Problems with Bazett QTc correction in paediatric screening of prolonged QTc interval

Abstract

Background Bazett formula is frequently used in paediatric screening for the long QT syndrome (LQTS) and proposals exist that using standing rather than supine electrocardiograms (ECG) improves the sensitivity of LQTS diagnosis. Nevertheless, compared to adults, children have higher heart rates (especially during postural provocations) and Bazett correction is also known to lead to artificially prolonged QTc values at increased heart rates. This study assessed the incidence of erroneously increased QTc values in normal children without QT abnormalities. Methods Continuous 12-lead ECGs were recorded in 332 healthy children (166 girls) aged 10.7 ± 2.6 years while they performed postural manoeuvring consisting of episodes (in the following order) of supine, sitting, standing, supine, standing, sitting, and supine positions, each lasting 10 min. Detailed analyses of QT/RR profiles confirmed the absence of prolonged individually corrected QTc interval in each child. Heart rate and QT intervals were measured in 10-s ECG segments and in each segment, QTc intervals were obtained using Bazett, Fridericia, and Framingham formulas. In each child, the heart rates and QTc values obtained during supine, sitting and standing positions were averaged. QTc durations by the three formulas were classified to < 440 ms, 440–460 ms, 460–480 ms, and > 480 ms. Results At supine position, averaged heart rate was 77.5 ± 10.5 beat per minute (bpm) and Bazett, Fridericia and Framingham QTc intervals were 425.3 ± 15.8, 407.8 ± 13.9, and 408.2 ± 13.1 ms, respectively. At sitting and standing, averaged heart rate increased to 90.9 ± 10.1 and 100.9 ± 10.5 bpm, respectively. While Fridericia and Framingham formulas showed only minimal QTc changes, Bazett correction led to QTc increases to 435 ± 15.1 and 444.9 ± 15.9 ms at sitting and standing, respectively. At sitting, Bazett correction identified 51, 4, and 0 children as having the QTc intervals 440–460, 460–480, and > 480 ms, respectively. At sitting, these numbers increased to 118, 11, and 1, while on standing these numbers were 151, 45, and 5, respectively. Irrespective of the postural position, Fridericia and Framingham formulas identified only a small number (< 7) of children with QT interval between 440 and 460 ms and no children with longer QTc. Conclusion During screening for LQTS in children, the use of Bazett formula leads to a high number of false positive cases especially if the heart rates are increased (e.g. by postural manoeuvring). The use of Fridericia formula can be recommended to replace the Bazett correction not only for adult but also for paediatric ECGs.

Influence of heart rate correction formulas on QTc interval stability

“…Nevertheless, when applied to the physiologically plausible QT durations, the effects of this problem are not large. Recently, we have also found preference for Fridericia and Framingham formulas when assessing QTc duration in school-aged children 59 .…”

QTc prolongation in adolescents with acute alcohol intoxication

“…The prominent role of HR in adolescents with alcohol intoxication may underlie the different effects seen in QTc based on the chosen correction formula. Most QT interval correction formulas lead to similar QTc values in the presence of baseline conditions and an HR of approximately 60 bpm [ 33 ]. The Bazett formula, however, generally shows a more prominent QTc prolongation than the Fridericia formula when the HR is above 60 bpm [ 33 ].…”

“…Most QT interval correction formulas lead to similar QTc values in the presence of baseline conditions and an HR of approximately 60 bpm [ 33 ]. The Bazett formula, however, generally shows a more prominent QTc prolongation than the Fridericia formula when the HR is above 60 bpm [ 33 ]. As in our study, the mean HR during alcohol intoxication was 88 bpm (IQR 26 bpm), and this phenomenon could explain the differences found between QTc B and QTc F , with a more pronounced QTc B prolongation compared to QTc F prolongation at the time of alcohol intoxication and when compared to a reference ECG.…”

“…Bazett’s formula is the most widely used in clinical practice and for research purposes and therefore enables comparisons to previous studies. However, since Bazett’s formula possibly overcorrects the QT interval at higher heart rates [ 33 ] and tachycardia occurs in 10% of children with alcohol intoxication [ 18 ], we also calculated the QTc with Fridericia’s formula.…”

A change in QT interval and ST-segment after radiofrequency catheter ablation in pediatric patients with Wolff–Parkinson–White syndrome

“…The PQ, QRS, QT, and JT intervals were measured in lead V5 or II. The tangential method was used to measure the QT and JT interval, and Bazett's and Fridericia's formulas were also used [8,9].…”