intro to arrhythmias Flashcards
What are the 3 ways of which depolarizations deviate from normal?
Rate of impulse
Impulse site of origin
Conduction (transport of impulse)
What are ions flow controlled by?
Gates
- voltage sensitive
- Can be modulated by ion conc. and metabolic conditions
Which parts of the heart are sodium dependent?
Atrial, Purkinje and ventricular cells
Which cells of heart are calcium dependent?
SA and AV node
Is the SA node repolarization controlled by I(k)?
Nope its controlled by different potassium channels and thus drugs that Block I(k) tend to have no affect on SA node
What is the key factor of pathophysiology of arrhythmias and drugs to treat them?
relation between resting potential of a cell and the number of the action potential that can be evoked
What is I(K)?
Its rapid I(kr) and Slow I(Ks) added to one another.
What is considered the refractory period?
The time between the end of phase 0 and the end of phase 3
What happens when you black Na channels?
Number of channels available at optimal conditions are decreased
- unavailable due to inactivation gate closure and drug blockage
What is the resting membrane potential of after Na channel blockers?
-55
which All Na+ channels are inactivated
- Increase refractory period of cell
- prolongs recovery time
What is the resting membrane potential of Av and Sa nodes?
-50– (-70) which is why they can depolarize even with a Na channel blocker
What are the factors that can lead to arrhythmias?
Ischemia Drug tox Hypoxia Acidosis/Alkalosis Electrolyte abnormalities Overstretching of cardiac fibers Excessive catecholamine exposure Autonomic influences Scarred or diseased tissue
What are the 2 factos that lead to arrhythmias?
Impulse formation
Impulse conduction problems
What are the 2 characteristics of impulse formation?
Diastolic and action potential interval
- diastolic is more important
Vegal discharge and what other drug will do what to diastolic interval?
Alter slope
Hyperpolerize
Achetylcholine and B-Adrenorecptor blocking drugs
What can increase slope of diastolic interval?
Hyperkale B-adrenoceptor stimulation Positive chronotropic drugs Fiber stretch Acidosis
What is afterdepolarization?
Membrane voltage oscillations that result in transient abnormal depole of cardiac myocytes during phase 2,3,4,
Early and Delayed
What happens in early afterdepolarization? Consequences?
Open Ca channel Last phase 2
Open Na channel Early phase 3
Inhibit K channel
Exacerbated by slow heart.
- Torsades des pointes or tachys
What happens in delayed afterdepolarization? Conseqences?
Elevated cytosolic Ca when cell is almost completely repolarized. Overloads SR and release Ca to cause depole.
Exacerbated by fast heart
What is reentry?
Impulse reenters and excites areas of the heart more than once
can be called circus movements
What needs to happen for reentry to occur?
- some type of block’
- Conduction time must exceed refractory period
What is the bundle of Kent?
Called Wolff-Parkinson-White syndrome
Abnormal electrical accessory connection between atria and ventricle.
allows impulse to be conducted without going through the AV node
name some Class 1A drugs?
Quinidine
Procainamide
Disopyramide
Name some Class 1B drugs?
Lidocaine
Mexilitine
