EP Lab Digest - February 2008 - (Page 24)

CRYOTHERAPY UPDATE FEBRUARY Roundtable Discussion on Cryoablation Procedures n September 24, 2007, a roundtable discussion on cryoablation took place at the Baylor Jack and Jane Hamilton Heart and Vascular Hospital in Dallas, Texas. Dr. Peter Wells and Dr. Rajjit Abrol of the Baylor Heart and Vascular Hospital in Dallas, along with Dr. George Van Hare of Stanford University Medical Center in Palo Alto, California, participated in this discussion, which was shown as a webcast on OR-Live. In this abridged summary, you’ll learn about techniques in EP ablation procedures using CryoCath’s technology. You’ll also hear how adult and pediatric electrophysiologists can successfully integrate this exciting technology into their practice. O Figure 1. When comparing a cryolesion with an RF lesion, a cryolesion is much more dense and homogeneous. In this photo, a cryotherapy zone can be seen in this cryoablation procedure. (Reprinted with permission from EP Lab Digest 2003;3(4):1,6,7.) PETER J.WELLS, MD: In this webcast, we will talk about what role cryoablation can play in the practice of interventional electrophysiology. I am joined by Dr. George Van Hare, who is a professor of pediatrics at the University of California San Francisco and Stanford, and by my colleague Dr. Rajjit Abrol. Raj was a fellow here with us in EP and has now moved on to be an attending and is one of the EP faculty here at Baylor. We’re going to spend the first part of this webcast covering some of the basic information about cryoablation. In order to really understand this, it’s important to know the history of ablation. The first ablations performed were actually epicardial surgical ablations done in the operating room, initially under cardiopulmonary bypass where the arrhythmia target was mapped and then cryoprobes using nitrous oxide were utilized to make discrete lesions to try to cure people of their arrhythmia. Much of the basic cryobiology that we’ll talk about today comes from this epicardial operating room data. Obviously, with the morbidity and expense of an open-heart approach, there was a tremendous push in the early 1980s to develop some sort of percutaneous cardiovascular access that could result in intracardiac ablation. The first research was direct-current ablation, which involved putting the full output of a defibrillator through a braided Dacron catheter — this created tremendous barotraumas and excitement in the EP lab. GEORGE F. VAN HARE, MD: Those were literally exciting days. PETER J.WELLS, MD: Sometimes that shock would overwhelm the insulation of the catheter, and you’d even have beautiful arcing lightning in the lab. From there we learned from our surgical colleagues that you could use radiofrequency (RF) energy. They’ve used RF for decades in the operating room, in the form of electrocautery devices. Catheters were developed in the early 1980s, and the first successful human RF ablation using a catheter was performed in 1985. It’s a very effective energy source. However, the history of cardiac ablation doesn’t stop with any one modality, and in 2007, you can see that we’ve advanced quite a bit.We can now deliver cryothermic energy through catheters and balloons. We can also deliver ultrasound energy through balloons, laser energy through fibers, and microwave energy through antennae. We can also deliver ethanol either directly into the target of an arrhythmia or interrupt its blood supply. Even more recently, we are now able to make bigger RF lesions by using catheters that have needles in them. GEORGE F.VAN HARE, MD: I should point out that many of these forms of energy delivery or catheter ablation techniques are not yet in clinical use, but they are in development. I think we’ll all be seeing these technologies in clinical practice at some point in the future. PETER J.WELLS, MD: Correct. Cryo, of course, is one approach that is now available for use in clinical practice. Other advantages such as three-dimensional (3D) mapping technologies, in which we build a geometric model of a cardiac chamber in which we want to ablate, facilitate identifying the site of origin. In addition, there is intracardiac imaging with ultrasound catheters, which is very important in order to see normal cardiac structures. Of course we haven’t yet mentioned magnetic navigation and robotic arm type devices, in which we don’t even have to be in the EP lab to use! So quite a bit has happened in the field of EP. Now we want to spend some time focusing on cryoablation. Cryoablation catheters come in 7 and 9 French (Fr) sizes. There is a wire that is connected to each electrode as well as a deflection wire, which makes the catheters steerable. There is also a thermocouple that is connected to the distal electrode so the temperature can be monitored.To create a lesion, high pressure liquid nitrous oxide is pumped down the injection tube and when it changes into the gaseous phase, absorbs heat and lowers temperature.Typically the temperatures that we reach with nitrous oxide are on the order of about -80 degrees Centigrade.To set up for a case, we hook up the electrical connection, much like you would with an RF catheter. After that we connect the coaxial cable, which transports and vacuums the nitrous oxide back.These are connected to the CryoCath console. Once the coaxial cable is connected, the console will recognize the catheter and know how much nitrous oxide can be delivered.You will see a digital readout of the temperature on the left side of the screen with timing right below it, in blue numbers. Once we’ve come on with cryo, you will see a very steep descent of the temperature/time curve down to a minimum value typically of -70 to -80 degrees Centigrade. GEORGE F. VAN HARE, MD: Remember, the larger the tip, the lower the temperature goes. PETER J. WELLS, MD: The 4mm catheter can be operated in a temperature control mode where the refrigerant is adjusted to maintain the temperature at -30º C in the cryomapping mode. However, the two larger catheters operate in flow mode only, where they drive the temperature all the way down. Unlike RF ablation, cryoablation extracts heat from the tissue. When the electrode is in contact with the endocardium, it is absorbing heat, and that produces a wavefront of cooling. The coldest temperatures are in direct contact to the electrodes. Therefore, in contrast to RF, where you can get very hot temperatures deep in the tissue, this tends to be a more controllable energy source. If the energy is delivered for a short period of time with temperatures that are -30 degrees or warmer, then that is considered the mapping mode, and we don’t typically create a lesion when we do that. If we get cold enough for long enough (i.e., -70 degrees Centigrade for more than 60 seconds), then we are out of the hypothermia cryomapping mode and are producing lesions. GEORGE F. VAN HARE, MD: The other important feature at -30 or -35 degrees is cryoadhesion, in which the catheter actually sticks to the myocardium very tightly; this is a very important feature that does not happen with any other energy source. RAJJIT ABROL, MD: It is important to point out the mapping features available on the 4mm, 6mm and 8mm catheters; we may not necessarily refer to it as ‘mapping’, since what we are doing is freezing the tissue in the range at which it is still reversible.With the 4mm catheter, it doesn’t get below 30 degrees if you’re in the mapping mode. We’ll talk about this later with the different catheters. PETER J. WELLS, MD: Cryomapping is a very important feature that unfortunately we do not really have available to us with RF. What happens when we decide to create a lesion? When discussing how a typical cryolesion compares to a typical RF lesion, we’ve come up with a crude rating scale to assess several different aspects of the lesion; we’ll talk in a moment about why that is clinically important. First of all, if you compare a cryolesion with an RF lesion (Figure 1), a cryolesion is much more dense and See ROUNDTABLE page 26

Table of Contents Feed for the Digital Edition of EP Lab Digest - February 2008

EP Lab Digest - February 2008 Creating the U-M Center for Arrhythmia Research: Interview with José Jalife, MD Texas Cardiac Arrhythmia Institute and St. David’s Medical Center Launch State-of-the-Art Training Center Contents Letter from the Editor Spotlight Interview: Caritas St. Elizabeth’s Medical Center 10-Minute Interview: Sue Deck, BS, RN, RCES Keeping Pace With a Blog Roundtable Discussion on Cryoablation Procedures Email Discussion Group: February 2008 Events Calendar Industry News and Products Classifieds Advertisers Index

EP Lab Digest - February 2008

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