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Background Resting electrocardiogram (ECG) identification of long QT syndrome (LQTS) has limitations. Uncertainty exists on how to classify patients with borderline prolonged QT intervals. We tested if exercise testing could help serve to guide which children with borderline prolonged QT intervals may be gene positive for LQTS. Methods Pediatric patients (n = 139) were divided into three groups: Controls (n = 76), gene positive LQTS with borderline QTc (n = 21), and gene negative patients with borderline QTc (n = 42). Borderline QTc was defined between 440-470 (male) and 440-480 (female) ms. ECGs were recorded supine, sitting, and standing. Patients then underwent treadmill stress testing with Bruce protocol followed by a 9-minute recovery phase. Results Supine resting QTc, age, and Schwartz score for the three groups were: (a) gene positive: 446 ± 23 ms, 12.4 ± 3.4 years old, 3.2 ± 1.8; (b) gene negative: 445 ± 20 ms, 12.1 ± 2 years old, 2.0 ± 1.2; and (c) control: 400 ± 24 ms, 15.0 ± 3 years old. The three groups could be differentiated by their QTc response at two time points: standing and recovery phase at 6 minutes. Standing QTc ≥460 ms differentiated borderline prolonged QTc patients (gene positive and gene negative) from controls. Late recovery QTc ≥480 ms distinguished gene positive from gene negative patients. Conclusion Exercise stress testing can be useful to identify children who are gene positive borderline LQTS from a normal population and gene negative borderline QTc children, allowing for selective gene testing in a higher risk group of patients with borderline QTc intervals and intermediate Schwartz scores.

Introduction: Resting electrocardiogram (ECG) identification of long QT syndrome (LQTS) has limitations. Uncertainty exists on how to classify patients with borderline prolonged QT intervals. We tested if exercise testing could help serve as a guide for which children with borderline prolonged QT intervals may be gene positive for LQTS. Methods: Pediatric patients (n=139) were divided into three groups: Controls (n=76), gene positive LQTS with borderline QTc (n=21), and gene negative patients with borderline QTc (n=42). Borderline QTc was defined between 440 to 470 (male) and 440 to 480 (female) msec. ECGs were recorded while supine, sitting, and standing. Patients then underwent treadmill stress testing using the Bruce protocol followed by a 9-minute recovery phase. Statistical analysis was completed to compare the QTc intervals amongst all three of the groups using t-test, ANOVA, and the Youden method to calculate sensitivity and specificity cut points. Results: Supine resting QTc, age, and Schwartz score for the three groups were: 1) Gene positive: 446 ± 23 msec, 12.4 ± 3.4 yo, 3.2 ± 1.8; 2) Gene negative: 445 ± 20 msec, 12.1 ± 2.8 yo, 2.0 ± 1.2; and 3) Control: 400 ± 24 msec, 15.0 ± 3 yo. The three groups could be differentiated by their QTc response at two time points: standing and recovery phase at six minutes. Standing QTc ≥ 460 msec differentiated borderline prolonged QTc patients (Gene positive and Gene negative) from controls with a specificity of 90% for gene positive versus control and 83% for gene negative versus control. A late recovery QTc ≥ 480 msec at minute six distinguished Gene positive from Gene negative patients with a specificity of >97%. Conclusions: Exercise stress testing can be useful to identify Gene positive borderline LQTS from a normal population and Gene negative borderline QTc patients, allowing for increased cost effectiveness by selectively gene testing a higher risk group of patients with borderline QTc intervals and intermediate Schwartz scores.

Orthostatic intolerance (OI) is common in teenagers (T) and young adults (A). Despite treatment with oral fluids, medication, and exercise, a significant number have symptoms from multiple organ systems and suffer low quality of life (QOL). Previous studies showed that acute intravenous (IV) hydration (IH) could help restore orthostatic tolerance; however, no data are available about the intermediate-term effects of IH. We therefore studied the efficacy of IH to improve QOL and manage medication-refractory OI patients. Our study population consisted of 39 patients (mean age = 16.1 ± 3.3) years; thirty-two were female. Average number of medications failed = 3.1. Average QOL score on self-reported OI questionnaire was 4.2 (normal QOL = 10). IV hydration consisted of normal saline (1-2 l/day, 3-7 days/week). 1) Orthostatic testing revealed Postural Orthostatic Tachycardia (24), Neurally Mediated Hypotension (14) or OI (1). 2) Average orthostatic change in heart rate was 48 ± 18 bpm. 3) IH was performed via intermittent IV access (10), PICC line (22), and Port (7). 4) Duration of IH varied from 1 week to 3.8 years (mean = 29 ± 47 weeks). 5) Overall, 79 % (n = 31) demonstrated clinically improved self-reported QOL. 6) Six patients who discontinued IH requested to restart treatment. (7) Complications consisted of upper extremity deep vein thrombosis (n = 3) and infection (n = 4). IH is an effective therapy to improve QOL in T&A with medication-resistant OI. Most patients continued to report improved QOL once IH was discontinued. IH should be considered a therapeutic option in medication-resistant OI patients with low QOL.