30
A S K
T H E
C L I N I C A L
I N S T R U C T O R
Ask the Clinical
Instructor
A Q&A column for those new to
the cath lab
Questions are answered by:
Todd Ginapp, EMT-P, RCIS, FSICP
Todd is the Cardiology Manager for Memorial Hermann
Southeast in Houston, Texas. He also teaches an online RCIS
Review course for Spokane Community College, in Spokane,
Washington, and regularly presents with RCIS Review Courses.
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)
Quantum Maverick Over-the-Wire Catheter Schematic
Note the 2 ports on the hub of the catheter, 1 for wire and 1 for indeflator.
www.bostonscientific.com
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
With either device, when loading from the
wire that is already in the artery, it is called
“back loading.” This can be difficult at
times, because you are dealing with a
small wire and a small lumen catheter.
Hold both the catheter tip and the end of
the wire in your fingertips, and use them
as a ‘base’ for lining them up.
After loading the device, the wire will
come out of the hub of the catheter. I am
often asked if there is a chance that the
wire can come out of the angled port. This
could only happen if the end of the wire
had punctured the balloon and somehow
managed to find the hole in the catheter
connected to the indeflator port. Highly
unlikely that this would ever happen.
S E P T E M B E R
2 0 0 9
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
With the OTW system, the catheter is laid
out straight on the table, and the wire that
comes out of the end of the catheter is
“benched” to maintain position. This is
important to prevent the wire from going
forward as the balloon is being advanced.
As the balloon makes progress, the tech
will advance up the wire, following the balloon, keeping the wire “benched” while at
all times watching fluoro to make sure the
wire is not advancing.
The “Y” hub of an OTW catheter. The wire
port is coaxial with the catheter. The indeflator port is off at an angle. Think of it this
way: it would be difficult to manage a
device with the wire NOT straight.
32
A S K
T H E
C L I N I C A L
When “walking” out an OTW device, is
imperative to do so without having the wire
move. It’s recommended to “bench” the
wire with your right hand, and use your left
hand to pull the catheter to your right hand.
Do this for a few centimeters at a time.
Move your body to maintain straight alignment with your arms and shoulders. It will
help you be smoother in this procedure.
I N S T R U C T O R
This is NOT the correct port to flush the
catheter to prepare it for use. A balloon
catheter will likely inflate if you try to flush
through this port. If that balloon has a
stent placed on it, you risk dislodging the
stent from the delivery device. Safety calls
for the stent delivery catheter to be discarded and another used if there is any
chance that the stent has come loose
from the catheter.
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
The proper port to flush the catheter. Note
are a couple of maneuvers that come
that it is coaxial with the rest of the
first. Of course, the wire should be
catheter. There will be a lot of resistance
when trying to flush because of the small
removed first, and precautions taken
diameter of the catheter.
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.
S E P T E M B E R
2 0 0 9
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 physi- The hub of the monorail catheter. Unlike
cian pushed to the point that the the OTW catheter, there is only 1 hub on
the end of the catheter, and that hub is for
catheter kinks, the catheter may not the
indeflator. No flushing can occur
be operational. Once the hypotube is through this port.
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
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
Quantum Maverick Monorail Catheter Schematic
The main difference in a monorail vs OTW system is that the wire comes out of the
catheter closer to the tip if the catheter. Note that there is only 1 ‘port’ on the hub.
www.bostonscientific.com
Once the tech loads the balloon and slides it
up to the physician (who should be benching the wire), the physician manages the balloon and wire, and will tell the tech when
they ‘have’ the wire. The tech then ensures
the balloon travels obstruction-free.
As mentioned, it is impossible to flush a
monorail catheter from this port. As with
the OTW catheter, if you try to flush
through a port that is intended for balloon inflation, you run the risk of equipment problems.
33
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
When connecting an indeflator to a balthe pressure on the plunger of the
loon catheter, allow enough air in the indesyringe to allow it to come back to
flator chamber to allow negative pressure
when pulling back the handle on the indethe “normal” state. The catheter is
flator. In most cases, you will only need 10
then “prepared” for use.
cc of saline/contrast in the chamber.
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. n
Carefully insert the needle into the tip of the
catheter, attach a syringe of flush and GENTLY flush the catheter until you see the flush
weep out of the wire exit port.
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:
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.