Angina Pectoris, Diagnosis of cause , management and treatment Flashcards
What is another name for coronary artery disease
Ischaemic heart disease
Define coronary artery disease
- Broad term encompassing syndromes that are caused by mycoardial ischemia - inbalance between carduac blood supply and myocardial oxygen and nutritional requirements
- This is really bad, since myocytes generate energy almost exclusively through Mitochondrial oxidative phosphorylation
Define angina pectoris
- crushing pain felt in the anterior cheest, commonly radiating to the left arm and jaw
- caused by insuffiienct perfusion of heart tissue leading to intermittent myocardial ischaemia
- Akin to someone sitting in your chest (heavy, tight, gripping)
in angina, there is a build up of metabolites, which activates nerves and causes a tight, gripping pain across the chest. Name some of these metabolites
- Adenosine
- Potassium
- Lactate
- Carbon Dioxide
Define stable angina
- Chest pain caused by temporacy lack of blood flow to myocardium,
- It’s onset is said to be predictable, and is brought about exercise, emotional stresss, extreme cold or heat, heavy meals, alcohol, cigarette smoking
Angina can be divided into typical, atypical and non-anginal chest pain. Describe the differences between
Typical angina:
- Constricting discomfort in the front of the chest, arms, neck and jaws
- Provided by physical exertion
- Relieved by rest or GTN spray
- Lasts 3-15 minutes
Atypical Angina:
- Sharp pain, prickling, pulsating
- Involves chest well, but can be anywhere
- Radiation patterns highly variable
- Random onset
- Lasts seconds, minutes, hours or all day
Define unstable angina
- chest pain that occurs without any stimulus, often at rest
- this is more seriousm as it suggests MI is imminent
Define prinzmetal angina (vary agina)
- Angina caused by coronary artery spasm
Define Acute Coronary syndromme
Basiclaly any condition that is chararcetrised by heart ischaemia (MI, unstable angina)
In order to define the cause of angina, various tests must be performed. An ECG is one of these tests, which can be performed at rest or during exercise. Describe how these tests are performed.
At rest ECG:
-
look at electrical activity of the heart at rest
- In MI, you could expect to see any one of ST depression, T wave inversion. or other changes of the shape of the T wave
During exercise ECG:
- Some abnormalities cannot be seen at rest, so must be done during exercise
- Patient is attached to an execise machine
- ST depression of 1mm is indicative of ischaemia
What is a positive test for ending the exercise ECG?
- Horizontal or downsloping ST-segment of at least 1mm in two leads
- Development of Angina
- A fall in blood pressure
Describe imaging tests used to diagnosis coronary heart disease
- Thallium Stress test - execise combined with scintigraphy (Gamma scan) - potassium analogue radioisotope - allows you to visualise areas of ischaemic myocardium - generally only if inital tests aren’t conclusive
Describe the bruce protocol
- test based on step increases in intensity of exercise on treadmill or bike
- There are 7 stages of 3 minutes
- Level of exercise is estimated in METs - the amount of energy expended - basically what changes is the speed and incline
- Many patients do not complete test, but completion of 9-12 minutes of exercise or reaching 85% of maximum predicted heart rate is usuall satisfactory
- Patient is conected to an ECG machine - ECG recorded intermitenly throughout
- Heart rate is measured constantly
- Blood pressure is measured before starting and at the end of each stage of exercise
- Typically stable for the early stages - but systolic pressure shold iincease as exercise levels increase - up to 225mm HG is normal, although athletes can have higher
- Diastolic pressure usually falls
Drug treatments for angina aim to reduce the myocardial oxygen demand.
Drug treatments for angina aim to reduce the myocardial oxygen demand.
Nitrates are reatment for myocardial ischaemia. Give an example of such drug, and explain how it reduces angina.
- Glyceryl Trinitrate (short term effects)
- Isosorbide mononitrate
Mechanism of action (GTN):
- GTN is a prodrug which can be converted to Nitric oxide, which is a POTENT vasodilator, hence mimicking the effects of endothelial release of NO
-
It acts on arteries AND COLLATERAL ARTERIES
- This is very important as it ensures coronary steal phenomenon does not occur
- GTN acts directly on smooth muscle cells and activates the soluble, Intracellular Guanylate cyclase - a nitric oxide receptor
- Increases formation of cGMP in smooth muscle, causing in myosin light chains to be dephosphorylated, intracellular calcium to be sequestered and result in relaxation
Results
Dilation of veins:
- reduces venous return and therefore reduces the preload (diastolic pressure that distends the left ventricle
Dilation of Arteries:
- Reduces after-load (pressure required by ventricles to eject blood)
DILATION OF THESE VESSELS REDUCES THE WORK THE HEART HAS TO WORK, AND THUS REDUCES THE OXYGEN DEMAND OF THE HEART.
Calcium channel blockers as a treatment for angina. Give examples of such drugs, and the mechanism of action. Rememeber that they block long-type voltage operated calcium channels.
- Nifedipene, Diltiazem, Verapamil, Amlodipine,
- Block voltage operated calcium chnannels in the heart (calcium required for depolarisation of SA node) and in vessels (released by Saroplasmic reticulum for muscle contraction)
- These drugs reduce calcium entry into the cells
Results:
- reduced peripheral resistance in vessels (since their ability to contract is reduced) because of dilation of the arteries (not much effect on the veins)
- Therefore reduces afterload and reduces myocardial demand
- reduced cardiac output (since heart cannot beat as fast and as hard)
Two types of Channel blockers:
-
Open channel blockers (like a cork in a bottle) - The pore through which calcium ions flow is blocked by drug
- Verapamil, Diltiazem
-
Alosteric Modulators (bind to site on the pore that isn’t the channel, causing conformational change and stops calcium from entering
- Nifedipine, Almodipine
