Overview of Warm Blood Cardioplegia
Cardioplegia is the practice of protecting the heart during surgery by temporarily and purposefully stopping it from beating. This is achieved through the use of a special solution rich in potassium, which is administrated to induce what’s known as diastolic cardiac arrest. The aim is to significantly lower the heart’s need for oxygen, which is very useful during surgeries when the supply of oxygen to the heart can fluctuate. The key goal of cardioplegia is to create a safe and still environment for the surgical procedure while preserving the function of the heart.
Initially, the technique was centered around cold crystalloid cardioplegia (CCC). This method utilized cold solutions known as crystalloids to halt the heart during surgery. Starting from the 1950s, this was the most popular approach used for heart-based surgical practices.
However, in the 1970s, surgeons started using blood as a tool for cardioplegia delivery. This was due to blood’s excellent oxygen-carrying ability, natural buffering skill provided by histidine, and excellent osmotic qualities. In fact, blood cardioplegia is currently used by around 72% of heart surgeons in the U.S.
Even though there are no nationwide standards for the cardioplegia solution formulation, the temperature of the solution is subject to discussion. While cold solutions are beneficial for reducing oxygen demand, they can unfortunately disrupt the heart’s natural regulatory processes. On the other hand, warm blood cardioplegia (WBC) can generate balanced metabolic surroundings for the heart, aiding in the revival of energy-exhausted heart tissue. The first use of continuous warm cardioplegia was reported by Lichtenstein et al. in a patient requiring an extended time frame of over 6 hours of surgery.
Anatomy and Physiology of Warm Blood Cardioplegia
The right and left coronary arteries, which are blood vessels that come from the base of the aorta, provide blood to the heart muscle. Most of the blood from the heart is sent to the right side of the heart through a structure called the coronary sinus. The coronary sinus is located in a groove on the back side of the heart and it empties directly into the right upper chamber of the heart, also known as the right atrium.
The white blood cells (WBC) are usually sent in the direction of blood flow through the aortic sinus (or directly through individual coronary openings). They can also be sent in the reverse direction of blood flow through the coronary sinus. This is done using a tube placed in the coronary sinus through the right atrial appendage, which is an extension of the right atrium. The release of these white blood cells can happen in bursts or continuously, depending on several factors such as the type and requirements of the surgery, the surgeon’s choice, and other technical factors.
Why do People Need Warm Blood Cardioplegia
The best temperature to use for stop-heart solution (known scientifically as “cardioplegia”) is still under debate. Cardioplegia is a solution used during heart surgery to temporarily stop the heartbeat. For the past 30 years, many surgeons have used a warm blood version of the cardioplegia solution (WBC for short) instead of a colder version, but not all doctors agree on which one is better.
The warm-blood method has shown promise as it can help our heart recover better after the surgery. By using the warm-blood solution first, then switching to a cold cardioplegia solution, doctors may be able to potentially ‘jump-start’ the heart in patients who have a higher risk of temporary loss of blood supply to the heart. What this means is, the warm-blood solution could initially stop the mechanical activity of the heart, reducing its energy needs, and help the cells in the heart to balance chemicals and recover its energy store known as ATP. This recovery stage can also help refocus the body’s oxygen towards repairing and restoring the heart’s metabolism.
There are several advantages to using the warm blood cardioplegia solution, including:
- Improved healing and repair of the heart.
- Better delivery and separation of oxygen.
- Reduced swelling of the cells in the heart.
- Decreased changes in the shape of red blood cells and the clumping together of these cells (known as rouleaux formation).
- Less impact on the cell processes that need ATP energy.
- Better stabilization of the cell membranes in the heart.
When a Person Should Avoid Warm Blood Cardioplegia
The Warm Heart Trial was a significant study that found that using warm blood during heart arrest (cardioplegia) in surgeries can reduce death rates and instances of low heart output. Furthermore, an analysis of multiple other studies published in 2010 found similar rates of death and heart attacks in surgeries that used warm blood or a cold fluid (cold crystalloid cardioplegia).
Another analysis compared using the cold fluid versus cold blood during heart arrest. This time, they found no notable differences in the chances of heart rhythm problems, death in 30 days, stroke, or new incidences of irregular heart rhythms between the two methods. However, using cold blood did result in fewer heart attacks during surgery.
Even though using warm blood during heart arrest has its advantages, it does come with some potential drawbacks:
– Problems with distribution of the solution used to stop the heart
– Difficulty in seeing the workings of the small blood vessels in the heart
– Need for more medications that tighten the blood vessels due to the widening effects of the warm blood
– Warm heart surgeries are complicated to perform
– Higher possibility of brain damage or strokes during surgery
– Need for more frequent dosing when using the warm blood technique intermittently
– A worsened injury from inadequate blood supply, especially when adding warm blood intermittently
– Weak protection for heart muscle, especially in surgeries that need a long period of stopping the blood flow in the main artery to the heart.
Possible Complications of Warm Blood Cardioplegia
One of the feared side effects of a type of heart protection method known as warm blood cardioplegia is the risk of strokes and neurological damage during or after surgery. Warm blood cardioplegia is a technique used to protect the heart during surgery by reducing its need for oxygen. A large clinical trial from Emory University had to stop early due to an unexpectedly high number of strokes and other neurological problems during or right after the operation.
Operating on a warm or slightly cool heart during surgery often causes the blood vessels to widen. This is a concern when the body’s blood circulation is being assisted using a heart-lung machine (known as cardiopulmonary bypass). The widening of the blood vessels can lower the blood’s pressure, requiring the use of certain medications known as alpha agonists to increase it.
Another issue with the warm blood cardioplegia method may make it harder for the surgeon to see while they’re operating. This is particularly a problem when the surgeon is trying to connect one part of a blood vessel to another, called a coronary anastomosis, particularly when it’s located further away in the heart.
What Else Should I Know About Warm Blood Cardioplegia?
In 1977, scientists introduced a new technique called warm-blood cardioplegia, which was meant to protect the heart during surgery. This method was designed to reduce heart damage that happens due to the temporary stoppage of blood supply during the operation (ischemic reperfusion injury).
Cardioplegia, which is the process of stopping the heartbeat to perform surgery safely, is usually carried out by injecting a solution, rich in potassium, mixed with the patient’s blood into their heart. While traditional heart-stopping techniques used cold solutions delivered at 4 degrees Celsius, this new method delivers the solution at 34–35 degrees Celsius.
Research has found this warm technique potentially less harmful to the heart, and it may also improve recovery after surgery. The delivery of warm-blood cardioplegia can happen in two ways – either forward from the aortic root or backward through a large vein found at the back of the heart, known as the coronary sinus.
Another traditional approach termed cold crystalloid cardioplegia (CCC), has shown good outcomes in heart surgeries but can cause a slow recovery of the heart function and metabolism after surgery. The use of cold temperature alone doesn’t significantly lower the heart’s oxygen demand and can have harmful effects on cells, leading to several cellular problems.
Those who endorse warm-blood cardioplegia believe that using the patient’s blood in the cardioplegia solution is more natural, providing better stability and flow and superior oxygen delivery compared to other solutions. Additionally, the antioxidant properties of blood may help reduce ischemic injury and limit reperfusion injury once the blood supply is restored post-surgery.
Other strategies to protect the heart during surgery include using a high potassium solution to stop the heart, lowering the heart’s temperature to reduce its oxygen requirement, monitoring the cardioplegia solution’s pressure to reduce heart swelling, using specific solutions to manage acid levels caused by ischemia, and avoiding too much oxygen, fluctuating calcium levels, high blood sugar, and high temperature.
Warm-blood cardioplegia holds promise, offering potential protection against ischemic injuries by removing the need for cold temperatures. However, it does present some drawbacks, including poor visualization during surgery, increased heart-stopping solution requirements, and a potential rise in neurological complications. Other potential issues include an immune system response, increased usage of medicines to counter blood vessel dilation, and higher fluid demands. Current evidence does not solidly support universally switching to this method. While it may offer some benefits for hearts already affected by a lack of oxygen, routine use of continuous warm-blood cardioplegia is not recommended at this time.
