Final answer:
The most detrimental effect of tachycardia in a patient with cardiac issues is increased myocardial oxygen demand due to the excessive heart rate, which compromises the heart's ability to pump blood effectively, potentially leading to myocardial ischemia.
Step-by-step explanation:
The most detrimental effect that tachycardia can have on a patient experiencing a cardiac problem is increased myocardial oxygen demand. Tachycardia, which is an abnormally high heart rate, can lead to a significant increase in the heart's oxygen requirements. When the heart's demand for oxygen surpasses the supply, it can result in myocardial ischemia, which is harmful especially for someone with pre-existing cardiac conditions. Additionally, at heart rates above 160 beats per minute, cardiac output starts to decrease because there is not enough time for the heart to fill properly between beats, leading to a decreased stroke volume. Factors such as hyperthermia can increase heart rate and the strength of contractions, while hypothermia can slow them down, affecting cardiac output. Moreover, the balance of electrolytes, such as sodium and potassium levels, plays a crucial role in the regulation of heart rate and the prevention of arrhythmias.