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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- AF = irregularly irregular rhythm, absent P waves, fibrillatory baseline on ECG
- Classify: paroxysmal (<7 days), persistent (>7 days or requiring cardioversion), long-standing persistent (>12 mo), permanent
- Stroke risk: CHA2DS2-VASc >=2 (men) or >=3 (women) = anticoagulate. DOACs preferred over warfarin for non-valvular AF
- Rate control first-line: BB or non-DHP CCB (diltiazem); target resting HR <110 bpm (lenient)
- Rhythm control: cardioversion, antiarrhythmics (amiodarone, flecainide, dofetilide), or catheter ablation for symptomatic patients
Overview
Atrial fibrillation is the most common sustained cardiac arrhythmia, characterized by disorganized rapid atrial electrical activity with ineffective atrial contraction. On ECG: irregularly irregular ventricular response, absent P waves, fibrillatory baseline. AF increases stroke risk 5-fold (LA appendage thrombus), doubles HF risk, and raises mortality 1.5-1.9x. The 2023 ACC/AHA/ACCP/HRS guideline emphasizes holistic, patient-centered care integrating risk factor modification with stroke prevention and symptom management.
Epidemiology
AF affects ~6 million Americans, projected to exceed 12 million by 2030. Prevalence: ~1% at age 60, ~10% by age 80. Risk factors: age, HTN (most common modifiable), HF, valvular disease (especially mitral stenosis), obesity, OSA, binge alcohol ("holiday heart"), hyperthyroidism, post-cardiac surgery (25-40% after CABG), and PE. AF is independently associated with cognitive decline and dementia.
Clinical Features
Symptoms
Palpitations (rapid, irregular heartbeat)
Dyspnea on exertion (loss of atrial kick reduces CO by 15-25%)
Fatigue and exercise intolerance
Lightheadedness or presyncope
May be asymptomatic (incidental finding)
Acute embolic stroke as first presentation
Chest pain with rapid ventricular rate (demand ischemia)
Signs
Irregularly irregular pulse — the hallmark
Pulse deficit (apical HR > radial pulse)
Variable S1 intensity on auscultation
Absent "a" wave in JVP
Signs of underlying cause: thyromegaly, mitral stenosis murmur, HF signs
Hemodynamic instability: hypotension, altered mental status, pulmonary edema
Investigations
First-line
12-lead ECGIrregularly irregular narrow QRS, absent P waves, fibrillatory baseline. If wide QRS irregular: AF with aberrancy vs pre-excited AF (WPW) — the latter is dangerous, do NOT use AV-nodal blockers
Basic labsCBC, BMP, TSH (hyperthyroidism = reversible cause), magnesium, LFTs, coags
TTELVEF, LA size, valvular disease (mitral stenosis), wall motion, RVSP
Second-line
CHA2DS2-VASc scoreCHF(1) HTN(1) Age>=75(2) DM(1) Stroke/TIA/VTE(2) Vascular disease(1) Age 65-74(1) Sex-female(1). Guides anticoagulation
HAS-BLED scoreEstimates bleeding risk — identify modifiable factors, NOT to withhold anticoagulation if stroke risk high
Ambulatory monitoringHolter (24-48 h), event monitor (2-4 weeks), or implantable loop recorder for paroxysmal AF documentation
Specialist
TEERule out LA appendage thrombus before cardioversion if AF >48 h or unknown duration and not anticoagulated >=3 weeks
EP studyPre-ablation assessment; if WPW + AF suspected
1
Acute — hemodynamically unstable
- Synchronized cardioversion immediately if hypotension, severe chest pain, pulmonary edema, or altered mental status
- Start anticoagulation as soon as feasible
- AF + WPW (wide QRS, delta waves): cardioversion or IV procainamide — do NOT use AV-nodal blockers (BB, CCB, digoxin, adenosine) as they may cause VF
2
Rate control
- First-line: BB (metoprolol, atenolol) or non-DHP CCB (diltiazem, verapamil) — use BB if concurrent HFrEF (non-DHP CCBs contraindicated in HFrEF)
- Target: resting HR <110 bpm (lenient, RACE II trial = non-inferior to strict <80)
- Adjunct: digoxin (rate control at rest only; useful in HFrEF but does not reduce mortality)
- Refractory: amiodarone for rate control as last resort; AV node ablation + pacemaker ("ablate and pace")
3
Rhythm control
- Consider when: symptomatic despite rate control, young, new-onset, AF with HFrEF (CASTLE-AF: ablation survival benefit)
- Cardioversion: electrical (synchronized DC) or pharmacologic (ibutilide IV, flecainide PO, amiodarone IV)
- AF >=48 h or unknown: anticoagulate >=3 weeks before OR TEE to rule out thrombus, then cardiovert, then anticoagulate >=4 weeks after
- AF <48 h: cardiovert and anticoagulate based on CHA2DS2-VASc
- Maintenance antiarrhythmics: flecainide/propafenone ONLY if no structural heart disease; amiodarone for any patient (but side effects); dofetilide; sotalol
- Catheter ablation (PVI): Class I for symptomatic AF refractory to >=1 antiarrhythmic; can be first-line in select patients
4
Stroke prevention
- CHA2DS2-VASc >=2 (men) or >=3 (women): anticoagulate
- CHA2DS2-VASc 1 (men) or 2 (women): may consider (shared decision)
- CHA2DS2-VASc 0 (men) or 1 (women): no anticoagulation. Aspirin alone NOT recommended for stroke prevention in AF
- DOACs preferred: apixaban 5 mg BID (lowest bleeding per ARISTOTLE), rivaroxaban 20 mg daily, dabigatran 150 mg BID, edoxaban 60 mg daily
- Warfarin (INR 2-3) required for moderate-severe mitral stenosis or mechanical valve — DOACs contraindicated
- LA appendage occlusion (Watchman): alternative if long-term anticoagulation contraindicated
5
Risk factor modification
- Weight loss >10% = 6x more likely to maintain sinus rhythm (LEGACY)
- Treat OSA with CPAP
- Control HTN, diabetes, hyperlipidemia
- Moderate alcohol or abstinence
Complications
- Cardioembolic stroke: 5x risk without anticoagulation; LA appendage is thrombus source in >90% of non-valvular AF
- Heart failure: Tachycardia-mediated cardiomyopathy (reversible) or worsening pre-existing HF
- Systemic embolism: Mesenteric, limb, renal, or splenic infarction
- Bleeding: From anticoagulation — intracranial hemorrhage most feared
- Cognitive decline: AF independently associated with dementia, even without clinical stroke
USMLE Step 2 CK Exam Tips
- 1Irregularly irregular + absent P waves = AF. Most common sustained arrhythmia tested
- 2New-onset AF: always check TSH (hyperthyroidism is reversible)
- 3AF + WPW (irregular WIDE complex): cardiovert or procainamide. AV-nodal blockers (diltiazem, metoprolol, digoxin, adenosine) CONTRAINDICATED — can cause VF
- 4DOACs preferred over warfarin for non-valvular AF. Exception: mechanical valve or moderate-severe mitral stenosis = warfarin only
- 5Aspirin ALONE is NOT recommended for AF stroke prevention — answer is always anticoagulation based on CHA2DS2-VASc
- 6Flecainide/propafenone: ONLY without structural heart disease. Structural disease = amiodarone or dofetilide
- 7"Pill-in-the-pocket": self-administered flecainide for infrequent paroxysmal AF without structural disease
- 8AF + RVR + hemodynamic instability = synchronized cardioversion
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