I am sure you often hear terms, such as, bypass surgery, heart block, pacemaker, a ‘hole in the heart’ etc. Here is a simple way to understand them. First, you need to know the basic anatomy and physiology of the heart.
Best way to describe them is to use an example of a two storied house, with two bed rooms in each floor (see picture above). The rooms in the first floor are the receiving chambers of the heart. The top left one receives de-oxygenated (impure) blood from the whole body. This room is called “Right atrium”. It then sends the blood to the bottom left chamber in the ground floor (right ventricle) through a trap door in its floor (see picture). The door is actually a heart valve called ‘Tricuspid valve”, as it has 3 cusps which open and closes like an umbrella allowing blood to go in only one direction and that is downwards. The bottom chambers are the pumping chambers of the heart. The right ventricle (bottom left room) then pumps the de-oxygenated blood out to the lungs (not shown in the diagram) to become oxygenated. Once oxygenated, the blood returns to heart and to the top right room (Left atrium)which receives it, and sends it to the ‘Left ventricle’ (the room on the right side on the ground floor) again through a trap door on its floor called “Mitral valve’. Then the left ventricle pumps out the pure, oxygenated blood to the rest of the body. This whole process is called a ‘Cardiac cycle’ and it takes only one relaxation and one contraction of the heart.
Surgically Correctable Common disorders of the Heart
Perhaps, you have noticed that there is no connection between the right and the left side of the heart. This is to prevent mixture of pure and impure blood. However, there may be a birth defect which creates a communication between the upper two rooms (see picture) or lower two rooms. They are septal defects, commonly known as a ‘Hole in the heart’. The defect communicating the two upper rooms (atriums) is called ‘Atrial septal defect’ and similarly the one causing abnormal communication between the ground floor rooms are called ‘Ventricular septal defect’. If the holes are too big then they are closed by open heart surgery. Sometime a small hole can be closed by a button like device. These devices are sent via thin catheters through the groin of the patient under local anesthesia and a surgery can be avoided.
Heart valve disease: The trap doors, as you see in the picture, are also prone to disease. They can shrink or can leak, allowing the blood to go back the wrong way. This can result to heart failure. In our country valve diseases are commonly due to rheumatic fever, a childhood disease with fever and joint pains. The vales, once diseased, can either be repaired or replaced with an artificial heart valve by open heart surgery. However, a simple, purely shrunk valve can again be opened up by a balloon, sent from the groin, thus avoiding surgery.
Pacemaker implantation: You will note that there is a generator on the roof of the house(colored in green). This is heart’s own generator. It sends out electrical impulses via (green colored) nerve bundles through out the heart muscle to make it contract in a regular rhythm. The generator itself or any of the major bundles can become non functional, disturbing the heart’s rhythm and then heart rate becomes very slow, often causing the patient to feel giddy. Sometimes the rate may become very slow and patient gets a blackout. This is called ‘Heart block’ (electrical). Then the doctors implant an artificial pacemaker from out side with an electrical lead or leads going down to heart muscles. The out side pacemaker is housed in a pocket just below the collar bone. The pacemakers are then programmed to suite the patients need.
Bypass surgery and Angioplasty: As a continuous contractile tissue heart muscles need continuous supply of oxygen through blood. This blood goes to the heart muscles via coronary arteries. As we need daily supply of water from a tank on the roof top of our home (see picture above), via the maroon colored pipes in the picture; similarly coronary arteries supply blood to our heart muscles from large blood vessel called ‘Aorta’ (replaced in the picture as a water tank). Just like our house hold water pipes, the coronary arteries can get clogged by atherosclerotic material made of cholesterol, fibrin and blood cells (platelets). When the blockage increases up to 70% in a major coronary artery, then the patient can experience chest pain (angina), particularly during heavy work, brisk walk or climbing stairs. If the blockage becomes 100% then blood supply ceases to the supply area and patient gets a minor or major heart attack depending on the area damaged.
At angioplasty, a thin balloon is passed from the groin and placed at the blocked area inside the coronary artery. The balloon is then expanded clearing the passage and a scaffold called ‘Stent’ is placed to prevent further collapse at the site of the blockade. World wide research trial (Syntax trial is one of them) showed that angioplasty and stenting should be performed only up to two blocked vessels and may be in a low risk 3 vessel disease. Also the research raised question about the long time benefit of stenting in case of diabetic patients.
If the blockages are many, irregularly shaped, spread over wide area and heart contraction is very poor then the patient is referred to heart surgeons for a “Bypass surgery”. In bypass surgery one or more arteries from chest wall or forearm or veins from the legs are used to bypass the blocked artery. It takes pure blood from the chest wall or from the aorta (see above) and simply jumps over the blocked area to reach the healthy area of the coronary artery to supply the fresh blood. Bypass can be done to cross up to seven such blockages but a 4 vessel bypass is most common. The tube which is used for bypass is called a "Conduit". There are different types of conduits. The best and longest lasting conduit is Internal Mammary artery. The second best is the artery from the forearm called radial artery. The third one is Saphenous vein which is taken from the leg(s). Hence, the shortest durability (7 to 10 years). In a single heart bypass all three can be used depending on the importance of the target blood vessel (See picture above). Previously, and still in many centers heart was made to stop to perform this intricate stitching, but now a days most surgeons are doing this operation on a beating heart (See below) by using an instrument called ‘Stabiliser’ (see another part this site to know more). The beating heart surgery has revolutionized the out come of bypass surgery.