Cryoablation: From Techniques to Tips and Tricks

*Bruno Papelbaum, André Sbaraini Brambilla and Bruno Kioshi Kimura Numata*

## **Abstract**

In this chapter, readers will be able to know a better mechanism of lesion formation, the benefits of the technique for specific arrhythmias, practical uses, and tips and tricks on the procedure. The chapter will also contain the first trials that validated the technique showing recent trials comparing cryoablation of atrial fibrillation versus medical treatment. The main idea is to explore how it works for clinical cardiologists and to show electrophysiologists how to use it practically. Readers will see a comparison of cryoablation versus radiofrequency versus laser to decide which one to be used, comparing total procedure time, success rates, and clinical experience.

**Keywords:** cryoablation, mapping, lesion formation, tips and tricks, atrial fibrillation

## **1. Introduction**

Cryoablation is a method of destroying tissue by freezing, and it was first used for cancer treatments by Dr. James Arnott. It can be performed via surgical or percutaneous approaches. In this chapter, the focus will be on catheter ablation for cardiac arrhythmia treatments, which means percutaneous ablation.

Cryoablation causes cellular damage, death, and tissue necrosis with direct injury to cells and indirect mechanisms. Tissue cooling forms ice crystals in the extracellular space, leading to hypertonicity of this space, osmotic tension taking water from inside the cells, and dehydrating them. The intracellular membrane is altered and damage to cytoplasmic enzymes occurs but warming still can reverse this process.

When the cooling process occurs rapidly, there is no time for cellular dehydration, and free water is trapped within cells during freezing. In this scenario, there is intracellular crystal formation, which is a stage just before cellular death.

During thawing, melting ice within the extracellular space results in cell swelling and the influx of free water into the intracellular space can result in ice crystal growth, which is maximized at −20° to −25°C [1].

The rapid expansion of nitric oxide causes a decrease in the temperature of the gas (Joule–Thompson effect), which is rapidly transferred by convection and conduction to the metallic walls of the cryoprobe. The cryoprobe consists of the hollow shaft, closed electrode tip, and integrated thermocouple for the distal temperature recording. The refrigerated fluid is delivered under high pressure to the distal electrode after the fluid goes through the tip, cooling occurs to −55 to −60°C and gas is aspirated through a separate return lumen. There is also the cryoablation balloon, specific for atrial fibrillation ablation with pulmonary veins isolation [2].

By 12 weeks, small full-thickness lesions disrupt local cellularity but preserve scaffolding. Damaged cells in the center are surrounded by fibrotic scar tissue.

The advantages of cryoablation over radiofrequency (RF) are the ability to monitor the ablation zone in real-time, less painful since cooling of tissues and nerves provide an anesthetic effect, low risk of thrombus formation, and ease of use, but care must be taken when performing right pulmonary vein isolation because phrenic nerve palsy may occur. Studies have found rates ranging from 3.5% to 10% of phrenic nerve injury with most cases being transient [3].

RF uses alternating current to produce electromagnetic energy at high frequency when it passes through the small probe, gives high density, the tissue is heated directly by a resistive effect and deeper tissues are heated by conduction. Tissue within 2–3 mm from the probe is heated to 50°C–60°C, leading to coagulation and permanent cell destruction, damaging the sarcoplasmic reticulum, and irreversibly


*Adapted from Recent Advances in Lesion Formation for Catheter Ablation of Atrial Fibrillation Circ Arrhythm Electrophysiol. 2016;9:e003299. Different energy sources and characteristics of lesion formation, areas of application, possible complications, and clinical experience.*

#### **Table 1.**

*Energy sources compared.*

#### *Cryoablation: From Techniques to Tips and Tricks DOI: http://dx.doi.org/10.5772/intechopen.105861*

disrupting electrophysiological properties. Energy is dissipated by the convection of blood. Later, tissue is replaced by fibrin and collagen scar, and weeks more, an 8–10 mm scar remains.

Laser is another energy source recently available for cardiac ablation. It produces high-energy optical waves via an optical coupling fiber and radiating fiber tip. Power, time, and energy vary from 30 to 80W, 60–180 seconds, and from 1.5 to 9 kilojoules, respectively. Ablation occurs through controlled dielectric heating. Spectroscopic absorption of electromagnetic frequencies is converted into vibrational kinetic energy of water molecules manifested as direct heat, indirect lesions by shock waves, and blast effects that disturb myocyte elasticity. The light beam is collimated, heats the tissue without dispersion and lines are well-demarcated. Lesion length is between 2 and 5 cm, with a depth of 4 mm, and deeper lesions occur with heat conduction. At high power, laser energy causes protein denaturation and coagulation, leading to membrane destruction and loss of water. Experimentally, 30W for 180 seconds or 50W for 60 seconds can create lesions 5–7 mm deep. Excess heat can cause craters, and duration beyond 60–80 seconds, risk of perforation. Advantages are long uniform lesions during a single application with low temperature (50°C), the reduced area of ablated tissue preserves contractility, reduces the risk of thromboembolism, and minimizes perforation.

Choosing energy source must be done according to physician experience, availability of consoles, location of arrhythmias, and success rates of the technique based on multiple trials (**Table 1**).
