What cardiovascular factors can be altered by drugs?
- Heart rate - Heart force of contraction - Blood vessel tone - Blood volume - Blood composition
What is a pulse?
What happens if the heart rate is too fast?
There is not enough time for the heart to refill in diastole (after systole contraction) - this means that the heart is beating but a pulse cannot be felt
What is the normal blood vessel tone?
Half-way between constriction and dilatation
What is the main organ involved in changing blood volume?
What are some common problems with the heart that may require drug treatment?
- Heart Disease - Injury - Anaesthesia - Shock
Where in the heart are places that might need drug treatment?
- Conducting system - Myocardium - Blood supply - Valves - Nerve supply
What drug types can be given to treat heart conducting system problems?
- Antiarrhythmics - Chronotropes
What drug types can be given to treat heart Myocardium problems?
What drug types can be given to treat heart blood supply problems?
What drug types can be given to treat heart valve problems?
- Vasodilators - Surgery
What drug types can be given to treat heart nerve supply problems?
Why is anaesthesia a problem?
It is a major change to the CV system - it depresses it - the animal is less able to maintain normal homeostasis - Bad anaesthesia can cause shock
What is shock?
Decreased blood perfusion to peripheral tissues in the body
What does blocking heart conduction do?
Stops the heart
What do you have to be aware of in calves hearts?
New born calves have a bad heart murmur because it takes the foramen ovale 2 days to close - don't mistake this for a severe problem!
What happens as consequences of heart failure?
- Upstream blood pressure increases which increases preload - Downstream blood pressure decreases which increases vasoconstriction and afterload - Blood dams back to lungs causing pulmonary oedema - Blood dams back to body causing ascites and peripheral oedema - Lack of forward blood flow to muscles and lungs causes tissue hypoxia (exercise intolerance)
What does increased preload do?
Increases cardiac output in the short term
- Preload is the filling pressure of the heart at the end of diastole
How do you measure downstream pressure?
Measure Arterial Blood Pressure - May not be able to feel a pulse which is not good
What are the three major types of heart failure?
- Cardiac Arrest - Acute heart failure - Chronic (congestive) heart failure
In simple terms what is acute heart failure?
On the verge of going into cardiac arrest and CHF - not commonly seen unless under anaesthesia
What is true of cardiac arrests?
Prevention is better than cure! - Treat the cause before it happens!
What procedure should you follow when presented with a patient with suspected cardiac arrest?
- Airways: check for clear airway by pulling tongue out
- Breathing: Look at chest to see chest rising and falling. Use an ambubag and give 4 breaths straight away
- Circulation: compress the chest 1/s. After this, give 15 compressions: 1-2 breaths stopping every 2-3 minutes to feel for a pulse
Persist for 15 minutes. If successful, treat for acute heart failure
- Drugs: asystole (heart stops) give atropine to start with, adrenaline after oxygenated blood goes to heart and brain, bicarbonate for acidosis. For fibrillation use DC defibrillator, give lignocaine, adrenline or bicarbonate
- ECG etc
What is fibrillation?
Rapid, irregular uncoordinated contraction of cardiac muscle walls
- Treated by DC defibrillation, lignocaine, adrenaline or bicarbonate
How does lignocaine help treat fibrillation?
- reduces the chance of cells firing
- It tends to synchronise cells but alse reduces C.O
What are the problems after CPR?
- Hypoxic myocardium and brain
- Bruising of myocardium
- Lung contusions/ pneumothorax
- Broken ribs
What is pulse?
Arterial palpation of the Heart beat
- Equivalent to measuring the heart rate
What physiological changes occur in an animal with CHF?
- CO decreases
- BP decreases
- Increased sympathetic tone (seen as vasoconstriction and tachycardia)
- Increased salt and water retention
How do you treat CHF long term?
When normal homeostatic mechanisms fail to keep arterial BP within normal range or when CO is inadequate for normal tissue perfusion
- Feed a low salt diet
- Give diuretics (e.g. frusemide)
- Give vasodilators (ACE inhibitors)
- Give long acting positive ionotropes
- Give antiarrythmics if necessary
What is the main group of drugs that cause vasodilation?
Angiotensin-converting enzymes (ACE) inhibitors
- given orally for long term treatment