Abstract
Background
The Fontan completion represents the final phase of univentricular repair, which drains the inferior vena cava against gravity into a higher-pressure pulmonary arterial circulation. The passive and anti-gravity characteristics of this circulation make encountering a failing Fontan not uncommon. Twenty years ago, experiments exploring the potential of vascular pumps to bolster the passive Fontan have started, and trials are still ongoing.
Aim of review
Through this review, our aim is to summarize the outcomes of these trials.
Key scientific concepts and findings of review
A total of ten trials have been included, encompassing 23 different settings. Three distinct designs were identified, of which two are classified as pump designs: the connecting chamber and the intravascular pump designs. Only one trial investigated the potential use of a compression device. The most frequently encountered design in vivo was the intravascular pump, accounting for 67 % of the cases. There were no reports of significant hemolysis or thrombosis. However, an increasing flow rate exceeding 5 L/min was associated with negative outcomes in the connecting chamber design due to rising upstream pressure in the SVC. In contrast, intravascular pumps did not exhibit this limitation.
Highlights
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Three devices are being trialed for failing Fontan support: the connecting chamber, intravascular pump, and compression device.
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The connecting chamber needs fewer RPM than the intravascular pump, which allows for potential transcatheter insertion.
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A drawback of the connecting chamber is the increased superior vena cava pressure at higher flow rates, limiting its effectiveness.
1
Background
The Fontan procedure is the final stage of three-stage palliation in patients with univentricular heart, whether Hypoplastic Left Heart Syndrome (HLHS) or other types of Univentricular heart. Fontan physiology results in diminished cardiac output and increased systemic venous pressure. Venous congestion can be complicated by Protein Losing enteropathy (PLE) [ ].
Directing systemic venous return from the lower part of the body to the pulmonary arteries, without intervening pumping chamber, is non-physiologic and results in inevitable systemic congestion [ ].
This systemic congestion is reflected gradually in intestinal lymphatics, leading to progressive intestinal lymphangiectasia and severe protein-losing enteropathy. Secondary lymphangiectasia does not only cause repeated admissions with edema and the need for albumin infusion, but it also causes impaired humoral and cellular immunity due to the loss of immunoglobulins and lymphocytes into the intestinal lumen [ ].
Several strategies have been proposed to overcome systemic venous congestion. Puente and colleagues, as well as Rinjberg et al., concluded that optimal Fontan hemodynamic could only be achieved by upsizing the 16–20 mm (45 mm 2 /L/min) conduit to a surface area of 125 mm 2 /L/min [ , ].
Fontan Takedown, after staged recruitment of the non-dominant ventricle followed by biventricular conversion, has been described by Doulamis in 2022. Results are better in cases of elective conversion compared to cases who already developed a failing Fontan [ ].
Mechanical circulatory support for left ventricular failure using pulsatile and, more recently, axial flow pumps is established. Axial flow pumps, however, are not well-versed in low-pressure circuits, such as those supporting the right ventricle or even a TCPC circulation. Patients with failing Fontan circulation may be able to reverse poor hemodynamics and subsequent organ failure with pump support [ ].
This article aims to explore all the in-vivo and in-vitro trials of different types of Fontan assist devices.
2
Methodology
2.1
Literature search
A comprehensive search was conducted across PubMed, Scopus, and Web of Science databases to identify relevant studies. The literature search was conducted from 1/1/2003 to 1/1/2024. English only articles were included in this study.
2.2
Keywords and inclusion criteria
The search strategy included the keywords “Fontan” and/or “vena cava assist devices,” focusing on both in vitro (animal or human) and in vivo studies.
2.3
Outcome parameters
The study examined the following outcome parameters:
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Device design: Connecting chamber ( Fig. 1 ), Intravascular pump ( Fig. 2 ), Compression device ( Fig. 3 )
Fig. 1
PRISMA flow chart shows the study selection process in this systematic review. No abbreviations.
Fig. 2
Diagrammatic representation of the Design 1 of Fontan Assist device: The connecting Chamber.
Fig. 3
Diagrammatic representation of the Design 2 of Fontan Assist device: The intravascular pump.
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Device settings: Pump rate or compression rate
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Flow rate achieved by each device setting
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IVC mean pressure
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Upstream pressure in the SVC
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Presence of evidence of hemolysis or thrombosis
2.4
Statistical analysis
Data analysis was performed using MedCalc statistical software (trial version). Numerical data were assessed for normality using the Shapiro-Wilk test and reported as mean ± SD for normally distributed data and as median and IQR for non-normally distributed data. Categorical data were presented as numbers and percentages. Numerical comparisons across three groups were conducted using ANOVA, while comparisons between two groups were analyzed using the independent t -test. Categorical data were assessed using the chi-square test. P values <0.05 were considered statistically significant.
2.5
Receiver-operating characteristic analysis
An SVC pressure exceeding 10 mmHg was chosen as a classification variable for conducting a receiver-operating characteristic analysis. This analysis aimed to determine the cut-off flow rate that predicts adverse outcomes, such as upstream pressure elevation, in the connecting chamber and intravascular pump designs.
3
Results
The literature search revealed three primary designs for the Fontan assist device: the connecting chamber (CC), which functions as a hydraulic chamber receiving anastomoses from the two peripheral pulmonary arteries and the superior and inferior vena cavae; the intravascular propeller or pump (IVP); and the compression device (CD). A total of 10 trials (met the inclusion criteria and relevant outcome parameters, while another 10 trials were excluded due to unmet outcomes [ ]. Some of the included trials examined varying pump speeds and device designs. Ultimately, 23 sets of adjustments were analyzed for their impact on inferior vena cava (IVC) and superior vena cava (SVC) pressures, along with the resulting flow rates ( Fig. 1 presents the PRISMA flow chart illustrating the selection process for the studies).
Among the 23 settings analyzed, 11 utilized the connecting chamber design, 9 utilized the intravascular pump design, and only 3 employed the compression device. Notably, the intravascular pump was the most frequently tested in vivo, accounting for 33 % of all adjustment sets, whereas 100 % and 91 % of the trials for the connecting chamber and compression device, respectively, were conducted in vitro ( Figs. 2, 3, and 4 illustrate these designs).
Across the three designs analyzed in Table 1 , the flow rate in trials using the compression device was significantly lower. Additionally, the connecting chamber required substantially fewer rotations per minute than the intravascular pump to achieve comparable flow rates (4000 RPM [4000–4775] vs. 12,000 RPM [9750–21,750], P < 0.01).
| Connecting chamber design N = 11 (design numbers) N = 5 (reports’ number) | Intravascular design N = 9 (design numbers) N = 4 (reports’ number) | Compression device N = 3 (design numbers) N = 1 (reports’ number) | P Value | ||
|---|---|---|---|---|---|
| Reference in text | 10, 12,14,16, 17 | 8,9,11, 15 | #13 | ||
| Pump speed (median (IQR)) | 4000 (4000–4775) | 12,000 (9750–21,750) | – | <0.01 | |
| In vitro/in vivo (n/%) | In vitro | 10 (91) | 3 (33) | 3 (100 %) | <0.01 |
| In vivo | 1 (9) | 6 (67) | 0 (0) | ||
| Flow rate (mean ± SD) | 4.9 ± 0.9 | 4.1 ± 1.7 | 2.5 ± 0 (Achieved 125 compressions per min) | 0.02 | |
| IVC Pressure (median (IQR)) | 11 (3–16) | 15 (4–17) | 15 (10–17) | 0.7 | |
| SVC Pressure (mean ± SD) | 7 ± 2 | 10 ± 2 | – | 0.2 | |
There were no significant differences in SVC or IVC pressures among the three device designs. Visual examination of the data suggested a distinctive pattern separating the performance of intravascular pumps and connecting chambers. Notably, SVC pressure appeared to be positively correlated with flow rate in the connecting chamber design, whereas it was negatively correlated in the intravascular pump design. To further validate this observation, we conducted a receiver operating characteristic (ROC) analysis, which indicated that a flow rate >5 in the connecting chamber design predicted an SVC pressure exceeding 10. Conversely, a flow rate <2.8 in the intravascular pump was associated with an SVC pressure >10 (see Figs. 5 and 6 for further details).
