Quantitative Flow Ratio is Set to Revolutionize the Interventional Cardiology Era, But are we there yet?
- 1. Shaikh Zayed Hospital, Pakistan
- 2. University of health and sciences, Pakistan
- 3. Lahore medical and dental college, Pakistan
Citation
Tariq MA, Nasir U, Ameer A (2018) Quantitative Flow Ratio is Set to Revolutionize the Interventional Cardiology Era, But are we there yet? J Cardiol Clin Res 6(3): 1135.
INTRODUCTION
Quantitative flow ratio is the technique to assess the degree of ischemia in a coronary vessel and derive the fractional flow reserve (FFR) without the conventional use of a pressure wire or induction of hyperemia. We believe that this technique advances the field forward by using 3D reconstruction of the entire coronary tree and using computer generated automatic lumped modeling for the calculation of QFR. Statistics reported on the comparison of invasive fractional flow reserve (FFR) and the newly introduced QFR are exceedingly high for a new diagnostic tool. However, there are still a few hurdles in the way. It has been a matter of long debate, whether QFR could be as sensitive and specific as the invasive FFR in patients with acute coronary syndrome (ACS). Recently, the agreement is that non culprit segments could be reliably assessed by invasive FFR. Nevertheless, Gaur’s et al [1] reported in a STEMI population that a comparable approach to QFR, which is FFRct, failed to achieve clinically meaningful sensitivities and specificities and hence, the study did not support the use of FFRct (QFR) in the post-STEMI setting. The discrepancy in the measurement may be attributed to the volume-to-mass ratio of the vessel in the post-STEMI setting and so the vessels with lowest volume-to-mass ratio <49 mm3 /g showed a poor diagnostic performance [1]. Briefly, after an episode of a STEMI, the coronary vessel undergoes a reduction in the size and decrease in the microvasculatory vasodilator response [2]. This is comparable to the invasive FFR in which, hyperemia is induced by the nitroglycerine prior to the procedure leading to an epicardial vasodilation and providing improved diagnostic accuracies [3].
Given, there are really few studies done which do not support the use of QFR in a setting of ACS patients still raises the question regarding the reliability of the test and hence it would be immature to use the test in a real clinical setting.
Below is a Table showing the recent studies done in patients with acute coronary syndrome to evaluate the diagnostic accuracies of FFR and QFR.
Table: Studies in support of the test.
First Author | Year | Index | Study Objective | Clinical setting | N, total | N, ACS Subjects |
Main findings |
Indolfi et al [3] | 2015 | FFR/iFR | iFR vs FFR comparison in ACS vs Stable patients | UA, STEMI, NSTEMI, Stable |
82 | 53 | Diagnostic accuracy was 79.5% in ACS and 84.4% in stable, p=0.497 |
Engstrom et al [4] |
2015 | FFR | PCI in IRA vs FFR guided revascularization in non-IRCA | STEMI | 627 | 627 | Significant risk reduction by FFR guided revascularization in the future events. |
Arena et al [5] |
2017 | FFR | FFR guided risk stratification in NSTEMI patients referred for invasive management. | NSTEMI | 2728 | 150 | FFR a reliable predictor for long term cardiovascular outcome among NSTEMI patients undergoing cardiac catheterization |
Thim et al [6] | 2017 | FFR/iFR | Follow-up FFR vs iFR comparison among patients with recent STEMI. Median follow-up: 16 days | STEMI | 157 | 157 | Overall Classification agreement was 84% between follow-up FFR and iFR. |
Smits et al [7] | 2017 | FFR | PCI in IRA vs FFR guided revascularization in non-IRCA | STEMI | 885 | 885 | Significant risk reduction by FFR in nonIRCA with composite c a r d i o v a s c u l a r outcome. |
Studies that do not support the test: | |||||||
Gaur et al [1] | 2016 | FFR/FFRct | FFR vs FFRct comparison 1 month after STEMI in patients with multivessel disease | STEMI | 124 | 124 | Diagnostic accuracy depends on volume to mass ratio with 83% in upper tertile and 56% in lower tertile range. Not reliable in STEMI patients. |
Hoeven et al [8] | 2017 | FFR/iFR | FFR vs iFR comparison among patients with acute STEMI and after 1 month in non-culprit vessels. | STEMI | 43 | 43 | Difference between baseline and follow up values was 23.3% for FFR vs 11.6% for iFR |