Principios de Radiofrecuencia 150-101313 Rev 02

Principios de RF Producción de lesiones por RF Principios electrofisiológicos Factores que afectan la generación y pérdidad de calor Factores que afectan la medida y forma de la lesión 150-101313 Rev 02

Producción de las lesiones por RF Similar a la electrocauterización El dispositivo no prduce directamente el flujo de calor Alta frecuencia de corriente alterna Agitación iónica Calentamiento por fricción El tejido cercano al electrodo es fuente de calor RF is similar to Electrocautery. The heat source is a high frequency alternating current which creates ionic agitation in the area surrounding the electrode. This creates heat as a result of the friction from the agitation. The tissue immediately adjacent to the electrode then becomes the source of heat. This heat, then, given adequate power and time, will propagate to the surrounding tissues via conduction. 150-101313 Rev 02

Generación del calor Produce muerte del tejido Tres factores Distancia entre los electrodos Intensidad de la corriente de la RF Duración de la aplicación de la corriente de RF Tissue Death Cell death occurs at about 50C Three factors affecting the heating of tissue to the point of cell death are: - Distance from the electrode - RF current intensity (Current/surface area of the electrode) - Duration of the application of RF current. 150-101313 Rev 02

Distancia del electrodo El calentamiento del tejido disminuye con el aumento de la distancia El calor genera variaciones como 1/r4 RF permite lesiones controlables Tissue heating decreases rapidly with distance. There is a finite distance from the electrode, beyond which an equilibrium is reached and the tissue will no longer heat to the point of cell death. (Heat varies as a function of distance. 1/r4, where r is radius.) Because of this, RF lesions are very controllable. The heat will dissipate and encompass the area comprising the electrode. In other words, the lesion size and shape is controlled by the size and shape of the electrode. 150-101313 Rev 02

Relación entre Potencia, Corriente e Impedancia P=I2R (I2=P/R) La potencia y la Impedancia determinan la corriente Corriente adecuada mayor volumen de la lesión por medida de electrodo Corriente muy baja lesión pequeña Power=Current squared times resistance (or impedance) P=I2R Power and impedance determine the amount of current getting to the lesion (I2=P/R). Adequate power and low impedance, will allow for greater current, and thus greater heat generation and maximum lesion volume. On the other hand, if power is low or impedance is high, the current will be low and the heat generation will be low. This will result in the ablation being too small. 150-101313 Rev 02

Intensidad de la corriente de RF, cont. Corriente muy alta y aplicada rápidamente Carbonización, limitación del calentamiento y del flujo de corriente Aumento de la resistencia eléctrica (impedancia) del tejido Menor volumen de la lesion que el deseado Áreas de vaporización del agua dispersas Forma irregular de las lesiones A veces volúmen mas grande del deseado Although adequate current is necessary for maximum lesion volume, if the current is too high and applied too rapidly several things can happen: Charring can occur around the electrode, limiting the current flow and heating. This can result in increased impedance and a smaller lesion volume than desired. There might also be scattered areas of water vaporization (or cavitation). This can result in irregularly shaped lesions or lesions larger than desired. 150-101313 Rev 02

Duración El objetivo es un calentamiento adecuado (sin sobrecalentamiento) en un tiempo adecuado. Se necesita tiempo para alcanzar la máxima medida de la lesión Calentamiento sin carbonización Tiempo para la conducción del calor al tejido circundante In order to create the maximum lesion size adequate heating, without overheating, and adequate time for propagation of the ablation is necessary. 150-101313 Rev 02

Etapas de RFA Calentamiento Calor por fricción Conductivo Conducción sobre tiempo . . . 150-101313 Rev 02

La medida y forma de la lesión depende de: 1. Calor generado 1/(distancia)4 (corriente)2 duración 3. Medida del electrodo: Grandes electrodos y grandes áreas pueden producir grandes lesiones 2. Pérdida de calor Conducción (Difusión del calor) Convección (vascularidad) 4. Configuración del electrodo Determina la forma de la lesión Thermal ablation size and shape depends upon - heat generated for an adequate length of time(which we have just discussed), - heat lost through conduction of heat to surrounding tissues - and heat lost through convection (for example, large or multiple vessels in the area of the ablation can pull heat away from the area) Ablation size and shape also depends upon the size and configuration of the electrodes. The shape of the curved electrodes along with the uninsulated tip of the cannula on the RITA® Device create a spherically-shaped lesion. The RITA System monitors heat generated and heat lost in real time. This given that the electrode size and shape is known, means that ablation size and shape of each lesion is easily predicted with this system. 150-101313 Rev 02

Lesiones predecibles Monitoreo del calor generado y el calor perdido. Monitoreo de temperatura por Termocuplas Inmediato conocimiento de la pérdida de calor vasos >3mm vasos <3mm Chequea las temperaturas al final de la ablación para asegurar la muerte de la celula en la periferia Duración del monitoreo (tiempo) Tiempo en función de la temperatura Predictable lesions are possible with the RITA System, which monitors heat generated and lost via thermocouples at the tip of each of the electrodes. This temperature monitoring allows for real-time measurement of heat lost. Large vessels (>3mm) tend to be what is referred to as a “heat sink” because they continually pull heat away from the ablation area. Smaller vessels (<3mm) tend to create a “heat sink” for a period of time, but are often eventually coagulated and cease to take heat away from the area. Once the ablation is complete and the power is shut off, temperatures can be monitored as an additional predictor of lesion size and shape (ie. temperatures above 50°C after 30 seconds to ensure cell death at the most distant areas of the ablation). The RITA System also allows for monitoring of time to ensure that the area is heated for an adequate amount of time. 150-101313 Rev 02

Lesiones predecibles, cont. Mantener la corriente adecuada Monitoreo del poder entregado y la impedancia Monitoreo de impedancia 35-100 Ohms es un rango razonable >100 Ohms puede indicar carbonización o disecación The RITA System also allows for real-time monitoring of power delivered and impedance. Based on the experience of clinical investigators doing ablations in the liver, 40-70 Ohms tends to be a reasonable range of impedance. Greater than 70 Ohms may indicate charring, dessication, or improper dispersive electrode placement. The continuous monitoring of temperature, time, power and impedance provides all the information needed to predict each lesion’s size and shape. 150-101313 Rev 02

Resúmen Producción de lesiones por RF Factores que afectan a la generación y pérdida de calor Factores que afectan la medida y forma de la lesión In summary, we’ve discussed the history of radiofrequency and how to create radiofrequency lesions. We’ve also covered all the factors affecting heat generation and loss, and factors affecting lesion size and shape. Questions? 150-101313 Rev 02

Referencias Organ, L.W (1976). Electrophysiologic Principios en la realización de lesiones por RF. Appl. Neurophysiol, 39, 69-76. Haag, R. and Cuschieri, A. (1993). Avances recientes en electrocirugía de Altafrecuencia: desarrollo de un sistema automatizado. J R Coll Surg Edinb, 38, 354-364. Burton, C.V. (1976). RF Generación de la lesión. Appl. Neurophysiol, 39, 77-79. Haines, D.E. (1993). Los Biophysics por la ablación del catéter de RF en el corazón: La importancia del monitoreo de la temperatura. PACE, 16, 586-591. 150-101313 Rev 02