What is the initial workup to find the cause of atrial fibrillation?

Initial Workup for Atrial Fibrillation

All patients with suspected or confirmed atrial fibrillation require ECG documentation, transthoracic echocardiography, and laboratory testing including thyroid function, electrolytes, complete blood count, and renal/hepatic function. 1

Mandatory Initial Evaluation

1. ECG Documentation (Required for Diagnosis)

• At least a single-lead ECG recording showing ≥30 seconds of rhythm with no discernible repeating P waves and irregular RR intervals is required to confirm the diagnosis 1, 2
• If initial ECG does not capture AF but clinical suspicion remains high:
  • Use 24-hour Holter monitor for frequent episodes 1
  • Use event recorder for infrequent episodes, allowing patient transmission when arrhythmia occurs 1
  • Consider implanted loop recorders for very infrequent episodes 1

2. Clinical History (Essential Components)

Document the following specific elements 1:

• Pattern classification: First episode, paroxysmal, persistent, long-standing persistent, or permanent 1
• Symptom characterization using EHRA score: Grade 1 (no symptoms) through Grade 4 (disabling symptoms) 1
• Temporal details: Onset date, frequency, duration, and modes of termination 1
• Precipitating factors: Alcohol, caffeine, sleep deprivation, emotional stress, exercise, large meals 1
• Response to prior medications if any have been administered 1

3. Physical Examination (Specific Findings to Document)

Assess for 1, 2:

• Irregular pulse (sensitive but not specific) 2
• Irregular jugular venous pulsations (characteristic of AF) 1, 2
• Variation in intensity of first heart sound or absence of previously heard fourth heart sound 1, 2
• Signs of valvular disease: Murmurs, clicks 1
• Signs of heart failure: Peripheral edema, pulmonary rales, S3 gallop 2
• Blood pressure measurement (hypertension is major risk factor) 1, 2

4. Transthoracic Echocardiography (Mandatory for All Patients)

Two-dimensional transthoracic echocardiography must be performed during initial workup to assess 1:

• Left and right atrial size 1
• Left ventricular size, wall thickness, and systolic function 1
• Valvular heart disease 1
• Peak right ventricular pressure (pulmonary hypertension) 1
• Pericardial disease 1
• Left ventricular hypertrophy 1

Note: Transthoracic echo has low sensitivity for detecting left atrial thrombus; transesophageal echocardiography is required if thrombus detection is clinically necessary 1

5. Laboratory Testing (Required for All Patients)

The following blood tests are mandatory 1, 3:

• Thyroid function tests (TSH at minimum) - particularly important for first episode, difficult rate control, or unexpected recurrence after cardioversion 1
• Serum electrolytes (sodium, potassium, magnesium) 1
• Complete blood count 1, 3
• Renal function (serum creatinine) 1
• Hepatic function tests 1
• Fasting glucose or HbA1c (diabetes screening) 1

Common pitfall: Thyroid function testing is frequently omitted despite guideline recommendations, with studies showing only 30-60% completion rates 4. This is a critical oversight as hyperthyroidism is a reversible cause of AF.

6. Chest Radiograph (Selective Use)

Obtain chest X-ray when 1:

• Clinical findings suggest pulmonary disease 1
• Heart failure is suspected 1
• Pulmonary vasculature abnormalities are suspected 1

Chest radiography is less important than echocardiography for routine AF evaluation 1

Additional Testing (When Indicated)

Exercise Testing

Consider when 1:

• Adequacy of rate control in permanent AF needs assessment 1
• Exercise-induced AF needs to be reproduced 1
• Ischemia must be excluded before initiating Class IC antiarrhythmic drugs 1

Transesophageal Echocardiography

Indicated for 1:

• Detecting left atrial appendage thrombus (most sensitive method) before cardioversion 1
• Guiding timing of cardioversion when AF duration >48 hours or unknown 1
• Identifying reduced LAA flow velocity, spontaneous LA contrast, or aortic atheroma 1

TEE reveals thrombus in 5-15% of patients before planned cardioversion 1

Electrophysiological Study

Reserve for specific scenarios 1:

• AF initiated by supraventricular tachycardia (AVNRT, AVRT, ectopic atrial tachycardia) 1
• Delta wave on ECG indicating pre-excitation/accessory pathway 1
• Coexisting atrial flutter that may benefit from catheter ablation 1
• Wide-complex tachycardia requiring differentiation from ventricular tachycardia 1

Sleep Study

Obtain when obstructive sleep apnea is suspected clinically 1

Search for Reversible Causes

Specifically evaluate for 1, 5:

• Hyperthyroidism (thyroid function tests mandatory) 1
• Alcohol consumption (detailed history) 1
• Acute illness: Pyrexial illness, infection, electrolyte imbalance 1, 6
• Cardiac conditions: Valvular disease (especially mitral), coronary artery disease, heart failure, hypertension, cardiomyopathy 1, 5
• Pulmonary disease: Chronic obstructive pulmonary disease 1, 5

Critical Timing Considerations

For AF duration <48 hours: Cardioversion can proceed with anticoagulation (LMWH acceptable) without mandatory TEE 1

For AF duration >48 hours or unknown duration: Either 3 weeks of therapeutic anticoagulation before cardioversion OR TEE to exclude thrombus is required 1

Hemodynamically unstable patients: Require urgent echocardiogram to assess LV/valvular function and right ventricular pressure, followed by urgent rate control or cardioversion 1