Author(s)
Nathaniel J. Barber; Emmanuel O. Ako; Gregorz, T. Kowalik; Mun H. Cheang; Bejal Pandya; Jennifer A. Steeden; Shahin Moledina; Vivek Muthurangu
Date
2016-12-09
Source
Circulation: Cardiovascular Imaging December 2016, Volume 9, Issue 12

Background
Conventional cardiopulmonary exercise testing (CPET) can objectively measure exercise intolerance, but cannot provide comprehensive evaluation of physiology. This requires additional assessment of cardiac output (CO) and arterio-venous oxygen content difference (a-vO2). We developed magnetic resonance (MR) augmented CPET (MR-CPET) to achieve this goal and assessed children with right heart disease.

Methods and Results
Healthy controls (n=10) and children with pulmonary arterial hypertension (PAH) (n=10) and repaired Tetralogy of Fallot (ToF) (n=10) underwent MR-CPET. All exercise was performed on a MR-compatible ergometer and oxygen uptake (VO2) was continuously acquired using a modified metabolic cart. Simultaneous CO was measured using a real-time MR flow sequence and combined with VO2 to calculate avO2. Peak VO2 was significantly lower in the PAH group (12.6±1.31 ml/kg/min,
p=0.01) and trended towards lower in the ToF group (13.5±1.29 ml/kg/min, p=0.06) compared to controls (16.7±1.37 ml/kg/min). Although ToF patients had the largest increase in CO, they had lower resting (3±1.2 l/min/m2) and peak (5.3±1.2 l/min/m2) values compared to controls (resting 4.3±1.2 l/min/m2, peak 6.6±1.2 l/ min/m2) and PAH patients (resting 4.5±1.1 l/min/m2, peak 5.9±1.1 l/min/m2). Both the PAH and ToF patients had blunted exercise induced increases in a-vO2. However, only the PAH patients had significantly reduced peak values (6.9±1.3 mlO2/100ml) compared to controls (8.4±1.4 mlO2/100ml, p= 0.005).

Conclusions
MR-CPET is feasible in both healthy children and children with cardiac disease. Using this novel technique we have demonstrated abnormal exercise patterns in VO2, CO and a-vO2.

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