A deflection mechanism for selectively inducing a bend in a catheter body includes an elongated deflection wire extending within a deflection lumen of the catheter body and into a handle. A guide track is formed within the handle and a thumb wheel is mounted proximal to the elongated guide track within the handle and supports a pinion gear; the thumb wheel and the pinion gear are adapted to be rotated about a common thumb wheel axis, which extends substantially perpendicular to the longitudinal axis. A rack arm extends obliquely to the longitudinal axis of the handle and includes runners received by the guide track, an attachment point coupling the deflection wire to the rack arm and a linear rack engaging the pinion gear. Rotation of the thumb wheel in a first direction draws the deflection wire proximally through the deflection lumen.