Ischemic Heart Disease and Hypoxia Flashcards
Define IHD
The term given to heart problems caused by narrowed heart (coronary) arteries that supply blood to the heart muscle
What is there a mismatch between in IHD
Demand and supply of oxygen
What are other names for IHD?
Coronary artery disease (CAD)
Coronary heart disease (CHD)
What are the 2 ways IHD manifests clinically?
Myocardial infarction
Ischemic cardiomyopathy
What is a reason the prevalence of IHD has increased over time?
Life expectancy has gone up and its more common in the older population
Why does sudden death occur in IHD?
Due to occlusion of arteries
What are the main signs and symptoms of IHD?
Angina/chest pain
Heart rhythm problems
Nausea, sweating, fatigue or shortness of breath, weakness or dizziness
Reduced exertional capacity
Leg swelling (when left ventricular dysfunction is present)
Diaphoresis (increased sweating)
When does leg swelling occur in IHD?
When left ventricular dysfunction is present
How does angina manifest?
Aching, burning, fullness, heaviness, numbness, pressure, squeezing
Radiation in arms (usually left but also can be right), back, jaw, neck, shoulder
High or low BP
Syncope
What is angina often mistaken for? When does this especially happen?
Indigestion or heart burn, especially if the pain doesn’t radiate and localised to the centre of the chest
How do heart rhythm problems manifest in IHD?
Palpitations Heart murmurs Tachycardia Atrial fibrillation Ventricular tachycardia or ventricular fibrillation
What is S3 and S4 gallop?
They are sounds heard that indicate left ventricular dysfunction, S3 is heard after the mitral valve opens as blood pours into the left ventricle
What is diaphoresis?
Increased sweating
What are non modifiable risk factors for IHD?
Age Gender (more common in males) Family history Ethnicity Genetics (eg hypercholesterolaemia) Past history of CVD
What are modifiable risk factors for IHD?
BP Cholesterol Smoking Diabetes BMI Diet (this is the biggest risk factor) Inactivity Stress/mental health Low social economic state Alcohol Income Social deprivation Environment Some medications
What are the 2 main causes of IHD?
Reduced coronary blood flow to a region due to obstruction
General decrease of oxygenated blood flow
What are some causes of obstruction causing reduced coronary blood flow?
Atheroma Thrombosis Spasm Embolus Coronary ostial stenosis Coronary arteritis
What are some causes of decreased flow of oxygenated blood?
Anaemia Carboxyhaemoglobulinaemia
Hypotension
What is the process by which an atherosclerotic plaque forms called?
Atherogenesis
What are some triggers for atherogenesis?
Endothelial dysfunction
Mechanical sheer stresses (HTN)
Biochemical abnormalities (elevated and modified LDL, DM, elevated plasma homocysteine)
Immunological factors (free radicals from smoking)
Inflammation (infection such as chlamydia, Helicobacter)
Genetic alteration
Describe a stable plaque
Fibrous cap of layers of VSMC surrounded by ECM network which is an effective barrier preventing rupture
They have a small necrotic core
Describe a vulnerbale plaque
Unresolved inflammation causes thinning of the fibrous cap
Areas where thinning has occurred are prone to rupture, if this happens there is thrombus formation and this leads to clinical events
What are the 5 ways IHD may present
Asymptomatic Chronic stable angina Acute coronary syndromes (unstable angina, non ST elevation MI or ST elevation MI Heart failure Sudden death
Once an atherosclerotic plaque has contact with flowing blood what happens?
Platelets can adhere to it
Fibrin is deposited
RBCs get trapped and a clot forms
How does hypoxia arise as a result of atherosclerosis?
Once the atherosclerotic plaque breaks through the endothelium and forms a clot, the clot can occlude a vessel
What is a coronary embolus?
When the clot formed by a ruptures atherosclerotic plaque breaks away and blocks a more distal artery
What is a collateral?
When small arteries anastomose together
What happens to collaterals in an acute episode?
They dilate within seconds and can double by the second or third day
How do collaterals develop in chronic atherosclerotic patients?
Slowly as the atherosclerosis gets worse
Why does ACS still occur even though collaterals exist?
Extensive atherosclerosis can damage the collaterals themselves, also if they get too big they may not be able to maintain blood supply
Is full recovery post MI possible?
Yes, in about a month its possible
How does infraction occur?
After occlusion there is no flow or very little flow to the muscle so function cannot be sustained
What occurs to muscle after infraction?
Small amount of collaterals open and blood seep into the infarcted area
Local blood vessels dilate, and area becomes overfilled with stagnant blood
Muscle fibres use all the remaining oxygen, haemoglobin becomes totally deoxygenated giving bluish brown hue & blood vessels appear engorged despite lack of blood flow
How much oxygen do cardiac muscle cells need?
1.3ml of oxygen per 100ml of tissue
How much blood supply is required to stop cardiac muscle from dying?
15-30%
What are causes of death after MI?
Decreased cardiac output
Ventricular fibrillations
Rupture of infarcted area
Damming of blood in the venous system
What is systolic stretch?
When there is dead muscle after MI, it is pulled on in systole and when it stretched it can become balloon shaped
How may the heart be damaged further after MI?
If there is excess exertion damage may occur as the heart has reduced reserve
How is risk of MI calculated?
JBS3 is used in GPs
Q risk is used in hospitals
What clinical examinations are done when diagnosing MI?
Heart auscultations
BP
BMI
GPE
What lab tests are done when diagnosing MI?
LDL HDL Triglycerides Lipoprotein A C reactive protein
What are the serum markers in patients with suspected acute cardiac events?
Troponins (I or T)
Creatine kinase with MB isozymes
Lactate dehydrogenase and lactate dehydrogenase isozymes
Serum aspartate aminotransferase
What are biomarkers for predicting death?
B-type natriuretic peptide CRP Homocysteine Renin Urinary albumin-to-creatinine ratio
What is seen on an ECG for stable angina?
Pretty much normal
If you want to see the changes do an exercise stress test, during stress test might see ST depressions indicating
What is seen on an ECG for unstable/NSTEMI angina?
ST depressions and T wave inversion
What is seen on an ECG for acute MI/STEMI angina?
ST segment elevation with T wave inversion, Q waves
What is transthoracic ECG used for?
Assess left ventricular function
Wall-motion abnormalities in ACS or AMI
Mechanical complications of AMI
What is transoesophageal ECG used for?
Assessing possible aortic dissection in the setting of AMI
What is stress ECG used for?
To evaluate hemodynamically significant stenosis in stable patients who are thought to have CAD
What is coronary angiography used for?
In vivo assessment of coronary arteries
How do HMG CoA reductase inhibitors work?
They lower LDL-C levels
and triglyceride levels
Raise serum HDL levels
How do bile acid sequestrates work?
Block enterohepatic circulation of bile acids and increase the fecal loss of cholesterol
How do CCBs work?
Relaxes coronary smooth muscle and produces coronary vasodilation to increase oxygen delivery to the heart
How do ACE inhibitors work?
Hypertension and atherosclerosis may be intimately linked through their effects on vascular endothelial dysfunction so they can help
How do beta blockers work?
Inhibit sympathetic stimulation of the heart, reducing heart rate and contractility; this can decrease myocardial oxygen demand and thus prevent or relieve angina in patients with CAD
How do antianginal agents work?
Reduces myocardial cellular sodium and calcium overload via inhibition of the late sodium current of the cardiac action potential
How do platelet aggregate inhibitors work?
Exert protection against atherosclerosis through inhibition of platelet function and through changes in the hemorrhagic profile
How do nitrates work?
They decrease myocardial oxygen demand by producing systemic vasodilation
What are the 2 main revascularisation therapies?
Percutaneous coronary intervention
CABG
How does percutaneous coronary intervention work?
Angiography and stent placement helps improve blood flow
When is percutaneous coronary intervention used?
To treat stable CAD
How does CABG work?
A vessel from another part of your body to create a graft that allows blood to flow around the blocked or narrowed coronary artery
When is CABG performed?
In people who have several narrowed coronary arteries
What are some preventative measures for IHD and MI
Do physical activity Stop smoking Healthy diet Reduce weight if overweight Reduce stress at home and work
What do Q risk and JBS3 show?
Risk of MI in the next 10 years
