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      Drugs & Diseases > Cardiology

      Atrial Fibrillation Workup

      Updated: Nov 18, 2019
      • Author: Lawrence Rosenthal, MD, PhD, FACC, FHRS; Chief Editor: Jeffrey N Rottman, MD  more...
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      Workup

      Approach Considerations

      When atrial fibrillation (AF) is suspected during auscultation of the heart with irregularly irregular beats, obtaining a 12-lead electrocardiogram (ECG) is the next step. Because AF is due to irregular atrial activation at a rate of 350-600 bpm with irregular conduction through the atrioventricular (AV) node, it appears on ECG as irregularly irregular narrow complex tachycardia. Fibrillatory (F) waves may be evident or may be absent. Unless the heart is under excess sympathetic or parasympathetic stimulation, the ventricular rate is usually between 80 and 180 bpm.

      With an abnormality in the intraventricular conduction system, the QRS complexes may become wide. It is important to pay attention to the electrocardiographic signs of associated cardiac diseases, such as left ventricular hypertrophy (LVH) and preexcitation.

      Various cardiac diseases, including ischemic heart disease, valvular diseases, and cardiomyopathy, are associated with AF. Therefore, after the diagnosis of AF is confirmed with ECG, an evaluation of serum cardiac biomarkers and B-type natriuretic peptide (BNP) is usually required to investigate for underlying heart disease. More invasive cardiac tests (eg, cardiac catheterization) may be required depending on signs and symptoms and findings on initial tests. The ECG is also necessary to monitor the QT and QRS intervals of patients receiving anti-arrhythmic medications for AF.

      Chest radiographic findings are usually normal in patients with AF. However, chest radiography may provide evidence of congestive heart failure, as well as signs of lung or vascular pathology (eg, chronic obstructive pulmonary disease, pulmonary embolism, pneumonia). In addition, many other noncardiac diseases, such as hyperthyroidism, and many infections and inflammatory diseases, have been associated with AF. Accordingly, chest radiography, thyroid function tests, complete blood cell (CBC) count, and serum chemistry may be helpful, and other tests should be considered, depending on the patient’s presentation. If a reversible cause of AF (eg, hyperthyroidism) is found, it should be treated and the patient should be reassessed afterward.

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      Electrocardiography

      Electrocardiographic (ECG) findings usually confirm the diagnosis of atrial fibrillation (AF) and include the following:

      • The ventricular rate is typically irregular (irregular QRS complexes)

      • Discrete P waves are absent, replaced by irregular, chaotic F waves, as shown in the image below

        Ventricular rate varies from 130-168 beats per min Ventricular rate varies from 130-168 beats per minute. Rhythm is irregularly irregular. P waves are not discernible.
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      • Look also for aberrantly conducted beats after long-short R-R cycles (ie, Ashman phenomenon)

      • Heart rate (typically in the 110-140 range, but rarely over 160-170)

      • Preexcitation

      • Left ventricular hypertrophy

      • Bundle-branch block or intraventricular conduction delay

      • Acute or prior myocardial infarction

      QRS duration appears to be an independent predictor of incident AF among women, but not in men, based on findings from 15,314 participants from the Atherosclerosis Risk in Communities (ARIC) study. [51]  The underlying mechanism for the difference between men and women is not yet clear.

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      Laboratory Studies

      Laboratory studies in patients with atrial fibrillation (AF) are aimed at uncovering underlying disorders, which may be particularly important to address when ventricular rate is difficult to control. One study suggests that minor elevations in troponin I levels upon hospital admission is associated with higher mortality and cardiac events, which may be useful for risk stratification. [52]

      Laboratory studies indicated include the following:

      • Complete blood cell (CBC) count (looking for anemia, infection)

      • Levels of serum electrolytes and blood urea nitrogen (BUN)/creatinine (looking for electrolyte disturbances or renal failure)

      • Cardiac enzymes levels: Creatine kinase (CK) and/or troponin level (to investigate myocardial infarction as a primary or secondary event)

      • B-type natriuretic peptide (BNP) level (to evaluate for congestive heart failure)

      • D-dimer level (if the patient has risk factors to merit a pulmonary embolism workup)

      • Thyroid function studies (to assess for thyrotoxicosis, a rare, but not-to-be-missed, precipitant)

      • Digoxin level (may be obtained when appropriate for toxicity; generally considered safe to give digoxin to patient with AF on digoxin for rate control without waiting for lab values if patient presents with AF with rapid ventricular response [RVR])

      • Toxicology testing or ethanol level

      Relatively recent studies indicate that increased plasma trimethylamine-N-oxide (TMAO) levels are associated with incident AF independent of traditional AF risk factors and of dietary choline intake. [53] More studies are needed to evaluate endogenous metabolic factors that impact the relationship between TMAO and cardiovascular disease.

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      Echocardiography

      Echocardiography may be used to evaluate for valvular heart disease, left and right atrial size, left ventricular (LV) size and function, left ventricular hypertrophy (LVH), and pericardial disease. Transthoracic echocardiography has low sensitivity in detecting left atrial (LA) thrombus, and transesophageal echocardiography is the modality of choice for this purpose. [54]

      Transthoracic echocardiography (TTE) is helpful for making the following determinations:

      • Evaluate for valvular heart disease

      • Evaluate atrial and ventricular chamber and wall dimensions

      • Estimate ventricular function and evaluate for ventricular thrombi

      • Estimate pulmonary systolic pressure (pulmonary hypertension)

      • Evaluate for pericardial disease

      Transesophageal echocardiography (TEE) is helpful for making the following determinations:

      • Evaluate for atrial thrombus (particularly in the LA appendage)

      • To guide cardioversion (if thrombus is seen, cardioversion should be delayed)

      • When TEE is planned, the concurrent use of TTE may increase cost without providing significant additional information.

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      CT Scanning and MRI

      In patients with atrial fibrillation (AF) and a positive D-dimer result, chest computed tomography angiography (CTA) may be necessary to rule out pulmonary embolus.

      Three-dimensional imaging technologies (CT scan or MRI) are often helpful to evaluate atrial anatomy if AF ablation is planned. Imaging data can be processed to create anatomic maps of the left atrium and pulmonary veins.

      Preablation delayed-enhancement magnetic resonance imaging (DE-MRI) in patients with AF may be an important tool to not only determine the extent of atrial disease but also to predict treatment outcome. [55, 56]  In the international multicenter Delayed Enhancement-MRI Determinant of Successful Catheter Ablation of Atrial Fibrillation (DECAAF) trial, DE-MRI prior to ablation therapy for atrial fibrillation was able to stage atrial fibrosis and predict ablation success. [55, 56]  Moreover, the greater the extent of fibrotic tissue ablated during the procedure, the better the outcome.

      The investigators reported that preablation stage of atrial fibrosis and postablation residual fibrosis were independent predictors of successful ablation or recurrent symptoms. [55, 56]  However, ablation of the pulmonary veins, the standard of care in AF ablation candidates, was not a significant predictor of treatment success. [55, 56]

      The DECAAF-II study is under way; this trial will compare the outcomes of patients who undergo index AF ablation using conventional methods to those of patients who undergo ablation that targets areas of left atrial fibrosis as identified on DE-MRI.

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      Other Studies

      Six-minute walk test or exercise testing

      Six-minute walk or exercise testing can help assess the adequacy of rate control (eg, target heart rate of 110 bpm or less during a 6-minute walk) in patients with suspected atrial fibrillation (AF). [36]  Exercise testing can exclude ischemia prior to treatment of patients with class Ic antiarrhythmic drugs and can be used to reproduce exercise-induced AF.

      Holter monitoring or event recording

      Holter monitoring and event recording may be helpful to establish a diagnosis (eg, in cases of paroxysmal AF not evident upon presentation) and evaluate rate control (eg, target average rate of 100 bpm or less).

      Electrophysiology studies

      Electrophysiology studies may help identify the mechanism of a wide-QRS tachycardia, a predisposing arrhythmia, or sites for curative ablation or AV node ablation.

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      Treatment & Management
       
       
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