BACKGROUNDCongenital long QT syndrome (LQTS) is an inherited ion channel disorder resulting in abnormal cardiac repolarization that can cause syncope and sudden death associated with a prolonged rate-corrected QT interval and polymorphic ventricular tachycardia. Several studies in adults showed that LQTS patients have altered QT adaptation to heart rate changes compared with normal subjects which forming a "hysteresis loop" in the QT-circle length plot. This study was to observe the QT interval changing during exercise testing in children long QT syndrome (LQTS) patients, explore the new diagnosis methods of LQTS.

METHODSThe subjects were divided into 3 groups according to 1993 LQTS diagnostic criteria. Group 1: LQTS group (n = 17) who scored > or = 4 points indicating definite LQTS. Group 2: Middle group (n = 16), patients who have prolonged QT interval but scored 1.5 to 3.5. Group 3: Normal control group (n = 18). The average age of all study population is (12.3 +/- 5.8) years. No case had beta-adrenergic antagonists administration before exercise testing. All subjects were underwent tread mill exercise testing and electrocardiograph in whole exercise testing and recovery were recorded. QT and heart rate changing during whole exercise testing period were recorded. DeltaQT, the QT interval at 1, 2, 4, 6 minutes into recovery subtract from the QT interval at a similar heart rate during exercise, were calculated.

RESULTSIn all three groups, QT intervals were shortening with the increasing of heart rate, but QTc had no significant change. DeltaQT at 1 minute ((45 +/- 11) ms), 2 minutes ((37 +/- 15) ms), 4 minutes ((23 +/- 12) ms) into recovery in LQTS group were significantly greater than that of the other two groups (P < 0.05, P < 0.01, P < 0.01, respectively). There was no DeltaQT significant difference between middle group and normal control group at recovery time. During the recovery phase in LQTS group, the QT interval remained shortened despite a decelerating heart rate, forming a hysteresis "loop" in the curve relating the QT interval to the cycle length.

CONCLUSIONSIn children LQTS patients, there is significant QT hysteresis loop in the relation of QT interval with heart rate during recovery of exercise testing, which could be useful to the early diagnosis for LQTS.

Adolescent ; Child ; Electrocardiography ; Exercise Test ; Female ; Heart Rate ; Humans ; Long QT Syndrome ; physiopathology ; Male

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a genetically determined disease that progresses continuously from conception and throughout life. ARVC/D manifests predominantly in young adulthood. Early identification of the concealed cases in childhood is of utmost importance for the prevention of sudden cardiac death later in life. Magnetic resonance imaging (MRI) is routinely requested in patients with a confirmed or suspected diagnosis of ARVC/D and in family members of the patients with ARVC/D. Although the utility of MRI in the assessment of ARVC/D is well recognized in adults, MRI is a low-yield test in children as the anatomical, histological, and functional changes are frequently subtle or not present in the early phase of the disease. MRI findings of ARVC/D include morphologic changes such as right ventricular dilatation, wall thinning, and aneurismal outpouchings, as well as abnormal tissue characteristics such as myocardial fibrosis and fatty infiltration, and functional abnormalities such as global ventricular dysfunction and regional wall motion abnormalities. Among these findings, regional wall motion abnormalities are the most reliable MRI findings both in children and adults, while myocardial fibrosis and fat infiltration are rarely seen in children. Therefore, an MRI protocol should be tailored according to the patient's age and compliance, as well as the presence of other findings, instead of using the protocol that is used for adults. We propose that MRI in children with ARVC/D should focus on the detection of regional wall motion abnormalities and global ventricular function by using a cine imaging sequence and that the sequences for myocardial fat and late gadolinium enhancement of the myocardium are reserved for those who show abnormal findings at cine imaging. Importantly, MRI should be performed and interpreted by experienced examiners to reduce the number of false positive and false negative readings.
Adult ; Child ; Compliance ; Death, Sudden, Cardiac ; Dilatation ; Fertilization ; Fibrosis ; Gadolinium ; Humans ; Magnetic Resonance Imaging ; Magnetic Resonance Spectroscopy ; Magnetics ; Magnets ; Myocardium ; Reading ; Ventricular Dysfunction ; Ventricular Function