A medical device includes a catheter shaft extending along a longitudinal axis and having a shaft lumen. A balloon includes a proximal balloon end coupled to the catheter shaft, an interior in fluid communication with the shaft lumen, and a distal balloon end. A lead wire extends from a proximal wire end through the shaft lumen and the interior to a distal wire end. The lead wire includes a stepped portion between a proximal wire surface and a distal wire surface. The distal balloon end is axially fixed to the proximal wire surface. The proximal wire surface is narrower than the distal wire surface. Other embodiments are described and claimed.