Which patient scenario best exemplifies paroxysmal arrhythmias?

Paroxysmal arrhythmias are characterized by intermittent episodes where the heart rhythm suddenly becomes irregular or fast, followed by a return to normal rhythm. This aligns perfectly with the scenario of a patient experiencing intermittent episodes of tachycardia. Such episodes can occur sporadically, often triggered by certain activities, stress, or other stimuli, but they are not persistent.

In contrast, the first scenario, which involves a constant heart rate change, does not fit the definition of paroxysmal arrhythmias because it suggests a more stable or continuous issue rather than intermittent episodes. The third scenario mentions chronic atrial fibrillation, which is a long-term condition, rather than an intermittent one, thus not representative of paroxysmal episodes. Lastly, a patient with a steady heart rhythm under exertion indicates a stable heart function with no arrhythmias present, which again does not embody the intermittent nature fundamental to paroxysmal arrhythmias. Therefore, the correct choice highlights the defining characteristic of paroxysmal arrhythmias through its emphasis on intermittent episodes of tachycardia.