Thursday, July 12, 2012

EKG Myth - "Can't be Ventricular Tachycardia with that Axis"


This is part of a series of posts detailing common electrocardiogram myths.


Myth: Ventricular Tachycardia always has an extreme axis

When evaluating a wide complex tachycardia, many providers will look at the QRS axis to rule out ventricular tachycardia if an extreme axis is not present. An extreme right axis deviation, also known as No Man's Land, is easiest to appreciate when leads I, II, and III are almost wholly negative.

The absence of an extreme right axis deviation does not rule out ventricular tachycardia.

In fact, the sensitivity of an extreme right axis deviation may only reach 20%[1]. More commonly, VT features a left axis deviation[2].

In 70% (n=172) of VT cases studied by Brugada et al had a Left axis deviation[2].

As with any cardiac rhythm, the axis is dependent on the origin and subsequent activation of the myocardium.

VT origin and QRS axis. An apical origin results in a superiorly directed axis in the frontal plane. In contrast, a basal origin leads to an inferior QRS axis (lower panel)[3].

In VT arising from the left ventricle, a RBBB-like morphology is most common[4]. If the origin is in the apex of the left ventricle near the inferiolateral wall, the classic extreme right axis deviation (right superior axis) will be present. Whereas, if the origin is in the left free wall a right inferior axis deviation will be present[5].

Two cases of Ventricular Tachycardia with an (A) inferior axis and a (B) right axis deviation[6].

In VT arising from the right ventricle, a LBBB-like morphology is most common[7]. If the origin is closer to the septum, a right axis deviation will be present. If the origin is the Right Ventricular Outflow Tract (RVOT), an inferior axis will be present with characteristic broad, monomorphic R-waves in leads II, III, and aVF. RVOT-VT is a common ventricular tachycardia in patients without known cardiac disease[8]. In some cases, VT arising from the right ventricle will have a normal axis.

VT with a normal axis, misclassified as SVT[9].

Any approach to the diagnosis of a wide complex tachycardia should include ruling in Ventricular Tachycardia if an extreme right axis deviation is present. However, clinicians should be mindful that the absence of an extreme right axis deviation cannot rule out Ventricular Tachycardia.

  1. Vereckei A, et al. New algorithm using only lead aVR for differential diagnosis of wide QRS complex tachycardia. Heart Rhythm 2008;5:89–98. [PubMed]
  2. Brugada P, et al. A New Approach to the Differential Diagnosis of a Regular Tachycardia with a Wide QRS Complex. Circulation 1991;83:1649-1659. [Full Text PDF]
  3. Wellens HJJ. Ventricular tachycardia: diagnosis of broad QRS complex tachycardia. Heart 2001;86:579-585. [Full Text]
  4. Surawicz B, Knilans TK. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, 6th ed. Philadelphia, PA. Saunders, 2008.
  5. Pellegrini CN, Scheinman MM. Clinical Management of Ventricular Tachycardia. Curr Probl Cardiol. 2010;35:453-504. [PubMed]
  6. Ibid 2.
  7. Ibid 4.
  8. Ibid 5.
  9. Ibid 2.

6 comments:

ECG Interpretation said...

NICE Post Christopher! To me - Axis is ONLY helpful if there is EXTREME Axis Deviation. If there is only slight-to-moderate LAD or RAD - then axis does NOT help in differentiation. If the axis is normal - it doesn't help. But IF the axis is either markedly left or markedly rightward - then VT is likely.

mb said...

Great job Christopher! I don't look at axis anymore for VTACH nor do I teach others to look either because, as stated in your first citation, aVR is a much more reliable clue for ventricular activity.

Brooks Walsh said...

Any ECG criterion that revolves around aVR warms the cockles of my heart. To think that some people disparage this lead, and call the ECG an "11-lead!"

I kind of wish that the Vereckei paper didn't rely so heavily on V(i)/V(t) - it looks like they captured a lot of VT on that 4th step. Hard to picture myself grabbing my reading glasses in the resus room, making little Xs on the ECG.

Christopher said...

Brooks,

If the V(i)/V(t) seems complex...you may in fact be human.

"Evaluating Vi/Vt ≤1.0 indicative of slow initial ventricular activation in VT is complicated." Sasaki K. A New, Simple Algorithm for Diagnosing Wide QRS Complex Tachycardia: Comparison With Brugada, Vereckei and aVR Algorithms. Circulation. 2009;120:S671. [Abstract]

So, Sasaki derived the following rules (tested against 107 WCT's):

1. Initial R in aVR,
2. Longest RS ≥100 ms, and
3. Initial r or q ≥ 40 ms.

Accuracy quoted as 86%, sens 86%, spec 97%.

Jarvik 7 said...

Very strong post. When people ask me about VT, I refer them to you.

Benjamin Dowdy said...

If it helps regarding Vi/Vt....I've always thought of this as which half of the QRS is wider. If the initial half is wider it suggests cell-cell depolarization until it hits the conduction system, hence a point in favor of VT. If the latter half is wider, it speaks to SVT with aberrancy...normal conduction until it hits a refractory cell, then cell-cell conduction.