Independent predictors of QTc prolongation
In best subset forward regression analysis only prior beta blocker usage
(HR 3.5, 95% CI 1.04-12.3, p=0.042) was found to be independent
predictor for potentially clinically significant QTc prolongation.
Baseline QTc ≥ 450 was significant enough to enter the final model
(p<0.10), however, in the final multiple regression model the
p-value was not statistically significant (HR 2.2, 95% CI 0.89-5.2,
p=0.09) Table 2.
During the two hours following CV (conventional monitoring), 3 (4%)
patients met the primary endpoint. Among them, two patients had median
QTc ≥ 500 msec (564 and 500 msec), and one had an increase of 11%. With
the use of the 7-day Holter, significant QTc prolongation was detected
in 39 patients (45%), significantly higher than the rate observed using
the conventional monitoring period (p<0.001). Notably, among
the 87 patients without clinically significant QTc prolongation detected
using conventional 2-hour monitoring, sixteen patients (18%) developed
new QTc prolongation during the first day, 8 patients (11%) during the
second day, and the rest thereafter. Importantly, as shown in Table 3,
more than half of the QTc prolongation were detected within the first 2
days. Notably, during the second day, 5 patients had QTc >
550 msec (baseline QTc was less than 480 msec in all of them).
Detection rates for every single day, and cumulative detection rates
over the monitoring period are depicted in Figure 3. There was a strong
recognizable pattern of detection rates favoring the first 48 hours of
the monitoring period.
Using McNemar test for comparison, the Holter monitoring was superior to
conventional monitoring in detecting the PE with an OR of 13; 95%CI
5-65; p<0.001.