Cardiovascular · Year 1 · from Cardiovascular

Case 1: Atrial Fibrillation with Rapid Ventricular Response

Patient Presentation

Demographics: 68-year-old male

Chief Complaint: Palpitations and lightheadedness for 2 days

History of Present Illness: A 68-year-old male with history of hypertension, type 2 diabetes, and sleep apnea presents with palpitations that started 2 days ago. He describes a rapid, irregular heartbeat that feels like his heart is "flopping around." He has associated lightheadedness, mild dyspnea on exertion, and fatigue. He denies syncope, chest pain, or leg swelling. He reports recent increased stress at work and increased alcohol consumption (4-5 drinks nightly for the past week). He is not on anticoagulation.

Physical Examination:

  • Vital Signs: BP 138/88 mmHg, HR 142 bpm (irregular), RR 18/min, SpO2 97% on room air
  • General: Anxious, mild distress
  • Cardiovascular:
  • Irregularly irregular rhythm
  • Variable S1 intensity
  • No murmurs, rubs, or gallops
  • Pulse deficit present (apical rate > radial rate)
  • Lungs: Clear bilaterally
  • Extremities: No edema

Workup

  • ECG:
  • Absent P waves
  • Irregularly irregular R-R intervals
  • Fibrillatory baseline (f waves)
  • Average ventricular rate 138 bpm
  • Narrow QRS complexes
  • No ST-T changes
  • Labs:
  • TSH 0.8 (normal)
  • K 4.1, Mg 1.8
  • Troponin negative
  • BNP 220 pg/mL (mildly elevated)
  • Echocardiogram:
  • LV ejection fraction 50%
  • Mild LA dilation (42 mL/m2)
  • No significant valvular disease

Diagnosis

New-onset atrial fibrillation with rapid ventricular response

Cardiac Arrhythmias Correlation:

Mechanism of Atrial Fibrillation:

  1. Disorganized Atrial Electrical Activity:
  • Multiple simultaneous reentrant wavelets
  • Chaotic atrial activation at 300-600 impulses/min
  • No coordinated atrial contraction (loss of "atrial kick")
  1. Reentry as Primary Mechanism:
  • Three requirements for reentry:
  • Anatomic or functional circuit
  • Unidirectional block
  • Slow conduction in alternate pathway
  • In AF: multiple micro-reentrant circuits
  • Pulmonary vein foci often trigger initiation
  1. AV Node as "Gatekeeper":
  • AV node cannot conduct all 300-600 impulses/min
  • Decremental conduction slows ventricular response
  • Still, irregular conduction produces irregularly irregular rhythm
  • Concealed conduction: impulses that penetrate AV node but don't conduct reset refractoriness

ECG Hallmarks:

  • Absent P waves: No organized atrial depolarization
  • Fibrillatory baseline: Chaotic low-amplitude atrial activity
  • Irregularly irregular R-R intervals: Pathognomonic finding
  • Variable S1: Beat-to-beat variation in ventricular filling

Contributing Factors in This Patient:

  • Hypertension: LA pressure overload, atrial stretch
  • Sleep apnea: Intermittent hypoxia, vagal/sympathetic swings
  • Alcohol ("Holiday Heart"): Acute trigger for AF
  • Age: Atrial fibrosis, electrical remodeling

Clinical Consequences:

  1. Symptoms: Palpitations from irregular rhythm, fatigue from suboptimal CO
  2. Hemodynamic: Loss of atrial contribution to ventricular filling (15-25% of CO)
  3. Thromboembolic Risk: Stagnant blood in non-contracting LA appendage

Treatment

Rate Control (Acute):

  1. IV metoprolol 5 mg every 5 minutes x3 for rapid rate control
  • Beta-blocker slows AV nodal conduction
  • Target HR <110 bpm
  1. Alternative: IV diltiazem

Rhythm vs. Rate Control Decision:

  • New-onset AF <48 hours: Can consider cardioversion
  • However, onset uncertain - likely need anticoagulation first
  • Rate control adequate for now

Stroke Risk Assessment - CHA2DS2-VASc Score:

  • C - CHF: 0
  • H - Hypertension: 1
  • A2 - Age >75: 0
  • D - Diabetes: 1
  • S2 - Stroke/TIA: 0
  • V - Vascular disease: 0
  • A - Age 65-74: 1
  • Sc - Sex category (female): 0
  • Total: 3 points - Anticoagulation indicated

Anticoagulation:

  • DOAC preferred: Apixaban 5 mg BID or rivaroxaban 20 mg daily
  • Reduces stroke risk by ~65%

Address Modifiable Factors:

  • Alcohol cessation
  • OSA treatment (CPAP)
  • BP optimization

Long-term Rhythm Control Consideration:

  • If symptoms persist despite rate control
  • Catheter ablation (pulmonary vein isolation) option

Clinical Image

Image Description: Twelve-lead electrocardiogram demonstrating atrial fibrillation. Note the absence of discrete P waves, irregularly irregular R-R intervals, and fibrillatory baseline activity. The QRS complexes are narrow, indicating supraventricular origin of the arrhythmia.

Source: Wikimedia Commons - CardioNetworks ECGpedia License: CC BY-SA 3.0 URL: https://commons.wikimedia.org/wiki/File:Afib_ecg_(CardioNetworks_ECGpedia).jpg

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