Mechanism of arrythmias
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Mechanism of arrythmias






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Mechanism of arrythmias Presentation Transcript

  • 1. Mechanism of Arrhythmias Dr Fuad Farooq
  • 2. Normal Sinus Rhythm Implies normal sequence of conduction, originating in the sinus node and proceeding to the ventricles via the AV node and His-Purkinje system EKG Characteristics: Regular narrow-complex rhythm Rate 60-100 bpm Each QRS complex is proceeded by a P wave P wave is upright in lead II & downgoing in lead aVR
  • 3. The mechanisms responsible for arrhythmias are generally divided into – – – Disorders of impulse formation Disorders of impulse conduction Combinations of both cardiac
  • 4. Disorders of Impulse Formation Can be – Disorder in Automaticity – Trigger activity
  • 5. Automaticity Automaticity is the property of a fiber to initiate an impulse spontaneously, without need for prior stimulation Characterized by – Inappropriate discharge rate of the normal pacemaker, the SA node (e.g., sinus rates too fast or too slow for the physiologic needs of the patient) – Discharge of an ectopic pacemaker that controls atrial or ventricular rhythm Ectopic pacemakers are often called latent or subsidiary pacemakers
  • 6. Automaticity Ectopic pacemakers are usually suppressed by overdrive suppression by the more rapidly firing SA node or by concealed conduction from neighboring fibers – Manifested when the SA discharge rate slows or block occurs at some level between the SA node and the ectopic pacemaker site – The discharge rate of the latent pacemaker can speed inappropriately and usurp control of cardiac rhythm from the SA node
  • 7. Recognizing Altered Automaticity on EKG Gradual onset (warming) and termination of the arrhythmia The P wave of the first beat of the arrhythmia is typically the same as the remaining beats of the arrhythmia (if a P wave is present at all)
  • 8. Decreased Automaticity Sinus Bradycardia
  • 9. Increased/Abnormal Automaticity Sinus tachycardia Ectopic atrial tachycardia Junctional tachycardia
  • 10. Triggered Activity • Triggered activity is initiated by after-depolarizations, which are depolarizing oscillations in membrane voltage induced by one or more preceding action potentials • Thus, triggered activity is pacemaker activity that results consequent to a preceding impulse or series of impulses, without which electrical quiescence will occurs
  • 11. Phase 1: Initial rapid repolarization Phase 0 : Rapid depolarization •Closure of the fast Na+ channels •Phase 0 and 1 together correspond to the R and S waves of the ECG •Opening of fast Na channels Phase 4: Resting phase •Associated with diastole portion of heart cycle •Potassium outward current through open, inwardly rectifying K+ channels ( Ikl ) Phase 2 Plateau phase Phase 3 Repolarization •K+ channels remain open •Allow K+ to build up outside the cell, causing the cell to repolarize •Corresponds to T wave on the ECG •Balance between the inward movement of Ca+ and outward movement of K + •Corresponds to ST segment of the ECG
  • 12. Can be: • Early after-depolarizations (EADs), arise from a reduced level of membrane potential during phases 2 (type 1 – augmented opening of Ca channels) and 3 (type 2 – augmented opening of Na channels) of the cardiac action potential • Late or delayed after-depolarizations (DADs), occur after completion of repolarization (phase 4 – secondary to increase cytosolic Ca++ levels), generally at a more negative membrane potential than that from which EADs arise
  • 13. • Causes of EAD include: 1. Low potassium blood level 2. Slow heart rate 3. Drug toxicity (i.e. quinidine causing torsades de pointes) • DAD may cause triggered activity due to: 1. Premature beats 2. Increased serum Ca++ level 3. Increased adrenaline levels 4. Digitalis toxicity
  • 14. Disorder of Impulse Conduction Can be: – Conduction block – Re-entry
  • 15. Mechanism of Reentry
  • 16. Mechanism of Reentry
  • 17. Reentrent Rhythms AV nodal reentrant tachycardia (AVNRT) AV reentrant tachycardia (AVRT) – Orthodromic – Antidromic Atrial flutter Atrial fibrillation Ventricular tachycardia
  • 18. Recognizing Reentry on EKG Abrupt onset and termination of the arrhythmia The P wave of the first beat of the arrhythmia is different as the remaining beats of the arrhythmia (if a P wave is present at all)
  • 19. Example of AVNRT
  • 20. Atrial Flutter Most cases of atrial flutter are caused by a large reentrant circuit in the wall of the right atrium
  • 21. Atrial Fibrillation Atrial fibrillation is caused by numerous wavelets of depolarization spreading throughout the atria simultaneously, leading to an absence of coordinated atrial contraction
  • 22. Thank You