Atrial Fibrillation (AFib) Study Notes

Atrial Fibrillation (AFib) Study Notes

Definition

• AFib is a type of arrhythmia originating in the atria (supraventricular tachycardia).

• Common and clinically important due to complications like thromboembolism, heart failure, and tachycardia-induced cardiomyopathy.

Etiology / Causes

1. Cardiac Causes

• Triggered by high left atrial pressures, leading to atrial dilation and atrial remodeling → abnormal conduction → AFib.

Key cardiac conditions:

1. Mitral stenosis (valvular AFib)

   • Rheumatic fever common cause.

   • Blood cannot flow from left atrium → left ventricle → increased LA pressure → dilation → remodeling.

2. Heart failure

   • Diastolic HF: Stiff ventricle → poor filling → high LA pressure.

   • Systolic HF: Ventricles congested → high filling pressures.

3. Cardiac ischemia / fibrosis

   • Ischemic tissue or fibrosis creates re-entrant circuits → ectopy → AFib.

   • Often secondary to coronary artery disease or myocardial infarction.

2. Non-Cardiac Causes

• Triggered by hypoxia, catecholamines, or electrolyte disturbances.

A. Pulmonary / Hypoxia-related

• Conditions: Pneumonia, COPD (chronic bronchitis), pulmonary embolism.

• Hypoxia → pulmonary vein ectopy → AFib.

B. Catecholamine Excess

• Stimulates beta-1 receptors in atrial cells → ectopic firing.

• Causes:

  • Sepsis

  • Postoperative state

  • Pheochromocytoma (adrenal tumor)

  • Thyrotoxicosis / hyperthyroidism

  • Sympathomimetics (cocaine, methamphetamine, PCP)

C. Electrolyte disturbances

• Hypokalemia

• Hypomagnesemia

• Can precipitate holiday heart syndrome (acute AFib after binge alcohol use).

Classification by Duration

1. Paroxysmal AFib

   • <7 days, often self-terminating.

2. Persistent AFib

   • 7 days, requires intervention to restore sinus rhythm.

3. Permanent AFib

   • Continuous AFib despite interventions; atrial remodeling is irreversible.

Complications

1. Thromboembolic Events

• Ineffective atrial contractions → stasis → thrombus formation (most commonly in the left atrial appendage).

• Potential embolic events:

  • Stroke / TIA

  • Acute mesenteric ischemia / ischemic colitis

  • Acute limb ischemia

2. Acute Heart Failure

• AFib with rapid ventricular rate (RVR) >150 bpm:

  • ↓ diastolic filling → ↓ stroke volume → ↓ cardiac output → hypotension.

  • ↑ LA pressure → pulmonary edema → dyspnea, orthopnea, PND.

• Termed unstable AFib if causing hypotension or pulmonary edema.

3. Tachycardia-induced Cardiomyopathy

• Chronic AFib with sustained HR >100 bpm → dilated cardiomyopathy (HF with reduced EF).

Diagnosis

1. 12-lead ECG

   • Irregularly irregular rhythm.

   • Variable R-R intervals.

   • Rate: slow, normal, or rapid.

2. Echocardiogram

   • Evaluate LA size, thrombus, valvular disease (mitral stenosis, prosthetic valve).

3. Holter Monitor / Loop Recorder

   • For paroxysmal / occult AFib.

Lab evaluation for reversible causes:

• Potassium / magnesium

• Thyroid function (thyrotoxicosis)

Management Goals

1. Rate control

2. Rhythm control

3. Anticoagulation (stroke prevention)

1. Rate Control

• Target HR <110 bpm (per trials).

• Medications:

  • Beta-blockers: Metoprolol, Carvedilol (avoid in bradycardia, decomp HF, severe COPD)

  • Non-dihydropyridine calcium channel blockers: Verapamil, Diltiazem (avoid in decomp HF, bradycardia)

  • Digoxin: Useful in HFrEF (<35% EF)

  • Amiodarone: Optional in select cases

2. Rhythm Control

• Goal: restore normal sinus rhythm.

• Indications:

  • Hemodynamic instability (hypotension, shock, pulmonary edema, angina)

  • AFib <48 hours (low thrombus risk)

• Methods:

  1. Direct Current Cardioversion (DCCV) – preferred

  2. Pharmacologic conversion: Amiodarone, Flecainide (risk of torsades due to QT prolongation)

  3. Radiofrequency ablation / Maze procedure: For refractory AFib

3. Anticoagulation

• Prevent stroke / thromboembolism.

• Risk assessment: CHA₂DS₂-VASc score

  • CHF = 1

  • Hypertension = 1

  • Age ≥75 = 2

  • Diabetes = 1

  • Stroke / TIA history = 2

  • Vascular disease (PAD, MI) = 1

  • Age 65–74 = 1

  • Female sex = 1

• Interpretation:

  • Score ≥2: anticoagulate

  • Score 1: consider clinical judgment

  • Score 0: generally no anticoagulation (aspirin if needed)

• Medication choice:

  • Non-valvular AFib: DOACs (rivaroxaban, apixaban, edoxaban, dabigatran)

  • Valvular AFib (mitral stenosis, prosthetic valve) or CKD: Warfarin (INR monitoring 2–3; 2.5–3.5 for prosthetic valve)

  • Bridging: IV heparin → transition to warfarin/DOAC if indicated

Acute / New-Onset AFib Management

Patient Status	Management
Hemodynamically unstable	Immediate DCCV
Hemodynamically stable	Rate control → consider rhythm control if persistent or symptomatic
AFib <48 hours	Can cardiovert if no thrombus risk
AFib >48 hours	Anticoagulate 3–4 weeks → TEE to rule out thrombus → cardiovert if safe

• Post-cardioversion anticoagulation: At least 4 weeks; duration based on CHA₂DS₂-VASc.

Key Concepts / Mnemonics

• Causes of AFib: “MAP”

  • M – Mitral valve / myocardial (cardiac)

  • A – Autonomic / atrial ectopy (catecholamines, hyperthyroid)

  • P – Pulmonary / hypoxia (lung disease, PE)

• Complications: Stroke, Heart failure, Tachycardia-induced cardiomyopathy

• Acute AFib approach: Stable → rate control; unstable → cardiovert

• Rate goal: <110 bpm

• Rhythm control: Indicated if hemodynamically unstable or AFib <48 hours

• Anticoagulation: Based on CHA₂DS₂-VASc score.