Percutaneous coronary intervention in saphenous vein graft disease

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Chapter 25 Percutaneous coronary intervention in saphenous vein graft disease

AZFAR G. ZAMAN, JAGATH. HERATH

KEY POINTS

image Long term outcome of CABG is limited by occlusive atherothrombotic disease of vein grafts in up to 50% of patients after ten years.
image Repeat surgical intervention carries a high risk of morbidity and mortality.
image PCI should be the preferred first route of revascularization in patients with previous CABG.
image Stent placement in vein grafts is associated with a high (up to 20%) risk of distal embolisation and consequent complications.
image Routine use of embolic protection devices significantly reduces procedural complications during vein graft PCI and where anatomy permits, their use is mandatory.
image Three types of embolic protection devices are available: distal occlusion, proximal occlusion and distal filter. The type to use is determined by lesion location in the vein graft.
image The routine use of glycoprotein IIb/IIIa inhibitors is not recommended for vein graft PCI. Some evidence suggests benefit in patients in whom a distal filter device is employed.
image The risk of restenosis with BMS is high (10–20%) and early data with DES show promising results in restenosis reduction.
image There is no benefit in using of PTFE coated stents over BMS.
image There is no evidence for the use of thrombectomy devices in vein graft PCI.
image For vein graft PCI both the radial and femoral access routes can be employed.

INTRODUCTION

Since first implantation of coronary grafts in 1967 the success of venous conduits in relieving myocardial ischaemia has been limited by their temporal attrition. Although internal mammary grafts have unsurpassed long term patency, utilisation is limited by scarcity. The use of gastroepiploic and radial arteries has been shown to be less than optimal.1 Consequently, in spite of declining surgical revascularization rates worldwide, the use of venous grafts seems unlikely to diminish and treatment of symptomatic patients with degenerated venous grafts will remain a problem for interventional cardiologists.

Atherosclerotic disease in vein grafts can be either discrete (focal) or diffuse and degenerative. Most clinical trials forming the evidence base for percutaneous intervention in vein grafts report outcomes in patients with discrete disease. Initial trials demonstrated a high percentage of adverse events. The recognition that these were largely secondary to distal embolisation led to development of protection devices that have revolutionized percutaneous intervention in vein grafts with a significant reduction in periprocedural adverse events.

Vein graft disease progression and its timing

Three interlinked pathological processes – thrombosis, neointimal hyperplasia and atherosclerosis, which are temporally distinct, contribute to vein graft disease.2,3 Awareness of the processes and their timing may help in optimising outcome from intervention.

Vein graft attrition occurring within a month of surgery is almost always due to graft thrombosis and the occlusion rate is 3 to 12% per month. Early thrombosis of vein grafts is caused by the combination of a prothrombotic state and technical factors present at the time of surgery.

Neointimal hyperplasia is defined as the accumulation of smooth muscle cells and extra cellular matrix in the intima and is the main pathological process that occurs one month to one year after graft implantation. It is similar to pathological changes that occur in native coronary arteries after balloon angioplasty.

Atherosclerosis is the main pathological process that contributes to vein graft occlusion one year and beyond after surgery.2 The predisposing factors and the basic process of atheroma development are similar to those documented in native coronary arteries. However, there are a few distinct topographic, temporal, and histological differences in the pathology of vein graft disease.

The distinct morphological difference seen in vein grafts compared to native coronary arteries is that vein graft atheroma is diffuse, concentric, and friable with poorly developed or absent fibrous cap with little calcification. Intravascular ultrasound studies reveal the absence of focal compensatory enlargement (‘Glagov’s law’) of diseased vein graft segments.3,4 Late graft thrombosis triggers recurrent ischaemia and is frequently seen in old degenerating grafts with advanced atherosclerotic disease.5

REVASCULARISATION FOR VEIN GRAFT DISEASE

Redo surgery

Recurrence of anginal symptoms is seen in up to 20% of patients within one year following surgical revascularisation followed by 4% of patients annually during the next 5 years, 19% at 10 years and 31% at 12 years.6

There are limited data comparing percutaneous revascularisation to repeat surgery in patients with angina recurrence. Repeat surgery achieves complete revascularisation in 92% of patients compared to 38% in the percutaneous intervention group. However, in-hospital complications are more common in surgical patients: death (7.3 % vs. 0.3%), Q-wave MI (6.1% vs. 0.9%), and low output syndromes (24% vs. 9%). Both procedures result in equal survival rates at one and six years with equal relief of angina but repeat intervention and/or revascularisation is more frequent in the percutaneous group (64% vs. 8%) at six years.7,8

Given the high morbidity and mortality of re-operation reduced symptomatic benefit as compared to first bypass surgery,8,9 percutaneous revascularisation should be the preferred first route for post surgery angina recurrence.

Percutaneous coronary intervention

Lesion pathology explains the different outcomes in vein grafts when compared to native coronary arteries.

Balloon angioplasty for vein graft disease has moderate procedural success limited by high periprocedural complication rate, high incidence of restenosis (35%) and high repeat revascularisation rate.10,11 Clinical trials show BMS to be superior to balloon angioplasty in vein graft lesions. The use of stents is associated with a high procedural success, superior clinical outcome, and reduced TLR. However, as compared to native vessels the restenosis rate remains high12,13 coupled with higher periprocedural complications.

The high incidence of periprocedural complications is in the guise of myocardial necrosis resulting from distal embolisation. The major advance in vein graft intervention has been the advent of embolic protection devices for which extensive trial evidence exists for reducing complications from embolisation (vide infra).

The significant problems associated with vein graft intervention are:

1. distal embolisation;
2. no reflow; and
3. aggressive restenosis.

The use of DES in native coronary arteries has shown promising results with significant reduction in restenosis rates.14,15 Limited data is available on the long term efficacy of DES in patients with vein graft disease. Most studies confirm a high procedural success rate but there is conflicting data on how DES would affect the clinical outcome. Two nonrandomized trials have shown a trend towards a reduction in MACE at six to nine months follow up.16,17 The use of DES was associated with a lower restenosis rate (10% vs. 26.7%, P=0.03) and TVR (4.9% vs. 23.1%, P <0.01) at six to nine months. However, one study showed similar clinical outcome at 30 days, 60 days and 1 year.18

Diffuse SVG disease

The optimal treatment strategy for diffusely degenerative SVG (grafts >3-years-old, isolated lesion length >20 mm in length or diffusely diseased segment with multiple/sequential stenosis) is challenging and controversial.

Unlike focal graft lesions, diffusely degenerative graft disease with large ulcerated fragile plaques with associated thrombus is associated with a low procedural success, higher complication rates and low long term patency rate.19

Endoluminal reconstruction by stenting of diffuse lesions (‘full metal jacket’) is a possible option and clinical trials reveal a high procedural success for stenting of diffuse lesions. However, it has been associated with a high incidence of death (11.1%) or myocardial infarction (9.4%) and frequent need for repeat angioplasty.20

EMBOLIC PROTECTION DEVICES

Embolic protection devices are catheter-based devices used to capture atherothrombotic debris released during percutaneous vascular interventions and can be divided into three types:

1. distal occlusion;
2. proximal occlusion; and
3. distal filtration.

The first recorded use of these devices was during carotid stenting21 and subsequent studies confirmed their efficacy in reducing the incidence of periprocedural embolic stroke and death. The high risk of periprocedural myocardial infarction and MACE during vein graft intervention led to exploration of embolic protection devices in this setting.

Distal occlusion devices

The distal occlusion devices have a large evidence base with early vein graft intervention studies using the GuardWire (Medtronic AVE, Santa Rosa, California). This is a temporary occlusion-aspiration system with a 2.8 F crossing profile. A guidewire with a central lumen and inflatable balloon is introduced beyond the lesion. The balloon (either 2.5–5 mm or 3–6 mm) is inflated (using saline/contrast solution) to occlude the vessel and thereby prevent antegrade flow. Following stent deployment over the central wire, any debris released is trapped by the inflated balloon and then aspirated through a 5 F monorail aspiration catheter. The balloon is then deflated and antegrade flow restored. The obvious downside of this device is the duration of ischaemia induced by balloon inflation. The advantage (over filter devices) is that the likelihood of debris passing around the device is minimised by the absolute occlusion thereby assuring complete debris removal.

An alternative device is the TriActiv system (Kensey Nash). In contrast to the GuardWire, this device utilises gas to fill the balloon and thus allows rapid inflation and deflation times. In addition there is an active flush and extraction system. In a randomised controlled trial, the TriActiv system was found to be non inferior to the GuardWire and Filter EZ systems.22

Distal filtration devices

The devices with most trial data are EZ-FilterWire (EPI, Boston Scientific), Spider and Microvena Trap (eV3, Minneapolis, Minnesota) and Angioguard (Cordis). The mechanism for all is similar. A non-occlusive filter within its own delivery sheath is delivered distal to the lesion and deployed. Once the sheath is removed the filter is released and assumes the shape of a windsock whose neck is composed of a nitinol loop fixed on its own wire. Following stent deployment, debris is caught in the filter which is then retrieved using a retrieval sheath passed over the wire. The FilterWire and Spider devices are 6 F compatible whilst the Angioguard requires a 7 F guiding catheter.

The major advantage with the filtration devices is flow preservation. One potential disadvantage is that the filter has pores of between 80 to 150 μm and, therefore, may allow debris smaller than 80μm to pass through. However, studies comparing to occlusive devices have failed to show a difference in MACE even though electron microscopy of material aspirated with the GuardWire reveal 50% of particles to be <100μm.23

Proximal occlusion devices

The Proxis (Velocimed, Maple Grove, Minnesota) is the only one of its kind licensed for use at the time of writing. Where the landing zone is inadequate, this type of device is the only one suitable for use. The Proxis is compatible with any guidewire. A sealing balloon is deployed proximal to the lesion and this occludes antegrade flow. Intervention is then performed in an environment of stasis created before the passage of any device whereas with the other products described above, prior stenosis dilation may be necessary before crossing with the device. The obvious advantage of the proximal occlusion device is that any and most importantly, all debris dislodged in the dilation process can be aspirated. The device is 7 F compatible with a maximum balloon size of 5 mm. Predilation balloons and stents are delivered through the Proxis system, deployed and then debris aspirated before balloon deflation and restoration of antegrade flow.

This system also has the advantage of allowing interventions on multisequential lesions, whereas distal devices require multiple catheter exchanges for sequential lesions.

Preliminary data from a non-randomized trial of 40 patients, demonstrated successful deployment in 95%.24 The reported MACE rate of 5% was much lower than that achieved with distal devices but data comparing the two are awaited.

A major limitation of this type of device is that they are contraindicated in ostial and proximal vein graft lesions.

Limitations of embolic protection devices

• The major limitation of distal devices is their requirement for a ‘landing zone’ distal to the lesion. Therefore, lesions within 30 mm of the graft to coronary anastomosis site cannot be safely protected with these devices and a proximal device is indicated.
• Most distal devices are bulky with large crossing profiles and poor torque. In order to cross the lesion, it may be necessary to predilate with consequent risk of embolisation.
• In the presence of subtotal occlusion and poor distal flow, it may be difficult to size the vein graft distal to the lesion. Undersizing the balloon or filter will lead to debris embolising around the occlusive site. Once again, a proximal occlusion device may be better suited under these circumstances.
• Embolisation secondary to incomplete apposition of inflated balloon or filter ring.
• Risk of retrieval device (for filter wires) snagging on stent struts.
• Proximal devices cannot be used in ostial or proximal vein graft lesions. They need a proximal ‘landing zone’ of 15 mm.

Clinical studies

The first such device evaluated in saphenous vein grafts with low thrombus burden was the GuardWire. A registry of 105 patients confirmed safety and reduction of MACE when compared to historical controls and led to the larger, randomized controlled, SAFER study.25 This study excluded patients with acute myocardial infarction or severe left ventricular dysfunction but did include patients with a higher thrombus burden than that in the SAFE registry.

Use of the device confirmed a beneficial effect in reducing 30-day MACE (9.6% vs. 16.5%, P = 0.004) and incidence of no reflow (3% vs. 9%, P = 0.02).

The first registry evaluating FilterWire safety and efficacy excluded high risk patients with acute myocardial infarction or severe left ventricular dysfunction.26 Confirmation of safety and efficacy led to direct comparison with the GuardWire (FIRE study) in patients with low thrombus burden and good pre procedural flow. Primary end-point analysis confirmed similar rates of successful deployment, angiographic and biomarker release and 30-day MACE.23 Subgroup analysis revealed superiority of the FilterWire in smaller vessels and eccentric lesions.

The proximal occlusion device (Proxis) has been shown to be safe and effective. The first clinical trial with this device, involving 600 patients (PROXIMAL trial) confirmed the Proxis device to be at least as good as the distal devices. Although the trial design was complex, direct comparison with the distal devices revealed a non-significant reduction in MACE (6.2% vs 11.2%, P = 0.89).27

In conclusion, therefore, the role of embolic protection devices for vein graft intervention is firmly established. They represent a partial but incomplete solution to distal embolisation and their use during vein graft intervention should be mandatory. The use of a particular device will often be determined by the lesion location and in some grafts with multiple lesions it is possible that no device can be employed.

THROMBECTOMY DEVICES

The benefit of thrombectomy on clinical end points is unproven. In the X-Sizer AMI registry there was no difference in TIMI flow grade 3.28 There may, however, be situations where the thrombus burden is so large as to preclude the use of embolic protection devices. In these rare instances the X-Sizer system (EndiCOR Medical, San Clemente, California) or the AngioJet device (Possis, Minneapolis, Minnesota) are available for use, although trial evidence of benefit is lacking.

GP IIB/IIIA RECEPTOR INHIBITORS IN VEIN GRAFT INTERVENTION

Even with appropriate use of embolic protection devices, acute complication rates after degenerative vein graft PCI may exceed 10%. This is most often secondary to ‘no-reflow’ resulting in Q or non Q-wave myocardial infarction. Adjunctive glycoprotein IIb/IIIa inhibitors have proven efficacy in patients with ACS undergoing PCI to native coronary arteries. Data supporting use in vein graft PCI, however, is lacking. Pooling results from several randomized trials29–34 suggested worse 30-day outcomes. More recently, a differential effect of GP IIb/IIIa agents has been reported.35 The authors reported on a pre specified subgroup analysis of the FIRE trial, where 651 patients undergoing vein graft PCI and stent insertion were randomized to the filter wire or distal occlusion embolic protection devices. Patients randomised to the distal occlusion device revealed a marked increase in MACE when assigned to GP IIb/IIIa inhibitors (16% vs. 6.3%; P=0.007). No difference was seen in patients in whom the filter device was used. Although the use of GP IIb/IIIa inhibitors was not randomly assigned, the results are nevertheless surprising given the central role of platelet aggregation in distal platelet embolisation. These findings underscore the recognition that pathophysiology of distal embolisation in vein graft PCI is multifactoral with involvement among others, of plaque embolisation and vasospasm. The difference between the two devices is most likely explained by the fact that the filter wire allows antegrade flow of small particulate matter and the reduced platelet aggregation and deposition with GP IIb/IIIa use translates to reduced MACE. During balloon occlusion use of these agents is unlikely to have a beneficial effect as embolic retrieval is facilitated by occlusion and aspiration of all particulate matter.

In conclusion, therefore, the use of filter wire devices may benefit from adjunctive therapy with GP IIb/IIIa inhibitors but use of occlusive embolic protection precludes GP IIb/IIIa therapy.

PTFE COVERED STENT

The aim of covered stents was to improve outcome in graft intervention through prevention of distal embolisation and reducing restenosis rate. This stent has a biocompatible PTFE membrane to ‘seal’ the lumen of the graft thus trapping embolic debris. In addition, the membrane would act as a mechanical barrier to prevent protrusion of proliferating tissue thereby inhibiting neointimal hyperplasia and restenosis.

However, three major randomised trials revealed no additional benefit in respect to restenosis and cumulative MACE when compared to BMS.36–38 Use in vein graft interventions, therefore, cannot be recommended except in emergency situations to seal perforations.

SUMMARY

Long term outcome after surgical revascularization is limited by attrition of vein grafts such that up to 50% have significant disease at ten years with angina recurrence. Repeat surgical revascularization is associated with high morbidity and mortality and PCI offers a safer alternative for revascularization in the majority of patients with vein graft disease. Nevertheless, vein graft PCI with stent deployment also carries risk (up to 20%) of procedure related complications, largely as a result of distal embolisation. The advent of embolic protection devices has reduced such complications significantly and their use should be mandatory. Use of glycoprotein IIb/IIIa inhibitors in selected groups may also help in reducing procedure related complications. Drug-eluting stents hold the promise of further reduction in long term complications resulting from decreased restenosis rates. Saphenous vein graft PCI remains a challenge for the interventionist. A better understanding of the pathophysiology and progression of vein graft atheroma coupled to pharmacological and technological advances have tilted the balance in favour of the patient such that vein graft PCI should be considered the first route for revascularization in affected patients.

REFERENCES

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35 Laarman GJ, Kiemeneij F, Mueller R, et al. Feasibility, safety, and preliminary efficacy of a novel ePTFE-covered self-expanding stent in saphenous vein graft lesions: the Symbiot II trial. Catheter Cardiovasc Interv. 2005;64(3):361-368.

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38 Schachinger V, Hamm CW, Munzel T, et al. A randomized trial of Polytetrafluoroethylene-Membrane-Covered stents compared with conventional stents in aortocoronary saphenous vein grafts. J Am Coll Cardiol. 2003;42:1360-1369.

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