Histological slide preparation and staining

For each ablation zone, two tissue specimens were photographed with a high-resolution digital camera. Histological slide preparation was performed by a histopathology specialist (JY). One specimen per ablation zone was fixed in 10% neutral buffered formalin, embedded in paraffin and sliced into 4-μm sections for haematoxylin and eosin (H&E) staining and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assays. The other specimen was embedded in optimal cutting temperature compound (Tissue Tek; Sakura Finetek, Tokyo, Japan), quenched in isopentane and frozen in liquid nitrogen before storage at −80 °C for evaluation of nicotinamide adenine dinucleotide (NADH) diaphorase activity. Trimmed tissue blocks were photographed immediately before slicing the specimen for histology slides.