Baseline characteristics
A total of 138 patients were screened for inclusion. From these, 75 patients were excluded, because of incomplete clinical data (n=12), significant artifacts and pressure-drift in pressure recordings (n=15) and angiographies of insufficient quality (n=36). The final study population consisted of 90 vessels from 63 patients. Clinical, angiographic, and physiological characteristics of the study population are shown in Tables 1 and 2. Most patients were male, had stable symptoms, and the most prevalent risk factors were hypertension and diabetes. The study comprised coronary stenoses of intermediate severity, both angiographically (diameter stenosis (DS%): 46.6 ± 12.8%) and physiologically [median FFR=0.86 (Q1-3, 0.76-0.89)]. 36 vessels (40%) had a positive FFR (<0.80) value.
Table 1
General characteristics of study populationn= 66
Baseline Demographics | |
Age (years) | 66.1±8.8 |
Gender (Male) | 71.2 (47) |
Medical History | |
Prior Myocardial infarction | 33.8 (22) |
Prior PCI | 29.2 (19) |
Hypertension | 84.6 (55) |
Diabetes | 47.7 (31) |
Current Smoker (<=6 Month) | 18.7 (12) |
History of other vascular disease | 2.6 (1) |
Renal Dysfunction (serum creatinine >2.0) | 6.2 (4) |
Clinical presentation | |
Stable symptoms | 56.1 (37) |
Unstable angina | 21.2 (14) |
NSTEMI (>5 days before enrollment) | 3.0 (2) |
STEMI (>5 days before enrollment) | 19.7 (13) |
Numbers are percentages (N) or mean ± standard deviation. |
Table 2
Quantitative coronary angiography analyses of vessels included in studyn=90
Vessel | |
Left anterior descending artery | 53.3 (48) |
Left Circumflex | 21.1 (19) |
Right coronary artery | 14.4 (13) |
Ramus | 4 (4.4) |
Diagonal | 2 (2.2) |
Obtuse marginal | 4 (4.4) |
Stenosis characteristics, 2D-QCA | |
Vessel length (mm) | 72.5 ± 19.1 |
Lesion length (mm) | 17.2 (10.9, 30.5) |
Reference diameter (mm) | 2.9 ± 0.6 |
Minimum lumen diameter (mm) | 1.5 ± 0.5 |
Diameter stenosis (%) | 46.6 ± 12.8 |
Area stenosis (%) | 59.2 ± 16.0 |
Stenosis characteristics, 3D-QCA | |
Reference volume (mm3) | 113.5 (72, 209.3) |
Plaque volume (mm3) | 35.7 (19.4, 75) |
Lumen volume (mm3) | 78.2 (42.9, 115.7) |
Bending Angle (0) | 17.0 (7.5.0, 28.0) |
Indices of coronary physiology | |
iFR | 0.90 (0.84, 0.95) |
FFR | 0.83 (0.76, 0.89) |
Numbers are percentages (N), mean ± standard deviation, or median (quartile 1, quartile 3) |
Correlations of FFR with QFR and anatomical severity of the stenosis
The correlation of FFR with both fixed-QFR [ρ = 0.841, (95% CI: 0.767 to 0.893), p<0.001] and contrast-QFR [ρ = 0.833, (95% CI: 0.755 to 0.887), p<0.001] was strong. These variables scatterplots are provided in Figure 2. Regression analyses identified a linear relationship, with a coefficient of determination (R2) of 0.75 for contrast-QFR, and 0.69 for fixed QFR (p<0.001 for both). The relationship of DS% with FFR, fixed- and contrast QFR is provided in Figure 3. DS% was modestly correlated with FFR [ρ=-0.561, (95% CI: -0.692 to -0.397), p<0.001], fixed-QFR [ρ=-0.657, (95% CI: -0.763 to -0.512), p<0.001] and contrast-QFR [ρ=-0.663, (95% CI:- 0.767 to -0.524), p<0.001].
Diagnostic performance of QFR against FFR
ROC analyses identified 0.78 as the optimal fixed-QFR cut-off against FFR≤0.80, with an area under the ROC curve (c-statistic) of 0.90 (95% CI: 0.86 to 0.97, p<0.001). This 0.78 fixed-QFR cut-off classified correctly 82.2% of total stenoses, with a sensitivity of 83.3% and specificity of 80.6%. The diagnostic performance of contrast-QFR was numerically better, with 0.80 as the optimal contrast-QFR cut-off against FFR≤0.80, and an area under the ROC curve (c-statistic) of 0.92 (95% CI: 0.86 to 0.97, p<0.001). This 0.80 contrast-QFR cut-off classified correctly 83.3% of total stenoses, with a sensitivity of 85.2% and specificity of 80.6%. Figure 4 shows the ROC curves of DS%, fixed-QFR and contrast-QFR against FFR≤0.80. No significant difference between the areas under the ROC fixed- and contrast-QFR curves was documented [difference in c-statistics 0.00 (95% CI: -0.01 to 0.00), p=0.684]. The area under the DS% ROC curve against FFR was significant yet smaller, 0.72 (95% CI: 0.61 to 0.83, p<0.001), and statistically inferior to that of both fixed- and contrast- QFR values.
Agreement of QFR with FFR
Since contrast-QFR is the one that is currently been tested in clinical trials, agreement analyses are only provided for it. Figure 5 provides the continuous agreement between contrast-QFR and FFR. A high concordance between these variables was observed and demonstrated by a Lin´s correlation coefficient of 0.819. Panel A of Figure 5 shows their Passing-Bablok regression line, that revealed constant (A=0.23, 95% CI: 0.22 to 0.33) and proportional (B=0.67, 95% CI: 0.58 to 0.75) differences between the indices. Their Bland-Altman plot (Figure 5, panel B) demonstrated some heteroscedasticity and proportional error, but a very small systematic bias (0.00); yet, significant imprecision on individual basis, as the 95% limits of agreement were wide (-0.15 to 0.16).