Skeletal muscle index determined by bioelectrical impedance analysis is a determinant of exercise capacity and a prognostic predictor in patients with congenital heart disease.
Sato M, Inai K, Asagai S, Harada G, Shimada E, Sugiyama H.J Cardiol. 2020 May 18:S0914-5087(20)30159-3. doi: 10.1016/j.jjcc.2020.04.011. Online ahead of print.PMID: 32439338
Take Home Messages
- Bioelectrical impedance analysis (BIA) has been introduced in several clinical fields, such as cardiology, nephrology, hepatology, nutrition, and rehabilitation.
- BIA is a non-invasive, rapid, and safe assessment method that involves the application of alternating currents to the body to acquire eight-polar tactile-electrode impedance.
- Skeletal muscle Index (SMI) determined by BIA is a determinant of exercise capacity and can be used as a prognostic predictor in patients with CHD.
Commentary from Dr. Soha Romeih (Aswan, Egypt), section editor of ACHD Journal Watch:
Patients with congenital heart disease (CHD) reportedly have reduced exercise capacity. Underlying cardiac anatomy, a sedentary lifestyle, and chronotropic incompetence are thought to be associated with exercise impairment (Figure 1). Bioelectrical impedance analysis (BIA) has been introduced in several clinical fields, such as cardiology, nephrology, hepatology, nutrition, and rehabilitation. BIA is a non-invasive, rapid, and safe assessment method that involves the application of alternating currents to the body to acquire eight-polar tactile-electrode impedance. The first signs of heart failure (HF) are thought to appear during exercise. If BIA parameters can predict impaired exercise capacity and detect unbalanced body composition, it could be used to evaluate the early stages of HF in patients with CHD.
The present study aimed to clarify the correlation between BIA parameters and exercise capacity as well as the prognostic importance of the skeletal muscle index (SMI) in patients with CHD.
This retrospective single-center study included 305 consecutive patients aged > 12 years with CHD. Patients with a cardiac pacemaker were excluded because the electric current generated by BIA could interfere with device function. Additionally, pregnant patients were excluded because BIA in pregnancy is unreliable.
Blood samples were obtained to analyze the hemoglobin, albumin, creatinine, sodium, and brain natriuretic peptide (BNP) levels. Using the M-mode of the parasternal short-axis view, the left ventricular fraction shortening (LVFS) was determined. Similarly, they measured the tricuspid annual plane systolic excursion using the M-mode of the apical 4-chamber view. The early mitral inflow velocity (E) was measured using pulsed Doppler imaging with the sample volume at the mitral tip. The early diastolic mitral annular velocity (e’) was measured at the septal annulus using TDI, and the E/e’ ratio was calculated.
The 6-minute walking test (6MWT) was performed. A cardio-pulmonary exercise test (CPX) on a treadmill using the ramp protocol performed to assess peak oxygen uptake (peakVO2) and oxygen uptake at the aerobic threshold (ATVO2).
Bioelectrical impedance analysis (BIA)
The BIA was performed in patients 2–4 h after lunch and the oral administration of medicines. In the present study, to compare skeletal muscle and mineral levels in a wide range of body sizes, skeletal muscle mass was indexed to height squared (that is, the Skeletal muscle index – SMI), and mineral content was indexed to height squared (that is, the mineral index, MI). Additionally, the Extracellular Index (EI), which is the ratio of Extra-cellular water (ECW) divided by the total body water, was assessed. The BIA parameters were blinded to physicians who determined the HF related admissions and those who performed the 6MWT and CPX.
Correlation between exercise capacity and bioelectrical impedance parameters
To clarify the factors associated with exercise capacity, the correlation between peak VO2 and BIA parameters in patients with biventricular as well as single ventricular morphology was determined. Reduced exercise capacity was defined as peak VO2 under 20 ml/kg/min.
Comparison of bioelectrical impedance parameters and exercise capacity with regard to ventricular morphology
To elucidate any influence that ventricular morphology might have, the BIA and exercise capacity (6MWT, peak VO2, and AT VO2) parameters of patients with biventricular morphology as well as those with single ventricular morphology were compared.
Skeletal muscle index as a predictor of HF-related admission
To clarify the prognostic role of SMI, the ratio of HF-related admission in patients with SMI above the median value in the present study was compared with that of patients with SMI equal to or less than the median value using a Kaplan–Meier analysis. HF-related admissions were identified as new-onset decompensated HF or decompensation of chronic HF with symptoms that warranted admission
The multivariate analysis revealed a significant correlation between peak VO2 and EI (r = -0.55) and peak VO2 and SMI (r = 0.49) Figure 2. The receiver operating characteristic curve analysis showed that the EI cut-off for peak VO2 <20 ml/kg/min was 0.386 [area under the curve (AUC), 0.77; sensitivity, 0.67; specificity 0.76], and the SMI cut-off was 7.6 kg/m2 (AUC, 0.78; sensitivity, 0.76; specificity 0.75).
Compared with patients who had biventricular morphology, patients with single ventricular morphology had a higher EI (mean, 0.381 vs. 0.387, respectively) and lower SMI (8.5 vs. 7.7, respectively), resulting in a lower peakVO2 (27.1 vs. 20.8, respectively).
Fig. 2. Receiver operating characteristic curve analysis of bioelectrical impedance parameters for predicting reduced exercise capacity (defined as peak VO2 under 20 ml/kg/ min) (A, edema index; B, skeletal muscle index). AUC, area under the receiver operating characteristic curve.
The Kaplan–Meier analysis showed that a low SMI was associated with an increased risk of future heart failure-related admissions. (Figure 3 below)
Fig. 3. The Kaplan–Meier analysis of the incidence of heart failure-related admissions of patients with biventricular (left) or single ventricular (right) morphology by SMI. The red line shows the patients with a high SMI. The blue line shows those with a low SMI. HF, heart failure; SMI, skeletal muscle index.
SMI determined by BIA is a determinant of exercise capacity and can be used as a prognostic predictor in patients with CHD.