QT interval is shortened in –
**Core Concept**
The QT interval represents the period of ventricular depolarization and repolarization on an electrocardiogram (ECG). It is influenced by the balance between the inward movement of potassium ions (K+) and the outward movement of sodium and calcium ions (Na+ and Ca2+). A shortened QT interval suggests an increase in the rate of repolarization or a decrease in the rate of depolarization.
**Why the Correct Answer is Right**
The correct answer is associated with a condition that leads to an increase in the efflux of potassium ions (K+) from the cardiac cells, thereby accelerating repolarization and shortening the QT interval. This is achieved through the activation of the ATP-sensitive potassium channels (K_ATP channels) in the myocardial cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is associated with a condition that prolongs the QT interval, not shortens it. The prolonged QT interval is due to the decreased efflux of potassium ions (K+) from the cardiac cells, leading to delayed repolarization.
**Option B:** This option is incorrect as it is associated with a condition that prolongs the QT interval, not shortens it. The prolonged QT interval is due to the decreased efflux of potassium ions (K+) from the cardiac cells, leading to delayed repolarization.
**Option C:** This option is incorrect as it is associated with a condition that prolongs the QT interval, not shortens it. The prolonged QT interval is due to the decreased efflux of potassium ions (K+) from the cardiac cells, leading to delayed repolarization.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that hypokalemia (low potassium levels) can lead to a prolonged QT interval, whereas hyperkalemia (high potassium levels) can lead to a shortened QT interval. This is because potassium ions play a crucial role in the repolarization of cardiac cells.
**Correct Answer:** B. Hyperkalemia. Hyperkalemia leads to an increase in the efflux of potassium ions (K+) from the cardiac cells, thereby accelerating repolarization and shortening the QT interval.