Cardiorespiratory fitness, muscle fitness, and physical activity in children with long QT syndrome: A prospective controlled study

Abstract

Background: In children with congenital long QT syndrome (LQTS), the risk of arrhythmic events during exercise commonly makes it difficult to balance exercise restrictions versus promotion of physical activity. Nevertheless, in children with LQTS, cardiorespiratory fitness, muscle fitness, and physical activity, have been scarcely explored.

Materials and methods: In this prospective, controlled, cross-sectional study, 20 children with LQTS (12.7 ± 3.7 years old) and 20 healthy controls (11.9 ± 2.4 years old) were enrolled. All participants underwent a cardiopulmonary exercise test, a muscular architecture ultrasound assessment, (cross-sectional area on right rectus femoris and pennation angle), a handgrip muscular strength evaluation, and a standing long broad jump test. The level of physical activity was determined using with a waist-worn tri-axial accelerometer (Actigraph GT3X).

Results: Peak oxygen uptake (VO_2peak) and ventilatory anaerobic threshold (VAT) were lower in children with LQTS than in healthy controls (33.9 ± 6.2 mL/Kg/min vs. 40.1 ± 6.6 mL/Kg/min, P = 0.010; 23.8 ± 5.1 mL/Kg/min vs. 28.8 ± 5.5 mL/Kg/min, P = 0.007, respectively). Children with LQTS had lower standing long broad jump distance (119.5 ± 33.2 cm vs. 147.3 ± 36.1 cm, P = 0.02) and pennation angle (12.2 ± 2.4° vs. 14.3 ± 2.8°, P = 0.02). No differences in terms of moderate-to-vigorous physical activity were observed (36.9 ± 12.9 min/day vs. 41.5 ± 18.7 min/day, P = 0.66), but nearly all children were below the WHO guidelines.

Conclusion: Despite similar physical activity level, cardiorespiratory fitness and muscle fitness in children with LQTS were lower than in healthy controls. The origin of this limitation seemed to be multifactorial, involving beta-blocker induced chronotropic limitation, physical and muscle deconditioning. Cardiovascular rehabilitation could be of interest in children with LQTS with significant physical limitation.

Keywords: cardiorespiratory fitness; inherited cardiac arrythmia; long QT syndrome; muscle fitness; pediatrics; physical activity.

FIGURE 1

Cardiorespiratory and muscle fitness analysis. (A) Cardiopulmonary exercise test on ergocycle. (B) Muscular ultrasound on right leg. (C) Anatomical cross-sectional area (yellow circle) of rectus femoris measured with ultrasound. (D) Pennation angle (yellow line) of right vastus lateralis; RF, Rectus femoris. The chosen anatomic site was at two third of the length from iliac spine anterior superior to upper edge of the patella on right leg. The probe was put in transversal plane and longitudinal plane for cross-sectional area and pennation angle, respectively.

FIGURE 2

VO_2peak comparison between LQTS and control groups. (A) VO_2peak comparison. (B) Percent-predicted VO_2peak comparison. For each group, the dark red square represents the mean value for each group, the black boxplot represents the first, second and third quartiles [e.g., Q1, median, Q3], respectively. LQTS, long QT syndrome.

FIGURE 3

Muscle fitness comparison between LQTS and control groups. (A) Pennation angle (°). (B) Anatomical cross-sectional area (cm²). (C) Handgrip strength (kg). (D) Standing long broad jump distance (cm). For each group, the dark red square represents the mean value for each group, the black boxplot represents the first, second, and third quartiles [e.g., Q1, median, Q3], respectively. LQTS, long QT syndrome.