Cardiovascular · Year 1 · from Cardiovascular

Case 2: Atrial Fibrillation with Rapid Ventricular Response

Patient Presentation

Demographics: 68-year-old female

Chief Complaint: Palpitations and fatigue for 3 days

History of Present Illness: A 68-year-old female with history of hypertension and obesity presents with a 3-day history of palpitations and progressive fatigue. She describes her heart as "fluttering" and feels short of breath with minimal exertion. She denies chest pain or syncope. She has never experienced this before.

Physical Examination:

  • Vital Signs: BP 135/88 mmHg, HR 142 bpm (irregularly irregular), RR 20/min, SpO2 96% on room air
  • General: Mild distress, appears fatigued
  • Cardiovascular: Irregularly irregular rhythm, variable S1 intensity, no murmurs
  • Lungs: Clear bilaterally
  • Extremities: Trace bilateral ankle edema

Workup

  • ECG Findings:
  • Absent P waves - replaced by fibrillatory waves (f waves)
  • Irregularly irregular R-R intervals
  • Ventricular rate 130-150 bpm
  • Narrow QRS complexes (88 ms)
  • No ST changes
  • ECG Interpretation:
  • Rate: ~142 bpm (variable)
  • Rhythm: Atrial fibrillation with rapid ventricular response
  • Axis: Normal (+45°)
  • Intervals: QRS 88 ms, QTc 410 ms (no PR as no P waves)
  • Conclusion: Atrial fibrillation with RVR
  • Labs: TSH: 0.1 mIU/L (suppressed), Free T4: 3.2 ng/dL (elevated)
  • Echocardiogram: Normal LV function, dilated left atrium

Diagnosis

New-onset atrial fibrillation with rapid ventricular response, secondary to hyperthyroidism

ECG Correlation: Atrial fibrillation is characterized by:

  • No organized P waves: Multiple chaotic atrial impulses (350-600/min) create fibrillatory baseline
  • Irregular R-R intervals: Variable conduction through AV node
  • Variable ventricular rate: Depends on AV node conduction properties

The AV node acts as a "filter," protecting the ventricles from the rapid atrial rates. The irregularly irregular ventricular response is pathognomonic. Hyperthyroidism increases adrenergic tone and can trigger or exacerbate atrial fibrillation.

Treatment

  1. Rate control: IV diltiazem bolus 20 mg, then infusion (avoid beta-blockers in thyrotoxicosis until controlled)
  2. Anticoagulation: CHA2DS2-VASc score = 3 (female, age, HTN) → Start anticoagulation with DOAC
  3. Treat underlying cause: Methimazole for hyperthyroidism
  4. Consider cardioversion once rate controlled and anticoagulated ≥3 weeks or TEE shows no LA thrombus

Clinical Image

Image Description: 12-lead ECG demonstrating atrial fibrillation with rapid ventricular response. Note the absence of P waves, irregularly irregular R-R intervals, and the fibrillatory baseline best seen in V1.

Source: Wikimedia Commons - Atrial fibrillation ECG License: CC BY-SA 3.0 URL: https://commons.wikimedia.org/wiki/File:Atrial_fibrillation.svg

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