Answers
1. All the drugs listed are commonly used in heart failure except alpha agonists. Alpha agonist drugs increase vascular resistance and would decrease the stroke volume of the weakened heart even more. The answer is (B).
2. Digitalis does shorten the action potential in some parts of the heart and at some doses, but this action is another result, not the mechanism, of its biochemical action. Sodium-calcium exchange is not blocked, it is merely altered. The most accurate description of the mechanism of action of digitalis in this list is that it increases intracellular calcium. The answer is (D).
3. The parasympathomimetic effects of digitalis can be blocked by muscarinic blockers such as atropine. The only parasympathomimetic effect in the list provided is increased PR interval, representing slowing of AV conduction. The answer is (D).
4. Acute severe congestive failure often requires vasodilators to reduce intravascular pressures in the lungs and the periphery. Both nitroprusside and furosemide have such vasodilating actions -in the context of acute failure. Positive inotropic agents such as digoxin and dobutamine are traditional agents for heart failure. Beta antagonists such as propranolol, on the other hand, are usually contraindicated in acute heart failure; they are used only if the failure is due to certain cardiomyopathies. The answer is (D).
5. The effects of digitalis include all the effects listed. The answer is (E).
6. Digitalis toxicity is facilitated by hypercalcemia, hypokalemia, or hypomagnesemia. It is also more likely if a patient begins taking quinidine after being stabilized on a dose of digitalis, because quinidine reduces the clearance of digoxin. The answer is (E).
7. Review the pharmacokinetics of the cardiac glycosides. The answer is (C).
8. The major cause of digitalis arrhythmias is increased automaticity. All the other effects listed are seen frequently. The answer is (E).
9. Although they are extremely useful in congestive heart failure, captopril and the other ACE inhibitors have no positive inotropic effect on the heart. The answer is (B).
10. Digoxin increases intracellular sodium and calcium and reduces sympathetic outflow to the heart (because the drug replaces the need for constant sympathetic stimulation of contractility). However, digoxin does not increase intracellular potassium; blockade of Na+/K+ ATPase increases intracellular sodium and calcium and very slightly reduces intracellular potassium. The answer is (A).
11. Potassium is the only monovalent cation in the list that is used for reversing mild to moderate digitalis toxicity. The answer is (I).
12. The ACE inhibitors have been shown to prolong life in heart failure patients even though these drugs have no direct positive inotropic action on the heart. The answer is (E).
13. Dobutamine is a beta-1-selective agonist often used in acute heart failure. The answer is (D).
14. The drug of choice in severe, massive digitalis overdose is digitalis antibody, Digibind. The answer is (A).
15. Although quinidine may have this beneficial effect, it is also much more likely than lidocaine to precipitate digitalis toxicity. The answer is (G).