Pharmacology of the CVS: Angina Flashcards
Define angina pectoris
- Angina: from the latin verb angere meaning “to choke or throttle”
- Pectoris: a reference to the Latin pectus, “breast”/chest
What are the symptoms of angina
- Feeling of cramping and severe constriction in the chest
- Referred pain in jaw, neck, shoulders and arms
- May be associated with shortness of breath, sweating, nausea & heart rate
Describe where the angina pain originates from
- Angina pain originates from heart muscle when there is a build up of lactic acid during anaerobic respiration
- Activates myocardial pain receptors
- Signal is sent via sensory neurons (cardiac nerves and upper posterior nerve roots) to the brain where there is then pain perception
Describe the traditional classification of angina
Based on the patients chest pain symptoms
Typical angina -
- Substernal chest discomfort of characteristic quality and duration
- Provoked by exertion or emotional stress
- Relieved by rest and or nitrates within minutes
Atypical angina -
- Presentation of two of the above characteristics
Non-anginal -
- Presentation of only one or none of the chest characteristics
Describe the new classification of angina
Based on aetiology and chest pain symptoms
Stable angina -
- Attributed to myocardial ischemia
- Coronary artery disease
Unstable angina -
- Due to complications from stable angina
Prinzmetal angina -
- Usually due to a spasm in the coronary arteries
- Tends to happen in cycles
Microvascular angina -
- Patients have angina symptoms but no evidence of coronary artery disease
- Normal or near normal coronary angiogram
State the causes and characteristics of stable angina
Stable angina -
There is a narrowed coronary artery lumen - restricted blood flow to the area of myocardium it supplies and the oxygen it receives is insufficient so the heart has to work harder - anaerobic respiration - pain
Characteristics -
- Follows a set pattern/predictable - recurrent episodes tend to have a similar onset pattern, duration and intensity
- Short duration radiation to left arm, neck, jaw or back - builds to a peak and lasts 2-5 mins
- Precipitated by exertion which increases cardiac oxygen demand
- Not life threatening but can be a warning sign of serious conditions e.g. heart attack/stroke
- Relieved by rest or taking medications
- Symptoms attributed to myocardial ischemia
Describe the cause and characteristics of unstable angina
Unstable angina -
Clot formation occludes artery - there is a critical reduction in blood flow so that oxygen supply is inadequate even at rest - causes pain
Characteristics -
- Unpredictable
- Pain symptoms more severe can persist and lasts longer
- Happens at rest with little exertion
- May not have a trigger
- Not usually relieved by rest and medications
- Progression from stable angina is impossible to predict
- Serious
Describe the cause and characteristics of prinzmetal angina
Prinzmetal angina -
Coronary spasm - critical reduction in blood flow so that oxygen supply is inadequate - causes pain
Characteristics -
- Usually occurs while resting and during the night or early morning hours
- Episodes last 5-15 minutes
- Rare - 1 in 100 angina cases
- Younger patients present with this
- Very painful and pain may spread to the head, shoulder or arm
- Associated symptoms are heartburn, nausea, sweating, dizziness, palpitation, migraines and raynauds
- Usually due to a spasm in coronary arteries - tends to come in cycles
- Can be relieved by taking medications
State the cause and characteristics of microvascular angina
Microvascular angina -
Impaired coronary circulation - reduced coronary perfusion - causes pain
Characteristics -
- Impaired coronary circulation due to coronary microvascular dysfunction from abnormal vasodilation or increased vasoconstriction
- Patients do not have obstructive coronary artery disease
- Occurs with exertion and at rest but may respond less well to nitrates
- Problem diagnosing it early as coronary microvasculature as the vessels under 300 um in diameter cannot be directly imaged
- Positron emission tomography or cardiac magnetic resonance can be used to assess coronary microvascular blood flow
- Treatment varies depending on cause
What are the treatment aims of angina
- To enhance quality of life through reduction of symptoms
- To improve prognosis and prevent complications such as MI and premature death
- Well tolerated, cause minimal side effects
Explain the 2 types of ischaemia and what can cause them that lead to angina
Vasospasms/a thrombus (blockage) leads to decreased coronary blood flow which causes supply ischaemia - causes angina
Fixed stenosis - there is increased oxygen demand which leads to demand ischaemia - causes angina
What are some factors that can influence angina presentation
- Increased sympathetic activity - increases heart rate so there is less diastolic time - less coronary artery perfusion which occurs in diastole
- Increased contractility - e.g. during exercise, emotion and stress
- Increased vasoconstriction - e.g. redistribution of blood flow in cold weather or after a meal blood is diverted to the GI tract
Describe the 3 main angina treatment strategies
To improve perfusion - increased oxygen delivery by improving coronary blood flow e.g. via coronary vasodilators
To reduce metabolic demand - reduce oxygen demand by decreasing cardiac work e.g. vasodilators that reduce afterload/preload and cardiac depressants that reduce heart rate/contractility
Prevention - prophylactic to reduce the risk of subsequent episodes e.g. lipid lowering drugs, anticoagulants, fibrinolytics and anti platelets
Give some examples and effects/adverse effects of nitrates as an antianginal drug
Examples - glyceryl trinitrate, isosorbide mononitrate
Effects -
- Peripheral venodilation - decreased intraventricular pressure - decreases cardiac preload
- Arterial dilation - decreases total peripheral resistance - reduces afterload
- Both of these actions lower oxygen demand by decreasing work of the heart
Adverse effects -
- Throbbing headache, flushing, syncope
- Postural hypotension
- Reflex tachycardia
Describe the mechanism of action of nitrates
- Organic nitrates mimic the effects of endogenous nitric oxide
- The nitric oxide cause dilation of smooth muscle leading to vasodilation
- It does this by activating guanylyl cyclase which causes conversion of GTP into cGMP
- This then activates protein kinase G which causes myosin light chain dephosphorylation
- There is then increased uptake of Ca2+ ions by the sarcoplasmic reticulum causing a decrease in cytoplasmic levels
- Activated K+ channels causing hyperpolarisation and the closing of voltage gated calcium channels - prevents smooth muscle contraction so allows better perfusion of tissues
