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Cardio > Drugs affecting cardiac rate and force > Flashcards

Drugs affecting cardiac rate and force Flashcards

1
Q

Dobutamine, adrenaline and noradrenaline are which kind of drug?

A

b-adrenoceptor agonists

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2
Q

What are the pharmacodynamic effects of b-adrenoceptor agonists upon the heart?

A

increase force, rate, CO and O2 consumption

decrease cardiac efficiency - O2 consumption increased more than cardiac work does

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3
Q

Which b-adrenoceptor agonists have a plasma half-life of approx. 2 mins?

A

adrenaline and dobutamine

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4
Q

Why is adrenaline given IV in a cardiac arrest?

A

positive inotropic and chronotropic actions

redistribution of blood flow to heart (constricts peripheries)

dilatation of coronary arteries

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5
Q

What is the route of administration of adrenaline in an anaphylactic shock?

A

IM (IV if enter cardiac arrest)

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6
Q

What is the route of administration of dobutamine?

A

IV infusion

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7
Q

In which condition would dobutamine be used?

A

acute, but potentially reversible, heart failure

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8
Q

What do the physiological effects of a b-adrenoceptor blockade depend upon?

A

the degree to which the sympathetic nervous system is activated

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9
Q

Which b-adrenoceptor antagonist is non-selective for b1 and b2 adrenoreceptors?

A

propranolol

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10
Q

Atenolol, bisoprolol and metoprolol block which adrenoceptor in a competitive manner?

A

B1

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11
Q

Which b-adrenoceptor antagonist is non-selective and a partial agonist?

A

alprenolol

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12
Q

What is the effect of non-selective b-adrenoceptor antagonists during exercise?

A

force and CO are significantly depressed - reduction in maximal exercise tolerance

myocardial O2 requirement falls -> better oxygenation of the myocardium

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13
Q

What are the CVS clinical used of b-adrenoceptor antagonists?

A

Arrhythmias
Angina
Heart failure
Hypertension

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14
Q

How do b-blockers work in treatment of AF and SVT?

A

delay condition through the AV node and help restore sinus rhythm

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15
Q

In which condition are b-blockers first line as alternative to CCBs?

A

angina

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16
Q

In which CVS condition does use of b-blockers seem paradoxical?

A

heart failure - studies show that low-dose b-blockers improve morbidity and mortality

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17
Q

Which b-blocker is often used in heart failure?

A

carvedilol - start low, go slow

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18
Q

B-blockers are no longer first line treatment for hypertension, unless…?

A

co-morbidites (e.g. angina) are present

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19
Q

What are the adverse effects of b-bockers (as a class)?

A 
Bronchospasm
Aggravation of cardiac failure
Bradycardia 
Hypoglycaemia 
Fatigue
Cold extremities
20
Q

Which b-blockers have less associated risk of bronchospasm?

A

b1-selective agents e.g. atenolol, bisoprolol, metoprolol

21
Q

If b-blockers can aggravate cardiac failure, why are they used in treatment of heart failure?

A

studies show that low dose b-blockers are used in compensated heart failure - patients may be relying on sympathetic drive to maintain an adequate CO and b-blockers reduce sympathetic drive so risk of crash - start low, go slow

22
Q

Which bADR receptors are implicated in fatigue caused by b-blockers?

A

b1 - cardiac output, and b2 - skeletal muscle perfusion in exercise are regulated by adrenoceptors

23
Q

Name a non-selective competitive antagonist of muscarinic ACh receptors?

A

atropine

24
Q

What is the effect of non-selective muscarinic ACh receptor antagonists?

A

Increase HR in normal subjects
No effect on arterial BP
No effect on response to exercise

25
Q

Why is the effect of atropine different in athletes?

A

SV is larger due to greater mass of cardiac muscle
Highly trained athletes have increased vagal tone
Atropine effect is exaggerated since blocks greater parasympathetic drive

26
Q

What are the clinical uses of atropine?

A

First line in severe bradycardia, particularly following MI - vagal tone is elevated.

Anti-cholinesterase poisoning (to reduce excessive parasympathetic activity)

27
Q

What is an alternative to atropine in severe bradycardia?

A

Glycopyrronium

28
Q

What is the name of a cardiac glycoside that increases contractility of the heart?

A

digoxin

29
Q

Drugs used in heart failure?

A

Digoxin
Dobutamine
b-blocker (low dose)

30
Q

What is the effect of digoxin (and other inotropes) on the Starling curve?

A

Shift upwards and left on the function curve, such that SV increases at any given EDP

31
Q

In heart failure, how is the Starling curve changed?

A

depressed and shifted right - cardiac contractility is reduced

32
Q

How does digoxin increase contractility of the heart?

A 
blocks the sarcolemma Na/K-ATPase:
Increase intracellular Na
Increase intracellular Ca
Increase Ca storage in SR
Increase CICR and therefore, contractility
33
Q

Which subunit on the Na/K-ATPase does digoxin bind to?

A

alpha subunit in competition with K+

34
Q

What can dangerously enhance the effects of digoxin?

A

low plasma K+ concentration (hypokalaemia)

35
Q

What are the indirect actions of digoxin on electrical activity?

A

Increased vagal activity;
slows SA node discharge,
slows AV node conduction - increases refractory period

36
Q

What are the direct effects of digoxin on electrical activity?

A

Shortens AP and refractory period in atrial & ventricular myocytes

37
Q

What effect on the electrical activity does a toxic concentration of digoxin have?

A

membrane depolarisation and oscillatory after-potentials - likely due to Ca2+ overload

38
Q

What are the clinical signs of digoxin toxicity?

A

Nausea, vomiting, anorexia, diarrhoea.
Blurred vision, yellow/green discolouration, haloes.
Palpitations, syncope, dyspnoea.
Confusion, delirium, fatigue

39
Q

Signs of digoxin toxicity on an ECG?

A

Down-sloping ST depression = reverse tick/sagging/scooped

Flattened, inverted, or biphasic T waves

Shortened QT interval

40
Q

Descrive a biphasic T wave and in which leads it would be seen.

A

initial negative deflection and terminal positive deflection
V4-6 (those with a dominant R wave)
First part is normally continuous with the depressed ST segment

41
Q

Why is the QT interval shortened due to digoxin toxicity?

A

it shortens the refractory period

42
Q

What are the different admin routes for Digoxin and in which scenario would they be used?

A

IV in acute heart failure

Orally in chronic heart failure

43
Q

In which arrhythmia is digoxin particularly indicated?

A

AF

44
Q

Which new drug would be useful in acute decompensated heart failure?

A

Levosimendan IV (calcium sensitiser)

45
Q

How do calcium sensitisers work?

A

Bind to troponin C in cardiac muscles sensitising it to the action of Ca2+ -> contraction

Also opens K-ATP channels in vasculature -> vasodilation - reduces after load and cardiac work

Cardio (15 decks)

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