Atrial Fibrillation and Atrial Flutter

Abnormal impulse formation (ectopic pacemaker activity)

• Pulmonary vein triggers: Ectopic foci within pulmonary veins fire rapidly and irregularly, most commonly originating from ostial regions near the left atrium. These triggers account for 90% of paroxysmal AF cases and are the primary target of ablation therapy.
• Enhanced automaticity: Increased intracellular calcium and cAMP in atrial myocytes from catecholaminergic stimulation, thyroid hormone excess, or inflammatory states drives spontaneous depolarization independent of the SA node.
• Ectopic activity from non-pulmonary vein sources: Superior vena cava, inferior vena cava, coronary sinus, and left atrial appendage regions may harbor automaticity, particularly in persistent AF.

Reentry mechanisms

• Substrate heterogeneity: Regional differences in atrial conduction velocity and refractory periods create unidirectional block and reentry circuits. Structural remodeling in the setting of chronic AF perpetuates these conditions.
• Spiral wave activity: Three-dimensional reentrant wavelets propagate chaotically through atrial tissue, creating the characteristic disorganized activity on ECG.
• Atrial flutter mechanism: Typical (Type I) AFL involves a macroreentrant circuit utilizing the cavotricuspid isthmus (CTI) between the inferior vena cava and tricuspid valve, producing organized atrial flutter waves at 250-350 bpm.

Electrical and structural remodeling

• Atrial fibrillation begets atrial fibrillation: Chronic AF promotes shortening of atrial refractory period, increased conduction slowing, and calcium handling abnormalities that perpetuate arrhythmia. This "AF remodeling" creates a vicious cycle rendering AF increasingly paroxysmal-to-persistent progression likely.
• Atrial dilation and fibrosis: Underlying cardiac disease causes stretch-induced activation of fibroblasts, excessive collagen deposition, and disrupted gap junctions, fragmenting electrical propagation and stabilizing reentry substrates.
• Ion channel dysfunction: Downregulation of L-type calcium channels, altered potassium channel expression (particularly IKACh and IKUR), and abnormal Na-K-ATPase function modify action potential duration and refractoriness.

Cardiac causes

• Structural heart disease: Left ventricular hypertrophy (hypertension, aortic stenosis), dilated cardiomyopathy (ischemic and nonischemic), valvular disease (mitral stenosis, mitral regurgitation), and previous myocardial infarction
• Acute coronary syndrome: Ischemia-induced automaticity and altered electrolyte homeostasis
• Heart failure: AF prevalence increases with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF); bidirectional relationship wherein AF worsens hemodynamics and HF promotes AF
• Congenital heart disease: Atrial septal defect, tetralogy of Fallot, transposition of great arteries (postoperative patients at high risk)
• Inflammatory/infiltrative disease: Myocarditis, pericarditis, amyloidosis, sarcoidosis, hemochromatosis
• Atrial myxoma and other tumors: Physical irritation of atrial tissue

Pulmonary causes

• Pulmonary embolism: Acute right atrial stretch and hypoxia
• Chronic obstructive pulmonary disease and pulmonary hypertension: Right atrial enlargement from cor pulmonale
• Acute hypoxemia: Any cause (pneumonia, acute respiratory distress syndrome)
• Obstructive sleep apnea: Repetitive hypoxia, negative intrathoracic pressure swings, and sympathetic activation

Metabolic and systemic causes

• Thyrotoxicosis: Increased adrenergic sensitivity and shortened atrial refractoriness; AF occurs in 10-15% of hyperthyroid patients
• Hypertension: Most common modifiable risk factor; responsible for ~30% of AF cases through LVH and atrial fibrosis
• Diabetes mellitus: Atrial structural and electrical remodeling independent of hypertension
• Obesity: Atrial stretch, systemic inflammation, autonomic dysfunction, and obstructive sleep apnea
• Chronic kidney disease: Electrolyte abnormalities, inflammation, anemia, and hypertension

Other risk factors

• Age: Exponential increase in prevalence with advancing age
• Male sex: 1.5-2 fold higher risk than females (though females have higher stroke risk once AF develops)
• Alcohol use: Particularly acute heavy consumption ("holiday heart syndrome"); chronic moderate-to-heavy use increases AF risk
• Caffeine and sympathomimetic drugs: May trigger paroxysmal episodes
• Genetic predisposition: Family history accounts for ~30% of AF risk; numerous common and rare genetic variants identified
• Recent surgery: Postoperative AF occurs in 10-50% of cardiac surgery patients, 1-2% of noncardiac surgery

Symptoms (highly variable; some patients completely asymptomatic)

• Palpitations: Most common symptom; described as rapid, irregular heartbeats or fluttering sensation in chest or neck
• Dyspnea: From reduced cardiac output, increased filling pressures, or anxiety; worsened with exertion
• Chest discomfort or angina: From demand ischemia, particularly in patients with underlying coronary artery disease
• Syncope/presyncope: From rapid ventricular response, reduced diastolic filling time, or severe LV dysfunction
• Fatigue and exercise intolerance: From chronotropic incompetence, reduced cardiac output, or prolonged rapid rates
• Asymptomatic presentation: Discovered incidentally on ECG; increasingly common with screening

Physical examination findings

• Irregularly irregular pulse: Pathognomonic finding; best appreciated by palpating radial artery for 15-30 seconds; distinguishes AF from other tachycardias
• Pulse deficit: Peripheral pulses less frequent than auscultated heart sounds due to poor ventricular filling at very short RR intervals; indicates rapid ventricular response
• Variable S1 intensity: Reflects changing LV filling from variable RR intervals
• New systolic murmur: From functional mitral regurgitation secondary to acute LV dilatation
• Signs of heart failure: Rales, elevated JVP, peripheral edema, hepatomegaly
• Hyperthermia, tremor, or signs of thyroid disease: From underlying hyperthyroidism
• Hemodynamic instability: Hypotension, altered mental status (particularly in rapid AF with RVR)

Electrocardiography (12-lead ECG)

• Atrial fibrillation hallmarks:
• Absent P waves; baseline appears "chaotic" or "fibrillatory" with fine or coarse fibrillatory waves (f-waves) at 350-600 bpm
• Irregularly irregular ventricular response with variable RR intervals (no two consecutive intervals identical)
• QRS complexes narrow (≤120 ms) unless aberrant conduction or pre-existing BBB present
• Ventricular rate varies from normal (<60 bpm) to rapid (>150 bpm) depending on AV nodal conduction and prior rate-controlling therapy

• Atrial flutter hallmarks:
• Regular or regularly irregular sawtooth atrial flutter waves (F waves) at 250-350 bpm, best visible in leads II, III, aVF
• Typical 2:1 AV conduction produces ventricular rate ~150 bpm (half the atrial rate); other ratios (1:1, 3:1, variable) possible
• Type I (CTI-dependent, counterclockwise): Negative flutter waves in inferior leads
• Type II (rare): Different morphology, often faster atrial rate (350-430 bpm)
• Atypical (left atrial) flutter: Variable morphology, often irregular conduction

Laboratory evaluation

• Thyroid function tests (TSH, free T4): Essential to exclude thyrotoxicosis in all new-onset AF; present in 5-15% of AF patients
• Complete metabolic panel: Evaluate electrolytes (hypokalemia, hypomagnesemia lower AF threshold), renal function (for drug dosing), glucose control
• Complete blood count: Assess for anemia (worsens symptoms, reduces oxygen delivery), infection
• Troponin and B-type natriuretic peptide (BNP): Troponin elevation indicates acute coronary syndrome; elevated BNP suggests HF and predicts worse outcomes
• Baseline INR: Establish baseline for anticoagulation eligibility

Cardiac imaging

• Transthoracic echocardiography:
• Standard initial imaging; assesses LV systolic and diastolic function, LA size (>40 mm diameter or >50 mL indexed associated with worse outcomes), valve pathology, and LV hypertrophy
• Identifies structural causes explaining AF etiology
• LA strain imaging emerging as predictor of AF recurrence post-ablation

• Transesophageal echocardiography (TEE):
• Superior visualization of LA appendage (LAA) to exclude thrombus prior to cardioversion in AF >48 hours duration without therapeutic anticoagulation
• Better assessment of complex valve disease
• Essential preoperative evaluation for AF patients undergoing cardiac surgery

• Cardiac MRI:
• Detects atrial fibrosis extent and distribution; increasingly used for catheter ablation planning
• Identifies infiltrative disease (sarcoidosis, amyloidosis, hemochromatosis)

• CT angiography: For pulmonary embolism evaluation if clinical suspicion high

Ambulatory rhythm monitoring (for paroxysmal AF diagnosis)

• Holter monitor (24-48 hours): Useful for frequent AF episodes; limited detection window
• Extended Holter/event monitor (7-14 days): Higher diagnostic yield than 24-hour Holter for paroxysmal AF
• Insertable loop recorder (ILR): Gold standard for detecting paroxysmal AF; implantable device monitoring continuously for up to 3 years; useful when symptoms suggest AF but standard monitoring nondiagnostic
• Smartphone/smartwatch ECG: Increasing prevalence in screening populations; validated for AF detection with high specificity

Acute management approach determined by hemodynamic stability and symptom severity

Hemodynamically unstable AF/AFL (acute cardioversion indicated)

• Indications: Hypotension, altered mental status, chest pain, severe dyspnea, signs of shock, or EF <30% with RVR
• Synchronized DC cardioversion:
• Initial energy: 100-200 J biphasic; escalate if unsuccessful
• Requires sedation (propofol, etomidate) and analgesia
• Pre-cardioversion TEE (if AF >48 hours) or anticoagulation bridge with LMWH/UFH required to minimize stroke risk
• Success rate >90% with synchronized shocks
• Transient bradycardia and hypotension common immediately post-conversion; have atropine/pacing available

• Rate control temporizing measure (if cardioversion unavailable): IV digoxin or IV beta-blocker to reduce ventricular rate acutely

Hemodynamically stable AF/AFL: Choose rate vs. rhythm control strategy

• Target resting heart rate <110 bpm (lenient rate control) shown equivalent to strict <80 bpm in AFFIRM trial; improves quality of life by simplifying medication regimens
• First-line agents:
• Beta-blockers (metoprolol, atenolol, carvedilol): First-line in most; AV nodal conduction blockade; slower onset but excellent chronic control; also reduce mortality post-MI; caution in HFrEF (use carvedilol/metoprolol succinate extended-release)
• Calcium channel blockers (diltiazem, verapamil): Effective nodal blockers; useful if beta-blocker contraindicated or concurrent hypertension; avoid in HFrEF
• Digoxin: Vagomimetic effect (AV nodal slowing); slow onset (hours); useful in sedentary patients or HFrEF; narrow therapeutic window; inadequate for exercise-induced tachycardia; toxicity risk with renal dysfunction

• Second-line agents (if monotherapy inadequate):
• Combination therapy: Beta-blocker + diltiazem/verapamil (enhanced nodal blockade; monitor for bradycardia, hypotension, heart block) or beta-blocker + digoxin
• Dronedarone: Non-iodinated benzofuran antiarrhythmic with rate-limiting properties; PACEMAKER trial showed 31% reduction in cardiovascular hospitalization; avoid in permanent AF or HFrEF

• Antiarrhythmic drugs:
• Class I agents (sodium channel blockers):
• Flecainide/Propafenone: "Pill-in-pocket" approach effective for infrequent paroxysmal AF in patients without structural disease; use with AV nodal blocker to prevent 1:1 conduction
• Sotalol: Class III + II properties; beta-blocking activity; effective but requires dose adjustment for renal function; QT prolongation risk
• Dofetilide: Class III agent; renal dosing required; baseline QTc <440 ms prerequisite; QT monitoring mandatory; expensive

• Class III agents (potassium channel blockers):
• Amiodarone: Most effective agent; broad spectrum (all four Vaughan-Williams classes); used for structural disease/HFrEF/post-op AF; significant toxicity (pulmonary fibrosis, hepatotoxicity, thyroid dysfunction, photosensitivity, corneal deposits) limits chronic use; baseline PFTs, LFTs, TSH required; annual monitoring
• Ibutilide: IV Class III agent; effective for acute cardioversion/chemical conversion; used in acute settings; QT prolongation/torsades de pointes risk; baseline QTc <440 ms required
• Dronedarone: Noted above; safer profile than amiodarone but less effective for persistent AF

• Proarrhythmic risk: All antiarrhythmics carry torsades de pointes risk (particularly Class III agents in hypokalemia); baseline ECG essential; QTc monitoring required with sotalol/dofetilide/ibutilide

Catheter ablation

• Pulmonary vein isolation (PVI):
• Gold standard for rhythm control, particularly paroxysmal AF; success rates 70-80% single procedure, up to 90% with repeat procedures
• Superior to antiarrhythmic drugs in symptom reduction and quality of life (AFFIRM substudy, CABANA trial)
• Circumferential ablation lesions around PV ostia electrically isolate ectopic triggers
• Performed with fluoroscopy and/or electroanatomic mapping (CARTO, EnSite

Thromboembolic (the dominant complication)

• Cardioembolic stroke: Loss of organized atrial contraction produces stasis in the left atrial appendage, satisfying Virchow's triad and generating fibrin-rich thrombus. AF confers a markedly increased stroke risk (classically cited as roughly fivefold). Signals: sudden maximal-deficit focal neurologic event, often large-vessel MCA territory or multiple vascular territories on imaging. Emergency — activate stroke protocol. Atrial flutter carries comparable risk and requires identical anticoagulation per the 2023 ACC/AHA/ACCP/HRS AF guideline.
• Systemic embolism: Acute limb ischemia (pulseless, pale, painful extremity), renal or splenic infarction, acute mesenteric ischemia (pain out of proportion to exam). Emergency.
• Post-cardioversion embolism from atrial stunning: Mechanical atrial function lags electrical recovery, so thrombus can form after successful conversion — hence anticoagulation for at least 4 weeks post-cardioversion regardless of rhythm.

Hemodynamic and myocardial

• Tachycardia-induced cardiomyopathy: Persistently rapid rates cause energy depletion and calcium mishandling; presents as new HFrEF with global hypokinesis that improves substantially with rate or rhythm control.
• Decompensated heart failure / demand ischemia: Loss of the atrial kick (up to ~20-30% of filling) is poorly tolerated in HFpEF, LVH, mitral stenosis, and hypertrophic cardiomyopathy.
• Pre-excited AF in WPW: Conduction down the accessory pathway yields an irregular, wide, polymorphic-appearing tachycardia that can degenerate to ventricular fibrillation. Emergency.
• 1:1 flutter conduction: Class IC agents slow the atrial rate, allowing the AV node to conduct every beat at rates near 200-250 bpm; always pair flecainide/propafenone with an AV nodal blocker.

Treatment-related

• Anticoagulant hemorrhage: Intracranial bleeding is the feared event — emergency; reverse with idarucizumab (dabigatran), andexanet alfa (factor Xa inhibitors), or 4-factor PCC plus vitamin K (warfarin).
• Proarrhythmia: Torsades de pointes with sotalol, dofetilide, ibutilide — watch QTc and potassium/magnesium.
• Digoxin toxicity: Nausea, yellow-green visual halos, atrial tachycardia with block, bidirectional VT.
• Ablation complications: Cardiac tamponade (emergency), phrenic nerve palsy, pulmonary vein stenosis, and rare but often fatal atrioesophageal fistula presenting weeks later with fever, dysphagia, and neurologic events.
• Tachy-brady syndrome: Prolonged conversion pauses may unmask sinus node disease and require pacing.

• The ECG buzzwords: Irregularly irregular rhythm with absent P waves = AF; sawtooth F waves in II, III, aVF with a ventricular rate near 150 = typical flutter with 2:1 block. A regular narrow tachycardia at exactly ~150 bpm should prompt a hunt for flutter waves (try vagal maneuvers or adenosine to unmask them — diagnostic, not therapeutic, in flutter).
• Single best next step in an unstable patient: Immediate synchronized cardioversion. Hypotension, ischemic chest pain, altered mentation, or pulmonary edema override every anticoagulation timing rule. Do not delay for a TEE.
• The one association examiners test — WPW with AF: An irregular, wide-complex, varying-morphology tachycardia in a young patient. Give procainamide (or ibutilide) or cardiovert; never adenosine, beta blockers, calcium channel blockers, or digoxin, since AV nodal blockade shunts conduction down the accessory pathway and can precipitate ventricular fibrillation.
• The 48-hour rule: If AF duration is ≥48 hours or unknown, either anticoagulate for ~3 weeks beforehand or obtain a TEE to exclude LAA thrombus; anticoagulate at least 4 weeks after cardioversion in every case because of atrial stunning. Long-term therapy is then driven by stroke risk score, not by the rhythm achieved.
• Anticoagulant selection: Per the 2023 ACC/AHA/ACCP/HRS guideline, DOACs are preferred over warfarin except in moderate-to-severe mitral stenosis or a mechanical prosthetic valve, where warfarin is required.
• Common distractor to avoid: Aspirin is not an acceptable substitute for oral anticoagulation in score-eligible AF. Another trap — rate control (rhythm-control agnostic) does not remove the need for anticoagulation, and successful ablation does not by itself justify stopping it.
• Reversible triggers worth naming: Holiday heart after a binge, thyrotoxicosis (check TSH in all new AF), obstructive sleep apnea, pulmonary embolism, and post-cardiac-surgery AF.
• Flutter-specific fact: Cavotricuspid isthmus ablation is highly effective and curative for typical flutter — far more definitive than for AF — yet stroke prophylaxis rules remain identical to AF.