Title: Ischaemic Heart Disease and its Treatment

Key words: angina, myocardial infarct, smoking, cholesterol, atherosclerosis, nitrates, beta blockers, calcium antagonists, magnesium

Date: Aug 2000

Category: 13. Specific Conditions

Type: Article

Author: DJE Candlish

 

 

Ischaemic Heart Disease and its Treatment

 

Introduction

This overview introduces ischaemic heart disease (IHD) and provides a summary of the causes of IHD and the diagnosis and treatment of its clinical manifestations.

IHD- The British Disease?

Ischaemic heart disease (IHD) is a major problem in the UK. It is the cause of death for one man in three and one woman in four. These mortality rates are among the highest in the world. One survey of British males found evidence of IHD in 1 in 6 aged 40-44 and 1 in 3 aged 55-59. The clinical manifestations of IHD include angina, myocardial infarct (MI) and, in severe cases, sudden death. Nearly 2 million people in the UK have angina.

The Importance of IHD

The cost of treatment and surgery for the many individuals affected has led to government initiatives to reduce the scale of the problem. These are aimed at promoting knowledge of the risk factors and preventive measures among the general public and the medical profession and improving access to emergency treatment. Smoking and high blood cholesterol levels are among the major modifiable risk factors. Drug treatment is necessary for many patients.

What causes IHD?

The heart is supplied with the oxygen it needs to function by the coronary arteries. IHD develops if this supply fails to meet the oxygen demand of the myocardium. The usual cause of reduced oxygen supply is restricted blood flow in the coronary arteries, due to atherosclerosis. Low blood pressure, anaemia and coronary artery spasm can also limit the oxygen supply to the heart, but are less important in IHD than atherosclerosis. Factors that increase myocardial oxygen demand include exercise, stress and myocardial hypertrophy.

Atherosclerosis

This condition is progressive and degenerative. It generally affects the aorta and larger arteries. Atherosclerosis leads to the accumulation of lipid and smooth muscle cells in the walls of arteries, eventually restricting blood flow. There are several stages in the development of atherosclerosis; fatty streaks, plaque formation and plaque growth. These stages may take many years. Fatty streaks may be seen early in life. It can take 20-30 years for plaques with a lipid core to form and even longer for clinically significant lesions to develop. As well as IHD, atherosclerosis can cause stroke and peripheral vascular disease.

What is Angina?

Angina is the most common form of IHD. It causes pain on exertion or when under stress or emotionally disturbed. The pain is a warning sign of the relative lack of oxygen in the myocardium. The pain is felt in the centre or left of the chest and is generally relieved by rest in 5-10 minutes. The most common cause of angina is severe coronary artery atherosclerosis.

Diagnosis can often be made by history alone. However, ECG tracings or coronary arteriography provide more specific confirmation. Coronary arteriography can also identify patients who could benefit from surgery, either by coronary angioplasty or coronary artery bypass grafting.

The prognosis in angina varies according to severity. Management involves reducing risk factors for IHD, stopping smoking, losing weight and so on. Drug treatment involves short and long acting nitrates, beta blockers, calcium antagonists and aspirin. Surgery is another option, for more severe cases.

 

Myocardial Infarction (MI)

Severe, prolonged myocardial ischaemia can cause the death of cardiac muscle cells in areas of the myocardium. This is known as myocardial infarction (MI) and affects around 200,000 people a year in the UK. It can cause death from cardiac arrhythmias. Severe, crushing pain in the chest is the major symptom of MI. The pain has a faster onset and lasts much longer than angina, persisting after rest. As with angina it is often felt by the patient to spread to the arms, throat and jaw.

MI is nearly always due to acute blockage of a coronary artery by a thrombus forming at the site of a ruptured atherosclerotic plaque. The infarction develops over an eight hour period so prompt, effective treatment can limit the damage and improve the outcome of patients surviving the initial onset. However, there will always be some permanent damage to cardiac tissue. This can be detected by the presence in the blood of cardiac enzymes released from damaged cardiac tissue.

Most deaths in the first hours after MI are due to arrhythmias, or irregularities in heartbeat, especially ventricular fibrillation. Around 40% of people affected by MI will die within one month. Half of all these deaths occurs within two hours and threequarters within 24 hours. Factors indicating a poor prognosis include previous MI, diabetes, hypotension, pulmonary oedema and heart failure.

Acute MI is managed first by pain relief while gaining access to a defibrillator in case of arrhythmias. Nitrates and aspirin reduce the strain on the heart. Oxygen is also given. The thrombus causing the MI should be tackled promptly by a thrombolytic agent, in addition to the aspirin. Beta blockers improve survival during and post-MI, as do nitrates and thrombolytics used together. Intravenous magnesium sulphate also prolongs survival but how it does so is unclear.

What is heart failure?

This is a progressive condition, mainly affecting the elderly. It occurs when the output from the heart is unable to meet the demands of the body. Symptoms include tiredness, shortness of breath(especially during the night) and swollen ankles. IHD is one of the most common causes of heart failure. Others include hypertension and myocarditis. The prognosis depends on the underlying cause, but is generally poor. Around 50% of severely affected patients will die within two years.

Managing the risk factors for IHD

The risk factors for IHD are cumulative, so the more that affect an individual, the more likely he or she is to develop IHD. Some risk factors, like age, male sex and family history cannot be altered. Others are modifiable, either by changes to lifestyle and diet or by drug treatment. These include smoking, hypertension, lipid disorders, diabetes mellitus, lack of exercise and obesity.

The first step in management of high risk individuals is to alter their lifestyle, reducing or stopping smoking, improving diet by reducing fat intake and increasing fruit and vegetable intake and encouraging regular exercise. The aim of these preventive measures is to reduce the progression of atherosclerosis. Drug treatment becomes necessary if these measures fail.

The main targets for pharmacological intervention are hypertension and hyperlipidaemia (eg. raised serum cholesterol). Serum cholesterol can be reduced by dietary changes or by use of lipid-lowering drugs. This has been shown to reduce heart attacks and overall mortality following MI.