Blaise Midnight, Biomedical Engineer with Zoetek Medical, talks about ECG Setup, Trace Issues, Patient Prep, and more – featuring the Welch Allyn CP 150.

Last week’s Tek Tip -> Maintenance for the Midmark Ritter UltraClave Sterilizer

Welcome to Tek Tips from Zoetek Medical. I’m Blaise Midnight and this installment is going to focus on ECG machines. We’re going to work with the Welch Allyn CP 150, but a lot of what we’re going over is valid with almost any kind of ECG machine. It has a lot to do with the quality of your ECG and how to get the very best tracing. We’re going to use this one as our model.


The very first thing we do is a quick overview. You always want to make sure that your patient cable is properly plugged into the unit and secured. Make sure that’s fully inserted. Some of them have little screws that hold them in – but some don’t – these can come partially loose and look like they’re plugged in – but they’re not. That can be an issue. Your power cord … you want to make sure that’s plugged in solid into the back of the machine and into the wall.

Visually check it to see to make sure there’s no cuts or bends or abrasions or obvious visual signs of damage same with your ECG patient cable. If you see that the outer insulation is starting to crack or break and there’s any indication of being able to see the wires inside that’s a good time to change your cable it can degrade the quality of your ECG and it could totally fail on you at an important moment. More common causes of failure are near the stress points near the ends of the cables where it goes into the acquisition module or comes out. These are the more common areas where they fail. Take a close look at those areas to see.

The next thing we want to go over is loading our paper. I have a new roll of paper here. We get a lot of calls from people who say their ECG machine isn’t working, and we find out they have the wrong paper from a different ECG machine. If you have multiple ECG machines of different models or different manufacturers, make sure that you have the proper paper. All the paper should have a part number printed on the bottom of it. Double check to make sure that if you find an ECG that was printed on this machine that it has the same part number as the new paper you’re putting into it.

To insert paper, press the small button on the side and the door opens. Other machines have various ways of popping the door open but that’s pretty typical. I like to take the top sheet. I want to set it in here so that my white bar is at the top and my little black indicator mark. This is kind of important. This tells the machine when one full page has been expelled and we slide it into our drawer here and set it down in flat. And then I usually just read this out a little bit. You’re going to waste the sheet paper and we plug it in. I power it on and we are good to go. When I go to start this ECG it will probably spit out this little piece of paper here to the next stop. So, you’ll get a full ECG on one sheet and it won’t start in the middle of one sheet and go on to the next. Those are the important parts of getting set up.


Next we want to talk about some of the common trace issues problems that you have to give you poor quality trace. And you’ll probably see a reoccurring theme in here. I’ve been working on ECG Machines for over 40 years. And one of the most common issues is your electrode to skin contact. And it’s very important that there is a very good contact and we’ll go over the best way to get a good contact there in case you aren’t already familiar. I’m gonna go over a bunch of other things as well.

One of the first things that we often will see is a wandering baseline where your baseline will kind of wander up and down. It will not be in a nice straight line. One of the very first reasons why that might happen could possibly be your electrode contact at your skin. Bad electrode contact or defective electrode could definitely cause this problem. We need to have really good contact throughout the whole path from the machine to the patient or vice versa patient to machine. Another reason why you often will get wandering baseline will be rapid breathing or excessive movement of the chest. A lot of times if you have a nervous patient or a patient who is uncomfortable in the whole situation. If they’re breathing a lot, sometimes you’ll get that kind of that kind of a movement. Most ECG Machines including this one have a baseline filter you can turn on and off and we can go through that in a few minutes. That will help alleviate a lot of that wander that you get.

Okay so that’s a wandering baseline. One of the next things that often happens is a muscle tremor and we’re gonna show you a graphic here of the muscle tremor what it would look like on an ECG Trace. If you notice you’ll see the waveform you have wandering along the base of the line, it’s not thick and black but you can see that there’s a lot of noise on that line that just follows the whole waveform and that is not acceptable for good reading. So that often comes from muscle movement. Your patient’s uncomfortable. Your patient is not in a relaxed position. They should be on a table or bed that fits them and they can relax. You want to make sure that patients are not cold and shivering. Things like these can cause a lot of your muscle tremor and give you a poor ECG.

The next is AC interference. AC interference is caused by poor connections and is one of the major reasons is bad connection at the skin. A bad connection anywhere in the patient circuit – the patient circuit being the patient cable, clips, the electrodes to the patient. AC interference is caused by electromagnetic waves that we are being bombarded with it every day. Some ways to prevent them from becoming excessive and giving you this dark black line that you see on this insert here. You see a dark line –  it’ll be very thick and dark and continuous. That’s the difference between an AC Interference and a muscle tremor interference. So, all of these waves are coming in there and if you don’t have a really good connection between your ECG Machine and your patient, if there’s a flaw anywhere in that line, all those leads act like little antennas and pick all that up and it transfers it to the machine and gives you a poor quality trace.

Some of the things that also will cause this is if you or the patient are touching an electrode during the ECG. They should be flat and relaxed in a relaxed position and not moving. They shouldn’t be touching the electrodes. They shouldn’t be touching any metal surfaces. Like they shouldn’t be touching the metal surface on the table or bed that they’re on they should be comfortable on an insulated surface like the padding on the top. You don’t want them touching anything like that.

Lead wires should be visually inspected on a regular basis. If your lead wire … one of your patient cables, has broken from stress or being run over or bent can cause a lot of AC interference. In that case, you would probably need to replace your patient cable. Zoetek Medical can provide patient tables for just about any ECG Machine you might have out there.

Another thing that’s important to prevent the interference is a good ground connection in your power cord. Like I said, you want to make sure that cord is plugged in tight and it’s not damaged and it is plugged into a well-grounded outlet. You don’t want to have it plugged into an outlet when the ground is questionable. Never ever used one of those cheater adapters that change from three prongs to two prongs. It eliminates not only the safety of the whole device but also is a great way to introduce a lot of interference. One of the things Zoetek does during a routine PM maintenance is we check all that. We check the condition of your power cord because it may look fine, but it isn’t, and it will give you problems. If we find a problem like that, we will recommend that we can replace that power cord or patient cable or whatever it is that might be causing the problem. Finally, most ECG Machines have a 60 hertz or an AC filter that should be turned on. I rarely ever see anyone who doesn’t want it turned on. So it probably should be turned on and left on in the settings. It will just be a great way to help you get a better quality ECG.


I want to talk a little bit about the electrodes that are out there and the connection between the patient and the electrode and between the electrodes and the cable itself. These are very important. I get untold number of calls from people who are having problems with bad ECG and it turns out that it’s poor contact at the electrode.

Some people still use these old suction type where you put some conductive gel and it goes on the patient and like sucks right on. And this would hook to your patient cable. There are plate electrodes with a strap to wrap it around and tighten it on. Some people still use these clip types that clip on to your arms and legs to do your ECGs. They still occasionally pop up, but they’re not very common. More common are using clips that clip onto your electrode of different styles like this. They come in different shapes, sizes and colors, but they pretty much all do the same. Inspect the tabs. I’ve often found that there are problems with tabs that have expired. They all have an expiration date on the package and you should check those and make sure that your tabs are not expired. If they are, they should be disposed of and replaced with fresh ones. Keep your tabs preferably in the pouch if they’re not going to be used up quickly. Fold over to keep that closed so that moisture doesn’t dry them out. Never store in the sunlight or over a heat register or anything like that, because that will degrade the quality of your electrode on here.

Now, these are standard silver chloride electrodes, they’re very stable. The silver chloride is great for being very stable and give you a good ECG without introducing excessive noise to your trace. These would be attached directly to the skin. However, we want to make sure our skin is properly prepared and the best way to do that is to clean the skin. If the patient has an excessive amount of hair, you should at least trim it down short or you could shave it but be very careful. We don’t want to irritate the skin because that can cause some anomalies in our ECG. But we want to keep the hair out of the way as much as possible. If there’s an extreme amount of hair, shaving it very carefully or trimming it very short is the best way to go.

Then I recommend that you take a mild soap and water and you clean that area of the skin. I’m using my arm as an example. But anywhere that you’re going to put the electrode, you want to clean it really good. You want to remove any oil lotion -anything they may have on their skin before you replace it. Then you’ll want to dry it really well. Then take another dry gauze pad. I recommend that you rub the skin a little bit. That will help bring the blood to the surface and will remove any dead skin or loose material that’s on the outside brings the blood to the surface and allows a much better electrical connection between the patient and the electrical.

Some people have in the past said to use alcohol pads, I recommend you don’t use alcohol pads as they have a tendency to dehydrate your skin and then it doesn’t give as good a contact. The only time you might want to use an alcohol pad is if, for some reason, the skin is very dirty or very oily or greasy, like if a mechanic came around at work and didn’t bother washing his hands and it’s covered with grease, you want to get some of that off. But, in general, just some water and a gauze pad is good. Make sure it’s nice and dry and rough it up before you replace before you place your tab on there.

The next thing we want to look at are clips. They come in different styles. But sometimes I found that these clips get all gummed up because people are putting these on in a hurry and rather than clipping onto the little tab part on the top here, they clip onto the sticky gooey part that’s underneath there that sticks to the patient. And after a period of time that gooey stuff builds up inside the little jaws of your clip here and you get a whole bunch of build up of that. And if that builds up too much and dries out it will not give you a good signal. So it’s worth it to take a look at that and if they look really beat up you can attempt to clean them or better yet they’re relatively inexpensive.

Get yourself a new set of these. I recommend that they all match. They should all be the same kind that gives you a better quality ECG. And again getting that spot clean and ready to be prepped to place your electrode down there Not only will the electrodes stick better, it will give you a better conduct.

The last thing is another type of contact electrode. This are often used more for monitoring but it has a snap on it. The only recommendation I have on that is of course make sure it isn’t expired that it’s not dried out. It’s a little more comfortable for the patient if you snap it to the electrode first.

You snap that on first and then re apply this because then you’re not trying to snap thing by pushing it on your patients. So that covers the patient prep part of this and again I wanna stress it’s really important and it will make a wonderful difference in the quality of your ECG.


We want to go over a little bit of the operation of the ECG Machine here. Now on your home screen when you first powered up you come up with some options for print out. The first option is when is to allow you to perform an ECG. But, before you go in and perform the ECG, it’s going to ask you to enter patient data. So, I’m just gonna push that once so we can see and then this one.  It’s set up for the patient ID, last name, age, first name, gender.

Sometimes you can program this and you can have it pre-programmed for you to have things like height, weight, age, all that. But yes things like that can be added. So you can enter all that information. And all this information is very important because it will all get stored in its memory. And if you ever need to recall any of this you can recall it from them –  things such as the name the patient, ID.  Things like that. The date of the ECG.  Those are things you can use to recall for future use or if you want to add another ECG to that. At that point we would enter that and we’ll hit the arrow and that would take us to the page we’ll get to in a minute.

So now we have a start a continuous ECG print out. If we push that button we will start printing out an ECG and it will continue to print out until we stop it manually with a button. It’ll just keep spitting out paper and it will print out in the format that’s pre-programmed in this unit. Things to know about this is that there is no data attached to this, like patient ID or name, and it does not save it into its memory. So, it’s strictly for your print out if you want it. I think it’s mostly used in emergencies or in that type of thing where you’re trying to catch an anomaly that only happens occasionally.

The next one is a Stat Print.  Stat Print is if you are in a hurry and have to take an ECG. You get the patient hooked up and this will bypass the patient data information entry form and immediately start taking an ECG for you. Again, often in an emergency situation where they got to get it really fast and they don’t want to waste the time to put in that information. This can be saved but you have to remember that you need to either go back in and update the patient information like the name the patient I D. Number. Otherwise, it will go into your directory but it will not be accessible because you can’t really look it up.

There’s no criteria to search for it because they won’t be attached. So, you have to remember to go back and put those in if you plan on saving it. Otherwise, you will get a print out that you could save a hard copy. All right. The last thing here is it has on the bottom is electrode placement. This is a nice little feature because you can push that before you do your ECG and it’ll give you an idea of how good your quality is. As you can see, we’re hooked up to our patient simulator. We’re getting an ECG waveform. There is a nice little button here called a view button that you can push and it will change what you see on your screen. So going from  wave 1, 2 and 3 we can push the view button and it’ll give us a lead 1 ,2, 3  – avr – abl – ebf – which is very common.

That’s in the first half of the screen. In the second half you see your chest feeds B one through B six. So, you can see all the leads and you can see that we have a nice wave form before we start our print. There are other waveform options that you can look at just by pushing this view button and then we’ll go back to the original along the bottom. Here we have our 10 millimeter per millivolt. That’s kind of a standard. What that means is for every millivolt signal that the ECG Machine picks up from the patient it will deflect on your screen 10 millimeters. It’s pretty standard. I don’t know very many people who do it at different speeds. But if you needed to you could change it. Basically the 20 mm to millivolts doubles the size and you can just step through the different options there. 25 millimeters per second is how quickly this trace is moving across the screen. 25 millimeters per second is pretty standard also. Very few people ever change it. As you see that little black line that refreshes the data going across. If they change it to 50 you’ll see that’s going twice as fast now. Just going by faster causes the distance between all of the Q. R. S.’s to be pushed out. But if your doctor or nurse or whoever is reading this they’re probably used to seeing it at 25 speed. Okay. Here you also have an option to change your filters. I recommend you leave the baseline and muscle filter on. But if you want to turn one of those off for some reason you can push this and it will go to no filter.

In that situation you’re probably gonna have a rough time getting a nice ECG without any kind of muscle artifact or AC interference. But it is possible. With patient movement there’s a muscle artifact that the muscle filter will help with. And then the last one is both baseline and muscle. And I pretty much say that’s probably where you want it to be.

We’re gonna go back and I’m going to do a standard EDCG, patient I. D, push that. I’m just gonna put in 543 or 432 or something whatever. Then we get next and it’s gonna ask age and I’m gonna put in just any age, 55, and next, and last name. I’m just gonna put in test and first name this is test number one. So we’re gonna be test number one, next.

So, all our information is in there we hit okay and then get this arrow here and it’ll start here giving you a trace. If you’re happy with how that looks, you push record and it is analyzing the data. It’ll take a couple of seconds to analyze the data and then it will come up on the screen where you can see all in like a preview mode. Then we’re gonna push the next button and it will print out a copy which I will spit out the side here and I’ll put it in front so you can see it. As soon as it’s done printing we will find that we have an ECG – all labeled. very clean, very clear, no artifact, no AC interference, no muscle artifacts. It looks really nice. Your patient data will all be up on the top here including an analysis.

At this point you have your choice to print it again, save the test which will save it in the memory, or start a continuous ECG Print which is like I said before it’s the one where it just continues to spit out paper. So you have your choice. I’m gonna save just for the heck of it. And at this point we want to choose local. If you have the options to have this connected to your network you can pick some of these other options but local will keep it on the machine itself and that’s pretty much how most people do it. So we’re gonna say local and we’re gonna save that and it will save it in its memory. Okay? And if you wanted to print you could or we exit and go back to our home screen.

Now the only other thing that really we want to go over quickly on here is our settings. In our settings these are where we can do something such as turning on our baseline filter and our muscle filter. These will help with again the AC artifact and the muscle artifact. This bottom one “save reminder” turned on that will give you a prompt after doing an ECG –  Do you want to save this or do you not? If you turn that off it will not give you that prompt and ask you that question. Now, Waveform Centering On –  we’re gonna insert a couple of wayeform printouts here so you can see what the difference is and this is pretty much depends on the doctor or nurse or whoever’s preference and some people like this on.

Some people don’t but the difference is with the waveform centering selected what it does is as you can see in this this picture here. The wave form will try to keep the waveform centered on each of the rows that the printout is on. So when you go from like lead one to like avr or avl on the next section over you can see that there’s a slight jump where it moved up a little bit. That’s what is known as your centering turned on. So keep centering every lead into the center of that page. Some people like it like that. Some people don’t. Now, waveform centering off, if we deselect that, that’s gonna look more like this one where you see that all the way across from left to right the waveform is on one continuous line and there’s no jumps up or down when it changes leads, it’s all continuous here.

So that’s an important thing. I get a lot of people call me and says, oh the thing keeps moving and this and they, that’s because someone’s gotten in there and turn that on. All right. These other things in here, like the default gain – again that’s 10mm per millivolt, that’s pretty standard. I don’t think you will ever want to change it. But if you do that’s where you can do it here. The other thing on this page we want to look at is under device. This is where you would set your date and time if you ever had to do that. Hit that , enter your date and time and when you’re all done hit OK. And here it allows you to turn on and off the adjustment for daylight savings time so that it would, if you were in an area like we are here in in New York or daylight savings time, it does take place, we want that on.

That covers the majority of this. We’re gonna head off or go back to our home screen and we’re back to our normal screen. Thank you for visiting Zoetek Medical and watching another Zoetek Medical Tek Tip. We covered the CP 150 by Welch Allyn but a lot of this information is relevant to just about any ECG machine out there. So thank you for joining us. I’m Blaise Midnight and remember … make sure you’ve got a good patient contact. Thank you.