Cardiac channelopathies

Question 1

What is the result of long QT syndrome

Answer 1

Delayed start for the T wave - repolarization is delayed

Question 2

What is the result of short QT syndrome

Answer 2

T wave starts early - ventricular repolarization is accelerated

Question 3

What is the normal QT time gap and how does it change for long and short QT

Answer 3

normal = 0.36s long=0.45, short =0.34s

Question 4

What is triggered activity of the myocardia

Answer 4

before full repolarization other depolarizations can occur reaching threshold level so another action potential is fired - this leads to an ectopic beat

Question 5

What is re-entrant excitation of myocardia

Answer 5

Different layers of cells contain the mutation - so have more or less ion channels - leads to spatial and temporal dispersion of action potential firing - leads to excitatory wave moving in a circular path and returning to its site of origin.

Question 6

What mutation is seen for LQT1,2,and 7

Answer 6

Loss of function in potassium channels - can’t contribute to repolarization so it takes longer to occur

Question 7

What mutation is seen in LQT3

Answer 7

Nav1.5alpha gain of function - Depolarization lasts for longer and the sodium channels take longer to close

Question 8

What mutation is seen in LQT8

Answer 8

Ca1.2alpha - Gain of function mutation - Calcium channels remain open maintaining the plateau phase of myocardia

Question 9

What mutations are seen in LQT1

Answer 9

High proportion of mutations in the transmembrane spanning domains

Question 10

How is LQT syndrome treated

Answer 10

Beta blockers - class 2 antiarrhythmic drugs - atenolol - Beta1 adrenergic selective antagonist 
cAMP linked receptor antagonists - cAMP dependent kinase channels linked with sodium influx - reduced sodium = reduced calcium channel opening = reduced heart rate and force of contractility

Question 11

How is short QT syndrome diagnosed

Answer 11

In normal patients the QT would normally shorten - in short QT sufferers it stays the same

Question 12

How is a short QT syndrome seen on the electrocardiogram

Answer 12

Short/absent ST segment
Tall/peaked T wave
QT interval is fixed

Question 13

What mutation is seen for SQT1-3

Answer 13

Gain of function in potassium channels - open too early and increased potassium efflux causes rapid repolarization

Question 14

What mutation is seen in SQT4and5

Answer 14

Loss of function in calcium channels - this shortens the plateau phase - repolarization can therefore occur earlier

Question 15

How is short QT treated

Answer 15

Implant defibrillator

Quinidine - potassium channel blocker may be effective