Ischaemic heart disease

An imbalance between myocardial perfusion and myocardial demand

Physiology

The myocardium is an area of active metabolism

Each muscle cell contains mitochondria which require a supply of oxygen and metabolic substrate

Tissue respiration

The left and right coronary arteries supply blood to the myocardium directly from the aorta.

Left anterior descending and circumflex artery

A large vein at the back of the heart called the coronary sinus empties blood into the right atrium

Pathophysiology

Mostly caused by atherosclerosis, (atheroma) progressive obstruction of the arterial lumen. This has three effects;

Infarction Ischaemia Aneurysm

Other causes of reduced perfusion include;

Spasm Embolus Ostial stenosis (eg syphilis)

The quality of the perfusate is also important;

Anaemia Altitude

Carboxyhaemoglobinaemia Hydrostatic hypoperfusion

Increased oxygen demand may be significant;

Exercise Thyrotoxicosis

Myocardial hypertrophy due to increased arterial resistance systemic hypoxia

Pathogenesis

Response to injury hypothesis

Stage 1. Functional alteration to endothelial cells without substantial morphological change

Caused by flow at branching points, high cholesterol, immunocomplexes, infection, chemical irritants in tobacco smoke, vasoactive amines

Stage 2. Endothelial damage, internal media affected

Stage 3. Endothelial damage to intima and media

Local damage leads to platelet adhesion, proliferation of smooth muscle cells, thrombosis formation, development of a plaque, cholesterol rich material enlarges the plaque surrounded by a fibrotic cap

Epidemiology

A disease associated with Western lifestyles

Correlates well with telephone ownership - Association or causality?

50% of Western deaths associated vascular pathology

Rheumatic heart disease is still a big poverty related problem, (eg. a third of cardiac cases in India)

UK - 1990 total mortality 1 083 per 100 000, IHD 292

Leading single cause of death every year

Aetiology

Diet

high fat/wrong sort of fat excessive eating

obesity lack of ACE vitamins

lack of water soluble fibre heavy alcohol consumption

Sedentary life style

low HDLs Failure to metabolise ingested substrates

Lack of coronary arterial vasodilation during exercise

Lack of myocardial exercise

Age

more time for atheroma development

Gender

amount of oestrogens oral contraception

HRT

Smoking

lowering of HDLs increased platelet viscosity

increased carboxyhaemoglobin levels

Predisposing disease

diabetes types I and II obesity

hypertension hyperlipidaemia

hypothyroidism

Psychological factors

increasing platelet viscosity higher levels of substrate in the blood

type A personality

Other factors

family history soft water

creased earlobes Helicobacter pylori

Degree of association

Risk factors

Age Gender Family history

Hyperlipidaemia Smoking Hypertension

Lack of exercise Diabetes mellitus Obesity

Personality type Gout Oral contraceptives

Alcohol Soft water Multifactorial aetiology

Diagnosis

Clinical – pain, shock Resting ECG

Exercise ECG Cardiac enzymes, AST LH CK

Isotope uptake, eg thalium – 201 Echocardiography

Coronary angiography Triponins

Complications of infarction

Cardiac arrhythmias Ventricular extrasystoles

Ventricular tachycardia Ventricular fibrillation

Atrial fibrillation Bradycardia or tachycardia

Conduction disturbances Cardiogenic shock

Cardiac failure Pericarditis

Aneurysm Thromboembolism

Management

Angina

Rest Anticipation/avoid sudden anaerobic exercise

Avoidance of cold Coronary arterial vasodilators

Glycerine trinitrate Longer acting nitrates

Coronary angioplasty CABG

Infarction

Oxygen Monitoring Intravenous cannulation

Pain management Fibrinolytic therapy Anticoagulation

ACE inhibitors Anxiety management Bed rest Rehabilitation

Ischaemic Heart disease - more aetiological theories

Bacteria

Chlamydia pneumoniae, (TWAR)

People with CHD are likely to have high levels of Chlamydia antibodies

Chlamydia DNA and proteins are often found in atheroma, (60 - 79% of cases), (some researchers found 0%)

Chlamydia DNA and proteins not found at all in healthy arteries

Live bacteria have been found in atheroma and have been cultured

Explains the rise and fall of the epidemic

There is an immuniological component in atheroma aetiology

Bad Start

CHD rates are falling in most western countries

Caused by malnutrition in foetal and early life

Explains variations throughout the UK, eg. People in NW England approximately twice more likely to die than people in London

Areas of high CHD mortality today match those of high infant mortality 60 years ago

Underweight babies are more likely to have hypertension, high cholesterol and diabetes

People who were small as babies have thicker left ventricles, as do people with CHD

The correlation applies across social classes and is partly independent of adult lifestyle