Shamus O'Meagher

Resistance training improves cardiac output, exercise capacity and tolerance to positive airway pressure in Fontan physiology☆

BACKGROUND Subjects with Fontan-type circulation have no sub-pulmonary ventricle and thus depend exquisitely on the respiratory bellows and peripheral muscle pump for cardiac filling. We hypothesised that resistance training to augment the peripheral muscle pump might improve cardiac filling, reduce inspiratory-dependence of IVC return to the heart and thus improve exercise capacity and cardiac output on constant positive airway pressure (CPAP). METHODS Eleven Fontan subjects (32+/-2 years, mean+/-SEM) had cardiac magnetic resonance imaging (MRI) and exercise testing (CPET); six underwent 20 weeks of high-intensity resistance training; others were non-exercising controls. After training, CPET was repeated. Four trainers had MRI with real-time flow measurement at rest, exercise and on CPAP in the trained state and following a 12-month detrain. RESULTS In the trained state, muscle strength increased by 43% (p=0.002), as did total muscle mass (by 1.94 kg, p=0.003) and peak VO2 (by 183 ml/min, p=0.02). After detraining, calf muscle mass and peak workload had fallen significantly (p<0.03 for both) as did peak VO2 (2.72 vs. 2.18 l/min, p<0.001) and oxygen pulse, a surrogate for SV (16% lower, p=0.005). Furthermore after detraining, SV on MRI decreased at rest (by 11 ml, p=0.01) and during moderate-intensity exercise (by 16 ml, p=0.04); inspiratory-dependent IVC blood return during exercise was 40% higher (p=0.02). On CPAP, cardiac output was lower in the detrained state (101 vs. 77 ml/s, p=0.03). CONCLUSIONS Resistance muscle training improves muscle mass, strength and is associated with improved cardiac filling, stroke volume, exercise capacity and cardiac output on CPAP, in adults with Fontan-type circulation.

Skeletal muscle abnormalities and exercise capacity in adults with a Fontan circulation

Objectives The peripheral muscle pump is key in promoting cardiac filling during exercise, especially in subjects who lack a subpulmonary ventricle (the Fontan circulation). A muscle-wasting syndrome exists in acquired heart failure but has not been assessed in Fontan subjects. We sought to investigate whether adults with the Fontan circulation exhibit reduced skeletal muscle mass and/or metabolic abnormalities. Design and patients Sixteen New York Heart Association Class I/II Fontan adults (30±2 years) underwent cardiopulmonary exercise testing and lean mass quantification with dual x-ray absorptiometry (DXA); eight had calf muscle 31P magnetic resonance spectroscopy as did eight healthy age-matched and sex-matched controls. DXA results were compared with Australian reference data. Setting Single tertiary referral centre. Results Peak VO2 was 1.9±0.1 L/min (66±3% of predicted values). Skeletal muscle mass assessed by relative appendicular lean mass index was significantly reduced compared with age-matched and sex-matched reference values (Z-score −1.46±0.22, p<0.0001). Low skeletal muscle mass correlated with poorer VO2 max (r=0.67, p=0.004). Overall, skeletal muscle mass T-score (derived from comparison with young normal reference mean) was −1.47±0.21; 4/16 Fontan subjects had sarcopenic range muscle wasting (T-score <−2.0) and 9/16 had less marked, but clinically significant wasting (T-score <−1.0 but ≥−2.0). Muscle aerobic capacity, measured by the rate constant (k) of postexercise phosphocreatine resynthesis, was significantly impaired in Fontan adults versus controls (1.48±0.13 vs 2.40±0.33 min−1, p=0.02). Conclusions Fontan adults have reduced skeletal muscle mass and intrinsic muscle metabolic abnormalities.

Exercise capacity and stroke volume are preserved late after tetralogy repair, despite severe right ventricular dilatation

Objectives To assess if exercise capacity and resting stroke volume are different in tetralogy of Fallot (TOF) repair survivors with indexed RV (right ventricle) end-diastolic volume (RVEDVi) more versus less than 150 ml/m2, a currently suggested threshold for pulmonary valve replacement (PVR). Design Cross-sectional study. Setting Single-centre adult congenital heart disease unit. Patients 55 consecutively eligible patients with repaired TOF (age at repair 2.3±1.9 years; age at evaluation 26.2±8.8 years; NYHA Class I or II). Interventions Cardiovascular MRI (1.5T) and cardiopulmonary exercise test. Main outcome measures Biventricular volumes and function; exercise capacity. Results 20 patients had RVEDVi below, and 35 had RVEDVi above 150 ml/m2, at time of referral. In the >150 ml/m2 group, fractional pulmonary regurgitation was higher (41±8 vs 31±8%, p<0.001). Although RV ejection fraction (EF) was lower (47±7 vs 54±6%, p=0.007), indexed RV stroke volume was higher (87±14 vs 64±10 ml/m2, p<0.001) in the >150 ml/m2 group. There were no significant differences in LVEF, indexed LV stroke volume or exercise capacity (% predicted peak work: 90±17 vs 89±11% and; % predicted VO2 peak: 84±17 vs 87±12%). Conclusions Exercise capacity and stroke volume are maintained with RVEDVi above compared with below a commonly used cut-off for PVR surgery. Optimal timing for PVR, thus, remains unclear.

Mechanisms of maintained exercise capacity in adults with repaired tetralogy of Fallot

BACKGROUND The mechanisms whereby cardiac output is augmented with exercise in adult repaired tetralogy of Fallot (TOF) are poorly characterised. METHODS 16 repaired TOF patients (25 ± 7 years of age) and 8 age and sex matched controls (25 ± 4 years of age) underwent cardiopulmonary exercise testing and then real-time cardiac MRI (1.5 T) at rest and whilst exercising within the scanner, aiming for 30% heart rate reserve (Level 1) and 60% heart rate reserve (Level 2), using a custom-built MRI compatible foot pedal device. RESULTS At rest, TOF patients had severely dilated RVs (indexed RV end-diastolic volume: 149 ± 37 mL/m(2)), moderate-severe PR (regurgitant fraction 35 ± 12%), normal RV fractional area change (FAC) (52 ± 7%) and very mildly impaired exercise capacity (83 ± 15% of predicted maximal work rate). Heart rate and RV FAC increased significantly in TOF patients (75 ± 10 vs 123 ± 17 beats per minute, p<0.001; 44 ± 7 vs 51 ± 10%, p=0.025), and similarly in control subjects (70 ± 11 vs 127 ± 12 beats per minute, p<0.001; 49 ± 7 vs 61 ± 9%, p=0.003), when rest was compared to Level 2. PR fraction decreased significantly but only modestly, from rest to Level 2 in TOF patients (37 ± 15 to 31 ± 15%, p=0.002). Pulmonary artery net forward flow was maintained and did not significantly increase from rest to Level 2 in TOF patients (70 ± 19 vs 69 ± 12 mL/beat, p=0.854) or controls (93 ± 9 vs 95 ± 21 mL/beat, p=0.648). CONCLUSIONS During exercise in repaired TOF subjects with dilated RV and free PR, increased total RV output per minute was facilitated by an increase in heart rate, an increase in RV FAC and a decrease in PR fraction.

Causes of death in tetralogy of Fallot in adults — An autopsy study

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Central blood pressure in children and adolescents: non-invasive development and testing of novel transfer functions

Central blood pressure can be estimated from peripheral pulses in adults using generalised transfer functions (TF). We sought to create and test age-specific non-invasively developed TFs in children, with comparison to a pre-existing adult TF. We studied healthy children from two sites at two time points, 8 and 14 years of age, split by site into development and validation groups. Radial and carotid pressure waveforms were obtained by applanation tonometry. Central systolic pressure was derived from carotid waveforms calibrated to brachial mean and diastolic pressures. Age-specific TFs created in the development groups (n=50) were tested in the validation groups aged 8 (n=137) and 14 years (n=85). At 8 years of age, the age-specific TF estimated 82, 99 and 100% of central systolic pressure values within 5, 10 and 15 mm Hg of their measured values, respectively. This TF overestimated central systolic pressure by 2.2 (s.d. 3.7) mm Hg, compared to being underestimated by 5.6 (s.d. 3.9) mm Hg with the adult TF. At 14 years of age, the age-specific TF estimated 60, 87 and 95% of values within 5, 10 and 15 mm Hg of their measured values, respectively. This TF underestimated central systolic pressure by 0.5 (s.d. 6.7) mm Hg, while the adult TF underestimated it by 6.8 (s.d. 6.0) mm Hg. In conclusion, age-specific TFs more accurately predict central systolic pressure measured at the carotid artery in children than an existing adult TF.

Preserved stroke volume late after tetralogy repair, despite severe right ventricular dilatation

The Authors’ reply We would like to thank Drs Masutani and Senzaki for their comments1 and Heart for the opportunity to respond. As stated in our study2, we did not find a significant difference in left ventricular (LV) volumes or function in patients with repaired tetralogy of Fallot (TOF) either above or below an indexed right ventricular (RV) end-diastolic volume of 150 mL/m2. We observed that as the RV became more dilated, …