Does the Nakata index predict outcome after Fontan operation?

We read with interest the article by Adachi et al. ‘Preoperative small pulmonary artery did not affect the midterm results of Fontan operation’ [1]. One of the main messages of the article is that Fontan operation can be successfully performed in patients with a preoperative PA index smaller than 250 mm/m. Further, the authors note that decreased pulmonary artery index postoperatively does not restrict functional efficacy of the Fontan circulation. From our point of view the predictive value Nakata index is less informative than the lower lobe index (LLI) which was introduced to optimize preoperative selection of Fontan candidates [2—4]. We use LLI as being more predictive to evaluate adequacy of the pulmonary vascular tree, given that central pulmonary arteries used for calculation of Nakata index can be enlarged before or during a Fontan operation [4]. The lowest Nakata index that precludes a successful Fontan operation is not known [5]. The authors have suggested that PA size at the hilum could be a good representative of the whole PA vascular bed. In the presence of low Nakata index, the normal LLI would automatically classify all these patients to be no longer in a risk category [4]. We observed in our series that the total lower lobe index is more informative than the Nakata index for the selection of candidates for a Fontan operation. In 13 patients (22%) with a low Nakata index (under 200 mm/m, lowest 125 mm/m), the presence of a normal total lower lobe index (>90 mm/m) enabled us to successfully perform ECFO combined with enlargement of the main pulmonary arteries in six of them [2]. Based on our experience, we believe that measurement of the lower lobe index is an important adjunct for the evaluation of candidates for Fontan operation.