A catheter includes an elongate shaft including a proximal portion and a distal portion extending from the proximal portion to a distal opening at a distal end of the shaft. The proximal portion defines a proximal guidewire lumen and has a first outer diameter. The distal portion defines a distal guidewire lumen in communication with the proximal guidewire lumen and has a second outer diameter smaller than the first outer diameter. A pressure sensor is coupled to the proximal portion such that the pressure sensor faces the proximal guidewire lumen. When the catheter is tracked to a treatment site within the vasculature, the pressure sensor is disposed proximal the treatment site, the distal opening is disposed distal to the treatment site, and the distal guidewire lumen fills with blood such that the pressure sensor senses a pressure of the blood at the distal end of the shaft.
