STRUCTURE AND FUNCTIONING
The heart is divided into four main chambers : each one is a bag of muscles with walls that are able to contract in order to push blood out. Each walls thickness varies according to the amount of work it does. The walls of the left ventricle are the thickest because it does most of the pumping.
The chambers on either side of the heart are arranged in pairs. Each side has an atrium, with thin walls, to receive blood from the veins. The atrium pumps blood into a thicker walled ventricle, through which the blood is pumped into a main artery.
The heart is involved in two separate circulatory functions. Oxygen rich blood is pumped from the heart into the body through the aorta. This is called systemic circulation. When this blood is returned to the heart, after the cells have absorbed all the oxygen and nutrients, the heart pumps the blood into the lungs through the pulmonary artery. Here, the oxygen supply is replenished and the blood is returned to the heart. This is known as pulmonary circulation.
Pulmonary veins bring the newly-oxygenated blood from the lungs to the heart. It reaches the left atrium, which contracts and pushes the blood out through the mitral valve into the left ventricle. Then the left ventricle contracts. The blood moves through the open aortic valve into the aorta, and on to the system of arteries and capillaries, and into the tissues.
The deoxygenated blood from the body comes back to the heart through a large vein called the inferior vena cava, and from the head through the superior vena cava. The blood goes into the right atrium, via the tricuspid valve, and into the right ventricle. The ventricular contraction sends the blood through the pulmonic valve into the pulmonary artery, and then to the lungs. From here, the blood comes into the pulmonary veins. And the process repeats itself, about 50-60 times a minute.
The two atria contract together and fill the ventricles with blood. Then both the ventricles contract together. This is controlled by an electrical timing system located in the right atrium : the sino-atrial node. The atrioventricular node delays the electrical impulse so that the ventricles contract only after the atria.
Intensive care was introduced in the sixties. This made it possible for specialised staff to monitor and measure vital parameters continuously. With the introduction of cardiac intensive care there has been a drastic reduction in mortality and morbidity in cases of heart attacks and cardiac failure.
Intensive cardiac care units in hospitals offer the right conditions for a patients brought in with fatal complications. These units have nurses and doctors round the clock attending to the patients. Every patients is connected to an ECG machine by electrodes to enable the staff to monitor blood pressure and heartbeat.
Another advancement in the field of intensive care has been the development of defibrillators. These are lifesaving instruments which convert dangerous heart irregularities to normal by applying a small electric shock.
While in the intensive care, the emphasis is on trying to save as many heart muscles as possible. But once the patients is out of danger, the doctor shifts the focus to rehabilitation. While rest is important, it is also important to slowly resume physical activity. Besides the cardiologist, a dietician and a physiotherapist would chalk out a programme to bring the patients back to normal.
In addition to the benefits obtained from intensive care, a number of drugs have made a foray into the treatment of heart attacks. These are drugs that help dissolve clots in the coronary arteries, aspirin and similar drugs which prevent blood clotting, and beta blockers and ACE inhibitors that restrict the extent of the damage to heart muscles. These drugs not only provide immediate benefit, but prevent long-term complications.
There are three categories of drugs used in the management of angina pectoris nitrates, beta blockers and calcium channel blockers.
Nitrates help relax vascular muscle. These are usually taken under the tongue or sprayed in the mouth for quick relief from symptoms such as pressure in the heart, radiating pain in the chest, pain in the back and teeth.
Beta blockers effectively treat angina by decreasing blood pressure and heart rate from normal to amount 50-60. However, these have some side-effect. Beta blockers have been found to lower good cholestrol and also cause asthma.
Though there are other side-effects like depression, hair loss, pain in the legs, fatigue and nightmares, it is important that the patients takes it without a break. An abrupt break can cause the symptoms to recur.
Through aspirin was created by a German chemist at the end of the 19th century to ease the pain of arthritis, since the early 1980s it has been approved for preventing second heart attack and stroke. Now it is increasingly being used in treating heart attacks as they occur. Aspirin works by interfering with the synthesis of prostaglandins, which help control the body response to injuries and infections. Prostaglandins act on the nervous system to help transmit pain. They signal blood platelets to form clots and also promote inflammation. But blood clots can cause heart attacks and inflammation is a likely culprit in atherosclerosis. Aspirin prevents blood clots and inflammation.
ACE inhibitors are angiotensin converting enzyme inhibitors that dilate arteries. Drugs in this category are also beneficial to patients with leaky valves.
These are wonder drugs used to decrease cholesterol level in the blood. Statins reduce the thickness of the plaque, thus increasing the lumen of the blood vessel. These drugs are probably as good as angioplasty in treating angina. Some of the statins in the market are simvastatin, Atorvastatin and Pravastatin.
In some cases of coronary artery disease medications alone may not be enough to remove the arterial obstructions. While cases of blocked artery were treated first with medicines and then surgery earlier, today there are various options such as angioplasty and stenting which have several advantages over conventional surgery.
The first balloon angioplasty performed in 1964 was a failure and did not have many takers. It became popular after it was performed successfully in Switzerland in 1977.
Known as percutaneous transluminal coronary angioplasty in medical parlance, balloon angioplasty takes around two hours and is very similar to an angiogram. Performed in a catheterisation lab, it is done under local anaesthesia. The doctor makes a tiny incision over an artery, usually in the thigh, to thread the catheter in. X-ray imaging helps the doctor keep track of the catheter. Once it reaches the site of the plaque the balloon is inflated, of a few seconds or a few mintures depending on the requirement, to flatten the plaque and open the passage.
Some patients experience chest pain when the balloon is inflated. This is because the inflated balloon interrupts blood flow in the artery. The catheter is then withdrawn and the doctor takes X-ray pictures to assess the success of the procedure. The patients is taken to the cardiac intensive care unit after the procedure and can leave the hospital in a day or two.
Angioplasty has a high success rate, but there are cases where the plaque returns and the artery becomes narrow again. This is called restenosis. Scaffoldings called stents have been developed to prevent the vessel from closing again.
The initial steps are similar to catheterisation where a small incision is made over an artery to insert the catheter. A stent, usually made of stainless steel, is first mounted on the deflated balloon on the catheter tube. When it reaches the site of the plaque the balloon is inflated. This expands the stent. The balloon is then deflated and removed, leaving the stent fixed in the plaque-affected area of the artery. Stents have been found to be useful in emergency situations and also in reducing restenosis.
OTHER ANGIOPLASTIC TECHNIQUES
1: Rotational atherectomy
2: Directional atherectomy
3: Laser angioplasty
Atherectomy is a process where a catheter with a rotor blade is used to remove plaque
In Laser angioplasty, the doctor uses a Laser catheter to vapourise the plaque.
It is a remarkable achievement that narrow valves can be opened using similar techniques, without surgery. The other successful interventions have been the closure of holes in the heart using devices delivered through catheters. A hole in the heart is a congenital defect and an infant born with such a defect is called a blue baby. Holes in the heart allow impure blood to flow into the body. Holes can be between the left and right atria or the left and right ventricles. In some cases the defect may be in the openings to the chambers. It can also be a case of pure blood mixing with impure blood flowing through the major vessels of the heart.
Symptoms of a congenital defect include inability to cry or swallow, blue colour and clubbing of finger nails. An X-ray, an ECG and other non-invasive tests can show the defect in the heart. The doctor then decides a treatment based on the test results.
Treatment often consists of surgery which can be performed even on a newborn. However, in some cases the hole may close on its own as the child grows. A hole between the left and right ventricle is a condition which commonly requires surgery. The hole is either sewn up. If the hole is too large, a plastic patch is used to close it.
Heart transplant was a grand milestone in cardiology and Dr. Christain Barnard, a south African surgeon, was the first to perform a successful transplant on a human being in 1967 candidates for a transplant are of course, patients of sick with heart disease that only a healthy donors heart can save them. People with other general disease such as diabetes are advised not to go in for the surgery because such conditions could hamper recovery.
The introduction of open heart surgery in the fifties was a landmark in cardiology. Surgery has made repairing defects of heart valves and congenital abnormalities possible. Advanced techniques currently available also make it possible to operate on babies from day one.
CORONARY ARTERY BYPASS SURGERY
Coronary artery bypass surgery was first performed in 1964. A procedure where the blocks in the coronary artery are bypassed using another blood vessel, it is an alternative for people who do not get relief from medications or angioplasty. This has been useful for some patients with angina.
The technique involves taking a blood vessel from the leg or the chest and attaching it in such a way that it bypasses the blocked coronary artery. The blocked vessel is not replaced. The number of graftings a patients needs depends on how many of his coronary arterise are blocked
Surgery requires cutting the breast bone from top to bottom to expose the cardiac region and the heart. The temperature is brought down to make the heart stop beating so that surgeons can operate on it. So during surgery, the patients is connected to a heart-lung machine where blood gets oxygenated and returns to the aorta to be circulated in the body.
The surgery may go on for three hours after which the patients remains in the intensive care unit for a few days. During this times, he may have a tube going down his larynx to ensure proper ventilation and a catheter to drain his urine. Medicines may be administered intravenously.
The patient starts feeling relaxed and well a day or two after the operation. However, pain in the operated area may persist for some time. Patient is encouraged to take a few steps two days after surgery but not allowed to sit for a long time to avoid swelling in the legs.
Complications infection, heart attack, stroke and death are rare. However, many experience a temporary decrease in thinking capacity and have problems with vision. Women seem to be at greater risk during surgery and seem to benefit less from bypass.