Reduced ejection Fraction HF 2: Digitalis Flashcards
General action of Digitalis on Heart
- Positive Inotropic
- Negative Chronotropic
- Negative dromotropic
- Ventricular arrhythmia
Mechanism of Action of digitalis
- Inhibits SAN
- Inhibits AVN
- Stimulates Atrial Contractility
- +ve inotropic (direct action)
- Toxic dose –> increase automaticity of Purkinje fibres —> Arrhythmia
Mechanism of Action of positive inotropic effect of Digitalis
Increases intracardiac calcium by inhibitin Na+k+ ATPase:
1. Inhibit Na+k+ ATPase
2. 2 K+ decrease intracellular , 3Na+ increase intracellular
3. blockage of Na+ Ca2+ exchanger –> retention of Ca2+
4. increased calcium induced Calcium induced calcium release —> Calcium secretion from sarcoplasmic reticulum
5. Increase contractility
Mechanism of Action of Negative Chronotropic/Bradycardia effect of Digitalis
both vagal stimulation & direct:
* Small dose: vagal tone only
* Large dose: vagal tone + direct inhibition of SAN
true or false, Atropine can antagonise high dose Digoxin bradycardia effect
false, at high dose, it works both Vagal & directly
effect of digoxin on excitability & Automaticity of the heart
- Increased excitability
- Increased Automaticity =especially in purkinje fibers due to -ve dromotropy (less conncection with SAN)
Effect of Digitalis on ECG
- Long P-R interval
- Depressed S-T segment
- Inverted T wave
- pulsus bigeminus & Trigeminus (arrhythmia)
effect of Digitalis on Cardiac Output
Increased, due to increased filling/ Stroke volume
effect of digitalis on BP
normalisation of increased systolic & decreased diastolic (reduce pulse pressure from both aspects)
effect of digitalis on kideny
- Increase GFR
- Decrease renin, Angiotensin, Aldosterone
effect of Digitalis on GIT
- Vomiting
- Affects CTZ center
effect of digitalis on CNS
- stimulates VMC
- Stimulates CTZ center
- toxic doses especially in elderly –> confusion & hallucinations
effect of digitalis on Endocrine
may cause Gynecomastia in males
Theraputic uses of Digitalis
- HF after other treatments & still symptomatic
- Atrial fibrillation
- Atrial flutter
Explain why digitalis is used in atrial fibrillation & Atrial flutter despite worsening Atrium (increase atrial conductivity)
to protect the ventricle, by delaying the Atrio-ventricular conduction, so ventricle will be:
* Slower
* More regular
* more efficient
Contraindications of digitalis
- Ventricular arrhythmia (worsens)
- Partial or complete heart block
- Cardiac ischemia (angina, infarction)
- Sick sinus syndrome/ impaired SAN
Drug interactions of digitalis
Decreasing activity of digitalis:
* Decreasing absorption: anti-acids (Mg & Al)
* Increasing K+: potassium sparring diuretics (spironolactone)
Increasing activity of digitalis:
* Hypokalemia: thiazide & Loop diuretics
* Hypercalemia: thiazide diuretics
* Beta blockers –> heart block
Manifestations of Digitalis toxicity
GIT:
* Nausea
* Vomiting
* Anorexia
* Diarrhea
* cramps
CVS:
* Bradycardia (less than 60bpm)
* Heart block
* atrial & ventricular Arrhythmia
* flutter & fibrillation (cause of death)
* pulsus bigeminus & trigeminus
CNS:
* Hallucination
* Delusion
* Confusion
* Convulsions
* Excitation
* Headache
* Coloured vision (chromatopsia)–> yellow & green vision
Factors that increase Digoxin toxicity
- Extermities of age
- Hypokalemia
- Drug interactions that increase its activity (thiazides, loop diuretics, beta blockers)
- Hyperclacemia
- Hypothyroidism
- Hypomagnesemia
- Kideny disease
Treatement of Digoxin Toxicity
- Stop digitalis
- Stop K+ depleting (thiazide & loop) diuretics
- oral activated charcoal
- if hypokalemic, give potassium chloride (but not in Heart block & renal impairment)
- Digoxin Antibody
drug of choice in Digoxin induced ventricular arrhythmia with heart block
Phenytoin
drug of choice in Digoxin induced ventricular arrhythmia without heart block
Lidocaine
drug of choice in Digoxin induced heart block or sinus bradycardia
Atropine
drug of choice in Digoxin induced ventricular fibrillation
Electro-cardioversion
