Advances in cardiac surgery continue with new techniques, as well as developments in extracorporeal circulation (ECC) technology aimed at minimizing procedural invasiveness. These innovations in ECC seek to mitigate adverse effects arising from blood contact with artificial surfaces, coagulation activation, hemodilution, and hypoperfusion, which lead to microcirculatory dysfunction. Minimally invasive extracorporeal circulation (MiECC) represents a more physiological approach to intraoperative perfusion, designed as a closed system that better preserves microcirculation and coagulation integrity, and improves organ perfusion.
In this study, the authors performed a multicenter, randomized, controlled trial comparing MiECC with conventional extracorporeal circulation (CECC) in all patients undergoing elective or urgent cardiac surgery without circulatory arrest. Procedures included CABG, AVR, or a combined operation. The MiECC system adhered to the specifications required in the European Community and employed Type II, III, and IV systems as described by Anastasiadis et al. in 2015.
The initially estimated sample size was 3,500 patients. However, due to COVID-19, the steering committee recommended early termination of the trial, resulting in data collection from 1,039 patients, with 522 in the CECC group and 517 in the MiECC group. The hypothesis was that MiECC would reduce the proportion of patients experiencing serious adverse events (SAEs) compared to CECC.
Preoperative characteristics were similar between groups, with an average age of 66 years, and 83% of participants were male. Most had a left ventricular ejection fraction (LVEF) >50% (71%), were classified as <III on the CCS scale (79%), and scored I or II on the NYHA scale (78%). The median EuroScore II was 1.24 (IQR 0.83–2.05). Of the total participants, 84% underwent CABG, 9% AVR, and 6% combined procedures. Elective surgeries comprised 87.1%, urgent surgeries 11.9%, and emergency surgeries 1%. Cardioplegia techniques were comparable across groups (blood cardioplegia in 80.9%, warm cardioplegia in 64.6%, antegrade in 88.7%, and intermittent in 98.2%). Average times for cardiopulmonary bypass and aortic cross-clamping were 88 and 57 minutes, respectively.
Primary SAEs included mortality, myocardial infarction, stroke, intestinal infarction, postoperative renal failure (AKIN III) and/or need for renal replacement therapy, reintubation, tracheostomy, mechanical ventilation >48h, reoperation, percutaneous intervention, sternal wound infection with dehiscence, and sepsis, assessed up to 30 days post-surgery. In the CECC group, 13.2% of patients experienced one or more SAEs, compared to 9.7% in the MiECC group. After adjusting for center stratification, the risk ratio (RR) was 0.73 (95% CI, 0.56–0.96; p = .025). The most frequent SAEs included reintubation (CECC 5% vs. MiECC 2.5%), reoperation (CECC 4% vs. MiECC 3.3%), mechanical ventilation >48h (CECC 2.7% vs. MiECC 2.5%), and AKIN stage III renal failure (CECC 1.9% vs. MiECC 2.5%). Mortality rates were 1.9% in CECC and 1.5% in MiECC (RR = 0.80; 95% CI, 0.36–1.74; p = .568).
Secondary outcomes assessed up to 30 days post-surgery included all-cause mortality, other SAEs (with 20 defined as secondary outcomes, most frequently cardiac arrest (1.3%), supraventricular tachycardia/atrial fibrillation requiring treatment (1.1%), inotropic support (1.4%), and vasodilator therapy (1.1%)), blood transfusions, ICU and hospital stays, and health-related quality of life (HRQoL) measured by the EQ-5D-5L survey, which includes a visual analog scale (VAS). These events occurred in 13.4% of the CECC group vs. 10.5% of the MiECC group (RR = 0.79; 95% CI, 0.53–1.18; p = .25). Red blood cell transfusions were required in 38.6% of CECC patients compared to 32.4% of MiECC patients (RR = 0.84; 95% CI, 0.7–1.01; p = .067), while other blood component transfusions occurred in 10.6% of CECC patients vs. 11.2% in MiECC (RR = 1.07; 95% CI, 0.81–1.41; p = .65). ICU (median 24 hours) and hospital stays (median 7 days) did not differ significantly between groups. Minor differences were observed in EQ-5D-5L descriptive system medians (0.80 for MiECC and 0.77 for CECC), with no significant differences in VAS scores. Average VAS scores were higher in MiECC (76.6 and 84.1 at 30 and 90 days, respectively) than CECC (73.3 and 81.9), with a significant difference (p < .001), indicating a higher perceived health status in the MiECC group.
These findings suggest that MiECC significantly reduces primary SAEs but does not significantly impact mortality, non-primary SAEs, hospital stays, or transfusion rates. However, MiECC had favorable treatment effects for nearly all outcomes, including perceived HRQoL. Due to sample size limitations from early trial termination, the study could not individually assess primary outcomes, although MiECC had lower event rates for all outcomes except AKIN III renal failure. This trial also showed a significant improvement in MiECC group HRQoL based on the EQ-5D-5L VAS.
This pragmatic study allowed diverse MiECC types, reflecting current clinical practice, and permitted various components to optimize CECC. However, biocompatible tubing, retrograde autologous priming, and centrifugal pumps were used in many CECC patients, reflecting a trend towards MiECC that may reduce intergroup differences. Additionally, lower EuroScore II values among participants may partly explain less pronounced findings than prior studies. The main study limitation was a smaller sample size due to early trial termination during the COVID-19 pandemic.
In conclusion, MiECC reduced primary SAEs compared to CECC, was safe for other SAEs, and improved perceived HRQoL. Continuing CECC’s convergence with MiECC is likely to further reduce differences between these technologies over time.
COMMENTARY:
MiECC represents a significant advancement in cardiac surgery, anticipated to be widely adopted given its theoretical benefits for patients. However, its widespread use has not been achieved, partly due to the learning curve required for all team members and continuous improvements in CECC techniques.
Perfusionists operate with non-reservoir circuits, reducing risks of air embolism or microbubbles but also limiting the safety margin for handling incidents. Without a venous reservoir, any drainage issue directly impacts pump flow, reducing safety in less experienced hands. Additionally, all blood aspirated from the surgical field and vented through cannulas must go to a cell saver. Using a centrifugal pump introduces nuances, as flow correlates with mean arterial pressure, and excessive VAD pressure can cause insufficient drainage, hemolysis, and microbubble formation.
Surgeons must carefully place venous cannulas to prevent air entry, which can compromise oxygenation and perfusion. These factors may explain MiECC’s renal effects (AKIN III stage, requiring renal replacement in CECC 1.9% vs. MiECC 2.5%).
For anesthetists, volume management is more complex, relying on pharmacologically induced vasoconstriction/dilation due to the lack of a venous reservoir. This directly impacts mean perfusion pressure and perfusion quality.
As noted in this article, routine CECC techniques, coupled with smaller circuits and oxygenators, reduce hemodilution and blood contact with air and foreign surfaces, producing results that closely mirror MiECC outcomes. In trained teams, no significant differences emerge, though MiECC shows advantages suggesting CECC’s future direction will increasingly resemble MiECC while balancing safety and blood-saving efficacy.
REFERENCES:
Angelini GD, Reeves BC, Culliford LA, Maishman R, Rogers CA, Anastasiadis K et al. Conventional versus minimally invasive extra-corporeal circulation in patients undergoing cardiac surgery: A randomized controlled trial (COMICS). Perfusion 2024; 0(0):1-12. doi:10.1177/02676591241258054
Anastasiadis K, Antonitsis P, Argiriadou H, Deliopoulos A, Grosomanidis V, Tossios P. Modular minimally invasive extracorporeal circulation systems; can they become the standard practice for performing cardiac surgery. Perfusion 2015; 30(3):195-200. doi: 10.1177/0267659114567555.
