Published April 2021
Maranda Herner, MD
Expert review – pending
Identify the key ECG findings for atrial fibrillation (AF) and use two key features to distinguish it from other supraventricular tachycardias (SVTs).
Plan to spend 5-15 minutes familiarizing yourself with the ECG and relevant background information. Have the image pulled up on the presenting screen or monitor. Have the image pulled up on the presenting screen or monitor. Have one learner provide a systematic interpretation of the ECG. If they do not do so on their own, prompt them to point out the distinguishing characteristics (mostly regular, atrial rate ~300bpm) of this SVT. Then ask them to commit to a specific diagnosis. Advance through the animations to highlight the abnormalities and final diagnosis.
Official ECG Read: Narrow complex tachycardia with irregularly irregular rhythm and no P waves with a ventricular rate around 100bpm. There is a slight left axis deviation and probably LAFB.
Teaching: Atrial fibrillation, typically occurs at an atrial rate of 300-600bpm from multiple micro re-entry circuits in the atria. The ventricular rate response to this atrial activity is limited by the refractory period and conduction speed in the AV node and ventricles. When SVT is too fast to differentiate, adenosine (6mg, then 12mg IV with 10cc saline immediately after) can slow the rate (increase the block) enough to see the Irregularly Irregular rhyme and fibrillation waves. Atrial fibrillation can be paroxysmal, persistent, or permanent, and all pose stroke risk warranting AC based on CHADSVAC score (except for reversible causes such as sepsis, hyperthyroidism, post-cardiac surgery, or toxins). Typically, atrial fibrillation is rate controlled to <110 bpm (RACE II 2010 trial) but recent studies have supported early rhyme control (via meds or ablation) in high-risk CVD patients (EAST AFNET-4, 2020 trial) or HFrEf <35% (CASTLE-AF, 2018 trial favoring ablation). Atrial fibrillation is often asymptomatic, but patients may experience palpitations or heart failure symptoms if they are dependent on the atrial kick, as is the case with diastolic dysfunction). AV nodal blocking agents include BB, CCB (except for decompensated HF), and digoxin. Before performing cardioversion in an otherwise stable patient, one must assure onset of atrial fibrillation occurred less than 48hrs prior or provide 3 weeks of uninterrupted anticoagulation with plans to continue for 4 weeks following conversion.
Take Home Points
- Atrial fibrillation is the most common irregularly irregular rhythm and is differentiated from atrial flutter and multifocal atrial tachycardia (MAT) by the absence of discrete p waves before the QRS.
- Atrial fibrillation can be rhythm controlled (meds or ablation) but most frequently is rate controlled with AV nodal blockers to HR <110bpm.
- Atrial fibrillation can be paroxysmal, persistent, or permanent— all have similar stroke risk and warrant anticoagulation.
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