Inotropes

Question 1

What is the mechanism of action of digoxin?

Answer 1

blocks sarcolemma Na+/K+ ATPase - increased intracellular Na+ - decreased Na+/Ca2+ exchange - increased intracellular Ca2+ - increased storage of Ca2+ in the SR - increased CICR - increased contractility, increases vagal activity - slows down SA node discharge - slows AV node conduction - increases refractory period, shortens AP and refractory period in myocytes - pro-arrhythmic

Question 2

What is the result of a toxic concentration of digoxin?

Answer 2

membrane depolarisation and oscillatory afterpotentials - due to Ca2+ overload - pro-arrhythmic

Question 3

How is digoxin used in heart failure?

Answer 3

IV in acute heart failure and oral in heart failure - patients who are symptomatic despite optimal use of other drugs

Question 4

How are inodilators used?

Answer 4

IV in acute heart failure that has failed to respond to other drugs

Question 5

What is the mechanism of action of inodilators?

Answer 5

inhibit phosphodiesterase in cardiac and smooth muscle - decreases cAMP concentration - increased contractility and decreased peripheral resistance

Question 6

Give examples of inodilators

Answer 6

amrinone, milrinone

Question 7

What is the mechanism of action of Ca2+ sensitizers?

Answer 7

bind to troponin C in cardiac muscle -sensitises it to Ca2+, opens K+ATP channels in vascular smooth muscle - vasodilation - reduces afterload - reduces cardiac work

Question 8

Give an example of a calcium sensitizer?

Answer 8

levosimendan

Question 9

What are the extracardiac side effects of digoxin?

Answer 9

nausea, vomiting, diarrhoea, blurred or yellow vision

Question 10

How do inodilators worsen survival?

Answer 10

pro-arrhythmic

Question 11

Why is digoxin used in heart failure with atrial fibrillation?

Answer 11

increased AV node refractory period - prevents spreading of arrhythmia to ventricles

Question 12

How are calcium sensitizers used?

Answer 12

IV in acute decompensated heart failure

Question 13

What is the role of an inotrope?

Answer 13

increase SV at any given end diastolic pressure

Question 14

Why does digoxin have a small therapeutic range?

Answer 14

competes with K+ to bind with ATPase - dangerously enhanced by hypokalaemia - less competition

Question 15

What are the cardiac side effects of digoxin?

Answer 15

arrhythmias, excessive depression of AV node conduction - heart block