in a screening population of athletes.29 However, one study of 2000 elite athletes age 14–35 in the UK found that only 0.4% of athletes had a QTc >460 ms, and another study detailing ECG findings in 32 561 young adults from the USA undergoing screening reported only 0.3% had a QTc >460 ms.10 34 Nonetheless, these QTc thresholds (440–460 ms) represent the approximate 90–95th percentile values for QTc distribution in the general population, and utilisation of these QTc cut-offs in a screening programme of athletes will have a <1% positive predictive value for LQTS in the absence of any personal or family history to indicate disease.29 31 In 2011, an international statement on ECG interpretation in athletes recommended that all athletes with a QTc >470 ms in men and >480 ms in women undergo further evaluation for LQTS to better balance false-positive and false-negative findings.7 Accordingly, it seems prudent to shift the QTc cut-off values that should trigger further evaluation in asymptomatic athletes with no concerning family history. This consensus group recommends cut-off values around the 1st percentile (QTc ≤320 ms) for a short QTc and around the 99th percentile (≥470 ms in men and ≥480 ms in postpubertal women) to indicate a prolonged QTc. These cut-offs will improve the positive predictive value if ECG is used for athlete screening while still identifying the most overt QTabnormalities and those individuals most like to experience QTc-related adverse events. These cut-offs are also consistent with thresholds defined by the 36th Bethesda Conference.35 However, it is critical that an athlete should not be obligated to a diagnosis of either SQTS or LQTS for falling below or above these QTc cut-off values, but rather these cut-off values should trigger the need for further evaluation. In other words, a prolonged QTc measurement on a single ECG does not equal LQTS. Further evaluation as outlined below and the use of scoring systems that account for personal symptoms, family history, as well as electrocardiographic features are helpful in clarifying the diagnosis. QTc cut-offs: relative versus absolute risk of a QT syndrome By definition, the 99th percentile cut-off for genetically confirmed LQTS assumes 1% of those with a value outside of this QTc threshold (≥470 ms in men, ≥480 ms in women) have a false-positive result. If one assumes that the prevalence of LQTS is 1 : 2000 individuals, and approximately half of these individuals will have a QTc above and half below these QTc thresholds (1 : 4000), then the positive predictive value of detecting true disease for a QTc outside the cut-off value is about 2.5%.29 30 However, once a prolonged QTc is identified, that individual has a 1 in 40 (rather than 1 : 2000) chance of having true disease. In other words, with no additional corroborative evidence, a single prolonged QTc value above the defined cut-off would suggest a 50-fold increase in relative risk for LQTS but only a 2.5% absolute risk. However, in an athlete with a QTc ≥500 ms, the predictive value now favours the presence of not only LQTS but possibly higher risk LQTS.34 36 Evaluation of a possible long or short QT syndrome An athlete identified as crossing the aforementioned QTc thresholds (≥470 ms men, ≥480 ms women) should have their personal history (exercise/emotion/Auditory-triggered syncope or seizures) and family history (exertional syncope, exercise/ Auditory-triggered ‘epilepsy’, postpartumtimed syncope/seizure, unexplained motor vehicle accidents, unexplained drowning, and premature, unexplained sudden death <50 years of age) reviewed. If their personal/family history is positive, then the athlete should be referred to a heart rhythm specialist for further evaluation. If the personal/family history is negative, then a repeat ECG should be obtained. If the follow-up ECG is within the QTc cut-off values, then no additional evaluation is needed and the athlete should be reassured and may continue sports participation. On the other hand, if the repeat ECG still exceeds the QTc cut-off values, then a screening ECG of the athlete’s firstdegree relatives (parents and siblings) should be considered and the athlete should be referred to a heart rhythm specialist or cardiologist as the possibility for newly discovered LQTS or SQTS has increased. Reversible, extrinsic factors, such as electrolyte abnormalities (hypokalaemia) or the presence of QT prolonging medications, must also be evaluated. If an athlete’s ECG shows a QTc ≥500 ms and no reversible causes are identified, then the athlete should be referred immediately to a heart rhythm specialist or cardiologist as the probability of LQTS and future adverse events has increased.36 Further testing including provocative treadmill stress and/or epinephrine QT stress testing along with genetic testing need to be considered carefully and should be performed and interpreted by a cardiologist familiar to the disease. Catecholaminergic polymorphic ventricular tachycardia CPVT is an inherited arrhythmogenic disorder characterised by ventricular ectopy induced by exercise or emotional nummer 5 | november 2013 | Sport & Geneeskunde 25 Pagina 24
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