Cardiac Glycosides

Question 1

Causes of heart failure

Answer 1

HEART PMI

Hypertension
pulmonary embolism
anaemia
arrhythmia
rheumatic heart disease
thyrotoxicosis
pregnancy
myocardial infarction
medication
infection

Question 2

Symptoms of right sided heart failure

Answer 2

Peripheral oedema
jugular vein distension
increased peripheral venous pressure
weight gain
Ascites
hepatosplenomegaly
fatigue

Question 3

Symptoms of left sided heart failure

Answer 3

Cyanosis
dyspnoea
tachypnoea
pulmonary congestion
tachycardia
restlessness

Question 4

Source of thevetin

Answer 4

Thevetia neriifolia (nut)

Question 5

Source of strophanthus G (ouabain)

Answer 5

Strophanthus gratus (seed)

Question 6

Source of convallotoxin

Answer 6

Lily of the Valley (Convallaria majalis)

Question 7

Examples of semi synthetic glycosides

Answer 7

Acetyl digoxin
Acetyl strophanthidin
Desacetyl lanatoside

Question 8

Plant families of cardiac glycosides

Answer 8

Scrophulariaceae
Apocyanaceae
Liliceae

Question 9

Effects of cardiac glycosides on cardiac function

Answer 9

Reduced chronotropy
Increased inotropy
Reduced dromotropy
Increased lusitropy

Question 10

What are the effects of increased inotropy on the cardiovascular system?

Answer 10

a. Increased cardiac output
b. Decreased heart size
c. Decreased venous pressure
d. Decreased circulating blood volume
e. Diuresis

Question 11

How does digoxin bring about reduced chronotropy

Answer 11

Via its vagal and extra vagal action by
- amplifying parasympathetic discharge to the heart via baroreceptors:
- direct stimulation of vagal center
- sensitization of SA node to acetylcholine

Question 12

Electrophysiological effects of cardiac glycosides

Answer 12

Decrease amplitude or inversion of T wave
Increased PR interval
Shortening QT interval
Depression of ST segment
Abnormal QRS wave

Question 13

Cardiac glycosides on Blood vessels

Answer 13

Mild direct vasoconstriction

Question 14

Effect of CG on Kidney

Answer 14

Causes diuresis in CHF patients

Question 15

Effect of CG on CNS

Answer 15

High doses stimulate the vomiting center causing nausea and vomiting and much higher doses causes hyperapnoea, mental confusion, visual disturbances, disorientation.

Question 16

What portion of the Na-K-ATPase pump does digoxin bind to?

Answer 16

Extracellular

Question 17

In high doses, digoxin toxicity is reversed by what? How?

Answer 17

K+ infusion

Binding of digoxin to the pump is slow, and the inhibition further depletes intracellular K+.

Question 18

Low potassium levels will reduce digoxin binding. True or false?

Answer 18

False. It increases it. Potassium infusion is used to treat toxicity, remember.

Question 19

What are other effects of low potassium levels?

Answer 19

Prolonged AP
Arrythmia

Question 20

What are the extracardiac adverse effects of cardiac glycosides?

Answer 20

Anorexia
nausea and vomiting
abdominal pain
visual disturbances
fatigue
Weakness
confusion
gynaecomastia
diarrhoea

Question 21

What are the cardiac adverse effects of cardiac glycosides?

Answer 21

Ventricular arrhythmias
atrioventricular block
Atrial arrhythmia
sinus bradycardia

Question 22

Precautions and contraindications for CG

Answer 22

Hypokalemia- Low K increases the binding to Na- K -ATPase
Elderly, renal or hepatic disease – More sensitive
Thyrotoxicosis – More prone to develop arrythmia.
Ventricular tachycardia – More prone to ventricular fibrillation
Myxoedema – Eliminate digoxin slowly and prone to toxicity

Question 23

Effect of digoxin on potassium

Answer 23

Mechanism: Digoxin & K inhibit each other binding to Na K ATPase

Effect: Hyperkalemia reduces digoxin activity
Hypokalemia potentiates digoxin toxicity

Question 24

Effect of digoxin on calcium

Answer 24

Mechanism: Enhances calcium absorption into the myocytes and accelerates overloading of calcium stores

Effect: Hypercalcemia potentiates digitalis-induced arrythmias

Question 25

Effect of digoxin on magnesium

Answer 25

Mechanism: Antagonizes the effect of calcium

Effect: Hypomagnesemia sensitizes the heart to digitalis-induced arrythmia

Question 26

Which drugs increase the serum concentration of CG?

Answer 26

Verapamil
amiodarone
spironolactone
Quinidine
propafenone
warfarin
cyclosporine
Macrolides

Question 27

What is the drug interaction of CG with diuretics?

Answer 27

Hypokalaemia, with increased risk of digitalis arrhythmias

Question 28

Treatment of acute digoxin toxicity

Answer 28

• STOP DIGOXIN administration!!!
• Acute toxicity in <2hrs: Decrease absorption by administering Activated Charcoal or Cholestyramine to decontaminate the GIT
• Supportive therapy: Rehydrate to increase renal clearance

Question 29

Treatment of chronic digoxin toxicity

Answer 29

• Supportive therapy
• Symptomatic bradycardia or heart block : Atropine/Digoxin specific Fab fragment
• Arrythmia: Lidocaine / Phenytoin

Question 30

Which drugs are used to treat arrhythmias from chronic digoxin toxicity?

Answer 30

Lidocaine / Phenytoin

Question 31

How to treat digoxin-induced hypokalaemia and hyperkalaemia

Answer 31

Treat with Potassium chloride (KCl) and therapeutic drug monitoring of digoxin and potassium.

Hyperkalemia: Digoxin specific Fab fragment , insulin and dextrose / sodium bicarbonate use.

Question 32

What is digoxin-specific Fab fragment (digibind fragment)?

Answer 32

Used in severe cases of life threatening digoxin toxicity, it was developed for measuring plasma concentration of digoxin by radioimmunoassay.

It acts by cross reacting with digitoxin. It is non-immunogenic with the digoxin-fab fragment rapidly excreted by kidney.

Question 33

Meaning of increased PR interval

Answer 33

Slower HR, dromotropy

Question 34

Shortened QT interval meaning

Answer 34

Depolarisation and repolarisation take longer

Question 35

Depressed ST segment meaning

Answer 35

Impaired blood flow

Question 36

Abnormal QRS wave meaning

Answer 36

Conduction abnormalities