Non‐pulmonary vein foci triggering atrial fibrillation: What is the underlying mechanism of "foci"?. Issue 3 (14th February 2023) - Nakashima, Takashi; Nagase, Masaru; Shibahara, Taro; Ono, Daiju; Yamada, Takehiro; Tanabe, Gen; Suzuki, Keita; Yamaura, Makoto; Ido, Takahisa; Takahashi, Shigekiyo; Aoyama, Takuma