Pulmonary Hypertension After Heart Transplantation in Patients Bridged with the Total Artificial Heart

Residual Pulmonary Vascular Resistance Increase Under Left Ventricular Assist Device Support Predicts Long-Term Cardiac Function After Heart Transplantation

Aims

We compared hemodynamics and clinical events after heart transplantation (HTx) in patients stratified by the severity of residual pulmonary vascular resistance (PVR) after left ventricular assist device (LVAD) implantation for bridge to transplantation.

Methods

We retrospectively analyzed patients who had undergone HTx at the University of Tokyo Hospital. We defined the high PVR group as patients with PVR of >3 Wood Units (WU) as measured by right heart catheterization performed 1 month after LVAD implantation.

Results

We included 85 consecutive HTx recipients, 20 of whom were classified in the high PVR group and 65 in the low PVR group. The difference in PVR between the two groups became apparent at 2 years after HTx (the high PVR group: 1.77 ± 0.41 WU, the low PVR group: 1.24 ± 0.59 WU, p = 0.0009). The differences in mean pulmonary artery pressure (mPAP), mean right arterial pressure (mRAP), and mean pulmonary capillary wedge pressure (mPCWP) tended to increase from the first year after HTx, and were all significantly higher in the high PVR group at 3 years after HTx (mPAP: 22.7 ± 9.0 mm Hg vs. 15.4 ± 4.3 mm Hg, p = 0.0009, mRAP: 7.2 ± 3.6 mm Hg vs. 4.1 ± 2.1 mm Hg, p = 0.0042, and mPCWP: 13.4 ± 4.5 mm Hg, 8.8 ± 3.3 mm Hg, p = 0.0040). In addition, pulmonary artery pulsatility index was significantly lower in the high PVR group than in the low PVR group at 3 years after HTx (2.51 ± 1.00 vs. 5.21 ± 3.23, p = 0.0033). The composite event including hospitalization for heart failure, diuretic use, and elevated intracardiac pressure (mRAP ≥ 12 mm Hg or mPCWP ≥ 18 mm Hg) between the two groups was significantly more common in the high PVR group. Residual high PVR was still an important predictor (hazard ratio 6.5, 95% confidence interval 2.0–21.6, and p = 0.0023) after multivariate Cox regression analysis.

Conclusion

Our study demonstrates that patients with residual high PVR under LVAD implantation showed the increase of right and left atrial pressure in the chronic phase after HTx.

Hemodynamic characterization of the Realheart® total artificial heart with a hybrid cardiovascular simulator

BACKGROUND

Heart failure is a growing health problem worldwide. Due to the lack of donor hearts there is a need for alternative therapies, such as total artificial hearts (TAHs). The aim of this study is to evaluate the hemodynamic performance of the Realheart® TAH, a new 4-chamber cardiac prosthesis device.

METHODS

The Realheart® TAH was connected to a hybrid cardiovascular simulator with inflow connections at left/right atrium, and outflow connections at the ascending aorta/pulmonary artery. The Realheart® TAH was tested at different pumping rates and stroke volumes. Different systemic resistances (20.0-16.7-13.3-10.0 Wood units), pulmonary resistances (6.7-3.3-1.7 Wood units), and pulmonary/systemic arterial compliances (1.4-0.6 mL/mmHg) were simulated. Tests were also conducted in static conditions, by imposing predefined values of preload-afterload across the artificial ventricle.

RESULTS

The Realheart® TAH allows the operator to finely tune the delivered flow by regulating the pumping rate and stroke volume of the artificial ventricles. For a systemic resistance of 16.7 Wood units the TAH flow ranges from 2.7±0.1 to 6.9±0.1 L/min. For a pulmonary resistance of 3.3 Wood units the TAH flow ranges from 3.1±0.0 to 8.2±0.3 L/min. The Realheart® TAH delivered a pulse pressure ranging between ~25 mmHg and ~50 mmHg for the tested conditions.

CONCLUSIONS

The Realheart® TAH offers great flexibility to adjust the output flow and delivers good pressure pulsatility in the vessels. A low sensitivity of device flow to the pressure drop across it was identified and a new version is under development to counteract this.

Experimental investigation of right-left flow balance concepts for a total artificial heart

A total artificial heart (TAH) must be designed to autonomously balance the flows of the systemic and pulmonary circulation to prevent potentially lethal lung damage. The flow difference between the systemic and pulmonary circulation is mainly caused by the bronchial (arteries) shunt flow and can change dynamically. The ReinHeart TAH consists of only one actuator that ejects blood alternately from the right and left pump chamber. This design entails a coupling of the right and left stroke and thus, complicates the independent adaptation of the right and left flow. In this experimental study on the ReinHeart TAH, four concepts to keep the flows well balanced were investigated using an active mock circulation loop for data acquisition. Three concepts are based on mechanical design changes (variation of pusher plate shape, flexible right pump chamber housing, and reduced right stroke volume) to achieve a static flow difference. In combination with these static concepts, a concept influencing the ratio of systole and diastole duration to respond to dynamic changes was studied. In total, four measurement series, each with 270 operating points, to investigate the influence of circulatory filling volume, heart rate, bronchial shunt flow, and lung resistance were recorded. In the course of this study, we introduce a concept deviation indicator, providing information about the efficiency of the concepts to balance the flows based on changes in lung's blood pressures. Furthermore, the distribution of the measured data was evaluated based on bubble plot visualizations. The investigated variation of the right pusher plate shape results in high lung pressures which will cause lethal lung damage. In comparison, a flexible right pump chamber housing shows lower lung pressures, but it still has the potential to damage the lungs. Reducing the stroke volume of the right pump chamber results in proper lung pressures. The flow balance can dynamically be influenced with a positive effect on the lung pressures by choosing a suitable systole-diastole-ratio. The results of this study suggest that an adequate right-left flow balance can be achieved by combining the mechanical concept of a reduced right stroke volume with an active control of the systole-diastole-ratio.

Pulmonary Pressure Assessment with the Total Artificial Heart

Reversal of pulmonary hypertension has been observed in patients during a bridge to transplant with a left ventricular assist device. Total artificial heart (TAH) implant prevents subsequent right heart catheterization. Consequently, controversy exists over whether the prosthetic right ventricle improves or exacerbates pulmonary hypertension. A pulmonary artery (PA) pressure monitor was placed in two patients undergoing TAH implant, as a bridge to transplant. One patient had pulmonary hypertension at implant; the other had normal pulmonary pressures. Daily measurements were taken of systolic, diastolic, and mean PA pressures throughout support. Patient 1 received successful transplant after TAH support of 91 days. Systolic/diastolic (mean) PA pressures steadily decreased from 55/39 (28) mm Hg at implant to 29/18 (7) mm Hg currently. Patient 2 received support for 101 days before death due to abdominal ischemic complications. Pulmonary arterial pressures stayed consistent throughout this period, from 26/17 (20) mm Hg at implant to 23/13 (17) mm Hg at the time of death. These findings suggest that an implantable PA pressure monitor may be useful in optimizing hemodynamics and planning appropriate timing of transplant with TAH support.