A 55-year-old patient who is diagnosed with an evolving myocardial infarction (MI) insists on going home. The cardiac-vascular nurse encourages the patient to be admitted because the greatest risk within the first 24 hours of sustaining an MI is:

Correct Answer: D

Rationale: Ventricular fibrillation, a lethal arrhythmia, is the greatest risk in the first 24 hours post-MI due to myocardial irritability from ischemia, often causing sudden cardiac death. Other complications (A-C) are serious but less immediate threats.

Correct Answer: B

Rationale: The cardiac cycle consists of two phases: systole and diastole. Systole (Choice B) is the contraction phase, during which the heart pumps blood out of the ventricles into the arteries. Diastole (Choice A) is the relaxation phase, allowing the heart to fill with blood. Tachycardia (Choice C) refers to a rapid heart rate, and bradycardia (Choice D) indicates a slow heart rate; neither defines a phase of the cycle. Thus, Choice B is correct.

Correct Answer: A

Rationale: The heart has three layers: endocardium (inner), myocardium (middle), and epicardium (outer). The epicardium is the outermost layer of the heart wall itself, while the pericardium is a separate sac surrounding the heart. 'Supracardium' is not a real term.

Correct Answer: C

Rationale: Small arteries and arterioles are the primary resistive vessels because their narrow lumens and muscular walls (tunica media) allow them to regulate blood flow and peripheral resistance through vasoconstriction and vasodilation.

Correct Answer: B

Rationale: At the arteriolar end, high hydrostatic pressure pushes oxygen and nutrients out; at the venular end, lower pressure allows wastes to enter via diffusion and osmosis. Capillary density correlates positively with metabolism, and arrangements vary by tissue.