What is the cause of this patient’s inferior ST depressions?

Written by Pendell Meyers, edits by Steve Smith

A nurse brought this ECG to me, stating that she had recorded it because she was just notified by the lab of an elevated troponin result. She asked me if I was worried about the ST depressions in the inferior leads. I did not know who the patient was, and I had no other clinical context.

I took a look and asked in return: “Is the patient on any unusual cardiac medications?”

The physician taking care of her overheard the conversation and told me that the patient was on mexiletine.

What do you think?

The rhythm is atrial flutter with 2:1 block. Flutter waves are clearly visible in leads II, III, and aVF, which create the illusion of ST depression in the inferior leads. Typical 2:1 atrial flutter has an atrial rate of ~300 bpm with a resulting ventricular rate of ~150 bpm. This patient interestingly has an atrial rate of slightly over 200 bpm with resulting ventricular rate of 106. This is very unusual, and I have only seen this in the setting of sodium channel blockade (decreased slope of phase zero, Na-dependent depolarization leading to decreased speed of action potential propagation) and/or extreme atrial dilation (the bigger the reentry loop, the longer it takes to do a lap).

I was able to recognize this simply because I have seen it several times before on this blog!

I later found out that the patient had been transferred from another institution after suffering a large stroke, and there was no clinical concern for ACS. Her elevated troponin was most likely due to a type II MI in the setting of significant stroke.

One more point
If this atrial rate were to slow even more, then the AV node might conduct every beat and the ventricular rate could go up, dangerously so.  See this post:

Wide complex tachycardia at a rate of 270

For this reason, do not try to convert the flutter with more sodium channel blockade unless you first block the AV node!  It can result in slower flutter and a faster ventricular rate.

Learning Points:

Atrial flutter frequently causes the illusion of ST segment changes.

Atrial flutter usually has an atrial rate of ~300 bpm, which results in a ventricular rate of ~150 bpm when there is regular 2:1 AV block. These rates can be affected by various pathologies or medications including sodium channel blockers.

Be careful of slowing atrial flutter without first blocking the AV node.

Here are some other similar posts:

What is the Diagnosis?

Is this inferor STEMI?

Powered by WPeMatico