Time to Assess the Role of Quality Control in CABG: The SMARTFLOW Trial Program

Intraoperative quality control is a cornerstone of cardiac surgery, and it is essential to ensure procedural effectiveness and patient safety. Evidence consistently shows that intraoperative assessment of the surgical procedure reduces postoperative complications, shortens hospital stay, and decreases overall healthcare costs. For example, intraoperative evaluation of valve function using transoesophageal echocardiography (TEE) is guideline-recommended for all valve repair and replacement procedures and has been associated with significantly lower mortality, stroke, and reoperation rates in large contemporary cohorts. Coronary artery bypass grafting (CABG) remains the most frequently performed cardiac operation, but high-quality data on standardized intraoperative quality control for CABG are lacking. Several techniques have been used for CABG quality control, including intraoperative coronary angiography and indocyanine-green fluorescence imaging; however, they are limited by cost, logistics, and the risk of false-positive findings due to acute oedema or graft spasm. Transit-time flow measurement (TTFM) is an ultrasound-based technology that allows direct, real-time quantification of graft flow, its directionality, and resistance to blood flow, enabling immediate correction of technical problems before chest closure. TTFM is simple, safe, and reproducible. Its interpretation has been standardized,1 and it is easily incorporated into a surgical routine. In the multicentre REQUEST registry, TTFM led to graft revision in 7.8% of patients, with marked improvement in graft flow in more than 90% of cases after revision.2 A meta-analysis of 35 studies including nearly 9000 patients and over 15 000 grafts reported a similar incidence of intraoperative graft revision (4.3%), underscoring that unrecognized technical errors are frequent yet correctable when identified intraoperatively. TTFM is estimated to be used in about one-third of CABG procedures, but exact utilization rates vary between centers and are not well documented. Graft failure remains a major determinant of long-term outcomes after CABG. A pooled patient-level analysis of seven randomized CABG trials with systematic graft imaging found that graft failure occurs in approximately one-third of patients within the first postoperative year and is strongly associated with myocardial infarction, repeat revascularization, and death.3 Large registry data further show that over 4% of patients require early postoperative coronary angiography for suspected graft failure, often necessitating PCI, and that such events are associated with higher rates of complications, prolonged hospitalization, and a 50% increase in hospital costs. Most failures occur within the first month and are predominantly due to technical problems such as kinking, overstretching, competitive flow, or anastomotic errors, all of which are potentially preventable through systematic intraoperative assessment. Consistently, meta-analytic data in patients with procedural myocardial infarction have identified acute graft failure as the leading underlying mechanism. Observational data suggest that TTFM use improves graft patency and clinical outcomes. In a sub-analysis of the Randomized On/Off Bypass (ROOBY) trial, 1-year graft patency was higher among patients who underwent intraoperative TTFM (83% vs 78%, P < .01), and several studies have found that abnormal TTFM measurements are strongly associated with graft failure, postoperative myocardial infarction, and the need for urgent revascularization. Nevertheless, most available studies are small, observational, and heterogeneous in their methodology. Despite expert consensus supporting its use, the absence of randomized evidence remains a barrier to broad adoption in clinical practice. The need for such evidence is particularly important in patients at increased risk of technical graft failure. Women undergoing CABG consistently experience worse outcomes than men, including higher operative mortality, greater risk of myocardial infarction, and lower long-term survival.4 The mechanisms underlying these disparities include smaller target vessels and conduits, more diffuse coronary disease, and higher rates of graft spasm, all of which increase the likelihood of early technical failure. A recent pooled analyses of randomized CABG trials found that graft failure is significantly more frequent in women than in men.5 Because TTFM specifically detects such technical issues intraoperatively, it represents a uniquely targeted strategy to address a correctable, mechanistic source of poor outcomes in women and other high-risk subgroups. Against this background, the Surgical Measurement for Accurate Revascularization using Transit-time FLOW (SMARTFLOW) trial has been designed as the first appropriately powered randomized evaluation of intraoperative graft assessment with TTFM in CABG. SMARTFLOW is an expertise-based, multicentre, single-blind, randomized trial conducted in approximately 20 centers in the ROMA Clinical Trials Network, comparing TTFM-guided graft assessment versus standard CABG without TTFM use. SMARTFLOW is structured as a trial platform. Its initial aim is to determine whether routine intraoperative assessment with TTFM reduces early graft failure (Table 1). It can then be extended to evaluate the impact of TTFM on clinical outcomes such as myocardial infarction, repeat revascularization, survival, and patient-reported quality of life. This approach reflects the key role of graft patency in determining long-term CABG outcomes and allows the trial to establish the impact on graft patency first, before evaluating longer-term clinical end-points. A very important aim is also to examine whether systematic intraoperative assessment can reduce the particularly high rates of graft failure seen in women or in other high-risk patient groups. SMARTFLOW-patency trial design Age >18 years First-time, non-emergent isolated multivessel CABG through median sternotomy Willing and able to provide written informed consent and comply with all study procedures, including QOL questionnaires Reoperation Emergency procedures Combined CABG and other cardiac or non-cardiac surgery Isolated single-vessel CABG Minimally invasive CABG Age >18 years First-time, non-emergent isolated multivessel CABG through median sternotomy Willing and able to provide written informed consent and comply with all study procedures, including QOL questionnaires Reoperation Emergency procedures Combined CABG and other cardiac or non-cardiac surgery Isolated single-vessel CABG Minimally invasive CABG SMARTFLOW-patency trial design Age >18 years First-time, non-emergent isolated multivessel CABG through median sternotomy Willing and able to provide written informed consent and comply with all study procedures, including QOL questionnaires Reoperation Emergency procedures Combined CABG and other cardiac or non-cardiac surgery Isolated single-vessel CABG Minimally invasive CABG Age >18 years First-time, non-emergent isolated multivessel CABG through median sternotomy Willing and able to provide written informed consent and comply with all study procedures, including QOL questionnaires Reoperation Emergency procedures Combined CABG and other cardiac or non-cardiac surgery Isolated single-vessel CABG Minimally invasive CABG By providing high-quality randomized data on the effect of TTFM on early graft failure, and by offering a platform capable of extending to clinical outcomes, the SMARTFLOW trials program has the potential to inform future guideline recommendations and to support a more consistent, evidence-based approach to intraoperative graft assessment. SMARTFLOW could help standardize quality control during CABG and improve outcomes in patients who are at the highest risk of technical graft failure. The SMARTFLOW trial program is partially funded by the Canadian Medical and Surgical Knowledge Translation Research Group (CMS) and Medistim. No funding was received for this work. The authors declare no conflicts. No new data were generated or analysed in support of this work.

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