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Atrial FibrillationHow to make ORDER out of CHAOS

Julia Shih, VMD, DACVIM (Cardiology)

October 27, 2018

Depolarization & ECG

Depolarization & ECG Depolarization & ECG

• Micro-reentrant circuits

• Requires large atria

• Atrial depolarization rate– Extremely rapid

Atrial Fibrillation

y p

– 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

Hemodynamic Consequences

– 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

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• Lone atrial fibrillation– Absence of overt cardiac disease

– Giant breed dogs

Lone vs. Acquired

• 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

Diagnosis: History, Clinical Signs

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

• Auscultation– Irregularly irregular rhythm

– Variable intensity S1, S2, S3

– Absent S4

+/ H t

Diagnosis: Physical Exam

– +/- 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

Diagnosis: ECG

– 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

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Differential Diagnoses (ECG)

Atrial Flutter

Differential Diagnoses (ECG)

Atrial Fibrillation with LBBBAtrial 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

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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

SynchronizationMode 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

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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

Pharmacological Cardioversion

• Quinidine– Sodium Channel Blocker (Class I Antiarrhythmic)

– Dose• PO: 5-20 mg/kg PO q2-6h

Sid Eff t– Side Effects • Weakness, lethargy

• Ataxia, seizures

• Gastrointestinal (anorexia, vomiting, diarrhea)

• Myocardial depression

• Proarrhythmia (QT prolongation, Torsade de Pointes)

• Drug Interactions (ex. digoxin, antacids, thiazides)

Pharmacological Cardioversion

• Amiodarone– Potassium Channel Blocker (Class III Antiarrhythmic)

– Also has class I, II, IV activity

– IV Dose2 /k IV l 5 10 i• 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

Pharmacological Cardioversion

• Amiodarone– Side Effects

• Gastrointestinal

• Neutropenia

• Thrombocytopenia• Thrombocytopenia

• Hepatotoxicity ***

• Hypothyroidism

• Keratopathy

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

• Hypersensitivity

Pharmacological Cardioversion

• Diltiazem– Calcium Channel Blocker (Class IV Antiarrhythmic)

– Not technically used for cardioversion

– DoseIV 0 1 0 25 /k IV l di d f ll d b• IV: 0.1 - 0.25 mg/kg IV loading dose followed by a

2 - 6 mcg/kg/min CRI

• PO: 0.5 - 4 mg/kg PO q8h

Pharmacological Cardioversion

• Other Options– Lidocaine

• 2mg/kg IV

– Procainamide6 8 /k IV l• 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)

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Maintaining Sinus Rhythm

• Humans: Only 20% of successfully cardiovertedpatients maintain NSR without chronic antiarrhythmic therapy

• Best Antiarrhythmic Choices:A i d– Amiodarone

– Sotalol

• What to do about lone

atrial fibrillation?

Rate Control

• Prolong AV Refractory Period & Slow Conduction

• “ABCD for SVT”

- Amiodarone- Beta-blockers

- Calcium Channel Blockers- Digoxin

Rate Control – Amiodarone

• Amiodarone– Potassium Channel Blocker (Class III Antiarrhythmic)

– Also has class I, II, IV activity

– IV Dose (Nexterone) – Numerous protocols2 5 /k IV l 5 10 i• 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

– Numerous Side Effects

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– 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 /k / i CRI2 - 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

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Rate Control – Digoxin

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

– Proarrhythmia• AV Block

Bi i• 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 – Other Options

• Other Options– Combination Therapy

• Digoxin + β-Blockers

• Digoxin + Diltiazem

• Careful with CCB + β Blocker combinations• Careful with CCB + β-Blocker combinations

– Humans:• Adenosine, Flecainide, Propafenone

Goal Heart Rate

• Goal Heart Rate– 140-160 bpm

– Breed and patient dependent

• Large and giant breed dogs normally have a sinus t < 90 b t / i d i l l h trate < 90 beats/min and require a lower goal heart

rate

– Maintain cardiac output

• Monitor via Holter

Other Therapies

• Overdrive Pacing

• Catheter Ablation

• Cryoablation

• AV Nodal Ablation &

Ventricular Pacing

• Device Therapy– Atrial pacemakers

– Atrial defibrillators

To Treat or Not To Treat

• 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?

Thank You!