Overview of Internal Mammary Artery Bypass
The main way that doctors treat severe heart disease that affects multiple blood vessels is through a surgery known as Coronary Artery Bypass Graft (CABG). This surgery uses different types of ‘grafts’ – pieces of healthy blood vessels taken from other parts of your body – to create a new pathway around the blocked heart arteries. Understanding the best kind of grafts to use is important for ensuring the best results from the surgery.
One of the most effective grafts is the Internal Mammary Artery (IMA). Using this artery as a graft tends to improve both the short term and long term health outcomes for patients who have had the CABG surgery. It has been proven to increase patient survival rates.
Another type of graft is the Saphenous Vein Graft (SVG), which is also used in CABG surgery. However, this graft is more likely to get blocked due to the buildup of fatty deposits, a process known as atherosclerosis. Therefore, it doesn’t work as well as the IMA graft over a long period of time. In fact, 10 years after surgery, the IMA graft tends to be performing well in about 90% of cases.
A study by Loop and others showed that patients who received an IMA graft had a higher survival rate than those who received an SVG graft. This was true regardless of whether the patients had disease in one, two, or all three of their coronary arteries. Since this study, the IMA graft has become the preferred choice for bypassing the main artery that provides blood to the front of the heart, known as the left anterior descending coronary artery.
The IMA graft has certain physical features that make it a good choice for this surgery. It’s less likely to develop early blockages from fatty deposits. In the future, we will go into more detail about the IMA, explaining its anatomy, how it’s used in surgery, possible complications, and why it’s important.
Anatomy and Physiology of Internal Mammary Artery Bypass
The internal mammary artery, also known as the internal thoracic artery, is a key artery that helps in supplying blood to the chest wall and breast. It typically originates separately from an artery in your lower neck called the subclavian artery. However, in some cases, it may originate from the same place as the artery supplying your neck and thyroid glands, known as the thyrocervical trunk.
From its point of origin, it moves in front of a part of the chest cavity, before passing under a large vein near your neck, and then moving behind the joint where your sternum (chest bone) and collarbone meet. The artery then moves in front of a part of the chest cavity called the parietal pleura. By the time it reaches your seventh rib, this artery splits into two: the superior epigastric artery and the musculophrenic artery.
When looked at closely under a microscope, this artery appears to be muscular, which is why it can sometimes spasm when handled during surgery. However, it is less likely to spasm than other arteries and veins, because it’s thinner and less muscular. Also, it produces a higher amount of a molecule called nitric oxide, which helps in widening blood vessels, reducing the chances of spasm.
The internal mammary artery is less likely to get hardened due to fat and cholesterol build-up, a condition known as atherosclerosis, compared to the veins often used as grafts in surgery. This is because it has a unique internal structure that makes it less susceptible to a process that can lead to atherosclerosis.
In comparison to veins used in grafting, this artery is narrower, and blood flows through it at about three times the rate. These characteristics, along with its resistance to atherosclerosis and ability to widen in response to certain substances, contribute to the long-lasting effectiveness of the internal mammary artery when used in bypass surgeries. This is why it’s often used in heart surgeries to improve blood flow to a part of the heart, known as the left anterior descending artery. This can significantly reduce the chances of needing repeat heart surgeries.
Why do People Need Internal Mammary Artery Bypass
Discussions about when to use coronary artery bypass graft (CABG) surgery, which is a procedure to improve blood flow to the heart, go beyond what we’re talking about here. However, let’s look at the recommended use of the internal mammary artery (IMA), a type of blood vessel found in the chest, as the preferred choice for this type of surgery.
The American College of Cardiology/American Heart Association guidelines suggest the following scenarios for using the IMA in a CABG surgery [11]:
- Using the left IMA to create a new pathway for blood to reach the left anterior descending artery, an important vessel supplying blood to the heart (this is a strongly supported recommendation, based on moderate evidence).
- When the left IMA can’t be used, the right IMA can be utilized to graft the left anterior descending artery (this is a somewhat strongly supported recommendation, based on moderate evidence).
- When it’s appropriate based on your anatomy and medical condition, another IMA could be used to connect to the left circumflex or right coronary artery. This is done to increase the chance of living longer and reduce the need for additional interventions (this is a somewhat strongly supported recommendation, based on moderate evidence).
- The IMA can be used to graft to the right coronary artery when there is a narrowing of more than 90% of the artery diameter (this is a somewhat supported recommendation).
When a Person Should Avoid Internal Mammary Artery Bypass
There are certain situations where performing a coronary artery bypass graft (CABG) – a type of heart surgery that improves blood flow to your heart – using a specific type of graft from the internal mammary artery (IMA – a blood vessel in your chest) is not suitable:
* If the IMA graft isn’t good enough for use in surgery
* If the patient is quite old, specifically over 85 years.
* If the patient is extremely overweight.
* If the patient isn’t stable, specifically referring to their blood pressure and heart rate (this is what we call hemodynamic instability).
* If the patient has serious lung disease.
* If the patient had prior surgeries in the chest area (as these can make it hard to obtain the IMA for use in the surgery).
* If the patient has a severe cancer or chronic disease that is expected to limit their lifespan to less than six months.
All these situations can make the surgery too risky. It’s worth noting most of these are also general reasons to avoid CABG, not just when using the IMA.
Equipment used for Internal Mammary Artery Bypass
When performing a coronary artery bypass graft (CABG) using a special type of graft called an internal mammary artery (IMA), there are a variety of tools and equipment that are required. In simpler terms, a CABG is a type of heart surgery that’s combined with IMA graft, which is the use of a blood vessel from the chest to bypass blocked arteries in the heart.
Here are the components used during this surgery:
- Operating room: This is the main location where the surgery takes place.
- Sterile drapes, gown, gloves: For the cleanliness and safety of both the medical professional and the patient, these are worn during the procedure.
- Electrocautery: A tool that uses heat to stop bleeding or remove tissue.
- Sternotomy saw: A special type of saw to cut the breastbone, to access the heart.
- Coronary scissors: Used specifically for cutting heart arteries.
- Needle holders, dissecting scissors, micro teeth forceps: Tools for cutting and holding items during surgery.
- Straight and Ring tip forceps: These are specialized clamps used to hold tissues during the surgery.
- Clamps: These are used to keep tissues or vessels in place during the surgery.
- Suction: A tool that removes blood and other fluids from the surgical field.
- Occlusion tips: Tools used to block or close off blood vessels temporarily.
- Papaverine hydrochloride: A medication that relaxes the muscles of your heart’s blood vessels.
- Vessel dilators and probes: Tools used to enlarge or examine the blood vessels.
- Graft markers: Tools that are used to mark where the graft will be placed.
- Silk ligatures: Threads used to tie off blood vessels.
- Harmonic scalpel: A surgical instrument used for cutting and coagulating tissue at the same time.
- Vessel loops and punches sutures: Tools used to make a hole in the vessel for the graft and to then close the vessel after the graft is placed.
These tools used together allow the surgeon to effectively perform the heart bypass surgery.
Who is needed to perform Internal Mammary Artery Bypass?
A Coronary Artery Bypass Graft (CABG) is a complex surgery that involves re-routing, or “bypassing,” blood around clogged veins in the heart. It takes a long time and requires a whole group of medical experts to ensure it goes smoothly. This team will take care of you before, during, and after the procedure.
Your primary care provider is like your main doctor, who looks after your overall health. The interventional cardiologist is a heart doctor who specializes in treating blockages in your heart. A structural heart disease specialist is another heart doctor who focuses on problems with the structure of the heart, like valves or chambers. The cardiothoracic surgeon is a doctor skilled in operations on the heart and chest, and for a CABG operation, will do the ‘bypass’ part of the surgery.
An anesthesiologist is a doctor who will put you to sleep during the surgery so you won’t feel any pain. You’ll also have a surgical assistant, a nurse assistant, and a surgical technician who help with the operation.
After the surgery, a cardiac rehabilitation specialist will help you recover and regain your strength. A nutritionist will advise you on the best foods to eat to help your heart health and recovery. Finally, a pharmacist will make sure you have the right medication to manage pain and aid your recovery.
Preparing for Internal Mammary Artery Bypass
Assessing the risk of surgery is a crucial part of preparing a patient. Two popular tools to predict potential difficulties and dangers during and after the operation are the Euro score system and the Society of Thoracic Surgeons (STS) Risk Model. These tools take into account factors like age, past heart attacks, blood vessel diseases, kidney failure, heart rate and blood flow, and the heart’s ability to pump blood.
The STS model also considers the urgency of the surgery, if it’s a repeat operation, if the patient is in shock, and the presence of long-term lung disease. It’s recommended for patients to keep taking aspirin, especially if they have acute coronary syndrome, a sudden reduction of blood flow to the heart. For those on P2Y12 inhibitors (medicines like clopidogrel, prasugrel, ticagrelor that prevent blood clots), these should be stopped a few days before elective Coronary Artery Bypass Graft (CABG), a surgery that improves blood flow to the heart. Beta-blockers, which slow the heart rate and reduce blood pressure, should also continue to be taken unless there’s a specific reason not to. An intravenous P2Y12 inhibitor (cangrelor) has recently been used to enable earlier CABG operations since it’s short-acting and can be stopped before surgery.
Each patient also needs to have a certain amount of blood, fresh frozen plasma (the liquid part of blood), and platelets (cells that help blood clot) matched to their blood type before the operation. On the day of surgery, the patient has to fast for at least six hours, and antibiotics should be given before the CABG to prevent infection.
How is Internal Mammary Artery Bypass performed
When performing a typical heart surgery called median sternotomy, the patient is laying flat on their back. A roll is placed between their shoulder blades to allow better access to the chest bone, or sternum. Then, the surgery is started by the patient being put to sleep with anesthesia.
After the patient is asleep, a cut is made down the middle of the chest or sternum. The internal mammary artery, or IMA (an artery located in the chest that supplies blood to parts of the chest and abdominal wall), is then harvested. This means the doctor removes it to use elsewhere. The left IMA is often harvested as a whole, while the right IMA is typically stripped of its surrounding tissues because it could interfere with healing of the chest wound. After the IMA has been harvested, an electrocautery tool (a tool that uses heat to cut through body tissues) is used to separate the vein and the IMA. Then, the IMA is separated from the chest wall to expose and cut off the tiny blood arteries.
To get the IMA, the doctor pulls it down carefully with a tool called curved DeBakey forceps and takes off the surrounding tissue. The “branches” are then divided and the IMA is taken from the subclavian artery (a major blood vessel) where it begins. The on-pump bypass heart surgery is then prepared for by placing the patient on a heart-lung machine that takes over the heart’s functions. The aorta, which is the biggest artery in the body, is opened and cannulas or small tubes are inserted into the aorta and right atrium (one of the four chambers of the heart).
Once these cannulas have been put in place and any air bubbles have been removed, they’re connected to the machine. The next steps include locating the diseased areas of the heart’s arteries, where the arteries that were harvested (removed) will be sewn onto. After this, the clamps on the aorta (to stop blood flow) are removed carefully to ensure no bleeding occurs. The chest wound is then closed and a drain is usually inserted to get rid of any fluid that builds up.
After surgery, the patient’s condition is closely watched in the intensive care unit specifically for heart disease related procedures.
Possible Complications of Internal Mammary Artery Bypass
After a heart bypass surgery, also known as coronary artery bypass grafting (CABG), some patients might face problems during and after surgery. These complications include:
* Excessive bleeding during or after surgery
* Heart muscle damage
* Problems with kidney function
* Irregular heart rhythms
* Strokes
* Fluid collecting around the heart leading to pressure on it
* Infections in the lungs
* Infections in the wound where the chest bone (sternum) was cut during surgery
* Failure of the bypass graft.
Only 1% of patients typically have strokes after this type of surgery, but it’s more likely to occur in those who are older, have diabetes or have had a previous stroke. Additionally, people with issues in their arteries, like hardening or narrowing, are more likely to experience a stroke after surgery.
Infections in the chest wound after surgery have become less common, but they’re still more likely in patients who are older, overweight, or have diabetes.
The most common issue with heart rhythm during or after surgery is atrial fibrillation, where the heart beats irregularly and often very fast. It’s usually treated with medicines and blood thinners to prevent blood clots. This condition can also increase the chances of having a stroke and other complications, and could potentially increase the risk of death associated with surgery.
What Else Should I Know About Internal Mammary Artery Bypass?
Strong research evidence indicates that a specific artery, called the internal mammary artery (IMA), tends to experience fewer changes due to a condition called atherosclerosis. Atherosclerosis is a disease where plaque builds up inside your arteries, which can restrict blood flow and cause complications. This artery, when compared to the superior vena cava graft (SVG), a type of graft usually made from a portion of a vein in the leg or the chest, has shown better patient outcomes and survival rates in the long run.
The IMA is considered more effective and reliable than venous or other arterial grafts – places where the vessels are transferred from one part of the body to another to reroute blood flow. This means that when it comes to treatments like a coronary artery bypass graft – a type of surgery that improves blood flow to the heart – the IMA is often the first choice. It’s known as the ‘gold standard.’ A ‘gold standard’ in medicine means it’s the best treatment we currently have available.
