When AF is suspected during auscultation of the heart with irregularly irregular beats, obtaining a 12-lead ECG is the next step. ECG findings usually confirm the diagnosis of atrial fibrillation and include:
The ventricular rate is typically irregular (irregular QRS complexes)
Discrete P waves are absent, replaced by irregular, chaotic F waves
Look also for aberrantly conducted beats after long-short R-R cycles (ie, Ashman phenomenon)
Heart rate is typically 110-140 beats/min but rarely over 160-170 beats/min
Pre-excitation, left ventricular hypertrophy (LVH), bundle-branch block or intraventricular conduction delay, and acute or prior myocardial infarction may be noted
Because AF is due to irregular atrial activation at a rate of 350-600 beats/min with irregular conduction through the atrioventricular node, it appears on ECG as irregularly irregular narrow complex tachycardia. Fibrillatory waves may be evident or may be absent.
Echocardiography may be used to evaluate for valvular heart disease, left and right atrial size, LV size and function, LVH, and pericardial disease. Transthoracic echocardiography has low sensitivity in detecting left atrial thrombus, and transesophageal echocardiography is the modality of choice for this purpose.
In patients with AF and a positive D-dimer result, chest CT angiography 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.
For more on the workup of AF, read here.
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Cite this: Yasmine S. Ali. Fast Five Quiz: Key Aspects of Atrial Fibrillation - Medscape - Sep 13, 2018.