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Arrhythmias
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Cardiac dysrhythmia
Cardiac dysrhythmia (arrhytmia) Abnormal electrical activity in the heart
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Electrical conduction system of the heart
Sinus node
Internodal pathways
AV node
Bundle of His
Right bundle branch
Left bundle branch
Purkinje fibers
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The effect of autonomic nervous system
sympathetic parasympathetic
heart rate (chronotropic) 1 increases decreases
contractility (inotropic) 1 increases decreases
conduction in AV node 1 increases decreases(dromotropic)
excitability (bathmotropic) increases decreases
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Cardiac action potential
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Phase 4 Phase 4
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Phases of the cardiac action potential Phase 0 – rapid depolarization phase - Na+
channels Phase 1 – K+ and Cl- channels Phase 2 – „plateau“ - Ca2+ channels Phase 3 – rapid repolarisation - K+ channels Phase 4 – resting potential (diastole) - K+
channels, 3Na+-2K+-ATPase, Ca2+-ATPase, 3Na+-1Ca2+-exchager
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SA node action potential
Phase 4
spontaneous diastolic depolarisation
Ca2+ channels
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ECG
P wave – atrial depolarisationPR segment – delay in the AV nodeQRS complex – ventricular depolarisationT wave – ventricular repolarisation
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Ethiology
Ischaemia, acidosis – coronary artery disease Ion disbalance – hypo-/hyperkalemia... Heart diseases – myocarditis, cardiomyopathies Autonomic nervous system dysbalance Thyroid diseases – hypo-/hyperthyreosis Toxins and drugs – caffeine, digitalis Other diseases – anaemia Genetic mutation Age
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Mechanisms of arrythmias
Increased automaticity
– Increased normal automaticity (in SA node)
– Abnormal automaticity (ectopic focus)
Triggerd activity
– Early afterdepolarization
– Delayed afterdepolarization
Reentry
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Increased automaticity
Increased automaticity - classification
– Increased normal automaticity (in SA node)
– Abnormal automaticity (ectopic focus)
Automaticity –ability to generate impuls
Increased normal automaticity– hyperirritability of SA node – faster activation of SA node
Abnormal automaticity (ectopic focus) – hyperirritability of other myocardial cells (e.g. ventricular cells)
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Mechanisms
Increased resting membrane potential
(ischemia – lower activity of Na/K-ATPase)
resting potential leads to earlier threshold membrane potential
Decreased threshold membrane potential = earlier threshold membrane potential
Faster spontaneous depolarization
(catecholamines)
More rapid slope of spontaneous depolarization (SA) or resting potential (e.g. ventricular cells)
threshold membrane potential
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Triggerd activity
2 types:
Early afterdepolarization New depolarization appears in phase 3 of
previous action potential Cause: slower repolarization – e.g. because of
hypokaliemia
Characterization: abnormal phase of repolarization in the previous impuls leads to earlier new depolarization
Delayed afterdepolarizationNew depolarization appears in phase 4 of previous action potential but sooner than normalCause: intracellular Ca concentration (digitalis)
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Reentry Circulation of the impulse
Possible mechanisms
Shorter refractory period 2 places in the heart are connected with 2 ways for impulse.
In the case of blocade of one way (extra beat, scar) – impulse is conducted by one way, returns by the second one and starts circulate
The way for impulse is longer than refractory period (hyperthrophy)
Atrioventricular reentry
impulse returns through accessory pathway
(WPW syndrome)
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Inherited arrhytmias
Long QT syndrome
Mutations (AD) of ion channels (K+, Na+, Ca2+ ) genes Ventricular extra beats, ventricular tachycardia Unconsciousness, synkope, ventricular fibrilation, sudden
death SADH – sudden arrhytmia
death syndrome
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Signs
Electrical
– Changes in the ECG Haemodynamic
– Decreased preload
– Decreased minute heart output Clinical
– Syncope
– Palpitation
– Sudden cardiac death
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Classification Mechanism
– Disorders of impulse generation– Disorders of impulse conduction– Combined
Site of origin– Supraventricular
• Sinus• Atrial• Junctional
– Ventricular Rate
– Tachycardia– Bradycardia
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Disorders of impulse generation
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Sinus arrhytmias Sinus tachycardia
– rate > 100 bites/min. (normal 60 – 100bites/min.)– physiological – newborns and children, physical
activity, stress– drugs – catecholamines– diseases – hyperthyreosis, anaemia...
Sinus bradycardia– rate < 60 bites/min. – physiological – sportsmen– diseases – hypothyreosis...
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Sinus arrhytmias Premature sinus contraction (Sinus extra beat) Sinus arrhytmia
– physiological – breathing Sick sinus syndrome
– inherited
– coronary artery disease
– hypertension
– idiopathic Sinus arrest
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Atrial arrhytmias Premature atrial contraction (extra beat)
Atrial rhythm Atrial (supraventricular) tachycardia Atrial flutter
Atrial fibrilation
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Junctional arrhytmias
Premature junctional contraction (extra beat) Junctional rhythm
Junctional (supraventricular) tachycardia
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Ventricular arrhytmias Premature ventricular contraction (extra beat)
Accelerated idioventricular rhythm Ventricular tachycardia
Polymorphic ventricular tachycardia Ventricular fibrilation
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Disorders of impulse conduction
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Heart blocks (AV blocks) 1st degree
2nd degree
– type 1 (Mobitz I, Wenckenbach)
– type 2 (Mobitz II)
3rd degree
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Left bundle branch block
Right bundle branch block
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Wolff-Parkinson-White syndrome