Overview of Retrograde Cardioplegia
Heart disease is a major health concern and is one of the top causes of death worldwide. In 2016, nearly 300,000 patients in the United States underwent heart surgery. For most of these surgeries, doctors needed to make sure the heart was not beating (an ’empty heart’) to perform the operation. This is achieved using a procedure called cardiopulmonary bypass, essentially using a ‘heart and lung machine’ to circulate oxygenated blood while the heart is temporarily stopped.
To protect the heart during this process, a special solution called cardioplegia is evenly delivered to the heart muscle. This solution helps to temporarily stop the heart and protect it from damage. There are different ways to deliver this solution, including forward (anterograde), backward (retrograde), or both.
This article discusses the important aspects of delivering the cardioplegia solution in a backward (retrograde) manner, its uses, and potential complications during heart surgery. Giving the solution in a retrograde manner means that it is delivered in the opposite direction to the usual flow of blood in the heart. This technique is frequently used in modern heart surgeries and the details around its usage will be explained.
Anatomy and Physiology of Retrograde Cardioplegia
The coronary arteries, which start from openings in the root of the aorta (the main blood vessel supplying the body), deliver fresh oxygen-rich blood to the heart muscle. After using this blood, full of nutrients, it circulates back to the right part of the heart through three main paths.
The main route is the coronary sinus, a vein that runs through a groove on the left side of the heart and pours directly into the right upper chamber of the heart, known as the right atrium. Right at the entry of this major vein, there’s a door-like structure called the “valve of Thebesius”. This valve is important when placing a catheter in the coronary sinus. Numerous veins, namely, the small, middle, great and oblique cardiac veins, all pour into the coronary sinus.
There are other ways for blood to be drained from the heart too. For instance, the anterior cardiac veins, there can be between two and five of them, all drain into the right atrium. On the other hand, the Thebesian veins carry the blood from the heart wall back to the lower right chamber of the heart, known as the right ventricle. Also, there are smaller drains like the arteriovenous, venovenous, and venoluminal connections that do not pour directly into the coronary sinus but come from the right upper and lower heart chambers.
Why do People Need Retrograde Cardioplegia
During the early stages of heart surgery that requires a machine to take over the work of the heart and lungs, a technique called ‘cardioplegia’ was used to protect the heart muscle. This was done by delivering a solution through the main artery leading to the heart (the aorta) or directly into the heart’s own arteries. However, it was observed that blockages in these arteries might prevent the solution from providing full protection.
This led to a growing interest in a backwards, or ‘retrograde’, method of delivering the cardioplegia. This means that the solution is delivered by way of the coronary sinus, a sort of collecting pool for the blood that has passed through the heart muscle. This is how it works: First, the surgeon places a tube called a ‘cannula’ in the aorta, to bring in fresh blood from the machine that’s on stand-by. Then, while the heart is still swollen, the surgeon accesses the coronary sinus through an opening in the right upper chamber of the heart, called a ‘right atriotomy’. A specialised delivery tube, which includes a removable flexible insert, is carefully advanced through this opening until it meets resistance in the coronary sinus. The flexible insert is then gently removed.
The next step involves placing drainage tubes to remove blood from the heart so that the machine can take over. Once everything is set up, the heart-lung machine is switched on, the aorta is temporarily closed off, and the cardioplegia solution is delivered via the tube in the coronary sinus.
To make sure the solution travels in the reverse (retrograde) direction – against the usual flow of blood – there’s a balloon near the tip of the delivery tube. The balloon is inflated before the first dose of the solution is given. In specific situations, especially if the surgeon doesn’t need to make any adjustments in the right atrium, a coronary sinus catheter can be placed through the skin. This is usually done through an access point in the neck’s right internal jugular vein.
When a Person Should Avoid Retrograde Cardioplegia
Before inserting a tube into the heart’s main vein (known as a ‘coronary sinus catheter’) to send a special solution used to protect the heart during surgery (this process is called ‘retrograde cardioplegia’), doctors need to thoroughly review any available images of the patient’s heart. This is to make sure the patient doesn’t have any unusual physical features in the heart area.
Particularly, if the person has a condition called ‘persistent left superior vena cava’ (PLSVC), it could cause significant problems with the delivery of the special solution during retrograde cardioplegia. In PLSVC, the main vein that would typically drain the left side of the head, neck, and arm doesn’t develop properly. Instead, the blood returns via the PLSVC and into the vein of the heart called the ‘coronary sinus’.
For patients with PLSVC, the special solution wouldn’t just go into the heart’s vessels. Instead, it tends to travel throughout the entire body because of this unusual vein routing. This prevents the protection of the heart, which this technique is designed to accomplish.
Equipment used for Retrograde Cardioplegia
A retrograde cardioplegia catheter is a special type of tube used to deliver a solution that protects the heart during surgery. These catheters can look different depending on their design. They can be inserted either through a small hole in the skin (usually in the right side of the neck) or directly by the surgeon through a hole made in the right upper chamber of the heart.
This catheter has a few important features. There’s an infusion port, which is an entry point where the protective solution (cardioplegia) is introduced. The catheter also has a manometer, which is a device that measures the pressure in the heart’s coronary sinus, an area that collects oxygen-depleted blood. Finally, there’s a balloon on the catheter that helps block the coronary sinus. This ensures the protective solution is delivered in a reverse flow (retrograde), ensuring the heart gets the right protection during surgery.
Possible Complications of Retrograde Cardioplegia
The biggest problem that can arise from retrograde cardioplegia delivery—a process used to protect the heart during surgery—is a ruptured coronary sinus, which is part of the heart’s blood system. Although it’s very rare, it can make the surgery more complicated and longer. This increases the patient’s exposure to cardiopulmonary bypass times, which means having a machine do the work of the heart and lungs during the surgery. This could also lessen the protection to the patient’s heart during the procedure and could potentially lead to worse outcomes.
What Else Should I Know About Retrograde Cardioplegia?
Cardioplegia is a technique used during heart surgery in which the heart is temporarily stopped so that the surgeons can operate without the disturbances caused by the heartbeats. Retrograde cardioplegia is a specific method of doing this where the heart-stopping solution is introduced into the heart from the point where it normally exits instead of where it enters (this is called “anterograde”).
Studies have found that a combination of both retrograde and anterograde cardioplegia provides better return of heart function than just anterograde cardioplegia alone. This is especially true in the parts of the heart affected by clogged blood vessels. The same research also suggests that retrograde technique enables more uniform cooling of the heart, which may lead to improved function of the left ventricle – the part of the heart responsible for pumping oxygenated blood into the body.
The innermost region of the heart muscle, the subendocardium, is especially sensitive to lack of oxygen. The retrograde cardioplegia method has been found to be more effective at protecting this part of the heart than only the anterograde method.
Other advantages of the retrograde method include allowing for longer surgeries that require the heart to be completely stopped. This is because the surgical team can introduce the heart-stopping solution into the heart whenever necessary through a tube in the coronary sinus, a part of the heart. This wouldn’t be possible with the anterograde cardioplegia, as it could disrupt the ongoing surgery, especially on the aortic or mitral valves or the aortic root. Importantly, during procedures on the aortic valve, it allows for flushing out any foreign material and de-airing of the blood vessels and the aortic root.
During repeat surgeries, old grafts might need to be cut, and any material that could potentially cause a blockage could be flushed out of the blood vessels and old grafts in a retrograde manner.