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!
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