Multicenter Assessment of Pre-Fontan Pulmonary Vascular Resistance

Background: Pulmonary vascular resistance (PVR) is a key parameter in evaluating univentricular circulations and is commonly calculated using the Fick principle. In pre-Fontan patients, however, Fick-derived PVR may be unreliable and cannot differentiate left and right lung contributions. An alternative Cath-CMR approach combines catheter-based pressure measurements with cardiovascular magnetic resonance (CMR) flow data to estimate PVR for each lung, but it does not account for proximal pulmonary artery resistance. To address this limitation, a computational fluid dynamics (CFD) method was developed to quantify left and right pulmonary artery resistances, including their proximal components. This multicenter study compares PVR estimates from the Fick, Cath-CMR, and CFD methods using pre-Fontan patient data from three institutions.

Methods: Retrospectively acquired clinical flow and pressure data from three medical centers over a ten-year period (Table 1) were analyzed for 42 pediatric pre-Fontan patients. The PVR was calculated using three approaches: the Fick method, the Cath-CMR method, and the CFD method, all expressed in indexed Wood units (iWU). The Fick method yielded only total PVR, whereas Cath-CMR and CFD provided both total and lung-specific PVR estimates. Total PVR values were used to classify patients by pulmonary hypertensive vascular disease (PHVD) risk. Comparisons across methods were performed using the Kruskal–Wallis test, with paired data evaluated by the Wilcoxon signed-rank test, intraclass correlation coefficient (ICC, 95% CI), and Bland–Altman analysis. Statistical significance was defined as p < 0.05.

Results: The mean Fick-based total PVR (1.80 ± 0.77 iWU) was significantly lower than values obtained with the Cath-CMR (2.56 ± 1.36 iWU, p = 0.003) and CFD (2.73 ± 1.48 iWU, p < 0.001) methods (Fig. 1). Agreement with Fick-derived PVR was poor for both Cath-CMR (ICC = 0.22, p = 0.055; 95% CI: –0.05 to 0.47) and CFD (ICC = 0.10, p = 0.220; 95% CI: –0.13 to 0.34). Compared to CFD, PHVD risk classification agreement was 79% for Fick and 93% for Cath-CMR (Fig. 2).


The CFD method yielded similar mean lung-specific resistances to Cath-CMR (LPA: 6.28 ± 3.19 vs. 5.50 ± 2.91 iWU, p = 0.237; RPA: 5.31 ± 3.74 vs. 5.26 ± 3.74 iWU, p = 0.752), with strong correlation for RPA and moderate correlation for LPA (Fig. 3). The LPA discrepancy likely reflects higher LPA proximal resistance in CFD estimates (LPA: 1.06 ± 1.26 iWU vs. RPA: 0.66 ± 0.69 iWU).

Conclusion: Total PVR estimates differed significantly between the Fick method and both Cath-CMR and CFD. CFD-derived lung-specific PVR closely matched Cath-CMR for the RPA, with modest discrepancies in the LPA attributable to higher proximal resistance. These findings highlight the impact of proximal resistance on PVR estimation, particularly in cases of branch pulmonary artery stenosis. Further studies are warranted to determine the most accurate approach for pre-Fontan patients.

Mean CMR Flow and Cath Pressure

Center	N	QSVC (L/min)	QLPA (L/min)	QRPA (L/min)	PSVC (mmHg)	PLPA (mmHg)	PRPA (mmHg)	PLA (mmHg)	ΔPL (PLPA – P<sub>LA)	ΔPR (PRPA – P<sub>LA)
1	16	1.07 ± 0.26	0.52 ± 0.20	0.56 ± 0.17	9.31 ± 1.49	8.88 ± 1.54	9.00 ± 1.55	4.44 ± 0.96	4.44 ± 1.26	4.56 ± 1.26
2	20	1.11 ± 0.33	0.47 ± 0.14	0.67 ± 0.25	12.30 ± 1.34	11.45 ± 1.28	11.85 ± 1.31	7.65 ± 1.53	3.80 ± 1.06	4.20 ± 1.11
3	6	1.00 ± 0.16	0.49 ± 0.14	0.51 ± 0.10	11.83 ± 2.14	10.83 ± 2.48	11.33 ± 2.42	7.83 ± 2.14	3.00 ± 1.67	3.50 ± 1.76
P-value	-	0.854	0.820	0.100	< 0.001	< 0.001	< 0.001	< 0.001	0.066	0.333

Figure 1: Comparison of total PVR between the three PVR estimation methods across all three centers indicates a significant difference between the Fick-based PVR and both the Cath-CMR and CFD-based PVR. In contrast, no statistical difference was found between the Cath-CMR-based PVR and CFD-based PVR.
Figure 2: Confusion matrix of Fontan failure risk stratification agreement for a) Fick vs. CFD and b) Cath-CMR vs. CFD, using PHVD as an indicator. In this context, “Normal” refers to a transpulmonary pressure gradient ≤ 6 mmHg and an indexed PVR ≤ 3 iWU, while “Elevated” indicates values exceeding one of these two thresholds.
Figure 3: The individual lung resistances using the Cath-CMR method correlate well with those of the CFD method, particularly for the RPA. However, the Cath-CMR-based LPA PVR estimates show a bias of -0.78 iWU relative to the CFD-based LPA PVR, which is likely due to the increased proximal resistance in the LPA.