Algorithm for Recanalization of Chronic Totally Occluded (CTO) Native Coronary Arteries Through a Diseased or Occluded Saphenous Vein Graft in Post Bypass Patients

Chronic total occlusion (CTO) desobstruction of a native coronary artery in a post coronary artery bypass graft (CABG) patient can be a challenging procedure. In principle, the 3 basic approaches of recanalization of occluded native coronary arteries can be used: antegrade wire escalation (AWE), antegrade dissection re-entry (ADR) and a retrograde technique. On the other hand, a previous implanted saphenous vein graft (SVG) – even when occluded – can be used as a conduit for retrograde access. Moreover, access through a graft might be less complex compared to the use of septal or epicardial collaterals. If the graft is still open or has a tapered stump, this should be considered as a suitable conduit. Literature on recanalization of occluded native coronary arteries trough a diseased or occluded SVG is limited. A flowchart with an algorithm in post CABG patients is proposed and illustrated by 3 clinical cases.


Introduction
About 30 years ago, Kahn and Hartzler performed the first percutaneous coronary intervention (PCI) through a saphenous vein graft (SVG) on a native coronary artery [1]. Although these landmark procedures were done a long time ago and many has changed regarding techniques and available materials, chronic total occlusion (CTO) desobstruction of a native coronary artery in a post coronary artery bypass graft (CABG) patient remains a challenging procedure [2,3].
Recanalization of an occluded coronary artery, by using a retrograde approach has significantly improved procedural success rates [4,5]. The most common retrograde conduits are septal collaterals followed by epicardial collaterals. Diseased or occluded SVGs are also suitable for retrograde access in CABG patients, but literature on these procedures is limited.

Figure 1: General strategy (AWE = antegrade wire escalation, ADR = antegrade dissection re-entry)
In function of the lesion characteristics (ambiguous or non-ambiguous cap, occlusion length and quality of the landing zone) different techniques are applied. AWE is mainly used in short lesions (< 20 mm length) with a non-ambiguous cap. ADR is mainly used in longer lesions ( > 20 mm length) with a non-ambiguous cap and an appropriate landing zone, whereas a retrograde technique is preferred for lesions with an ambiguous cap in the presence of suitable interventional collaterals (septal or epicardial) or graft (both arterial and venous). If present, SVG gain preference above septal and epicardial collaterals because of easier crossability, less tortuosity, larger caliber and less risk of perforation [6].
In case the SVG is occluded, usually the distal segment is visualized by collaterals. In case a retrograde approach is needed, access through the diseased or even occluded SVG is an additional option (Figure 2), especially when the collaterals are poorly developed or non-suitable for crossing with a wire or a microcatheter. If the graft is still open or diseased (with tapered stump), this graft should be considered as a suitable conduit and therefore can be used as for facilitated ADR.

Case series
The first case is a 73-year old male who presented with peri-operative ischemia during transurethral resection of the prostate (TURP). The electrocardiogram (ECG) showed diffuse ST-depression in all leads and ST-elevation in aVR with mildly elevated high-sensitive troponine T (19 ng/L, cut-off < 14). Transthoracic echocardiography (TTE) showed preserved left ventricle function (visual estimation about 60%) with no regional contractility abnormalities.
The patient was known with diabetes mellitus, peripheral arterial disease and coronary artery bypass graft (CABG in 2002) with left internal mammary artery (LIMA) on the 2 nd lateral branch of the circumflex (L2Cx), right internal mammary artery (RIMA) on the left anterior descending artery (LAD) and saphenous venous graft (SVG) originating from the aorta to the right coronary artery (RCA). Coronary angiography showed patency of the LIMA-L2Cx and RIMA-LAD. There was a CTO of the RCA and also a CTO of the SVG to the RCA (duration of occlusion of SVG unknown). There were epicardial collaterals originating from the Cx to the inferolateral (IL) branch from the RCA ( Figure 3A).
Because of the presence of ischemia and preserved contractility of the inferior wall on TTE, CTO desobstruction was planned. Double arterial access was implemented with use of supportive guiding catheters. Contrast injection of the LIMA was performed by 6 French (Fr) IMA guiding catheter through the left radial artery. Contrast injection of the RCA was performed by 7 Fr AR II through the right femoral artery. Because of unsuitable interventional epicardial collaterals from Cx to the IL-branch, we switched from the LIMA to the occluded SVG (the SVG was injected by 6 Fr AL 0.75 guiding catheter).
The first step is to "blindly" wire the SVG towards the native coronary artery (Figure 3B + C) by using a polymer jacket wire and MC. To confirm the wire being in the distal true lumen, visualization of the distal target via collaterals from the other branches is needed. This is confirmed by contrast injection in the donor artery (double access and in selected cases triple access is needed). Here, the SVG is wired using a Pilot 200 (Abbott, US) and Corsair MC (Asahi, Japan). After this, the native coronary artery is wired retrogradely from the SVG. Sometimes the SVG connects with a sharp angle and the use of Supercross 120° (Teleflex, US) or double lumen MC is needed ( Figure 4A). A double lumen catheter is advised if the SVG anastomosis is proximal from the distal cap. In this case, the native RCA was retrogradely wired through the SVG using a Gaia 3 (Asahi, Japan) and Corsair MC (Asahi, Japan).
If this is successful, the next step is retrograde wire escalation (RWE), reverse controlled antegrade and retrograde subintimal tracking (reverse CART) or CART. In this case, reverse CART was used ( Figure 4B). First, balloon insufflation of the RCA was performed over the antegrade wire in the native RCA, followed by wiring of the created space with the retrograde wire. This wire enters the AR II guiding. The retrograde MC is also advanced into the AR II guiding, after which the retrograde wire is exchanged for a RG3 (Asahi, Japan) or R350 (Teleflex, US) wire (externalization) (Figure 4C).

ISSN: 2641-0419
Page 5 of 12 Lesion preparation with antegrade ballooning is performed over the externalized system ( Figure 5A + B).

Figure 5. A + B: After externalization, antegrade lesion preparation (RCA = right coronary artery, SVG = saphenous vein graft)
The final step is to visualize and wire the distal vessel, either through collaterals or through contrast injection with a microcatheter/double lumen side port ( Figure 6A). Once an antegrade system is in place and has reached the distal vessel, the retrograde gear has to be removed to avoid jailing the retrograde wire with a stent. A Corsair MC (Asahi, Japan) and Sion Black (Asahi, Japan) were used to wire the distal portion of the vessel (the anastomosis of the occluded SVG was close to the distal cap). Pre-dilatation was again performed, followed by stenting with drugeluting stents (  TTE showed preserved left ventricle function without regional contractility abnormalities. Because of the unstable angina and preserved contractility of the inferior wall on TTE, CTO desobstruction was planned.
Triple arterial access was implemented. Contrast injection of the LIMA was performed by 6 Fr IMA guiding catheter through the left radial artery. Contrast injection of the left main was performed by 6 Fr EBU 3.75 through the left femoral artery and the occluded SVG was injected by 6 Fr AL 0.75 guiding catheter through the right femoral artery. During the procedure, we switched the EBU 3.75 to a 7 Fr AR II guiding catheter for injection of the native RCA.
Following the same steps in the flowchart, the first step is to "blindly" wire the SVG towards the native coronary artery with visualization of the collaterals (Figure 8A). The next step is to wire the native coronary artery retrogradely through the SVG, here by using Caravel (Asahi, Japan) MC and Gaia 3 (Asahi, Japan) wire ( Figure 8B).  Lesions preparation ( Figure 10A) and stenting of the mid and proximal segment (respectively 3.0 x 46 mm Cre8 Evo, Alvimedica, Italy + 3.0 x 26 mm Cre8 Evo) was performed with restoration of the antegrade blood flow in the RCA (TIMI III flow) ( Figure 10B).

Figure 10A: Lesion preparation. B. Result after stenting.
The third case is a 72-year old male who presented with stable angina. He had a normal ECG without elevated cardiac markers. He was known with CABG (SVG-RCA and LIMA-LAD). TTE showed mildly depressed left ventricle function due to hypokinesia from the inferior wall. Coronary angiography showed a CTO of the RCA with a severely diseased SVG and poor retrograde filling from septal branches (Figure 11). Double arterial access was implemented. Contrast injection of the SVG was performed by 6 Fr AL I guiding catheter through the right radial artery. Contrast injection of the RCA was performed by 7 Fr EBU 3.5 guiding catheter through the right femoral artery. Also following the same steps in the flowchart, the first step is to wire the SVG towards the native coronary artery. To connect the proximal cap with the distal vessel, the technique of facilitated ADR was used. A knuckle wire was used to dissect from the proximal CTO cap of the RCA beyond the graft anastomosis (Figure 12).

Figure 12. Antegrade knuckle wire (ADR = antegrade dissection re-entry)
Re-entry from the subintimal space towards the true lumen was performed using the Stingray LP (Boston Scientific, US) at the distal RCA landing zone (beyond the graft anastomosis, but before the crux) (Figure 13).

Figure 13: Stingray LP (LP = low profile)
The re-entry was facilitated by a 3.0 mm compliant balloon via the SVG in the landing zone of the distal true lumen. This balloon is inflated to maximize the target for re-entry by using the Stingray wire (Boston Scientific, US) (Figure 14).

Discussion
Total coronary arterial bypass grafting (CABG) provides better outcome then internal mammary artery (IMA) in combination with saphenous vein grafts (SVGs) [7]. Nevertheless, CABG with SVGs is still widely applied. SVGs will develop over time more atherosclerosis and will be occluded in 50% of the cases in 10 years' time post CABG [8]. Native coronary arteries also show accelerated atherosclerosis in post CABG patients [9] and therefore new CTOs could originate.
The three conventional techniques of CTO PCI remains the basis, but a retrograde approach through the SVG is suitable. Literature on retrograde CTO recanalization through a SVG is limited [10,11]. More recently, a larger United States (U.S.) registry was published [12].
Dautov et al [10] [12]. The registry showed that the use of SVGs for retrograde crossing was associated with higher rates of procedural success (81% vs. 74%; p = 0.04) and no difference in inhospital major adverse cardiac events (6.4% vs. 4.4%; p = 0.22) in comparison with retrograde CTO PCI through other collaterals. Moreover, they also report that SVGs are used as collateral conduits in 11.7% of the retrograde PCIs, which is less in Europe and Japan (3.9 % to 8.2%).
Post CABG patients represent an important portion of the CTO procedures. In Japan, these number is relatively low (9.7%) [13]. In Europa it is intermediate (17%) [14] and in the United States high (36.5 %) [15].
J-CTO score in post CABG patients is higher, making the procedure more complex. But, it's worth of investment for treating the native coronary arteries because of the poor rate of patency success of SVG on the long term [8]. PCI of SVGs is associated with poor long-term results and higher event rates [16].
The ongoing multicenter and randomized PROCTOR (Percutaneous Coronary Intervention of the native coronary artery versus venous bypass graft in patients with Coronary Artery Bypass graft) study will provide new insights in recanalization of the native coronary artery versus recanalization of the SVG in post CABG patients.

Conclusion
Despite all the different techniques which can be used for CTO desobstruction in post CABG patients, the complexity remains.
Retrograde crossing of a SVG for native CTO PCI is associated with high rates of success, but is challenging. Therefore we propose a flowchart with algorithm for practical guidance.

Declaration of conflict of interest:
No potential conflict of interest was reported by the authors.