The normal QT interval is controversial and multiple normal durations have been reported. In general, the normal QT interval is less than 400-440 ms (0.4 to 0.44 seconds).

Among patients with long QT syndrome but a normal resting QTc value, defined as less than 450 ms, the deep neural network distinguished long QT syndrome from normal with an AUC of 0.83 vs. 0.67 ...

Compared to those with a normal QT interval, patients with a prolonged QT interval were older (70 years on average versus 63 years), more often had co-existing conditions such as hypertension ...

Rotterdam, the Netherlands - An abnormally prolonged heart-rate-corrected QT (QTc) interval, compared with a normal one, more than doubled the long-term risk of sudden cardiac death (SCD ...