Novel Strategies for the Prevention of Bypass Graft Failure

The dynamics of vein graft remodeling induced by hemodynamic forces: a mathematical model

Although vein bypass grafting is one of the primary options for the treatment of arterial occlusive disease and provides satisfactory results at an early stage of the treatment, the patency is limited to a few months in many patients. When the vein is implanted in the arterial system, it adapts to the high flow rate and high pressure of the arterial environment by changing the sizes of its layers, and this remodeling is believed to be a precursor of future graft failure. Hemodynamic forces, such as wall shear stress (WSS) and wall tension, have been recognized as major factors impacting vein graft remodeling. Although a wide range of experimental evidence relating hemodynamic forces to vein graft remodeling has been reported, a comprehensive mathematical model describing the relationship among WSS, wall tension, and the structural adaptation of each individual layer of the vein graft wall is lacking. The current manuscript presents a comprehensive and robust framework for treating the complex interaction between the WSS, wall tension, and the structural adaptation of each individual layer of the vein graft wall. We modeled the intimal and medial area and the radius of external elastic lamina, which in combination dictate luminal narrowing and the propensity for graft occlusion. Central to our model is a logistic relationship between independent and dependent variables to describe the initial increase and later decrease in the growth rate. The detailed understanding of the temporal changes in vein graft morphology that can be extracted from the current model is critical in identifying the dominant contributions to vein graft failure and the further development of strategies to improve their longevity.

Revision of vein bypass grafts: factors affecting durability of interventions

Once the failing vein graft is identified and characterized, the clinician must choose the appropriate intervention to maintain graft patency. Limited by the single-institution, retrospective studies that are pervasive in this area, definitive data to guide these decisions are limited. In general, open surgical revisions appear to offer a modest benefit in primary patency, but likely at the cost of increased periprocedural morbidity. Although endovascular revisions are more prone to failure, these recurrent lesions are often amenable to reintervention so that the secondary patency rates for both endovascular and open interventions may be similar. Given this, endovascular intervention as an initial treatment modality seems a reasonable approach for favorable lesions. Factors associated with poor outcome for endovascular revision include longer lesions (stenosis >2 cm in length), multiple stenoses, lesions occurring within 3 months of graft placement, or interventions for graft thrombosis, where endovascular failures are high and open surgery as an initial approach is warranted. The optimum method for percutaneous intervention remains a shifting landscape. No techniques as of yet appear clearly superior to standard balloon angioplasty, but initial investigations would suggest that cutting balloons offer a modest improvement and are worthy of consideration.

Upregulated TRPC1 channel in vascular injury in vivo and its role in human neointimal hyperplasia

Occlusive vascular disease is a widespread abnormality leading to lethal or debilitating outcomes such as myocardial infarction and stroke. It is part of atherosclerosis and is evoked by clinical procedures including angioplasty and grafting of saphenous vein in bypass surgery. A causative factor is the switch in smooth muscle cells to an invasive and proliferative mode, leading to neointimal hyperplasia. Here we reveal the importance to this process of TRPC1, a homolog of Drosophila transient receptor potential. Using 2 different in vivo models of vascular injury in rodents we show hyperplasic smooth muscle cells have upregulated TRPC1 associated with enhanced calcium entry and cell cycle activity. Neointimal smooth muscle cells after balloon angioplasty of pig coronary artery also express TRPC1. Furthermore, human vein samples obtained during coronary artery bypass graft surgery commonly exhibit an intimal structure containing smooth muscle cells that expressed more TRPC1 than the medial layer cells. Veins were organ cultured to allow growth of neointimal smooth muscle cells over a 2-week period. To explore the functional relevance of TRPC1, we used a specific E3-targeted antibody to TRPC1 and chemical blocker 2-aminoethoxydiphenyl borate. Both agents significantly reduced neointimal growth in human vein, as well as calcium entry and proliferation of smooth muscle cells in culture. The data suggest upregulated TRPC1 is a general feature of smooth muscle cells in occlusive vascular disease and that TRPC1 inhibitors have potential as protective agents against human vascular failure.

The PRoject of Ex-vivo Vein graft ENgineering via Transfection IV (PREVENT IV) trial: study rationale, design, and baseline patient characteristics

BACKGROUND

Coronary artery bypass graft (CABG) surgery with autologous vein graft (VG) conduit is one of the most frequently performed operations in the United States. Unfortunately, many VGs become occluded during long-term follow-up largely because of neointimal hyperplasia. A novel approach to preventing neointimal hyperplasia is with the double-stranded oligonucleotide edifoligide (Corgentech Inc, South San Francisco, Calif). Edifoligide inhibits E2F, a transcription factor that activates cell-cycle genes responsible for neointimal hyperplasia.

METHODS

PREVENT IV is a phase-III, multicenter, randomized double-blind placebo-controlled trial of ex vivo treatment of autologous VGs with edifoligide in patients undergoing initial CABG surgery. The primary end point is VG failure, defined as death or > or =75% stenosis in a treated VG at 12- to 18-month angiographic follow-up. Secondary end points include major adverse cardiac events through at least 5 years and adverse events through 30 days.

RESULTS

Enrollment of 3014 patients from 107 sites was completed on October 22, 2003. The baseline and procedural characteristics of the PREVENT IV population are generally well matched to a contemporary population of patients undergoing initial CABG from the Society of Thoracic Surgeons National Database. Angiographic follow-up is ongoing and scheduled to be completed in March 2005.

CONCLUSIONS

The PREVENT IV data will establish whether VG pretreatment with an E2F transcription factor decoy, edifoligide, can improve graft patency and reduce the long-term morbidity and mortality of patients undergoing CABG surgery.