Atrial FibrillationHow to make ORDER out of CHAOS

Julia Shih, VMD, DACVIM (Cardiology)

August 18, 2019

Depolarization & ECG

Depolarization & ECG Depolarization & ECG

• 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 oxygendemand

• Chronic tachycardia results in myocardial failure

• Structural and electrical remodeling

Hemodynamic Consequences

• 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 vs. Acquired

• Lone AF– Incidental finding– Mild exercise

intolerance

• Acquired AF– Weakness– Lethargy– Syncope– Cough– Tachypnea– Dyspnea

Diagnosis: History, Clinical Signs

• 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, palemucous membranes

Diagnosis: Physical Exam

• 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

Diagnosis: ECG

Atrial Fibrillation

50mm/s

25mm/s

Differential Diagnoses (ECG)

Atrial Flutter

Differential Diagnoses (ECG)

Atrial Fibrillation with LBBB 

Ventricular Tachycardia 

Differential Diagnoses (ECG)

Multiform ventricular tachycardia 

OR

Atrial fibrillation with a right bundle branch block and VPCs

Differential Diagnoses (ECG)

Atrial fibrillation with a right bundle branch block

Differential Diagnoses (ECG)

Focal atrial tachycardia with right bundle branch block

Other Diagnostics

• Blood Work

• Thoracic Radiographs

• Echocardiography

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)

Electrical Cardioversion

• Options– Transthoracic

• Monophasic vs. Biphasic Shock

– Intracardiac (TVEC)

– Transesophageal

Electrical Cardioversion

Synchronization Shock Sinus Rhythm

Electrical Cardioversion

Synchronization Mode Off

Shock Ventricular Fibrillation

Electrical Cardioversion - Risks

• Overall Safe – Complications Rare

• Theoretical Risks:– Anesthetic complications

– Shock induced myocardial damage

– Thromboembolic complications

– Induction of ventricular arrhythmias

– Induction of bradycardia

– Sudden death

Electrical Cardioversion

• Success Rate > 90%

• Maintenance of Sinus Rhythm– Lone AF: 690 days

– Acquired AF: 73 days

Pharmacological Cardioversion

• 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

• Drug options:– Quinidine– Amiodarone

Pharmacological Cardioversion

• Other Options– Lidocaine

• 2mg/kg IV

– Procainamide• 6 – 8 mg/kg IV slow

(up to 20mg/kg IV)

• 20-50 mcg/kg/min CRI

– Humans:• Propafenone (Class Ic)

• Flecainide (Class Ic)

• Dofetilide (Class III)

• Ibutilide (Class III)

Rate Control

• Prolong AV Refractory Period & Slow Conduction

• ABCDs for SVT

‐ Amiodarone/Sotalol‐ Beta-blockers

‐ Calcium Channel Blockers‐ Digoxin

Rate Control – Beta Blockers

• β-Blockers– IV

• Esmolol 0.25 – 0.5 mg/kg IV slow followed by a 50 – 200 mcg/kg/min CRI

– PO• Atenolol D: 0.25 – 1.5 mg/kg PO q12-24h

C: 6.25 – 12.5 mg/cat PO q12-24h

• Metoprolol D: 0.4 – 1.0 mg/kg PO q8-12h

C: 2 – 15 mg/cat PO q8h

• Propanolol D: 0.2 - 1.0 mg/kg PO q8h

C: 2.5 – 5.0 mg/cat PO q8-12h

Rate Control – CCBs

• Calcium Channel Blockers– Not affected by sympathetic drive

– Diltiazem:• IV: 0.1 - 0.25 mg/kg IV slow followed by a

2 - 6 mcg/kg/min CRI

• PO: 0.5 – 4 mg/kg PO q8h

– Give slowly IV

– Side Effects• Gastrointestinal

• Lethargy

Rate Control – Digoxin

• Digoxin

– Parasympathetic activation, sympathetic inhibition

– Na+‐K+ ATPase Inhibitor

– Negative chronotrope, positive inotrope

– Overridden by heightened sympathetic tone

– Slow onset, long t1/2– Dose: 

• D: 0.003 – 0.005 mg/kg PO q12h

• C: 0.03125 mg/cat PO q48h

Rate Control – Digoxin

• Digoxin Toxicity– Gastrointestinal (anorexia, vomiting, diarrhea)

– Proarrhythmia• AV Block

• Bigeminy

• 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: 0.6 - 1.2 ng/mL

Rate Control – Sotalol

• Sotalol– Potassium Channel Blocker

– Beta-Blocker

– Dose:• 1-3 mg/kg PO q12h

– Side Effects:• Gastrointestinal

• Negative inotropy

• Bronchoconstriction

Rate Control – Amiodarone

• Amiodarone– Potassium Channel Blocker (Class III Antiarrhythmic)

– Also has class I, II, IV activity

– IV Dose (Nexterone) – Numerous protocols• 2.5 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

Rate Control - Amiodarone

• Amiodarone– Side Effects

• Gastrointestinal

• Neutropenia

• Thrombocytopenia

• Hepatotoxicity

• Hypothyroidism

• Keratopathy

• Drug Interactions– (antiarrhythmics, theophylline, methotrexate, cyclosporine)

• Hypersensitivity

Goal Heart Rate

• Goal Heart Rate– In hospital ECG: < 160 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– Ideally <125 bpm

Thank You!