Which electrolyte abnormalities are most associated with a prolonged QT interval and torsades de pointes?

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Multiple Choice

Which electrolyte abnormalities are most associated with a prolonged QT interval and torsades de pointes?

Prolonged ventricular repolarization is what sets the stage for torsades de pointes, and the electrolytes that most influence this are potassium and magnesium. When potassium is low, the outward potassium currents that help the heart return to its resting electrical state are reduced, so the ventricular action potential lasts longer. That lengthens the QT interval and increases the risk of early afterdepolarizations, which can trigger torsades. Magnesium plays a stabilizing role in the heart and helps regulate calcium entry and membrane excitability; when magnesium is low, these stabilizing effects disappear, making afterdepolarizations more likely and further prolonging the QT. The combination of hypokalemia and hypomagnesemia creates a perfect setup for torsades and is a classic precipitant. In contrast, high potassium tends to shorten the QT interval and can cause other conduction abnormalities, not the torsades pattern. High calcium also tends to shorten the QT interval. Sodium disturbances like hyponatremia don’t directly prolong ventricular repolarization to the same degree, so they’re not the typical culprits for torsades.

Prolonged ventricular repolarization is what sets the stage for torsades de pointes, and the electrolytes that most influence this are potassium and magnesium. When potassium is low, the outward potassium currents that help the heart return to its resting electrical state are reduced, so the ventricular action potential lasts longer. That lengthens the QT interval and increases the risk of early afterdepolarizations, which can trigger torsades. Magnesium plays a stabilizing role in the heart and helps regulate calcium entry and membrane excitability; when magnesium is low, these stabilizing effects disappear, making afterdepolarizations more likely and further prolonging the QT. The combination of hypokalemia and hypomagnesemia creates a perfect setup for torsades and is a classic precipitant.

In contrast, high potassium tends to shorten the QT interval and can cause other conduction abnormalities, not the torsades pattern. High calcium also tends to shorten the QT interval. Sodium disturbances like hyponatremia don’t directly prolong ventricular repolarization to the same degree, so they’re not the typical culprits for torsades.

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