SWOT analysis of coronary artery bypass surgery by the use of intraoperative epiaortic imaging and functional graft assessment

At least since the long-discussed results of the Syntax study, aortocoronary bypass grafting (CABG) surgeons not only focus on the strengths but also look for strategic and methodic weaknesses of CABG. In heart team discussions, many of us had been particularly and painfully confronted with the lower incidence of strokes by interventional myocardial revascularization, although surgical revascularization was undoubtedly the better treatment option in multivessel coronary artery disease with regard to cardiac death and myocardial infarction. To avert the threat of improving percutaneous coronary intervention (PCI) technologies and to overcome the shortcoming of higher stroke rates in CABG, many opportunities were found to gain competitive advantages over percutaneous coronary intervention. In particular, efforts were made to reduce perioperative stroke rate and to improve long-term longevity of coronary bypass grafts. Off-pump surgery, minimized cardiopulmonary bypass circuits, T- and Y-grafting, arterial conduits, complete revascularization and many other perioperative strategies were inaugurated and widely adopted. Doing so, a systematic SWOT analysis (i.e. strengths, weaknesses, opportunities and threats) was induced, which is well known from business competition or project planning. Since turn of the millennium, the new opportunity of intraoperative transit-time flow measurement (TTFM) was inaugurated and was additionally and routinely used in CABG surgery to validate bypass graft function. More recently, TTFM was supplemented by high-frequency ultrasound (HFUS) 2D imaging of the aorta and the heart. The combination of TTFM and HFUS comfortably allowed displaying the ascending aorta to identify the best spot for aortic manipulation and to evaluate the completed anastomoses and grafts by 2D imaging and by functional bypass flow analyses. While the benefit of this technology is obvious, the scientific benefit of TTFM and epiaortic HFUS in CABG surgery could not well shown. Even today the clinical use of TTFM/HFUS varies significantly between surgeons, cardiovascular centres and countries. However, early supportive data led to a class IIa recommendation of TTFM/HFUS for bypass graft assessment and aortic screening before manipulation in the European Society of Cardiology/European Association for Cardio-Thoracic Surgery 2018 Guidelines on Myocardial Revascularization. During the last few years, more prospective clinical data become evident [1–3]. To date, these results were preliminary and not fully consistent. However, the REQUEST trial was the first large multicentre trial that prospectively evaluated the impact of intraoperative TTFM/HFUS assessment in coronary artery bypass grafting. In the multi-institutional study, 1046 CABG patients were analysed in 7 high volume centres in the USA and Europe based on a structured study protocol for intraoperative TTFM/HFUS application [3]. In conclusion, the authors of the baseline manuscript reported intraoperative strategy changes compared to the initially planned surgical concept in 25% of the patients. These changes included the site of aortic manipulation era, conduit choice and coronary targeting. Most of the changes were driven solely by the ultrasound findings. Of note, intraoperative graft revision was performed in 7.8% of patients and was not associated with increased MACCE rate. The present manuscript by Rosenfeld et al. [4] now gives more insights into subgroup populations of the REQUEST trial to evaluate the benefits of TTFM/HFUS for specific surgical conceptions. In detail, the value of TTFM and HFUS was explored for on- versus off-pump CABG, arterial versus venous conduits and the 3 anatomical coronary territories. Using the same combined end point of strategy change in terms of aortic manipulation, conduit choice and anastomotic revisions, the authors could show various benefits by using intraoperative ultrasound evaluation: (i) in OPCAB surgery, strategy changes to the aorta were found in 14.7%. This was four-fold more frequent than in on-pump surgery; (ii) intraoperative surgical bypass graft revision rate was 4.7% of all arterial and 2.4% of all venous conduits. Indication for revision was based on TTFM/HFUS evaluation in 60–65%; and (iii) with a per graft incidence of 5.1%, the inferior territory was more jeopardized for graft revision than the lateral and anterior coronary territory. Again, decision for revision was predominantly based on ultrasound findings (50–67%). These study results leave room for interpretation and discussion. While it is still understandable that graft revisions were more frequently required in arterial versus venous grafts and that the aorta is screened more often during off-pump operations, it is more surprising that bypass revisions affected the inferior wall above average. For the sceptics and late adapters, it is quite remarkable that an early bypass revision led to improved TTFM parameters in 82% of cases, with no additional MACCE in those patients. Ultimately, the very low rates of perioperative MACCE events, the low re-catheterization, reintervention and the low stroke rate suggest the benefit of the strategy of intraoperative ultrasound use. In other words, the surgeons obviously identified almost all graft failures intraoperatively, at least all major ones. Thus, intraoperative use of TTFM/IFUS is a valuable add-on to address intraoperative challenges and become an important element for improving CABG results, especially with regard to perioperative stroke. This is even more true for our real-world patients, who are clearly more challenging than study patients. Besides, TTFM/HFUS CABG subgroups may benefit from further image modalities, like a preoperative routine CT evaluation and intraoperative TEE, which we still usually apply in most valve patients. It is obvious that pre- and intraoperative imaging is becoming more and more important and relevant. Thus, we welcome TTFM and HFUS as a valuable and routine tool assisting us to improve our CABG performance.