Definition of Saphenous Vein Graft Failure

# Definition of SVG Failure
Saphenous vein graft occlusion is defined as a complete, 100% occlusion of a saphenous vein graft. 
Saphenous vein failure is defined as an occlusion of the vein graft or a 75% or greater stenosis.

# Potential for Pre-Operative SVG Failure
It should be noted that studies of SVGs that are not implanted show that about 1% of veins are already stenosed by > 50% before implantation.

# Percutaneous coronary intervention (PCI) to treat saphenous vein graft failure
There are many different choices to consider when deciding the most appropriate treatment for SVG stenosis, including PTCA, PCI with bare metal or drug-eluting stents, PCI with covered stents, embolic protection devices, debulking/thrombus removal, and surgical revascularization.

## Percutaneous transluminal coronary angioplasty (PTCA)
PTCA has high initial revascularization success rates in the treatment of SVG stenosis.  However, it is also associated with high rates of periprocedural complications, including acute vessel closure secondary to dissection and in-situ thrombosis.  Additional complications include distal embolization and no reflow, which can lead to periprocedural infarction.
In modern interventional cardiology, PTCA is not often used as the sole means of treatment for SVG stenosis.  Instead, stenting has become the cornerstone of treatment, while the use of PTCA has been limited to pre-dilation and post-dilation.

## PCI with bare metal stents (BMS) or drug-eluting stents (DES)
Most current vein graft treatment strategies utilize PCI with stents (BMS or DES), since stenting is a superior treatment when compared to PTCA alone.  As demonstrated in the SAVED (Saphenous Vein De Novo) Trial, the use of stents is associated with higher revascularization success rates, decreased restenosis rates, and improved clinical outcomes when compared to PTCA.  Generally, DES are preferred over BMS, since DES are associated with reduced rates of restenosis and target vessel revascularization.
Despite their higher success rates, stents are not immune to restenosis.  Predictors for restenosis include long stent length, multiple stents, overlapping stents, smaller vessel size, diabetes mellitus, and stenosis at the coronary or aortic anastomosis.

## PCI with covered stents
Theoretically, stents covered with a polymer membrane would have higher success rates than standard BMS and DES.  One would expect covered stents to effectively trap friable atheroma and isolate the graft lumen from the diseased wall, thereby reducing incidence of restenosis, distal embolization, and no reflow in comparison to traditional stents.  However, the RECOVERS (The Randomized Evaluation of polytetrafluoroethylene COVERed stent in Saphenous vein grafts) and STING (STents IN Grafts) trials did not show any advantage in using covered stents when compared to bare metal stents for SVG lesions.

## Embolic protection devices
During PCI of SVGs, atheroembolic debris can be liberated.  This debris contains vasoactive substances that can contribute to no reflow, which can in turn considerably increase the risk of major adverse clinical events (MACE).  Fortunately, embolic protection devices help capture this debris and improve outcomes in PCI for SVG stenosis.  Therefore, it is recommended that these devices should be utilized in the intervention of most SVG lesions.
Currently, the FDA has approved five embolic protection devices in the United States.  Specifically, these devices include one distal occlusion device, three filters, and one proximal occlusion device.
The FDA-approved distal occlusion device is called the PercuSurge Guardwire, which involves inflating a balloon distal to the stenosis to occlude flow, thereby trapping the debris and vasoactive substances and preventing them from flowing downstream.  Due to its small size, it requires little landing zone to deploy.  The SAFER (Saphenous vein graft Angioplasty Free of Emboli Randomized) trial showed that when compared to conventional guidewires, balloon occlusion devices (PercuSurge Guardwire) reduced the rates of infarction and no-reflow after intervention.  Despite these advantages, the PercuSurge Guardwire may not be the best option for all, as some patients may not tolerate the necessary 3-5 minutes of ischemic time associated with this device.  Additionally, it is known to cause both hemodynamic and arrhythmic complications.
Filter devices allow continual distal perfusion while macroscopic emboli are trapped in the filter.  The FIRE (FilterWire EX During Transluminal Intervention of Saphenous Vein Grafts) trial showed that FilterWire may be preferred over PercuSurge Guardwire due to improved clinical outcomes.  While they may reduce ischemic time, filter devices are associated with their own set of potential complications. They are more difficult to deliver than balloon occlusion devices, so their own delivery may lead to distal embolization, and they may not trap microscopic mediators of no reflow.  Additionally, they require a significant landing zone distal to the lesion for the filter placement, which can be problematic for certain distal lesions that do not have enough room.  There have also been case reports of filter entrapment in the graft after the completion of the PCI.
The FDA-approved proximal occlusion device is called the Proxis device.  Some advantages of this decide are that its deployment does not require crossing the stenosis, it provides superior support that is helpful where balloon or stent delivery is difficult, and it provides protected crossing of the lesion, if required.  However, as shown by the PROXIMAL (Proximal Protection During Saphenous Vein Graft Intervention Using the Proxis Embolic Protection System) trial, in terms of overall outcomes, there is no significant difference in death, MI, or target vessel revascularization (TVR) between distal and proximal embolic protection devices.

## Debulking/thrombus removal
Data has not demonstrated a durable clinical benefit associated with debulking/thrombus removal.  However, there are certain situations in which debulking techniques may be useful when treating saphenous vein grafts.  For instance, severely calcified and stenotic lesions can make regular stent insertion especially difficult.  When SVG lesions are too calcified to be crossed by a balloon or adequately dilated prior to stent placement, debulking and thrombus removal can change the compliance of the vessel wall.  In addition, this technique is also useful if a lesion is at the aorto-ostial junction.  Adjunctive stenting leads to better short and long term results.
There are several debulking/thrombus removal techniques, including directional coronary atherectomy, transluminal extraction catheter thrombectomy, rotational atherectomy, and laser atherectomy.
- Directional coronary atherectomy (DCA) uses a circular cutting blade that excises atheroma into a chamber for removal.  It is useful for aorto-ostial lesions and focal lesions in large vessels.  However, due to its bulky nature, it is generally not used in vessels with angulation, tortuosity, or heavy calcification.  CAVEAT II (Coronary Angioplasty Versus Excisional Atherectomy Trial) examined how PTCA and DCA compared in the treatment of patients with coronary artery bypass graft stenoses.  This study demonstrated that DCA was associated with higher initial angiographic success rates and larger acute luminal dimensions in comparison to PTCA.   However, despite these successes, DCA also displayed an increased rate of non-Q wave myocardial infusion and distal embolization than PTCA.  Furthermore, both techniques displayed similar restenosis rates.
- Transluminal extraction catheter (TEC) thrombectomy is designed to remove thrombus from SVGs prior to stenting.  It operates through the use of cutting blades with a rotating catheter and an external suction device.  However, because the TEC Best trial showed no benefit of TEC prior to the stenting of SVGs, this technique has fallen out of favor.  Furthermore, TEC is also associated with a significant incidence of distal embolization and no reflow.
- Rotational atherectomy (RA) uses a rotating cutting blade to grind calcified atheroma.  Despite its ability to grind calcification, this method is associated with high rates of no reflow, distal embolization, perforation, and dissection.  Furthermore, this method is contraindicated for lesions located in the body of SVGs or in degenerated vein grafts.
- Laser atherectomy uses monochromatic light energy to disrupt plaques.  Despite this approach's innovation, there is no evidence that this strategy improves outcomes in lesions, and it has been complicated by high rates of dissection and perforation.

## Surgical revascularization
Given increased perioperative mortality, surgical revascularization is not an optimal treatment strategy, as many patients with graft disease are poor surgical candidates.  However, surgery may be required in patients with multi-vessel disease and when PCI fails.
Additionally, reoperation is not strongly encouraged, as it does not provide the same level of revascularization and resolution of angina as the initial procedure.  Furthermore, a LIMA may be jeopardized in a reoperation.

## Making a selection
At the earliest signs of recurrent ischemia, it is important to strongly consider the possibility of a patent but stenosed SVG, so that the graft lesion can be treated before the graft becomes completely occluded.  Prompt treatment is essential, since a graft is lost once it becomes completely occluded.
Regardless of treatment choice, all patients should be given statins and aspirin (begun immediately following CABG), which are effective in the secondary prevention of SVG stenosis.
For most SVG lesions, PCI with stenting appears to be the therapy of choice.  DES are associated with a decreased restenosis rate over BMS, and should be used preferentially if the patient is able to tolerate dual platelet therapy for a minimum of a year.  Furthermore, embolic protection devices should be strongly considered for all SVG lesions, especially those with high risks for distal embolization.  
In cases in which stent delivery and expansion may be difficult due to heavily calcified and stenotic lesions, atherectomy devices, used with stenting, may be considered.  Furthermore, these devices can be useful in lesions that are aorto-ostial.
Zoghbi et al. conducted a study to investigate the role of pretreatment with nitroprusside before SVG intervention.  They studied sixty-four consecutive patients with normal preprocedural cardiac enzymes that underwent SVG PCI, without the use of embolic protection devices.  They found that pretreatment with nitroprusside results in a lower magnitude and frequency of post-procedural cardiac enzyme elevation.  Thus, it is important to consider nitroprusside use.
Finally, while GP IIb/IIIa inhibitors are frequently used in the setting of SVG intervention, their benefit has not been fully evaluated in randomized trials of this lesion subset.

## Other concerns
As with all medical procedures, complications for SVG intervention can occur.  Risk factors for complications include: older graft age (>3-5 years), the presence of thrombus, and diffuse disease.
Although PCI with stenting is effective for focal lesions, there is uncertainty regarding the best treatment for diffusely degenerated SVGs.  In these cases, it is often a better choice to abandon the graft and intervene on the native vessel instead.
As mentioned above, prevention of no reflow should be attempted with embolic protection devices, pretreatment using nitroprusside and the avoidance of high-pressure inflations and unnecessary pre/post-dilation and oversizing.  However, in the event that no reflow develops, it should be aggressively managed with intracoronary vasodilators (i.e. diltiazem, nicardipine, adenosine, and nitroprusside).

## Pathological findings
Images courtesy of Professor Peter Anderson DVM PhD and published with permission  PEIR, University of Alabama at Birmingham, Department of Pathology
- Saphenous vein coronary bypass graft: Gross, natural color, external view of heart with thrombosed veins
- Saphenous vein coronary bypass graft: Thrombosis, Acute: Gross, fixed tissue but well shown cross sections of bypass graft and anastomotic site with thrombosis. 61 yo male, with and acute infarct treated with streptokinase and two days later had bypass. Died 5 days post op. Two veins are thrombosed
- Myocardial Infarct Acute Reflow Type: Gross, fixed tissue but good color. A very enlarged heart with moderate LV dilation and high anterior wall hemorrhagic infarct. Initially treated with streptokinase and two days later had saphenous vein grafts. Both grafts are thrombosed. He died after 5 days