✓ Usually due to ischemia in the conducting system, usually in the AV node
✓ Also can arise from fibrosis
Main causes of ectopic pacemaker
✓ Ischemia or catecholamines
Most common causes of after-depolarizations
✓ Most often caused by elevated intracellular calcium that triggers abnormal action
potentials
✓
✓ Associated with hypercalcemia, excessive catecholamines, and heart failure
How do after-depolarizations manifest?
✓ Ectopic beat, premature contractions, extra beats, extrasystole, or tachycardia
✓
✓ Manifest as tachyarrhythmia
2 ways to fix after-depolarizations
✓ Calcium-channel blockers
✓ Beta-blockers
Sodium/calcium exchange pump ratio
✓ 3:1 ratio: 3 sodium pumped in, 1 calcium pumped out
Effects of class I (sodium-channel blockers) on the action potential
✓ Prolong depolarization (EXCEPT FOR CLASS 1B)
3 class 1A drugs
✓ Disopyramide
✓ Quinidine
✓ Procainamide
Kinetics of class IA drugs
✓ Intermediate kinetics
Effects of class 1A drugs on action potential
✓ Slow depolarization
✓ Prolong depolarization and refractory period
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