Ischaemic Heart Disease Flashcards
What is a heart attack?
Blockage of blood vessels
= heart starved of oxygen
What dos increased myocardium demand increase?
Coronary artery blood flow
What is the equation for oxygen demand?
Blood flow X arteriovenous O conc difference
Why does O act as a vasoconstrictor?
O deficiency dilates coronary arteries
Decsribe what happens during hypoxia
AMP cannot be regenerated to ATP =
Adenosine rises in myocardium
Adenosine acts as direct vasodilator
Accumulation of lactate H+ ions + prostacyclin = vasodilation
When does myocardia ischaemia occur?
Myocardial oxygen demand exceeds myocardial oxygen supply
What is myocardial oxygen supply affected by?
Diastolic perfusion pressure
Coronary vascular resistance
O-carrying capacity
What is myocardial oxygen demand affected by?
Wall tension
HR
Contractility
What are the causes of ischaemic heart disease?
Atherosclerosis
Arteritis
Embolism + endocarditis
Coronary artery wall thickening
Coronary spasm
Congenital arterial disease
Describe what stenosis does
Increases resistance to floe
O supply may not be able to meet demand
Diminished coronary reserve
Raised resistance
What happens when the coronary arteries are narrowed?
Blood flow to heart slows or stops
= myocardial ischaemia + hypoxia pain
What is a result from ischaemic heart disease?
Chest pain
SOB
Myocardial infarction
What are the modifiable risk factors?
Hypertension
Hypercholesterolaemia
Smoking
Diabetes
Sedentary lifestyle
Obesity
What are non-modifiable factors?
Age
Male gender
Family history
What is the primary symptom associated with ischaemic heart disease?
Chest pain
Why is pain caused?
Pain from myocardium after switching to anaerobic metabolism (low O supply)
What is stable angina?
Experienced on exertion or emotional stress
Relieved by rest
What is unstable angina?
Incomplete occlusion-angina on minor exertion
Blockage = angina at rest
What is variant angina?
Diffuse coronary vasospasm
Describe what happens as a consequence of ischaemia
ATP deficiency
ATP produced non-aerobically
= lactic acid produced
Dissociates into H+ + lactate
Low ATP + high H+ = abnormal ventricular contraction
What can happen as a consequence of persistent ischaemia?
Infarction
What are the consequences of myocardial ATP deficiency?
Impairment of ventricular systolic pumping action
Decreased compliance of myocardium during diastole
Pulmonary congestion + dyspnea
What does extended myocardial ischaemia lead to?
Myocardial necrosis (infarction)
What is the development of myocardial infarction promoted by?
Turbulence + rupture of atheroma
Thrombocyte activation
Abnormal function of endothelium
Sympathetic nervous stimulation increases cardiac work
How can you identify myocardial infarction?
Enzyme markers
What are the main enzyme markers?
Troponin
= signify rupture of cardiomyocyte
What are the therapy principles?
Reduce O demand
OR
Increase O supply
Describe smooth muscle relaxation
Nitric oxygen
ACh binding to G protein receptors = IP3 production
IP3 releases Ca2+
Ca2+ + calmodulin form complex which stimulate NO synthase to produce NO
NO diffuses from cell to muscle cells
NO activates guanylyl cyclase kinase to make cGMP
cGMP activates protein kinase G
Activates myosin light chai phosphatase
Dephosphorylates myosin light chains = smooth muscle relaxation
What are examples of nitrates?
Glyceryl Trinitrate (GTN)
Isosorbide nitrate
What are nitrates indication?
Stable angina
Variant angina
Acute coronary syndrome
What are the side effects of nitrates?
Tachycardia
Headache
Postural hypotension
Describe the mechanism of action for nitrates
Acts directly on smooth muscle through cGMP mechanism
Coronary microvessels contain enzyme to convert NO
What is the dose of nitrates dependent on?
Dilation of coronary vessels
What is the 1st part of Nicorandil mechanism?
Dual mechanism
Relaxation of venous vasculature
Systemic + epicardial arteries
Coronary blood flow maximised, pre-load + afterload reduced
What is the 2nd part of Nicorandil mechanism?
Dual mechanism
Opens ATP-dependent K+ channels
Hyperpolarisation = arterial dilation
Cardiac repolarisation = reduced cardiac work
What are examples of beta-blockers in angina treatment?
Atenolol
Carvedilol
Propranolol
What is the indication of beta-blockers?
Stable angina
Variant angina
What is the mechanism of action of beta-blockers?
Block beta-1 adrenoreceptor
+ reduced generation of intracellular cAMP
= decreased HR
= reduce force of contraction
= reduce O demand
What are the side effects of beta-blockers?
Bronchospasm
Hypoglycaemia
Interact with CCB
What are examples of CCB?
Verapamil
Nifedipine
Diltiazem
What is the indication of CCB?
Stable angina
Variant angina
What is the mechanism of action of CCB?
Peripheral vasodilation
Reduced cardiac work
What are the side effects of CCB?
AV blockage
Oedema
Hypotension
