Gibbs’ studies include restrospective electrocardiogram data from up to 1531 patients with a corrected QT interval length of minimum 500 ms. All patients were treated at Telemark Hospital Trust between 2004 and 2014.

(1) QT prolongation was only registered in 12% of the medical records. 50% of the patients died during a mean follow-up period of 952 days. Patients hospitalized due to aborted cardiac arrest, stroke or head trauma had more than doubled risk. Heart failure and male gender were also independent predictors of long-term mortality, in addition to electrolyte disturbances, age and medication with known and possible risk for torsades des points.

Gibbs and her coworkers also constructed a corrected QT mortality score based on these findings. Increasing score was associated with increased mortality.

(3) Corrected QT intervals of at least 500 ms were independently associated with 30-day mortality. The risk was almost doubled compared to age-, sex-, comorbidity-, and diagnosis-matched patients without QT prolongation. During the following three years, there was no difference in mortality between the groups.

(2) 6.5% of the patients had a genetic diagnosis of long QT syndrome. The estimated population prevalence is only 1:2000. Thus, the prevalence were 130-fold higher in the patients.