Atrial Fibrillation
Cardiology
Illness script · Cardiology
Atrial Fibrillation
Chaotic, disorganized atrial electrical activity causing irregularly irregular rhythm and loss of coordinated atrial contraction.
This illness script for Atrial Fibrillation covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common sustained cardiac arrhythmia; prevalence rises sharply after age 65
- HTN is single biggest modifiable risk factor
- Structural heart disease: valvular (especially mitral), HF, cardiomyopathy
- Thyrotoxicosis, alcohol ('holiday heart'), OSA, obesity
- Acute triggers: PE, pneumonia, post-cardiac surgery, electrolyte disturbance
- Family history / lone AF in younger patients (<60, no structural disease)
02
Presentation
- Palpitations, dyspnea, fatigue, lightheadedness; may be asymptomatic (incidental ECG finding)
- Irregularly irregular pulse on exam — pathognomonic
- Rapid ventricular rate (often 110–160 bpm) if uncontrolled
- Absence of 'a' wave on JVP; possible S1 variability
- Acute onset <48 h vs. persistent >7 days vs. permanent — drives management
- Signs of decompensated HF if poorly tolerated (pulmonary edema, hypotension)
03
Pathophysiology
- Multiple reentrant wavelets or rapid focal discharges (often pulmonary vein foci) override sinus node
- Loss of organized atrial depolarization → no true P waves, fibrillatory baseline
- Irregular AV nodal conduction → irregularly irregular ventricular response
- Stasis in left atrial appendage → thrombus formation → embolic stroke risk
04
Diagnostics
- ECG: absent P waves, irregularly irregular narrow QRS, fibrillatory baseline — diagnostic
- Holter/event monitor if paroxysmal and not captured on resting ECG
- Echo (TTE/TEE): assess LV function, valvular disease, LAA thrombus before cardioversion
- TSH, BMP, CBC, LFTs to identify reversible causes
- CHA₂DS₂-VASc score to stratify stroke risk and guide anticoagulation
05
Management
- Rate control first (goal HR <110 bpm at rest): metoprolol or diltiazem IV/PO; digoxin in HF
- Rhythm control (cardioversion or antiarrhythmics): preferred if symptomatic, new-onset, or HF with reduced EF
- Anticoagulate ≥3 weeks before elective cardioversion if AF >48 h OR obtain TEE to exclude LAA thrombus
- DOACs (apixaban, rivaroxaban) preferred over warfarin for non-valvular AF; warfarin for mechanical valves/rheumatic MS
- Catheter ablation (pulmonary vein isolation) for symptomatic paroxysmal AF refractory to antiarrhythmics
- Avoid non-dihydropyridine CCBs (diltiazem/verapamil) in decompensated HF with reduced EF
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Atrial Flutter
Regular 'sawtooth' flutter waves at ~300 bpm with fixed 2:1 or 3:1 block; ventricular rate often exactly 150 bpm
Multifocal Atrial Tachycardia
Irregular rhythm but with ≥3 distinct P-wave morphologies; strongly associated with COPD/hypoxia
Frequent Premature Atrial Contractions
Irregular but intermittent — distinct early P waves present; not sustained chaotic activity
Atrial Fibrillation with WPW (pre-excitation)
Irregular wide-complex tachycardia with delta waves; AVOID AV-nodal blockers (risk of VF) — use procainamide
Keep reading
Full library- Asthma ExacerbationAcute worsening of reversible airflow obstruction from bronchospasm, mucosal edema, and mucus plugging in a known or new asthmatic.
- Bacterial MeningitisAcute bacterial infection of the subarachnoid space causing meningeal inflammation, often rapidly fatal without treatment.
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.