Dynamic QT Interval Changes from Supine to Standing in Healthy Children.

QT-interval variations in response to exercise-induced increases in heart rate have been reported in children and adults in the diagnosis of long QT syndrome (LQTS). A quick standing challenge has been proposed as an alternative provocative test in adults, with no pediatric data yet available. A standing test was performed in 100 healthy children (mean age, 9.7 ± 3.1 years) after 10 minutes in a supine position with continuous electrocardiographic recording. QT intervals were measured at baseline, at maximal heart rate, at maximal QT, and at each minute of a 5-minute recovery while standing. Measurements were taken in leads II/V5 and were corrected for heart rate (QTc). On standing, the heart rate increased by 29 ± 10 beats per minute (bpm). The QT interval was similar at baseline and on standing (394 ± 34 ms vs 394 ± 34 ms; P = 1.0). However, QTc increased from 426 ± 21 to 509 ± 41 ms (P < 0.001). The 95th percentile for QTc at baseline and maximal heart rate was 457 ms and 563 ms, respectively. At 1 minute of recovery, the QT interval was shorter (375 ± 31 ms) compared with baseline (394 ± 34 ms; P < 0.001) and standing (394 ± 34 ms; P < 0.001). QTc reached baseline values after 1 minute of recovery and remained stable thereafter (423 ± 23 ms at 1 minute; 426 ± 22 ms at 5 minutes; P = 1.0). This first characterization of QTc changes on standing in children shows substantial alterations, which are greater than those seen in adults. Two-thirds of the children would have been misclassified as having LQTS by adult criteria, indicating the need to create child-specific standards.

Dionne A ，Fournier A ，Dahdah N ，Abrams D ，Khairy P ，Abadir S ... -  《-》

The brisk-standing-test for long QT syndrome in prepubertal school children: defining normal.

Filippini LHPM ，Postema PG ，Zoubin K ，Hermans BJM ，Blom NA ，Delhaas T ，Wilde AAM ... -  《-》

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

Andršová I ，Hnatkova K ，Helánová K ，Šišáková M ，Novotný T ，Kala P ，Malik M ... -  《BMC Pediatrics》

The phenomenon of "QT stunning": the abnormal QT prolongation provoked by standing persists even as the heart rate returns to normal in patients with long QT syndrome.

Patients with long QT syndrome (LQTS) have inadequate shortening of the QT interval in response to the sudden heart rate accelerations provoked by standing-a phenomenon of diagnostic value. We now validate our original observations in a cohort twice as large. We also describe that this abnormal QT-interval response persists as the heart rate acceleration returns to baseline. To describe a novel observation, termed "QT stunning" and to validate previous observations regarding the "QT-stretching" phenomenon in patients with LQTS by using our recently described "standing test." The electrocardiograms of 108 patients with LQTS and 112 healthy subjects were recorded in the supine position. Subjects were then instructed to stand up quickly and remain standing for 5 minutes during continuous electrocardiographic recording. The corrected QT interval was measured at baseline (QTc(base)), when heart rate acceleration without appropriate QT-interval shortening leads to maximal QT stretching (QTc(stretch)) and upon return of heart rate to baseline (QTc(return)). QTc(stretch) lengthened significantly more in patients with LQTS (103 ± 80 ms vs 66 ± 40 ms in controls; P <.001) and so did QTc(return) (28 ± 48 ms for patients with LQTS vs -3 ± 32 ms for controls; P <.001). Using a sensitivity cutoff of 90%, the specificity for diagnosing LQTS was 74% for QTc(base), 84% for QTc(return), and 87% for QTc(stretch). The present study extends our previous findings on the abnormal response of the QT interval in response to standing in patients with LQTS. Our study also shows that this abnormal response persists even after the heart rate slows back to baseline.

Adler A ，van der Werf C ，Postema PG ，Rosso R ，Bhuiyan ZA ，Kalman JM ，Vohra JK ，Guevara-Valdivia ME ，Marquez MF ，Halkin A ，Benhorin J ，Antzelevitch C ，Wilde AA ，Viskin S ... -  《-》

Effect of change in posture and exercise on repolarization in patients with long QT syndrome with HERG channel mutations.

Walker BD ，Krahn AD ，Klein GJ ，Skanes AC ，Yee R ，Wang J ，Hegele RA ... -  《CANADIAN JOURNAL OF CARDIOLOGY》