Stanford Cardiac Arrhythmia Service

Cryoablation

Just as radiofrequency catheter ablation uses  heat to treat many arrhythmias, catheter-based cryoablationtreats heart rhythm problems by freezing small areas of hear tissue.   

How it works

Catheter cryoablation works by using a special gas that travels through the plastic tube called a catheter, which is inserted into the body and positioned at the site of the heart rhythm problem.  As the special gas changes pressure, it produces a large decrease in temperature, usually to -40 to -70 degrees C at the catheter tip.  Because all of the cooling occurs at the tip of the catheter, only the tip gets cold. 

There are a number of unique aspects to catheter cryoablation.  As the temperature decreases, the region of heart tissue that is cold enough to affect the heart tissue’s electrical properties gradually increases.   This gradual effect on the heart tissue, permits the physician to observe changes in electrical properties of the affected gradually.  Stopping cryoablation will usually result in  recover of the properties of the heart tissue’s properties in these outermost regions.  This property usually permits the physician to regulate the size of the region of heart tissue more precisely.   When applied to particularly sensitive regions of the heart such as the A-V node, which conducts electrical signals from the top chambers of the heart to the lower heart chambers, this property of catheter cryoablation may significantly decrease the risk of unintentional damage to the A-V node, reducing the risk of the need for a permanent pacemaker during catheter ablation in this region.  There is also experimental evidence that catheter cryoablation may result in a decreased degree of damage to the inner layer of th heart tissue and may result in decreased risk of blood clot formation following ablation but data are limited regarding this effect.   Catheter cryoablation may result in decreased ability to damage critical structures such as arteries of the heart.  It also may result in decreased damage to the esophagus.

Catheter cryoablation is performed in the same manner as radiofrequency catheter ablation and involves inserting the catheter, a plastic tube, into the blood vessel usually the vein in the groin called the femoral vein but sometimes in the artery.  From there the catheter is advanced to the heart region responsible for the heart rhythm problem.  The catheter also has electrodes which permits one to records the electrical signals of the heart to obtain essentially an electrocardiogram (EKG or ECG) from within the heart).  These electrical recordings are used to help determine the correct location for catheter ablation to be performed.  Sometimes catheter cryoablation uses other techniques to determine the location of the catheter with respect to the heart structures.  These include intracardiac echocardiography (see section on intracardiac echocardiography), advanced imaging techniques, and 3-dimensional mapping (see section onf 3-dimensional mapping)

Catheter cryoablation may be used to treat a number of heart rhythm problems. It is most commonly used to treat specific forms of supraventricular tachycardia, types of fast heart rhythms of the upper heart chambers (see section on SVT).   Cryoablation catheters used to treat these arrhythmias has a tip that is used to freeze a localized region of heart tissue. 

Balloon Catheter Cryoablation of Atrial Fibrillation

Catheter cryoablation may also be used to treat atrial fibrillation, (see section on Atrial Fibrillation)  but a special balloon catheter has been developed for this purpose.  The cryoablation balloon catheter consists of a balloon-within-a-balloon structure in which a special gas is delivered to the balloon at the end of the catheter.  The balloon is first inflated and then positioned next to the part of the heart to be ablated, in this case, the region surrounding the pulmonary vein, the tubes that connects the lungs to the left atrium. .The pulmonary veins are felt to be the triggers of atrial fibrillation in most patients.  The special gas ungoes a pressure change that results in a large temperature drop, causing the left atrial tissue in contact with the balloon to freeze.   Freezing continues for about 4 minutes and is often repeated one or more times outside each of the four pulmonary veins.  Following the freezing process, it is routine to check for elimination of heart signals from the pulmonary veins.   In some patients, particularly those with persistent atrial fibrillation, atrial fibrillation that does not stop on its own, additional ablation in other regions of the the left atrium may be performed.

Catheter balloon cryoablation represents the first FDA (Food and Drug Administration, the federal agency that approves medical devices) device designed specifically for the treatment of atrial fibrillation.  Previously available catheters had a tip designed for the treatment of heart rhythm problems such as supraventricular tachycardia and ventricular tachycardias.   Since catheter ablation of atrial fibrillation is directed towards preventing electrical signals from coming out of the pulmonary veins, it is necessary to deliver multiple lesions surrounding each of  the pulmonary veins.    The balloon cryoablation is designed to block the electrical signals by freezing the entire region around the pulmonary vein at once.  The FDA approved the cryoablation balloon in December, 2010 based on a pivotal study performed over several years.  In this study there was approximately a 70% freedom from atrial fibrillation and approximately an 80% freedom of symptomatic atrial fibrillation.   As the trial progressed, the success increased further.  While there is no large comparative trial of catheter cryoablation and radiofrequency ablation, a comparison of the only available multicenter trials using these two technologies suggests that the success rate is modestly  higher with catheter cryoablation.

Cryoablation at Stanford

The Stanford Arrhythmia team has a long-history with catheter cryoablation, beginning with its inception and the most recent dlinical trials.  Among the faculty at Stanford currently is one of the co-inventors of catheter cryoablation, resulting in the current technology used for catheter cryoablation used today. The Stanford team was the first to use the standard tip cryoablation catheter on the West coast and has among the greatest experience with its use for supraventricular arrhythmias.

The Stanford Arrhythmia team was one of the centers involved in the pivotal multicenter trial leading to the FDA approval of the balloon catheter cryoablation system.  In addition it was one of the centers allowed to use the technology prior to the  FDA approval as part of the Continued Access Protocol.  Among the faculty at Stanford is one of the approximately 10 trainers for physicians learning the technique after FDA approval.

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