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Repeat revascularisation after bypass surgery: a real challenge

  • The fate of arterial and venous bypass grafts, presented by K J Botman (Eindhoven, NL) - Slides
  • Prevention of no reflow, presented by U Limbruno (Grosseto, IT) - Slides
  • Stent armamentarium, presented by P Agostoni (Utrecht, NL) - Slides
  • Strategies after recurrent failure, presented by B J Gersh (Rochester, US) - Slides


This session was dedicated to a increasingly important issue: the performance of repeat revascularisation in patients with previous coronary artery surgery (CABG). As highlighted during the presentations, the challenge of secondary revascularisation after CABG stems from the fact that the patients are frequently older, have co-morbidities, more diffuse atherosclerotic disease and present specific challenges, like the treatment of treacherous degenerated saphenous vein (SVG) grafts. In addition to that, assessment of the functional relevance of stenoses and risk stratification is more complex than in patients without surgical grafts.

Review of arterial and venous grafts

A thorough review of the fate of arterial and venous grafts was made by the cardiac surgeon KJ Botman. The long-term superiority of internal mammary artery (IMA) grafts over SVG and radial artery grafts in terms of sustained patency was discussed, and the importance of the interaction between distal run off and graft patency was stressed. At a time when fractional flow reserve (FFR) has reached its majority of age and is widely used by interventional cardiologist, Dr Botman presented the view of a surgeon on how FFR assessment of coronary stenoses may influence the number of grafts implanted during CABG. The results of modelling and in-vitro studies investigating the relationship between FFR and predicted flow through grafts revealed significant differences in the behaviour of SVG and IMA grafts. In both cases, graft flow was influenced by FFR values in the vessel receiving the graft, with a slower decline of flow as FFR increased in IMA than in SVG reflecting the lower conductance of IMA at the time it is implanted. These findings were tested in vivo in a population of patients undergoing CABG (96 IMA, 24 RA and 205 SVG) by surgeons that were blinded to baseline FFR values. Among other factors, an FFR<0.75 at baseline was identified as an independent predictor of graft patency at 1 year follow-up, confirming that graft patency is influenced by stenosis severity.

Prevention of no reflow

A second dimension of the challenge, the prevention of no reflow phenomenon during SVG PCI, was discussed by Dr U Limbruno. Atherothrombotic embolism in SVG was associated in the past with 32% and 15% rates of moderate and severe rise in cardiac enzymes during PCI, respectively. The development of embolic protection devices (EPD), and the positive results of studies on their use (like the pioneer SAFER trial and in the non-inferiority FIRE, PRIDE, AMETHYST and SPIDER trials), have contributed to a safer treatment of patients with SVGs and to IA recommendation in the 2010 ESC guidelines on myocardial revascularisation. Failure to demonstrate its value in native vessel interventions during primary PCI is due not only to the presence of side branches left unprotected by the EPD, but also to the higher content of atheromatous gruel in the embolic material and higher amount of intraluminal material in SVGs than in culprit vessels of myocardial infarction. The problem of EPD underuse was discussed. In Dr Limbruno’s view, while distal EPD use may be not technically feasible in 43%, the availability of proximal EPD has decreased that figure to 23%, by using either proximal or distal EPD in specific circumstances. Besides, it is possible that in cases with low atheroembolic risk (non-degenerated grafts), use of EPD results in less benefit than in severely diseased SVGs, an idea behind the rationale of the “gentle” PCI approach proposed by some authors. Finally, some strategies for the treatment of acute or subacute occlusion of SVGs were proposed, like the staged approach suggested by Flavia et al in which, after initial recanalisation with a thin balloon is performed, thrombotic burden is decreased with intensive (IIb IIIa inhibitors) antithrombotic treatment before the final stenting procedure.

Stent armamentarium

Stenting has been demonstrated to be superior to balloon angioplasty in SVG treatment. However, there is controversy about the use of drug eluting stents (DES) in SVG as an alternative to bare metal stents (BMS) with the aim of reducing restenosis, given the potential obstacles for DES healing in the specific pathological substrate of SVF attrition. Doctor Agostoni, one of the co-authors of the RRISC trial, presented his views on the grounds of that study and further meta-analytical evidence of comparative studies on the subject. While the initial results of the RRISK trial suggested that DES were superior to BVMS in preventing repeat revascularisation of SVGs, follow-up data revealed a worrying increase in death in patients receiving sirolimus eluting stents (15/38, 39% in DES, versus 5/37, 13% in BMS, p=0.01). However, this was not found in the SOS study (using paclitaxel DES) nor in pooled analyses of reported DES vs BMS comparisons in SVG PCI. The latest, as yet unpublished, contribution to this debate is the ISAR-CABG study, including 610 patients treated with different DES, which revealed significant differences in MACE (15% DES, 22% BMS, p=0.03) at 1 year follow-up, driven by repeat revascularisation and without significant differences in death between both groups. Finally, some insights on the VELETI trial, an IVUS-monitored study comparing the safety and efficacy of medical treatment vs stenting in SVG stenoses, were provided. The study has demonstrated that medical management is inferior to stenting due to a rapid progression of stenosis severity that led to a 22% SVG occlusion at follow-up, an observation that, at a difference with native coronary vessels, raises doubts as to the applicability of FFR as a decision making tool in SVGs in deferring PCI.

Strategies after recurrent failure

All these considerations on the challenge of PCI after CABG were summarised and analysed from a personal perspective from Dr BJ Gersh in the final lecture of the session. The likelihood that this problem will continue in the near future can be inferred from the fact that, in the USA alone 2,340,650 CABG have been performed over the last 8 years. Surgical secondary revascularisation is impeded by a number of obstacles: in addition to the patient risk profile and anatomical considerations made above, the surgeon may have less suitable grafts or may fear to damage the existing patent conduits during the re-operation in a graft dependant coronary circulation. This may explain why, as reported by Yau et al, re-CABG is declining and PCI is used more frequently as the technique of choice. In any case, several patient subsets are clearly acknowledged as candidates for re-CABG, particularly those with occluded LAD graft and those with large ischemic areas. On the other hand, PCI requires careful planning due to the characteristics of the disease (which frequently includes chronically occluded vessels) and may benefit from the use of FFR in a context in which frequently it is difficult to point to a stenosis. Functional imaging is important not only to identify those patients in whom secondary revascularisation (either with re-CABG or PCI) is important for prognosis or for symptom relief, but also those that are unlikely to benefit due to small ischaemic or viable areas of myocardium.

Summary

A great session dedicated to improving the management of these patients which present frequently forgotten high risk profiles and constitute a challenge for the Heart Team.

References


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SessionTitle:

Repeat revascularisation after bypass surgery: a real challenge

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.