Anesthesia and Euthanasia
Anesthesia was induced with ketamine (10 mg/kg), midazolam (0.5 mg/kg), and atropine (0.04 mg/kg) intramuscularly. Each animal received antibiotic prophylaxis (1000/100 mg of amoxicillin–clavulanic acid), thiopental sodium (4 mg/kg), midazolam (0.5 mg/kg), and sufentanil citrate (6 μg/kg) through an intravenous line. The animals were intubated and ventilated with a mixture of oxygen and air (1:1 vol/vol). Anesthesia was maintained by a continuous intravenous infusion of midazolam (0.7 mg/kg per hour), analgesia was obtained with an infusion of sufentanil citrate (6 μg/kg per hour), and muscle relaxation was obtained with pancuronium bromide (0.1 mg/kg per hour). During the operation, each animal received a continuous infusion of saline solution (300 mL/h). Metoprolol was administered intravenously (range, 5–20 mg) to reduce the mechanical irritability of the heart until a heart rate of approximately 70 beats per minute was obtained. Postoperatively, amoxicillin–clavulanic acid (150 mg per 20 kg) was administered, and analgesia was obtained with 25 μg of fentanyl transdermally for 3 days. The animals were put to death with pentobarbital sodium (200 mg/kg) intravenously, after having been heparinized to obtain an activated clotting time (Hemotec, Inc, Englewood, CO USA) of at least four times the control value.
Surgery and Experimental Model
After a partial sternotomy, harvest of the ITA, partial heparinization (activated clotting time of >200; not counteracted), and immobilization of the coronary artery (OD of 3.0 mm) by the Octopus 3 Tissue Stabilizer (Medtronic, Inc, Minneapolis, MN USA), the bypass was constructed. After construction, the coronary artery was ligated ±1.0 cm upstream with three medium hemoclips, the ITA was tagged onto the epicardium, and the pericardium was closed.
Before chest closure, graft flow (milliliters per minute) was monitored for 2 hours with a transit time flow probe (diameter, 3.0 mm; flowmeter model T208; Transonic Systems, Inc, Ithaca, NY USA), at a mean blood pressure of 90 mm Hg. After ITA clamping for 30 seconds, the coronary peak hyperemic flow response was determined (45 minutes after construction, in duplicate at an interval of at least 10 minutes) as the peak graft flow divided by the baseline flow.
The LITA-to-LAD bypass in two animals and LITA-to-LAD and right internal thoracic artery (RITA) to right coronary artery (RCA) bypasses in one animal were constructed. The anastomoses (n = 4) were evaluated intraoperatively by flow measurements and at 6 months by angiography, IVUS (n = 1, RITA-RCA), OCT (n = 1, RITA-RCA), SEM (n = 1, LITA-LAD), and histology (n = 2, LITA-LAD).
All catheterization was performed before death, at 6 months. All anastomoses (n = 4) were visualized by angiography and graded by two independent observers according to the FitzGibbon criteria.
Intravascular ultrasound acquisition of the RITA-to-RCA bypass was performed using an ultrasound catheter (Revolution 45 MHz Catheter; Volcano Corporation, Rancho Cordova, CA USA), with an automated pullback speed of 0.5 mm/s. The frequency domain OCT system (C7 Dragonfly; LightLab Imaging, Inc, Westford, MA USA) was used for imaging the RITA-to-RCA bypass, with an automated pullback speed of 20 mm/s and a continuous flush of contrast by manual injection. Intimal hyperplasia and the dimension of the bypass (ie, the reference lumen area of the RCA and the RITA 1.0 cm downstream and upstream to the anastomosis, respectively, and the anastomotic orifice) were recorded and assessed by two independent investigators.
SEM and Histologic Analysis
The anastomotic surface of one anastomosis was evaluated using a scanning electron microscope (Philips XL30LAB; FEI Europe, Eindhoven, The Netherlands).
Two anastomoses were embedded in methyl methacrylate, sectioned in transverse planes (at 300-μm intervals) and stained with hematoxylin and eosin. The dimensions [ie, coronary lumen area (reference part, 1.0 cm distal to the anastomosis) and the anastomotic orifice], neointimal hyperplasia, adverse remodeling, and chronic inflammatory cell reaction were assessed (AnalySiS; Soft-Imaging Software GmbH, Münster, Germany).
The data are presented as mean (SD) or as noted otherwise.
All anastomotic procedures were performed by one investigator (D.S.). The mean (SD) anastomotic construction time was 6.8 (1.0) minutes, mounting of the graft required 28 (3) minutes, and all anastomoses were constructed without interrupting coronary flow. The intraoperative mean (SD) peak hyperemic flow response was 4.3 (1.3) [base flow, 50 (17) mL/min), and all anastomoses showed consistent graft flow up to 2 hours after construction [43 (15) mL/min at t = 2 hours].
At follow-up, all anastomoses (n = 4) were fully patent (FitzGibbon grade A; Fig. 3A). In one animal, an imperfect occlusion of the hemoclip at the LAD proximal to the anastomosis was found, resulting in a partial occlusion (approximately 40% residual lumen); however, it had not affected anastomotic patency.
Intravascular ultrasound acquisition of the RITA-to-RCA bypass demonstrated a lumen area of 10.1 mm2 for the RCA and 11.8 mm2 for the RITA. The anastomotic width, measured with both IVUS and OCT, was 2.2 mm. Limited neointimal formation and a 0.06-mm intimal coverage of the intraluminal part of the connector along the full circumference of the anastomosis were found with OCT (n = 1; Figs. 3B–D).
SEM and Histology
Scanning electron microscopy demonstrated complete endothelial coverage of the anastomotic surface, and a smooth and patent orifice was seen. The endothelial surface is completely continuous from the coronary artery, covering the connector and the laser rim, to the LITA (Fig. 4B).
Histology showed minimal intimal hyperplasia, without lumen-narrowing neointimal formation (Fig. 4C). The initial intraluminal exposed coronary adventitial rim (Fig. 2C) was completely remodeled and replaced by streamlining neointimal tissue, which caused the anastomotic orifice to expand over time from ±2.5–3.1 mm2 (LAD, ±4.5 mm2) at the time of construction to 3.8 (0.6) mm2 at 6 months (LAD, 8.6 (0.7) mm2). The extravascular spring of the connector (Fig. 1A3) was fully integrated in a maze of connective tissue, between the LITA and the LAD, and did not induce adverse erosion effects to either one of the adjacent arteries. In addition, the initial intraluminal exposed fork was incorporated into the upper wall of the outflow tract of the LAD and covered by a layer of neointima (Fig. 4D). No adverse remodeling (eg, erosion, luxation, or pseudoaneurysm formation) was demonstrated over time, and no excessive chronic inflammatory cell reaction was found.
This pilot study evaluated the long-term results of the zero-ischemia ELANA coronary connector in a porcine OPCAB model at 6 months. The ELANA bypass was assessed by multiple imaging modalities at 6 months, which demonstrated fully patent anastomoses and consistent healing and remodeling with minimal intimal hyperplasia.
The ELANA Connector: Healing of an Unconventionally Constructed Anastomosis
In contrast to other coronary anastomotic connectors,4,5 the unconventional “reciprocal” construction requires connection of the vessel walls as a first step, before making the arteriotomy, hence allowing a completely nonocclusive, simple, and bloodless construction. In addition, in contrast to the conventional hand-sewn, intima apposed to intima anastomosis, the facilitated ELANA anastomosis has some unconventional features, which were comprehensively examined in this pilot study at 6 months’ follow-up. The unconventional anastomosis construction, with (1) a laser-punched arteriotomy, (2) active compression of the vessel walls between the fork and ring of the connector, (3) apposition of the intima of the graft to the adventitia of the coronary artery, and (4) the residual implant (ie, the extravascular spring at the back of the connector and the intraluminal, blood-exposed fork) had no detriment on the long-term patency or remodeling of the anastomosis. Moreover, neither erosion effects nor lumen-narrowing intimal hyperplasia, but rather consistent and streamlining neointimal coverage along the full circumference of the connector, was seen at 6 months’ follow-up. Despite the preexistent undersizing [ie, mismatch of the anastomotic area (±2.5–3.1 mm2) to the target coronary (±4.5 mm2)], which increased over time due to the physiological growth of the porcine coronaries (lumen LAD, 8.6 (0.7) mm2), the anastomotic area expanded (3.8 (0.6) mm2).
Optical coherence tomography acquired high-resolution, in vivo “near-histologic” images. This imaging technique offers a 10-fold higher resolution than IVUS does, which results in acquisition of easy-to-interpret images without loss of detail.6,7 This technique is the criterion standard for the assessment of coronary device (eg, stents) coverage; however, its resolution is just higher than the dimension of endothelial cells, and therefore, it cannot characterize tissues. Thus, its implication in the current application (ie, assessment of intimal coverage of the intraluminal fork) is not validated. However, OCT has potential in the (experimental) ad interim assessment of the anastomosis coverage (ie, acquiring near-histologic data), without the need to kill the animal. In addition, it might have clinical implications as a follow-up assessment technique (ie, assessment of connector and vessel wall apposition, anastomotic healing, and remodeling).
Limitations and Future Perspectives
There are some limitations. This is a pilot study, and inherently, a limited number of anastomoses were evaluated. However, the obtained long-term data in this study provide a “proof of concept,” and hence, it stimulates the ongoing quest and research toward a clinically useful, unconventional anastomotic connector. With regard to the undersizing of the anastomosis, the connector will be downsized to an oval-shaped configuration, with proper matching of anastomotic flow area to coronary lumen area, to target clinically relevant small-caliber coronary arteries (1.2-mm inner diameter). Moreover, to further simplify and accelerate the anastomosis construction, the newly designed connector will be completely sutureless, applicable for (robotic assisted) minimally invasive or totally endoscopic OPCAB procedures.8–12
In this pilot study, the ELANA coronary connector showed an excellent healing response with only minimal streamlining intimal hyperplasia formation on the long-term in the porcine OPCAB model. Hence, this new concept, after ameliorations, might be a potential alternative to hand-sutured anastomosis in (minimally invasive) OPCAB surgery.
The authors thank Glenn Bronkers, Rik Mansvelt Beck, Anouar Belkacemi, Freek Nijhoff, Noortje van den Dungen, Petra van der Kraak, Niklank Noest, Sander van Thoor, Aryan Vink, Steven Chamuleau, Frebus van Slochteren, Tycho van der Spoel, Sanne Jansen of Lorkeers, Chris Schneijdenberg, and colleagues from the Utrecht University Central Animal Facilities for the constructive contributions. The authors thank Volcano Corporation (Rancho Cordova, CA USA) for supporting the experimental use of an IVUS console.
1. Stecher D, de Boer B, Tulleken CA, Pasterkamp G, van Herwerden LA, Buijsrogge MP. A new nonocclusive laser-assisted coronary anastomotic connector in a rabbit model. J Thorac Cardiovasc Surg. 2013; 145: 1124–1129.
2. Stecher D, Pasterkamp G, van Herwerden LA, et al. A new sutureless coronary anastomotic device—Excimer Laser Assisted Non-occlusive Anastomosis (ELANA)—in an off-pump porcine bypass model. Innovations. 2012; 7: 111.
3. Fischell TA, Virmani R. Intracoronary brachytherapy in the porcine model: a different animal. Circulation. 2001; 104: 2388–2390.
4. Suyker WJ, Buijsrogge MP, Suyker PT, Verlaan CW, Borst C, Gründeman PF. Stapled coronary anastomosis with minimal intraluminal artifact: the S2 Anastomotic System in the off-pump porcine model. J Thorac Cardiovasc Surg. 2004; 127: 498–503.
5. Matschke KE, Gummert JF, Demertzis S, et al. The Cardica C-Port System: clinical and angiographic evaluation of a new device for automated, compliant distal anastomoses in coronary artery bypass grafting surgery—a multicenter prospective clinical trial. J Thorac Cardiovasc Surg. 2005; 130: 1645–1652.
6. Agostoni P, Stella PR. Optical coherence tomography: new (near-infrared) light on stent implantation? Heart. 2009; 95: 1895–1896.
7. Burris N, Schwartz K, Brown J, et al. Incidence of residual clot strands in saphenous vein grafts after endoscopic harvest. Innovations. 2006; 1: 323–327.
8. Balkhy HH, Wann LS, Krienbring D, Arnsdorf SE. Integrating coronary anastomotic connectors and robotics toward a totally endoscopic beating heart approach: review of 120 cases. Ann Thoracic Surg. 2011; 92: 821–827.
9. Bonatti J, Lee JD, Bonaros N, Schachner T, Lehr EJ. Robotic totally endoscopic multivessel coronary artery bypass grafting: procedure development, challenges, results. Innovations. 2012; 7: 3–8.
10. Srivastava S, Gadasalli S, Agusala M, et al. Robotically assisted beating heart totally endoscopic coronary artery bypass (TECAB). Is there a future? Innovations. 2008; 3: 52–58.
11. Diegeler A, Matin M, Kayser S, et al. Angiographic results after minimally invasive coronary bypass grafting using the minimally invasive direct coronary bypass grafting (MIDCAB) approach. Eur J Cardiothorac Surg. 1999; 15: 680–684.
12. Falk V, Diegeler A, Walther T, et al. Total endoscopic computer enhanced coronary artery bypass grafting. Eur J Cardiothorac Surg. 2000; 17: 38–45.
This is a pilot study evaluating the anastomotic healing of a novel Excimer Laser Assisted Nonocclusive Anastomotic (ELANA) coronary connector at 6 months in a porcine off-pump coronary artery bypass model. Four anastomoses were examined in three animals by angiography, intravascular ultrasound (IVUS), optical coherence tomography (OCT), and scanning and histology. At follow-up, all the anastomoses were fully patent. Scanning electron microscopy demonstrated complete endothelial coverage of the anastomotic surface. The IVUS and OCT acquisitions confirmed the histologic findings.
There still is no widely used clinically accepted coronary anastomotic device, despite the fact that this has been the goal of a number of start-up companies during the last decade. In this pilot study, this ELANA connector showed an excellent healing response at 6 months. Further studies are keenly anticipated to further define the clinical utility of this new device.
Keywords:©2014 by the International Society for Minimally Invasive Cardiothoracic Surgery
CABG; New technology; OPCAB; Animal model; Anastomotic devices