Biophysics of radiofrequency ablation using an irrigated electrode

Area of Science:

• Cardiovascular Interventions
• Biophysics of Ablation
• Radiofrequency Energy Application

Background:

• Previous studies suggest irrigated electrodes create larger lesions than non-irrigated ones by preventing interfacial boiling.
• It was hypothesized that maximal myocardial temperature shifts deeper into the myocardium during irrigated ablation.

Purpose of the Study:

• To investigate the biophysics of irrigated ablation by correlating temperatures and impedance with lesion morphology.
• To compare irrigated and non-irrigated ablation modes.
• To evaluate the impact of irrigant rate, composition, temperature, and blood flow velocity.

Main Methods:

• In vitro ablation with and without irrigation using a blood-superfused system, measuring temperatures, impedance, energy, and lesion morphology.
• Assessed normal saline (room temp and iced) and dextrose as irrigants at 20 and 100 cc/min.
• Performed finite element simulations of myocardial temperature, comparing models based on electrode vs. interfacial temperature assumptions.

Main Results:

• Irrigated ablation with saline produced larger lesions and greater energy deposition by delaying impedance rise and preventing coagulum.
• Irrigation at 100 cc/min saline eliminated impedance rise, independent of blood flow; 20 cc/min was flow-dependent.
• Maximal myocardial temperature was consistently within 1 mm of the endocardial surface, contradicting the deeper shift hypothesis.

Conclusions:

• Saline irrigation creates larger lesions by preventing coagulum and impedance rise, though interfacial boiling still occurs without preventing lesion growth.
• Maximal myocardial temperature is superficial (<1 mm from endocardium) during irrigated ablation.
• Higher irrigation rates mitigate blood flow effects; saline is more effective than dextrose, with no added benefit from iced saline.