What occurs with an abrupt rise in impedance during RF ablation?

An abrupt rise in impedance during radiofrequency (RF) ablation indicates that the electrical resistance within the tissue has increased significantly. This change typically signifies the formation of coagulum—most often, a char or coagulated tissue that develops at the tip of the ablation electrode. When the tissue is heated to high temperatures during RF ablation, proteins denature and the tissue begins to coagulate, leading to a buildup of this char.

This charred material can insulate the underlying tissue from the RF energy, causing the impedance to increase. As the coagulum forms, it can prevent effective energy transmission, leading to limited heat delivery to surrounding tissues and potentially affecting the lesion size and the effectiveness of the procedure. This understanding is critical for managing RF ablation procedures and ensuring optimal outcomes.