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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.

The following is a more accessble plain text extract of the PDF sample above, taken from our Cardiology Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

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

Management
- 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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