Differential Diagnosis oF AF

Diferential Diagnosis of Atrial Fibrillation

ECG

During atrial fibrillation the atrial impulses discharge at a rate of 350-600 per minute, resulting in small (or "fine"), irregular f (fibrillation) waves. The amplitude of these waves varies and may be especially prominent (or "coarse") in lead V1. As only occasional impulses penetrate the atrioventricular node, a totally irregular ventricular rhythm results, which is the characteristic of this arrhythmia.

Atrial fibrillation with "coarse" f waves (and ventricular ectopic). Rapid atrial fibrillation with a rapid ventricular response may easily be mistaken for other supraventricular arrhythmias-for example, atrial

flutter or supraventricular tachycardias. Variation in the RR interval is the important clue. At very high heart rates, with a short RR interval, beat to beat variation may be subtle but may become more obvious if the carotid sinus is massaged or the speed of the electrocardiogram trace increased. In a young atient with fast atrial fibrillation it is important to consider an underlying pre-excitation syndrome, such as the Wolff-Parkinson-White syndrome, as traditional drugs such as digoxin or verapamil will accelerate the ventricular response by blocking atrioventricular node impulses and increasing conduction through the accessory pathway. Finally, atrial fibrillation with a bundle branch block pattern on the QRS complex may be difficult to distinguish from a ventricular tachycardia: again, the important difference is the irregularity of the RR interval present in atrial fibrillation.

Electrophysiology study

• May help identify the mechanism of a wide-QRS-tachycardia.
• May help identify a predisposing arrhythmia.
• May help identify sites for curative ablation or AV node ablation.

Rhythm

AF also presents with an irregularly irregular rhythm when you feel for the pulse.

Laboratory Studies

• An electrocardiogram (ECG) should be obtained to establish the diagnosis of atrial fibrillation; look for pre-excitation; determine heart rate; and evaluate for left ventricular hypertrophy, bundle-branch block, or prior MI. The ECG is also useful to follow the QT and QRS intervals of patients receiving anti-arrhythmic medications for atrial fibrillation.
• Complete blood count, thyroid, hepatic, and renal function panels are often helpful, especially when ventricular rate is difficult to control.
• A toxicology screen or ethanol level may be appropriate to rule out acute intoxication.

Imaging Studies

• Transthoracic echocardiogram (TTE)
• 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 echocardiogram (TEE)
• Evaluate for left atrial (LA) 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.
• Computed tomography (CT) or magnetic resonance imaging (MRI): If atrial fibrillation ablation is planned, then 3-dimensional imaging technologies (CT scan or MRI) are often helpful to evaluate atrial anatomy. Imaging data can be processed to create anatomic maps of the left atrium and pulmonary veins.
• Chest radiography: May help evaluate lung parenchyma and pulmonary vasculature in the appropriate clinical context.

Diseases that mimic AF

· Supraventricular tachycardia

o The rhythm for this condition is regularly irregular. Hence, able to differentiate with atrial fibrillation. Aside that, there is an inverted P wave before the QRS complex.

· Wolff Parkinson White Syndrome

o ECG read will have the P wave close to the QRS complex.

· Overactive thyroid (Hyperthyroidism)

o Thyroid storm can cause atrial fibrillation.

o Can rule this out with a blood test.

· Atrial flutter

o Not every P wave will produce a QRS complex. P waves are strong and only a QRS complex will be form for every 2 or 3 P wave.

· Sick Sinus Syndrome

o Can cause atrial fibrillation

o Usually bradycardia