Prolonged QT

Question 1

What is Torsades de pointes?

Answer 1

• type of polymorphic ventricular tachycardia
• QRS twisting around baseline

Question 2

Where does the QT interval start and end?

Answer 2

• b of Q and e of T

Question 3

What is the Px of prolonged QT syndrome?

Answer 3

1. prolonged repolarisation of muscle cells in the heart after contraction
2. Random spontaneous depolarisations (after depolarisation) occur in some myocytes
3. Depolarisations spread through ventricles, ventricles contract prior to proper repolarisation

Question 4

What two outcomes can arise from the heart immediately after Torsades de pointes?

Answer 4

• terminate spontaniously and revert back to sinus rhythm
• progress to VT

Question 5

What are the causes of prolonged QT?

*use VITAMIN CDE

Answer 5

• V - critical ischaemia
• I - myocarditis - adenovirus
• T - hypothermia
• A - X
• M - hypo K,Ca, Mg
• I - antipsychotics, citalopram, flecanide, sotalol, amiodarone, macrolide, abx
• N - X
• C - congenital long QTS
  
  • Romano-ward: w/o deafness
  • Jervell & Lange-Nielsen: w deafness
• D - X
• E - Hyperthyroidism

Question 6

What formula is used to calculate corrected QT interval?

Answer 6

• Bazett’s formula
• QTc = QT/square root HR

Question 7

How would you measure QTc for irregular rhythms?

Answer 7

• Calculate QTc for longest and shortest RR intervals and average them

Question 8

What is the acute Mx of torsades de pointes?

Answer 8

• Correct the cause
• Magnesium infusion (even if they have a normal serum magnesium)
• Defibrillation if VT occurs

Question 9

What is the long term mx of prolonged QT syndrome?

Answer 9

• Avoid medications that prolong the QT interval
• Correct electrolyte disturbances
• Beta blockers (not sotalol)
• Pacemaker or implantable defibrillator