Myocardial Infarction, Angina and Heart Failure Flashcards
What is a myocardial infarction (MI)?
- Death of heart muscle resulting from a blockage of a coronary artery
- Blockage deprives the heart of oxygen (ischemia) causing injury to the heart muscle, chest pain and may result in irreversible death of heart muscle (infarct)
What is ischemic heart disease?
- Myocardial blood flow not meeting metabolic demand of the myocardium
- Reduction in coronary blood flow usually related to progressive atherosclerosis with increasing occlusion of coronary arteries
What are causes of atherosclerosis?
Response to damage of the tunica intima
What increases risk factors of atherosclerosis?
- Increasing age
- Smoking
- Male
- Obesity
- Kidney disease
- Hypertension
- Diabetes
- High blood cholesterol
How do atheromas develop?
1) Damage of artery endothelium
2) Stimulation of inflammatory response
3) Injured cells release chemotactic agent and mitosis inducing factors
4) Macrophages attracted to site, invading damaged endothelium and take up lipid from blood, particularly LDLs
5) Lipids oxidise, further damaging cells and increasing chemotaxis, more macrophages arrive at the site
6) Macrophages transform into lipid-laden foam cells, forming fatty streak
7) Collagen and elastin fibres deposited
8) Lumen decreases
9) Assists platelet adhesion and clot formation
What is coronary atherosclerosis?
Coronary artery lumen reduced by more than 75% causing ischemia
What is collateral circulation?
- Tiny collateral blood vessels grow when needed
- By the time a coronary blockage develops over a time, these multiple collaterals grow and make alternative routes around the blockage creating a ‘Natural Bypass’.
What is angina pectoris?
- Blockage of the coronary artery may result in ischemia
- Severe pain caused by a fleeting deficiency in blood delivery to the myocardium (lack of oxygen and increased lactic acid stimulate nerve endings)
- Myocardial cells are weakened but do not die
- Most commonly occurs when stressed or during physical activity
What is treatment for an MI?
- If the plaque is still ‘soft’ an angioplasty or stent may be inserted
- Coronary bypass
How to diagnose angina or MI?
- History of pain
- Other signs and symptoms
- Vitals
- Electrocardiogram
- Blood test for cardiac enzymes
What would an MI show on an ECG?
- Raised S-T segment in two or more lead tracings
- Confirmation of an MI may involve the presence of cardiac biomarkers
How do defibrillators work?
- Electric shock used to correct life-threatening heart rhythm
- Detects dangerous rhythm
- Applies shock if necessary to stop heart
- Heart restarts
- Changed resuscitation rate from <5% to 70-80%
What is heart failure?
- When the heart fails to pump sufficient blood to meet the body’s usual needs
- Myocardial infarction is a common cause of heart failure
- Can begin on either right or left side and leads to failure of the other and complete failure
- When output is diminished, blood “backs up” within parts of the circulatory system
What is left ventricular heart failure?
- The left ventricle is the thickest muscle of the heart and needs the greatest blood supply. It is the first to suffer from diminished blood supply
- Left ventricular failure causes back pressure on the lungs which may result in pulmonary oedema
- Left ventricular failure often causes of right ventricular failure
What is right ventricular heart failure?
- Left ventricular failure is a common cause of right ventricular failure
- Results in a back-up of blood in the venous system (systemic circulation)
- Results in peripheral oedema and system failure
What is treatment of heart failure and MI?
- Prevention - lifestyle
- Surgery - angioplasty, stent placement, coronary artery bypass
- Medication e.g acute = streptokinase, chronic = beta blockers, diuretics, ACE inhibitors
- Pain management - important since pain stimulates stress response causing injury to heart muscles
What occurs to cardiac output with heart failure?
Cardiac output is decreased which is determined by stroke volume x heart rate
What is preload?
- Decreased venous return lowers heart muscle stretch, lowering cardiac contractility and cardiac output
- Pressure on the myocardium when heart relaxed
- Preload in the right side of the heart depends on systemic venous return to the heart
- Preload on the left side of the heart depends on venous return from the lungs
What is afterload?
- The force or pressure against which the ventricle must eject blood
- To maintain cardiac output, the ventricle must increase its force of contraction
- An increased force of contraction will increase the oxygen demand of the heart
What is the effect of oxygen deprivation on cells?
- Damages cells causing potassium, calcium, and magnesium leave the cells
- Electrolyte disturbances cause decreased contractility of the heart muscle
How is heart failure compensated then decompensated?
- Initially compensated by renal system and activation of the sympathetic nervous system
- Causes increase in heart rate and contractility (cardiac output) and an increase in salt and water retention (blood volume)
- In decompensated heart failure, stroke volume is decreased and peripheral and pulmonary oedema develops
What is preserved ejection fraction (HFpEF)?
- Diastolic heart failure
- The heart muscle contracts normally but the ventricles do not relax during filling
What is reduced ejection fraction (HFrEF)?
- Systolic heart failure
- The heart muscle does not contract effectively and less oxygen-rich blood is pumped out to the body
What is left ventricular ejection fraction (LVEF)?
Measures how much blood the LV pumps out with each contraction
