Lecture 13 (Cardiac channelopathies) Flashcards
What are the segments and intervals of a normal ECG? (2)
Segments
P - QRS - ST - T
Intervals
P-R Q-T T-P
What do P and QRS stand for as segments of normal ECG?
P atrial depolarization
QRS ventricular depolarization
What is long and short QT?
Both conditions which alter ECG
Repolarization accelerated in short QT
Repolarization is delayed or slowed in long QT
Repolarization still occurs but at a different interval
What are the implications of Long QT? (4)
Triggered activity, longer plateau phase, myocytes depolarized for too long(1)
Depolarisations that fire extra AP (2) - ectopic beat
Ectopic beat which can lead to ventricular tachycardia (increase in contraction number) means loss of coordinated contraction in ventricular muscles (3)
Which leads to ventricular fibrillation which means you don’t have co-ordinated contraction of muscles (4)
What are implications of both long and short QT? (2)
Re-entrant excitation due to spatial heterogeneity (variation of expression patterns in myocytes)
Causes extra APs, ectopic beats etc…
(Spread down two branches, as it loops back round it triggers extra APs (ventricular tachycardia)) (1)
Duration of AP is slightly different, means that tissue cant respond properly as tissues out of sync (2)
What are potential effects of Long QT syndrome? (3)
-Twisting backwards and forwards, characteristic pattern of ECG for heart problems
-Syncope (fainting)
-Sudden death – torsades de pointes
How many subunits of transmembrane domain come together to form K+ channel in Long QT?
4 subunits
What are the dominant mutations of Long QT?
Q1/E1 is dominant
Why can Long QT lead to deafness?
High potassium endolymph is important for hearing, the Q1/E1 complex secretes K+, mutation in Q1/E! usually causes deafness due to this
What effect does mutations in Long QT have on K+, Na+ and Ca2+ channels? (3)
Are they gain/loss of function mutations?
Loss of function in Potassium channels, reduced potassium efflux which slows down repolarization
(more likely for an after depolarization)
Sodium channels are gainer function mutations, inactivation is impacted so they stay open for longer
Voltage gated calcium channels also stay open for longer, prolongs plateau phase, they are gainer function mutations
What are the treatment for Long QT?
Blockers – class 2 antidysrhythmic drugs
Atenolol - B1 selective antagonist
cAMP linked receptor
How can B1 receptor be used to treat Long QT?
B1 receptor is cyclic Amp receptor, by blocking B1 receptors helps patients regulate their heartbeat
How many mutated genes are there in Short Qt syndrome?
8 mutated genes in patients which are mix of gain and loss of function genes
(high presence in males)
How can you recognise short QT from ECG?
Distinct structure of ECG
How does QT interval change with exercise in short QT?
QT interval stays same, stays same in exercise, change in depolarization to accommodate
