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Coronary wedge pressure varies with systemic blood pressure, which in turn may fluctuate during PCI due to various clinical and procedural factors. The study aims to evaluate the impact of peri-procedural variation in wedge pressure (Pw) on serial measurements of Index of Microvascular Resistance (IMR) in patients undergoing PCI for NSTEACS.
Wedge pressure was measured immediately before and after PCI with St. Jude CertusTM PressureWireTM (St. Paul, Minnesota, USA) during prolonged occlusive intra-coronary balloon inflation. Serial IMR were then derived with Pa x Tmn x (Pd-Pw)/(Pa-Pw) and compared between the following approaches by imputing: 1) numerically the smallest Pw measured (Pwm) overall; 2) the smallest Pwm pre- and post-procedurally for pre and post procedural IMR, respectively; 3) Pw (Pwd) derived from mutiplying Pa at the time of FFR and Tmn determination by the ratio of the overall smallest Pwm/concurrently measured Pa; 4) Pwd from the ratio of pre- and post-procedural Pwm/respective concurrently measured Pa.
50 patients were included for analysis. Overall, 82% were males and the mean age was 65. 78% of the patients presented with NSTEMI, while the rest had UAP. No significant difference was noted in peri-procedural Pwm both numerically (19.9 vs. 20.8 mmHg, p=0.36) and as a ratio to concurrently measured Pa (23.2% vs. 23.5%, p=0.75). Pwm, particularly when corrected for Pa, is highly reproducible on repeated measures (correlation coefficient: 0.979). A significant difference was noted in Pa measured at different stages of the procedures (11.9-13.5mmHg; p<0.001). Consequently, a significant difference in IMR was evident when the absolute Pwm value was used, as compared with when Pwd was used in its derivation (Mean difference: -3.3 and -0.25 for pre and post procedural IMR, respectively; p =0.001 and 0.015, respectively).
Wedge pressure does not change significantly peri-procedurally in patients undergoing PCI for NSTEACS, and is highly reproducible on repeated measures. A single Pw measurement is therefore sufficient in serial estimation of IMR during PCI. Where there is a significant variance in Pa during a PCI however, the measured Pw should be corrected for concurrently measured Pa when IMR is calculated.
IMAGING: FFR and Physiologic Lesion Assessment