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Hamra Lecture 3- Arrythmias

Arrythmia an abnormality of impulse initiation, impulse conduction or both
SA node rate of pacemaking 60-100 bpm
AV junction rate of pacemaking 40-60 bpm
Purkinje fibers 20-40 bpm
Tachycardia >100 bpm
Bradycardia <60 bpm
Abnormal automaticity Arrythmia associated with non-pacemaker cells that develop automaticity
Triggered activity Oscillations in membrane potential that trigger an action potential
Sinus arrythmia Inspiration causes an acceleration and Expiration causes a deceleration, NORMAL
Abnormal automaticity depolarizes tissues by inactivating fast Sodium channels
Can you overdrive suppress abnormal automaticity? NO
Early afterdepolarization can lead to a Torsades de pointes
Delayed afterdepolarization leads to a ITI- Calcium driven, transient inward current
1st degree block Consistent prolongation of the PR interval but all impulses get through.
Two types of 2nd degree block Wenckebach (also MobitzI) and Mobitz (also called MobitzII)
Wenckeback Progressive prolongation through the AV node with an eventual dropped beat----prolonged PR interval
Mobitz Dropped beats without prolongation of the PR interval
Wenckebach reflects an abnormality in which region? AV node
Mobitz reflects an abnormality in which region? His bundle and/or bundle branches, usually an anatomical lesion and much worse!
3rd degree block Complete block through the AV node and another latent pacemaker takes over
What can cause an AV block Increased vagal tone, Calcium channel block, Beta-blocker, Digitalis, Hyperkalemia
Re-entry An arrhythmogenic mechanism in which the impulse does not die out but instead continues to circulate and re-excite tissue
Conditions for re-entry to occur Unidirectional block, Slowed conduction over an alternate pathway, Re-excitation of tissue proximal to the block
Re-entry is promoted by things that Slow conduction velocity, shorten the refractory period or a combination of both
Wolf-Parkinson-White syndrome Patients have an accessory pathway that uses Sodium channels (fast!) instead of the normal Calcium channels (slow) used by the AV node- causes premature excitement and tachycardia
Wolf-Parkinson-white EKG Delta wave, retrograde P waves and wdie QRS intervals
Created by: mcasto