Key result
QRS widening via sequential pacing was the main contributor to QT prolongation (Pearson 0.79; 95% CI 0.75-0.84), with Bazett's formula showing the highest sensitivity to interval prolongation.
Why the study?
There is increasing interest in computing corrected QT intervals in patients with prolonged depolarization, prompting evaluation of prolonged QRS effects on QT and frequency-correction formulas.
How does prolonged QRS affect the QT interval and the diagnostic accuracy of frequency-correction formulas in patients undergoing aortic valve implantation?
How does prolonged QRS affect the QT interval and the diagnostic accuracy of frequency-correction formulas in patients undergoing aortic valve implantation?
In patients with prolonged QRS, the Framingham and Hodges formulas provide more accurate QT correction than the Bazett formula, which is overly sensitive to ECG interval prolongation.
Background: there is increasing interest for computing corrected QT intervals in patients with prolonged depolarization. We aimed to analyze the effect of prolonged QRS in the QT and in the diagnostic accuracy of frequency-correction. Methods and Results: in 28 patients admitted for self-expanding aortic valve implantation, sequential pacing was performed in the AAI mode in two different phases: before and immediately after the release of the prosthesis. We evaluated the accuracy of the Bazett, Fridericia, Framingham and Hodges formulas with the reference of the QT at 60 bpm (QTc/deviation). The widening of the QRS was the main contributor to the QT prolongation (Pearson 0.79; CI95%: 0.75–0.84). Prolongation in other intervals (ST segment and T-wave) significantly contribute in the higher frequency range (p < 0.05). The Bazett’s formula displayed the highest QTc/deviation, while Framingham and Hodges retrieved the lowest QTc/deviation and the best fit (p < 0.001). In addition, the Bazett’s formula displayed the highest correlation between variations in the QTc/deviation and the widening of the QRS (Pearson coefficient −0.54; p < 0.001) in comparison with the Fridericia, Framingham and Hodges formulas (−0.51, −0.37 and −0.38 respectively; p < 0.001). There was also a linear effect of the heart rate in the QTc/deviation obtained with the Bazett’s formula (p = 0.015), not observed for other formulas. Conclusions: The prolonged depolarization of the ventricles introduces direct and linear prolongation in the QT interval, but also a non-linear distortion in cardiac repolarization that contributes for QT prolongation at the higher frequency range. The Bazett’s formula displays significantly higher sensitivity to prolongation of ECG intervals.
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Colunga et al. (2019) studied patients admitted for self-expanding aortic valve implantation (n=28). QRS widening via sequential pacing vs. Baseline (before prosthesis release) was evaluated on QT prolongation (Pearson 0.79, 95% CI 0.75-0.84). QRS widening via sequential pacing was the main contributor to QT prolongation (Pearson 0.79; 95% CI 0.75-0.84), with Bazett's formula showing the highest sensitivity to interval prolongation.
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