Digitalis ECG

 

– Also called cardiac glycosides

– Digitalis are in fact only small positive inotropic with some peripheral vascular effects.

– At the level of myocardial cell, digitalis bind to membrane receptors and inhibit Na + / K + ATPase membrane.

This blocks the outlet of extracellular Na + => [Ca2 +] int high (Na + exchanger / Ca2 +) => increasing the contractile force of the myocardial cell.

– Digitalis also have an indirect effect by enhancing vagal tone -> negative chronotropic effect

– Action on baroréceptices activating cells of the aortic arch, carotid sinus

A- Pharmacological actions:

1- Cardiac effects:

– Increase the contractile force: positive inotropic

– Increase the excitability of the myocardium: Positive effect bathmotropic

– Decrease in heart rate: negative chronotropic effect

– Decrease the conduction of electrical influence: negative dromotropic

2- extracardiac effects:

– Rein: improves renal perfusion; anti-aldosterone effect, so an indirect diuretic effect

– Vessels: arteriolar vasoconstriction; increase venous tone (preload)

– CNS: stimulation of vagal centers and vomiting

– Autonomic Nervous System: activation of vagal tone (at all levels) that inhibits condairement-friendly effect.

– Digitalis sensitize the heart to action inotropic catecholamine

– Oxygen consumption decreases on insufficient heart

– Effect negative dromotropic: at the node of Aschoff and Tawara-His bundle refractory periods are elongated and conduction velocity is slowed down.

– The negative effect explains bathmotropic property to trigger an intrinsic pacemaker in the atria and ventricles, causing the arrhythmia, net in case of digitalis intoxication.

– At the level of the CNS: the digitalis to toxic doses cause a cortical excitation (occipital) causing hallucinations and visual disturbances.

– A toxic level at the SNV sympathetic activation with increased release of catecholamines; the consequences of which remain unclear.

– At the heart insufficient improvement in cardiac output induced vasodilation

3- ECG:

Digitalis impregnation A- / B- Digitalis Intoxication

Digitalis impregnation A- / B- Digitalis Intoxication

(Impregnation Signs)

– Sinus bradycardia or AV block 1st degree (moderately high PR)

– Flattening of the T wave; negativity but asymmetric

– Shortening of QT

– Base Offset cupuliforme concave upward ST

– Appearance of a wave U

B- Digitalis Intoxication:

* Aggravating factors at the cellular level:

– Overload intracellular calcicosodique

– Drop extracellular potassium (hypokalemia)

– High level of sympathetic tone

* The toxic concentrations:

– ≥ 3 ng / ml for digoxin

– ≥ 45 ng / ml for digitoxin

* Medicines that increase digitalis toxicity: amiodarone (but possible association); quinidine (with digoxin); verapamil (digoxin); erythromycin; ibuprofen; indomethacin; antacids; coal; … cholestyramine. (Sulfasalazine-induced against a sharp decrease in digoxin).

* Note: severe intoxication often result in hyperkalemia

1- extracardiac Events:

– Digestive: vomiting; transit disorders

– Eyepieces: dyschromatopsia yellow, green, scotoma, colorful halo

– Neurological: headache, insomnia, neuralgia V, convulsion, depression

– More rarely: rash; gynecomastia; diffuse arterial spasm

2- Cardiac Events:

– Av conduction disorders (BAV …) and atrial rhythm disorders, ventricular

– Tachysystole atrial always evocative; flutter or atrial fibrillation rarer

– Junctional tachycardia

– ESV, ESA, TV, FV

– Bidirectional Ventricular tachycardia (several automation households)

– At a late stage, intraventricular conduction disorders and inexcitability

* Treatment:

– Stop all administration of digitalis and serum sample

– Gastric lavage drug if taken before 3:00.

– Serum 5% glucose infusion

– Systematic potassium intake unless initial hyperkalemia, renal insufficiency, conduction disorders of degree.

– Driving up a pacing probe if CCHB with slow escape rhythm

– Atropine so minor conduction defects (sinus bradycardia, BSA, minor BAV)

– Immunotherapy in case of mass poisoning with signs of severity (Anti-Fab)

– Dihydantoïne in case of symptoms of ventricular rhythm or lidocaine (amiodarone, propranolol may also be used)

C- Indications and cons-indications:

1- Indications:

* Congestive heart failure: more effective when the heart is dilated, there is an ACFA, the patient is not in hypovolemia, the IC is not terminal.

* Supraventricular rhythm disorders

This is the preferred indication of digitalis: FA, flutter

2- Contraindications:

– BAV degree unaided

– Atrial rhythm disease and sinus dysfunction

– Ventricular tachycardias

– Repetitive ESV, polymorphic

– Wolff-Parkinson-White syndrome

– Ionic disorders: hypokalemia, hypercalcemia

– Obstructive or restrictive heart disease

– Aortic stenosis.

3- pharmacokinetic properties:

Digitoxin (Digitaline®):

Fat largest => almost complete digestive resorption; almost completely metabolized by the liver; biliary and urinary elimination; high plasma protein binding (90%) => greater plasma half-life (4-6 days)

Digoxin (Nativelle®)

Water solubility greater => lower digestive resorption (<80%); low protein binding (20%); minimal hepatic metabolism (10%); higher renal elimination. ½ life = 36 hours

Lanatoside (Cédilanide®):

As digoxin

– Competition between potassium and digitalis at the myocardial cell: decrease the local concentration of K + ions leads to increased fixation of digitalis

– The other positive inotropic: sympathetic and related amines, glucagon, phosphodiesterase inhibitors, sodium channel agonist

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