The successful development of surgical interventions to the beating heart under direct endoscopic visualization has been limited by the difficulty of obtaining a clear image and working area in the presence of blood as it moves within the heart. Several attempts have been made to establish and develop a cardioscopic technique for this purpose.1 Most of these attempts were performed on arrested hearts (without circulating blood) or on explanted hearts to facilitate visualization of intracardiac structures.2–4
We have previously demonstrated a novel approach that allows for sufficient visualization of intracardiac structures of a beating heart with a two-fold design: a bypass circuit for the systemic circulation and a second cardiac circuit that perfuses the heart with a clear solution.5 The objective of this study was to improve the visualization of the left side of the heart without using an aortic clamp and to maintain a clear field for a longer time, during which to perform beating-heart mitral valve surgery with the assistance of a direct endoscopic image.
Visualization of left ventricular (LV) structures, including the mitral valve, was accomplished through an endoscope (Olympus GIF-140, 9.8 mm, 103 cm; Olympus, Center Valley, PA USA), powered by a light source (Olympus CLV-U40) and video processor (Olympus CV-140), via the LV apex. All video images were recorded digitally at the time of the experiment (DCR-TRV480; Sony Corporation, Tokyo, Japan). The fiberoptic endoscope was placed in a flexible, transparent, outer sheath made of polyurethane with an inner diameter slightly wider than the diameter of the endoscope, which was designed and had fabricated in-house (Fig. 1). A communicating space was left between the endoscope and the inside of the sheath, which allowed for continuous infusion of a transparent irrigation solution to keep the area in front of the lens clear of blood.
This study protocol and subsequent amendments were approved by the Institutional Animal Care and Use Committee. All animals were treated in accordance with the Guide for the Care and Use of Laboratory Animals, published by the National Institutes of Health (NIH publication No. 86-23, Revised 1985).
Twelve male Holstein calves, weighing 66.9 to 101.4 kg, were anesthetized by intramuscular injection of ketamine (10 mg/kg) and isoflurane inhalation via mask and maintained with inhaled isoflurane (0.5%–2.5%) with the animals intubated and mechanically ventilated.
Imaging and Surgical Approach
A median sternotomy was performed, and cardiopulmonary bypass (CPB) was instituted after full heparinization (300 IU/kg) with perfusion through the right carotid artery (22-Fr arterial cannula; Medtronic Perfusion Systems, Minneapolis, MN USA) and bicaval venous drainage (a 28-Fr and a 36-Fr venous cannula; Medtronic Perfusion Systems).
In our final model, a perfusion cannula (20 Fr; Medtronic Perfusion Systems) was inserted into the pulmonary artery PA and the left atrium (LA) to perfuse the Ringer's lactate solution. Another cannula (20 Fr; Medtronic Perfusion Systems) was inserted into the lateral wall of the left ventricle through a purse-string suture to drain the irrigation solution. First, 1000 mL of normothermic Ringer's lactate solution was administered for 1 minute to the pulmonary artery, using a separated roller pump to flush out blood in the lung vessels. Then, the irrigation solution (the Ringer's lactate) was continuously infused through the LA cannula and the outer sheath of the endoscope at a rate of 3.0 L/min to provide a transparent field in the left heart chambers, and visualization was obtained (Fig. 2). During irrigation, the LV drainage cannula was partially clamped to keep the LV pressure high enough to maintain the shape of the ventricle but lower than the systemic pressure to ensure that the aortic valve would keep closed. With this irrigation method, oxygenated blood was supplied to the heart through the coronary arteries; meanwhile, the LA and LV were filled with the Ringer's lactate.
Procedures were terminated by administration of potassium chloride (240 mEq/kg) after image acquisition and procedures were completed.
This irrigation method and the outer sheath described above were applied for the last 3 of the 12 experiments. In the first nine experiments with other irrigation methods or without the outer sheath, the clear image was not obtained. With this method, a clear visual field was obtained once the irrigation solution was initiated to the LA and the left ventricle, after the completion of lung-vessel irrigation. This clear field was maintained long enough (>30 seconds) to perform procedures, and the working area for mitral valve edge-to-edge repair was well maintained. Figure 3, showing still images captured from the video acquired from the beating heart, displays the sequence of the edge-to-edge repair of mitral valve using a clip (HX-201UR-135L; Olympus) in the last experiment, and Figure 4 shows the excised heart of that calf, indicating the successful completion of this valve repair procedure.
Systemic Effects of Perfusion
During imaging of the heart, the left chambers were totally isolated from the systemic circulation with the Ringer's lactate solution using our method described earlier. Hemodilution was minimized in the last experiment by using a hemoconcentration circuit (hematocrit: 24.6% at pre- and 22.2% at post-endoscopy-guided procedure).
This is the first in vivo study to report the success of an intracardiac procedure for mitral valve repair under direct endoscopic visualization of the beating heart using transparent perfusate. Beating-heart cardioscopy has been approached variably in the past. In the majority of prior studies, images of intracardiac structures have been obtained through a direct contact between the cardioscope and cardiac tissue or via the use of a transparent balloon chamber to displace blood between the lens of the scope and the object viewed.1,2,6,7 However, with these methods, depth of field is extremely limited, and the scope window or the balloon must be pressed directly against the target structures for visualization. Therefore, interventional procedures should be limited to the target that does not move along with the cardiac motion like septal or ventricular defect repair even if a good image is obtained with these methods. In contrast, a method irrigating the heart chambers8 provides a transparent working environment in which the endoscope does not obstruct the working area at all, so that the in vivo image of moving structures, such as heart valves, are clearly obtained, which is essential for interventional procedures. Although this previously reported method is complicated by blood clouding the field of view when isolation of the heart is incomplete, our technique of irrigation and effective drainage achieved continuous clear imaging for several minutes without any hemodynamic instability. In addition, keeping the LV pressure high enough so as not to have the ventricle collapse but lower than the systemic pressure so as to have the aortic valve keep closed is essential for an interventional endoscopic procedure through the LV.
Alternative real-time imaging techniques to visualize the structures inside the beating heart have been described, including two- and three-dimensional echocardiography and fiberoptic infrared endoscopy.9 The main limitation of such echocardiography-guided approaches is a low-quality visualization as a result of shadowing induced by catheters and surgical instrumentation. In contrast, cardioscopy offers more detailed, high-magnification pictures of the target and provides greater confidence for fine instrument manipulations.10 Therefore, cardioscopy has many potential advantages, especially when applied for procedures such as valve repair, which requires a more detailed image and delicate manipulations. In addition, the use of extracorporeal circulation provides a hemodynamically stable environment, which could improve the safety and accuracy of complex valvular and intracardiac interventions.
The goal of this study was to assess the feasibility of our technique for direct endoscopy-guided mitral valve repair in the beating heart; therefore, the approach was not yet percutaneous, and we did not collect data on the CPB time or procedure time, the survival of the animals, or attempt to wean them from CPB, which was a limitation of the study. However, our study demonstrates the technical potential of minimally invasive beating-heart surgery under endoscopic visualization because the irrigation method and the insertion of endoscope could be achieved percutaneously or through an apical approach. Another limitation is that the clear field was maintained with this system only for a short period (>30 seconds but <1 minute) at a time, which will not be long enough to perform complex procedures. We acknowledge that our fiberoptic instrumentation is larger than would be ultimately desirable for a minimally invasive approach. In addition, we need to develop and refine percutaneous cannulation methods, irrigation methods, and surgical tools for a minimally invasive approach.
In conclusion, we showed the technical feasibility of beating-heart mitral valve surgery under direct endoscopic imaging. Although this study was performed under open-chest conditions, our successful experiment is a first step to lead to closed-chest intracardiac surgery with direct endoscopic visualization.
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This article from Dr. Horai and his group at the Cleveland Clinic describe preliminary work examining the feasibility of endoscopy-guided mitral valve repair in the beating heart. Fiberoptic cardioscopy was conducted in 12 calves. Systemic perfusion was maintained by cardiopulmonary bypass through a median sternotomy. Ringer's lactate solution was administered via the pulmonary artery to flush out the blood and allow better visualization of the left heart chambers. The endoscope was inserted through the left ventricular apex. In one experiment, an edge-to-edge repair was successfully performed using an endoscopic clip. Crystalloid perfusion was able to maintain a clear field long enough (>30 seconds) to perform simple procedures. The visualization shown in Figure 3 was quite remarkable.
Readers are to be reminded that this was a feasibility study and no attempt was made to wean animals from bypass or survive the animals. The approach clearly was not percutaneous or even through a small incision. Moreover, the clear field was maintained only for a very short period of time of less than one minute. This clearly would not be enough time to perform a complex procedure. However, this interesting and innovative small study demonstrates the feasibility of beating heart mitral surgery under direct endoscopic imaging. Further refinement of the fiberoptic technology, instrumentation, and technique will be needed before this novel approach is ready for clinical application.
Keywords:© 2011 Lippincott Williams & Wilkins, Inc.
Minimally invasive; Mitral; Endoscopy