EMS was called for middle-aged man, found slumped over a table at restaurant. He had quite a poor mental status and could not offer any medical history. Per the staff he had just arrived, and not eaten or drank anything.

Although he is carrying a home glucometer, his blood sugar is 160. He has a new-ish looking hospital wrist band on, but no shoes.

Systolic BP in the 80s, and HR around 160. Dry, hot skin, and the rest of the exam isn’t revealing. IVs are started, and a rhythm strip obtained:

And a 12-lead:

So, what do we have so far? And what do we do with the ECG findings?

What does the ECG show?

Yes, it’s an SVT (supraventricular tachycardia), in the sense that it is not a ventricular rhythm, and the rate is > 100. When we use the term SVT like this, we mean that it could be sinus tachycardia, atrial fibrillation or flutter, MAT, or whatever.

All “SVT” means in this sense is “not ventricular tachycardia!”

That being said, it is quite regular, so there are basically 3 possibilities: sinus tach, atrial flutter, or PSVT (i.e. AVNRT or AVRT).

A heart rate around 150 would be consistent with atrial flutter, true. But we don’t see flutter waves where we expect to. Instead we see fairly consistent P-waves, correctly oriented. From the rhythm strip we see the P-waves (red arrows) very clearly.

But suppose these aren’t P-waves, but instead flutter waves?

Then we should find a similar appearing flutter wave exactly half-way between red arrows, at a point labeled by the green arrows. Instead, we find nada. So, atrial flutter is darn unlikely, and the rhythm is overwhelmingly more likely to be sinus tachycardia.

“But the rate is > 150, this means SVT.”

Many readers have labeled this as SVT in an unstable patient, and that the best initial approach is electrical cardioversion.

In fact, many readers correctly saw that the rhythm was sinus tachycardia, but nonetheless went on to recommend cardioversion, because the HR > 150.

Do NOT (attempt) cardioversion of sinus tachycardia, no matter the heart rate or BP!

If the patient has sinus tachycardia, then what would you expect cardioversion to accomplish? What is the electricity “treating,” and what beneficial change in the physiology would you be expecting post-shock?

If you shock PSVT ( AVNRT/AVRT) or atrial flutter , you will “break” the reentrant loop of current. That’s good.

( AVNRT/AVRT) or , you will “break” the reentrant loop of current. That’s good. If you shock sinus tach, you’ve wasted 200J that could be used on another patient! Bad.

Despite the common misconception, ACLS does not define SVT as a HR > 150. They only comment that a heart rate under 150 is unlikely to cause hemodynamic problems.

You can have sinus tachycardia at 150, 160, 180, etc. Conversely, you can have a PSVT at 160, 150, or 130! Here is a case report of 2 SVTs that both had heart rates < 140.

So, what happened with the patient?

The medic realized that this was sinus tachycardia, which is usually a compensatory mechanism when some other issue is going on. Hypoglycemia was ruled out, and there were no rashes to suggest anaphylaxis. There was no blood on the patient or floor. This still left a lot of possibilities; for example, was there a weird overdose or toxicologic issue?

Regardless, he recognized that, despite being unstable with a heart rate > 150, cardioversion wasn’t going to help. He got 2 large lines in, blasted in a few liters, and saw that the heart rate came down a bit during transport.

In the ED, another ECG was obtained:

This guy turned out to be septic, very sick, with a lactate of 7. Turns out he had been treated for a bone infection at another hospital, but his homeless status allowed the infection to come roaring back.

After more fluids, antibiotics, and other supportive therapies, he improved to the point that he “flips staff off and occasionally swears in response to questions.” Mission accomplished!