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Assessment of prolonged QT and JT intervals in ventricular conduction defects

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Abstract

The JT interval or Bazett's QTc − QRS has been advocated for detection of prolonged repolarization in ventricular conduction defects (VCDs). However, the use of neither JT nor QTc − QRS has been validated, and normal limits for rate-adjusted JT have not been established for VCDs or for normal ventricular conduction. Functional relations among RR, JT, and QT intervals were evaluated in 11,739 adult men and women with normal ventricular conduction and in 1,251 subjects with major VCD. The results showed that JT adjustment obtained as QTc − QRS retained a strong residual correlation with ventricular rate (r = 0.54), making its use ill-advised. In contrast, QT adjustment as a linear function of the RR interval for VCD as QTRR,QRS = QT − 155 × (60/heart rate − 1) − 0.93 × (QRS − 139) + k, with k = −22 ms for men and −34 ms for women, removed the rate dependence and produced upper 2% and 5% normal limits at 460 and 450 ms, respectively, which are identical to those in normal conduction. As an alternative, equally effective linear JT adjustment formulas were derived, including newly required normal standards. Thus, detection of prolonged repolarization in VCD requires the use of the JT interval or a bivariate model for QT with RR and QRS intervals as covariates.

Section snippets

Study population

Source data for this investigation were derived from 3 different population studies previously described in detail: the Third National Health and Nutrition Examination Survey,3 the Cardiovascular Health Study,4 and the Atherosclerosis Research In Communities Study.5 Subjects with a history of heart attack, coronary bypass surgery, or coronary angioplasty were excluded. Electrocardiographically based exclusions for the group with normal conduction included a QRS interval ≥120 ms and other major

Results

The first relevant point to consider is the possible adequacy of the use of QTc − QRS, appropriately denoted as JTc for rate adjustment. The plot of JTc versus ventricular rate in the VCD group (Figure 1) shows that this adjustment retained a profound dependence of the adjusted JT interval on ventricular rate, with a high residual correlation (r = 0.54). This level of residual correlation was even higher than in subjects with normal ventricular conduction (r = 0.32).3

In considering possible

Discussion

A critical result from the present investigation was that QT adjustment in VCDs obtained as QTc − QRS retained a strong residual correlation with ventricular rate (r = 0.54). The correlation was even larger than that for QTc in normal conduction (r = 0.32).3 This renders the use of QTc − QRS in VCDs as disadvantageous, and its potential retention of risk information2 does not remove its fundamental flaws by statistical manipulations. In contrast, QT adjustment for VCD as QTRR,QRS = QT − 155 ×

Acknowledgements

The investigators thank the staff and participants in the Atherosclerosis Research In Communities Study and the Cardiovascular Health Study for their important contributions. For the full list of participating investigators and institutions in the Cardiovascular Health Study, see About CHS: Principal Investigators and Study Sites at http://chs3.biostat.washington.edu/chs. Atherosclerosis Research In Communities research members are listed in reference 5.

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This study was supported by contracts NO1-HC-15103, NO1-HC-35129, NO1-HC-55015, NO1-HC-55016, NO1-HC-55018 through NO1-HC-55022, and NO1-HC-85079 through NO1-HC-85086 from the National Heart, Lung, and Blood Institute, Bethesda, Maryland.

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