2.3. Instantaneous Wave-Free Ratio Measurements
stenosis
STENOSIS
The intervention strategy of interest was iFR-guided physiologically complete one-stage revascularization, in which the virtual PCI planning of non-culprit lesions and the intervention itself were performed in one stage directly following treatment of the culprit lesion and other critical stenosis of more than ninety percent (iFR is an invasive diagnostic tool produced by Philips, with co-registration tools available via SyncVision software (version 4.1.0.5, Philips Volcano, Zaventem, Belgium). In iFR technology, a wire-based pressure transducer measures the aortic and coronary pressures distal to the stenosis in an isolated period during diastole when the relationship between pressure and flow is linear and constant. iFR is subsequently calculated. After the distal point iFR is calculated based on five heartbeats, the pullback co-registration with the last angiogram is obtained. During pullback, a pressure wire is slowly withdrawn under fluoroscopic control to the tip of the guiding catheter, measuring the ratio of every millimeter. Following pullback, the software transposes the ratio results to the results of the last angiogram, allowing the operator to directly observe pressure drops in the coronary artery. This allows virtual PCI planning, which in turn allows the operator to see the final estimated results of distal iFR by placing a virtual stent in the SyncVision software. Patients with an iFR ≤0.89 were considered severely ischemic and were recommended to undergo PCI treatment. The mandatory PCI result evaluation by iFR was performed. In patients with a post-PCI iFR ≤0.89 further PCI optimization was recommended, if feasible. Further optimization feasibility was determined based on information from post-PCI pullback co-registration. The concept of iFR is like that of fractional flow reserve (FFR), but it is easier to perform and provokes less patient discomfort since hyperemic agents are not needed. Moreover, iFR allows PCI planning based on pullback co-registration results as multiple lesions do not interfere with result calculations. In this study, the patients treated using virtual PCI planning by iFR co-registration were assigned to the iFR-guided group.