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What changes are seen on an ECG of a patient taking digitalis?
↑ PR interval, ↓ QRS duration, ↓ QT, and ↓ ST segment, flattened inverted T wave
What does inhibition of the 3Na/2K pump result in physiologically?
↑ free intracellular Ca²⁺, ↑ # of troponin C molecules to bind Ca²⁺, ↑ intensity of actin-myosin interaction
How does digitalis effect action potential at therapeutic concentrations?
↓ action potential duration
How does digitalis effect action potential at toxic concentrations?
↑ slope of phase 4, less negative maximal diastolic membrane potential
The negative chronotropic action of digitalis results from?
stimulation of vagal nucleus and direct depressive action upon SA and AV nodes
What therapy is extremely effective in the case of life-threatening digoxin overdose?
Digoxin immune Fab
What are the most common arrhythmias caused by digitalis?
ventricular extrasystoles, 2nd or 3rd AV block
What are the common electrolyte disturbances that can alter digitalis effects?
hyper or hypokalemia
What are the major contraindications of digitalis?
chronic cor pulmonale (hypoxia increases sensitivity of digoxin), COPD
What are the therapeutic uses of digitalis?
acute and chronic systolic heart failure, atrial fib, atrial flutter, nodal tachycardia
What receptors does dopamine activate at different dose levels?
med: D1, β1, β2
high:D1, D2, β1, β2, α1
What is the therapeutic use of dopamine?
Acute decompensated heart failure
cardiogenic, neurogenic, septic shock
(especially for poor renal perfusion)
the clinical picture)
What are the main mechanisms by which β1 agonist increase cardiac contractility?
↑ phosphorylation of troponin C, and ↑ opening of voltage gated Ca²⁺ channels
What are the therapeutic uses of dobutamine?
acute decompensated heart failure, or cardiogenic shock when the left ventricular function is severely depressed
How do phosphodiesterase inhibitors work?
Inhibition of phosphodiesterase isozyme 3 → ↑ cAMP
→ ↑ free intracellular Ca²⁺ in myocardium
→ ↓ phosphorylation of myosin light chain in smooth muscle
What are the therapeutic uses of phosphodiesterase inhibitors?
acute decompensated heart failure, or cardiogenic shock when pts don't respond to other therapies OR are on beta blockers
What are the mechanisms by which ACE inhibitors improve chronic heart failure?
reducing preload and afterload
What do broad spectrum antibiotics do to the bioavailability of digoxin?
(less GI bugs to metabolize digoxin)
What are the adverse effects of combining digoxin with loop or thiazide diuretics?
hypokalemia and hypomagnesemia
What effect does spironolactone have on the serum concentration of digoxin?
increases the serum concentration by 30% (can lead to toxicity)
What classes of drugs are used in all stages of heart failure?
ACE inhibitors and Angiotensin receptor antagonists
What vasodilatory drug have the greatest impact on both preload and afterload?
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