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Phys2 Intro Arrhyth
Question | Answer |
---|---|
arrhythmia | an abnormality of impulse initiation, impulse conduction, or both. |
Types of impulse INITIATION arrhythmias | 1.Normal Automaticity (associated w/ normal automatic pacemaker). 2.Abnormal Automaticity (associated w/ non-pacemaker cells that develop automaticity). 3.Triggered activity (Em oscillations triggering an AP) |
impulse CONDUCTION arrhythmias | Associated w/ a delay or block of conductance. Ex: 1.AV delay. 2.Block and re-entry. |
Impulse initiation arrhythmia: Normal pacemakers: latent pacemakers | 1.Atrial conduction: 60-80 bpm. 2.AV node: 40-60 bpm. 3.Ventricular Purkinje: 20-40 bpm. **SA node is the normal pacemaker (60-100 bpm) |
Impulse initiation arrhythmia: Normal pacemakers: abnormal Sinus rhythm from ANS? | Sinus Bradycardia < 60-100 bpm < Sinus Tachycardia. **Usually in response to metabolic disturbances. |
Impulse initiation arrhythmia: Normal pacemakers: Sinus Arrhythmia? | Inspiration: Accelerates HR. Expiration: Decelerates HR. **this is a normal cyclic rhythm that is due to stretch receptors activating the ANS. |
How do latent pacemakers cause impulse initiation arrhythmias? | 1.They become enhanced. 2.SA node becomes depressed/damaged. 3.conduction block. **These emerge via Inc parasymp tone, Ischemia, drug toxicities, Electrolyte disturbances. |
Impulse initiation arrhythmia: Abnormal Automaticity | Tissue becoming automatic due to: 1.Ischemia. 2.Infarction. 3.Hypoxia. 4.acidosis. |
Can arrhythmias generated from abnormal automaticity be overdrive suppressed? | NO, the body doesn't have any physiologic control over them since they are damaged. They compete with the SA node. |
Impulse initiation arrhythmia: Triggered activity | 1.Early afterdepolarizations (EAD): occur before phase 3 repolarization. 2.Delayed Afterdepolarizations (DAD): occur after phase 3 repolarization **Afterdepolarization is an oscillation of Em following the upstroke of an AP |
What ion could be responsible for EADs and DADs? | Ca2+ |
Impulse conduction arrhythmia: conduction block: 1st degree block | Prolonged P-R interval (>0.2sec), but every impulse gets through the AV node. |
Is a bundle branch block considered a 1st degree block? | NO, despite the fact that it is included in the P-R interval, it would cause a wide QRS if it were blocked. |
Impulse conduction arrhythmia: conduction block: 2nd degree block | **Not ALL impulses get through AV node 1.Wenckebach (Mobitz Type 1): Progressive prolongation thru AV node w/ eventual dropped beat. 2.Mobitz Type II: Dropped beats without P-R interval prolongation (VERY BAD) |
Impulse conduction arrhythmia: conduction block: 2nd degree block: Mobitz Type II P wave to QRS ratios | Can be seen with 2:1 or 3:1 Pwave:QRS |
Impulse conduction arrhythmia: conduction block: 3rd degree block | COMPLETE block through the AV node. P wave doesn't conduct through the node. **Must relay on a latent pacemaker so look for a decreased HR. |
What could contribute to AV node blockage? | 1.Inc Vagal tone (M receptors dec AV conduction). 2.Ca2+ Channel blockers. 3.Beta-Blockers (Symp can't activate B1 receptors). 4.Digitalis. 5.Hyperkalemia |
Impulse conduction arrhythmia: Re-entry | arrhythmia where the signal doesnt die out, it recirculates and re-excites tissue. **can be ordered or random, anatomical or functional |
In what conditions would re-entry be necessary? | 1.Unidirectional block. 2.Slowed conduction (over alternative pathways). 3.Re-excitation of tissue proximal to the block (refractory period of proximal tissue must be shorter than propagation around the block). |
Wolf-Parkinson-White syndrome (WPW) | Pt has an alternative pathway to transmit the signal from the atria to the ventricles that is faster than the AV node. **This causes pre-excitation |
Why do you see Atrial tachycardia with WPW? | RE-ENTRY!! After the impulse travels down the AV node, the ventricular contraction (depolarization) then sends the impulse back up the accessory pathway to depolarize the atria. |
Supraventricular tachycardia | Is due to the circus rhythm seen in WPW patients with re-entry. |
How does WPW pre-excitation effect the EKG? | 1.Shortens the P-R Interval. 2.Widens the QRS **DELTA WAVE: represents the early excitation of the ventricles, widening the QRS. |
How does WPW re-entry atrioventricular tachycardia effect the EKG? | 1.Orthodromic (Anterograde down AV node): Creates RETROGRADE P Waves immediately after QRS. 2.Antidromic (retrograde up AV node): Very wide QRS w/ retrograde P wave following. |