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Clinical Studies > Heart Drugs > Flashcards

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
Q

How does lignocaine help treat fibrillation?

A
  • reduces the chance of cells firing
  • It tends to synchronise cells but alse reduces C.O
26
Q

What are the problems after CPR?

A
  • Hypoxic myocardium and brain
  • Acidosis
  • Bruising of myocardium
  • Lung contusions/ pneumothorax
  • Broken ribs
27
Q

What is pulse?

A

Arterial palpation of the Heart beat

  • Equivalent to measuring the heart rate
28
Q

What physiological changes occur in an animal with CHF?

A
  • CO decreases
  • BP decreases
  • Increased sympathetic tone (seen as vasoconstriction and tachycardia)
  • Increased salt and water retention
29
Q

How do you treat CHF long term?

A

​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
Q

What is the main group of drugs that cause vasodilation?

A

Angiotensin-converting enzymes (ACE) inhibitors

  • given orally for long term treatment
31
Q

Apart from ACE inhibitors what else can be used as a vasodilator?

A
  • Nitrates
  • Calcium channel blockers

Used for both acute and chronic heart failure

32
Q

Do ACE inhibitors have any effect in normal animals (Ie those without CHF)?

A

No

33
Q

What do ACE inhibitors do?

A
  • 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
Q

What are some indications of ACE inhibitors?

A
  • CHF
  • Especially mitral regurgitation
  • Control of arterial BP during anaesthesia
  • Navicular Disease
  • +- Diuretics
35
Q

What are the side effects of vasodilators?

A

Other side effects are specific to individual drugs and may include:

  • Hypotension
  • Reflex Tachycardia
  • Anorexia
  • Vomiting
  • Diarrhoea
  • Coughing
36
Q

What are commonly used vasodilators?

A
  • Captopril
  • Enalapril (prodrug)
  • Quinapril
  • Benazepril
37
Q

What Calcium channel blockers can be used for CHF?

A
  • Vasodilators
    • Nicardipine
    • Nifedipine
  • Antiarrythmics
    • Verapamil
    • Diltiazem
38
Q

What do Calcium Channel Blocker Drugs do?

A

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
Q

What positive ionotropes can be used in CHF?

A
  • Sympanomimetics
    • e.g. Adrenaline
  • Cardiac glycosides
    • e.g. digoxin
  • Phosphodiesterase inhibitors (PDI)
    • e.g. etamiphylline
40
Q

What are the effects of PDIs?

A
  • Positive Ionotropy
  • Vasodilation
  • Bronchodilation
  • CNS stimulation
  • Diuresis
41
Q

What are the indications of PDIs?

A

Mild - Moderate CHF

42
Q

What are the side effects of PDIs?

A
  • Sudden death in people
  • None Obvious in dogs
43
Q

What are some potential causes of arrythmias?

A
  • 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
Q

What are some PDIs?

A
  • Methylxathines
    • Caffeine
    • Theophylline
      • Aminophylline
      • Etamiphylline
    • Theobromine
  • Synthetic
    • Milrinone
    • Oxpentifylline
    • Sildenafil
    • Pimobendan
45
Q

What is the definition of arrythmias?

A
  • Abnormal Cardiac Rhythm
    • Impulse formation
    • Conduction
    • Rate of regularity
46
Q

What is the Vaughan Williams Classification of Antiarrythmic drugs?

A
  • 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
Q

What are some other drugs that act as antiarrythmics?

A
  • Muscarinic Antagonists
  • Digoxin
  • Isoprenaline
  • Adenosine for supraventricular tachycardias
  • Calcium for ventricular tachycardia due to high potassium
  • Magnesium
48
Q

What are some non-drug treatment options for patients with arrythmias?

A
  • Pacing
  • DC cardioversion
  • CPR
49
Q

What are diuretics?

A

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
Q

How do diuretics affect CHF?

A
  • Reduce preload
  • Reduce pulmonary and cerebral oedema
  • Hyperkalaemia
  • Hypercalcaemia
  • Uraemia
  • Epistaxis
  • Hypertension
51
Q

What are the different groups of diuretics?

A
  • Loop diuretics
  • Thiazides
  • Osmotic Diuretics
  • Potassium sparing diuretics
  • Carbonic Anyhydrase inhibitors
  • Mercurials
52
Q

How does Frusemide act?

A
  • 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
Q

What Drugs should be used for different types of CHF?

A
  • 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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