An Implantable X-Ray-Based Blood Pressure Microsensor for Coronary In-Stent Restenosis Surveillance and Prevention

Coronary artery disease is a leading cause of mortality in the U.S. and percutaneous coronary intervention with stent placement is a common treatment. Stents often fail through coronary in-stent restenosis. Periodically monitoring restenosis could help alert the physician of any problems earlier, reduce myocardial reinfarctions, and improve outcomes. Currently, there are no inexpensive and noninvasive techniques to monitor stent patency. We describe an X-ray-addressable blood pressure (X-BP) microsensor. The X-BP has a column of radio-opaque liquid that changes its length with blood pressure. The X-BP allows for the noninvasive evaluation of the pressure drop across a stent and the fractional flow reserve (FFR) on radiographs. A FFR threshold of 0.75-0.8 is clinically established as the cutoff for the identification of hemodynamically significant stenosis that requires intervention. The X-BP membrane was modeled and the X-ray signal-to-noise ratio of different sensor dimensions was experimentally determined. Based on this data, optimal design parameters were selected. The sensor was prototyped and tested under microscope with radiographs and video fluoroscopy. The sensor has a potential dynamic range of 0-200 mmHg, and can reliably resolve the clinically important pressure drop of 20%-25% across the dynamic range for an FFR value of 0.8-0.75 or less. The X-BP also has a time constant <;32 ms with no appreciable hysteresis. We believe this sensor can be used for periodic screening of coronary in-stent restenosis.