QRS axis change during ventricualr tachycardia (VT)

QRS AXIS IN VT

1. AXIS CHANGE DURING VT

2. QRS axis depends on the direction of spread of depolarization during NSR and VT. QRS axis depends on the site of origin of VT

3. In a normal ECG the frontal plane QRS axis is between −30˚ and + 90˚, with the axis most commonly lying at around 60. 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 the heart.

4. In VT the sequence of cardiac activation altered and the impulse no longer follows the normal pathways .

5. 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.

6. 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 tachycardia. 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.

7. 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 present. Whereas, if the origin is in the left free wall a right inferior axis deviation will be present

8. 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.

9. 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.