Atrial Fibrillation 10/2/2018. Depolarization & ECG. Atrial Fibrillation. Hemodynamic Consequences

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1 Depolarization & ECG Atrial Fibrillation How to make ORDER out of CHAOS Julia Shih, VMD, DACVIM (Cardiology) October 27, 2018 Depolarization & ECG Depolarization & ECG Atrial Fibrillation Hemodynamic Consequences Micro-reentrant circuits Requires large atria Atrial depolarization rate Extremely rapid Loss of atrial contraction Reduction in stroke volume Irregularly irregular rhythm Due to AV nodal properties Loss of atrial contraction Normally ~10-15% of total cardiac output At rapid heart rates, accounts for up to 30% ventricular filling Tachycardia reduces diastolic filling time Further drop in stroke volume and cardiac output Tachycardia increases myocardial work and oxygen demand Chronic tachycardia results in myocardial failure Structural and electrical remodeling 1

2 Lone vs. Acquired Diagnosis: History, Clinical Signs Lone atrial fibrillation Absence of overt cardiac disease Giant breed dogs Acquired atrial fibrillation Secondary to cardiac disease resulting in secondary atrial enlargement Dogs: DCM, CVD Cats: HCM, RCM, UCM Lone AF Incidental finding Mild exercise intolerance Acquired AF Weakness Lethargy Syncope Cough Tachypnea Dyspnea Diagnosis: Physical Exam Diagnosis: ECG Auscultation Irregularly irregular rhythm Variable intensity S1, S2, S3 Absent S4 +/- Heart murmur +/- Tachycardia +/- Tachypnea, Dyspnea, Crackles, Dull lung sounds (pleural effusion) Variable pulse quality +/- Jugular venous distension, abdominal fluid wave, pale mucous membranes ECG Findings Irregularly irregular rhythm Irregular R-R intervals Absent P waves Presence of fibrillation waves (F waves) Fine baseline undulation May not be apparent Narrow/supraventricular QRS morphology Tachycardia Diagnosis: ECG Diagnosis: ECG 50mm/s Atrial Fibrillation 25mm/s 2

3 Atrial Flutter Atrial Fibrillation with LBBB Ventricular Tachycardia Multiform ventricular tachycardia OR Atrial fibrillation with a right bundle branch block Atrial fibrillation with a right bundle branch block and VPCs Other Diagnostics Blood Work Thoracic Radiographs Echocardiography Focal atrial tachycardia with right bundle branch block 3

4 Methods of Treatment Rhythm Control - Cardioversion Restoration of sinus rhythm Electrical or pharmacological cardioversion Patients may revert back to atrial fibrillation Rate Control Slow the heart rate Improves diastolic filling (cardiac output) Options Transthoracic Monophasic vs. Biphasic Shock Intracardiac (TVEC) Transesophageal Synchronization Shock Sinus Rhythm Synchronization Mode Off Shock Ventricular Fibrillation - Risks Overall Safe Complications Rare Theoretical Risks: Anesthetic complications Shock induced myocardial damage Thromboembolic complications Induction of ventricular arrhythmias Induction of bradycardia Sudden death Success Rate > 90% Maintenance of Sinus Rhythm Lone AF: 690 days Acquired AF: 73 days 4

5 Greatest success with recent onset atrial fibrillation Atrial fibrillation begets atrial fibrillation Limited success Requires continuous cardiac monitoring for: Sinus node dysfunction Atrioventricular block Ventricular arrhythmias Atrial flutter Quinidine Sodium Channel Blocker (Class I Antiarrhythmic) Dose PO: 5-20 mg/kg PO q2-6h Side Effects Weakness, lethargy Ataxia, seizures Gastrointestinal (anorexia, vomiting, diarrhea) Myocardial depression Proarrhythmia (QT prolongation, Torsade de Pointes) Drug Interactions (ex. digoxin, antacids, thiazides) Amiodarone Potassium Channel Blocker (Class III Antiarrhythmic) Also has class I, II, IV activity IV Dose 2 mg/kg IV slow over 5-10 min Repeat up to a dose of 10 mg/kg Post-Cardioversion Oral amiodarone 10-25mg/kg PO q12h for ~1 week Reduce to 5mg/kg PO q24h over 2-3 weeks Amiodarone Side Effects Gastrointestinal Neutropenia Thrombocytopenia Hepatotoxicity *** Hypothyroidism Keratopathy Drug Interactions (antiarrhythmics, theophylline, methotrexate, cyclosporine) Hypersensitivity Diltiazem Calcium Channel Blocker (Class IV Antiarrhythmic) Not technically used for cardioversion Dose IV: mg/kg IVloading dose followed dby a 2-6 mcg/kg/min CRI PO: mg/kg PO q8h Other Options Lidocaine 2mg/kg IV Procainamide 6 8 mg/kg IV slow (up to 20mg/kg IV) mcg/kg/min CRI Humans: Propafenone (Class Ic) Flecainide (Class Ic) Dofetilide (Class III) Ibutilide (Class III) 5

6 Maintaining Sinus Rhythm Rate Control Humans: Only 20% of successfully cardioverted patients maintain NSR without chronic antiarrhythmic therapy Best Antiarrhythmic Choices: Amiodarone Sotalol What to do about lone atrial fibrillation? Prolong AV Refractory Period & Slow Conduction ABCD for SVT - Amiodarone - Beta-blockers - Calcium Channel Blockers - Digoxin Rate Control Amiodarone Rate Control Beta Blockers Amiodarone Potassium Channel Blocker (Class III Antiarrhythmic) Also has class I, II, IV activity IV Dose (Nexterone) Numerous protocols mg/kg IV slow over 5-10 min Follow by 0.8 mg/kg/hr for 6 hours Then 0.4 mg/kg/hr for 18 hours Chronic Oral Dosing 10-25mg/kg q12-24 PO Goal: Reduce to 5mg/kg PO q24h over 2-3 weeks Numerous Side Effects β-blockers IV Esmolol mg/kg IV slow followed by a mcg/kg/min CRI PO Atenolol D: mg/kg PO q12-24h C: mg/cat PO q12-24h Metoprolol D: mg/kg PO q8-12h C: 2 15 mg/cat PO q8h Propanolol D: mg/kg PO q8h C: mg/cat PO q8-12h Rate Control CCBs Rate Control Digoxin Calcium Channel Blockers Not affected by sympathetic drive Diltiazem: IV: mg/kg IV slow followed by a 2-6 mcg/kg/min / CRI PO: mg/kg PO q8h Give slowly IV Side Effects Gastrointestinal Lethargy Digoxin Parasympathetic activation, sympathetic inhibition Na + -K + ATPase Inhibitor Negative chronotrope, positive inotrope Overridden by heightened sympathetic tone Slow onset, long t 1/2 Dose: D: mg/kg PO q12h C: mg/cat PO q48h 6

7 Rate Control Digoxin Rate Control Other Options Digoxin Toxicity Gastrointestinal (anorexia, vomiting, diarrhea) Proarrhythmia AV Block Bigeminy i Atrial and ventricular tachyarrhythmias Treat arrhythmias with Class I agents (e.g. lidocaine) Potentiated by hypokalemia and renal dysfunction Digoxin Levels Check trough levels 6-8 hours post pill Goal Therapeutic Range: ng/ml Other Options Combination Therapy Digoxin + β-blockers Digoxin + Diltiazem Careful with CCB + β-blocker combinations Humans: Adenosine, Flecainide, Propafenone Goal Heart Rate Other Therapies Goal Heart Rate bpm Breed and patient dependent Large and giant breed dogs normally have a sinus rate < 90 beats/min and require a lower goal heart rate Maintain cardiac output Monitor via Holter Overdrive Pacing Catheter Ablation Cryoablation AV Nodal Ablation & Ventricular Pacing Device Therapy Atrial pacemakers Atrial defibrillators To Treat or Not To Treat Thank You! What to do with lone AF and a normal HR? What are the long term consequences of AF at normal heart rates? Does atrial fibrillation cause DCM? 7