Impact of hydrostatic pressure on fractional flow reserve: in vivo experimental study of anatomical height difference of coronary arteries

Fluid-filled versus sensor-tipped pressure guidewires for FFR and Pd/Pa measurement; PW-COMPARE study

BACKGROUND

Fluid-filled pressure guidewires are unaffected by the previously inevitable hydrostatic pressure gradient (HPG). This study aimed to compare simultaneous pressure measurements with fluid-filled and sensor-tipped pressure guidewires.

METHODS

Fifty patients underwent fractional flow reserve (FFR) and Pd/Pa measurement with a fluid-filled and a sensor-tipped pressure guidewire simultaneously. To assess maneuverability, patients were randomized with respect to which pressure guidewire was used to cross the lesion first. Lateral fluoroscopy was used to estimate height difference between catheter tip and distal wire position (and thus HPG). Agreement between pressure measurements was studied.

RESULTS

Measurements were performed in LM (4% (n = 2)), LAD (44% (n = 22)), LCX (26% (n = 13)), and RCA (26% (n = 13)). Simultaneous pressure measurements showed excellent agreement (mean FFR difference - 0.01 ± 0.03 (r = 0.959, p < 0.001), mean Pd/Pa difference - 0.01 ± 0.04 (r = 0.929, p < 0.001)). FFR was ≤0.80 in 42.6% (n = 20) with fluid-filled FFR measurements versus 46.8% (n = 22) by sensor-tipped FFR measurements. Mean height difference was 15 ± 34 mm, and strongly dependent on the coronary artery (LAD 45 ± 10 mm, LCX -23 ± 16 mm, RCA -13 ± 17 mm). There was a strong correlation between height difference and difference in pressure ratios between sensor-tipped and fluid-filled pressure guidewires (FFR r = -0.850, p < 0.001; Pd/Par = -0.641, p < 0.001). Largest FFR differences were present in the LAD (-0.04 ± 0.02). After HPG correction, mean difference between HPG-corrected sensor-tipped FFR and fluid-filled FFR was 0.00 ± 0.02, mean Pd/Pa difference was 0.01 ± 0.03.

CONCLUSIONS

This study shows excellent overall correlation between FFR and Pd/Pa measurements with both pressure guidewires. Differences measured with fluid-filled and sensor-tipped pressure guidewires are vessel-specific and attributable to hydrostatic pressure gradients (NCT04802681).

Potential effects of the hydrostatic pressure gradient on hyperemic and nonhyperemic pressure ratios

When measuring hyperemic and nonhyperemic pressure ratios with traditional sensor-tipped wires, the inevitable hydrostatic pressure gradient (HPG) may influence treatment decisions. This study aimed to simulate and analyze the effect of a hydrostatic pressure gradient on different indices of functional lesion severity. A hypothetical Pd-Pa height difference and subsequent hydrostatic pressure gradient based on previous literature was applied to the pressure measurements from the CONTRAST study. The effect on three indices of functional lesion severity (FFR, Pd/Pa, and dPR) was assessed and possible reclassifications in functional significance by the different indices were analyzed. In 602 pressure tracings, simulated hydrostatic pressure gradients led to an absolute change in Pd of 3.18 ± 1.30 mmHg, resulting in an overall increase in FFR, Pd/Pa, and dPR of 0.02 ± 0.04 for all indices (P = 0.69). Reclassification due to the hydrostatic pressure gradient when using dichotomous cutoff values occurred in 13.4, 22.3, and 20.6% for FFR, Pd/Pa, and dPR, respectively. The effect of hydrostatic pressure gradient correction differed among the coronary arteries and was most pronounced in the left anterior descending. When considering the gray zone for the different functional indices, the hydrostatic pressure gradient resulted in reclassification in only one patient out of the complete patient population (1/602; 0.17%). The hydrostatic pressure gradient can influence functional lesion assessment when using dichotomous cutoff values. When taking the gray zone into account, its effect is limited.NEW & NOTEWORTHY This study systematically simulated the effect of hydrostatic pressure gradients (HPG) on real-world hyperemic and nonhyperemic pressure ratios, showing correction for HPG leads to reclassification in functional significance from 13.4 to 22.3% for different functional indices. This was most pronounced in nonhyperemic pressure ratios. A new pressure guidewire (Wirecath) is unaffected by HPG. The ongoing PW-COMPARE study (NCT04802681) prospectively analyzes the magnitude and importance of HPG by simultaneous FFR measurements.

Impact of height difference between coronary ostium and location of intracoronary pressure sensor on fractional flow reserve measurements

BACKGROUND

During fractional flow reserve (FFR) measurements, distal coronary pressure (Pd) can be influenced by hydrostatic pressure changes resulting from the height difference (HD) between the coronary ostium and the location of the distal pressure sensor.

AIMS

We investigated the effect of aortocoronary HD on the FFR measurements in each coronary artery.

METHODS

In this retrospective cohort study, we analyzed 257 patients who underwent FFR measurements and coronary computed tomography (CCTA) within a year. Using CCTA, we measured HD as the vertical distance between the coronary ostium and a matched point of the distal coronary pressure sensor identified on coronary angiography.

RESULTS

The location of the Pd sensor was higher than the coronary ostium in the left anterior descending artery (LAD) (-4.64 ± 1.15 cm) and lower than the coronary ostium in the left circumflex artery (LCX) (2.54 ± 1.05 cm) and right coronary artery (RCA) (2.03 ± 1.28 cm). The corrected FFR values by HD were higher in the LAD (0.78 ± 0.09 to 0.82 ± 0.09, P<0.01) and lower in the LCX and RCA than the original FFR values (0.87 ± 0.07 to 0.85 ± 0.08, P<0.01; 0.87 ± 0.10 to 0.86 ± 0.10, P<0.01, respectively). Using an FFR cut-off value of 0.8, the concordance rates between the FFR and corrected FFR values were 77.8%, 95.2%, and 100% in the LAD, LCX, and RCA, respectively.

CONCLUSION

HD between the coronary ostium and the distal coronary pressure sensor may affect FFR measurements and FFR-guided treatment decisions for coronary artery disease.

Coronary Microvascular Vasodilatory Function: Related Clinical Features and Differences According to the Different Coronary Arteries and Types of Coronary Spasm

Background: In the clinical setting; the microvascular vasodilatory function test (MVFT) with a pressure wire has been used in ischaemia patients with non-obstructive coronary arteries (INOCA), including vasospastic angina (VSA) and microvascular angina (MVA). The exact factors that affect the microvascular vasodilatory function (MVF) in such patients are still unknown. We aimed to identify the factors, including clinical parameters and lesion characteristics, affecting the MVF in such patients. Methods: A total of 53 patients who underwent coronary angiography, spasm provocation tests (SPTs) and MVFTs were enrolled. In the MVFT, the coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) were measured. Of the 53 patients, MVFT data in the left anterior descending coronary artery (LAD) were obtained from 49 patients, and the clinical parameters were checked in all of them. Based on the results of the SPT, coronary spasms were divided into focal spasm, diffuse spasm, and microvascular spasm (MVS). To assess the lesion characteristics influencing MVF, MVFT data were compared according to the types of coronary spasm and coronary vessels in 73 vessels of the 53 patients. Results: In 49 patients who underwent the MVFT in the LAD, the IMR was higher in active smokers (n = 7) than in former smokers (n = 15) and never smokers (n = 27, p < 0.01). In the 73 coronary arteries in this study, the type of coronary spasm did not correlate with the CFR or IMR, whereas a higher IMR were more frequently observed in cases of focal spasm than in cases of diffuse spasm (p = 0.03). In addition, the IMR was higher in the right coronary artery (RCA) than in the LAD (p = 0.02). Conclusion: These results indicate that the smoking status affected the MVF in patients with INOCA, suggesting the possibility of improvement in the MVF by smoking cessation in such patients. In addition, in the assessment of MVF, it may be important to take into account which coronary artery or types of coronary spasm are being evaluated.

Mechanisms of gradual pressure drop in angiographically normal left anterior descending and right coronary artery: Insights from wave intensity analysis

BACKGROUND

This study evaluated the mechanism of decline in coronary pressure from the proximal to the distal part of the coronary arteries in the left anterior descending (LAD) versus the right coronary artery (RCA) from the insight of coronary hemodynamics using wave intensity analysis (WIA).

METHODS

Twelve patients with angiographically normal LAD and RCA were prospectively enrolled. Distal coronary pressure, mean aortic pressure, and average peak velocity were measured at 4 different positions: 9, 6, 3, and 0 cm distal from each coronary ostium.

RESULTS

The distal-to-proximal coronary pressure ratio during maximum hyperemia gradually decreased in proportion to the distance from the ostium (0.92±0.03 and 0.98±0.03 at 9 cm distal to the LAD and RCA ostium). WIA showed the dominant forward-traveling compression wave gradually decreased and the backward-traveling suction wave gradually decreased in proportion to the decrease in coronary pressure through the length of the non-diseased LAD but not the RCA.

CONCLUSIONS

The pushing wave and suction wave intensities on WIA were diminished in proportion to the distance from the ostium of the LAD despite the wave intensity not changing across the length of the RCA, which may lead to gradual intracoronary pressure drop in the angiographically normal LAD.

FFR=1.0 flow changes after percutaneous coronary intervention

BACKGROUND

The present study investigated the relationships between physiological indices and increased coronary flow during percutaneous coronary intervention (PCI) using a novel index of "anticipated maximum flow" [AMF; theoretical coronary flow of fractional flow reserve (FFR) = 1]. FFR-guided PCI aims to increase coronary flow, whereas recent studies have reported that PCI does not necessarily increase coronary flow despite improvement in FFR.

METHODS

This retrospective analysis was performed in 71 functionally significant lesions treated with elective PCI. AMF obtained by hyperemic average peak coronary flow velocity (h-APV) divided by FFR would not change after PCI given the constant microvascular resistance, which is the assumption of FFR as a surrogate of coronary flow. We evaluated the relationship between AMF and coronary flow during PCI.

RESULTS

Post-PCI AMF was significantly different from pre-PCI AMF (p = 0.022), which impacted discordance between FFR improvement and change in coronary flow. Coronary flow increase >50% was associated with smaller minimum lumen diameter (p = 0.010), greater diameter stenosis (p = 0.003), lower pre-PCI FFR (p < 0.001), lower pre-PCI coronary flow reserve (p = 0.001), higher pre-PCI hyperemic stenosis resistance (p < 0.001), lower pre-PCI h-APV (p = 0.001), and lower pre-PCI AMF (p = 0.031). Pre-PCI AMF provided significant incremental predictive capability for coronary flow increase >50% when added to the clinical model including pre-PCI FFR.

CONCLUSION

Pre-PCI AMF provided incremental ability to predict increased coronary flow after PCI and impacted the discordance between FFR improvement and increased coronary flow.

Diagnostic performance and limitation of quantitative flow ratio for functional assessment of intermediate coronary stenosis

BACKGROUND

This study aimed to simultaneously investigate diagnostic performance and limitation of quantitative flow reserve (QFR) for assessing functionally significant coronary stenosis, focusing on factors affecting diagnostic accuracy of QFR.

METHODS

This study evaluated 1) QFR diagnostic accuracy compared with fractional flow reserve (FFR) in patients with stable coronary artery disease (Cohort-A, n = 95) and 2) QFR reproducibility for non-culprit lesions (NCLs) assessment between acute and staged (14±5 days later) procedures in patients with ST-segment elevation myocardial infarction (STEMI) (Cohort-B, n = 65). All coronary angiography image acquisition was performed before the introduction of QFR system into our institution.

RESULTS

Cohort-A showed good correlation (r = 0.80, p<0.0001) between QFR and FFR; diagnostic accuracy of QFR for FFR ≤0.80 was 85.2% (sensitivity 80.4%, specificity 91.0%, positive predictive value 91.1%, negative predictive value 80.0%). There were 14 lesions showing discordance between QFR and FFR, which was primarily attributable to inadequate lesion visualization due to vessel overlap/tortuosity and/or insufficient intra-coronary contrast-media injection. In Cohort-B, there was also excellent correlation between acute and staged QFR; classification agreement of acute and staged QFR was 92.3%. Five lesions showed discordance between acute and staged QFR, 4 were due to limited image acquisition and/or high coronary flow velocity at acute phase of STEMI and 1 was borderline ischemia.

CONCLUSIONS

QFR-derived physiological assessment of intermediate coronary stenosis is feasible, even in the acute setting of STEMI. Adjusting some technical factors may further improve the diagnostic performance of QFR.