Options for the failing ventricle in pediatric heart disease

Current Treatment Options for the Failing Fontan Circulation

The Fontan operation was introduced in 1968. For congenital malformations, where biventricular repair is unsuitable, the Fontan procedure has provided a long-term palliation strategy with improved outcomes compared to the initially developed procedures. Despite these improvements, several complications merely due to a failing Fontan circulation, including myocardial dysfunction, arrhythmias, increased pulmonary vascular resistance, protein-losing enteropathy, hepatic dysfunction, plastic bronchitis, and thrombo-embolism, may occur, thereby limiting the life-expectancy in this patient cohort. This review provides an overview of the most common complications of Fontan circulation and the currently available treatment options.

Cardiac Magnetic Resonance Imaging of Mechanical Cavopulmonary Assistance

Mechanical circulatory support (MCS) options are limited for patients with dysfunctional single ventricle physiology. To address this unmet clinical need, we are developing an axial-flow blood pump to provide mechanical assistance to the cavopulmonary circulation. In this study, we investigate the use of high-resolution cardiac magnetic resonance imaging (MRI) to visualize the complex fluid flow conditions of mechanical circulatory assist in two patient-specific Fontan anatomies. A three-bladed axial-flow impeller coupled to a supportive cage with a four-bladed diffuser was positioned in the inferior vena cava (IVC) of each Fontan anatomy. Cardiac magnetic resonance (CMR) imaging and power efficiency studies were conducted at physiologic relevant parameters with cardiac outputs of 2, 3, and 4 L/min with impeller rotational speeds of 2000 and 4000 rpm. The axial-flow impeller was able to generate improved flow in the total cavopulmonary connection (TCPC). The higher rotational speed was able to redistribute flow in the TCPC anastomosis aiding in removing stagnant blood. No retrograde flow was observed or measured in the superior vena cava (SVC). As an extension of the CMR data, a scalar stress analysis was performed on both models and found a maximum scalar stress of approximately 42 Pa for both patient anatomies. The power efficiency experiments demonstrated a maximum energy gain of 8.6 mW for TCPC Anatomy 1 and 12.58 mW for TCPC Anatomy 2 for a flow rate of 4 L/min and at 4000 rpm. These findings support the continued development of axial blood pumps for mechanical cavopulmonary assist.

Externally applied compression therapy for Fontan patients

BACKGROUND

Limited therapeutic options are available for Fontan patients with dysfunctional or failing single ventricle physiology. This study describes the evaluation of an alternative, non-invasive, at-home therapeutic compression treatment for Fontan patients. Our hypothesis is that routinely administered, externally applied compression treatments to the lower extremities will augment systemic venous return, improve ventricular preload, and thus enhance cardiac output in Fontan patients.

METHODS

To initially evaluate this hypothesis, we employed the NormaTec pneumatic compression device (PCD) in a pilot clinical study (n=2). This device is composed of inflatable trouser compartments that facilitate circumferentially and uniformly applied pressure to a patient's lower extremities. Following an initial health screening, test subjects were pre-evaluated with a modified-Bruce treadmill exercise stress test, and baseline data on cardiorespiratory health was collected. After training, test subjects conducted 6 days of external compression therapy at-home. Subjects were then re-evaluated with a final treadmill stress test and data acquisition of new cardiorespiratory parameters.

RESULTS

Both subjects demonstrated improvement in exercise duration time, peak oxygen volume, and ventilator threshold, as compared to the baseline evaluation.

CONCLUSIONS

These findings are promising and provide the foundation for future studies that will focus on increasing study participation (sample size) to better assess the clinical benefit of compression therapy for Fontan patients.