- Finet Law
- Main stem stenting
- guidance of stenting
Left main intervention by PCI has long been a no-go area in interventional cardiology. Probably based on studies from the 1980s with good surgical results as compared to medical therapy and on the presumed impact in case of failure; both acute and during follow-up. Subsequently protected main stem PCI was the start, followed by patients that were deemed inoperable. In the subset of patients with relative or absolute contra indications to bypass surgery, the results were as might have been expected with a negative patient population selection as a bias, not excellent. Many attempts were made in the nineties and thereafter to describe, compare and improve outcomes of main stem stenting, among others by Park et al. Nevertheless outcomes over a longer period were not as good as bypass surgery.
With the development of newer drug eluting stents; the so-called second and third generation and the sub analysis of studies like the Syntax , left main intervention became an accepted treatment mode for many interventional cardiologists. Recently supported by the published results of dedicated randomized trials like the NOBLE and EXCEL. According to the 2014 European Guidelines left main intervention is recommended in isolated left main with a SYNTAX score of less or similar to 22. Albeit that the discussion is not closed yet, since the 3-years long-term follow-up results of NOBLE and EXCEL were not parallel. Today's policy in many centers is a hart team discussion and the restriction to lower Syntax score lesions. Left main lesions are seen in 5–10% of all angiographic procedures whereas the percentage of myocardium perfused by the left main is more than 75% of the total. By implementing the European guidelines the absolute number of left main stenting will be relatively low per center: only up to 5% of all cases performed. In general, the overall opinion is that left main procedures must be performed by experienced operators in experienced centers.
The procedure of left main stenting is basically not different from any other PCI although specific characteristics of the left main should be taken in account. In general a differentiation is made between ostial lesions, shaft and distal bifurcational lesions of the main stem. By the localization itself the SYNTAX score is influenced. The distal bifurcational lesions are more complex and more common, the mid shaft lesion is relatively simple to stent but rather rare. The ostial lesions are frequently calcified in combination with calcifications of the aortic root and difficult to visualize by angiography also the precise delivery of a stent is a challenge. The left main artery has the highest elastic content of all coronary arteries and thus the high change of recoil.
One of the major issues with the main stem is sizing with diameters that vary between 3.5 and 7.5 mm. The size is different from other coronary arteries and finding an appropriate stent size can be hard with the ranges that are available from the manufacturers. Appropriate sizing is of major importance for the immediate and long term outcome of the procedure of left main stenting; undersizing can lead to restenosis and acute and late stent thrombosis while oversizing can cause immediate complications like dissections and on the long run restenosis.
To further asses the left main stem several modalities are available like FFR, QCA, IVUS and OCT. Only FFR has proven to be of help in the decision making with documented better long-term outcomes and has a European guideline class 1 recommendation. However FFR can only determine whether to perform a procedure or to defer it plus it can help to determine if inducible ischemia has disappeared post procedure, FFR does not help to clarify the anatomy or to determine the size of the vessel.
Coronary angiography has strong limitations in visualizing especially the ostium of the left main and due to the two dimensional nature it can be hampered by over projection, this is one of the reasons QCA is not believed to be accurate enough for sizing and next to this with QCA in general an underestimation of the vessel diameter will occur.
IVUS is an elegant technique to asses lumen and wall characteristics due to a deeper penetration; there is a clear advantage over OCT especially of value in large diameter main stem vessels. For the visualization of the ostial part of the left main, IVUS seems superior to OCT as well since no contrast injection is needed, whereas with the use of OCT contrast loss may hamper the visualization of the ostium. For evaluation of the more distal part of the left main OCT is probably as least as good as IVUS.
IVUS is probably most helpful in stent sizing, although there is believed to be a tendency to oversizing. By accurately detecting the beginning and ending of the atherosclerotic plaque proximal and distal landing zones of the stent can be determined. IVUS is very helpful in the determination of the diameter and length of the stents being used. After stenting optimal stent placement and deployment can be checked. For instance stent malapposition stent under-expansion, geographical miss and large by angiography undiscovered stent-edge dissections can be detected.
So after determining the necessity of the procedure with FFR, IVUS seems to be the equipment of choice to interrogate the anatomy and then guide the procedure including optimal stent choice and evaluating the result of the procedure. Of note is that in contrast to FFR hard evidence is lacking for this general believe and statement. However IVUS has shown convincing long term positive outcomes in patients where IVUS is used to perform left main stem PCI through large registries which show long-term mortality benefit.
With all the information obtained from IVUS in the treatment of left main disease and the strong suggestion that the outcome of the procedure can be improved a world wide spread use in this procedure seems obvious. But there is a great variation in the clinical use of the intra vascular imaging as is described in a clinical survey. Whereas in Japan in more than 90% of the cases IVUS is used, this percentage is in experienced European centers around 10%. The explanation is most likely the extra cost in combination with a minimal prolongation of the procedure time. So although IVUS seems to be of added value in left main stenting the penetration rate in interventional centers is apart from Japan low. A simple, less costly and no time consuming methodology might be welcome to help optimizing the results.
In this issue of Cardiovascular Revascularization Medicine a research paper of Rigatelli et al. describe a methodology to improve the outcome of left main stem stenting. The Finet law regulates the fractal geometry of human bifurcation and has the potential to increase the accuracy of stent-sizing. This retrospective study describes the combined use of QCA with the Finet law in the treatment of mainly ostial left main stem lesions. The results show a better outcome when the methodology is applied and a lower long-term mortality with the combined technique. These results are very encouraging with a relatively easy method that is ready and available in almost every catheterization laboratory with no extra costs and minimal prolongation of the procedural time.
As the authors describe there are shortcomings to this study and although I do think the method can be very helpful, a large scale randomized multicenter study versus IVUS should be performed to yield definite answers, but due to the relatively low incidence of the isolated left main and many other factors these studies are not likely to be performed.
My personal idea is that this is an interesting method that can help in better sizing left ostial main stem lesions but that for this moment a more widespread use of IVUS for left main disease should strongly be encouraged and should be standard procedure. The development of a combination device of FFR and IVUS may be the beginning of further improvement of left main interventions and with even more promising sophisticated imaging tools to come in the nearby future.
Cardiovascular Revascularization Medicine, 2018-10-01, Volume 19, Issue 7, Pages 731-732, Copyright © 2018 Elsevier Inc.