Which disorder can become more severe when associated with sinus tachycardia?

The disorder that can become more severe when associated with sinus tachycardia is myocardial infarction. Sinus tachycardia refers to an elevated heart rate, which can increase myocardial oxygen demand. In the context of myocardial infarction, where there is already compromised blood flow and oxygen supply to the heart muscle due to blockages, this increased heart rate can exacerbate the condition. It places additional stress on the heart, which can lead to worsening ischemia and potentially increase the extent of the heart damage.

In contrast, while conditions like congestive heart failure, angina pectoris, and atrial fibrillation can certainly be influenced by heart rate, the specific mechanism of worsening due to sinus tachycardia is most pronounced in the case of a myocardial infarction. In angina, for instance, while an increased heart rate may trigger pain due to increased oxygen demand, it doesn't necessarily escalate the underlying condition in the same direct manner as in myocardial infarction.