Lecture on Atrial Fibrillation

Jul 8, 2024

Lecture on Atrial Fibrillation

Introduction

  • Atrial Fibrillation (AFib): A type of arrhythmia, specifically a supraventricular tachycardia originating in the atria
  • Common problem with multiple associated complications

Etiology of Atrial Fibrillation

Cardiac Causes

  1. High Left Atrial Pressure
    • Mitral stenosis (valvular AFib, often due to rheumatic fever)
    • Congestive Heart Failure (CHF)
      • Diastolic heart failure (difficulty in filling)
      • Systolic heart failure (too congested to accept more blood, causing dilation)
  2. Atrial Remodeling
    • Caused by high pressure, mitral stenosis, CHF
    • Leads to abnormal electrical circuits (re-entrant circuits)
  3. Ischemia and Fibrosis
    • Cardiac ischemia → Fibrosis → Remodeling → AFib
    • Usually due to coronary artery disease or myocardial infarction

Non-Cardiac Causes

  1. Pulmonary-related hypoxia
    • Lung diseases (e.g., pneumonia, COPD, pulmonary embolism)
    • Hypoxia triggers ectopy near pulmonary veins
  2. Catecholamine Surge
    • Sepsis, postoperative states, pheochromocytoma, thyrotoxicosis
    • Affecting beta-1 receptors causing ectopy and AFib
  3. Electrolyte Disturbances
    • Hypokalemia, hypomagnesemia
    • Holiday heart syndrome (binge drinking)
  4. Sympathomimetics
    • Drugs like cocaine, methamphetamines, PCP

Types & Terminologies of AFib

  • Paroxysmal AFib: Lasts less than 7 days, may revert to normal sinus rhythm without intervention
  • Persistent AFib: Lasts more than 7 days
  • Permanent AFib: Continued for more than a year, unlikely to revert to normal rhythm

Complications of AFib

  1. Thromboembolic Complications
    • Ineffective atrial contractions → blood stasis → thrombus
    • Potential for emboli causing stroke, mesenteric ischemia, leg ischemia
  2. Acute Heart Failure
    • AFib with Rapid Ventricular Rate (RVR > 150 bpm)
    • Decreased filling time → decreased cardiac output
    • Risk of pulmonary edema, hypotension, shock
  3. Dilated Cardiomyopathy
    • Chronic AFib with elevated heart rate leading to heart dilation and failure

Diagnosis of AFib

  1. 12-lead ECG
    • Check for rate, irregular rhythm (variable R-R interval)
    • Confirm AFib presence
  2. Echocardiogram
    • Assess for left atrial thrombus, valvular problems, atrial dilation
  3. Holter Monitor or Loop Recorder
    • Monitor for occult AFib
  4. Labs
    • Check for electrolyte disturbances and thyrotoxicosis

Treatment of AFib

Goals

  1. Rate Control: Target HR < 110 bpm
  2. Rhythm Control: Restore normal sinus rhythm if necessary
  3. Anticoagulation: Prevent thromboembolic events

Rate Control

  • Beta-blockers (e.g., Metoprolol, Carvedilol)
  • Calcium Channel Blockers (e.g., Verapamil, Diltiazem)
  • Digoxin for patients with heart failure (HFrEF < 35%)

Rhythm Control

  • Direct Current Cardioversion: Preferred for hemodynamically unstable patients, AFib < 48hrs
  • Pharmacological Cardioversion: Amiodarone, Flecainide, Lidocaine (risk of torsades de pointes)
  • Radiofrequency Ablation or Maze Procedure: For refractory cases

Anticoagulation

  • Chad's VASc Score: Determines need for anticoagulation
    • Score ≥ 2: Anticoagulate
    • Score = 1: Clinical judgment
    • Score = 0: Usually no anticoagulation
  • Choices
    • Non-valvular AFib: DOACs (e.g., Rivaroxaban, Apixaban)
    • Valvular AFib or CKD: Warfarin (monitor INR)
  • Bridging Therapy: Heparin followed by long-term anticoagulation

Acute AFib Management

  • Hemodynamically Unstable: Immediate cardioversion
  • Stable: Rate control first, Rhythm control if needed, Anticoagulate accordingly