Transcript Sinus Node
Roger A. Freedman, M.D. • Anatomy of the cardiac conduction system • Relationship between intracardiac events and ECG • Bradyarrhythmias • Pacemakers THE CONDUCTION SYSTEM Heart Beat Anatomy SINUS NODE Sinus Node (SA Node) • The Heart’s ‘Natural Pacemaker’ - 60-100 BPM at rest Heart Beat Anatomy AV NODE Sinus Node (SA Node) Atrioventricular Node (AV Node) • Receives impulse from SA Node • Delivers impulse to the HisPurkinje System • 40-60 BPM if SA Node fails to deliver an impulse Heart Beat Anatomy BUNDLE OF HIS Sinus Node (SA Node) Atrioventricular Node (AV Node) Bundle of His • Begins conduction to the Ventricles • AV Junctional Tissue: 40-60 BPM Heart Beat Anatomy THE PURKINJE NETWORK Sinus Node (SA Node) Atrioventricular Node (AV Node) Bundle of His Bundle Branches Purkinje Fibers • Bundle Branches • Purkinje Fibers • Moves the impulse through the ventricles for contraction • Provides ‘Escape Rhythm’: 20-40 BPM Impulse Formation In SA Node Atrial Depolarization Delay At AV Node Conduction Through Bundle Branches Conduction Through Purkinje Fibers Ventricular Depolarization Plateau Phase of Repolarization Final Rapid (Phase 3) Repolarization Normal EKG Activation Reading EKGs Intervals and Timing Normal Ranges in Milliseconds: • PR Interval 120 – 200 ms • QRS Complex 60 – 100 ms • QT Interval 360 – 440 ms Reading EKG Squares Intervals and Timing • Each square = 40 ms • Each interval = 200 ms Ca2+ in Calcium channel blockers (verapamil, diltiazem) slow sinus rate and slow or block conduction through AV node K+ out Na+ in Sodium channel blockers (flecainide, propafenone, amiodarone) widen the QRS K+ out Potassium channel blockers (dofetilide, sotalol, amiodarone) prolong the QT interval Prolonged QT interval RHYTHM DISORDERS Bradyarrhythmias Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Bradycardias Impulse Conduction Disorders Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Bradycardia Sinus Bradycardia Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Bradycardia • Sinus Arrest Sinus Arrest * Animation • Failure of sinus node discharge • Absence of atrial depolarization • Periods of asystole Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders • Sinus Bradycardia • Sinus Arrest • Brady/Tachy Syndrome Impulse Conduction Disorders Brady/Tachy Syndrome • Intermittent episodes of slow and fast rates from the SA node or atria • Brady <60 BPM • Tachy >100 BPM Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Arrest • Sinus Bradycardia • Brady/Tachy Syndrome • Sino-atrial Exit Block Sino-atrial Exit Block • Transient block of impulses from the SA node • Identified by P-P interval relationship Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Arrest • Sinus Bradycardia • Brady/Tachy Syndrome • Sino-atrial Exit Block • AV block First-Degree AV Block • PR interval > 200 ms • Delayed conduction through the AV Node - Example shows PR Interval = 320 ms Second degree AV block Second-Degree AV Block - Mobitz I * Animation Known as Wenckebach Block • Progressive prolongation of the PR interval until there is failure to conduct and a ventricular beat is dropped Third-Degree AV Block * Animation • No impulse conduction from the atria to the ventricles – Ventricular rate = 37 BPM – Atrial rate = 130 BPM – PR interval = variable Third degree AV block Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Arrest • Sinus Bradycardia • Brady/Tachy Syndrome • Exit Block • 1st Degree AV Block • 2nd Degree AV Block • 3rd Degree AV Block Bradyarrhythmia Classifications Classification Based on Disorder Impulse Formation Disorders Impulse Conduction Disorders • Sinus Arrest • Sinus Bradycardia • Brady/Tachy Syndrome • Exit Block • 1st Degree AV Block • 2nd Degree AV Block • 3rd Degree AV Block • Bundle Branch Block Bundle Branch Block Left bundle branch block Left bundle branch block Right bundle branch block Causes of Bradyarrhythmias Congenital Heart Disease • Present at birth due to genetics, environment Acquired Heart Disease • Acute Myocardial Infarction, Ischemic Heart Disease, Dilated or Hypertrophic Cardiomyopathy, Hypertension, Valvular Heart Diease, Post-operative Drug-induced Neurocardiogenic • Hypersensitive Carotid Sinus Syndrome • Vasovagal Syncope Biventricular pacing • Also known as Cardiac Resynchronization Therapy (CRT) • Therapy for patients with bundle branch block, depressed left ventricular ejection fraction, and heart failure • Goal is to pace RV and LV simultaneously to resynchronize contraction of the heart (both interventricular resynchyronization and intraventricular LV resynchronization) CRT-pacemaker Summary • Anatomy of the cardiac conduction system • Relationship between intracardiac events and ECG • Bradyarrhythmias • Pacemakers