Objectives: The explanation for restrictive right ventricular (RV) physiology after tetralogy of Fallot (ToF) repair is not known. We hypothesized that restrictive RV physiology is associated with fibrosis of the right ventricular outflow tract (RVOT) as detected on cardiac MRI.
Methods: 29 patients (10.5±2.8 years, 14 females) with ToF repair were included 9.6±2.9 years after total correction. The subjects were examined with delayed contrast enhanced (DE) MRI to detect fibrosis of the RV and echo/Doppler-cardiography to detect and measure end-diastolic antegrade flow in the pulmonary artery. One patient was excluded due to suboptimal DE-MRI. Fisher´s exact test was used to determine if the asscociation between restrictivity and fibrosis was significant and the odds ratio (OR) was calculated.
Results: Fourteen patients showed fibrosis in the RVOT on DE-MRI and echo/Doppler showed restrictive physiology in 11 of these 14 patients. Of the remaining 14 patients without fibrosis in the RVOT on DE-MRI, two showed restrictive physiology on echo/Doppler. The OR of having RVOT fibrosis was 22 (CI 3.0-157.4, p=0.0018) in patients with restrictive RV physiology. In addition, fibrosis was seen at the place of the ventricular septum defect patch and in one patient there was a minor area of fibrosis separate from the RVOT.
Conclusion: Restrictive physiology of the RV is associated with fibrosis of the RVOT. Therefore, fibrosis of the RVOT may constitute the substrate that partly explains restrictive physiology in ToF patients after repair.

Figure: Example of DE-MRI in one patient showing fibrosis of the RVOT (white arrows).