Transstenotic coronary pressure gradient measurement in humans: in vitro and in vivo evaluation of a new pressure monitoring angioplasty guide wire

Abstract

Objectives: The present study was designed to investigate 1) the feasibility and accuracy of coronary pressure measurements with a novel 0.015-in. (0.038 cm) fluid-filled guide wire, and 2) the effect of the guide wire itself on stenosis hemodynamics.

Background: To assess the functional results of coronary angioplasty, measurements of the transstenotic pressure gradient have been advocated. However, this gradient is no longer routinely measured because it is not reliable when determined with the angioplasty catheter.

Methods: A fluid-filled 0.015-in. guide wire to be connected to a conventional pressure transducer was developed. Five wires were tested for their frequency response characteristics and for their accuracy in measuring hydrostatic pressure. In an in vitro model of stenosis (reference diameter 4 mm), the pressure gradient was determined at incremental flow levels for varying stenosis severity with and without a 0.015-in. guide wire through the narrowing. In 37 patients, the transstenotic pressure gradient was measured before and after angioplasty and compared with obstruction area and percent area stenosis as determined by quantitative coronary angiography.

Results: The correlation between the actual pressure and the pressure recorded by the guide wire was excellent (r = 0.98) despite a slight underestimation (-3 +/- 5%). Phasic pressure recordings were precluded by a long time constant of 16 +/- 4 s. The presence of the guide wire produced a significant overestimation (> 20%) of the pressure decrease only in cases of tight stenosis (> 90% area reduction). Furthermore, a theoretic 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 recorded throughout the study in 34 (94%) of 36 patients. The mean pressure gradient decreased from 30 +/- 19 before to 3 +/- 5 mm Hg after angioplasty (p < 0.01). A curvilinear relation was found between the pressure gradient and both percent area stenosis (r2 = 0.67) and obstruction area (r2 = 0.72). A sharp increase in pressure gradient was noted once the stenosis exceeded 75% area reduction.

Conclusions: Mean transstenotic 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 and of immediate postangioplasty results.