Value of the "Standing Test" in the Diagnosis and Evaluation of Beta-blocker Therapy Response in Long QT Syndrome.

INTRODUCTION AND OBJECTIVES: Patients with congenital long QT syndrome (LQTS) have an abnormal QT adaptation to sudden changes in heart rate provoked by standing. The present study sought to evaluate the standing test in a cohort of LQTS patients and to assess if this QT maladaptation phenomenon is ameliorated by beta-blocker therapy. METHODS: Electrographic assessments were performed at baseline and immediately after standing in 36 LQTS patients (6 LQT1 [17%], 20 LQT2 [56%], 3 LQT7 [8%], 7 unidentified-genotype patients [19%]) and 41 controls. The corrected QT interval (QTc) was measured at baseline (QTcsupine) and immediately after standing (QTcstanding); the QTc change from baseline (ΔQTc) was calculated as QTcstanding - QTcsupine. The test was repeated in 26 patients receiving beta-blocker therapy. RESULTS: Both QTcstanding and ΔQTc were significantly higher in the LQTS group than in controls (QTcstanding, 528 ± 46ms vs 420 ± 15ms, P < .0001; ΔQTc, 78 ± 40ms vs 8 ± 13ms, P < .0001). No significant differences were noted between LQT1 and LQT2 patients. Typical ST-T wave patterns appeared after standing in LQTS patients. Receiver operating characteristic curves of QTcstanding and ΔQTc showed a significant increase in diagnostic value compared with the QTcsupine (area under the curve for both, 0.99 vs 0.85; P < .001). Beta-blockers attenuated the response to standing in LQTS patients (QTcstanding, 440 ± 32ms, P < .0001; ΔQTc, 14 ± 16ms, P < .0001). CONCLUSIONS: Evaluation of the QTc after the simple maneuver of standing shows a high diagnostic performance and could be important for monitoring the effects of beta-blocker therapy in LQTS patients.

Ischemic time as a predictor of physical recovery in the first months after heart transplantation.

Functional results after heart transplantation range from modest to spectacular improvement. Little is known about factors to predict functional result. This study aimed to identify these factors. We present a prospective study including all consecutive transplant recipients (n = 55) in a two-year period whose survival was greater than two months. Perioperative, donor, and recipient issues were systematically analyzed. Exercise capacity was assessed by symptom-limited treadmill exercise testing two months after transplantation. Exercise capacity was classified as satisfactory or poor depending on achieving or not 4.5 METs (metabolic equivalents), respectively. Thirty-three patients (60%) showed a good exercise capacity (>4.5 METs), whereas the remaining twenty-two patients (40%) were unable to exceed this threshold. The variables which correlated with exercise capacity in univariate analysis were recipient age, inotropic treatment, ischemic time, ventricular assist device, etiology, urgent transplant, and INTERMACS score. Among them only recipient age and ischemic time were proved to be correlated with exercise capacity in the multiple regression analysis. Thus, younger patients and those who had received an organ with shorter ischemic time showed greater exercise capacity after transplant. These findings strengthen the trend toward reducing ischemic time as much as possible to improve both survival and clinical recovery.