dysrhythmias

what does each part of an ecg correspond to

• p wave is atrial depolarisation

• qrs is ventricular depolarisation

• t wave is ventricular repolarisation

classifications of dysrhythmias

• ventricular

• superventricular

fibrillation

rapid chaotic and irregular activity

flutter

• rapid activity but more regular than fibrillation

paroxysmal definition and examples

• disorders ocurring in attacks

• eg atrial fibrillation, paroxysmal supraventricular tachycardia, sinus bradycardia, second degree AV node block

paroxysmal supraventricular tacychardia PSVT symptoms, triggered by

• palpitations, chest pain, shortness of breath

• arises from AV node re entry

• occurs in attacks

• triggered by anxiety, stress, smoking and stimulants

• no previous cardiovascular health problem

what is dysthymias caused by

• damage caused by cardiovascular conditions eg ischaemic heart disease and myocardial infarctions

• genetic disorders

• metabolic disorders

• caffeine overdose

mechanisms by which dysrhythmias arises

• ectopic pacemakers

• after depolarisations

• heart block

• re entry circuits

• accessory pathways

ectopic pacemaker

• abnormal site which generates electrical impulses in heart outside of normal pacemaker

when does automacity increase

• ischaemic cardiac muscle

• more spontaneous action potentials

after depolarisations

• early or delayed

• early occur during phase 2 or phase 3

• delayed occur after cell has fully repolarised

early after depolarisations

• arise from prolonged opening of calcium channels in phase 2

• or reduced potassium eflex during phase 3

delayed after depolarisations

• calcium overload in the cytoplasm

• due to spontaneous release from intracellular stores

heart block - each type

• 1st degree - av node delays signal but impulse still reach ventricle

• 2nd degree - delay at av node, intermittent failure to ventricle, missed heartbeats qrs complex, fainting, dizzy

• 3rd degree - no signals to ventricles, reduced CO

types of second degree heart block

• Mobitz Type I, where the PR interval progressively lengthens until a beat is missed

• Mobitz Type II, where some beats are unexpectedly dropped without prior PR interval lengthening.

risk factors of heart block

age, fibrosis of conduction pathways, coronary artery disease, genetic predispositions

re entry circuits

• electrical impulse continuously loops through parts of the heart conduction system or muscle

• loop rather than in one direction

local re entry circuits

• required non conducting structure that forces electrical signal to split and travels two separate pathways

• one branch must be damaged

AV node re entry circuit

• premature atrial contraction may travel down slow pathway

• slow pathway can encounter fast pathway so impulse travels backwards through fast pathway

what is a common cause of paroxysmal supraventricular tachycardia

AV node re-entry

Bundle of Kent

• congenital accessory pathway

• found in wolff-parkinson white syndrome

• leads to serious dysrhthymias

• facilitates formation of global re entry circuits

• no regulation for impulses

most common dysrhythmia

atrial fibrillation

what does atrial fibrillation result from

• ectopic pacemaker

• or local re entry circuits within atria

characteristics of atrial fibrillation

• lack of distinc p wave

• atria become non functional

• reduced time for ventricles to fill, dec CO, fatigue, inc risk of thromboembolism

ventricular fibrillation

• ventricles lose co-ordinated control

• cessation of cardiac output

• no recognisable p wave, qrs compelxes or t waves

what are significant risk factors of ventricular fibrillation

• coronary artery disease

• history of myocardial infarctions

flaws in the vaughan williams system

• class v/unclassified drugs

• antidysrhythmic drugs have multiple sites of action eg amiodarone has multiple