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QRS axis change during ventricualr tachycardia (VT)


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QRS axis change during ventricualr tachycardia (VT)

  2. 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. 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. 4. • In VT the sequence of cardiac activation altered and the impulse no longer follows the normal pathways .
  5. 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. 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. 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. 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. 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.