Risk factors involved in the development of angina
Atherosclerosis is the process where the artery walls thicken due to deposition of fatty materials such as cholesterol. A high intake of fat and cholesterol increases formation of athlerosclerotic plaques. Smoking narrows coronaries when toxic substances damage blood vessels and repair occurs by platelet aggregation. High blood pressure damages the arteries due to the force exerted by the blood on the vessels. Patients with uncontrolled diabetes have high levels of blood glucose which can disrupt the arterial walls. Stress causes the secretion of adrenaline and cortisol which increases blood glucose. As the age increases the blood vessels become more narrowed. Family history of heart disease and being male increases the likelihood of developing angina.
Investigations leading to diagnosis of angina
For the diagnosis of angina it is important to understand the cause of the chest pain so that it can be distinguished from other conditions which cause chest pain such as a pneumothorax or gastro-oesphageal reflux. It is important to take a history to find out when their symptoms occur and what triggers them. Patients have a normal resting ECG reading between attacks. However, during an attack, an ECG reading can show a transient ST depression, T wave inversion or other T wave shape abnormalities. An ECG can also be obtained while the patient is exercising on a bike or a treadmill. Cardiac scintigraphy and coronary angiogram can be used to identify any narrowing of coronary arteries and severity of any blockages present.
Management of angina
The goals of the treatment of angina are to provide symptom relief, prevent future attacks and reduce risk of a heart attack or stroke. Conservative management is important to reduce the risk of developing further complications of angina. If a patient has a 30 pack year habit of smoking and they should be encouraged to visit a smoking cessation clinic. If the patient suffers from hypertension and diabetes they should be educated on how to control these conditions and the importance of compliance with medication. If the patient has a ‘large appetite’ or a ’sweet tooth’ they need to be offered dietary advice on how to have a healthy balanced diet. They should also be encouraged to take up physical activities such as brisk walking, swimming or cycling in order to reduce his weight.
There are a number of medications available for the treatment of angina, these include nitrovasodilators, beta blockers and calcium channel blockers. Rapidly acting nitrovasodilators can be used to stop ongoing attacks or to prevent angina while longer acting nitrovasodilators can be used as a prophylaxis measure. These drugs react with cellular thiols in smooth muscles to release nitrite ions which get reduced to nitric oxide. This then stimulates guanylate cyclase to produce cyclicGMP which cause vasodilation. Vein dilation causes reduced central venous pressure and therefore preload. This leads to decreased ventricular end diastolic volume causing a reduction in the strength of the myocardial contraction which therefore means oxygen demand by the heart is decreased. Total peripheral resistance is also reduced causing a decreased afterload because there is some arterial dilatation. This allows the left ventricle to maintain cardiac output with a smaller stroke volume therefore the oxygen demand is reduced. Nitrovasodilators can also increase the perfusion of the ischaemic myocardium by dilating coronary collateral vessels which increase in number and diameter during significant coronary stenosis. This provides ischaemic myocardium an alternative pathway to obtain blood flow. Finally, nitrovasodilators can stop coronary vasospasms, stop platelet aggregation and thrombosis formation. Examples of nitrovasodilators include glyceryl trinitrate, isosorbide mononitrate and erythrityl tetranitrate. Glyceryl trinitrate is administrated by the sublingual route to avoid first pass metabolism and side effects include headache and dizziness.
Beta adrenergic receptor blockers are used for the prophylaxis of angina and to reduce the sympathetic drive. Increasing sympathetic drive causes an increase in blood pressure and heart rate which increases oxygen demand which causes ischaemia if oxygen demand is not met. Ischemia causes pain, and pain is responsible for increasing the sympathetic drive, therefore a vicious circle is created. Administering beta blockers reduces sympathetic drive, thereby reducing blood pressure and heart rate to reduce myocardial activity and therefore a drop in oxygen demand. The heart stays longer in diastole therefore there is an increase perfusion of blood into the left ventricle before contraction occurs. Beta blockers are particularly useful if the patient has hypertension but they are not to be given if the patient suffers from asthma. Examples of beta blockers include atenolol and propranolol.
Calcium channel blockers block voltage gated calcium ion channels that allow the flux of calcium ions in the smooth muscle cells and cardiac myocytes. These drugs prevent angina mainly by arteriolar vasodilatation and decreasing afterload. They also prevent coronary vasospasms so they are particularly useful in variant angina. Examples of calcium channel blockers include nifedipine, amlodopine and felodipine. Other drugs include aspirin to reduce platelet aggregation to stop development and progression of plaques. Drugs such as statins lower cholesterol by blocking HMG-CoA reductase, an enzyme involved in cholesterol production. Potassium channel openers such as nicorandil cause venous and arterial dilation of the systemic and coronary circulation.
Surgical treatment is suggested only if medication fails to treat the symptoms of angina. A coronary angioplasty involves a balloon being blown inside a narrowed artery to widen the vessel and placing a stent to prevent the vessel narrowing. A coronary artery bypass graft involves bypassing a blockage in an artery by using the great saphenous vein from the patient’s leg. This creates an alternative way for blood to flow through to the heart, bypassing the blocked part of the coronary artery
It is important for patients with Angina understand the risk factors that contribute to the formation of atherosclerotic plaques because they can lead onto angina. Modifiable risk factors are important to change. These include following lifestyle advice such as smoking cessation, increased physical activity and controlling diabetes to decrease chances of developing complications such as depression, stroke, heart attack and ultimately death. New ideas are emerging on how to combat atherosclerosis. A vaccine is being developed against T-cell receptors which interact with LDL to prevent arterial inflammation occurring, so that reduced cytokines and other inflammatory cells are not activated at the site of atherosclerosis.