Did You Know?
Interesting Fact
The heart doesn’t beat in isolation—it’s tuned to the body’s circadian rhythms. One of the key players in ventricular repolarisation is the IKr current, carried by the hERG potassium channel. But IKr density naturally dips in the early morning hours. Less IKr means less “reserve” for bringing heart cells back to baseline after each beat.
At night, the QT interval lengthens as parasympathetic tone dominates. But as morning approaches, the body surges with sympathetic activity: cortisol rises, adrenaline floods in, and sudden arousals from sleep (an alarm clock, a loud noise, or even a vivid dream) jolt the nervous system. For most people, the heart adapts. But in LQT2, where IKr is already compromised, this combination is dangerous.
Registry data show that LQT2 events cluster right after waking (6–8 a.m.), when repolarization is most fragile and sympathetic surges are strongest. This timing explains why many LQT2 patients experience cardiac arrests not during exertion, but during something as ordinary as being startled awake. It’s a striking reminder that arrhythmia risk is not just about what you do, but when your biology is primed for it.
Long QT Syndrome Type 2
Patients with LQT2 tend to present ventricular arrhythmia in response to emotional stress (49%) or sudden auditory stimuli (eg, an alarm-clock), and less frequently during sleep (22%) or exercise (29%). Up to 20% of cases can have a nondiagnostic ECG before stimuli.
Patients with LQT2 tend to present ventricular arrhythmia in response to emotional stress (49%) or sudden auditory stimuli (eg, an alarm-clock), and less frequently during sleep (22%) or exercise (29%). Up to 20% of cases can have a nondiagnostic ECG before stimuli.
The clinical presentation of LQT2 is distinguishable from other types of LQTS by the fact that episodes of torsades de pointes (TdP) are often stimulated by the sudden sympathetic ‘fight or flight’ stimulation I.e. ‘you almost gave me a heart attack!’ response to a surprise (they mean cardiac arrest).
Unfortunately for women with LQT2 the postpartum hormones (prolactin and oxytocin) have been found to increase the risk of QT prolongation and therefore adverse cardiac events in postpartum women with LQT2.
In LQT2, the QT interval is prolonged as a result of the mutated hERG channel where Phase III IKr K+ (potassium) takes longer. As the influx of the calcium current from Phase II is greater than the relative potassium current in Phase III going out, it is enough to reverse the repolarisation of the heart cell and cause an early afterdepolarisation.
The mutation means that the hERG channel has a loss of function, but not always completely absent.
The door on the train has a voltage sensor that triggers the door to open at the station. In LQT2 the electricity goes to the door telling it to open, but the door malfunctions. It might open late, only open halfway, flicker open and shut or jam or not open at all. The passengers are ready to de-train but the door's behaviour is too erratic so they're trapped inside.