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%. More commonly, VT features a left axis deviation.
|In 70% (n=172) of VT cases studied by Brugada et al had a Left axis deviation.|
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).|
In VT arising from the left ventricle, a RBBB-like morphology is most common. 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.
|Two cases of Ventricular Tachycardia with an (A) inferior axis and a (B) right axis deviation.|
In VT arising from the right ventricle, a LBBB-like morphology is most common. 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. In some cases, VT arising from the right ventricle will have a normal axis.
|VT with a normal axis, misclassified as SVT.|
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.
- 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]
- 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]
- Wellens HJJ. Ventricular tachycardia: diagnosis of broad QRS complex tachycardia. Heart 2001;86:579-585. [Full Text]
- Surawicz B, Knilans TK. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, 6th ed. Philadelphia, PA. Saunders, 2008.
- Pellegrini CN, Scheinman MM. Clinical Management of Ventricular Tachycardia. Curr Probl Cardiol. 2010;35:453-504. [PubMed]
- Ibid 2.
- Ibid 4.
- Ibid 5.
- Ibid 2.