Rowie Harper’s recovery began the way all great comebacks do: one small, painful step at a time.

The ICD was implanted three days after the cardiac arrest—a small device under the skin near her collarbone, wired to her heart, ready to shock it back into rhythm if the dangerous arrhythmia returned.

She woke from surgery groggy, Jordan’s hand in hers, his eyes red from another sleepless night.

“Hey,” he whispered, kissing her forehead. “Welcome ...