An in vitro analysis of the PediMag and CentriMag for right-sided failing Fontan support.

OBJECTIVE: Right-sided mechanical circulatory support for failing Fontan physiology has been largely unsuccessful due to inherent hemodynamic differences between these patients and the target populations for most assist devices. This study uses advanced benchtop modeling of Fontan physiology to examine the use of PediMag and CentriMag to improve failing Fontan hemodynamics. METHODS: Each device was attached to a compliance-matched, patient-specific total cavopulmonary connection in vitro model that used resistances, compliances, and programmable waveforms to establish "failing Fontan" baseline hemodynamics (cardiac output [CO] = 3.5 L/min and central venous pressure ∼17 mm Hg). The ability of the assist devices to improve failing Fontan hemodynamics (reduce inferior vena cava pressure and augment CO) was investigated. RESULTS: Requiring complete Fontan pathway restriction, PediMag reduced inferior vena cava pressure by ∼10 mm Hg and supported CO augmentation up to 5 L/min. This was accompanied by an increase in superior vena cava pressure of ∼6 mm Hg. CentriMag produced similar hemodynamic changes without the need for pathway restriction or an increase in superior vena cava pressure. CONCLUSIONS: PediMag and CentriMag right-sided support led to a decrease in inferior vena cava pressure and augmentation of cardiac output. In the case of CentriMag, this is accomplished without an increase in superior vena cava pressure or the need for restrictive banding. This work provides further data to help with the optimal design of a Fontan assist device to ameliorate the growing need.

In Vitro Examination of the VentriFlo True Pulse Pump for Failing Fontan Support.

The current methodology of Fontan palliation results in a one "pump" circulatory system with passive flow to the lungs. Inherent hemodynamic differences exist between a biventricular circulatory system and this modified physiology, leading to a host of long-term complications. Mechanical circulatory support (MCS) is a potential option to combat these pathophysiological conditions. In this study, we examine the VentriFlo True Pulse Pump as a MCS option to support a failing Fontan patient. An in vitro circulatory loop was used to model a failing Fontan patient, reproducing pathophysiological pressures and flow rates. The VentriFlo True Pulse Pump was positioned as a right sided support, testing multiple cannulation and baffle restriction strategies, as well as various pumping parameters including flow rate, frequency, stroke volume and the ejection to filling time ratio. A 10 mm Hg decrease in IVC pressure and 0.75 L/min increase in cardiac output were achieved using a complete baffle restriction strategy. Additional cannulation and banding strategies were not as successful. Pump flow rate and frequency significantly impacted hemodynamics, while the ejection to filling time ratio did not. Though not ideal, complete baffle restriction was necessary to achieve successful support. The ability to tune individual pumping parameters for a given MCS device will have a substantial impact on the pressures and flow augmentation seen in a Fontan circulation. Both future pump design and off-label VADs for Fontan use should consider the pump configuration and parameter combinations presented here, which offered successful support.

A Method for In Vitro TCPC Compliance Verification.

The Fontan procedure is a common palliative intervention for sufferers of single ventricle congenital heart defects that results in an anastomosis of the venous return to the pulmonary arteries called the total cavopulmonary connection (TCPC). Local TCPC and global Fontan circulation hemodynamics are studied with in vitro circulatory models because of hemodynamic ties to Fontan patient long-term complications. The majority of in vitro studies, to date, employ a rigid TCPC model. Recently, a few studies have incorporated flexible TCPC models, but provide no justification for the model material properties. The method set forth in this study successfully utilizes patient-specific flow and pressure data from phase contrast magnetic resonance images (PCMRI) (n = 1) and retrospective pulse-pressure data from an age-matched patient cohort (n = 10) to verify the compliance of an in vitro TCPC model. These data were analyzed, and the target compliance was determined as 1.36 ± 0.78 mL/mm Hg. A method of in vitro compliance testing and computational simulations was employed to determine the in vitro flexible TCPC model material properties and then use those material properties to estimate the wall thickness necessary to match the patient-specific target compliance. The resulting in vitro TCPC model compliance was 1.37 ± 0.1 mL/mm Hg-a value within 1% of the patient-specific compliance. The presented method is useful to verify in vitro model accuracy of patient-specific TCPC compliance and thus improve patient-specific hemodynamic modeling.

Can time-averaged flow boundary conditions be used to meet the clinical timeline for Fontan surgical planning?

Cardiovascular simulations have great potential as a clinical tool for planning and evaluating patient-specific treatment strategies for those suffering from congenital heart diseases, specifically Fontan patients. However, several bottlenecks have delayed wider deployment of the simulations for clinical use; the main obstacle is simulation cost. Currently, time-averaged clinical flow measurements are utilized as numerical boundary conditions (BCs) in order to reduce the computational power and time needed to offer surgical planning within a clinical time frame. Nevertheless, pulsatile blood flow is observed in vivo, and its significant impact on numerical simulations has been demonstrated. Therefore, it is imperative to carry out a comprehensive study analyzing the sensitivity of using time-averaged BCs. In this study, sensitivity is evaluated based on the discrepancies between hemodynamic metrics calculated using time-averaged and pulsatile BCs; smaller discrepancies indicate less sensitivity. The current study incorporates a comparison between 3D patient-specific CFD simulations using both the time-averaged and pulsatile BCs for 101 Fontan patients. The sensitivity analysis involves two clinically important hemodynamic metrics: hepatic flow distribution (HFD) and indexed power loss (iPL). Paired demographic group comparisons revealed that HFD sensitivity is significantly different between single and bilateral superior vena cava cohorts but no other demographic discrepancies were observed for HFD or iPL. Multivariate regression analyses show that the best predictors for sensitivity involve flow pulsatilities, time-averaged flow rates, and geometric characteristics of the Fontan connection. These predictors provide patient-specific guidelines to determine the effectiveness of analyzing patient-specific surgical options with time-averaged BCs within a clinical time frame.