Cardiac Ablation

Cardiac Ablation

Energy flows freely through the ablation catheter because it has a very low resistance. When this energy encounters the higher impedance of human tissue, heat is produced, causing the cells to die. Once the cells are no longer viable, they are unable to propagate electrical signals. RF ablation is a standard treatment for supraventricular tachycardia (SVT) such as atrioventricular nodal reentry tachycardia (AVNRT) and accessory pathways. It is also used in the treatment of ventricular tachycardia (VT) using a specialized cooling system.

An important part of an ablation procedure is catheter performance. An ablation catheter must be maneuverable to access the appropriate location within the chamber and remain stable during RF delivery. Yet, it must still allow the physician to maintain precision and control when making fine, micromovements. This is especially important when ablating near critical structures such as the atrioventricular node (AV node). In addition, the curve geometry of the catheter is important for site access. Certain curve shapes may promote more efficient access to specific anatomical sites.

The cardiac ablation system generates RF energy and then delivers it through the ablation catheter. This system includes an RF generator, an interface box (or switch box), and cables that connect the catheter to the system. Neither the generator nor the interface box are used in the sterile field. They are typically placed near the bedside, though some labs may place them in an adjacent area or control room. There is a sterile cable that connects the ablation catheter to the interface box.

There are two types of RF ablation - temperature control and fluid cooled. Both methods are highly successful in the treatment of supraventricular tachycardia (SVT) and ventricular tachycardia (VT), respectively.

Temperature Controlled RF Ablation
Temperature control RF ablation has been approved in the US since 1995 for the treatment of SVT. The physician sets a target temperature, typically 55-65 degrees Celsius, and then the generator automatically adjusts the power (Watts) to achieve and maintain that target temperature. Throughout the ablation, the generator displays data (either on a laptop or through the electrophysiology recording system monitor) on temperature, power, and impedance. The physician can assess tissue contact or loss of contact and verify appropriate heating during the course of the ablation procedure. One key indicator of a successful RF ablation is non-inducibility of the presenting tachyarrhythmia.

Fluid Cooled RF Ablation
Fluid cooled ablation was approved in the US in 1999 for the treatment of VT. This technology uses circulating, room temperature saline to reduce the electrode tip temperature during RF ablation, decreasing the likelihood of an impedance rise. Thus, it allows for the potential of delivering greater total energy. Higher total energy delivery can produce lesions of greater volume and depth which is critical for the treatment of VT as the arrhythmogenic circuits often lie deep within the ventricles and are more difficult to pinpoint to an exact location. Thus deeper and larger lesions enhance the ability to successfully ablate the aberrant tissue.

Room temperature saline is constantly circulated within the catheter tip. The RF generator works in conjunction with a saline pump to deliver the cooling fluid while RF is being delivered to the cardiac tissue. Because the electrode is being cooled continuously and greater overall energy can be delivered, a standard 4 mm tip can successfully create larger lesions.

Boston Scientific provides both temperature and fluid cooled ablation systems approved by the FDA.