The Only Constant Is Change


In this excellent article from the March 2007 Journal of the Emergency Medical Services, Tim Phalen discusses the importance of performing serial 12 lead ECGs.

Here are some of the highlights.

“Acute myocardial infarctions (AMIs) aren’t like broken bones and, therefore, ECGs aren’t static like X-rays. If an EMS crew were treating a hip fracture and could somehow perform the X-ray on scene, what would it show? A broken hip, of course. And if the X-ray wasn’t performed until the patient arrived at the emergency department (ED), would the broken hip still be visible?


When dealing with a fracture, whether the X-ray is obtained immediately, in 10 minutes or in 10 hours, the interpretation and diagnosis usually won’t change. But what’s true for X-rays isn’t necessarily true for ECGs. In fact, an ECG can significantly change in a very sort period of time — as can the corresponding interpretation.”

“[I]t can be difficult to determine if the presence of LBBB on the ECG of a suspected AMI patient is preexisting or is a new onset. If the LBBB is infarct-induced, it has a high mortality rate — up to 60%. Therefore, the patients who may need reperfusion the most are the least likely to receive it. However, dynamic changes on serial ECGs shed light on the situation. A hallmark of infarct is change over time. If a patient has had an LBBB for the past 15 years, it’s not likely to change much during the next 15 minutes. But when changes occur in a short period of time, suspect AMI.”

Those are some excellent points.

It’s also helpful to understand the expected appearance of baseline abnormalities. For example, the rule of “appropriate T-wave discordance” states that with bundle branch blocks and paced rhythms, the T-wave should be deflected opposite the terminal deflection of the QRS complex. So LBBB is an abnormal finding, but discordant T-waves (and ST-segments) within the context of LBBB are a normal finding (to a point).

On the other hand, while baseline abnormalities like LBBB or paced rhythm may cause a discordant shift of the ST-segment and T-wave, the ST-segment should not be moving! A moving ST-segment suggests dynamic changes in supply v. demand characteristics.

In other words, ischemia.

Updated 01/15/2016

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