A 72-year-old woman from Mumbai presents with palpitations and mild dyspnea for 3 days. She has a history of hypertension and type 2 diabetes. Vital signs: BP 146/88 mmHg, HR 78/min (irregular), RR 16/min. Physical examination reveals an irregular pulse with no murmurs. A 12-lead ECG is obtained and shows the following features: absence of P waves, irregular R-R intervals, and a ventricular rate of 60–100 bpm. What is the most likely diagnosis?

Explanation

## Diagnosis of Atrial Fibrillation on ECG **Key Point:** Atrial fibrillation (AF) is characterized by the absence of organized P waves, an irregular ventricular response, and a baseline that may show fine or coarse fibrillatory waves. ### ECG Hallmarks of Atrial Fibrillation | Feature | Atrial Fibrillation | Atrial Flutter | Sinus Arrhythmia | PACs | |---|---|---|---|---| | **P waves** | Absent; replaced by fibrillatory waves | Sawtooth pattern (flutter waves) | Present and normal | Present (abnormal morphology) | | **R-R intervals** | Irregularly irregular | Regular or regularly irregular | Variable but organized | Mostly regular with ectopic beats | | **Ventricular rate** | 60–100 (controlled) or >100 (uncontrolled) | Usually 150 bpm (2:1 block) | Varies with respiration | Baseline rate maintained | | **AV conduction** | Variable | Fixed ratio (2:1, 3:1, etc.) | Normal | Normal | ### Analysis of This Case 1. **Absence of P waves** → No organized atrial activity 2. **Irregular R-R intervals** → Irregularly irregular pattern (pathognomonic for AF) 3. **Ventricular rate 60–100 bpm** → Controlled ventricular response 4. **Clinical context:** Hypertension and diabetes are major risk factors for AF **High-Yield:** The **"irregularly irregular" rhythm** is the single most important ECG finding for diagnosing atrial fibrillation. This occurs because the AV node receives random atrial impulses and conducts them unpredictably to the ventricles. **Clinical Pearl:** In elderly patients, AF may present insidiously with palpitations, dyspnea, or even heart failure. Stroke risk assessment using CHA₂DS₂-VASc score is mandatory, and anticoagulation should be considered if the score ≥1 (female) or ≥2 (male). **Mnemonic:** **AF = Absent P + Irregularly Irregular** — the two cardinal ECG features. ### Fibrillatory Waves In AF, the baseline between QRS complexes may show: - **Fine fibrillatory waves** (amplitude <1 mm) — difficult to see - **Coarse fibrillatory waves** (amplitude >1 mm) — more easily visible The presence of fibrillatory waves (rather than flat baseline) helps distinguish AF from other arrhythmias.