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Drift is a frequent problem affecting intracoronary (IC) pressure measurements. It is generally assumed that drift occurs early on in the procedure and that the pressure gradient at the coronary ostium, measured at the end of the procedure, equals the drift at the time of physiological assessment in the coronary artery, the peri-procedural drift. A pressure drift of ± 2 mmHg is considered acceptable, while measurements should be repeated for larger pressure offsets. The quadratic stenosis pressure gradient-velocity (ΔP-v) relationship can be derived from combined pressure and flow velocity measurements during the response to a hyperemic stimulus. Since pressure gradient must be zero at no flow, the zero-flow intercept of this curve reveals peri-procedural drift. We hypothesized that post-procedural drift does not correspond to peri-procedural drift.
In 70 patients, we analyzed 120 IC pressure and flow velocity tracings obtained in reference, stenotic and stented vessels during the response to a bolus of adenosine. Corresponding ΔP-v relationships and their intercepts were derived. Residual pressure gradient at the ostium was measured 89 times.
Peri- and post-procedural drift did not match in 42% of the cases. Post-procedural drift exceeded the ±2 mmHg range for 64 ostium measurements (72%), which were associated with 87 IC measurements (73%). However, peri-procedural drift was within the acceptable range for 30 of those IC tracings (34%). Conversely, peri-procedural drift exceeded ±2 mmHg in 20 (61%) of the 33 IC measurements with acceptable drift at the ostium. Hence, for 17% of the tracings, unacceptable drift during the physiological appraisal was not noticeable at the ostium.
Post-procedural drift at the coronary ostium rarely matches peri-procedural drift. Mechanical stresses on the pressure sensor during the procedure are the likely culprit. Drift correction of individual IC tracings based on the intercept of the ΔP-v relationship can avoid inadvertent diagnostic misclassification due to unrecognized peri-procedural drift, and reduce repeat IC assessments, thereby lowering procedural time, cost, and patient discomfort.
IMAGING: FFR and Physiologic Lesion Assessment