Cryoablation refers to a technology that uses a cold stimulus to alter certain heart muscle cells so that they can no longer produce or transmit an electrical stimulus. The technique is an alternative to heat-based radiofrequency ablation and, like the latter, represents a minimally invasive method of ablating cardiac muscle cells in the right or left atrium to treat recurrent atrial fibrillation.
What is cryoablation?
Cryoablation is a cold technique used to treat cardiac arrhythmia, particularly recurrent atrial fibrillation. It is an alternative to radiofrequency ablation, in which specific areas of cells in the right or left atrium are obliterated with heat via cardiac catheterization. It is also a minimally invasive procedure based on a cardiac catheter that is advanced into the right atrium via appropriate veins, usually starting in the groin. The left atrium is accessed via a puncture of the atrial septum. The cell areas responsible for generating the arrhythmia are precooled through the tip of the cryoablation catheter and then permanently electrically inactivated at temperatures as low as below minus 75 degrees Celsius. They can subsequently neither generate nor transmit electrical impulses. The cells are only changed in their electrophysical properties, i.e. they do not die completely. Cryoablation is largely painless. Ablation using a cryoballoon catheter can be considered a variant of ablation using a cryoablation catheter. The technique is used to electrically isolate the pulmonary veins in the left atrium, which play a major role in recurrent atrial fibrillation by transmitting uncoordinated electrical impulses.
Function, Effect, and Objectives
In addition to targeted obliteration of benign and malignant tumors, the main application of cryoablation is in the treatment of recurrent atrial fibrillation. The procedure can be performed as an alternative to radiofrequency ablation. Scientific studies have shown that atrial fibrillation is mainly caused by muscle cells of the pulmonary veins opening into the left atrium. Therefore, one of the main goals of cryoablation is to electrically isolate the pulmonary veins from the left atrium so that the uncoordinated electrical signals from the atria can no longer be transmitted. The cryoablation catheter is advanced into the right atrium via a suitable vein, and after puncturing the atrial septum, it can be placed in the left atrium near the junctions of the pulmonary veins. First, the tissue to be ablated is precooled and the physician performing the procedure can check electrophysiologically whether the subsequently planned ablation would be target-oriented and whether there are no unintended side effects or complications. Conversely, this means that cryoablation can be stopped after the electrical check and the precooled cells recover and remain functional. Thus, cryoablation provides additional safety because of the verifiability of the effect even before the actual irreversible ablation. This is particularly important when tissue close to the AV node in the right atrium must be ablated. The ablation itself consists of an extraordinary cold stimulus transmitted from the catheter tip to the surrounding myocardial cells. The cells treated in this way irreversibly lose their ability to generate or transmit electrical impulses themselves. The cryoablation catheter can be used in the left as well as the right atrium. As an alternative to the cryoablation catheter, the cryoballoon catheter has been developed for the treatment of electrical pulmonary vein isolation only. At the anterior end of the cryoballoon catheter, a tiny balloon can be filled with gaseous coolant. The actual cold stimulus to obliterate the adjacent tissue is created by evaporation of the coolant. The catheter is placed so that the tiny balloon successively closes the entrances of the four pulmonary veins in the left atrium as completely as possible in order to achieve electrical isolation of the veins by inactivating the surrounding cardiac muscle cells. It is still possible to check during the treatment whether the isolation of the pulmonary veins was successful.The cryoballoon procedure is somewhat simpler and safer to use than ablation with the cryoablation catheter, so that the technique can also be used by hospitals that do not have a differentiated cardiac center. The principle of action of cryoablation has been used in open heart surgery for decades. Only minimally invasive methods are relatively new.
Risks, side effects, and hazards
One of the main problems after cryoablation to treat atrial fibrillation is the recurrence of cardiac arrhythmia, which can usually be resolved by re-ablation once or twice. But even then, the success rate is only 70 to 80 percent. Success is considered to be a period of two years in which no recurrent atrial fibrillation has occurred. After cryoballoon treatment, only one or two of the four pulmonary veins may be reconnected electrically, which can be taken into account when re-ablation may become necessary. The risk that ablation of myocardial cells near the AV node will render the node itself nonfunctional is significantly lower with cryoablation than with radiofrequency ablation, because the possibility of functional testing after pre-cooling of the tissue area largely eliminates this risk. A rare complication is the formation of a blood clot (thrombus) on the catheter, which can become dislodged and, in extreme cases, cause a stroke. To minimize this problem, the patient should be placed under coagulation inhibition prior to the procedure. During electrical isolation of the pulmonary veins, infections can occur in very rare cases. If puncture of the atrial septum is required, bleeding at the puncture site has been reported in very rare cases.
