Despite the medical advances in the area of mechanical circulatory support (MCS), there remain very few options for smaller pediatric patients, especially infants who are the highest risk of death while on the heart transplant waiting list.1 The majority of patients require left ventricular mechanical support only though approximately 10% of patients will require biventricular support.2 The Berlin Heart EXCOR is an extracorporeal pulsatile ventricular assist device that has been approved by the U.S Food and Drug Administration (FDA) for use in pediatric patients. It was first used in North America in 2000.3 The Berlin Heart (BH) differs from many MCS devices in that it is a pneumatically driven pulsatile pump device with two sets of artificial valves within the pumping mechanism.1 The BH’s primary drawback is a 20–30% risk for neurologic complications when used to support the systemic ventricle.1 , 4 This high stroke rate comes in large part from thrombus formation on the valves of the device. The BH valves are made of polyurethane (PU) trileaflet valves that significantly reduce the backflow compared with mechanical valves, allowing for more antegrade flow5; however, the risk of thrombosis is higher because back flow helps to prevent thrombus formation.5 Most protocols require that the valves be transilluminated daily to monitor for thrombus formation5; however, none of the protocols call for routine echocardiographic color-Doppler monitoring of the valves.
Materials and Methods
We have found that accurate assessment of both the inflow and outflow valves can be obtained at the bedside using a standard echocardiogram machine. Ultrasound gel is applied to the transducer as per usual and the transducer is placed directly onto the BH valve casing (Figure 1). The valve leaflets can be seen by two-dimensional imaging and regurgitation detected by color Doppler mapping. The ultrasound gel is safe to use on the BH casing and tubing with no degradation of the plastic.
A previously healthy 7 year old male presented with severe biventricular heart failure due to Uhl’s anomaly. He experienced a progressive decline in myocardial function and was placed on the BH assist device biventricularly. Serial echocardiograms were performed including direct imaging of the BH valves which showed increasing left ventricular BH (LVBH) valve regurgitation. Four days after the acute worsening of valve regurgitation, the patient required a pump exchange which demonstrated clot in the circuit.
Our patient also had a Quadrox D oxygenator in series with his right ventricular BH (RVBH) to allow for lung recovery secondary to acute respiratory distress syndrome. Ten days after placement of the oxygenator, an increase in the patient’s central venous pressure (CVP) and decreased left-sided filling were noted. Color Doppler evaluation of the RVBH valves showed significant regurgitation. This was concerning for increased afterload due to the downstream oxygenator in the circuit. The RVBH and oxygenator were exchanged without difficulty and repeat echo showed no valve regurgitation (Figure 2).
A previously healthy 9 month old female with idiopathic dilated cardiomyopathy developed progressive heart failure with unstable hemodynamics requiring MCS with LVBH. Direct imaging of the BH valves initially showed trivial regurgitation which became notably worse 6 days before pump exchange with large amount of thrombus noted in the outflow valve and cannula.
A previously healthy 9 month old male with idiopathic dilated cardiomyopathy had LVBH placed due to worsening heart failure. Six days after implantation, there was echocardiographic evidence of mild BH valve regurgitation. A follow-up echocardiogram 1 month after implantation showed worsening to moderate regurgitation and he underwent pump exchange for thrombosis later that day.
The BH remains one of the only viable options for infants and young children who require MCS. Unfortunately it carries a high risk of neurologic complications, of which ischemic stroke is the most common.1 Current strategies to reduce this risk include heparin-coated blood interfaces,6 transilluminating the PU valves,5 and decreasing the amount of support time.
We present a new technique, utilizing standard echocardiographic color Doppler, to monitor for the development of valve dysfunction. While current practice of visualizing the valves by transillumination to detect thrombus remains essential, we believe assessment of valve competency using color Doppler can yield important additional information and help explain changes in pump physiology.
We have utilized this technique on several patients and as detailed above have shown that there is an association between increasing valve regurgitation and need for pump exchange. Valve regurgitation could either be primary, related to small thrombi formation on the valve leaflets, or secondary, related to an increase in the valve afterload. Small thrombi are thought to create changes in valve regurgitation that may not be visible to the human eye via transillumination and before significant hemolysis has begun. An increase in afterload could be related to the pump circuit, such as an oxygenator in line that requires an exchange,2 or related to distal thrombus in the circuit. Some portions of the circuit are not able to be visualized by transillumination and changes in valve regurgitation by color Doppler could raise the level of suspicion for thrombosis in those sections and pending pump dysfunction. If the valve dysfunction is due to circuit thrombosis, we believe this could ultimately lead to earlier recognition, which if treated could reduce the risk of neurologic insults. In our patient with an in-line oxygenator, detection of increased valve regurgitation due to the additional afterload of the downstream oxygenator explained poor output and indicated the need for prompt circuit exchange. The valve should be subsequently reassessed twice weekly or if there are clinical concerns. While this proposed surveillance would result in more frequent echocardiograms, we feel that the benefit to patient safety and reduction in neurological complications outweigh the added cost of the echocardiograms.
In the current era of MCS, there are few options for our smallest patients and the main option that does exist carries a significant burden of neurologic injury. Early recognition of pump thrombosis or increased afterload leading to valve failure could allow for earlier pump exchange. Echocardiographic color Doppler can detect changes in the BH valve competency which could hopefully allow for earlier recognition of thrombus reducing the stroke risk. This would ultimately lead to shorter hospital stays and less treatments for the associated complications.
Limitations of this current investigation include the small retrospective case series and lack of an established protocol to monitor the development of worsening regurgitation. Another limitation is that the degree of regurgitation is currently qualitative, as quantification of valvar regurgitation in this setting has not been studied. Further research is needed to determine actual causality of valve insufficiency, as our observations present associations only.
The authors thank all the sonographers who made this possible.
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