Author + information
- Aleksander Kempny, MD⁎ (, )
- Rafael Alonso-Gonzalez, MD, MSc and
- Konstantinos Dimopoulos, MD, MSc, PhD
- ↵⁎Adult Congenital Heart Centre, Royal Brompton and Harefield NHS Foundation Trust, Sydney Street, London SW3 6NP, United Kingdom
We congratulate Shafer et al. (1) on their recent publication. We would like to raise some points and would be grateful to the researchers if clarification could be provided to better understand their methodology and results. With regards to the patient population, we were somewhat surprised to see that young patients, seemingly undergoing operations in the last decade or so, all underwent atriopulmonary Fontan. Total cavopulmonary connection has been the surgery of choice in the last 2 decades because it provides a better hemodynamic profile and reduces the risk of arrhythmia generated by an enlarging right atrium.
The results of this study were obtained in young and asymptomatic patients a few years post-Fontan operation. We wonder whether the conclusions can be generalized to the whole population of patients with Fontan circulation, including those with very large right atria and those with a “failing Fontan.”
The inert gas rebreathing method is indeed one of the most accurate methods for noninvasive assessment of cardiac output. This method requires appropriate and strict adjustment of respiratory pattern. A rebreathing bag of a volume of 1.5 to 2.5 liters should be used for several breaths and should be emptied at each breath for the technique to provide accurate results (2). Such adjustment of breathing pattern during exercise produces little change in cardiac output in healthy individuals but could significantly affect cardiac output in patients with Fontan circulation. In fact, an optimal respiratory breathing pattern during exercise has been suggested in Fontan patients, resulting in the most efficient pulmonary augmentation of blood flow (3). The lack of a significant increase in cardiac index from “exercise” to “exercise plus inspiratory load,” as seen in this study, would appear to contradict previous data on the beneficial effects of negative inspiratory pressure in Fontan patients (4). We wonder whether this relates to the technique used for measuring cardiac output.
Furthermore, it appears unclear to us whether the increase in stroke volume in these patients was accounted for entirely by the skeletal muscle and ventilatory pumps. Complete separation of the effects of the muscle and ventilatory pumps is difficult to achieve, even with such a carefully designed protocol such as the one used in this paper, as demonstrated by the change in minute ventilation in both patients and controls on “zero-resistance cycling” (Fig. 4 of their paper ). The latter proved to be statistically nonsignificant, but we wonder whether this was due to the Bonferroni post hoc adjustment for multiple comparisons, which is known to inflate type II errors.
- American College of Cardiology Foundation
- Shafer K.M.,
- Garcia J.A.,
- Babb T.G.,
- Fixler D.E.,
- Ayers C.R.,
- Levine B.D.
- Fogel M.A.
- Shekerdemian L.S.,
- Bush A.,
- Shore D.F.,
- Lincoln C.,
- Redington A.N.