Rationale and design of a randomized trial evaluating an external support device for saphenous vein coronary grafts

Handling non-ignorable missing intimal hyperplasia data - Lessons from the VEST trial

Non-ignorable missing data arise often in clinical trials. The VEST trial, a randomized, within-patient-controlled study, assessed the effect of an external scaffold for saphenous vein grafts on intimal hyperplasia (IH) one year after coronary artery bypass graft surgery. It was anticipated that approximately 13 % of grafts would be occluded and unsuitable for intravascular ultrasound, resulting in missing IH values at 1-year. Given graft occlusion is a negative outcome and higher IH is associated with occlusion, this missing data is non-ignorable. To address this, we developed a novel two-part method for the MNAR (missing not at random) scenario in the VEST trial. This method combines penalized multiple imputation with a modified Wilcoxon signed-rank test. We evaluated the approach's performance against alternatives in a series of simulation studies. The new method did not show type I error inflation. Under trial assumptions, it provided adequate power. However, if missing data exceeds 20 %, power decreases notably with the double penalization method due to underestimation of the treatment effect. When missing data is balanced between arms, penalized multiple imputation alone is more powerful and unbiased. Conversely, for unbalanced MNAR data, as might occur with a treatment effect on IH, the penalized multiple imputation with a modified Wilcoxon signed-rank test approach is more powerful. The VEST trial showed more occlusions than expected, balanced across arms, resulting in potential underestimation of the true treatment effect. However, given the potential for unbalanced missingness, this approach was suitable and could be applied in other settings with similar challenges.

Intimal hyperplasia, saphenous vein graft disease, and clinical outcomes: Insights from the CTSN VEST randomized trial

BACKGROUND

Diffuse intimal hyperplasia and graft irregularity adversely affect the long-term patency of saphenous vein grafts (SVGs) and clinical outcomes of patients undergoing coronary artery bypass grafting (CABG). The VEST trial evaluated the efficacy of external graft support in limiting the development of intimal hyperplasia (IH) at 1 year postsurgery. In the present secondary analysis, we explored the associations between graft disease and IH and clinical events. We also examined risk factors for early graft occlusion.

METHODS

VEST is a within-patient randomized, multicenter trial that enrolled 224 patients with multivessel coronary disease undergoing CABG surgery, of whom 203 were evaluated by 1 year postsurgery. Intimal hyperplasia, lumen uniformity, graft stenosis, and graft perfusion were measured by intravascular ultrasound and angiography. Major cardiac and cerebrovascular events (MACCE; including death, myocardial infarction, stroke, and revascularization) were recorded over a median follow-up of 3 years.

RESULTS

Worse lumen uniformity, greater stenosis, and worse graft perfusion were associated with higher IH values and an increased incidence of clinical events. Consistent with previous findings, we identified endoscopic vein harvesting, female sex, and transit time flow measurement of pulsatility index and flow as risk factors for SVG occlusion during the first year postsurgery.

CONCLUSIONS

In this secondary analysis of the VEST trial, we observed an association between intimal hyperplasia area and clinical measures of SVG disease at 1 year postsurgery. More severe SVG disease and larger areas of IH were associated with a higher incidence of 3-year MACCE. Ongoing follow-up to 5 years will further elucidate the impact of SVG disease on long-term clinical outcomes of CABG.