Answers

1. A. Verapamil is an L-type calcium channel blocker. Nitroglycerin and isosorbide are both organic nitrates and have no direct effect on L-type calcium channels at the SA node, while propranolol and metoprolol are p-adrenoceptor blockers and will slow heart rate by blocking the actions of norepinephrine and epineph-rine on p-receptors at the SA node.

2. D. Nitroglycerin can reduce preload, which in turn reduces wall tension and increases subendocardial blood flow. Nitroglycerin also reduces afterload, but this is a small effect compared to the reduction in preload. Its effects on heart rate and contractility are minimal, and if anything reflex tachycardia and increase in contractility would be detrimental effects of too much nitroglycerin.

3. C. Nitroglycerin can increase heart rate via an increase in sympathetic tone to the heart due to an excessive decrease in blood pressure; propranolol would block the p-receptors responsible for the tachycardia. Propranolol does not decrease preload, and its effect to decrease afterload would exacerbate the decrease in afterload produced by nitro-glycerin. Propranolol does not increase myocardial contractile force and could actually increase the incidence of vasospasm by unmasking a-adrenocep-tors in the coronary blood vessels.

4. B. Both diltiazem and propranolol would produce the effects listed in A, C, D, and E. Only diltiazem would dilate vessels in spasm. Propranolol would tend to produce vasoconstriction, not vasodilation.

5. D. An increase in time spent in diastole would increase subendocardial blood flow. Metoprolol does not decrease preload or increase afterload; in fact the opposite is likely to occur. Metoprolol does not affect collateral blood flow or flow through a concentric stenosis.

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