14 & 15: Cardiac rhythm problems Flashcards
What is syncope?
Loss of consciousness + loss of tone
What are the three categories of arrhythmias?
- Fast
- Slow
- Disorganised
By what mechanisms can certain drugs cause arrhythmias?
Usually by inhibiting K channels
What is the mechanism of VT initiation in LQTS?
- Prolongation of AP duration
- Risk of reactivation of Ca channels is increased
What are the risk factors for VT in:
LQT1
LQT2
LQT3
LQT1 - during exercise
LQT2 - shock, loud noises
LQT3 - inactivity
Why does the axis vary for polymorphic VT?
- Pattern of re-entry is changing
- There is no fixed anatomical substrate to centre it
How do you distinguish polymorphic VT from VF?
IN VT
- Rate is relatively constant
- QRS complexes remain identifiable and relatively ordered
What is the treatment for LQTS?
High risk: medical treatment (beta blockers) + surgical (ICD)
Low risk: beta blocker therapy and lifestyle modifications
What is the most likely cause of a broad complex, monomorphic tachycardia?
Ventricular Tachycardia
What are the four requirements of re-entrant activation?
- Trigger
- Unidirectional block
- Slow conduction/shortened APD
- Circuit
What causes slow conduction in ischemic tissue?
- Lower ATP impairing function of Na/K/ATPase
- Results in altered transmembrane gradients of Na and K, resulting in partial membrane depolarisation
- Inactivates sodium channels
- Also increased electrical resistance due to acidosis (gap junction coupling)
What reduces AP duration in ischemic tissue?
- Hyperkalemia due to increased extracellular K
- Increases inward K current
What causes DADs in ischemic tissue?
- Impaired Ca homeostasis increases [Ca]i
- Leads to episodic release of Ca from SR
- Increased efflux of Ca via NCX
- Membrane depolarised
What is the most common ectopic trigger for re-entrant arrhythmia immediately after MI?
DADs
Why are ectopic beats more likely occur 24 hours post MI?
Ischaemic myocytes in the infarct region and border zone are electrically active but highly unstable
