Coronary artery disease, angina and myocardial infarction
The two coronary arteries (left and right) rise from the aortic root branching in the cardiac walls into a network of capillary veins carrying oxygen and nutrients to the myocardium to support the heart's mechanical pumping function. The accumulation of fatty substances and the hardening of the arteries (atherosclerosis) causes local or general narrowing of the coronary arteries (stenosis). A mild narrowing does not impair myocardial circulation. However, when the narrowing is considerable (over 50% of the diameter), it starts to restrict blood flow in the coronary artery. When the required increase in blood flow is restricted during exercise, this results in local myocardial ischemia (lack of oxygen), which causes the typical symptoms of angina: a feeling of tightness, or a dull or burning pain in the chest, or sometimes a feeling of discomfort which passes when at rest. The pain can radiate from the chest to the neck and arms and sometimes to the upper abdomen or back. Transient ischaemia, which passes at rest, does not damage the myocardium.
The symptoms of angina can remain stable for several years, occurring regularly under similar situations and passing soon after the physical or emotional stress is over, or after a dose of nitroglycerine tablets or spray. However, if the inner arterial membrane ruptures and causes a local blood clot to form (thrombosis), coronary artery stenosis may become severe very quickly - stable angina becomes unstable and the symptoms appear under significantly less stress or even at rest, and last longer before they pass. If the blood clot blocks a vessel, circulation will be reduced or will stop completely, depending on the extent to which the vessel is blocked. This causes a severe local lack of oxygen (ischaemia), which may lead to a myocardial infarction if the condition persists. A myocardial infarction causes irreversible damage to the heart tissue. There are two factors that determine the extent of myocardial damage: the size of the area to which the blocked coronary artery supplies blood, and the severity of the blockage (whether the artery is totally or only partly blocked) and how long the condition remains. A few weeks after a myocardial infarction, fibrous collagen scarring will replace the affected area. The scarred tissue does not contract and cannot participate in the pumping function of the left ventricle. Instead, the scarred area may bulge outwards as the healthy tissue contracts, creating an aneurysm, which further impairs the pumping efficiency of the left ventricle.
Diagnosis
The possibility of coronary artery disease (CAD) is considered when you have experienced chest pains or shortness of breath. A preliminary diagnosis is based on the symptoms, an interview, a physical examination, and ECG monitoring. To confirm a suspected diagnosis, a patient is typically referred to an exercise test to monitor symptoms, heart rate, blood pressure, and possible changes in the ECG. In some cases, a myocardial perfusion scan is performed in connection with exercise ECG monitoring. A myocardial perfusion scan is a type of nuclear medicine procedure to study blood flow in the myocardium. When invasive forms of treatment, such as balloon angioplasty or bypass surgery, are considered, coronary angiography is performed to examine the stenoses in more detail. Computerised tomography angiography (CT angiography) is an alternative to coronary angiography, although the results are not as accurate as those obtained by invasive angiography.
The prognosis of coronary artery disease presenting as stable angina is good. When the symptoms are mild and do not significantly affect the patient's quality of life, conservative treatment is usually sufficient. Typically, this includes a healthier diet, regular exercise, weight control and stopping smoking, reducing high blood pressure to a safe level, prescribing statins to help lower cholesterol levels, and starting aspirin treatment to prevent blood clots when not contraindicated. These measures prevent the slow narrowing of the coronary arteries and reduce the risk of abrupt rupturing of a stenosis and of subsequent blood clots. Additionally, beta blockers or calcium channel blockers are prescribed to limit the number of angina attacks, and nitroglycerine (tablets or spray) to treat an attack.
Invasive treatment is required to improve myocardial blood flow when severe symptoms of a stable coronary artery disease cannot be controlled by medications. The choice between balloon angioplasty and bypass surgery is based on the findings from a coronary angiography. Urgent or immediate coronary angiography is performed when angina is unstable or the patient is having a myocardial infarction. If the symptoms and changes in the ECG suggest sudden complete coronary artery occlusion, the primary concern is to remove the occlusion and secure blood flow to the myocardium, and to prevent, or at least minimise, the extent of myocardial damage. Blood flow is secured by emergency balloon angioplasty or thrombolytic therapy. The latter is a viable option when the onset of pain (occlusion occurred) was less than 2 to 3 hours beforehand. Coronary angiography is performed either immediately or on the next day after the occlusion has been successfully dissolved by thrombolytic therapy.
When invasive treatment is required, the choice between balloon angioplasty and bypass surgery is based on the findings from coronary angiography, the prognosis, and discussions with the patient. Balloon angioplasty is often combined with stenting, where a small wire mesh tube is placed in the artery to ensure that it remains open. Some stents elute a drug to the surrounding tissue to further reduce the risk of recurring stenosis. After stent placement, patients must take potent antiplatelet medications for 3 to 12 months to inhibit blood clotting. It is important to understand that balloon angioplasty and bypass surgery do not cure coronary artery disease. After the operation, it is vitally important to maintain a healthy diet and life-style, and to take medications (see above) to effectively prevent a turn for the worse in condition, recurrence of the symptoms, and the need for additional invasive operations.