Resting Indices of Coronary Lesion Severity: Not Always as Simple as It Seems

Diagnostic performance of CT-derived resting distal to aortic pressure ratio (resting Pd/Pa) vs. CT-derived fractional flow reserve (CT-FFR) in coronary lesion severity assessment

Background

Computed tomography-derived fractional flow reserve (CT-FFR) has emerged as a promising non-invasive substitute for fractional flow reserve (FFR) measurement. Normally, CT-FFR providing functional significance of coronary artery disease (CAD) by using a simplified total coronary resistance index (TCRI) model. Yet the error or discrepancy caused by this simplified model remains unclear.

Methods

A total of 20 consecutive patients with suspected CAD who underwent CTA and invasive FFR measurement were retrospectively analyzed. CT-FFR and CT-(Pd/Pa)_rest values derived from the coronary CTA images. The diagnostic performance of CT-FFR and CT-(Pd/Pa)_rest were evaluated on a per-vessel level using C statistics with invasive FFR<0.80 as the reference standard.

Results

Of the 25 vessels eventually analyzed, the prevalence of functionally significant CAD were 64%. The Youden index of the ROC curve indicated that the best cutoff value of invasive resting Pd/Pa was 0.945 for identifying functionally significant lesions. Sensitivity, specificity, negative predictive value, positive predictive value and accuracy were 85%, 91%, 92%, 83% and 88% for CT-(Pd/Pa)_rest and 85%, 58% 69%, 78% and 72% for CT-FFR. Area under the receiver-operating characteristic curve (AUC) to detect functionally significant stenoses of CT-(Pd/Pa)_rest and CT-FFR were 0.87 and 0.90.

Conclusions

In this study, the results suggest CT-derived resting Pd/Pa has a potential advantage over CT-FFR in triaging patients for revascularization.

Prognostic Value of Resting Distal-to-Aortic Coronary Pressure in Clinical Practice

BACKGROUND

The resting distal-to-aortic coronary pressure ratio (Pd/Pa) is a universally available, hyperemia-free physiological index of coronary stenosis. We investigated clinical outcomes according to resting Pd/Pa versus hyperemic fractional flow reserve (FFR).

METHODS

From the IRIS-FFR (Interventional Cardiology Research Incooperation Society Fractional Flow Reserve) registry, 7014 lesions in 4707 patients with valid resting Pd/Pa and FFR were included in this study. The primary outcome was major adverse cardiac events (MACE; a composite of cardiac death, myocardial infarction, and repeat intervention). The MACE rate was compared among resting Pd/Pa ≤0.92 and FFR ≤0.80. A marginal Cox model accounted for correlated data in patients with multiple lesions.

RESULTS

During a median follow-up of 2.0 years, 223 MACEs occurred. Resting Pd/Pa was an independent predictor for the occurrence of MACE (adjusted hazard ratio [aHR], 1.89 [95% CI, 1.32-2.71]; P=0.001) over clinical and angiographic variables. When resting Pd/Pa and FFR were added into a multivariable model, MACE was no longer significantly associated with resting Pd/Pa (aHR, 1.35 [95% CI, 0.93-1.97]; P=0.12) but remained to be associated with FFR (aHR, 2.34 [95% CI, 1.56-3.54]; P<0.001). Compared with lesions with normal value of resting Pa/Pa and FFR, lesions with abnormal values of either resting Pd/Pa (aHR, 2.12 [95% CI, 1.17-3.84]; P=0.014) or FFR (aHR, 2.32 [95% CI, 1.52-3.55]; P<0.001) or both (aHR, 2.37 [95% CI, 1.57-3.57]; P<0.001) showed a significantly increased risk of the occurrence of MACE.

CONCLUSIONS

Resting Pd/Pa appeared to be a less-robust prognostic index than FFR. Resting Pd/Pa could be used as a prognostic index when hyperemic agents are contraindicated or not easily available. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01366404.

Influence of increased heart rate and aortic pressure on resting indices of functional coronary stenosis severity

Baseline assessment of functional stenosis severity has been proposed as a practical alternative to hyperemic indices. However, intact autoregulation mechanisms may affect intracoronary hemodynamics. The aim of this study was to investigate the effect of changes in aortic pressure (Pa) and heart rate (HR) on baseline coronary hemodynamics and functional stenosis assessment. In 15 patients (55 ± 3% diameter stenosis) Pa, intracoronary pressure (Pd) and flow velocity were obtained at control, and during atrial pacing at 120 bpm, increased Pa (+30 mmHg) with intravenous phenylephrine (PE), and elevated Pa while pacing at sinus heart rate (PE + sHR). We derived rate pressure product (RPP = systolic Pa × HR), baseline microvascular resistance (BMR = Pd/velocity), and stenosis resistance [BSR = (Pa − Pd)/velocity] as well as whole-cycle Pd/Pa. Tachycardia (120 ± 1 bpm) raised RPP by 74% vs. control. Accordingly, BMR decreased by 27% (p < 0.01) and velocity increased by 36% (p < 0.05), while Pd/Pa decreased by 0.05 ± 0.02 (p < 0.05) and BSR remained similar to control. Raising Pa to 121 ± 3 mmHg (PE) with concomitant reflex bradycardia increased BMR by 26% (p < 0.001) at essentially unchanged RPP and velocity. Consequently, BSR and Pd/Pa were only marginally affected. During PE + sHR, velocity increased by 21% (p < 0.01) attributable to a 46% higher RPP (p < 0.001). However, BMR, BSR, and Pd/Pa remained statistically unaffected. Nonetheless, the interventions tended to increase functional stenosis severity, causing Pd/Pa and BSR of borderline lesions to cross the diagnostic threshold. In conclusion, coronary microvascular adaptation to physiological conditions affecting metabolic demand at rest influences intracoronary hemodynamics, which may lead to altered basal stenosis indices used for clinical decision-making.