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Heart Drugs Flashcards

1
Q

What cardiovascular factors can be altered by drugs?

A
  • Heart rate - Heart force of contraction - Blood vessel tone - Blood volume - Blood composition
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2
Q

What is a pulse?

A

-

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3
Q

What happens if the heart rate is too fast?

A

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

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4
Q

What is the normal blood vessel tone?

A

Half-way between constriction and dilatation

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5
Q

What is the main organ involved in changing blood volume?

A

The kidneys

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6
Q

What are some common problems with the heart that may require drug treatment?

A
  • Heart Disease - Injury - Anaesthesia - Shock
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7
Q

Where in the heart are places that might need drug treatment?

A
  • Conducting system - Myocardium - Blood supply - Valves - Nerve supply
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8
Q

What drug types can be given to treat heart conducting system problems?

A
  • Antiarrhythmics - Chronotropes
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9
Q

What drug types can be given to treat heart Myocardium problems?

A

Inotropes

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10
Q

What drug types can be given to treat heart blood supply problems?

A

Vasodilators

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11
Q

What drug types can be given to treat heart valve problems?

A
  • Vasodilators - Surgery
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12
Q

What drug types can be given to treat heart nerve supply problems?

A

Chronotropes

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13
Q

Why is anaesthesia a problem?

A

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

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14
Q

What is shock?

A

Decreased blood perfusion to peripheral tissues in the body

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15
Q

What does blocking heart conduction do?

A

Stops the heart

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16
Q

What do you have to be aware of in calves hearts?

A

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!

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17
Q

What happens as consequences of heart failure?

A
  • 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)
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18
Q

What does increased preload do?

A

Increases cardiac output in the short term

  • Preload is the filling pressure of the heart at the end of diastole
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19
Q

How do you measure downstream pressure?

A

Measure Arterial Blood Pressure - May not be able to feel a pulse which is not good

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20
Q

What are the three major types of heart failure?

A
  • Cardiac Arrest - Acute heart failure - Chronic (congestive) heart failure
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21
Q

In simple terms what is acute heart failure?

A

On the verge of going into cardiac arrest and CHF - not commonly seen unless under anaesthesia

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22
Q

What is true of cardiac arrests?

A

Prevention is better than cure! - Treat the cause before it happens!

23
Q

What procedure should you follow when presented with a patient with suspected cardiac arrest?

A
  • 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
24
Q

What is fibrillation?

A

Rapid, irregular uncoordinated contraction of cardiac muscle walls

  • Treated by DC defibrillation, lignocaine, adrenaline or bicarbonate
25
How does lignocaine help treat fibrillation?
- reduces the chance of cells firing - It tends to synchronise cells but alse reduces C.O
26
What are the problems after CPR?
- Hypoxic myocardium and brain - Acidosis - Bruising of myocardium - Lung contusions/ pneumothorax - Broken ribs
27
What is pulse?
Arterial palpation of the Heart beat - Equivalent to measuring the heart rate
28
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
29
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 * Rest * Feed a low salt diet * Give diuretics (e.g. frusemide) * Give vasodilators (ACE inhibitors) * Give long acting positive ionotropes * Give antiarrythmics if necessary
30
What is the main group of drugs that cause vasodilation?
Angiotensin-converting enzymes (ACE) inhibitors - given orally for long term treatment
31
Apart from ACE inhibitors what else can be used as a vasodilator?
- Nitrates - Calcium channel blockers Used for both acute and chronic heart failure
32
Do ACE inhibitors have any effect in normal animals (Ie those without CHF)?
No
33
What do ACE inhibitors do?
* Blocks the enzyme (angiotensin- converting enzyme) that converts angiotensin I to angiotensin II * Most effects from this are due to the **decrease in Angiotensin II levels** which means there is less vasocontriction resulting in arterial and venous dilation * Reduction in pre and afterload * Reduction in myocardial work and oxygen consumption * Reduction in pressure across valves * Also reverse cardiac hypertrophy seen in heart failure (myocardial remodelling) *
34
What are some indications of ACE inhibitors?
* CHF * Especially mitral regurgitation * Control of arterial BP during anaesthesia * Navicular Disease * +- Diuretics
35
What are the side effects of vasodilators?
Other side effects are specific to individual drugs and may include: * Hypotension * Reflex Tachycardia * Anorexia * Vomiting * Diarrhoea * Coughing
36
What are commonly used vasodilators?
* Captopril * Enalapril (prodrug) * Quinapril * Benazepril
37
What Calcium channel blockers can be used for CHF?
* Vasodilators * Nicardipine * Nifedipine * Antiarrythmics * Verapamil * Diltiazem
38
What do Calcium Channel Blocker Drugs do?
Block the inward Ca2+ current across membranes of myocardial cells and vascular smooth muscle - Inhibits phase 4 of the AP and contractile mechanisms of SM and Vascular muscle - Slows phase 0 in SA and AV nodes
39
What positive ionotropes can be used in CHF?
* Sympanomimetics * e.g. Adrenaline * Cardiac glycosides * e.g. digoxin * Phosphodiesterase inhibitors (PDI) * e.g. etamiphylline
40
What are the effects of PDIs?
* Positive Ionotropy * Vasodilation * Bronchodilation * CNS stimulation * Diuresis
41
What are the indications of PDIs?
Mild - Moderate CHF
42
What are the side effects of PDIs?
* Sudden death in people * None Obvious in dogs
43
What are some potential causes of arrythmias?
* Delayed afterdepolarisation (late phase 3 or early phase 4) * Excess intracellular calcium due to: * Excess adrenergic stimulation * Digitalis overdose * Re-entry (unidirectional block in a connecting purkinje pathway) * Abnormal pacemaker * Heart Block
44
What are some PDIs?
* Methylxathines * Caffeine * Theophylline * Aminophylline * Etamiphylline * Theobromine * Synthetic * Milrinone * Oxpentifylline * Sildenafil * Pimobendan
45
What is the definition of arrythmias?
* Abnormal Cardiac Rhythm * Impulse formation * Conduction * Rate of regularity
46
What is the Vaughan Williams Classification of Antiarrythmic drugs?
* **Class 1: Sodium Channel Blockers** ​Reduce the excitability of conducting tissue _1a_ atrial fibrillation e.g. Quinidine _1b_ ventricular ectopic beats e.g. Lignocaine _1c_ e.g. Flecainide * **​​​****Class 2: ​​ß Blockers** **​**Reduce Automaticity for stress induced tachycardias e. g. Propanolol * **Class 3: Potassium Channel Blockers** Prolong APs e. g. Amiodarone * **Class 4: Calcium Channel Blockers** Block nodes & Damaged muscle for atrial tachycardias e.g. verapamil
47
What are some other drugs that act as antiarrythmics?
* Muscarinic Antagonists * Digoxin * Isoprenaline * Adenosine for supraventricular tachycardias * Calcium for ventricular tachycardia due to high potassium * Magnesium
48
What are some non-drug treatment options for patients with arrythmias?
* Pacing * DC cardioversion * CPR
49
What are diuretics?
Drugs that act on the kidneys to increase urine production - most of them block reabsorption of ions from tubules - Water is kept in tubules by osmotic pressure
50
How do diuretics affect CHF?
* Reduce preload * Reduce pulmonary and cerebral oedema * Hyperkalaemia * Hypercalcaemia * Uraemia * Epistaxis * Hypertension
51
What are the different groups of diuretics?
* Loop diuretics * Thiazides * Osmotic Diuretics * Potassium sparing diuretics * Carbonic Anyhydrase inhibitors * Mercurials
52
How does Frusemide act?
* It inhibits active Cl- transport in the thick ascending limb of the loop of Henle * This decreases the total resorption of Na+, Cl- and K+ * Decreases osmolality of the medulla * Increases osmolality of the filtrate presented to the DCT to help water resorption -\> now isoosmolar so much more water goes through DCT into the CD * up to 20% of filtered Na+ is excreted * Redistributes blood flow from juxtamedullary area to outer cortex
53
What Drugs should be used for different types of CHF?
* Pulmonary Oedema: Frusemide +- oxygen * Mild CHF: ACEI/ Frusemide/ PDE inhibitors * Dilated cardiomyopathy: digoxin * Hypertrophic cardiomyopathy: ACEI * Arrythmias: Check before using drugs

Clinical Studies (19 decks)

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