Biophysics of HPSD ablation
RF ablation lesion formation is a result of thermal injury occurring in the resistive and conductive phases.21 The superficial tissue (~ 1 to 2 mm) is heated at the catheter-tissue interface directly by resistive (ohmic) heating.21 The superficial heated tissue extends the heat passively to deeper tissue layers in a time dependent manner during the conductive phase.24 The standard RF lesion using low to moderate power and relatively long duration is created predominantly by conductive heating [Figure 1A]. In contrast to standard ablation, HPSD ablation creates a larger zone of direct resistive heating of tissue with a shorter temperature decay time. This increases the ratio of resistive to conductive tissue heating with irreversible injury of the resistive endocardial zone and less endocardial sparing [Figure 1B]. The lesion geometry in HPSD ablation is altered due to the change in balance between resistive and conductive heating. The maximal width of a standard ablation lesion is in the subendocardium resulting in a tear-drop shaped lesion (endocardial sparing due to smaller resistive zone). On the other hand, the HPSD ablation lesion width is maximum in the endocardium as well as the subendocardium.21Lesions with HPSD ablation have lesser depth and bigger diameter with similar lesion volumes as standard ablation.25Shallower lesions with HPSD ablation may be favorable for thin tissues like the atria. HPSD ablation can potentially reduce collateral damage to neighboring structures like the esophagus due to reduction in the conductive heating phase.