QRS axis change during ventricualr tachycardia (VT)
AXIS CHANGE DURING VT
• QRS axis depends on the direction of spread
of depolarization during NSR and VT.
• QRS axis depends on the site of origin of VT
• In a normal ECG the frontal plane QRS axis is between
−30˚ and + 90˚, with the axis most commonly lying at
• A change in axis of more than 40˚ to the left or right is
probably suggestive of VT during Tachycardia.
• Lead AVR is situated in the frontal plane at -210 when
the axis is normal QRS complex is entirely negative
• when QRS is positive in lead AVR the tachycardia is
originating from apex and moving towrds the base of
• In VT the sequence of cardiac activation
altered and the impulse no longer follows the
normal pathways .
• The QRS axis is not only important for the
differentiation of the broad QRS tachycardia but
also to identify its site of origin and etiology.
• VT origin in the apical part of the ventricle has a
superior axis (to the left of -30˚).
• An inferior axis is present when the VT has an
origin in the basal area of the ventricle.
• Previous work showed that the presence of a
superior axis in patients with RBBB shaped QRS
very strongly suggests VT.
• This does not hold for an LBBB shaped
• On the contrary, presence of an inferior axis in
LBBB shaped QRS tachycardia argues for a VT
arising in the outflow tract of the right ventricle.
• In VT arising from the LV, a RBBB-like
morphology is most common.
• If the origin is in the apex of the LV near the
inferiolateral wall, the classic extreme right
axis deviation (right superior axis) will be
• Whereas, if the origin is in the left free wall a
right inferior axis deviation will be present
• In VT arising from the RV, 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 RVOT, an inferior axis will be
present with characteristic broad, monomorphic
R-waves in leads II, III, and aVF.
• RVOT-VT is a common VT in patients without
known cardiac disease.
• In some cases, VT arising from the right ventricle
will have a normal axis.
• 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