Which of the following can commonly cause sinus tachycardia?

Sinus tachycardia is defined as an elevated heart rate originating from the sinus node, typically exceeding 100 beats per minute. The common causes of sinus tachycardia include physiological responses like exercise and fever. During exercise, the body requires increased oxygen delivery to tissues, leading to an elevated heart rate to facilitate this increased blood flow. Similarly, fever results in an elevated metabolic rate, which also prompts an increase in heart rate to help meet the body's heightened demands.

Option A, low blood pressure, can lead to compensatory mechanisms that may increase heart rate, but it does not directly cause sinus tachycardia. Instead, it may result from various conditions that could independently affect heart rhythm. Option C, bradycardia, describes a slow heart rate and is counter to the concept of tachycardia, as it reflects the opposite physiological state. Option D, cardiac arrest, is a critical condition where the heart ceases functioning effectively, thus cannot lead to sinus tachycardia, as there is no organized electrical activity or heart rate to measure.

Thus, exercise and fever are direct and common triggers for sinus tachycardia, as they naturally stimulate the body's cardiovascular response to increased activity or stress, making the selection of