February 2020 ECG Lesson : A Sneaky Rhythm

Travis Barlock, MD

By: Forrest Turner, MD and Travis Barlock, MD
Editors: Drs. Littmann and Gibbs

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Forrest Turner, MD

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Case: 
A 63-year-old male with a history of traumatic brain injury and associated seizure disorder presented from a skilled nursing facility after experiencing syncope and recurrent seizures. EMS reported occasional heart rates in the 200s. The patient received 5 mg of midazolam IM and the seizure activity resolved. On evaluation, he appeared to be post-ictal and minimally responsive. He had a normal pupillary exam and was withdrawing all four extremities. He was tachycardic at 136/min, blood pressure 105/75 mmHg, respiratory rate 20/min and oxygen saturation 95% on room air.
 
The following electrocardiogram was obtained:

Interpretation by ECG software, confirmed by a physician
Sinus tachycardia with frequent premature ventricular complexes​

What is your interpretation of the ECGs?

​Correct interpretation of the ECG
Atrial flutter with 2:1 AV conduction and frequent premature ventricular complexes

Summary of key ECG findings:

• Narrow-complex tachycardia, regular except for the PVCs, at a rate of 136/min
• Differential diagnosis includes sinus tachycardia, ectopic atrial tachycardia, reentrant paroxysmal supraventricular tachycardia, and atrial flutter
• In sick hospitalized patients, regular supraventricular tachycardia frequently turns out to be atrial flutter with 2:1 AV conduction (“2:1 flutter”)
• 2:1 flutter is frequently misdiagnosed as sinus tachycardia both by the ECG interpretation software and by providers

CLUES:

Clues to recognizing 2:1 flutter include the following simple “tricks”

• If you see a regular SVT, always entertain the possibility of 2:1 flutter
• The interpretation software indicates sinus tachycardia but there is something wrong with the P-wave morphology (as in the current case) or with the PR interval (too short or too long)
• Usually it is simple to prove the presence of 2:1 flutter by using the “halving” method: measure the R-R interval and try to find P waves at one half of this distance
• In typical atrial flutter, the P waves (flutter waves) are negative in the inferior leads
• If uncertain, intravenous adenosine, by creating higher-grade AV block, can easily expose the flutter waves.

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In this enlargement of the inferior leads, see the negative P waves spaced at exactly half of the R-R intervals.

Significance of finding?

Significance of recognizing 2:1 flutter in cases initially interpreted as sinus tachycardia

• Sinus tachycardia is not a primary arrhythmia; its treatment includes treating the underlying condition such as hypovolemia, fever, sepsis, thyrotoxicosis and heart failure
• Atrial flutter, on the other hand, is a primary arrhythmia; initial treatment should focus on rate control with intravenous diltiazem, beta- blocker and/or digoxin
• Chronic management options include rate control and anticoagulation vs. rhythm control
• First-line treatment for rhythm control is catheter ablation; its success rate approaches 90%
• Indications for anticoagulation are identical to those in atrial fibrillation
• Atrial flutter is frequently the result of right heart pathology such as atrial septal defect, obstructive sleep apnea, tricuspid regurgitation and pulmonary hypertension; recognizing atrial flutter should prompt evaluation for these listed conditions

HOspital Course

Hospital Course
The patient’s pre-hospital report of extreme tachycardia raised the possibility of 1:1 flutter and possibly syncope due to the dysrhythmia rather than seizure. Cardiology evaluated the patient and recognized the atrial flutter. The patient was given IV diltiazem which resulted in excellent rate control. It was felt that because of his brain injury and seizures, the patient was not a candidate for chronic anticoagulation. Catheter ablation was discussed but eventually rejected. Echocardiogram revealed right ventricular dilatation and hypokinesis, moderate tricuspid regurgitation, moderate pulmonary hypertension and marked right atrial dilatation.

Dr. Littmann’s Comments

Atrial flutter with 2:1 AV conduction (“2:1 flutter”) is one of the most commonly missed ECG diagnosis, both by the interpretation software and by providers. 2:1 flutter should always be entertained if the computer diagnoses “sinus tachycardia” but there is either an abnormal P-wave morphology and/or an abnormal PR interval. Consistent misreadings by the interpretation software include sinus tachycardia with first-degree AV block, sinus tachycardia with very short PR intervals, and ectopic atrial tachycardia. The most important factor in recognizing 2:1 flutter is to always consider this diagnosis in sick patients who present with a regular SVT. Once the diagnosis of 2:1 flutter is entertained, it is usually easy to prove it by using the “halving method”: recognizing negative P waves in the inferior leads whose distance is exactly half of the R-R intervals. If uncertain, the use of IV adenosine, by exposing the flutter waves, can be very helpful.
 
From the ED physician’s perspective, the most important job is to recognize the flutter and provide rate control. In patients who present repeatedly with atrial flutter, it is also prudent to suggest to the accepting team that curative treatment with catheter ablation should be entertained and discussed with cardiology.