A 72-year-old woman from Mumbai with a history of hypertension and diabetes presents with palpitations and dyspnea on exertion for 3 days. On examination, she is in sinus rhythm with an irregular pulse. Blood pressure is 145/88 mmHg, heart rate 78/min (irregularly irregular). Her 12-lead ECG shows absence of P waves, irregular RR intervals, and a ventricular rate of 60–100 bpm. What is the most likely diagnosis?

Explanation

## Diagnosis: Atrial Fibrillation with Controlled Ventricular Response ### ECG Features of Atrial Fibrillation **Key Point:** Atrial fibrillation (AF) is characterized by the **absence of organized P waves** and an **irregularly irregular ventricular rhythm**. The ventricular rate determines whether the response is "controlled" or "rapid." | Feature | Atrial Fibrillation | Atrial Flutter | Multifocal Atrial Tachycardia | |---------|-------------------|-----------------|-------------------------------| | P waves | Absent (replaced by fibrillation waves) | Sawtooth pattern (flutter waves) | Multiple morphologies present | | RR interval | Irregularly irregular | Regular or regularly irregular | Irregular | | Ventricular rate | Variable (60–150 bpm) | Usually 150 bpm (2:1 block) | 100–150 bpm | | Atrial rate | 350–600 bpm | 250–350 bpm | 100–150 bpm | ### Why This Patient Has AF with Controlled Rate 1. **Absence of P waves** — characteristic of AF; the atria are firing chaotically at 350–600 bpm, creating an irregular baseline (fibrillation waves) that is often not visible. 2. **Irregularly irregular pulse** — the AV node conducts impulses unpredictably, resulting in variable RR intervals. 3. **Ventricular rate 60–100 bpm** — this is within the "controlled" range. A rate >100 bpm would be "rapid ventricular response." 4. **Risk factors present** — hypertension and diabetes are major risk factors for AF. **High-Yield:** The term "controlled" refers to a resting ventricular rate <100 bpm; "rapid" refers to >100 bpm at rest. Both are AF; the distinction guides rate-control therapy. **Clinical Pearl:** In AF, the irregularly irregular rhythm is best detected by palpating the pulse or observing the monitor for variable RR intervals. A regular rhythm in a patient with "AF" should prompt reconsideration of the diagnosis (consider atrial flutter with fixed block instead). **Mnemonic:** **"AF = Absent P, Irregularly Irregular"** — if you see organized P waves (even if abnormal), it is not AF.