Cardiac Glycosides Flashcards
Causes of heart failure
HEART PMI
Hypertension
pulmonary embolism
anaemia
arrhythmia
rheumatic heart disease
thyrotoxicosis
pregnancy
myocardial infarction
medication
infection
Symptoms of right sided heart failure
Peripheral oedema
jugular vein distension
increased peripheral venous pressure
weight gain
Ascites
hepatosplenomegaly
fatigue
Symptoms of left sided heart failure
Cyanosis
dyspnoea
tachypnoea
pulmonary congestion
tachycardia
restlessness
Source of thevetin
Thevetia neriifolia (nut)
Source of strophanthus G (ouabain)
Strophanthus gratus (seed)
Source of convallotoxin
Lily of the Valley (Convallaria majalis)
Examples of semi synthetic glycosides
Acetyl digoxin
Acetyl strophanthidin
Desacetyl lanatoside
Plant families of cardiac glycosides
Scrophulariaceae
Apocyanaceae
Liliceae
Effects of cardiac glycosides on cardiac function
Reduced chronotropy
Increased inotropy
Reduced dromotropy
Increased lusitropy
What are the effects of increased inotropy on the cardiovascular system?
a. Increased cardiac output
b. Decreased heart size
c. Decreased venous pressure
d. Decreased circulating blood volume
e. Diuresis
How does digoxin bring about reduced chronotropy
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
Electrophysiological effects of cardiac glycosides
Decrease amplitude or inversion of T wave
Increased PR interval
Shortening QT interval
Depression of ST segment
Abnormal QRS wave
Cardiac glycosides on Blood vessels
Mild direct vasoconstriction
Effect of CG on Kidney
Causes diuresis in CHF patients
Effect of CG on CNS
High doses stimulate the vomiting center causing nausea and vomiting and much higher doses causes hyperapnoea, mental confusion, visual disturbances, disorientation.
What portion of the Na-K-ATPase pump does digoxin bind to?
Extracellular
In high doses, digoxin toxicity is reversed by what? How?
K+ infusion
Binding of digoxin to the pump is slow, and the inhibition further depletes intracellular K+.
Low potassium levels will reduce digoxin binding. True or false?
False. It increases it. Potassium infusion is used to treat toxicity, remember.
What are other effects of low potassium levels?
Prolonged AP
Arrythmia
What are the extracardiac adverse effects of cardiac glycosides?
Anorexia
nausea and vomiting
abdominal pain
visual disturbances
fatigue
Weakness
confusion
gynaecomastia
diarrhoea
What are the cardiac adverse effects of cardiac glycosides?
Ventricular arrhythmias
atrioventricular block
Atrial arrhythmia
sinus bradycardia
Precautions and contraindications for CG
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
Effect of digoxin on potassium
Mechanism: Digoxin & K inhibit each other binding to Na K ATPase
Effect: Hyperkalemia reduces digoxin activity
Hypokalemia potentiates digoxin toxicity
Effect of digoxin on calcium
Mechanism: Enhances calcium absorption into the myocytes and accelerates overloading of calcium stores
Effect: Hypercalcemia potentiates digitalis-induced arrythmias
Effect of digoxin on magnesium
Mechanism: Antagonizes the effect of calcium
Effect: Hypomagnesemia sensitizes the heart to digitalis-induced arrythmia
Which drugs increase the serum concentration of CG?
Verapamil
amiodarone
spironolactone
Quinidine
propafenone
warfarin
cyclosporine
Macrolides
What is the drug interaction of CG with diuretics?
Hypokalaemia, with increased risk of digitalis arrhythmias
Treatment of acute digoxin toxicity
- 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
Treatment of chronic digoxin toxicity
- Supportive therapy
- Symptomatic bradycardia or heart block : Atropine/Digoxin specific Fab fragment
- Arrythmia: Lidocaine / Phenytoin
Which drugs are used to treat arrhythmias from chronic digoxin toxicity?
Lidocaine / Phenytoin
How to treat digoxin-induced hypokalaemia and hyperkalaemia
Treat with Potassium chloride (KCl) and therapeutic drug monitoring of digoxin and potassium.
Hyperkalemia: Digoxin specific Fab fragment , insulin and dextrose / sodium bicarbonate use.
What is digoxin-specific Fab fragment (digibind fragment)?
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.
Meaning of increased PR interval
Slower HR, dromotropy
Shortened QT interval meaning
Depolarisation and repolarisation take longer
Depressed ST segment meaning
Impaired blood flow
Abnormal QRS wave meaning
Conduction abnormalities
