A novel algorithm to predict the QT interval during intrinsic atrioventricular conduction from an electrocardiogram obtained during ventricular pacing

A comprehensive formula for computing corrected QT intervals in patients with wide QRS

BACKGROUND

There is increasing interest in developing appropriate methods for correction of the QT intervals in patients with prolonged depolarization of the ventricles. From an experimental model of controlled heart rate and QRS widening, we aimed to develop a new formula with better performance.

METHODS

After exclusions, incremental pacing was performed (AAI mode; 50-120 bpm) in 17 patients admitted for self-expanding aortic valve implantation in two different phases: before and immediately after the release of the prosthesis. Mixed linear models were built to predict variation in QRS and JT intervals, and subsequently calculate the corrected QT (QT_QRS-C). Internal and external validation on a new cohort of 48 patients was performed.

RESULTS

Significant QRS widening (32.5 ms; CI95%:31.5-33.6) and QT prolongation (35.4 ms; CI95%:33.4-37.4) was observed after the release of the prosthesis. The best fit formula was computed as QT_QRS-C = QT_measured - (1.058*QRS_measured - 108.397) - (0.0496*JT_measured - 11.038). Internal validation provided a good correlation between measured and predicted QT (Pearson's coefficient:0.76; CI95%:0.70-0.80). In an external cohort (n = 48), the QRS widening was 28.4 ms(CI95%:21.8-35.1) and the JT widening was 16.58 ms(CI95%:8.73-24.4). Compared to other formulas, our proposed formula tends to display better performance as a result of a combination of appropriate correlation (Pearson's:0.75), being the closer to identity line (slope 0.83) and minimizing the relative standard error of the estimates (RSE 0.11).

CONCLUSIONS

We developed a formula with better performance for QT correction in patients with wide QRS.

Assessment of QT interval in ventricular paced rhythm: Derivation of a novel formula

OBJECTIVE

The objective of the study was to determine the optimal formula to estimate QT interval adjusting for QRS prolongation during right ventricular (RV) pacing.

METHODS

This observational study included individuals (n = 43) with a newly implanted permanent ventricular pacemaker, who had a narrow QRS complex before pacemaker insertion. QT interval with RV pacing was related to QT interval before pacemaker implantation. The validation cohort (n = 442) had permanent RV pacing in DDD mode.

RESULTS

A new QTc formula was derived utilizing the constants from the relationship between the spline heart rate QT correction (QTcRBK) before and after pacing; specifically, QTcRBK_PACED = QTcRBK × 0.86. The JT interval from paced complexes was highly heart rate (HR) dependent and was not accurate for QT assessment. Previous, QTc formula for paced complexes were not highly correlated with QT before pacing unless a robust HR correction is added. Formulae subtracting a fixed amount from QTc_PACED markedly overestimated QTc before pacing.

CONCLUSION

We proposed a new, simple formula for QT estimation in RV pacing. JT interval in paced complexes is highly HR dependent and is not accurate for QT assessment. The new spline approach for HR correction for the QT, once incorporated into some previously proposed formulae, blunts HR dependency and improves prediction of QT before pacing. QTcRBK_PACED*0.86 and QTcRBK_PACED - (QRS*0.5) demonstrated the best balance of relatively strong correlation to QTc before pacing and accurate QTc prolongation identification. Abnormal QT for QTcRBK_PACED*0.86 as defined by the 97.5th and 99th percentile are 469 and 479 ms respectively.

The QT Interval Dynamic in a Human Experimental Model of Controlled Heart Rate and QRS Widening

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.

Comparison and Validation of Recommended QT Interval Correction Formulas for Predicting Cardiac Arrhythmias in Patients With Advanced Heart Failure and Cardiac Resynchronization Devices

QT interval prolongation is an important marker for the development of cardiac arrhythmias (CAs). Optimal methods to estimate QT/QTc intervals in patients with ventricular pacing (VP) and its correlation with CA have not been widely investigated. We aimed to validate the currently available formulas for QT determination during VP and to compare their abilities in predicting the occurrence of CA (atrial fibrillation [AF] and malignant ventricular arrhythmias [VAs] in patients with advanced heart failure and cardiac resynchronization therapy). Consecutive patients with advanced heart failure who underwent cardiac resynchronization therapy implantation between August 2001 and April 2015 were included in a retrospective study. Four proposed formulas for QT correction in VP rhythms were evaluated. One hundred eighty patients were enrolled. During 44 months of follow-up, 43 patients (37.7%) developed AF and 16 patients (8.9%) developed VA. There was no correlation between corrected QT increments and AF risk with any of the formulas for paced rhythms. Regarding VA, higher corrected QT values measured with Massachusetts' formula (QTcM) were found to have a higher risk of event (p = 0.036) (Beta = 1.012 [1.001 to 1.023]). Each 1 ms increase in QTc increased the probability of experiencing VA by 12‰. QTcM >444 was found to be a strong predictor of VA. In conclusion, there are significant differences in mean QTc interval measured by the currently advised formulas. QTc interval was not associated with AF in any of the formulas. Only the QTcM formula showed a significant stepwise increase in the risk of experiencing malignant VA.