Qt Interval, Variation in clinical trials

Exercise Induced QT Interval Changes in Response to Intermittent and Continuous Graded Exercise Tests

Long QT syndrome (LQTS) is an inherited heart defect where the heart takes longer to recover between beats. LQTS is a known condition predisposing young footballers to sudden cardiac death (SDC). The existence of LQTS can be established by measuring the QT interval in an electrocardiogram (ECG). Currently pre-participation cardiac screening is performed in young athletes but players may only be screened at 16 years old using only a resting ECG, and a medical check including a questionnaire on family and medical history. However, the sensitivity and specificity of the screening to investigate underlying causes of SCD could be improved with the addition of an exercise stress test or cardiopulmonary exercise test (CPET). Certain abnormalities in the heart may only become apparent when the heart has been stressed (e.g. via exercise). This is particularly important as in young athletes these abnormal rhythms manifest during rest and recovery rather than at peak exercise. The CPET measures changes in the ECG in response to exercise that increases in intensity in a continuous manner until the participant cannot exercise any long. However, football is characterised by high- intensity bouts of exercise interspersed with low-intensity bouts or pauses. Therefore, the continuous test does not reflect the movement patterns of football and may not stress the cardiovascular system in a similar manner. To address this, intermittent graded exercise tests have been developed to reflect the intermittent movement pattern. As yet there is limited evidence on whether there are any differences in ECG changes during intermittent exercise. Specifically, it is not clear how an intermittent movement pattern might affect the QT interval.