Temporary heart pump rapidly lowered lung pressures in transplant candidates

Patients with advanced heart failure who are waiting for a new heart often face a hidden obstacle: high pressures in the lungs. Pulmonary hypertension can render a candidate ineligible for transplantation, because a donor heart unaccustomed to elevated pulmonary afterload risks acute right ventricular failure. A new retrospective study now reports that a temporary heart pump, the Impella 5.5, was associated with rapid and substantial reductions in pulmonary vascular resistance, mean pulmonary artery pressure, and pulmonary artery systolic pressure among patients bridged to orthotopic heart transplantation.

The study, published in Frontiers in Cardiovascular Medicine, analyzed 75 patients treated at two tertiary cardiac centers between October 2018 and August 2025. All had an Impella 5.5 placed during a hospitalization that culminated in heart transplantation. The device is a micro-axial, transaortic pump first commercially available in 2019 that provides temporary left ventricular support, reducing ventricular filling pressures and myocardial oxygen consumption while improving coronary and systemic perfusion. Although originally developed for cardiogenic shock, its use has expanded toward longer-duration support as a bridge to definitive advanced heart failure therapy.

The researchers collected right heart catheterization and echocardiographic data obtained before device implantation and while the pump was in place. The primary outcomes were changes in pulmonary vascular resistance calculated by both the Fick and thermodilution methods, mean pulmonary artery pressure, and pulmonary artery systolic pressure. Secondary outcomes included qualitative right ventricular systolic function, the transpulmonary gradient, and the pulmonary artery pulsatility index. The primary analysis was unpaired and used all available observations at each time point, with a paired analysis performed among patients who had complete data at both time points.

The results were striking. Median pulmonary vascular resistance by the Fick method fell from 2.8 Wood Units to 1.5 Wood Units, and by thermodilution from 2.4 Wood Units to 1.3 Wood Units, both with p-values below 0.001. Median mean pulmonary artery pressure dropped from 35.5 mmHg to 24.5 mmHg, and pulmonary artery systolic pressure fell from 48 mmHg to 37.5 mmHg, again both highly significant. Pulmonary capillary wedge pressure and right atrial pressure also declined significantly, while cardiac index and cardiac output measured by both methods rose, consistent with improved forward flow during device support.

Among secondary outcomes, the pulmonary artery pulsatility index, a surrogate measure of right ventricular performance, increased from 1.9 to 3.4, a change that reached statistical significance. By contrast, the transpulmonary gradient did not change significantly in the primary analysis, and the proportion of patients with at least moderate right ventricular dysfunction on echocardiography was essentially unchanged. The median duration of Impella 5.5 support was 19 days, and the median time from device implantation to the first catheterization during support was 14 days.

A subgroup analysis focused on the patients with the most severe baseline pulmonary hypertension, those with a pulmonary vascular resistance above 3 Wood Units, the threshold at which current International Society of Heart and Lung Transplantation guidelines call for stepwise evaluation of reversibility. In this paired analysis of 27 patients, resistance by the Fick method fell from 4.0 to 2.0 Wood Units, mean pulmonary artery pressure declined from 42.0 to 29.0 mmHg, and pulmonary artery systolic pressure fell from 54.0 to 40.0 mmHg. Notably, the transpulmonary gradient also decreased significantly in this subgroup, from 13.5 to 9.0 mmHg, a pattern the authors interpret as possibly reflecting reversal of pulmonary vascular remodeling rather than unloading of the left side of the heart alone.

The clinical context matters. Pulmonary hypertension, defined in this literature as a mean pulmonary artery pressure above 20 mmHg, is estimated to affect 60 to 70 percent of patients with heart failure with reduced ejection fraction, and irreversible disease limits transplant candidacy because of the risk of donor right ventricular failure. Current guidelines permit consideration of temporary or durable mechanical circulatory support to assess the reversibility of refractory pulmonary hypertension, but the evidence behind that recommendation comes exclusively from durable devices. Existing data on temporary support in pulmonary hypertension had been limited to case series and small cohorts.

The safety profile observed in the study was consistent with prior reports on the device. Hemolysis, defined as a lactate dehydrogenase level at least three times the upper limit of normal, occurred in 16 percent of patients, and a hemoglobin drop of at least 5 g/dL occurred in 17 percent. Device complications requiring operative intervention occurred in 8 percent, limb ischemia in roughly 3 percent, acute stroke in 4 percent, and the need for hemodialysis in 4 percent, with all dialysis cases occurring after transplantation. No deaths occurred during the index admission or within 30 days of discharge, and 12 percent of patients were readmitted within 30 days.

The authors are careful about what their data can and cannot show. The retrospective design and modest sample size limit causal inference, and there was no control group, which would have been ethically difficult to construct in this high-risk population. Confounding from concurrent heart failure therapies, including inotropes, diuretics, and vasodilators, was inherent to the observational design. Standing weight on the days of catheterization fell significantly during support, suggesting improved volume status, which the authors argue is likely a downstream effect of improved renal perfusion under mechanical support rather than an independent confounder, though this remains a possibility. Differences in catheterization practices between the two centers, including abbreviated protocols at one site while the device was in place, introduced variability and substantial missing data.

Selection bias is another caveat, since the patients who received the pump may not represent the full spectrum of transplant candidates with pulmonary hypertension. Of the patients with an open transplant evaluation who did not progress to advanced therapies, only one was ultimately declined for transplantation because of severe pulmonary hypertension, and that patient did not undergo repeat catheterization while supported, limiting assessment of hemodynamic response. The authors conclude that temporary left ventricular unloading with the Impella 5.5 can meaningfully lower pulmonary pressures and resistance during transplant evaluation, but they call for larger prospective studies with standardized hemodynamic monitoring to determine whether temporary support can truly reverse fixed pulmonary hypertension, as has been described with durable left ventricular assist devices.

Subject of Research: The effect of temporary left ventricular unloading with the Impella 5.5 device on pulmonary hypertension in patients bridged to heart transplantation

Article Title: Improvement in pulmonary vascular resistance with IMPELLA 5.5 as a bridge to orthotopic heart transplantation

Article References: Rankin, J., Imielski, B., Howard-Green, A., Saxena, A., Raman, D., Seals, A., Paik, K. S., Patel, P. A., Mishkin, J., Khan, H., Adeniyi, A. O., Lata, A., & Gilbert, O. (2026). Improvement in pulmonary vascular resistance with IMPELLA 5.5 as a bridge to orthotopic heart transplantation. Frontiers in Cardiovascular Medicine, 13, Article 1935715. https://doi.org/10.3389/fcvm.2026.1935715

Image Credits: AI Generated

DOI: 10.3389/fcvm.2026.1935715

Keywords: heart failure, pulmonary hypertension, Impella 5.5, mechanical circulatory support, heart transplantation, pulmonary vascular resistance, right heart catheterization, left ventricular unloading, bridge to transplant, retrospective study, Improvement, pulmonary