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 (1986–1994), 486 (6%) participants had QRS duration≥120 ms. During a follow-up of up to 18 years, 3,045 (38%) deaths occurred. There were significant non-linear relationships 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 [HR (95% CI): 4.75, (1.86, 12.11)] was associated with increased risk of mortality more than prolonged QT [HR (95%CI):1.50 (1.03, 2.17)] in participants with QRS ≥120 ms (Interaction p=0.02). In participants with QRS duration <120ms, prolonged QT and JT were equally predictive of all-cause mortality [HR (95%CI): 1.27(1.06, 1.54)] and [1.31 (1.10, 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 individuals with prolonged QRS.

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