Exercise in carriers of truncated Titin variants: more evidence before the greenlight.
Description:The Task Force on Sports Cardiology and Exercise in Patients with Cardiovascular Disease of the European Society of Cardiology recommends that ‘it would be reasonable to permit intensive exercise and competitive sports in most individuals with pathogenic variants implicated in dilated cardiomyopathy (DCM) in the absence of overt clinical features of the disease’.1 Although the natural history of most pathogenic variants is unknown, special consideration is given to individuals with pathogenic variants that are associated with an increased risk of life-threatening arrhythmias such as lamin A/C or filamin C mutations.1 Individuals with arrhythmogenic right ventricular cardiomyopathy caused by desmosomal variants also have a similar recommendation.2 In these individuals, exercise may have an adverse effect on cardiac function that could potentially result in fatal arrhythmias.3 They should therefore not engage in any competitive sports or recreational exercise of high or very high intensity irrespective of the severity of left ventricular (LV) dysfunction and dilatation.4 However, the Task Force did not make such specific recommendations for carriers of truncated Titin variants (TTNtv).1 TTN is the largest known protein in biology, spanning half the cardiac sarcomere.5 It is therefore a critical component of the cardiac sarcomere that is essential for its mechanical and regulatory functions. TTNtv have been implicated as major disease alleles, responsible for more than 25% of familial cases of DCM, but these variants are also found in 2–3% of the apparently healthy general population.6 It has been postulated that once the TTNtv gets incorporated into the sarcomere, it is unable to function normally, thus leading to gain-of-function/dominant negative phenotypes, resulting in DCM.7 In this edition of the Journal, Savonitto et al.8 have explored, perhaps for the first time, the relationship between lifelong exercise intensity and the development of cardiac manifestations in subjects carrying a TTNtv’.8 This was a retrospective cohort study that included all carriers of TTNtv enrolled in the Familial Cardiomyopathy Registry of Cardiovascular Department of the University of Trieste, Italy. The patient population comprised both the probands (the first family members diagnosed with TTN cardiomyopathy) and their relatives; both the affected (phenotype-positive) and the healthy (phenotype-negative) carriers of the TTNtv. The primary end-point of the study was the development of LV systolic dysfunction, defined as the occurrence of LV ejection fraction below 45%, either at baseline or during the follow-up. The secondary end-points were the occurrence of life-threatening or non-life-threatening arrhythmias, or specifically of atrial fibrillation or flutter, during follow-up. Each patient was evaluated using multiple electrocardiograms (ECGs) and Holter ECGs during follow-up. The study subjects were then grouped into athletes and non-athletes, based on their engagement in a minimum of 4 h of higher-intensity sports (≥6 METs) per week for at least 6 years. The investigators recruited a total of 117 subjects, 27% females and 66% probands, and followed them up for a median of 7.2 years. The results showed that vigorous exercise was not associated with the primary or any of the secondary end-points. Thus, the investigators concluded that, intensive physical activity did not appear to have a significant impact on the development of LV systolic dysfunction or arrhythmias in carriers of TTNtv. The authors also discussed the limitation of the study, including the retrospective study design, the small sample size from a single-centre, and the possibility of social desirability bias, given that the subjects could have altered their responses to align with perceived societal expectations. However, the most important limitation was the selection bias, given that deceased patients with TTNtv in the Familial Cardiomyopathy Registry were excluded from the analysis. The deceased patients could have developed LV dysfunction and died of arrhythmic or heart failure complications. Therefore, by design, the study failed to determine the true impact of intensive exercise on the study end-points. Hence the study conclusion should have been ‘Among the survivors of subjects carrying TTNtv in the Registry, intensive physical activity did not appear to have a significant impact on the development of LV systolic dysfunction or arrhythmias’. As suggested by the authors, the subject is important and should be explored further in a large, multi-ethnic, and multi-centre prospective study.









