In contrast to Long QT Syndrome (LQTS), there is often no specific trigger (such as a loud noise or exercise) for an episode of arrhythmia. Short QT syndrome must be differentiated from the normal variant, secondary causes of QT prolongation, and deceleration dependent shortening of QT interval.

Short QT syndrome must be differentiated from normal variant, secondary causes of QT prolongation, and deceleration dependent shortening of QT interval.

• Normal variant: The presence of shorter QT interval does not automatically qualify for a diagnosis of SQTS. It may also represent a normal variant in the general population. Up to 2 % population has QT interval of ≤ 360 msec. This highlights the importance of using the diagnostic criteria for a final diagnosis of SQTS.
• Acquired causes of SQT interval: Conditions like hyperkalemia, acidosis, hyperthermia, hypercalcemia, digitalis, Acetylcholine, and catecholamines are a few causes of SQT interval. For more acquired causes click here.
• Deceleration dependent shortening of QT interval: This is a paradoxical ECG phenomenon termed as a deceleration-dependent shortening of QT interval. A strong parasympathetic stimulation not only leads to bradycardia but also leads to the activation of acetylcholine-sensitive K+ channels (KACh).In this case, the QT interval shortens paradoxically with bradycardia instead of prolongation. This change is a transient one and shall revert when the parasympathetic stimulus is decreased^[1].