Recurrent myocardial ischaemia after CABG is a common clinical problem. Angiographic studies have found that within 10 years after the operation, half of all vein grafts are totally occluded or have severe atherosclerotic disease.1–4
Repeated bypass surgery is more technically challenging than a first operation, is associated with higher morbidity and mortality, and provides less symptomatic relief.5,6
Angioplasty is therefore often attempted. However, the results of balloon angioplasty in SVG are less favourable than those in native vessels regarding complication and restenosis rates.7,8,11,12
Stent implantation has been shown to be superior to balloon angioplasty in observational as well as in randomised trials.13,14
Despite these encouraging findings the absolute restenosis rate after PTCA of SVG is still high and subsequent clinical sequelae are meaningful.15
Interventional treatment of in-stent restenotic lesions is associated with a repeat recurrence rate of 50% regardless of the technique performed.16,17
Thus, it seemed reasonable to attempt to reduce the incidence of restenosis, either prophylactically by combining the primary intervention of a de novo lesion with VBT or as an adjunctive treatment modality.
While VBT in native coronary arteries is now very solidly documented in five randomised trials,18–22
only one randomised trial for the treatment of SVG disease exists.17
Gamma radiation was applied to in-stent restenotic lesions exclusively. A very prominent reduction of restenosis rate (iridium-192 15%, placebo 43%, p = 0.004) and of the composite end point of death, Q wave myocardial infarction, and target vessel revascularisation (iridium-192 32%, placebo 63%, odds ratio 0.27, 95% confidence interval 0.13 to 0.57, p < 0.001) has been shown. Considering the complexity of the treated lesions, it was concluded that VBT is of special value for patient subsets at high risk for recurrent events. The present data from the RENO registry reflect a subgroup of patients having undergone β irradiation in SVG during routine clinical practice. The high rates of six month clinical and angiographic follow up that were achieved (100% and 91%, respectively) give particular strength to the observations that can be made.
Performing VBT in SVG lesions is feasible and safe. Nevertheless, the primary success rate was comparably low. This was because of insufficient back up of the guiding catheter to allow passage of the relatively stiff 5 French radiation delivery catheter to the target lesion. More flexible delivery catheters with a lower profile may be preferable for VBT in SVG.
In-hospital complications were infrequent (4.5%), and comparable with other series of coronary interventions in SVG.11,12
This seems to be favourable, since interventions in SVG lesions usually are associated with the highest risk and the prevalence of patients with unstable angina and ostial lesion location, as well as lesion length, was above average.
The six month MACE rate of 26.7% observed in the present registry compares with those reported in the radiotherapy arm of the available trials,17–22
where the MACE rate varied between 18–29% for patients treated for in-stent restenosis and between 14–19% for de novo lesions. Of note, 7.5% of the overall MACE rate was caused by non-cardiac deaths. These deaths were not procedure related and reflect the high level of morbidity of the study population. Yet, in light of the limited sample size, the number should be regarded with caution. The need for target vessel revascularisation was 16.4% in this registry, while it was 11–34% in previously conducted studies. This seems to be especially favourable, for several reasons. Firstly, the absolute rate of reinterventions is at the lower end of the results reported in previous trials. Secondly, the incidence of reintervention in a high risk patient subset reported in this trial is essentially the same as in a population at average risk. It should also be stressed that several exclusion criteria often used in randomised trials did not apply in this registry. Although the protocol initially discouraged the irradiation of lesions longer than 30 mm, this was nevertheless done for 21 lesions (30.9%) and a pullback manoeuvre was used for 17 (25.0%).
Several points demand special attention. Usually, the implantation of a new stent in conjunction with VBT is associated with an increased risk for late thrombosis and eventual late thrombotic occlusion, as well as an increased likelihood of target vessel revascularisation caused by geographic miss and consecutive edge effect.20,24–26
In the population studied, no such observation could be made. De novo lesions, although of smaller length, exhibited a larger acute gain, a smaller late loss, and neither total occlusion nor an edge effect. Thus, stent implantation for de novo lesions in SVG may not necessarily be attributable to a higher rate of repeat reinterventions or MACE. Yet, to draw any valid conclusions, larger sample sizes are imperative.
Although the results of the present series are very encouraging, they suffer from the limitations of all registries. They cannot be seen as direct evidence of the efficacy of VBT, especially in a heterogeneous population. The sample size was small, limiting conclusions concerning clinical end points.
Angiographic follow up was not mandatory, resulting in an incomplete data set. Nevertheless, the actual angiographic follow up rate was high and not only driven by clinical need but more often based on a compassionate manner. Quantitative coronary angiography was performed retrospectively. Thus, angiography was performed in a non-standardised manner resulting in potential errors in determining true vessel dimensions. Since SVG, in contrast to native coronary arteries, are of greater diameter and do not pose the problem of overlay with other vessels, sources of error are likely to be acceptable.
It is important to emphasise limitations resulting from the open nature of this trial, since patients and operators were not blinded to the treatment. Thus, the possibility of bias cannot be excluded despite the prospective design of the registry.
Adjunct VBT with β radiation for de novo and in-stent restenotic lesions in SVG is feasible and can be safely performed. At six months’ follow up, the restenosis rate compares very favourably with previously reported data acquired in populations with a much lower likelihood of recurrence, and MACE rates are similar to those obtained in the VBT arms of published randomised controlled trials. Thus, β VBT might be of special value for high risk patient subsets. It would be desirable to confirm the results in a randomised controlled trial.