Lecture 2: Atrial Arrhythmias PDF

Lecture 2: Atrial Arrhythmias PGY 412 Dr. R Rasmusson  Disturbances of Impulse Conduction 1. Impulse Conduction - First degree AV block (long) - Second Degree AV Block (episodic conduction failure) - Third Degree AV Block (complete conduction failu...

Lecture 2: Atrial Arrhythmias PGY 412 Dr. R Rasmusson  Disturbances of Impulse Conduction 1. Impulse Conduction - First degree AV block (long) - Second Degree AV Block (episodic conduction failure) - Third Degree AV Block (complete conduction failure) 2. In AV block conduction impairment can be in AV node and/or His-Purkinje system  Disturbances of Impulse Conduction 3. Impulse Conduction Failure a. During initiation of reentry in patient with WPW syndrome, premature beat is blocked in one part of pathway enabling the impulse at a later time to propagate through the same site, but from a different direction b. In patient with healing myocardial infarct and scar tissue  Types of Arrhythmias 1. Arrhythmias - site of origin – sinus node, atrium, AV node, ventricle - nature of disturbance – premature beat, tachycardia, fibrillation - examples atrial premature beat atrial tachycardia atrial fibrillation ventricular premature beat ventricular tachycardia ventricular fibrillation Rhythmic activity starts at the SA node  Regions of slow electrical activity include: – the sino-atrial node (SA node) – the Atrio-Ventricular node (AV node)  Slow propagation usually is accompanied by slow (Calcium Mediated) action potential upstrokes  Fast propagation requires a large current source.  Current flows longitudinally from a region of depolarization. Current flow changes the potential of surrounding tissue.  Electrical gradients tend to dissipate. Fenton and Cherry, thevirtualheart.org  The current flow can be detected at the body surface, if the source is large enough. The Electrocardiogram (EKG, ECG) The Electrocardiogram (EKG, ECG) The Electrocardiogram (EKG, ECG) The Electrocardiogram (EKG, ECG) The Electrocardiogram (EKG, ECG)  The electrocardiogram P-Wave corresponds to excitation of the Atrium.  The electrocardiogram QRS complex corresponds to depolarization of the ventricle.  The electrocardiogram T wave corresponds to the repolarization of the ventricle.  Initiating Events for Triggered Arrhythmias Two types – Early After Depolarizations (EADs) – Delayed Afterdepolarizations (DADs) Excessive Action Potential duration can lead to EADs  Disturbances of Impulse Initiation 1. Impulse initiation Normal Sinus Rhythm (60-100b/min) Sinus Tachycardia (>100 b/min) Sinus Bradycardia (< 60 b/min)  Disturbances of Impulse Conduction 1. Impulse Conduction - First degree AV block (long) - Second Degree AV Block (episodic conduction failure) - Third Degree AV Block (complete conduction failure) 2. In AV block conduction impairment can be in AV node and/or His-Purkinje system Disturbances of Rhythm - Arrhythmias  Disturbances of Rhythm - Arrhythmias 1. Arrhythmias resulting from regional disease generating differences in electrical properties in heart. a. Myocardial infarct b. WPW syndrome 2. Arrhythmias resulting from triggered activity 3. Arrhythmias resulting from abnormal electrical properties that are present throughout the heart Arrhythmias Associated with Long QT Interval Decrease in repolarizing currents in cells throughout the heart can lead to a lengthening of QT interval, ventricular arrhythmias and sudden cardiac death. a. Drug induced b. Familial (inherited) long QT syndrome due to malfunction of a K or Na channel  Basis of Individual Ionic Currents INa - Na channel, protein Ito - K channel, protein IKr - K channel, protein (ERG) IKs - K channel, protein (KvLQT) ERG channel frequent target for drugs that bind to and block channel and lead to ↑QT interval and arrhythmias. Drugs can also block other K channels Drugs that can prolong QT interval in Tables 2 & 3 http://heart.bmjjournals.com/cgi/content/full/89/11/13 63  Basis of Individual Ionic Currents INa - Na channel, protein (LQT3) (5-10%) Ito - K channel, protein IK - K channel, ERG (LQT2) (~30-40%) IK - K channel, KvLQT (LQT1) (~50%) Proteins involved in familial (inherited) long QT syndrome (LQTS). Effects result from mutations in proteins that make the protein function abnormally (decrease K current) and result in long QT interval, arrhythmias and sudden cardiac death LQT3 LQT2 LQT1  Excessive AP Prolongation Excitatory currents re-activate and interact with other currents (e.g. Na/Ca exchange) Often associated with Bradycardia Found in Long QT syndrome Adverse drug reactions resulting in diminished Potassium Currents relative to Calcium Currents.  Can form an Ectopic Focus Can lead to re-entrant arrhythmias  Delayed After Depolarizations Associated with high heart rates. Associated with Calcium loading in heart. Can also cause re-entrant arrhythmias Cardiac Arrhythmias Fenton and Cherry, thevirtualheart.org