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.