Dilated cardiomyopathy is a disease in which the heart muscle becomes enlarged and weakened, losing its ability to pump blood efficiently. In adults, mechanical circulatory support has become a well-established bridge to transplantation, but in small children the options have long been painfully limited. The Jarvik 2015 was designed specifically to close that gap. It is a miniaturized, implantable, continuous-flow axial pump that weighs roughly 12 grams and measures about the size of an AA battery, small enough to fit within the thorax of a young child while generating sufficient flow to sustain the systemic circulation.

The device operates on an axial-flow principle: an impeller suspended within a compact housing spins at high rotational speed, drawing blood from the left ventricular apex and expelling it into the ascending aorta. Unlike pulsatile devices of earlier generations, which used bulky chambers and mechanical valves to replicate the natural heartbeat, continuous-flow pumps like the Jarvik 2015 provide steady perfusion. This design reduces the number of moving parts in contact with blood, lowers the risk of mechanical failure, and permits implantation through a less extensive surgical approach, a critical advantage when the patient’s chest is only a fraction of the size of an adult’s.

The Hangzhou team, led by corresponding author Qiang Shu of the Department of Cardiac Surgery, with Ru Lin of the Department of Heart Failure and Mechanical Circulatory Support serving as a lead author, described the meticulous planning and multidisciplinary coordination that the implantation demanded. The effort spanned cardiac surgery, cardiovascular medicine, cardiac intensive care, anesthesiology, ultrasound imaging and perfusion services, and it drew on international expertise. Adachi Iki of the Congenital Heart Surgery program at Baylor College of Medicine and Texas Children’s Hospital in Houston contributed guidance, and the team received device-handling training from Antonio Amodeo, Surgical Director of the Heart Failure Unit at Bambino Gesù Children’s Hospital in Rome, whose group performed the first human implantation of a miniaturized axial-flow ventricular assist device in a child in 2020.

The clinical course, however, was not without complications, and it is in the team’s handling of these setbacks that the report carries its greatest scientific value. One of the central challenges in ventricular assist device therapy, particularly in children, is the management of antithrombotic therapy. The surfaces of any artificial pump activate the coagulation cascade, creating a persistent risk of pump thrombosis, the formation of clots within the device that can impair or completely stop blood flow. At the same time, aggressive anticoagulation exposes the patient to bleeding, including hemorrhagic stroke, which remains one of the most feared complications of pediatric mechanical circulatory support. Prior research, including the work of Rosenthal and colleagues at Stanford on modified anti-thrombotic guidelines, has shown that standardized protocols can significantly reduce stroke rates in children supported by ventricular assist devices, and the Hangzhou team acknowledged guidance from Christopher S. Almond of Stanford University School of Medicine specifically in the treatment of pump thrombosis in this child.

The recognition and management of pump thrombosis in a pediatric patient requires constant vigilance. Surveillance depends on trends in lactate dehydrogenase and plasma-free hemoglobin, markers of hemolysis that rise when red blood cells are sheared across obstructed pump surfaces, along with echocardiographic assessment of pump function and power consumption data from the device controller. Because the child in this case was among the first in China to receive the Jarvik 2015, the team had to interpret these signals without the accumulated local experience that larger Western centers enjoy, relying instead on protocols refined during the PumpKIN trial, the international pediatric trial of the Jarvik 2015 that has been the backbone of the device’s clinical development for nearly a decade.

The PumpKIN trial, formally titled the Pediatric Pulse, Kinetics and Hemodynamics study, grew out of the National Heart, Lung, and Blood Institute’s contract program to develop a miniaturized pediatric continuous-flow pump. Baldwin, Adachi and colleagues described its design in 2017, and Adachi updated its status in 2018. A prospective multicenter feasibility study published in the Journal of Heart and Lung Transplantation in 2024 by Almond, Davies, Adachi and colleagues demonstrated the device’s feasibility in smaller children with heart failure, and compassionate-use reports published in the ASAIO Journal by Spinner and colleagues have documented individual cases in which the device served as a bridge to transplant when no other option existed. The Hangzhou case adds to this growing body of experience and, importantly, extends it to a Chinese clinical context, where the regulatory, financial and logistical barriers to obtaining such devices have historically been formidable.

Indeed, the report highlights a dimension of pediatric mechanical circulatory support that rarely appears in the technical literature: the economics of keeping a child alive on an implanted heart pump. The authors thank the Zhejiang Women and Children’s Foundation and the Future Smile Charitable Foundation, whose fundraising enabled many generous individuals in the community to contribute financially to the child’s medical treatment and care. Implantable ventricular assist devices for children are extraordinarily expensive, and in the absence of robust insurance coverage or clinical trial sponsorship, charitable funding can be the deciding factor between a viable bridge to transplantation and no treatment at all. The case therefore stands as both a scientific advance and a social one, demonstrating a pathway through which a single child in end-stage heart failure could access technology available in only a handful of centers worldwide.

The underlying disease that brought the child to surgery, dilated cardiomyopathy, remains one of the most common indications for heart transplantation in children. When medical therapy with inotropes, diuretics and neurohormonal agents fails, the options narrow to extracorporeal membrane oxygenation, paracorporeal pulsatile devices such as the Berlin Heart EXCOR, or, increasingly, implantable continuous-flow pumps. Extracorporeal membrane oxygenation is intended only for short-term stabilization, and the Berlin Heart, while effective, confines children to bedside support with substantial stroke and infection risks. The Jarvik 2015 occupies a different niche: because it is fully implantable, children supported with it can potentially be extubated, mobilized, rehabilitated and even, in some centers, discharged home while awaiting a donor heart, transforming the waiting period from an intensive care ordeal into something approaching a tolerable childhood.

The concept of bridging is central to the field. Data from adult programs have shown that some patients supported with left ventricular assist devices experience myocardial recovery sufficient for device deactivation, as documented in case reports of LVAD deactivation after cardiac function recovers, and pediatric teams hope similar bridges to recovery may one day be possible. For now, however, the realistic goal in end-stage pediatric dilated cardiomyopathy is a bridge to transplantation, and every successful case strengthens the argument that children too small for adult-sized devices deserve access to purpose-built technology. The miniaturized pediatric continuous-flow device has already been shown, in a report by Adachi, Spinner, Tunuguntla, Elias and Heinle published in 2019, to achieve a successful bridge to heart transplant, and each additional documented implantation refines the collective understanding of patient selection, implantation technique and postoperative management.

The ethical framework surrounding the Hangzhou case was similarly thorough. The clinical research project was approved by the Hospital Ethics Board and Hospital Academic Committee of the Children’s Hospital Affiliated to Zhejiang University School of Medicine and by the National Health Commission of the People’s Republic of China under trial authorization number 2022-IEC-019. Written informed consent for publication was obtained in accordance with applicable ethical guidelines, and the authors declared no competing interests, noting explicitly that the affiliation of one author with an artificial heart technology company did not constitute a conflict for this study. Qiang Shu, a member of the World Journal of Pediatrics editorial board, was recused from the journal’s review of the manuscript, which was handled by another editor through the standard peer review process.

For the global pediatric cardiology and cardiac surgery community, the significance of this report lies less in any single technical maneuver than in the proof it provides that complex, high-stakes pediatric mechanical circulatory support can be successfully exported beyond the small circle of centers that pioneered it. The Jarvik 2015’s journey, from design concept through the PumpKIN trial framework, through the first human implantation in Rome, through compassionate use cases in North America and now through a documented implantation and management experience in Hangzhou, reflects the slow, deliberate accumulation of evidence required to make a new therapy standard of care. Every additional case contributes to the anticoagulation algorithms, the troubleshooting protocols and the surgical techniques that will determine whether children everywhere with end-stage heart failure gain access to a viable bridge to a new heart. The child in Hangzhou, supported by a pump the size of a battery and an international network of expertise, embodies that progress.

A device designed to rescue failing hearts in adults has exposed a hidden challenge in children: a pump can fit inside a small chest and still place an overwhelming burden on the rest of the circulation. In a case report published in the Journal of Artificial Organs, surgeons describe severe right-heart failure after implanting a HeartMate 3 left ventricular assist device in a 12-year-old girl with advanced dilated cardiomyopathy. The child’s heart had progressively lost its ability to circulate blood, leaving her dependent on catecholamine drugs—powerful medications such as adrenaline-like agents that temporarily strengthen contraction and raise blood pressure. The HeartMate 3, or HM3, was implanted to provide durable mechanical support for the failing left ventricle, alongside placement of a pacemaker for her complete atrioventricular block. Although the device could be accommodated anatomically, the patient developed a dramatic postoperative collapse in right-sided cardiac performance. The report suggests that pediatric implantation cannot be judged solely by whether the pump physically fits. The interaction between pump output, heart rate, chest anatomy and a child’s smaller blood volume may be equally decisive.

The HM3 is a continuous-flow left ventricular assist device, meaning that it uses a rapidly rotating internal rotor to draw blood from the left ventricle and propel it into the aorta. It does not replace the heart’s entire function: it primarily unloads the left ventricle and supplies systemic blood flow, while the right ventricle must still move blood through the lungs so that it can refill the left side. In adults, the device has shown strong clinical performance, including lower rates of pump thrombosis than earlier generations because of its design features and blood-flow patterns. Pediatric use has expanded as clinicians confront a shortage of donor hearts and growing numbers of children with end-stage heart failure. Yet a child’s cardiovascular system is not simply a scaled-down adult system. A smaller thoracic cavity can constrain the position of the pump and its inflow cannula, while lower circulating blood volume and different vascular resistance alter the relationship between pump speed and physiologic demand. The Japanese team’s report focuses on that relationship, particularly in a patient whose body surface area was only 1.07 square meters.

The girl was 138 centimeters tall and weighed 28.9 kilograms when she underwent implantation. Her underlying disease, dilated cardiomyopathy, weakens the heart muscle and enlarges the ventricular chambers, reducing the force available to eject blood. She also had complete atrioventricular block, a failure of electrical conduction between the atria and ventricles that can produce an abnormally slow or unreliable heartbeat. Before surgery, her pulmonary artery pulsatility index, or PAPi, was 2.3, with no obvious clinical evidence of right-heart failure. PAPi is a hemodynamic measure calculated from the difference between pulmonary artery systolic and diastolic pressures divided by right atrial pressure. In practical terms, it estimates how effectively the right ventricle generates pulsatile pressure to drive blood through the lungs relative to the pressure backing up in the venous system. Lower values have been associated with a greater risk of right-ventricular failure after implantation of a left-sided assist device. In this case, the preoperative number did not signal an immediate crisis, but the postoperative measurements changed sharply.

After the HM3 was implanted, the patient’s central venous pressure remained between 15 and 18 millimeters of mercury, substantially higher than expected in a stable circulation. Central venous pressure reflects the pressure in the large veins near the right atrium and rises when the right ventricle cannot accept or eject blood efficiently. At the same time, her PAPi fell from 2.3 to just 0.2, a change indicating profound impairment of right-heart function. This pattern is physiologically important because a left ventricular pump can increase the movement of blood out of the left side without automatically increasing blood flow arriving from the right. If the right ventricle cannot propel blood through the pulmonary circulation, the left ventricle may become underfilled even while the mechanical pump continues to operate. The resulting mismatch can raise venous pressure, reduce effective circulation and trigger a difficult cycle of congestion. The authors concluded that the child had developed severe right-heart failure despite the absence of an obvious preoperative warning.

The consequences extended beyond abnormal pressure readings. The child developed a massive left pleural effusion, an accumulation of fluid in the space between the lung and the chest wall, together with hypoxemia, or abnormally low oxygen levels in the blood. The fluid and impaired lung expansion made respiratory recovery difficult, delaying extubation until the seventh postoperative day. In a patient with a new ventricular assist device, a large pleural effusion can have several possible causes. Surgical injury to lymphatic vessels, obstruction of venous drainage and excess fluid administration can all contribute. The clinical team therefore investigated whether disruption of lymphatic flow or a subclavian vein occlusion was responsible. Lymphangiography, an imaging technique that maps lymphatic vessels, and treatment aimed at the venous obstruction did not improve the effusion. That lack of response shifted attention back to the circulation: elevated right-sided pressures were likely forcing fluid out of the blood vessels and into the pleural space.

The decisive improvement came not from replacing the pump, but from retuning the interaction between the pump and the child’s own heart. During cardiac catheterization, the clinicians adjusted the HM3’s rotational speed and modified the pacemaker settings that controlled the patient’s heart rate and ventricular activation. These changes lowered central venous pressure and were followed by rapid improvement in the pleural effusion. The report does not portray pump speed as a simple “more is better” setting. A continuous-flow device’s output depends on rotational speed, the pressure difference across the pump and the amount of blood available to enter it. Increasing speed can enhance left-sided unloading and systemic flow, but if the right ventricle cannot supply that flow, suction, underfilling or excessive ventricular interaction may worsen the imbalance. In a small child, a speed that seems modest or appropriate by adult standards may represent comparatively intensive circulatory support. Coordinating the mechanical flow with the child’s heart rate was therefore central to recovery.

The mechanical environment inside the chest may also have contributed. The authors emphasize that previous reports of HM3 implantation in small pediatric patients have concentrated largely on anatomical accommodation—whether the pump, cannula and surrounding structures can be positioned without direct compression. Computed tomography and virtual surgical simulation can help estimate chest dimensions and identify a workable implantation route. But the present case indicates that an anatomically successful operation may still create functional problems. A device occupying a substantial fraction of a small thoracic cavity could alter the position or filling of the ventricles, compress adjacent structures or change the geometry of the right heart. The two ventricles are connected not only by blood flow but also by the interventricular septum and the tight space around them. When one ventricle is unloaded or changes shape, the septum can shift and influence the other ventricle’s ability to contract and fill. These effects, combined with relatively high pump support for body size, could raise the right ventricle’s workload after implantation.

The case also highlights why pediatric patients with complete atrioventricular block may require particularly careful calibration. The pacemaker determines how rapidly the ventricles contract and how their electrical activation is coordinated. Heart rate affects venous return, ventricular filling time, oxygen consumption and the amount of blood the right ventricle must send through the lungs. A rate that is too slow may fail to sustain circulation, while a rate that is too fast can shorten filling time and increase the heart’s energy demand. Abnormal activation patterns can make contraction less efficient, further reducing right-ventricular output. In this patient, pacemaker settings and HM3 speed were adjusted together rather than in isolation, reflecting the fact that mechanical and electrical support are coupled systems. The improvement after those changes suggests that the postoperative failure was at least partly reversible through hemodynamic optimization, although a single case cannot establish which adjustment had the greatest effect.

For clinicians, the report offers a warning against relying on a single preoperative measurement or a device-sizing checklist when treating very small children. The patient’s PAPi before surgery was not severely abnormal, yet her postoperative value revealed major right-heart dysfunction. Continuous monitoring of central venous pressure, pulmonary artery pressures, oxygenation, ventricular filling and the behavior of the pleural effusion may be necessary as the circulation adapts. The case also supports using catheter-based assessment to test pump and pacemaker settings under direct hemodynamic measurement when routine adjustments fail. Still, the findings come from one patient, and the report cannot determine how often this complication occurs or whether the same mechanism applies to all small children receiving an HM3. Larger pediatric registries and physiologic studies will be needed to define safe relationships between body size, pump speed, heart rate and right-heart reserve. The broader message is immediate, however: in pediatric mechanical support, “fits in the chest” is only the beginning of the engineering problem.