Hypercalcaemia in ECG is diagnosed by
**Core Concept**
Hypercalcaemia, an elevated calcium level in the blood, can cause various ECG changes due to its effects on cardiac membrane excitability. The underlying principle is the alteration of the ionized calcium concentrations, which affects the cardiac action potential and repolarization.
**Why the Correct Answer is Right**
The P-R interval prolongation in hypercalcaemia is a result of the increased calcium ion concentration affecting the sinoatrial (SA) node and atrioventricular (AV) node, leading to a prolongation of the time it takes for the electrical impulse to travel through the AV node. This is due to the increased calcium influx through the L-type calcium channels in the cardiac myocytes. The increased calcium ion concentration also affects the repolarization phase, leading to a prolongation of the QT interval.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to hypercalcaemia in ECG.
* **Option B:** This option is incorrect because hypercalcaemia does not typically cause QRS widening.
* **Option D:** This option is not specific to hypercalcaemia; it can be seen in various other conditions.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that hypercalcaemia can cause a range of ECG changes, including P-R interval prolongation, T-wave flattening or inversion, and QT interval prolongation. These changes can be subtle and may not always be present, so a high index of suspicion is necessary for diagnosis.
**Correct Answer: C. P-R interval prolongation.**