Hysteresis of the RT interval with exercise (deltaRT >25 ms) identified long-QT syndrome with 73% sensitivity, 92% specificity, 79% positive predictive value, and 90% negative predictive value.
Case-Control (n=63)
Does hysteresis of the RT interval with exercise identify patients with long-QT syndrome?
Hysteresis of the RT interval during exercise testing provides a noninvasive marker with high specificity and negative predictive value for diagnosing long-QT syndrome.
p-value: p=0.003
BACKGROUND: The diagnosis of the long-QT syndrome (LQTS) may be difficult to establish in patients with normal or borderline prolongation of the QT interval. Noninvasive markers are needed to identify patients with LQTS. METHODS AND RESULTS: Fourteen patients with known LQTS, 9 unaffected family members, and 40 control subjects underwent modified Bruce protocol exercise testing. The RT interval (peak of R wave to peak of T wave) and rate-corrected RT interval (RTc) were measured during exercise and recovery. The RT interval at 1 minute into recovery was subtracted from the RT interval at a similar heart rate during exercise (deltaRT). The RTc shortened by 61 milliseconds (ms) in the LQTS patients compared with 23 to 26 ms in the other two groups (P=.003 by ANOVA). The RT interval shortened in a linear fashion in all patients but demonstrated persistent shortening during recovery in the LQTS patients. This was manifested as a hysteresis loop in the curve relating the RT interval to cycle length. The hysteresis loop was present in 13 of 14 LQTS patients and only 4 of 40 control subjects. DeltaRT >25 ms had a sensitivity of 73%, a specificity of 92%, a positive predictive value of 79%, and a negative predictive value of 90% for LQTS. CONCLUSIONS: Hysteresis of the RT interval with exercise may be useful for the diagnosis of LQTS.
Krahn et al. (Tue,) conducted a case-control in Long-QT syndrome (LQTS) (n=63). Modified Bruce protocol exercise testing vs. Unaffected family members and control subjects was evaluated on RTc shortening (p=0.003). Hysteresis of the RT interval with exercise (deltaRT >25 ms) identified long-QT syndrome with 73% sensitivity, 92% specificity, 79% positive predictive value, and 90% negative predictive value.