Phasic pressure measurements for coronary and valvular interventions using fluid‐filled catheters: Errors, automated correction, and clinical implications

Figures

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  Figure 1. Artifacts when measuring pressure using fluid‐filled catheters. Aortic pressure from a single cardiac cycle contrasting the signal from a 0.014″ pressure wire (red) with a fluid‐filled guide catheter (blue). After matching the tracings for offset, timing, and gain, the fluid‐filled guide catheter still displays “ringing” despite vigorous flushing. These oscillations arise from the fluid‐filled system's acting like a damped harmonic oscillator, and can be corrected with our described technique [Color figure can be viewed at wileyonlinelibrary.com]

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  Figure 2. Progressive correction of fluid‐filled catheter pressure. Matching the raw pressure tracing from a fluid‐filled guide catheter (blue) to a high‐fidelity 0.014″ pressure wire (red) requires a series of corrections. (Upper left) Raw tracings without any correction. Root mean square (RMS) difference in gray equals about 15 mmHg. (Upper right) After correcting the fluid‐filled guide for the average offset, the mean pressures become equal and the RMS difference falls to approximately 5 mmHg. (Middle left) Further correction matches the timing of the two tracings, reducing their RMS difference to 1.6 mmHg. (Middle right) Additionally, the gain can differ between the two pressure transducers, and its correction brings the RMS difference down to 1.5 mmHg in this case. (Lower left) Finally, the oscillatory behavior of the fluid‐filled guide catheter can be described using two parameters (frequency and a unitless damping factor), bringing the RMS difference well below 1 mmHg [Color figure can be viewed at wileyonlinelibrary.com]

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  Figure 3. Sequential improvement in matching fluid‐filled catheter and pressure wire. For 26 coronary lesions from 23 subjects, the root mean square (RMS) difference between aortic pressures measured with a 0.014″ high‐fidelity pressure wire and fluid‐filled guide catheter fell with sequential corrections mirroring the example in Figure 2. Matching the average pressure offset and adjusting for timing provided the largest absolute improvements. However, additional adjustments for differential gain as well as the harmonic oscillator behavior of the fluid‐filled system brought the median RMS well below 1 mmHg. Repeated measures ANOVA detected a systematic difference (p < .001) among corrections, with each paired t test demonstrating a significant reduction in the RMS value (p < .001) even after Bonferroni correction [Color figure can be viewed at wileyonlinelibrary.com]

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  Figure 4. Impact of catheter correction on coronary pressure assessment. Correcting the guide catheter pressure to match the pressure wire improves subsequent measurements in the coronary vessels. Colors are used differently in this figure, since the fully corrected catheter pressure provides the best reference (shown in red here like the wire in Figure 2) and the catheter with only offset correction shown in blue (similar to the partially corrected tracings in Figure 2). Gray rather than red for the pressure wire indicates its distal location, and filled color highlights the pressure difference. As quantified in the main text, whole‐cycle coronary FFR measurements (example on left) demonstrated a smaller impact than diastolic measurements (example on right) when additionally corrected for timing, gain, and oscillations. The example on the left shows a large 0.02 impact on whole‐cycle Pd/Pa (here, FFR since tracing was made during hyperemia) after correcting the aortic pressure, mainly due to timing. The example on the right shows a large 0.03 change in diastolic Pd/Pa after correcting the aortic pressure, mainly due to suppression of oscillations that shift the apparent onset of diastole…