How to tell if a stress ECG is positive or not

This video was taken from our Exercise Stress ECG Essentials course. By the end of this lesson, you will know and be able to use the basic criteria for identifying a "positive" stress test.

This course covers all the essentials of exercise stress testing–what it is, when to do it, and how to do it. Along the way, we will discuss issues such as which mode of exercise to use (e.g., treadmill versus cycle ergometer), when it’s safe to continue and when to stop the test, how to deal with ECG artifacts, and how to describe test results.

[00:00:00] So, we know now that our ST segment is really the key to seeing if there is myocardial ischemia during stress testing. So, here we have our ST segment and here we have our baseline isoelectric, when the baseline and the ST segment are on the same level. When we talk about change, we're looking for a significant change in the ST segment, from where it was in the standing pre-stress ECG. Greater than or equal to 1 mm,

[00:00:30] which is 0.1 mV, at standard calibration, is considered a significant change. So, we're talking about one little box if we're at standard calibration. So, here we have our baseline, PR segment. Here's our ST segment. Here, we're about 1.5 boxes, so this is significant. Greater than a millimeter, greater than or equal to a millimeter. This ST segment is basically flat, it's horizontal, so this is called horizontal ST segment depression. And other than this little hitch, here in the J point,

[00:01:00] it really wouldn't matter if we measure the ST segment, here or here or here, we're going to get the same amount of depression from baseline. So, that's your horizontal ST segment depression. On the other hand, sometimes our ST segment slopes down over time. Somewhere in here, we're going to our T wave. Here, we have it downsloping. This is what its called when it goes down, downsloping ST segment. And in this case, we're going to get a very different measurement if we measure the ST segment, here or here or here. So, we need some sort of guideline as to

[00:01:30] where we're going to measure our ST segment. Here's our baseline, PR segment. If I measure here, I might get a millimeter. If I measure here, I'm close to 2 mm, certainly over a millimeter and half the depression. So, if we have this downsloping ST-segment depression, we have to have some sort of standard to where we're going to measure the depression. The J point is where the QRS ends and the ST segment begins. A very common approach to this is to go 80 milliseconds, which is two little boxes,

[00:02:00] at standard calibration, after the J point. Some people will call that 80 milliseconds post QRS, it’s the same thing. So, we find our J point and we go over two little boxes. Now, here, our J point isn't right on the line, so we start wherever the J point is and we go two little boxes over, that would put us, here. And here, is where we'd measure ST-segment depression. Here's our J point. Sometimes, it's hard to see exactly where that is but this seems to be it. We go two boxes over, two small boxes. So, here, we're in the middle of the box

[00:02:30] this set should be one box, two boxes. Here's our measurement point, two little boxes, which is 80 milliseconds at standard calibration, 0.08 seconds after the J point. That's our measurement point before the ST depression. Sometimes, we have a nice flatline in terms of the ST segment, horizontal ST depression. Really wouldn't matter where we measured this, it would all be the same. Sometimes, we have a downsloping ST segment. We should describe it as such and we have to be careful where we measure there because we're going to get a different

[00:03:00] number. So, greater than or equal to a millimeter of ST depression is significant. We should describe whether it's horizontal or downsloping and it's typical to measure at 80 milliseconds, post J point. ST is the key for ischemia. How much change we see is important? We want to be as precise as we can in describing it. Greater than or equal to a millimeter is significant. Where did we measure this? Many people will use 80 milliseconds after the QRS, also known as 80 milliseconds after the J point.