Ask the Clinical Instructor

I’m new to the cath lab, and I can’t figure out why a physician uses monorail one time and over the wire the next. What’s the reason? — CVT student, New York

_____________________________ If you’ve read these articles over the last couple of years, you will have heard this before: “It’s all physician preference.” Unfortunately, in this case, the same answer applies. With a couple of exceptions addressed later, the use of a monorail system versus an over-the-wire system is physician preference. If you ask physicians, they will give you their opinion that a certain system (or platform) is the “best” in any specific situation. You can also find physicians that will say the exact opposite. Let’s break down these two systems, and discuss when one might be used over the other. First, let me issue a disclaimer that despite the use of any statement or photograph, I do not endorse any specific products. The products shown/referenced in this article were randomly chosen for illustration purposes only. Over the Wire (OTW) The name of this platform describes itself exactly. The device is intended to travel the entire distance of the wire, with the wire running through the lumen of the device from the tip to the end. The tip of the device is placed on the end of the wire, and advanced over the length of the wire until the wire comes out the opposite end of the device at the hub. As almost a general rule, OTW systems require the 300 cm wire to place and remove the catheter from the body. If you have ever been stuck having to use an OTW balloon when you only have a 180cm wire in place, you know that it CAN be done, but it is not recommended. The tips and tricks for those maneuvers are beyond the scope of this article. The exchange of this device usually requires 2 people to perform. It can be performed by one person, but usually requires some long arms and contorted body positions to accomplish. An experienced team can remove and insert OTW catheters without much delay or problems. Only experience and teamwork helps develop this skill. One advantage of an OTW system is that once the balloon is in the artery, a couple of things can be accomplished that cannot be accomplished with a monorail system. 1. The physician can use the balloon as additional support for the wire, particularly in tortuous or difficult to cross lesions. The balloon can be advanced closer to the tip of the wire to provide support and prevent buckling of the wire, or help to direct it in a certain way. This is why many physicians will start their cases with the wire and the OTW balloon being inserted at the same time. 2. If the physician needs to change wires, they can do so. The wire can be removed and “placement” is retained. This usually happens once the physician has the balloon beyond the point of the lesion. The physician can then insert another wire through the balloon into the artery. 3. Also, the physician would be able to administer contrast, or medications, through the balloon. A common use of this is in difficult cases or chronic total occlusions (CTO). If the physician wants to confirm that the balloon is in the lumen of the artery, and not in the sub-intimal portion of the vessel, contrast can be administered through the balloon. To prepare the catheter for the initial insertion, it should be flushed prior to use. With an OTW system, there are two ports. There is the port that the wire comes through, and the port that the indeflator is connected to in order to inflate the balloon. Of course, the wire port is what should be flushed. This allows lubrication for the wire to pass through the catheter, as well as remove as much air as possible from the lumen of the catheter. CAUTION: If you accidentally ‘flush’ through the indeflator port, the balloon in the device will inflate. This is particularly a problem if you are dealing with a stent device. If you see this happen, remove the device from use and obtain another. The incidence of stent dislodgement after slight balloon inflation is high. To prepare the catheter for contrast/medication administration, there are a couple of maneuvers that come first. Of course, the wire should be removed first, and precautions taken to prevent inadvertent air administration. A 3 cc syringe should be placed on the hub where the wire came out, and the plunger pulled back to try and draw blood back into the syringe. THIS WILL TAKE TIME, since it is a smaller lumen catheter. Once the blood has come back to the hub of the catheter, the physician can utilize a 3 cc syringe to line up a “meniscus to meniscus” contact between the blood in the hub of the catheter and the media in the syringe. This prevents air from being in the catheter, which could eventually end up in the coronary artery. NOTE: If contrast is being administered, the physician will want to liberally flush the catheter before putting the wire back in. As you have probably experienced, contrast can become sticky, which can cause problems further into the case. A few moments now can save a lot of problems down the road. Monorail (Rx) Monorail is also sometimes called “Rx” or “single operator exchange – SOE.” The concept of this design is that the wire comes out of the catheter relatively close to the tip of the catheter. The physician is able to advance and remove devices almost solely by themselves. Generally, assistance in loading and unloading on/off the wire is necessary. With the monorail system, a short (180 cm) or long (300 cm) wire can be used. For true single operator usage, a shorter wire will be used. Should a long wire need to be used, there are a couple of options. The first option would be to use an “extension” system, such as the DOC wire (Abbott Vascular, Redwood City, CA) or the Cinch system (Cordis Corporation, Miami, FL), which can lengthen the wire from the 180 to 300 lengths. Typically, these extensions work on wires within that same brand. Another option is to run a long wire down alongside the existing short wire, utilizing the short wire as guide. Some physicians will argue that there is more “pushability” with the catheter. Once caution in this is that the construction of the catheter requires the utilization of a “hypotube” within the catheter. With the OTW system, all “pushability” is based upon the wire, since the catheter is completely over the wire. With a Rx system, only a small portion of the catheter is over the wire. That is why the Rx balloons are generally stiffer and ‘springy,” in order to provide support. If the physician pushed to the point that the catheter kinks, the catheter may not be operational. Once the hypotube is kinked, delivering contrast/saline media to the balloon to inflate it is likely to be impeded because of the kink. This is not recoverable, as it might be in an OTW system. A limitation of the Rx systems is that you can’t administer medications as you can in an OTW system. Also, you can’t exchange wires through the Rx system. If the physician “forgets” that they are using an Rx system and removes the wire, they will quickly realize that they will have to remove the catheter and start over. There is no way to recover your wire through the catheter at that point. To prepare the catheter for initial use, BEWARE: the catheter is springy and stiff. Care must be used in handling these catheters, as they are not as forgiving as OTW catheters. We discussed how to flush the OTW catheter for first use. What would happen if you flush the hub of an Rx catheter? Of course, the balloon would inflate. In most cases, this is not a problem for a balloon catheter, but as described earlier, can be a big problem with a stent delivery device. While the Rx system has a short ‘wire through lumen’ distance and often does not need flushing, there can be times when you need to flush. A common scenario where you would always want to flush the Rx catheter is when it has been used earlier in the case, and now it has been sitting on your back table for some time. Contrast can be in the short lumen that the wire moves through, which can make it sticky and obstructed. In these cases, use the little needle that comes in the Rx kits to flush your catheter. You place that needle on the end of a syringe and flush from the tip of the catheter until you see flush come out of the port where the wire exits on the catheter. TREAT THESE NEEDLES AS ANY OTHER ‘SHARPS’ THAT YOU HAVE ON YOUR TABLE! A Note on Catheter Balloon Preparation Most manufacturers publish recommendations for balloon preparation in their directions for use (DFU) or instructions for use (IFU). Most of the recommendations are fairly similar. They advise utilizing a syringe filled with a contrast/saline mixture and attaching it to the indeflator hub of the catheter. They advise to “pull negative” pressure on the syringe, and allow any remaining air to be withdrawn in the syringe. When there are no more air bubbles, release the pressure on the plunger of the syringe to allow it to come back to the “normal” state. The catheter is then “prepared” for use. Many physicians are quite adamant about following this process, and that is okay. My experience is that with a properly used indeflator, the exact same thing is being accomplished without the initial steps listed above. When the balloon catheter is past the Touhy-Borst device and in the body, the indeflator can be hooked up to the inflation port, and the indeflator can be “pulled negative.” When that occurs, the exact same thing happens as what is described above. Of course, you will not want to do this with a stent delivery device until it is closer to the coronary artery/lesion, based upon the physician preference. While we offer our thoughts and observations, you should still follow your physician preferences/facility protocol for balloon preparation prior to use. We have gone over some basic points concerning the usage of OTW and Rx systems. You should rely on your vendors for additional education. The vast amount of information and personal experience of tips and tricks are well beyond the space limitations of this article. Next month, we’ll cover a question concerning appropriate groin preparation of our cath patients. Email your question to tginapp@rcisreview.com Acknowledgements. We would like to thank Sherrell Gibson, RN and Sara Hensley, RT, for helping with the photos in this article. _____________________________ CORRECTION:M Alert reader Dean Springstead RN, BSN, CCRN, pointed out an error in our July 2009 column on mean arterial pressure. We incorrectly stated that PVR stands for peripheral vascular resistance and that MAP= cardiac output (CO) x peripheral vascular resistance (PVR). Dean correctly notes that PVR actually stands for pulmonary vascular resistance and that total peripheral resistance is known as systemic vascular resistance, or SVR. Thus, the correct formula for MAP = [cardiac output (CO) x systemic vascular resistance (SVR)] + central venous pressure (CVP). CVP is usually so small that it can be eliminated from the formula without changing the product of the equation. Our thanks to Dean for contacting us about this error.

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