology shows some unexpected variation (ie, beats #2, 8, 12, 13 in the long lead II rhythm strip lack the distinct notching seen in the other beats).

PEARL #4: Of note — I did not mention the hemodynamic status of the patient in today's case. Surprisingly, younger adult patients with WPW who develop very rapid AFib will often remain hemodynamically stable for long periods of time despite the exceedingly rapid ventricular response. This may provide another “soft” clue that the rhythm is not VT, in which the patient is likely to be more symptomatic.

PEARL #5: Not all patients with WPW are at risk of developing potentially life-threatening tachyarrhythmias. As a result — not all patients who are incidentally discovered to have WPW need referral to an EP (ElectroPhysiology) cardiologist.

The risk of developing VFib during AFib in a patient with WPW is greatly increased when the SPERRI (Shortest Pre-Excited R-R Interval) measures below 220-250 msec. This corresponds to a shortest R-R interval that is barely more than one large box in duration — which is essentially what we see for the R-R intervals between beats #7-8; 9-10; 12-13; 21-22; and 28-29 in Figure-2. Given this high risk of deterioration to VFib for the WPW-associated arrhythmia in today's case — prompt cardioversion and EP referral (for catheter ablation of the AP) are clearly indicated!

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NOTE: In the Addendum below — I've reproduced in Figures-3, -4, -5 and -6 (from my ECG-2014-ePub) — those Sections that review the basics for ECG diagnosis of WPW — and — assessment of the common arrhythmias expected with WPW.

CLICK HERE — to download a PDF of the content in these 4 figures.

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Acknowledgment: My appreciation to Abdullah Al Mamum (from Dhaka, Bangladesh) for allowing me to use this case and this tracing.

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Additional Relevant Material to Today's Case:

See ECG Blog #185 — for review of the Systematic Ps, Qs, 3R Approach to rhythm interpretation.

NOTE: The following blogs and reference materials provide more info on WPW:

Predicting AP Location with WPW from the ECG — See ECG Blog #76.
ECG Blog #153 — Reviews the ECG Diagnosis of WPW (as well as implications when WPW is found in an asymptomatic patient).
ECG Blog #18 — Reviews another case of Very Fast AFib.
ECG Blog #37 — Lead misplacement and Very Fast AFib.
ECG Blog #81 — Reviews a case of subtle WPW (presenting as a Tall R in Lead V1).
ECG Blog #87 — Reviews a case with intermittent conduction over the AP in a patient with WPW.
ECG Blog #121 — Reviews a case of subtle WPW (with illustration of the Concertina Effect).
ECG Blog #157 — Can you diagnose ischemia and/or infarction when there is WPW?
For the case I presented in the March 11, 2020 post in Dr. Smith's ECG Blog — which illustrates similar ECG findings as seen in today's case (ie, very fast AFib + WPW).

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ADDENDUM (2/16/2022):

I've reproduced in Figures-3, -4, -5 and -6 (from my ECG-2014-ePub) — those Sections that review the basics for ECG diagnosis of WPW — and — assessment of the common arrhythmias expected with WPW.