Atrial Fibrillation See Arrhythmia Diagnosis 

The evaluation of atrial fibrillation involves diagnosis, determination of the etiology of the arrhythmia, and classification of the arrhythmia. A minimal evaluation should  be performed in all individuals with AF.  This includes a history and physical examination, ECG, transthoracic echocardiogram, and routine bloodwork. Certain individuals may benefit from an extended evaluation which may include an evaluation of the heart rate response to exercise, exercise stress testing, a chest x-ray, trans-esophageal echocardiography, and other studies. 

Screening 

Screening for atrial fibrillation  is not generally performed, although a study of routine pulse checks or ECGs during routine office visits found that  the annual rate of detection of AF in elderly patients improved from 1.04% to 1.63%; selection of patients  for prophylactic anticoagulation would improve stroke risk in that age category. 

Routine primary care visit. 

This estimated sensitivity of  the routine primary care visit is 64%. This low result probably reflects the pulse not being checked routinely or carefully. 

Minimal evaluation 

The minimal evaluation  of atrial fibrillation should generally  be performed in all individuals with AF. The goal of this evaluation is  to determine the general treatment regimen for the individual. If results of the general evaluation warrant it, further studies may be then performed. 

History  and physical examination 

The history  of the individual's atrial fibrillation episodes is probably the most important part  of the evaluation. Distinctions should be made between those  who are entirely asymptomatic when  they are in AF (in which case the AF  is found as an incidental finding  on an ECG or physical examination)  and those who have gross  and obvious symptoms due to AF and  can pinpoint whenever they go into AF or revert to sinus rhythm. 

Routine bloodwork 

While many cases of AF have no definite cause, it may  be the result of various other problems. Hence, renal function  and electrolytes are routinely determined, as well as thyroid-stimulating hormone (commonly suppressed  in hyperthyroidism and of relevance if amiodarone is administered for treatment) and  a blood count. 

In acute-onset AF associated with chest pain, cardiac troponins or other markers  of damage to  the heart muscle may be ordered. Coagulation studies (INR/aPTT) are usually performed, as anticoagulant medication may be commenced. 

Electrocardiogram 

Atrial fibrillation  is diagnosed on an electrocardiogram (ECG), an investigation performed routinely whenever an irregular heart beat is suspected. Characteristic findings are  the absence of  P waves, with unorganized  electrical activity in their place,  and irregular R-R intervals due to irregular conduction  of impulses to  the ventricles.

When ECGs are used for screening,  the SAFE trial found that electronic software, primary care physicians  and the combination  of the two had  the following sensitivities  and specificities: 

• Interpreted by software: sensitivity = 83%, specificity = 99% 
• Interpreted by a primary care physician: sensitivity = 80%, specificity = 92% 
• Interpreted  by a primary care physician with software: sensitivity = 92%, specificity = 91% 

If paroxysmal AF is suspected but an  ECG during  an office visit only shows a regular rhythm, AF episodes may be detected and documented with the use  of ambulatory  Holter monitoring (e.g. for  a day). If  the episodes are too infrequent  to be detected by Holter monitoring with reasonable probability, then the patient  can be monitored  for longer periods (e.g.  a month) with an ambulatory event monitor.

Echocardiography

A non-invasive transthoracic echocardiogram (TTE)  is generally performed in newly diagnosed AF, as well as  if there is  a major change in the patient's clinical state. This ultrasound-based scan of the  heart may help identify valvular  heart disease (which may greatly increase the risk of stroke), left  and right atrial size (which indicates likelihood that AF may become permanent), left ventricular size and function, peak right ventricular  pressure (pulmonary hypertension), presence of left ventricular hypertrophy and pericardial disease. 

Significant enlargement of both the left and right atria is associated with long-standing atrial fibrillation and, if noted at the initial presentation of atrial fibrillation, suggests that the atrial fibrillation is likely  to be of  a longer duration than the individual's symptoms. 

Extended evaluation 

An extended evaluation is generally not necessary  in most individuals with atrial fibrillation, and  is only performed if abnormalities are noted  in the limited evaluation, if  a reversible cause of the atrial fibrillation is suggested, or if further evaluation may change  the treatment course. 

Chest X-ray 

A chest X-ray is generally only performed if  a pulmonary cause of atrial fibrillation is suggested,  or if other cardiac conditions  are suspected (particularly congestive heart failure.) This may reveal an underlying problem in  the lungs  or the blood vessels in the chest.  In particular, if an underlying pneumonia is suggested,  and then treatment of  the pneumonia may cause  the atrial fibrillation  to terminate on its own. 

Transesophageal echocardiogram 

A normal echocardiography (transthoracic or TTE) has a low sensitivity for identifying thrombi (blood clots) in the heart. If this is suspected - e.g. when planning urgent electrical cardioversion - a transesophageal echocardiogram (TEE) is preferred. 

The TEE has  much better visualization of the left atrial appendage than transthoracic echocardiography. This structure, located  in the left atrium, is the place where thrombus is formed in more than 90%  of cases in non-valvular (or non-rheumatic) atrial fibrillation or flutter.  TEE has  a high sensitivity for locating thrombus in this area and  can also detect sluggish bloodflow in this area that is suggestive of thrombus formation. 

If no thrombus  is seen on TEE,  the incidence of stroke, (immediately after cardioversion is performed), is very low. 

Ambulatory holter monitoring 

A Holter monitor is a wearable ambulatory heart monitor  that continuously monitors  the heart rate  and heart rhythm for  a short duration, typically 24 hours. In individuals with symptoms of significant shortness of breath with exertion or palpitations on a  regular basis, a holter monitor may be of benefit  to determine if rapid  heart rates (or unusually slow heart rates) during atrial fibrillation are  the cause  of the symptoms. 

Exercise stress testing 

Some individuals  with atrial fibrillation do well with normal activity but develop shortness of breath with exertion. It may be unclear if  the shortness  of breath is due to a blunted heart rate response to exertion due to excessive AV node blocking agents, a very rapid  heart rate during exertion, or due  to other underlying conditions such as chronic lung disease  or coronary ischemia. An exercise stress test will evaluate the individual's heart rate  response to exertion and determine if  the AV node blocking agents are contributing to  the symptoms.