What substance is released from a crushed limb that leads to tall tented T waves and potential heart blocks?

The correct answer is potassium. When a limb is crushed, a condition known as crush syndrome may occur, which is characterized by the release of several substances from damaged cells into the bloodstream. One of the key components released is potassium. Elevated levels of potassium in the bloodstream, or hyperkalemia, can significantly affect cardiac function.

Tall, tented T waves on an electrocardiogram (ECG) are indicative of hyperkalemia. This change occurs because excess potassium alters the resting membrane potential of cardiac myocytes, which can lead to electrical instability and increased excitability of the heart. The disrupted ion balance can also lead to potential heart blocks or arrhythmias, which are serious conditions that can result from the altered electrical conduction pathways in the heart.

While calcium, sodium, and magnesium play important roles in cardiac function and muscle contraction, they do not specifically cause the characteristic tall tented T waves associated with hyperkalemia in the context of limb crush injuries. Therefore, potassium is the critical substance linked to these cardiac changes in this scenario.