What is transcatheter radiofrequency ablation? Could you please introduce the treatment principle? Prof. Liu Shaostian: The medical profession has tried many ablation methods or ablation energy, such as radiofrequency ablation, cryoablation, ultrasound ablation, laser ablation, microwave ablation, etc., but now the most common clinical use is radiofrequency ablation. Transcatheter radiofrequency ablation is to send the standard test and ablation electrode catheter into the heart through the blood vessels, first determine the specific mechanism causing tachycardia through cardiac electrophysiological examination, and then locally release the controlled radiofrequency current to the metal end of the catheter (commonly known as “big head”). The contact between the “big head” and the tissue generates heat, which dehydrates the local myocardial tissue and causes dry necrosis, thus blocking the abnormal electrical activity and achieving the treatment purpose. Radiofrequency ablation is the most commonly used ablation energy for cardiac arrhythmias mainly because of its controllable energy, limited ablation damage, and clear boundaries. For example, a temperature-controlled ablation catheter can produce irreversible dry necrosis of the local myocardium and terminate the tachycardia when the temperature between the distal end and the tissue reaches 55°C. If the mechanism of tachycardia is focal ectopic excitability increase, the site of ablation is localized to where the ectopic excitatory foci are located; the mechanism by which most tachycardias occur is folding back, i.e., the current keeps turning in circles on the loop. If the loop is in the atrium, it causes atrial tachycardia and atrial flutter; if the loop is in the atrioventricular node or involves both atria and ventricles, it can cause atrioventricular node or atrioventricular foldback tachycardia, or what we call supraventricular tachycardia; similarly, a loop in the ventricle can cause ventricular tachycardia. In the case of retrograde tachycardia, ablation involves blocking the retrograde loop and preventing the current from circulating in the loop. The mechanism of atrial and ventricular fibrillation is more complex and in most cases multiple foldback and/or ectopic excitability increases are involved at the same time. Are there different procedures for transcatheter radiofrequency ablation? Prof. Shao-Shen Liu: Yes, it depends on the use of different calibration methods and ablation catheters. On the one hand, transcatheter radiofrequency ablation is performed with different scaling methods, including the traditional two-dimensional scaling method and the three-dimensional scaling method that has been commonly used in the last decade or so. The so-called calibration test is to present the complex electrophysiological information and anatomical structure of the heart in relation to the surgeon, and the operator determines the mechanism of tachycardia on the basis of experience, and cardiac electrophysiological examination is the key to successful transcatheter ablation treatment of tachycardia. Even for the simplest supraventricular tachycardias, if catheter ablation is unsuccessful, the most common reason is a lack of knowledge of the mechanism of rare supraventricular tachycardias, such as Mahaim or PJRT; another common reason for failure is a lack of knowledge of the cardiac anatomical variants associated with the tachycardia. Two-dimensional labeling mostly uses X-rays to determine the anatomic site of the labeling and ablation catheter within the selection, and body surface and intracavitary ECGs are recorded by multidetector cardiac electrophysiology. This approach has a high success rate for guiding ablation of common types of arrhythmias such as supraventricular tachycardia, but for complex arrhythmias, the information provided by two-dimensional scaling is not as detailed and accurate. Three-dimensional scaling can link the electrical activity of different parts of the heart to the three-dimensional anatomical position relationship and present it visually and clearly to the physician. The use of 3-D cardiac specimens can improve the accuracy of complex tachycardia diagnosis, such as understanding whether the mechanism of tachycardia is folding or focal ectopic excitation elevation, and the location of the folding loop and ectopic excitation foci. In addition, three-dimensional speciation can also accurately guide successful catheter ablation because it provides three-dimensional information about the electrical anatomy of the heart, which is particularly suitable for speciation and ablation of complex tachyarrhythmias. On the other hand, catheter technology for radiofrequency ablation has continued to improve. In the early days, the distal electrode length of the ablation catheter was smaller as well as the proximal electrode, and the intraoperative damage was also smaller, but the chances of complete removal of ectopic excitatory foci or foldback loops were also small. Later, the ablation catheter with relatively long distal electrode, commonly known as “big head” catheter, has different specifications such as 3.5 mm, 4 mm and 8 mm, and the first two are more frequently used in clinical practice. In the past 10 years, a cold saline infusion ablation catheter has also been used in clinical practice. This is because the main mechanism of ablation is to use thermal energy to remove the electrical activity of abnormal myocardial tissue. However, sometimes this thermal energy accumulates on the surface of the myocardium, while the deep myocardial areas to be ablated are not sufficiently heated. The cold saline infusion ablation catheter generates local heat while spraying cold saline (in most cases the same saline as room temperature, but “cold saline” relative to body temperature) around the “big head”. This cools the distal end of the ablation catheter and the local myocardial tissue surface, allowing the energy to go deeper and improving the effectiveness of the ablation. The key to successful ablation is not only the ablation energy and temperature, but also the pressure between the distal end of the ablation catheter and the myocardial tissue. Under the condition of certain output energy, the ablation catheter cannot achieve effective ablation if the distal end of the ablation catheter is not well attached to the myocardial tissue and the pressure is too small; if the attachment is too tight and the pressure is too large, the phenomenon of “pop” is likely to occur, increasing the risk of myocardial perforation. The application of pressure ablation catheter can provide the operator with real-time information about the pressure between the distal end of the ablation catheter and the myocardial tissue, which is helpful for the operator to adjust the catheter in time to keep the pressure within a reasonable range as much as possible. The progress of transcatheter radiofrequency ablation is multifaceted. In addition to the continuous improvement and advancement of the calibration technology and ablation catheter technology, our understanding of arrhythmias is also progressing and deepening, and our understanding of the mechanisms of tachycardia is becoming more and more complete and thorough, and the clinical experience of doctors in the calibration and ablation of various tachycardias is also gradually accumulating, so the indications for catheter ablation are slowly becoming broader and broader. The indications for catheter ablation are becoming more and more widespread. What is the difference between transcatheter radiofrequency ablation and normal surgery, and what are the advantages of the former? Prof. Liu Shao-steady: Transcatheter ablation for various tachyarrhythmias is a minimally invasive procedure that involves puncturing a few small openings of about 2 mm in diameter at the root of the patient’s thigh or subclavian area, and sending the test and ablation catheter into the heart via the peripheral vasculature, which has the advantages of small trauma and fast recovery. The disadvantages such as too much trauma and incomplete electrophysiological examination and specimen measurement are now basically not done. Today, the surgical treatment of tachyarrhythmias is basically minimally invasive transcatheter ablation.