3.1 Sub-group analysis of patients with severely prolonged QTc interval (>500ms)
There were 163 patients with severely prolonged QTc interval (> 500 ms), corresponding to a prevalence of 3.5% (and to 42.6% of the overall aLQTS group).
Female patients and patients on QT prolonging drugs were more likely to have a severely prolonged QTc interval (table 2). Additionally, use of a greater number of drugs and particularly, intake of antibiotics, antipsychotics or antidepressants were associated with severely prolonged QTc interval (table 2). There was also a trend for prolonged QTc intervals in patients on diuretics (table 2). Of note, despite the fact that clinical factors per se did not lead to severely prolonged intervals, there was a tendency for a severely prolonged QTc interval in patients with a greater number of risk factors (p=0.55) (table 2). No statistically significant differences were found regarding age, clinical presentation and type of risk factors present.
Using logistic regression, patients on antibiotics had the greatest odd of severely prolonged QTc interval (OR 4.860; 95% confidence interval (CI95%) 1.497-14.631; p =0.008). Female patients had an odd almost 2.5 times greater of severely prolonged QTc (OR 2.473; CI 95% 1.663-3.747; p < 0.001). Remaining OR are shown on figure 2.