Torsades des Pointes

Question 1

What is it?

Answer 1

Distinctive polymorphic ventricular tachycardia in which the QRS amplitude varies and the QRS complexes appear to twist around the baseline. (multiple ventricular foci with the resultant QRS complexes varying in amplitude, axis and duration.) Associated with prolonged QT.

Question 2

Pathophysiology of tornadoes des pointes?

Answer 2

Dysfunctional ion channels -> long depolarisation.
Leads to early after depolarisation (of ventricles) which can lead to premature ventricular contraction - and trigger tdP with the R on T phenomena.

Question 3

Pathophysiology of long QT?

Answer 3

Normal: Q-T represents cardiac repolarisation, so if it is long then depolarisation is delayed.
Intracellular excess of positively charged ions extends ventricular repolarisation and results in long QT. This pathophysiology explains why some drugs/electrolyte states trigger Long QT.

Question 4

What is the formula for CTc?

Answer 4

Bazett formula (QTc = QT/root of RR)

Question 5

Normal QT interval?

Answer 5

0.35-0.44s

Question 6

Prolonged QT in men?

Prolonged QT in women?

Answer 6

> 0.44s

>0.46s

Question 7

Risk Factors for Torsades des Pointes?

Answer 7

• Long QT
• Female sex: testosterone may shorten action potential.
• Electrolyte imbalance: hypok/m/c
• Structural heart disease - including ischaemic heart disease
• Pharmacological

Question 8

4 risk categories for TdP drugs?

Answer 8

Known risk, possible risk, conditional risk and drugs to avoid in congenital long QT.

Question 9

Which class of anti-arrthymic drugs can trigger TdP/Long QT?

Answer 9

I and III
I: mostly sodium channel blockers.
III: amiodarone/sotalol etc.

Question 10

Common QT prolonging drugs?

Answer 10

Amiodarone
Flecainide
Sotalol
Azithromycin
Ciprofloxacin
Erthromycin
Haloperidol
Chlorpormazine
Citalopram
Ondansetron
Fluconazole

Question 11

What drugs might indirectly prolong QT?

Answer 11

Hypokalaemia: diuretics

Question 12

How might TdP present?

Answer 12

Palpitations, dizziness, syncope, VF -> SCD

Question 13

Treatment of TdP?

Answer 13

• Stop drugs that are prolonging QT.
• Correct electrolyte abnormalities.
• Mg 2g IV over 10 minutes.
• Adverse features (usual) -> synchronised cardioversion.

Question 14

Mechanism of action Magnesium?

Answer 14

Blocks calcium inflow -> promotes resting repolarization and suppress the amplitude of early after-depolarisations.

Question 15

Long term management of LQTS (acquired and congenital)?

Answer 15

Acquired - remove predisposing factor.

Congenital - beta blockers, cardiac pacing. thoracic sympathectomy. ICD

Question 16

Recreational drug associated with TdP? Implications?

Answer 16

Cocaine
“Extreme caution in the prescription of QT prolonging drugs to patients who have recently used cocaine or have a history of cocaine misuse”

Question 17

Another type of polymorphic VT?

Answer 17

Bi-directional VT - associated with digoxin toxicity.

Question 18

ECG signs of TdP?

Answer 18

Tall U waves

R on T

Question 19

Preceding signs of TdP on ECG

Answer 19

• Giant T-U waves

Long QT and bigeminy (short and long beats)