Mechanical Circulatory Support in Children

During recent years enormous progress has been made with various types of Mechanical Circulatory Support (MCS). The simplest and often life-saving device is the Intraaortic balloon Pump (IABP) which can easily be inserted via femoral artery access. This form of MCS is very common in the Coronary Care Unit and in ischemic syndromes following open heart surgery or catheter intervention. Ventricular assist devices supporting either the left or right ventricle or both are more complex and their use can be very helpful in postcardiotomy heart failure, as well as bridge to transplant. The most complex form of circulatory support in pediatric patients is the use of ECMO. Thousands of lives have been saved by this form of circulatory support, especially in neonatal care units. The use of ECMO in postoperative patients, however is still controversial. It should be emphasized that pediatric MCS is a developing area and indications or contraindications are still evolving as well as more sophisticated support devices. Recently, a new family of ventricular assist devices, the Medos-HIA system was developed by Reul et al (1) at the Helmholtz-Institute in Aachen, Germany. This system was optimized in intensive in vitro (2) and in vivo studies (3). Stimultaneously, a new pneumatic driving system was developed. The left ventricular support system (LVAD) is available in three different sizes with 10, 25 and 60 ml stroke volume. The right sided pumps (RVAD) are designed with 10% less stroke volume (9, 22.5 and 54 ml) in order to compensate for the bronchial shunts. The CAD-CAM design of the pumps has been optimized by hydrodynamic studies, the valve geometry corresponds to normal human semilunar valves. Improvements in function and manufacturing techniques resulted in a leaflet thickness in the order of only 0.2 mm. These valves have low transvalvular gradients, rapid closure and minimal regurgitation. The ventricles are made of a double-layer polyurethane membrane and the three-leaflet polyurethane valves are seamlessly integrated into the inand outflow conduits. Since the pump is totally transparent, air-free filling, as well as the functional status of the pump and eventual thrombus formation during long-term use, can easily be optically controlled. The drive-unit can be operated by external electrical power and pressure supplies, an internal compressor and a battery also allow for mobile applications. positive pressures up to 300 mmHg and negative pressures up to -80 mmHg can be generated at frequencies up to 180 bpm. It has a fixed rate operation mode as well as the possibility of ECG triggering and the whole system is operated via an interactive touch-screen monitor. Its first clinical application was on February 2 1994 at the University of LObeck, Germany (Department of Cardiac and Thoracic Surgery, Director. Prof. Dr. H. Sievers). It was first used in children during the same month at the Charite, Berlin, Germany by Prof. Konertz. At the same time this was its first application for cardiac transplantation, which was successfully performed after 5 days of assisted circulation. In March 1994 its first pediatric application was also performed at the Charite. The system was successfully used in a baby for bridging a postoperative cardiac insufficiency after correction of a congenital coronary anomaly. Up to early 1997 a total of 120 patients in Germany, Belgium and France was treated with the system. The age of the patients ranged from newborns to 75 years of age, most were older than 45 years. The majority of applications was LVAD, followed by biventricular assist (BVAD). A singular RVAD was extremely rare. The indications were distributed in 50% to cardiogenic shock including bridge to transplant and 50% to postoperative heart failure. Intended use was recovery of the failing heart in 57% and bridge to transplantation in 43% of all cases. Depending on the indications, the results show, that patients under cardiogenic shock have a high mortality and only a few could be successfully weaned and transplanted. In contrast, post-cardiotomy heart failure has a success rate of about 50% either by weaning the patient or by transplantation. When the results were analyzed with respect to the indication, 40% of the bridging candidates proved successfully transplanted. Within the group of patients intended for cardiac recovery, 45% were successfully weaned from cardiac assist. The main cause of death was multi-organ failure. The highest complication rate resulted from bleeding, which required re-exploration in 23% of cases. Other complications were lung and liver failure, as well as capillary leaks. No technical defects of the pumps and drive units were observed. In many cases the system was applied at a very late stage. When it is used at an early stage and coagulation and infection parameters are carefully controlled, the results are comaprable or even exceed those of other,