QT prolongation in the setting of QRS >120 ms is believed to be triggered by prolonged depolarization rather than repolarization. Hence, JT interval is suggested as an alternative to QT interval when QRS duration is prolonged. It is unclear, however, if JT and QT intervals portend similar risk of mortality for different durations of QRS. We examined the association between QT and JT, separately, with all-cause mortality across different levels of QRS duration in 8,025 participants (60 ± 13 years, 41% white and 54% women) from the Third National Health and Nutrition Examination Survey. At baseline (1986 to 1994), 486 participants (6%) had QRS duration ≥120 ms. During a follow-up of up to 18 years, 3,045 deaths (38%) occurred. There were significant nonlinear relations of QT and JT intervals with mortality (p <0.001). Hence, QT and JT were categorized as prolonged (>95th percentile), shortened (<5th percentile), and normal (reference group). In multivariate-adjusted Cox regression models, prolonged JT (hazard ratio [HR] 4.75, 95% confidence interval [CI] 1.86 to 12.11) was associated with increased risk of mortality more than prolonged QT (HR 1.50, 95% CI 1.03 to 2.17) in participants with QRS ≥120 ms (interaction p = 0.02). In participants with QRS duration <120 ms, prolonged QT and JT were equally predictive of all-cause mortality (HR 1.27, 95% CI 1.06 to 1.54, and HR 1.31, 95% CI 1.10 to 1.55, respectively). Similar patterns were observed with shortened QT and JT intervals. In conclusion, although both QT and JT intervals are predictive of mortality, JT is more predictive in the setting of QRS duration >120 ms supporting the use of JT interval in patients with prolonged QRS.
Prolonged QT interval has been shown to be one of the strongest risk factors of mortality in various populations. Prolonged QT interval is routinely encountered by clinicians and is present in 8.7% of the general population. In patients with QRS duration ≥120 ms, QT interval increases because of prolonged duration of QRS, and thus, JT interval is recommended to be used for identifying patients at higher risk of torsades de pointes. Because QT interval is considered primarily as a measure of repolarization more than the depolarization abnormality, special considerations must be taken in the presence of QRS >120 ms where depolarization abnormality becomes a significant part of QT interval. Therefore, JT interval is thought to convey better prognostic information regarding mortality risk specifically attributable to repolarization abnormalities. Because of this, the American College of Cardiology and American Heart Association recommend measuring JT interval instead of QT interval when QRS is >120 ms. Both QT and JT interval are known to be associated with mortality. However, it is not well established if QT interval mortality risk is similar for patients with QRS duration ≥120 and <120 ms. If both JT and QT intervals provide similar prognostic information regardless of QRS duration, this will suggest they can interchangeably be used for risk stratification in patients with both normal and prolonged QRS duration. This may also help to simplify risk management of such patients. Thus, we aimed to examine the risk of mortality associated with QT and JT intervals in community-dwelling adults at different levels of QRS duration.
Methods
The National Health and Nutrition Examination (NHANES) III survey was conducted using a representative sample of the noninstitutionalized US population that included subjects who participated in the survey both during an in-home interview and subsequent visit to a mobile examination center for a period of 6 years from 1988 to 1994. As part of the in-home interview, data were obtained that included complete medical history encompassing the subject’s smoking history and medications, demographics, body mass index, blood pressure measurements, and total serum cholesterol levels. Blood pressure readings were taken during the in-house evaluation and again during their visit at the mobile examination center. These blood pressure measurements were averaged for each subject for this study. Elements of history were obtained by self-report. History of heart failure, cerebrovascular accident, and coronary artery disease were categorized as history of cardiovascular disease. NHANES III participants who were 40 to 90 years with quality electrocardiograms (ECGs) and had medical anthropometric measurements, and mortality data available by 2006 were included in this particular study. Trained technicians recorded standard 12-lead ECG (using Marquette Medical Systems, Milwaukee, Wisconsin) during the study visit at mobile examination center. These electrocardiographic recordings were then analyzed digitally using computerized automated analysis of the electrocardiographic data with the classification of electrocardiographic abnormalities using Minnesota ECG Code Classification. All the electrocardiographic abnormalities detected by the software were later on confirmed by an ECG coder visually. The participants of the NHANES III survey were followed up until December 31, 2006, for mortality. Probabilistic matching method was used as a link between the NHANES III participants and the National Death Index for identification of vital status and the cause of death in subjects who died. Gender, date of birth, and social security number were part of 12 identifiers that were used to match the participants. The period between NHANES III examination and December 31, 2006, or date of death with whichever occurring first was defined as the follow-up duration.
Categorical variables were reported as frequency and percentage, whereas continuous variables were reported as mean ± SD. Statistical significance for differences in the baseline characteristics between patients with <120 and ≥120 ms of QRS duration were tested using the chi-square for categorical data and t test for continuous data. Because of nonlinear relations of QT and JT intervals as evidenced by restricted cubic spline models adjusted for model 2 covariates, QT and JT intervals were divided into 3 groups: more than the ninety-fifth percentile (prolonged), fifth to ninety-fifth percentile (normal), and less than the fifth percentile (shortened). In the Cox regression models, we used the fifth to ninety-fifth percentile group as the reference group. Adjusted and unadjusted Cox proportional hazard regression models were used to compute hazard ratios and 95% confidence intervals for the association between QT and JT intervals with mortality. Multivariable models were adjusted as follows: model 1 adjusted for age, gender, race, and heart rate; model 2 adjusted for covariates in model 1 with the addition of antihypertensive medication use, systolic blood pressure, high-density lipoprotein cholesterol, total cholesterol, body mass index, smoking status, diabetes, and history of cardiovascular disease (composite of history of congestive heart failure, history of cerebrovascular accident, history of coronary heart disease). Mortality rates were calculated per 1,000 person-years. Statistical significance was defined as p <0.05. SAS, v 9.2 (SAS, Inc., Cary, North Carolina) was used for all analyses.
Results
A total of 8,025 subjects were included in the analysis. The mean age was 60 ± 13 years. There were 41% white, 27% black, and 54% women. The mean QT interval was 407 ± 32 ms, and mean JT interval was 309 ± 31 ms. The mean QRS duration was 98 ± 14 ms with 486 participants (6%) having QRS duration ≥120 ms. Participants with QRS duration ≥120 were more likely to be older, white, men, diabetic, ever smoker, hypertensive, had history of cardiovascular disease, and have higher systolic blood pressure, whereas less likely to be black and had lower cholesterol, high-density lipoprotein, and heart rate ( Table 1 ). There were no differences in BMI and diastolic blood pressure between the 2 groups. During a follow-up of up to 18 years (median 14, interquartile range 12 to 16), 3,045 deaths (38%) occurred, of which 286 (59%) occurred in patients with QRS duration ≥120 ms. The mortality rate per 1,000 person-years for participants with normal, prolonged, and shortened QT interval were 2.3, 3.5, and 4.0, respectively. For normal, prolonged, and shortened JT interval, the mortality rates were 2.3, 3.3, and 4.1 per 1,000 person-years, respectively. There were significant nonlinear relations of QT and JT intervals with mortality ( Figures 1 and 2 ). In multivariable-adjusted Cox proportional hazard models, prolonged and shortened QT and JT intervals (compared with normal) were associated with increased risk of mortality ( Table 2 ). However, the magnitude for association of mortality with prolonged JT was greater than prolonged QT interval in patients with QRS ≥120 ms versus QRS <120 ms, with p = 0.02 for the interaction between the 2 groups.
| Characteristics | QRS duration (ms) | p-value | |
|---|---|---|---|
| <120 (n = 7539) | ≥ 120 (n = 486) | ||
| Age (years) | 60±13 | 67±12 | <0.001 |
| Males | 3369 (45%) | 313 (64%) | <0.001 |
| White | 2916 (39%) | 301 (62%) | <0.001 |
| Black | 2007 (27%) | 112 (23%) | <0.001 |
| Mexican | 2394 (32%) | 69 (14%) | <0.001 |
| Antihypertensive medication use | 1720 (23%) | 145 (29%) | <0.001 |
| Systolic blood pressure (mmHg) | 133±20 | 139±21 | <0.001 |
| Diastolic blood pressure (mmHg) | 75±9 | 74±11 | 0.06 |
| Total Cholesterol (mg/dl) | 217±44 | 211±42 | 0.007 |
| High Density Lipoprotein Cholesterol (mg/dl) | 51±16 | 48±15 | <0.001 |
| Body mass index (kg/m 2 ) | 28±6 | 28±6 | 0.56 |
| Heart Rate (beats per minute) | 68±12 | 67±11 | 0.02 |
| Diabetes mellitus | 855 (11%) | 73 (15%) | 0.02 |
| Ever smoker | 4541 (60%) | 319 (65%) | 0.02 |
| Previous cardiovascular disease ∗ | 238 (3.2%) | 62 (13%) | <0.001 |
∗ Previous cardiovascular disease includes history of congestive heart failure, previous stroke and previous coronary artery disease; Continuous variables are expressed as mean ± standard deviations, while categorical as frequency (percentages).
| Events | Models | QRS duration (ms) | |
|---|---|---|---|
| <120 (2759/7539) | ≥120 (286/486) | ||
| Prolonged QT interval (>462 ms) | Model 1 ∗ | 1.34(1.13,1.60) | 1.48(1.04,2.12) |
| Model 2 † | 1.27(1.06,1.54) | 1.50(1.03,2.17) | |
| Prolonged JT interval (>362 ms) | Model 1 ∗ | 1.36(1.16,1.60) | 5.53(2.21,13.87) |
| Model 2 † | 1.31(1.10,1.55) | 4.75(1.86,12.11) | |
| Shortened QT interval (<359 ms) | Model 1 ∗ | 1.30(1.09,1.53) | 1.64(1.32,2.05) |
| Model 2 † | 1.26(1.06,1.50) | 1.65(1.31,2.07) | |
| Shortened JT interval (<261 ms) | Model 1 ∗ | 1.42(1.22,1.66) | 1.16(0.85,1.57) |
| Model 2 † | 1.41(1.21,1.66) | 1.18(0.85,1.63) | |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
