TRANSSTENOTIC CORONARY PRESSURE-GRADIENT MEASUREMENT IN HUMANS - IN-VITRO AND IN-VIVO EVALUATION OF A NEW PRESSURE MONITORING ANGIOPLASTY GUIDE-WIRE

Objectives. The present study was designed to investigate 1) the feasi bility and accuracy of coronary pressure measurements with a novel 0.0 15-in. (0.038 cm) fluid-filled guide wire, and 2) the effect of the gu ide wire itself on stenosis hemodynamics. Background. To assess the fu nctional results of coronary angioplasty, measurements of the transste notic pressure gradient have been advocated. However, this gradient is no longer routinely measured because it is not reliable when determin ed with the angioplasty catheter. Methods. A fluid-filled 0.015-in. gu ide wire to be connected to a conventional pressure transducer was dev eloped. Five wires were tested for their frequency response characteri stics and for their accuracy in measuring hydrostatic pressure. In an in vitro model of stenosis (reference diameter 4 mm), the pressure gra dient was determined at incremental flow levels for varying stenosis s everity with and without a 0.015-in. guide wire through the narrowing. In 37 patients, the transstenotic pressure gradient was measured befo re and after angioplasty and compared with obstruction area and percen t area stenosis as determined by quantitative coronary angiography. Re sults. The correlation between the actual pressure and the pressure re corded by the guide wire was excellent (r = 0.98) despite a slight und erestimation (-3 +/- 5%). Phasic pressure recordings were precluded by a long time constant of 16 +/- 4 s. The presence of the guide wire pr oduced a significant overestimation (>20%) of the pressure decrease on ly in cases of tight stenosis (>90% area reduction). Furthermore, a th eoretic model based on the fluid dynamic equation predicted that this overestimation was inversely proportional to the reference diameter of the vessel, yet was only slightly influenced by the flow. The lesion was crossed in all but one patient (97%) and pressure gradient was rec orded throughout the study in 34 (94%) of 36 patients. The mean pressu re gradient decreased from 30 +/- 19 before to 3 +/- 5 mm Hg after ang ioplasty (p < 0.01). A curvilinear relation was found between the pres sure gradient and both percent area stenosis (r2 = 0.67) and obstructi on area (r2 = 0.72). A sharp increase in pressure gradient was noted o nce the stenosis exceeded 75% area reduction. Conclusions. Mean transs tenotic pressure gradients can be easily and reliably recorded with a 0.015-in. fluid-filled guide wire. This ability should facilitate the functional assessment of coronary stenoses of intermediate severity an d of immediate postangioplasty results.