This last week, the 1st week of February 2021, a number of interesting papers related to QFR® were published in the international literature, which I would like to describe briefly in the following paragraphs.
QFR® in Review
A very complete review in Future Cardiology about the QFR technology was written and accepted for publication (on-line publication will follow soon) by Dr Enrico Cerrato from the Interventional Cardiology Unit, San Luigi Gonzaga University Hospital, Rivoli, Turino in Italy and multiple Italian and Spanish co-authors with Prof Guanluca Campo from the Cardiovascular Institute, Ferrara University, Italy and Prof Javier Escaned from Hospital Clinico San Carlos, Madrid, Spain as the final authors. They describe the historical developments of the wire-based technologies (FFR & iFR and all Dp/Da derivatives), and observe that indeed the worldwide usage is still very much limited. This has also opened the opportunity to develop alternative techniques, such as the CT-based solutions, such as FFR_CT and others, as well as the angio-based solutions, of which the QFR® is the most extensively validated and published. The authors describe in detail the proposed acquisition guideline and the basic principles of the QFR®.
The next part of the paper emphasizes the various clinical trials, starting with the various FAVOR Trials leading up now to the FAVOR III Outcome Trial with Niels Holm as PI, which should demonstrate that the QFR® is non-inferior to the current gold standard FFR in a population of 2000 patients, as well as the FIRE Trial with G Campo as the PI, in 1500 patients 75 years and older, which should answer the question whether complete revascularization is better than treating the culprit lesion alone. Next, a summary is given of the use of QFR® in specific settings, such as QFR® in ACS, QFR® post-PCI which has demonstrated already that the QFR® post-PCI < 0.90 is an independent predictor of adverse clinical events. Next, QFR® after coronary scaffolding, QFR® in aortic stenosis, QFR® in in-stent stenosis, and QFR® and microcirculatory dysfunction.
The paper concludes with unexplored settings and limitations and with a future perspective. Altogether a great paper, that is really recommended reading.
The healing process in resorbable magnesium scaffolds (RMS)
Actually, a few weeks before, Dr Enrico Cerrato and co-authors from the Interventional Cardiology Unit at the Gonzaga University Hospital, Turino, Italy and other Italian and Spanish sites under the supervision of Dr F Varbella published also a paper in Catheter and Cardiovascular Interventions (doi.org/10.1002/ccd.29397) about the healing process in resorbable magnesium scaffolds (RMS). They followed 44 patients and 49 lesions over a period of 12 months with OCT and QFR®. They found that the mean lumen area decreased significantly over the 12 months from 8.12 mm2 to 7.54 mm2. However, the functional results as determined by the QFR was not affected.
The authors concluded that the RMS implantation in a real-world population leads to significant decrease in mean lumen area without significant functional impairment. But also that two different patterns of RMS resorption were found, which need to be further investigated.
Invasive coronary physiology after stent implantation: another step towards precision medicine
Dr Simone Biscaglia and many famous co-authors under the final supervision by Prof Guanluca Campo from Ferrara University in Italy and Prof Greg Stone from CRF in New York, USA wrote an extensive state-of-the-art Review in JACC Interventions (2021;14:237–46; doi.org/10.1016/j.jcin.2020.10.055) on the available evidence to support the assessment of the physiologic status of the coronary artery immediately post-PCI with the aim to improve patient outcome after the procedure. The lead author has contributed to this field already with the famous Hawkeye trial, where they found in 751 vessels in 602 patients that a QFR® post-PCI value of < 0.89, was associated with a 3-fold increase in risk for vessel oriented composite endpoint in 2 years. Similarly, Dr Kogame in another study found a post-PCI QFR® threshold of 0.91.
The authors of this review paper recognize that over the past 20 years multiple studies have demonstrated the benefit of physiologic measurements post-PCI, but in routine clinical practice, it is hardly used. Pullback techniques may identify stent-related issues, overlooked stenoses and diffuse disease. The authors propose in a central illustration in this paper what the proper workflow should be for the various physiologic indices, whether it is Pd/Pa, FFR, iFR or QFR®, and if an abnormal post-PCI physiologic index value is found, what the possible next step could be, such as post-dilatation, an additional stent, IVUS / OCT investigation, etc. More features from the pull-back data, such as focal or diffuse abnormality, the shape of the curve, etc. may further refine the corrective actions. The authors also see a new evolution of physiology-guided PCI by predicting any abnormalities post-PCI from the pre-PCI results: virtual PCI.
QFR® in patients with severe aortic stenosis undergoing a TAVI procedure
It is known that aortic stenosis (AS) affects the hyperemic response and therefore FFR values that would be measured prior to a TAVI procedure. In order to obtain a proper assessment of the presence and extent of the functional significance of the coronary arteries, the FFR could therefore only reliably be measured post-TAVI. The question therefore was raised by the investigators whether QFR® could bring value in these patients, but then measured prior to the TAVI, and not post-TAVI. Dr Sejr-Hansen and colleagues from the department of Cardiology at Aarhus University Hospital in Denmark published a paper in Catheterization and Cardiovascular Interventions (doi.org/10.1002/ccd.29518) about the application of QFR® in patients with AS undergoing TAVI. This is a retrospective analysis of data from Aarhus hospital, the Imperial College London and the Academic Medical Center in Amsterdam.
They analyzed a total of 28 patients from these three sites; in all patients both FFR and iFR were measured pre- and immediately post-TAVI, while QFR® was measured only pre-TAVI. They found that the diagnostic accuracy of pre-TAVI QFR® with post-TAVI FFR and iFR was 83% and 52%, respectively. Also, looking only at pre-TAVI data, the diagnostic accuracy of the QFR® versus pre-TAVI FFR and pre-TAVI iFR, was 76% and 61%. This is in line with the hypothesis that the FFR measurement is less accurate in the case of severe AS; in addition, the correlation with the iFR remains low, whether measured pre- or post-TAVI.
As a result, the authors concluded, that the pre-TAVI QFR® showed a good diagnostic performance, and therefore could become a wire-free, safe and quick way of evaluating CAD in patients with severe AS undergoing TAVI. This would allow the physician to plan the revascularization based upon QFR® derived from the pre-TAVI coronary angiography
and, if indicated, conduct PCI prior/peri-procedure or at a later staged procedure.
Leiden, February 8, 2021
Johan HC Reiber, PhD
Medis Medical Imaging