Atrial Appendage Micrograft Transplants to Assist Heart Repair After Cardiac Surgery

BACKGROUND AND SIGNIFICANCE

Globally, each year 17.9 million people die of cardiovascular diseases. Ischemic heart disease (IHD) is the cause in half of these cases, thus making it the global leading single cause of death. While 126.5 million patients suffer from IHD worldwide, in Europe 30.3 million patients are afflicted.

IHD is hallmarked by progressively enlarging atherosclerotic coronary plaques. These disease hotspots not only drive myocardial hypoxia, cardiomyocyte hibernation, apoptosis and interstitial fibrosis but are prone for erosion and rupture. Plaque rupture forcefully activates the hemostatic system resulting in thrombotic coronary occlusion, myocardial infarction (MI), and death of cardiac tissue. Due to improved acute care, the patients increasingly survive the acute phase, and the site of injury eventually gets replaced by a scar that typically restricts the filling and pumping of the heart. Depending on the extent of injury and the resulting scar, eventually the increased workload leads to adverse remodeling and emergence of heart failure (HF), an irreversible and incapacitating clinical syndrome with poor prognosis. HF due to an ischemic etiology has been reported to vary from 29% to 45%. For instance, a recent meta-analysis suggests the "all-type" HF prevalence, including the previously unrecognized cases via population-based echocardiographic screening, to be as high as 11.8% among general population aged above 65 years.

CABG surgery is the preferred revascularization method for patients with severe progressed IHD. In Europe, more than 245,000 CABG surgeries were carried out in 2016. Regardless of age, CABG surgery has been shown to have an overall beneficial effect on ischemic symptoms and mortality.

Cardiac healing by regeneration rather than scarring could tilt the IHD with its complications towards an increasingly manageable, even curable, disease. While the hearts of some vertebrates heal by regeneration throughout their lifespan, in rodents this capacity is limited to the first week of life. Very early in life, also the human heart seems to possess capacity to regenerate after ischemia.

It has proved complex to activate cardiac regenerative repair in adult human heart. Many stem, progenitor and differentiated cells have been tested in this regard. While these investigations have provided promising results, the therapies remain complex and costly, highlighting the need for more clinically straightforward approaches. Cells derived from atrial appendages have been shown to be capable of stimulating regenerative cardiac healing in the context of ischemic cardiac damage. As positioned by the European Society of Cardiology, many tissue-engineered approaches, including epicardial extracellular matrix (ECM) patch transplantation, are highlighted as promising future therapies for ischemic HF. These approaches could improve the local persistence and viability of the co-transplanted cells-a major obstacle identified in previous studies.

GENERAL CONCEPT

In this trial, the patient's own heart tissue from the right atrial appendage is used for therapy. Neither the left nor the right atrial appendage (LAA and RAA, respectively) directly contribute to the heart's pumping function. A piece of the RAA can be safely harvested upon insertion of the right atrial cannula during the set-up of the heart and lung machine at the beginning of CABG. In the AAMS2 trial, a piece of the RAA tissue is used as epicardially transplanted, patch-encased, and mechanically expanded atrial appendage micrografts (AAMs). This therapy can be administered during single CABG surgery.

PREVIOUS RESULTS

In a preclinical mouse model of MI and HF, the effects of epicardial AAMs-patches were compared to acellular ECM patches. The results demonstrated myocardial tissue protection, attenuated scarring, and retained cardiac function. Further, mass-spectrometry-based quantitative proteomics demonstrated widespread regenerative and cardioprotective effects in the myocardium, including decreased oxidative stress and AAMs-mediated induction of myocardial glycolytic metabolism, a process associated with an increased regenerative capacity of myocardium. The AAMs-patch therapy has proceeded to clinical use. Following the first-in-man application of AAMs, the safety and feasibility of the epicardial AAMs transplantation during CABG was recently confirmed. Moreover, as this study suggested increased thickness of the viable myocardium in the scar zone, it provided the first indication of therapeutic benefit.

OBJECTIVES AND OVERVIEW

This AAMS2 randomized double-blinded and controlled trial evaluates the effect of epicardially transplanted AAMs as an adjuvant therapy to CABG surgery. The trial's primary endpoints are changes in cardiac function and structure as evaluated using late gadolinium enhancement cardiac magnetic resonance imaging (LGE-CMRI) at 6-month follow-up after surgery as compared to preoperative LGE-CMRI. The trial enrolls 50 patients in a 1:1 group allocation ratio to the two study groups: 1.) collagen-based patch + AAMs + CABG (treatment arm) and 2.) collagen-based patch + CABG (control arm). Autologous RAA tissue is harvested from the RAA during CABG from all participants and based on randomization, the piece of RAA tissue is either processed to AAMs perioperatively or cryostored for biochemical analyses. The AAMs, embedded in fibrin matrix gel, are placed on a collaged-based patch, which is then epicardially sutured in place. To pinpoint the ischemic scar area as the epicardial transplantation site, LGE-CMRI is done preoperatively. Study blood samples are collected preoperatively as well as at 3- and 6-month follow-up after surgery. Transthoracic echocardiography (TTE), LGE-CMRI, symptom-scaling measures, and 6-minute walking test (6MWT) are performed preoperatively and at the 6-month follow-up.

METHODS

1. Patient selection, enrolment, ethics, and timeline-The patients meeting the both eligibility, inclusion as well as exclusion criteria, as evaluated by either a cardiologist or a cardiac surgeon, are selected from the hospital's list of elective cardiac surgeries. The patients' medication is optimised according to the current guidelines by the treating cardiologist. The usual waiting time on the list ranges between 2 and 8 weeks. This time allows medication changes to take effect before surgery. Later, the recruited patients are called for a clinical control visit (denoted as the 3-month follow-up) and a dedicated trial visit (at 6-8 months postoperatively, denoted as the 6-month follow-up).

All patients are provided with information describing the trial. Before a subject undergoes any study procedure, an informed consent discussion will be conducted and written informed consent to participate is required. The trial will be conducted following the Declaration of Helsinki on Ethical Principles for Medical Research Involving Human Subjects. The study has been approved by the Ethics Committee of Hospital District of Helsinki and Uusimaa (HUS; Dnr. HUS/12322/2022), and the Finnish Medicines Agency Fimea (FIMEA; Dnr. FIMEA/2023/004090). The estimated start of the patient recruitment is March 2024 with an estimated full study completion date on January 2027. The participant is excluded from the trial (screening failure), if, after optimisation of medication, a visible scar cannot be identified or left ventricular ejection fraction (LVEF) is ≥50% in the preoperative LGE-CMRI. This applies also if the LGE-CMRI has not been performed prior to CABG. 2. Endpoints-The trial endpoints are listed in a separate section. The primary endpoints focus on changes in cardiac fibrosis as evaluated by LGE-CMRI and circulating levels of N-terminal prohormone of brain natriuretic peptide (NT-proBNP). The secondary endpoints center on other efficacy parameters as well as both safety and feasibility of the therapy. 3. Randomization and blinding-Patients are randomized into CABG or AAMs groups using sex-stratified block randomization via the openly available online tool at www.sealedenvelope.com with block sizes 2 and 4, and stratification according to sex (female, male). Randomization is carried out by the study nurse. 50 participants that are treated during CABG either with Hemopatch® or the AAMs-patch are randomized. The research nurse texts the Sealed Envelope service phone number 'AAMS2' (the trial abbreviation) with and command 'randomise', and the participant pseudonym. The research nurse receives then the allocation by a text message. This is done on a previous day of patient's CABG to allow adequate time to setup practicalities required for the perioperative AAMs-patch assembly. The study nurse oversees the allocation in a double-blinded manner, where the patient and the evaluating cardiologist and radiologists remain blinded to the study group allocation. Given the nature of the treatment (transplant vs. no transplant) it is impossible to blind the operating surgeon or the study nurse to the allocations intraoperatively. However, the cardiac surgeon is blinded when planning the anastomoses prior CABG. All LGE-CMRI and TTE measurements as well as laboratory analyses are done by researchers blinded to the group allocations. In this trial, if considered acutely mandatory to remove the epicardial patch material, it is done without consideration of the randomization. Hence, no emergency unblinding is required in this trial. 4. Preparation and administration of atrial appendage micrografts-A piece of the RAA is harvested at the beginning of cardiac surgery upon right atrial cannulation. The RAA tissue is weighed and mechanically processed into micrografts as previously described by using the Rigeneracon blade (Rigenera-system, HBW s.r.l., Turin, Italy). Dedicated CE-marked instrumentation kits to support tissue processing in the operating room are obtained from EpiHeart Oy (Helsinki, Finland). After RAA grinding, the cold cardioplegia supernatant is removed and the AAMs pellet is collected with 0,4mL of the Tisseel (Baxter AG, Vienna, Austria) fibrinogen solution diluted with 0.9% NaCl (1:1 relation). Then, the AAMs-fibrinogen mixture is spread onto a cooled sterile metallic dish to be mixed in situ with 0,2mL of thrombin solution diluted in 1:30 relation with 0.9% NaCl. The AAMs-fibrinogen-thrombin mixture then undergoes spontaneous gelling for at least 10-15 minutes. Then, the gelled AAMs-fibrin gel is maintained cooled (+6 - +8oC), covered, and sterile waiting for transplantation. When all the anastomoses are ready, the AAMs-fibrin gel is lifted onto a collagen-based matrix (HEMOPATCH Sealing Hemostat \[45 mm × 45 mm; catalog ref. 1506256; Baxter International Inc., Illinois, USA). Next, the edges of the Hemopatch® are moistened with sodium bicarbonate (4.2-8.4%), which activates the polyethylene glycol-coating of the patch. Immediately after, to achieve proper epicardial adherence, the AAMs-patch with the moistened patch edges is transplanted onto the epicardium of the scarred border zone of the myocardium by using a dry gauze with uniform pressure for 2 minutes. The transplantation site is assessed prior CABG with LGE-CMRI to the ischemia-induced scar. In this trial, the AAMs patch shall wait, at maximum, 6 hours prior transplantation. 5. General data protection regulation-The data collected during the trial will fulfil EU regulations for personal health data protection, including General Data Protection Regulation (GDPR). 6. Adverse events-As a part of overall safety evaluation of the trial method, adverse events are subdivided to (1) major adverse cardiac and cerebrovascular events (MACCE), (2) anticipated SADE (serious adverse device effects), (3) other SAE (serious adverse events), (4) unanticipated SADE. All of these events are continuously monitored and reported to regulatory bodies. Here, the MACCE comprise i.) death (all-cause), ii.) MI, iii.) any acute coronary revascularizatio

• Efficacy: Change in left ventricular wall thickness [Time frame: 6 months]
• Efficacy: Change in viable left ventricular myocardium [Time frame: 6 months]
• Efficacy: Change in movement, systolic or diastolic function of the left ventricle [Time frame: 6 months]
• Efficacy: Change in left ventricular ejection fraction [Time frame: 6 months]
• Efficacy: Change in New York Heart Association (NYHA) class [Time frame: 6 months]
• Efficacy: Change in Canadian Cardiovascular Society (CCS) class [Time frame: 6 months]
• Efficacy: Major adverse cardiovascular and cerebrovascular events (MACCE) [Time frame: 6 months]
• Efficacy: Deaths due to primary cardiovascular cause [Time frame: 6 months]
• Efficacy: Postoperative days in hospital [Time frame: 1 week, up to 10 days]
• Efficacy: Changes in the quality of life [Time frame: 6 months]
• Efficacy: Local changes in systolic and diastolic function [Time frame: 6 months]
• Efficacy: Changes in myocardial strain and LVEF [Time frame: 6 months]