On July 23, a Minimally Invasive Direct Coronary Artery Bypass (MIDCAB) procedure was successfully performed at the Department of Cardiovascular Surgery at Guangdong Provincial People's Hospital, which lasted two and a half hours. This is the first MIDCAB procedure to use indocyanine green (ICG) fluorescence imaging for graft assessment, performed by Professor Liu Jian, an expert in minimally invasive cardiovascular surgery at the hospital.

Research indicates atherosclerotic coronary artery disease (CAD) is among the cardiovascular diseases with the highest rates of incidence and mortality globally. Coronary artery bypass grafting (CABG) procedures are an effective approach for treating complex coronary artery lesions ^[1]. Recently, as minimally invasive surgical techniques and tools have improved, Minimally Invasive Direct Coronary Artery Bypass (MIDCAB) has become a promising option for treating CAD. This procedure involves smaller incisions and does not require cardiopulmonary bypass, making it a less invasive choice for patients.

Professor Jian Liu is one of the few experts in China with expertise in a variety of techniques, including percutaneous interventions, totally endoscopic surgery, various small-incision procedures, and traditional open-heart surgeries. He is also the first in South China to perform numerous minimally invasive cardiovascular procedures and use innovative devices and he is a leading expert in delivering related training.

This procedure was performed with HyPixel UX5, Mindray¡¯s latest 4K NIR 3D endoscope fluorescence imaging system, which confirmed the benefits of fluorescence endoscopy for minimally invasive cardiac surgery. This marks the beginning of incorporating fluorescence endoscopy into such procedures.

What distinct advantages does fluorescence endoscopy offer for minimally invasive cardiac surgery? What significance does the first fluorescence-guided MIDCAB procedure hold for clinical practice? As minimally invasive techniques become more prevalent, what additional potential might fluorescence endoscopy reveal?

Recently, Mindray had the privilege of speaking with Professor Liu, where he shared his practical experience and insights on fluorescence-guided minimally invasive cardiac surgery.

Q: Mindray
A: Professor Liu

Q: What motivated you to use fluorescence endoscopy in MIDCAB?

A: In MIDCAB, the methods for assessing graft and anastomosis patency during the operation are somewhat limited. At present, many centers rely on the surgeon's experience to assess graft patency, lacking objective measures. To address this, some centers utilize a "flow probe," specifically a transit-time flow meter (TTFM), to assess the grafts. This tool helps to quickly identify graft patency issues that may arise from anastomosis and other factors during the procedure. However, TTFM has its limitations: blood flow in the grafts can vary with different blood pressure levels, which may lead to an overestimation of flow under high blood pressure and impact the accurate assessment of graft and anastomosis stenosis. Coronary arteriography (CAG) is the "gold standard" for assessing the degree of stenosis, and gives a clear picture of how narrow arteries are. However, it requires radiation and contrast agents and must be done in a hybrid operating room or catheterization lab. This procedure involves radiation exposure, and some patients may develop contrast-induced kidney problems. Additionally, its high cost limits its use for evaluating grafts during bypass surgery. So, we had been looking into whether there¡¯s a way to assess coronary arteries that¡¯s as effective as CAG but cheaper and easier to access.

Near-infrared fluorescence laparoscopic technology with Indocyanine green (ICG) has seen rapid advancement in gastrointestinal, liver, and lung surgeries, partly because it helps assess areas with vascular enrichment. This has led us to explore the potential of applying ICG fluorescence endoscopy in MIDCAB procedures. Outside China, some surgeons performing CABG through a "median sternotomy" use ICG contrast imaging to assess the patency of vascular anastomoses. However, there had been no recorded instances of ICG fluorescence endoscopy being used in MIDCAB procedures worldwide.

Our center (Cardiac Surgery Department of Guangdong Provincial Cardiovascular Institute, Guangdong Provincial People's Hospital) is a national training base for minimally invasive techniques, as designated by the National Health Commission. We are also a leading training base for thoracoscopic cardiovascular surgery in South China. I possess extensive experience in both minimally invasive cardiac surgery and the use of endoscopic techniques. With the ongoing improvements in ICG fluorescence endoscopy, which now offers much better penetration and clarity, we believe it¡¯s the right time to test how effective this technology is for MIDCAB procedures.

Q: So, how do you assess the performance of fluorescence endoscopy in surgery? What aspects do you find particularly valuable?

A: Firstly, the system provides clear images and a detailed view of the surgical field. By magnifying the field 3-5 times in 4K high definition, it helped us easily identify the left internal mammary artery and quickly locate and retrieve the graft vessel.

Secondly, we used the system for ICG fluorescence angiography to evaluate the patency of the anastomosis right after it was done. This helped us check if the graft vessel was narrowed, if the anastomosis was unobstructed, and if we needed to perform any additional intervention on the graft or anastomosis. With a penetration depth of up to 8 mm, the system can penetrate the thin layer of fat on the graft vessel and the heart tissue distal to the anastomosis. This enables the surgeon quickly assess the quality of the graft vessel and the anastomosis.

In summary, the intraoperative ICG fluorescence angiography worked as expected, giving clear images that effectively revealed blood flow in the graft vessels after surgery. In this regard, this technique demonstrates potential comparable to CAG.

Thirdly, from a health economics perspective: It's important to note that the transit-time flow meters and probes commonly used today are quite expensive, which limits their use in many hospitals. Additionally, these flow probes are consumable and can only be used 10-20 times, which adds to the overall cost. In contrast, ICG fluorescence endoscopy involves using fluorescence imaging, without incurring additional costs. This can lower the cost associated with vascular assessments in minimally invasive cardiac surgery, lessen the financial burden on insurance and patients, and benefit more CAD patients.

Q: How has the patient been doing since the surgery?

A: We used ICG fluorescence angiography and a transit-time flow meter (TTFM) for cross-validation, ensuring that the graft flow and anastomosis were functioning as desired. The patient had a smooth recovery. The endotracheal tube was removed 3 hours after surgery, and the patient was moved to a regular ward on the first day. That afternoon, the chest tube was also removed, and the patient started moving around for rehab. By the third day, with satisfactory follow-up results, the patient was discharged. With minimally invasive procedures and quick recovery techniques, cardiac surgery no longer means cutting open the chest and leaving a long, vertical scar. Now, it¡¯s less traumatic and recovery happens much faster.

Q: What unique benefits do you think fluorescence endoscopy can bring to patients in minimally invasive cardiac surgery?

A: The minimally invasive cardiac surgery, which needs to be successful both now and in the future, is primarily aimed to help patients recover faster and get back to their normal lives sooner. This is done by reducing the amount of trauma they experience during surgery, shortening their hospital stay, and speeding up their recovery process. A notable advantage of ICG fluorescence endoscopy is that it poses no extra damage or risk to the patient, since ICG is almost entirely safe for the body. ^[2]

Moreover, unlike CAG, fluorescence endoscopy uses light instead of radioactive materials, which removes the radiation risk for both the patient and the surgeon. Due to its radiation risks, CAG can only be used before or after a procedure, not during it. This restriction impacts how well we can assess the graft and anastomosis during the procedure, which is the most critical part of coronary artery bypass surgery. Fluorescence endoscopy avoids the radiation and kidney damage associated with CAG during surgery. It also has the potential to provide a quality assessment of the surgery that is nearly as good as CAG. This is its unique advantage.

Q: What does the future look like for using fluorescence endoscopy in minimally invasive cardiac surgery? What technical innovations and improvements are still needed?

A: From this procedure, we see that ICG fluorescence endoscopy could be a great tool for checking the patency of grafts and anastomoses during minimally invasive cardiac surgery. Of course, we still need to explore further, such as the harvesting of grafts during surgery, the adequate dissection of target vessels, the timing and dosage of ICG injection, setting up appropriate exposure parameters, switching between white light and fluorescence, and improving the ability of fluorescence endoscopy to penetrate and identify details. These steps will help us find the best practices for MIDCAB procedures. We are also conducting research to delve deeper into these areas. In the future, we aim to establish consensus and guidelines for the use of fluorescence endoscopy in minimally invasive cardiac surgery by continuing our own research and the synergy between medicine and engineering.