Which one of the following electrocardiographic changes is found in hypercalcaemia –
**Core Concept**
Hypercalcaemia is a condition characterized by elevated serum calcium levels, which can have various effects on the cardiovascular system. One of the electrocardiographic (ECG) changes associated with hypercalcaemia is a prolongation of the QT interval, which can lead to arrhythmias and other cardiac complications.
**Why the Correct Answer is Right**
The prolongation of the QT interval in hypercalcaemia is caused by the increased calcium ions binding to the cardiac cells' surface, leading to a decrease in the inward sodium and potassium currents (I_Na and I_K). This results in a delay in the repolarization phase of the cardiac action potential, causing a prolongation of the QT interval. The QT interval is measured from the beginning of the Q wave to the end of the T wave, and a prolongation of this interval can be a sign of hypercalcaemia.
**Why Each Wrong Option is Incorrect**
* **Option A:** Prolongation of the PR interval is not typically associated with hypercalcaemia. The PR interval is the time from the beginning of the P wave to the start of the QRS complex, and it is more commonly affected by conditions that alter the conduction through the atrioventricular (AV) node.
* **Option B:** Widening of the QRS complex is not a characteristic ECG finding in hypercalcaemia. The QRS complex represents the depolarization of the ventricles, and widening of this complex is more commonly associated with conditions that affect the ventricular conduction, such as bundle branch blocks or ventricular hypertrophy.
* **Option D:** Flattening of the T wave is not a specific ECG finding in hypercalcaemia. While T wave abnormalities can be seen in various cardiac conditions, flattening of the T wave is not a characteristic feature of hypercalcaemia.
**Clinical Pearl / High-Yield Fact**
In patients with hypercalcaemia, it is essential to monitor the ECG regularly for signs of cardiac toxicity, as elevated calcium levels can lead to life-threatening arrhythmias. A prolongation of the QT interval is a critical finding that requires prompt intervention to correct the hypercalcaemia.
**Correct Answer:** C. Prolongation of the QT interval.