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17 Cards in this Set
- Front
- Back
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what do inotropes do? (3)
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increase force of ventricular contraction
increase intracellular Ca++ -> augment actin & myosin shifts Frank Starling curve upward to increase SV & CO |
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what are 3 examples of digitalis glycosides?
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digoxin
digitoxin ouabain |
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what are the 2 desired effects of digitalis?
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- mechanical: increases contractility of failing heart
- electrical: prolongs refractory period of AV node in those w supraventricular arrythmias |
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what is the sarcoplasmic reticulum?
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internal membrane system of muscle where Ca++ is stored & later released to initiate muscle contraction; it is then returned to the SR by Ca ATPase
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draw mechanism of digitalis' ionotropic effect
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Lilly Fig XXX
need to show that digitalis has inhibitory effect on Na+K+ ATPase which causes intracellular Na to rise -> decreased transmembrane Na+ gradient -> decreased Ca++ driven from cell (Na/Ca exchanger) -> increased Ca in SR -> increased Ca released when action potential excites the cell |
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what is the main electrical effect of digitalis?
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on the AV node - vagal effect: slows conduction velocity & increases refractoriness
-> decreases rate of transmission of atrial impulses to ventricles in supraventricular arrythmias |
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what effects does digitalis toxicity have?
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increases vagal tone, increases inhibition Na/K/ATPase pump
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draw how digitalis affects the action potential?
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lilly fig XXX
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when is digitalis not useful in heart failure?
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those associated w normal contractility
eg high output failure assoc w thyrotoxicosis pulm congestion caused by mitral stenosis pure diastolic dysfunction |
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is digoxin rate or rhythm control?
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rate - slows down impulses via AV node -> decreases ventricular rate
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what is the pharmacokinetics of digoxin?
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excreted unchanged by kidney
needs a series of loading doses maintenance dose depends on renal fn |
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what is the significance of the toxic: therapeutic ratio of digoxin
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quite low - toxicity easy to happen
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where are extracardiac signs of dig toxicity usually seen & why?
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usually GI
thought to be mediated by action of digoxin on area postrema of brain stem |
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what is the most common arrythmia seen in digoxin toxicity?
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development of ventricular extrasystoles
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what is the most common cause of non re-entrant SVT & why?
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digoxin toxicity
due to increased automaticity |
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what is the commonest cause of digoxin intoxication?
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decreased potassium eg diuretic used -> further inhibits na/k/atpase pump
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what is the treatment of digoxin induced tachyarrythmia?
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give K+ if hypokalaemic
+/- IV lignocaine +/- temporary pacemaker in high grade AV block +- admin Fab fragments of antidigitalis antibodies if severe intoxication |
