Atrial Fibrillation

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As of the time of this writing, I am a second-year internal medicine resident physician, and have been involved in the care of at least fifty patients (averaging nearly one patient per work week, a very conservative estimate) with Atrial Fibrillation (AFib), an abnormal heart rhythm.  According to MKSAP 17 Cardiovascular Medicine, it is the #1 most common sustained cardiac arrhythmia, or abnormal electrical activity of the heart.  Among people aged 40 years old and beyond, physicians expect a whopping 1 in 4 people to become afflicted with the arrhythmia.  It is indeed age-related, the older you get, the more likely you are to develop AFib.  This abnormal heart rhythm confers a 5x increased risk of stroke, and increased risk of heart failure and dementia.

Etiology

  • Reversible/Treatable:  hyperthyroidism, pulmonary embolism, and cardiac surgery.
  • Chronic Conditions:  uncontrolled hypertension, anatomical pathology of the heart itself, and obstructive sleep apnea.

Clinical Presentation

  • Palpitations
  • Lightheadedness/Dizziness
  • Chest pain
  • Syncope (loss of consciousness)
  • Shortness of breath
  • Low blood pressure (severe presentation, usually with advanced pathology including diastolic dysfunction or restrictive cardiomyopathy)
  • Asymptomatic (found incidentally)

It is also important to note that some patients may first arrive in the ER with heart failure signs and symptoms (lower extremity edema, JVD, and pulmonary crackles/rales due to a fluid overload state) secondary to tachycardia-related cardiomyopathy.

CLASSIFICATIONS:
  • First-detected-
  • Paroxysmal-  AFib that starts and stops spontaneously
  • Persistent-  7 days duration or more
  • Long-standing-  more than 1 year.

Acute Management

Whether the condition is acute or chronic, there are three goals:  PREVENT STROKE, CONTROL HEART RATE, RELIEVE SYMPTOMS.

ANTICOAGULATION – PREVENT STROKE
1.  Assess with CHADS-VASc Score
CHA2DS2-VASc score 0 = Aspirin or no therapy
Score 1 = none or ASA or oral anticoagulant
Score 2+ = Oral anticoagulant

2.  For Cardioversion:  if AFib<48hrs, anticoagulation not necessary; if AFib ?duration or >48hrs, patient needs 3 weeks of therapeutic anticoagulation prior to CV.  TEE can be performed alternatively – if negative, can do CV now.
AFTER CV, need anticoagulation for minimum of 4 weeks.

If the patient develops hypotension, myocardial ischemia, heart failure, perform immediate synchronized cardioversion regardless of duration of AFib.

atrial fibrillation w/rapid ventricular response (RVR)
  • A common pathological variant, wherein patient’s heart rate (HR) is greater than 100 bpm.
  • Immediate control will restore cardiac function and symptoms.
  • Target HR 60-110 (acutely)
  • HR control with:  metoprolol, esmolol (fast acting), diltiazem (most used at my institution), verapamil.
    • Add Digoxin for hard-to-control patients, or if heart failure too.
    • If evidence of “preexcited AFib,” procainamide is the drug of choice.
  • Avoid CCBs in patients with LV dysfunction.
  • Pharmacologic cardioversion (CV) without structural disease:  flecainide, propafenone, or ibutilide.

Long-Term Management

Anticoagulation – prevent stroke (4% risk per year with nonvalvular AFib without comorbidities)

  • Assess with CHADS-VASc Score
  • If the patient has high-risk features:  mitral stenosis, rheumatic heart disease, prior systemic embolism, prosthetic heart valve, left atrial appendage thrombus, HOCM — give anticoagulation regardless of score.
  • Choose either vitamin K antagonist or a NOAC.
  • Warfarin
    • Vitamin K antagonist
    • Target INR 2-3
    • Low cost
    • Good for both non-valvular and valvular AFib cases (mitral stenosis or mitral valve replacement)
  • Nonvalvular AFib, choose one NOAC agent (no INR monitoring):
    • Apixaban
      • superior to warfarin for stroke prevention, similar rate of GI bleeding.
    • Rivaroxaban
      • Less intracranial and fatal bleeding c/w warfarin, but higher risk of GI bleeding c/w warfarin.
      • ONCE daily dosing
    • Dabigatran
      • superior to warfarin for stroke prevention, less intracranial bleeding but has higher GI bleeding risk.
    • All NOACs are renally-excreted (therefore, dose adjust).
  • If patient has had an acute coronary syndrome or revascularization within 12 months:
    • Administer low-dose Aspirin + oral anticoagulation
  • If patient got a coronary stent:
    • ASA + Plavix + anticoagulant for 6-12 months (for DES).
  • NO survival advantage or stroke reduction when comparing rate vs. rhythm control!
  • Usually start with rate control (BB or nondihydropyridine CCBs).
  • If still symptomatic, can try rhythm control regimen.
    • Cardioversion followed by anti-arrhythmic therapy.
    • “Pill-in-the-pocket” (flecainide or propafenone) only when develop an episode of AFib.  For infrequent AFib without other structural or conductive heart disease.  Should first be supervised.
  • Catheter ablation if refractory to above modalities (e.g. pulmonary vein isolation).
    • Anticoagulation for 2-3 months after ablation.

Bibliography

ACP MKSAP 17:  Cardiovascular Medicine, pp. 55-58

Image obtained via Google web search.

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