Exercise induced worsening of mechanical heterogeneity and diastolic impairment in Long QT syndrome

Funding Acknowledgements Type of funding sources: None. Background Left ventricular (LV) mechanical dispersion and prolonged myocardial contraction are associated with symptoms in long QT syndrome (LQTS) mutation carriers. Sub-clinical LV diastolic impairment has also been reported in this group. Purpose To investigate at rest and during exercise the combined effect of prolonged myocardial contraction and increased mechanical dispersion on myocardial diastolic function and symptoms in LQTS subjects. Methods 47 LQTS patients (36 LQT1, 11 LQT2) underwent a bicycle exercise test in semi-supine position. ECG and echo parameters were recorded at rest, peak exercise (p.e) and were compared with 35 healthy individuals. Results No difference was seen between LQTS and control subjects for age (45 ± 15 vs 47 ± 13 years, p = 0.2), gender (53 vs 54% females, p = 0.3) or LV Ejection Fraction (65 ± 6 vs 67 ± 7%, p = 0.3). LQTS subjects, compared to controls, had not only prolonged QTc interval, but also longer contraction duration (tGLS), total isovolumic time (t-IVT), delayed early relaxation phase (tESR) and markedly decreased filling time (FT) at rest and p.e. Unlike controls, these electromechanical disturbances deteriorated further with exercise, during which additional decrease of the LV systolic (GLS) and diastolic myocardial function (ESR) and attenuated LV stroke volume response (Δ SV: +2 ± 0.5 vs +4 ± 1 vs +32 ± 4%, p< 0.0001) were noted. Such abnormal response to exercise was of greater degree in symptomatic patients and in the LQT1 subgroup and appeared to be amplified by b-blocker therapy (p < 0.05). Worsening myocardial contraction dispersion (SD-tGLS) at p.e was the strongest discriminator for previous clinical events (AUC 0.960, 95% CI 0.020 - 0.995, p < 0.0001) and its discriminating power excelled further by adding early relaxation delay. Conclusions Our findings suggest that in LQTS subjects prolonged and dyssynchronous mechanical contraction during exercise may be associated with inadequate cardiac output increase and symptoms. Table 1. REST PEAK LQT CONTROL p- LQT CONTROL p- QTc (ms) 453 ± 42 413 ± 17 < 0.0001 455 ± 44 390 ± 19 < 0.0001 GLS (%) 17.3 ± 4.3 18.7 ± 1.3 0.05 19.1 ± 32.6 23.5 ± 11.6 0.0001 tGLS (%) 47 ± 7.2 42 ± 6.3 0.0001 58.7 ± 10 40.1 ± 5.8 < 0.0001 ESR (%) 1 ± 0.3 2 ± 0.3 < 0.0001 1.1 ± 0.4 2.8 ± 0.4 < 0.0001 tESR (%) 61.4 ± 6.8 58.7 ± 4.1 0.03 69.7 ± 5.9 56.1 ± 2.9 < 0.0001 SD TGLS (ms) 58 ± 8 31 ± 8 < 0.0001 61 ± 8 24 ± 10 < 0.0001 Exercise response in long QT syndrome patients and controls