QT interval

Question 1

QT interval

Answer 1

🫀 QT Interval
* Inversely proportional to H-R
* Time from start of Q wave to end of T
* Represents period of ventricular systole
(from isovolumic contraction to isovolumic relaxation)

Question 2

QTc

Answer 2

Prolonged if > 440 msec (♂), > 460 msec (♀)
→ associated w/ ↑ risk of Torsades if > 500 msec
→ short if < 350 msec

★ Normal QTc is usually ½ the preceding R–R interval

🧠 QT is measured in Lead II or V5-6

Question 3

QTc

Answer 3

🫀 QTc

Estimates QT at a standard H.R. of 60
For H.R. not 60 → QTc used

⸻

🧠 Bazett’s Formula

QTc = \frac{QT}{\sqrt{RR}} \quad (RR \text{ in seconds})

⭐ Bazett’s formula = most used
* Undercorrects @ HR < 60
* Overcorrects @ HR > 100

Question 4

• Congenital short QT assoc. w/ ↑ risk of

Answer 4

→ Paroxysmal AF
→ Paroxysmal VF
→ Sudden cardiac death

Question 5

⚠️ Causes of QT prolongation:

Answer 5

• • Hypokalemia → causes apparent QTc prolongation due to fusion of T + U
• • Hypomagnesemia
• • ypocalcemia → typically prolongs ST, leaving T
• Hypothermia
• MI
• ROSC post cardiac arrest
• Raised ICP
• Congenital
• Drugs-Antipsychotics, antiarrhythmics-Ia, Ic and III;TCA,antiemetics

Question 6

Short QTc

Answer 6

• Hypercalcemia
• Congenital
• digoxin

Question 7

Osborne waves seen in

Answer 7

• Hypothermia
• Hypercalcemia
• Brain injury
• SAH
• MI
• Brugada syndrome
• Takotsubo CMP

Question 7

Congenital short QT

Answer 7

suspect if:
1. lone AF in young adults
2.Failure of QT to increase with HR slowing
3.QTc<350msec with tall T
4.Family H/O sudden cardiac death

It is:
Autosomal dominant
Inherited disorder of K+ channels
QTc- 300-350msec with tall T waves
Asso with paroxysmal AF/VF, sudden cardiac death