Updated: 8/2/2019

Atrial Fibrillation

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Snapshot
  • A 68-year-old male presents with palpitations, lightheadedness, and weakness. These symptoms appear to worsen with increased alcohol intake. Medical history is significant for hypertension being treated with hydrochlorothiazide. On physical exam, the patient appears uncomfortable. There is an irregularly irregular pulse when palpating the radial artery. On cardiac auscultation, the first heart sound (S1) is of variable intensity. There is mild bibasilar crackles on pulmonary auscultation and an absence of peripheral edema.  An electrocardiagram is obtained. 
Introduction
  • A supraventricular tachyarrhythmia secondary to uncoordinated atrial contractions
    • results in an irregularly irregular rhythm
      • non-repetitive pattern in the RR interval
    • may reduce cardiac output
    • may result in thrombus formation in the atrium
    • most common site of origin for ectopic foci is pulmonary veins
  • Pathogenesis
    • usually due to an underlying cause 
      • e.g., atrial enlargement and inflammation or infiltrative disease affecting the atrium
  • Causes include
    • structural abnormalities
      • e.g., left atrial enlargement, mitral and aortic stenosis, mitral and aortic regurgitation, and malignancy
    • conduction abnormalities
      • e.g., Wolff-Parkinson-White (WPW) syndrome
    • medications
      • theophylline and digoxin
    • cardiac functional abnormalities
      • e.g., myocardial infacrtion, pulmonary embolism, and coronary artery disease
    • hyperthyroidism
    • electrolyte disturbances
      • e.g., hypomagnesemia and hypokalemia
    • cardiomyopathies
      • e.g., dilated and hypertrophic cardiomyopathy
    • alcohol abuse ("holiday heart syndrome")
    • post-operatively after heart surgery
      • especially after coronary artery bypass grafting (CABG)
  • Epidemiology
    • most common arrhythmia
Presentation
  • Symptoms
    • asymptomatic
    • in symptomatic cases
      • palpitations
      • shortness of breath (suggesting heart failure)
      • lightheadedness
  • Physical exam
    • irregularly irregular pulse
    • focal neurological deficit if this results in an embolic stroke
    • in cases of atrial fibrillation leading to heart failure
      • elevated jugular venous pulse (JVP)
      • bibasilar rales on pulmonary auscultation
      • peripheral edema
Evaluation
  • Electrocardiogram (EKG or ECG) 
    • irregularly irregular rhythm
    • absent P waves
    • if arrhythmia is not captured on ECG then
      • Holter monitoring in the outpatient setting
        • these patients are hemodynamically stable
      • telemitry in the inpatient setting
  • Transthoracic echocardiogram (TTE)
    • can assess atrial size and ventricular function, thickness, and size
    • can also assess for valvular and pericardial disease, and peak right ventricular pressure
    • transesophageal echocardiogram (TEE) is more sensitive in detecting thrombi in the left atrium
  • Laboratory testing
    • thyroid stimulating hormone (TSH) and free T4 level 
      • hyperthyroidism is a possible cause of atrial fibrillation
    • electrolyte level
Differential
  • Multifocal atrial tachycardia (MAT)
    • commonly seen in patients with pulmonary disease
      • e.g., chronic obstructive pulmonary disease (COPD)
  • Premature atrial contractions (PACs)
    • associated with alcohol, caffeine, and nicotine use 
  • Atrial flutter
  • Wolff-Parkinson-White syndrome
Treatment
  • Hemodynamically unstable patients
    • synchronized cardioversion 
  • Hemodynamically stable patients
    • slowing of the ventricular rate
      • patients with new onset atrial fibrillation become symptomatic due to rapid ventricular response (except in cases of stroke)
      • intravenous β-blockers or nondihydropyridine calcium channel blocker
        • wheezing (COPD/asthma) 
          • use calcium channel blocker or titratable beta blocker (esmolol) 
    • long-term management
      • rate control (preferred)
        • β-blocker or nondihydropyridine calcium channel blocker
        • digoxin if the patient is hypotensive 
      • rhythm control
        • antiarrhythmics
          • depends on patient's comorbidities
      • anticoagulation
        • in order to decrease the risk of thromboembolism
        • stroke risk stratification CHA2DS2-VASc score
          • Congestive heart failure = 1 point
          • Hypertension = 1 point
          • Age (75 years or older) = 2 points
          • Diabetes = 1 point
          • Stroke/transient ischemic attack/thromboembolism = 2 point
          • Vascular disease = 1 point
            • e.g., previous myocardial infarction and peripheral artery disease
          • Age (65 - 74 years) = 1 point
          • Sex category (female) = 1 point
        • score of 0 or 1 use
          • aspirin
          • conservative monitoring
        • score of 2 or more use oral anticoagulation
          • dabigatran
          • rivaroxaban
          • apixaban
            • novel anticoagulants contraindicated in renal failure
          • warfarin 
            • international normalized ratio (INR) target of 2-3
            • only warfarin should be used with vascular lesions (eg. mechanical valves)
Prognosis, Prevention, and Complications
  • Prognosis
    • increased risk of stroke
  • Complications
    • atrial mural thrombi emboli to cerebral vessels
      • can cause ischemic stroke and transient ischemic attack
    • atrial thrombus to common iliac artery
      • requires immediate embolectomy to remove occlusion and preserve limb
 

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Questions (8)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M2.CV.170) A 43-year-old man comes to the emergency room complaining of chest discomfort. He describes the feeling as "tightness," and also reports weakness and palpitations for the past hour. He denies shortness of breath, diaphoresis, or lightheadedness. He has no significant past medical history, and does not smoke, drink, or use illicit drugs. His father had a myocardial infarction at age 72. He is afebrile, heart rate is 125 bpm, and his blood pressure is 120/76. He is alert and oriented to person, place, and time. His electrocardiogram is shown below. Which of the following tests should be ordered in the initial work-up of this patient's condition? Review Topic

QID: 104176
FIGURES:
1

Urine free cortisol level

0%

(0/22)

2

Blood alcohol level

5%

(1/22)

3

Chest x-ray

18%

(4/22)

4

Thyroid stimulating hormone level (TSH)

55%

(12/22)

5

Urine metanephrines

18%

(4/22)

M2

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