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Atrial Fibrillation

General1

  • Most Common sustained Arrhythmia
  • 95% of patients are > 60 y/o
  • Causes: Atrial enlargement, elevated atrial pressure, atrial infiltration or inflammation
    • Leads to increase in LA load and thus LA pressure thus predisposes to afib
    • Precipitants of atrial dilation and/or conduction remodeling
      • Advanced age
      • Systemic hypertension (MC underlying condition)
      • MV dysfunction (MS/MR)
      • LV failure (CHF)
      • CAD and related factors (T2DM and smoking)
      • Obesity and OSA
      • Chronic hypoxic lung disease (COPD)
      • Alcohol
    • Triggers of increased automaticity
      • Subclinical or Overt Hyperthyroidism
      • Excessive alcohol use
      • Increased sympathetic tone
        • Acute illness (sepsis, PE, MI, myocarditis)
        • Cardiac Surgery (Post cardiac surgery due to pericarditis)
      • Sympathomimetic drugs (cocaine, theophylline, amphetamines)

Definitions

Paroxysmal AFib (≥2 episodes that terminate spontaneously or with intervention within 7 days of onset)

  • 70% at one year to 90% at 4 years of recurrence
  • Triggers: Ectopic Foci (Pulmonary Ventricular sites)
  • Treatment:
    • Amiodarone, Flecainide, sometimes Ablation (works better): Pulmonary vein potentials in the LA

Persistent AFib (≥2 episodes, each lasts >7 days)

  • Triggers: Electrophysiologic remodeling fibrosis
    • SVC or coronary sinus most commonly
    • Non-Pulmonary Ventricle sites
  • Treatment
    • Cardioversion if unstable
    • Medical therapy
    • Ablation usually doesn’t work, try after medicine

Long-standing Persistent or Permanent AFib (>6-12 months)

  • Triggers: Chronic Substrate Fibrosis

AFib w/ Rapid Ventricular Response (RVR)

  • HOCM, HFpEF, Impaired cardiac function
  • Symptoms
    • Exercise intolerance, fatigue, palpitations, chest pain, light headedness, hemodynamic instability
    • Tachycardia-mediated cardiomyopathy

Features

  • Irregularly irregular rhythm w/ Narrow QRS and variable p waves
    • No distinct P waves, absent A waves, narrow QRS
      • Rate: 100-110 BPM
    • Disorganized atrial impulses all over the atria
      • Usually starts in LA (Pulmonary veins)
      • MC location of ectopic foci (ablate them)
    • Multiple reentrant circuits that coexist
    • P waves occur at a rate between 350-600, ventricular rates slower than atrial rates
    • Rate is determined by AV nodal conduction; arises from uncoordinated or loss of atrial contraction (Chaotic rapid atrial electrical activity)
  • Tachycardia may continue despite beats that fail to conduct to the ventricles, indicating that the AV node is not participating in the tachycardia circuit
  • Ashman Phenomenon: Aberrantly conducted beats after long-short R-R cycles

Complications

  • Loss of atrial contributions to ventricular filling
  • Predisposition to thrombus formation in the left atrial appendage w/potential embolization (Thromboembolic Stroke)
  • In patients with MS or HOCM, conversion to sinus rhythm increases embolic risk
  • More likely for stoke 5x

Diagnosis and Work-up

  • Diagnosis: EKG to Confirm
    • TTE and TSH/Free T4
      • To assess for atrial thrombi, hyperthyroidism, baseline for long-term
      • Hypertension MCC
    • TEE if TTE shows valvular disease
    • Exercise stress test after starting medications
    • Holter, telemetry to identify asymptomatic episodes
    • EPS: to test for SVTs (AVNRT/MAT)
  • W/U: CMP, TSH, Echo

Management2

Rhythm/Rate

Acute Afib w/RVR

ACC 2023 Guideline - Acute Afib

Unstable Afib w/RVR

  • Immediate Cardioversion

Stable Afib w/RVR

  • 1B: Non-dihydropyridine CCBs or BBs

    • Severe COPD: CCBs (Cardizem)
    • CAD: BBs (Metoprolol Tartrate)

  • 2A: IV Magnesium

  • 2A: Digoxin if can't use BBs or CCBs
    • Total IV loading dose:
      • Normal renal function: 8-12 mcg/kg ideal body weight (usually ~600-1,000 mcg).
      • Renal insufficiency: 6-10 mcg/kg ideal body weight.
      • Typically, 50% of the total loading dose is given initially, followed by 25% given twice, every six hours.
        • The first IV dose (typically ~400-600 mcg) takes effect within roughly 1-4 hours. Monitor for effect. If an adequate heart rate is achieved, then subsequent doses may be omitted. If bradycardia occurs, further administration should be held
  • 2B: Amiodarone
  • Radiofrequency Ablation (RFA)
    • 1 year success rates approach 70-80%
    • Afib recurrence after RFA in 20-40% of patients
      • OSA independently increases the risk of incident atrial fibrillation and increases the risk of recurrent AF after ablation by promoting atrial structural and electrical remodeling including atrial enlargement and low-voltage areas with conduction abnormalities
        • Treatment of OSA with CPAP improves arrhythmia-free survival post-catheter ablation
      • Repeat ablation is primarily considered for those with symptomatic AF recurrences (often drug-refractory) occurring at least 3 months or more post-ablation
      • At 1-year follow-up more patients randomized to repeat ablation with RF (58%) were AF-free compared with those who underwent cryoablation (43%)5
    • Complications (<5%)

Anticoagulation

Resources

  1. https://www.ncbi.nlm.nih.gov/books/NBK526072/ ↩

  2. https://pubmed.ncbi.nlm.nih.gov/30144419/{:target="_blank"} ↩

  3. https://pubmed.ncbi.nlm.nih.gov/12466506/{:target="_blank"} ↩

  4. https://pubmed.ncbi.nlm.nih.gov/22894575/{:target="_blank"} ↩

  5. https://pubmed.ncbi.nlm.nih.gov/23210695/{:target="_blank"} ↩