Cloned from: Dysrhythmias



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All cardiac arrhythmias are caused by...
Disturbance in impulse formation or impulse conduction or both in combination
3 cellular mechanisms responsible for cardiac arrhythmias
1. Automaticity
2. Triggered activity
3. Re-entry of excitation
Determinants of pacemaker rate
1. Maximum diastolic potential (ACh)
2. Slope of diastolic depolarization (ACh, NE)
3. Changes in the level of threshold potential
Mechanism of hypokalemia induced tachycardia
Hypokalemia decreases K permeability-exaggerates depolarizing current during diastole- increase in slope in pacemaker potential in ectopic pacemakers
Stretching of pacemaker tissue can generate inward (depolarizing) current via...
Non-selective Stretch Activated Channels (SAC)- increases diastolic slope
Responsible for ST segment changes associated with ischemia or infarction
Current of injury
A transient sub-threshold depolarization that follows (and is triggered by) a preceding action potential.
Delayed after depolarization
DADs result from...
Abnormally elevated levels of intracellular Ca2+
Possible causes of DADs
1. Cardiac glycoside toxicity (primary cause)
2. High concentrations of catecholamines
3. Ischemia
4. Rapid heart rates
5. All in combination
-All of these contribute to increased intracellular calcium
A transient depolarization that occurs during the later part of the action potential plateau (phase 2) or final repolarization (phase 3)
Early after depolarization
Though to be responsible for some forms of prolonged QT syndrome
EADs
EADs are believed to underlie this polymorphic ventricular tachycardia
Torsades de pointes
Possible causes of EADs
1. Acidosis
2. Quinidine (prolong AP duration)
3. Slow heart rate
4. Hypokalemia
3 requirements for re excitation of entry
1. Geometry for a conduction loop (functional or physical)
2. Slow conduction
3. Unidirectional block
P-R interval > 0.2 s consistent P-R interva
1st degree AV block
Lengthened P-R interval (>0.2 s) with intermittent conduction failure to ventricles - dropped R waves
2nd degree AV block
Gradually increasing P-R interval leading to conduction failure to ventricle
Wenckebach periodicity (Type of 2nd degree AV block)
Constantly lengthened P-R interval leading to   conduction failure to ventricles
Type II AV block (Type of 2nd degree AV block)
No consistent P-R interval. Complete failure of conduction between atria and ventricles
3rd degree AV block
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