A 72-year-old woman from Mumbai presents with palpitations and dyspnea for 3 hours. She has a history of hypertension and diabetes. Vital signs: BP 145/92 mmHg, HR 156 bpm (irregular), RR 22/min, SpO₂ 94% on room air. On auscultation, the heart sounds are irregular with no murmurs. An ECG is obtained urgently. The ECG shows a rapid, irregular rhythm with a ventricular rate of 140–160 bpm. P waves are not clearly visible; instead, there are fine, irregular baseline undulations (fibrillatory waves) between QRS complexes. The QRS duration is 0.08 seconds. What is the most likely diagnosis?

Explanation

## Diagnosis: Atrial Fibrillation with Rapid Ventricular Response ### ECG Hallmarks of Atrial Fibrillation **Key Point:** Atrial fibrillation (AF) is characterized by the absence of organized P waves and the presence of irregular baseline undulations (fibrillatory waves or 'f waves'), combined with an irregularly irregular ventricular rhythm. ### Distinguishing AF from Other Rapid Arrhythmias | Feature | Atrial Fibrillation | Atrial Flutter | Ventricular Tachycardia | Sinus Tachycardia | |---------|-------------------|-----------------|------------------------|-------------------| | **P waves** | Absent; replaced by fibrillatory waves | Sawtooth pattern (regular) | Absent or buried in QRS/T | Visible, upright in II | | **Baseline** | Irregular undulations | Regular sawtooth | Smooth or regular | Smooth | | **Ventricular rhythm** | Irregularly irregular | Regular or regularly irregular | Regular | Regular | | **QRS duration** | Normal (≤0.12 s) unless aberrancy | Normal unless aberrancy | Broad (>0.12 s) | Normal | | **Rate** | 100–180 bpm | 250–350 atrial; 75–150 ventricular | 140–250 bpm | 100–160 bpm | ### Key ECG Findings in This Case 1. **Fibrillatory waves:** Fine, irregular baseline undulations between QRS complexes — pathognomonic for AF 2. **Irregularly irregular rhythm:** The ventricular rate varies unpredictably (140–160 bpm) because the AV node conducts atrial impulses at random intervals 3. **Normal QRS duration (0.08 s):** Indicates supraventricular origin; the narrow QRS excludes ventricular tachycardia 4. **Absent P waves:** No organized atrial depolarization **High-Yield:** The **irregularly irregular rhythm** is the clinical hallmark of AF — it is the only common arrhythmia with this pattern. Atrial flutter, by contrast, has a regular or regularly irregular ventricular response. ### Clinical Context **Clinical Pearl:** Common triggers for AF include: - Hypertension (present in this patient) - Diabetes (present in this patient) - Acute illness (infection, MI, PE, thyrotoxicosis) - Alcohol excess - Structural heart disease In elderly patients with hypertension and diabetes, AF is very common and often presents with rapid ventricular response due to high sympathetic tone or reduced AV nodal refractoriness. ### Management Implications **Mnemonic: CHADS₂-VASc** = Risk stratification for stroke in AF - **C**ongestive heart failure - **H**ypertension (this patient) - **A**ge ≥75 years - **D**iabetes (this patient) - **S**troke/TIA/thromboembolism - **V**ascular disease - **A**ge 65–74 years - **S**ex category (female) - **c**linical factors This patient has a CHADS₂-VASc score of ≥2 and requires anticoagulation (unless contraindicated). **Key Point:** Acute management of AF with RVR includes: 1. Rate control (beta-blocker, calcium channel blocker, or digoxin) 2. Anticoagulation (if CHA₂DS₂-VASc ≥1 in males or ≥2 in females) 3. Correction of underlying cause (e.g., hyperthyroidism, infection)