Arrhythmias Flashcards
1
Q
Describe the initiation and spread of electrical activation
A
- SAN- intrinsic pacemaker
- Wave of electricity through myocardium when activated
Atria–> AVN (delay) –> bundle of His –> down septum –> Purkinje fibres - Co-ordinated heart beat
- SAN in RA near superior vena cava opening
2
Q
What is sinus rhythm?
A
- Normal rhythm from SAN- cardiac pacemaker
- 60-100bpm normally
3
Q
Describe cardiac action potentials
A
- Occur at cellular level
- Different sections have different action potentials
4
Q
What is automaticity?
A
- Depolarise without stimulation
- AP starts with flat line- threshold potential
- SAN- unstable resting potential- gradually rises with Na and Ca influx
- Potential decreases with K efflux (repolarisation)
- Na spontaneous inward movement- funny channels allow this (gradual rise) until threshold reached
- Normal AP after this
5
Q
Describe inherent rates of automaticity
A
- SAN, AVN and Purkinje fibres
- SAN- 60-100pm
- AVN- 40-50pm
- PF- 35pm
- SAN pacemaker- fastest rate
- Once AVN and PF activated by adjacent cell- own automaticity becomes irrelevant
6
Q
Describe pacemaker modulation
A
- HR changes due to PNS and SNS effect on pacemaker cells
- PNS slows- hyperpolarisation, slow depolarisation- automaticity slower- less APs in same time frame
- SNS- speeds up- reduced depolarisation, steeper slow, more rapid APS in the same time frame
7
Q
What are the effects of parasympathetic and sympathetic nervous systems on the heart?
A
- Sympathetic: increases HR, increases conduction through AVN
- Parasympathetic: decreases HR, decreases conduction through AVN
8
Q
What are the mechanisms of arrhythmogenesis?
A
- Automaticity
- Re-entry
- After depolarisation (triggered activity)
9
Q
Describe how automaticity causes arrhythmia
A
- Normal phenomena (ANS)
- Modulated by drugs
- Overactive/underactive/fails
- Induced wrong time
10
Q
Give examples of automaticity causing arrhythmia
A
- Sinus tachycardia: fever, exercise, absence of clear driver, hyperthyroidism
- Sinus bradycardia: hypothyroidism, SAN diseased, hypothermia, chronotropic incompetence
- Focal atrial tachycardia: areas not SAN, abnormal atrial section firing after than SAN- pacemaker
11
Q
What is re-entry?
A
- Most common
- Short circuit forms 2 anatomically/ functionally distinct pathways
- Focus of treatment usually- burning/freezing circuit
- Small, can form in ventricles, atria, AVN or combo
12
Q
What are the two pathways that re-entry requires?
A
- Path 1: slow conduction, short refractory period (need to be able to recover quickly)
- Path 2- rapid conduction, long refractory period
13
Q
Describe how pathway mechanism works
A
- Combination of pathways and formation due to non-electrically active tissue drives re-entry
- Electrical impulse conducted both pathways simultaneously
- Fast path activates everything below system and sends upwards signal that collides with slow- collision stops them
14
Q
Describe re-entry with an ectopic beat- premature
A
- May travel down slow conduction pathway (Fast still recovering)
- Refractory period differentiation becomes significant
- May reach bottom of fast when it recovers- goes up fast
- Formation of a circuit- slow has recovered, so travels down slow pathway
- Everything above and below activated
- Wave re-enters pathway- re-entry
15
Q
What are the combination factors that lead to re-entry circuits?
A
- 2 pathways with different conduction velocities and recovery times
- Around an area which is electrically inert
- Requires tissue not electrical active to go around
