May 2020 ECG Lesson: “Treated for Atrial Flutter”

By: Mark Kastner, MD and Rachel Plate, MD
Editors: Drs. Littmann and Gibbs

Rachel Plate, MD

Mark Kastner, MD

---

Case:
A 69-year old man with ischemic cardiomyopathy (LVEF 30%), and a history of both ventricular tachycardia and recurrent atrial flutter, s/p ICD placement, presented with one day of palpitations and associated lightheadedness. His cardiac medications included amiodarone and apixaban (Eliquis). His heart rate was 131 beats/min and regular, blood pressure was 103/84 mmHg. On exam he was slightly diaphoretic and anxious, but in no acute distress. The ECG interpretation software indicated sinus tachycardia with nonspecific intraventricular conduction delay and acute inferior infarct (LCX). This was over-read by the providers as atypical atrial flutter. He received IV amiodarone bolus and drip.

The following electrocardiogram was obtained:

Presentation ECG

​Here is the patient’s baseline ECG for comparison:

What is your interpretation of the ECGs? Do you agree that this was atrial flutter?

Correct interpretation of the ECG:

• RELATIVELY SLOW AND SLIGHTLY IRREGULAR VENTRICULAR TACHYCARDIA.

 Summary of Key Clinical and ECG Findings (see annotated ECG below):

• Relatively slow and slightly irregular wide-complex tachycardia (WCT); rate 131 beats/min
• QRS width is 4.5 mm = 180 ms, very wide (see green arrows and numbers)
• In a patient with ischemic cardiomyopathy, 90-95% of WCT is ventricular tachycardia (VT) (Ref. 1)
• WCT with more QRS complexes than P waves (see red arrows): 100% specific for ventricular tachycardia (Ref. 1)
• QRS complexes are bizarre, do not fit a bundle branch block pattern
• Northwest QRS axis, QRS predominantly negative in leads I and II (see purple box)
• Initial R wave in aVR (see black box)
• Tachycardia with wide, bizarre QRS complexes, NW axis and initially upgoing QRS in aVR: almost certainly VT (Ref. 1,2)

• Explanation: the ventricles are normally depolarized from right to left and from above to below; if the QRS axis is going towards the right shoulder (NW axis, initial R in aVR), then the impulse is coming from the ventricles rather than going towards the ventricles.

• R-R intervals alternate between 11 mm and 12 mm (440 ms and 480 ms) (see blue numbers)
• Cycle length alternans, seen in this case, is uncommon but can be present in ventricular tachycardia
• If you see a wide complex tachycardia, VT must be high on your differential diagnosis. If you are not certain, give IV adenosine. Adenosine, by creating AV block, should expose atrial flutter. If it did not do anything to the tachycardia, VT remains the most likely diagnosis (Ref. 1). In this case, atrial flutter was “diagnosed” but adenosine was not given to prove it.

Hospital Course:

​The patient remained in WCT overnight. Next morning, he underwent successful electrical cardioversion and was discharged home with a diagnosis of atrial flutter. Over a follow-up of 3 months, he did not have recurrence of the tachycardia.

Dr. Littmann’s Comments:

​Ventricular tachycardia (VT) is often misdiagnosed as SVT. This phenomenon was first described almost 50 years ago. Despite numerous publications and reviews raising awareness to this problem, the misdiagnosis of WCT, unfortunately, continues to be very common. As described above, there are numerous ECG clues that can help you diagnose VT. The most important factor, however, is the clinical likelihood: of all WCTs, about 80% are VT. In patients with heart disease, 90-95% of WCT is VT. “Probable VT” should always be your default diagnosis. It is OK not to remember any of the ECG clues listed by Drs. Kastner and Plate. If you are not sure, just give IV adenosine.
 
In this case, it is reasonable to raise a few additional legitimate questions:
• Why was the VT relatively slow? The patient was on amiodarone which, by suppressing conduction velocity of the reentry circuit, can markedly slow down the rate of VT.
• Why did the ICD not shock the patient? Probably because of the relatively slow heart rate. ICDs are usually programmed to deliver shocks at faster rates.
• Would it have been important to diagnose, or at least consider, the diagnosis of VT? Yes, because an attempt could have been made to overdrive pace the ventricles with the help of the pacemaker/ICD. Slow VTs are uniquely susceptible to overdrive pacing. If successful, it could have immediately resolved the tachycardia and cardioversion, even hospital admission, may have been avoided. In addition, the ICD could have then been reprogrammed to provide automatic overdrive pacing if a similar tachy-event were to be detected in the future.

References:

​1. Littmann L, Olson EG, Gibbs MA. Initial evaluation and management of wide-complex tachycardia: a simplified and practical approach. Am J Emerg Med 2019;37:1340-5.
 
2. Vereckei A, Duray G, Szénási G, Altemose GT, Miller JM. A new algorithm using only lead aVR for the differential diagnosis of wide QRS complex tachycardia. Heart Rhythm 2008;5:89-98.