Cardiac Arrhythmias
Atrial Fibrillation
Chaotic atria, no P waves, irregularly irregular pulse — and a fivefold stroke multiplier
Atrial fibrillation is the most common sustained arrhythmia: chaotic wavefronts replace organized atrial contraction. ECG shows no P waves, fibrillatory baseline, irregularly irregular R-R. About 33 million people are affected; stroke risk rises fivefold.
- Global prevalence~33 million people; ~5% over age 65
- ECG hallmarkNo P waves; irregularly irregular R-R
- Trigger sourcePulmonary vein ectopics (90%+)
- Stroke risk≈ 5× baseline; 15-20% of ischemic strokes
- Anticoag scoreCHA2DS2-VASc ≥ 2 (men) / ≥ 3 (women)
- First-line DOACsApixaban, rivaroxaban, dabigatran, edoxaban
Interactive visualization
Press play, or step through manually. Watch sinus rhythm dissolve into chaotic atrial wavelets — and see how that chaos prints on the ECG.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
The arrhythmia in one sentence
Atrial fibrillation replaces the SA node's single organized impulse with hundreds of disorganized wavelets per minute. The atria quiver instead of contracting. Some of those wavelets reach the AV node and capture the ventricles randomly — irregular, often fast, almost never coordinated.
Where AF starts — the pulmonary veins
In over 90% of cases, AF is initiated by rapid ectopic firing in cardiac muscle sleeves that extend into the four pulmonary veins as they enter the left atrium. Michel Haïssaguerre's 1998 discovery of this anatomic source turned AF from a chronic medical problem into a procedural one. Pulmonary vein isolation by catheter ablation electrically disconnects these sleeves from the atrium and is now standard of care for symptomatic paroxysmal AF.
What sustains AF after the trigger fires is the atrial substrate: an enlarged, scarred, fibrotic left atrium provides multiple unstable re-entry circuits. Risk factors that build that substrate are hypertension, obesity, sleep apnea, valvular disease (especially mitral), heart failure, hyperthyroidism, and aging itself. Lose weight, treat OSA, control BP — and recurrence rates fall by 30-50%.
What it looks like on the ECG
Three signs together are diagnostic: (1) absence of discrete P waves, (2) fibrillatory or undulating baseline at 350-600 atrial bpm, (3) irregularly irregular R-R intervals. The QRS is usually narrow because the impulse reaches the ventricles through the normal His-Purkinje system. Heart rate at presentation is typically 110-160 bpm before treatment; 70-90 bpm after AV-nodal blockade.
Worked clinical example
A 71-year-old hypertensive woman with diabetes presents with new palpitations and shortness of breath. Vitals: HR 142, BP 132/84. ECG: no P waves, irregular R-R, narrow QRS. Echo: LA 4.6 cm (enlarged), EF 55%, no thrombus. CHA2DS2-VASc: hypertension 1, age 65-74 territory but she is 71 so still 1, diabetes 1, sex female 1 — total 4. Decision:
- Anticoagulate. CHA2DS2-VASc 4 in a woman gives ~4% annual stroke risk without therapy. Apixaban 5 mg twice daily cuts that to ~1% and reduces major bleeding versus warfarin.
- Rate control first. Metoprolol 25 mg twice daily; titrate to resting HR <110 (lenient) or <80 (strict). Diltiazem if beta blocker contraindicated.
- Consider rhythm control. EAST-AFNET 4 showed early rhythm restoration within 1 year reduces CV events; pulmonary vein isolation has 60-70% 1-year success for paroxysmal AF.
- Treat substrate. Weight loss, OSA evaluation, BP control to < 130/80.
CHA2DS2-VASc — the anticoagulation scorecard
| Risk factor | Points | Interpretation |
|---|---|---|
| Congestive heart failure | 1 | Includes LVEF ≤ 40% |
| Hypertension | 1 | Resting BP > 140/90 or on treatment |
| Age ≥ 75 | 2 | Strongest individual risk factor |
| Diabetes | 1 | Type 1 or 2 |
| Stroke/TIA/thromboembolism (prior) | 2 | Doubles the score weight |
| Vascular disease | 1 | MI, PAD, aortic plaque |
| Age 65-74 | 1 | Mid-tier age stratum |
| Sex (female) | 1 | Counts only when total ≥ 2 |
Threshold: anticoagulate at score ≥ 2 in men and ≥ 3 in women. DOACs are first-line; warfarin for mechanical valves and moderate-to-severe mitral stenosis (where DOACs lack evidence).
Common mistakes
- "AF on aspirin is fine." Aspirin is not adequate stroke prophylaxis in AF; DOACs reduce stroke by 60-70% versus aspirin's modest 20%.
- Restoring sinus rhythm and stopping anticoagulation. Atrial stunning persists for weeks after cardioversion; risk decisions are by score, not by current rhythm.
- Giving an AV-nodal blocker to AF with WPW. A delta wave on baseline plus AF means conduct via the accessory pathway — beta blockers and verapamil funnel impulses there. Procainamide or DC cardioversion.
- Calling new AF "lone." Almost no AF is truly lone; look for OSA, occult hyperthyroidism, alcohol, and undertreated hypertension.
- Missing rate-related cardiomyopathy. Persistent fast AF for months drops EF; rate control or restoration of sinus rhythm reverses it.
Frequently asked questions
What causes atrial fibrillation?
Most AF originates from rapid ectopic firing in muscle sleeves that extend into the pulmonary veins. These triggers fire into atria whose substrate has been remodeled by hypertension, left atrial enlargement, obesity, sleep apnea, valvular disease (especially mitral), or hyperthyroidism. Once initiated, multiple re-entrant wavelets perpetuate the arrhythmia. Acute triggers include alcohol binges (holiday heart), surgery, sepsis, pulmonary embolism, and electrolyte shifts. AF begets AF — chronic AF remodels atria further, making restoration of sinus rhythm progressively harder.
Why is the rhythm irregularly irregular?
Hundreds of disorganized depolarizations per minute bombard the AV node from many directions. The AV node has its own refractory period and conducts impulses to the ventricles randomly, depending on which arrivals find it ready. There is no pattern to the gaps between R waves — that randomness is what irregularly irregular means. Untreated, ventricular rates often run 110-160 bpm; with AV blockade, 70-90 bpm is typical.
Why does AF cause stroke?
The left atrial appendage is a narrow blind pouch with trabeculated walls. When the atrium does not contract, blood stagnates there, satisfying Virchow's stasis criterion. Thrombus forms and can embolize into the systemic circulation, most often to the brain. Roughly 15-20% of all ischemic strokes are attributable to AF. Strokes from AF tend to be larger and more disabling than other ischemic strokes because of the often substantial size of embolic clots.
What is CHA2DS2-VASc and when do you anticoagulate?
A risk score assigning points for Congestive heart failure (1), Hypertension (1), Age ≥75 (2), Diabetes (1), Stroke/TIA history (2), Vascular disease (1), Age 65-74 (1), Sex female (1). Score 0 in men or 1 in women: anticoagulation not recommended. Score 1 in men or 2 in women: consider. Score ≥2 in men or ≥3 in women: anticoagulate. Standard agents are direct oral anticoagulants — apixaban, rivaroxaban, dabigatran, edoxaban — which match or outperform warfarin with fewer intracranial bleeds and no INR monitoring.
Rate or rhythm control — which is better?
Historically, AFFIRM and RACE trials found no mortality difference. Recent EAST-AFNET 4 showed that early rhythm control within 1 year of diagnosis reduces cardiovascular events. Pulmonary vein isolation by catheter ablation maintains sinus rhythm in roughly 60-70% at 1 year for paroxysmal AF, less for persistent. Rate control alone is reasonable for older, less symptomatic patients with persistent AF. Anticoagulation decisions are independent of which strategy is chosen — restoring sinus rhythm does not eliminate stroke risk.
What is paroxysmal vs persistent vs permanent AF?
Paroxysmal AF self-terminates within 7 days, often within minutes to hours. Persistent AF lasts longer than 7 days or requires cardioversion to terminate. Long-standing persistent is more than 12 months continuous. Permanent AF is when patient and clinician accept the rhythm as ongoing without further attempts at restoration. The classification matters for ablation candidacy and outcomes — pulmonary vein isolation is more durable in paroxysmal disease.
When is cardioversion safe?
If AF has been present less than 48 hours, electrical or pharmacologic cardioversion can be performed without prior anticoagulation. Beyond 48 hours or unknown duration, either anticoagulate for 3 weeks before plus 4 weeks after, or perform transesophageal echo to exclude left atrial appendage thrombus before shocking. Unstable patients with hypotension or angina go to immediate cardioversion regardless of duration. After successful cardioversion, atrial stunning persists for weeks — anticoagulation must continue.