Overview of Myocardial Protection
Heart surgery has come a long way, and it was soon found that in order to treat complex heart conditions, surgeons needed to stop the flow of blood through the heart. This would let them open the heart and perform surgery without blood getting in the way. This finding led to the creation of two important techniques for open-heart surgery.
The first technique, introduced by John Lewis and Mansur Taufic in 1953, was based on the idea of blocking the flow of blood into the heart. A year later, Walton Lillehei introduced a method called “controlled cross circulation”. This method was very effective in treating heart diseases that were previously impossible to operate on, such as ventricular septal defect, atrioventricular septal defect, tetralogy of Fallot, and pulmonary stenosis.
However, these techniques had some drawbacks. Surgeons found it challenging to operate on a beating heart, there was a risk of air bubbles entering the bloodstream when the left side of the heart was exposed, and they had trouble seeing and controlling the flow of blood from the coronary sinus and pulmonary veins. Therefore, it became clear that they needed to stop the heart entirely to effectively perform open-heart surgery. This marked the start of a new era in heart surgery.
Now, we will review the methods used to protect the heart during surgery, which are essential in modern heart surgeries. These methods aim to keep the heart safe and healthy during and after the procedure.
Anatomy and Physiology of Myocardial Protection
Your heart is an organ that performs a lot of work, and like any hard-working machine, it needs to be well cared for to keep doing its job. To do this, doctors may sometimes use a technique called ‘myocardial protection’ during heart surgery. It basically involves stopping your heart from beating temporarily, decreasing its need for energy, while ensuring its cells stay safe and intact. It also makes the surgery easier to perform and safer for you, eliminating unnecessary movements and reducing your risk of developing an air bubble in your blood vessels (air embolism).
During heart surgery, there’s a stage called ‘intraoperative myocardial ischemia’. This is a fancy way of saying that the heart’s blood flow is temporarily reduced, causing a lack of oxygen and increase in a chemical called lactate. This imbalance can harm cells if allowed to continue for too long. Therefore, treatment is crucial to prevent cell damage.
Mitochondria, tiny structures inside cells that produce energy, also need to stay protected throughout this process. If these mitochondria are damaged, cells can potentially die. To avoid this, doctors aim to keep certain ‘doors’ (mPTP) within the mitochondria closed, and activate some protective pathways to maintain energy supply within the cells.
On resuming blood flow to your heart after the surgery, your heart can face challenges due to something called myocardial reperfusion injury. Your heart’s functioning might get temporarily impaired due to intense mechanical stress. Additionally, there can be an excessive production of harmful molecules and other damaging processes. Disturbances in heart rhythm and no-flow phenomenon, where blood flow fails to resume despite optimal medical treatment, are also potential complications that need to be tackled.
The foundation of this whole process, called cardioplegia, lies in understanding and controlling the interaction between various chemicals (like potassium) and heart cells. By utilizing this knowledge, doctors can safely and temporarily stop your heart, ensuring it remains healthy during complex heart surgeries.
More recently, we’ve found out that restarting the blood flow can also cause some damage. One particularly critical issue is called calcium overload, where too much calcium enters heart cells and causes damage. Consequently, the proper regulation of calcium during and after surgery is crucial, and physicians carefully evaluate both the beneficial and detrimental effects of this process.
Why do People Need Myocardial Protection
During heart surgeries, it’s vital to protect the heart muscle when blood flow needs to be temporarily stopped. This is especially important in certain procedures where the heart must be paused, or “arrested” using a technique called cardioplegia.
Depending on the procedure, access to the heart’s inner chambers may be necessary – these are known as ‘open-heart’ surgeries. Examples include replacing or repairing heart valves, like the aortic or mitral valve. When the heart isn’t stopped, these kinds of surgeries aren’t classified as ‘open-heart’. Instead, they might be labelled as ‘closed-heart’, ‘beating heart’, or ‘bypass’ surgeries. However, even if direct access to the heart’s chamber isn’t needed, procedures that involve stopping the heart like coronary artery bypass grafting, are also considered ‘open-heart’ surgeries.
Besides these, protecting the heart muscle is also crucial in surgeries involving congenital heart defect repairs, complex reconstructive procedures, heart transplants, or when using devices such as extracorporeal membrane oxygenation or ventricular assist devices.
The method used to protect the heart during these surgeries could range from cardioplegia, cooling the heart (hypothermia), or using mechanical support. The choice depends on the specific procedure and the patient’s condition. The main goal is to minimize the injury caused by stopping and then restarting blood flow (known as ischemia-reperfusion injury), prevent any permanent damage, and improve the results after the surgery.
When a Person Should Avoid Myocardial Protection
If a person has heart problems, doctors may use certain protection strategies when carrying out treatment. However, these methods need to be carefully thought through for each individual patient, to avoid making their condition worse.
For example, one technique doctors use to protect the heart is called hypothermia, which is lowering the body’s temperature to reduce the demand for oxygen in the heart muscle. This can’t be used in people with a condition called cryoglobulinemia, where abnormal proteins cause their blood to clump together in cold temperatures. If their body is cooled, it can cause serious blood clots and make their condition worse.
Another method is using a cross-clamp on the heart’s main artery, the aorta, during surgery. But if the aorta is heavily calcified, a condition known as a porcelain aorta, it becomes brittle and can easily break. Applying a cross-clamp to a porcelain aorta increases the risk of stroke or tearing this essential artery, which can lead to serious complications.
Patients with severe infections, either in the whole body or in a localized area, may not be suitable for these heart protection methods, as the stress of surgery could make their condition worse. The same applies to individuals with severe imbalances in their body’s chemistry, or if they were born with anomalies affecting how their heart works. In these cases, doctors need to consider personalized approaches to protect the heart, to reduce risks and meet specific needs of the patient.
Equipment used for Myocardial Protection
The process of stopping the heart, known as cardioplegia, during heart surgery requires a variety of special equipment and tools. These are used to make sure that the heart-stopping medicines are correctly delivered and that the heart is protected during the procedure. The necessary equipment includes:
Cardioplegia delivery systems: These are used to pump the special heart-stopping medicine directly into the blood vessels that supply the heart. They usually include a pump to control the medicine’s flow and pressure, and flexible tubes and needles (cannulas) to deliver the medicine. There are different ways to deliver the medicine. In the past, clear liquid solutions were used and were given using a simple infusion set from the anesthesia team. But doctors prefer using the patient’s blood to carry the medicine nowadays. They add the medicine to the blood using a special pump connected to the heart and lung machine (CPB), which gives them precise control of the amount, temperature, and blood mix.
Temperature control equipment: Cool body temperature (hypothermia) is often used to protect the heart during surgery. Devices and systems to adjust and maintain temperature, such as cooling gadgets, heat exchangers, and thermostatic blood warmth systems, are used to control the drug’s temperature and the body. This is crucial to avoid getting the body too hot or too cold.
Oxygenators and pumps: These are used to add oxygen to the blood and move it around the body during the procedure. Even though they aren’t directly involved in stopping the heart, they’re crucial in keeping blood flow going while the heart is stopped.
Monitoring systems: These are important to keep an eye on how well the heart-stopping process is working and how the heart is doing overall. They may include devices to measure pressure, flow meters, and temperature sensors to monitor the delivery of the heart-stopping drug and the heart’s protection state continuously.
Heart-stopping solution preparation equipment: This includes equipment to mix the heart-stopping drug and sterile containers. This makes sure the drug is prepared correctly and kept in sterile (germ-free) conditions. The heart-stopping drug often has a high concentration of potassium to stop the heart and other additives to lessen the effects of not having enough blood supply to the heart (ischemia).
Cannulation devices: Tubes (cannulas) are used to access the heart’s blood vessels to deliver the heart-stopping drug and remove blood from the heart during surgery. Picking the correct tubes and placing them correctly is vital to adequately protect the heart.
Who is needed to perform Myocardial Protection?
Protecting the heart effectively during heart surgery is a complex task that needs a team of skilled professionals. Each team member has specific skills and plays a significant role in making sure patients get the best results from the operation. Here’s who is involved:
– Heart Surgeons: These are specialized doctors who perform your heart surgery.
– Anesthesiologists: They are responsible for making sure you don’t feel any pain during the surgery. They “put you to sleep” safely before the operation starts, and “wake you up” when it’s over.
– Perfusionists: They ensure that your heart’s blood supply keeps going while your heart is stopped for the surgery.
– Surgical Nurses: They assist the surgeons during surgery and are responsible for your care and monitoring before and after the operation.
– Cardiac Surgical Technologists: They handle the surgical instruments, ensuring they are always ready and in good condition.
– Clinical Perfusion Scientists: They monitor and manage your body’s vital functions during the surgery.
– Biomedical Engineers: They operate and maintain the equipment used during your heart surgery.
– Pharmacists: They work with your doctor to choose the best medications for you and ensure the correct administration before, during, and after surgery.
All these professionals work together to ensure that your heart surgery goes smoothly and safely.
Preparing for Myocardial Protection
The heart safety system is a part of a larger machine that’s generally used in heart bypass surgeries. You can check out our previous article for more information on this machine.
How is Myocardial Protection performed
When it comes to heart surgery, it’s crucial to protect the heart (myocardial protection) and the body, particularly the brain (cerebral protection). This is achieved with the help of a machine that maintains blood circulation throughout the body, and does the job of the heart and lungs (CPB machines). However, additional methods are needed to ensure the heart can survive the process.
Early surgeons invented two primary methods to protect the heart during surgery. A doctor named Bigelow suggested cooling the body (hypothermia), while another named Melrose introduced a technique where the heart was temporarily made dormant, or “put to sleep,” (cardioplegia). Other techniques came about as medical science advanced over the years. It’s important to understand that these are all forms of myocardial protection and not just cardioplegia alone.
Interestingly, the two initial methods evolved and contribute to today’s methods in heart surgery. Bigelow’s concept of hypothermia laid the groundwork for modern deep hypothermic arrest. In contrast, Melrose’s cardioplegia technique served as the foundation for future developments in this area.
Originally, a solution containing 2.5% potassium citrate was used to cause the heart to stop, or “arrest,” while supporting it with the heart-lung machine. Unfortunately, this method often resulted in heart issues after surgery, leading to a temporary shift towards methods that didn’t use cardioplegia. Instead, three main approaches were used: operating on a heart in the process of beating, hypothermia, and preconditioning the heart to ischemia, or a shortage of oxygen.
In hypothermia, the body is cooled down to slow its metabolic rate and oxygen demand. When the body temperature is quite cold (around 4 degrees Celsius), the heart’s oxygen consumption is reduced by about 97% and can tolerate being without its regular blood supply for around 45 minutes— much longer than the 15 minutes at normal body temperature.
Ischemic preconditioning is a more modern method of protecting the heart during surgery. There are two general types: local and remote. Local ischemic preconditioning involves inducing a state of temporary oxygen loss before aortic cross-clamping (a process of halting blood flow in the aorta, which is the main artery in your heart). Remote ischemic preconditioning induces brief episodes of oxygen deprivation followed by a restoration of blood flow in a part of the body away from the heart, for example, a limb, which helps to protect the heart from any potential injury.
Despite the potential setbacks in some of the historical methods, they have all contributed to the medical advances in heart surgery. The common goal of these techniques is to minimize injury to the heart during surgery, providing the best possible outcomes for patients.
Possible Complications of Myocardial Protection
Heart surgery is a complex procedure and has some associated risks, even with all the measures taken to protect the heart during the operation. Here’s what can go wrong, why, and what these complications might look like:
The use of special techniques to safeguard the heart tissue can still lead to heart muscle (myocardial) damage. This can be caused by lack of oxygen and blood flow to the heart (ischemia) during surgery and subsequent restoration of blood flow (reperfusion) which can lead to inflammation, high levels of harmful molecules (oxidative stress), and flooding the cells with calcium, leading to further damage. This could cause the heart to temporarily lose function (myocardial stunning), develop life-threatening reperfusion injuries, and irregular heartbeats (arrhythmias).
Special fluids (cardioplegic solutions) used to protect the heart during surgery might cause problems with calcium levels in the cells. Too much calcium can harm cells and not enough calcium followed by a sudden influx can cause severe heart damage. This is known as the calcium paradox.
These cardioplegic fluids have to maintain a fine balance of minerals like potassium, calcium, and sodium. Too much or too little can disrupt the heart’s normal functioning.
Sometimes, these solutions might not reach all parts of the heart, leaving some areas unprotected. This is a challenge especially in patients with significant blockages in the heart arteries or complex heart disorders.
Lowering body temperature (hypothermia) is also used during heart surgery to reduce the heart’s demand for oxygen, but it can cause problems with blood clotting (coagulopathy), irregular heartbeats (arrhythmias), and other body-wide issues related to low temperature. It’s also not appropriate for patients with a certain blood disorder because it could cause blood cells to cluster together (clumping).
Long exposure to the cardioplegic solutions can be toxic to heart cells. Certain substances in these solutions, like preservatives and other added components, can harm the heart if not managed properly.
Using heart-protection techniques and a heart-lung machine (CPB) can lead to unstable blood pressure and heart rate (hemodynamic instability) during surgery. This could complicate the surgery and make recovery more challenging.
Finally, the use of heart-protection techniques can increase the risk of infections because it involves multiple IV lines and access points. Strict measures to maintain sterility and careful monitoring are crucial to reduce this risk.
What Else Should I Know About Myocardial Protection?
Heart surgery can be a complex process that often involves the use of a heart-lung machine, also known as Cardiopulmonary Bypass (CPB). This machine does the work for your heart and lungs while they are stopped for surgery. A significant part of ensuring at successful heart surgery involves protecting the heart muscle during the process, particularly during operations like valve replacements and coronary artery bypass grafting, which is a procedure to improve blood flow to the heart.
Thanks to medical advancements over the years, we’ve developed several strategies to protect the heart during these surgical procedures. These strategies include deliberately cooling the body (hypothermia), stopping the heart with a special solution (cardioplegia), and selectively feeding blood to specific heart areas (regional perfusion). However, each approach comes with its own benefits and potential challenges, which further makes it important to choose the right method depending on each person’s unique situation.
The evolution of heart surgery has been closely linked with the development of these protective techniques. Developing a deep understanding of these methods is very important for heart surgeons, as it allows them to protect the heart effectively during surgery. For a successful operation, surgeons must maintain a balance between performing the procedural steps and ensuring the protection of the heart muscle. Training new surgeons on the advantages and challenges of different heart protection methods is crucial to continually improve patient outcomes and advance the field of heart surgery.