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Differential Diagnosis
- Atrial fibrillation
- Atrial flutter with 2:1 conduction
- Atrial flutter with variable conduction
- ST-elevation myocardial infarction
- Ventricular pre-excitation
Diagnosis
The diagnosis in this case is atrial flutter with variable conduction. The ECG reveals an irregularly irregular rhythm with atrial flutter waves best seen in lead II and in the lead II rhythm strip. There is variable ventricular conduction with a ventricular rate of 96. There are T-wave inversions in the lateral leads (I, aVL, V5, and V6) that were present on prior ECGs but no signs of significant ST-elevation or ventricular pre-excitation.
Discussion
The differential for an irregularly irregular rhythm includes: atrial fibrillation; atrial flutter with variable conduction; and multifocal atrial tachycardia. Atrial fibrillation lacks organized atrial activity (ie, no P waves), whereas atrial flutter is an organized rhythm that occurs when a re-entrant circuit forms in the right atrium, usually in a counterclockwise fashion, leading to inverted flutter waves in the inferior leads (II, II, and aVF, [Figure 2]).1
It is characterized by an atrial rate of approximately 300 beats per minute (bpm). In the absence of treatment or atrioventricular block, the most common atrial to ventricular response is 2:1.1,2 This patient had known atrial flutter and was on carvedilol for blood pressure and rate control.
The presence of atrial flutter itself does not warrant any acute intervention if appropriately rate controlled (heart rate < 110 bpm),3 but this patient’s clinical presentation is concerning for heart failure exacerbation. An emergency department transfer is indicated. Other indications include non-rate controlled or symptomatic atrial flutter. In unstable patients, synchronized cardioversion is indicated.
What to Look For
- “Sawtooth” appearing P waves that tend to be negatively deflected and best seen in the inferior leads.
- The atrial rate tends to approximate 300 bpm.
- 2:1 conduction is the most common type of atrial flutter, and the ventricular rate tends to be around 150 bpm.
Pearls For Initial Management, Considerations For Transfer
- Refer to an emergency department for heart rates > 110 bpm, if symptomatic, or with signs/symptoms of heart failure.
- If able, synchronized cardioversion is indicated when unstable while arranging for emergency referral via ambulance.
References
- Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th ed. Elsevier; 2008.
- Link MS. Evaluation and Initial Treatment of Supraventricular Tachycardia. NEJM. 2012;367(15):1438-1448. doi:10.1056/NEJMcp1111259
- Van Gelder IC, Groenveld HF, Crijns HJGM, et al. Lenient versus Strict Rate Control in Patients with Atrial Fibrillation. NEJM. 2010;362(15):1363-1373.