(nose) bridge
頞 refers specifically to the bridge of the nose, the bony upper part between the eyes.
頞 combines 安 (possibly phonetic) with 頁 (head), suggesting a part of the head. The exact historical development is uncertain.
The left side 安 looks calm, and the right side 頁 means head or page. Picture a calm face where the bridge of the nose sits prominently between the eyes on the head.
For アツ, imagine pressing on the bridge of your nose and saying 'ats!' as if it's a pressure point: ats -> アツ.