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Arrhythmias Notes

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This is an extract of our Arrhythmias document, which we sell as part of our Cardiology Notes collection written by the top tier of University Of Leicester students.

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Arrhythmias Bracdycardias = <60bpm Tachycardia = >100bpm
- SVT - arise from atria of atrioventricular junction
- VT - arise from ventricles Sinus arrhythmia
- Inspiration = decreased parasympathetic tone = Increased HR
- Expiration = Increased parasympathetic tone = decreased HR Causes regularly irregular pulse Mechanism of arrhythmia production
- Accelerated automaticity o Increased frequency of pacemaker potentials due to
? Decreased threshold
? Increased slope of depolarization
- Triggered activity o Myocardial damage can cause oscillations of the transmembrane potential at the end of an action potential o These oscillations may reach threshold triggering another AP o E.g atrial tachycardia from digoxin toxicity or ventricular arrhythmia in long QT syndrome
- Re-entry loops o Occurs when a ring of excitable cardiac tissue surround an inexcitable core e.g scar tissue o Can cause episodes of tachycardia e.g paroxysmal tachycardia

Bradycardias2 causes o Failure of impulse formation i.e sinus bradycardia o Failure of impulse conduction from atria to ventricles i.e AV block

Sinus bradycardiaCauses o Extrinsic (i.e outside factors affecting normal node)
? Hypothermia
? Hypothyroidism
? B blockers o Intrinsic (i.e node disease)
? Ischaemia/infarction o 'Sick sinus' syndrome
? Usually caused by fibrosis of SA node
? Can lead to tachy-brady syndrome

- Treat underlying cause
- Temp/permanent pacing
- Warfarin for tachy-brady syndrome

Heart BlockBlock in AV node or bundle of His = AV block Block lower in conduction system = bundle branch block

AV block has 3 forms 1) 1st degree AV block (heart block) a. Prolongation of PR interval > 5 small squares b. Every P wave is followed by QRS i.e delayed conduction 2) 2nd degree AV block (heart block) a. Some P waves conduct, some don't 2 types a) Mobitz type 1/Wenckebach a. Almost always a disease of the AV node b. Progressive prolongation of PR interval until a P wave fails to conduct b) Mobitz type 2/Hay a. Almost always a disease of the distal conduction system (purkinje/his) b. Every 2nd or 3rd P wave fails to conduct, therefore absent QRS complex (2:1/3:1) c. PR interval is normal and consistent and most P waves followed by QRS d. Can progress without warning to complete heart block - needs pacemaker. May be caused by MI 3) 3rd degree/complete AV block a. All atrial activity fails to conduct to ventricles

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