Nearly 6.2 million adults (2.2%) in the United States are diagnosed with HF according to the National Health and Nutrition Examination Survey data [1]. End-stage HF carries a high risk of mortality. LVADs have become an important component of the treatment of end-stage HF over the past decades and were shown to improve survival in these patients. LVADs can be used as a bridge to transplantation, a bridge to recovery, or as destination therapy (DT). DT LVAD is used in patients who are not eligible for heart transplantation (HT) [2, 3, 4, 5, 6, 7, 8]. PH after LVAD implantation increases the risk of RVF and this is associated with increased postoperative morbidity and mortality [9, 10, 11, 12].

This article discusses the treatment of PH after LVAD implantation and provides an overview on the pathophysiology, the management of PH in left heart disease (LHD), and the effect of LVAD on right heart hemodynamics.

PH was previously defined as elevated mean pulmonary artery pressure (mPAP) (25 mmHg or more) during right heart catheterization at rest. The cutoff has been recently reduced to 20 mmHg [13, 14, 15]. World Health Organization Group 2 PH (due to LHD) is a known complication of both heart failure with reduced ejection fraction (HFrEF) as well as heart failure with preserved ejection fraction (HFpEF). A pulmonary capillary wedge pressure (PCWP) $>$15 mmHg is typically required for the diagnosis of group 2 PH as it indicates passive pulmonary venous congestion. PCWP of 12–15 mmHg together with high clinical suspicion that increases with exercise can also be seen. There is no consensus in the literature on the exact prevalence of PH in HF patients given the heterogeneous diagnostic tests and criteria. However, the estimated prevalence ranges between 30 to 50%. It’s more prevalent in females, elderly, and in patients with hypertension or metabolic syndrome. With the progression of HF, the prevalence increases to about 70% in advanced HF patients [16, 17, 18, 19, 20, 21, 22, 23].

The pathophysiology of group 2 PH is related to elevated LA pressure that causes an increase in pulmonary venous pressure, PCWP and PH due to retrograde congestion. Additionally, prolonged pulmonary congestion leads to increased pulmonary vascular resistance (PVR) due to pulmonary vascular remodeling where pulmonary artery (PA) adapts to the afterload by an increase in wall thickness and a decrease in lumen diameter (Fig. 1). Histopathology findings in the PA include intimal fibrosis and medial hypertrophy. These changes are thought to be mediated by the imbalance between vasoactive mediators as endothelin (ET)-1 and vasodilative mediators as nitric oxide (NO) and prostacyclin. Transpulmonary pressure gradient (TPG) above 12 mmHg (which is the difference between mPAP and PCWP) indicates the presence of fixed PH. Diastolic pulmonary gradient (DPG), the difference between diastolic PA pressure and PCWP, can be used to divide group 2 PH into isolated postcapillary PH where DPG is 7 mmHg and postcapillary PH with a precapillary component where DPG is $\ge$7 mmHg [24, 25, 26, 27, 28, 29, 30]. The degree of PH is related to LHD severity and duration. Longstanding PH results in RVF and it is associated with poor outcomes in these patients [31, 32, 33, 34, 35, 36].

Fig. 1.

Right heart hemodynamic consequences of left side heart failure. (A) Physiologic flow from the right ventricle to the left side through pulmonary circulation. (B) In left side heart failure, there’s a backward pressure transmitted from elevated filling pressure to pulmonary circulation with eventual right ventricular failure. LA, left atrium; LV, left ventricle; MPAP, mean pulmonary artery pressure; PCWP, pulmonary capillary wedge pressure; PH, pulmonary hypertension; PVR, pulmonary vascular resistance; RA, right atrium; RV, right ventricle.

There are anatomic and morphologic differences that exist between the RV and LV. The RV has a thinner wall and less muscular mass, mainly contracts longitudinally, unlike the LV which has strong transitional and rotational contraction forces. Normally, the RV pumps blood into a low pulmonary pressure circuit, and is able to keep output flow with an energy cost of about one-fifth of the LV which has to overcome the higher systemic pressure. Thus, the RV is more sensitive than the LV to afterload elevation and it cannot adapt to it. Additionally, there exists an interdependence between both ventricles through the interventricular septum, where LV contractility contributes nearly half of the RV work, particularly in the final twisting effect. With advanced left sided HF, elevated filling pressure transmits to the pulmonary circulation and RV. Additionally, chronic volume overload, subsequent pulmonary artery remodeling and increased PVR further increase the afterload. The RV compensates for the elevated pressure by hypertrophy, then it undergoes remodeling and dilation which eventually leads to significant reduction in the RV output and RV failure [37, 38, 39, 40, 41, 42].

Historically, it was thought that an LVAD is contraindicated with PH associated with elevated PVR due to presumed increased risk of RVF [43]. However, the LVAD has been proven to be an effective therapy for end-stage HF and related PH. It can also improve the eligibility for HT as the chronic unloading of the LV may promote reversal of PVR elevation, thus reducing PH to an acceptable range for heart transplantation [44, 45, 46, 47, 48]. The effect of the LVAD on PA pressure and RV function has been an area of interest in the past decade [12, 49, 50]. Persistent PH after LVAD implantation increases the risk of RVF which is one of the most challenging complications of LVAD therapy, particularly early after implantation [13, 51]. Some studies have found an association between the increased preoperative PVR and the development of RVF after LVAD implantation [52], while other studies have failed to prove the same association [53, 54].

During the perioperative period, preexisting PH can be exacerbated by LVAD implantation. Possible contributing factors include the ischemia during cardiopulmonary bypass (CPB), protamine reversal, blood transfusion, physical compression of the pulmonary vessels, and pulmonary vasoconstriction due to hypercarbia and hypoxia [55]. As described above, the RV is very sensitive to changes in afterload, so postoperative PH frequently results in RVF [51]. Other mechanisms of RV failure after LVAD include volume overload from increased LV output that leads to an increased venous return and decreased RV contractility in the setting of interventricular septum leftward shift and less septal contractility. Additionally, anchoring of the LVAD to the heart apex might alter the final twisting pattern of the heart’s contraction. Acute ischemia in the perioperative period, excessive volume substitution, and arrhythmias can precipitate RVF in these patients. The prevalence of RV failure after LVAD implantation ranges from 4% to 50%. This large variation is likely related to the heterogeneity in the population characteristics and the diversity of RVF definition in the studies [50, 56, 57, 58, 59, 60, 61, 62].

Long-term, LVADs can lower PA pressure via LV unloading with resultant pulmonary decongestion [63, 64, 65, 66] but persistent elevation of PVR remains in over 40% [67, 68, 69]. Some studies on end-stage HF patients with PH who underwent LVAD implantation followed by HT reported a survival rate in these patients comparable to transplant patients with no previous PH [70, 71] albeit confounded by selection and/or survivor biases. The reduction in PA pressure should theoretically improve the long-term RV function and output, as it reduces afterload [72, 73]. However, RV dysfunction has been reported as a sequela of LVAD implantation in multiple studies due to the same mechanisms as early RVF [56, 57].

RVF after LVAD is defined by the Interagency Registry for Mechanically-Assisted Circulatory Support (INTERMACS) as elevation in central venous pressure (CVP) to $>$16 mmHg, as well as clinical manifestations (e.g., peripheral edema, ascites, hepatomegaly, or worsening renal/hepatic function). RVF is stratified by INTERMACS according to the duration of inotropes or vasodilators use, and the need for right-sided mechanical support. RVF is associated with a lower postoperative survival rate (59% vs. 79%) and a longer hospital stay (32 vs. 22 days). The 6 months RVF-associated mortality is 29%, and survivors suffer reduced quality of life and functional capacity [74, 75, 76, 77, 78, 79].

Of note, some studies have found that LVAD recipients who develop RVF requiring RVAD support had lower preoperative PA pressures than those who did not require RVAD support [54, 80, 81, 82] possibly due to the failing RV unable to generate high preoperative pulmonary pressures in the setting of elevated PVR [72, 83].

Multiple medical therapies have been approved for the treatment of group 1 PH or PAH (previously called primary PH) e.g., phosphodiesterase 5 inhibitors (PDE5i), ET receptor antagonists, and prostacyclins. These medications are associated with improvement in pulmonary hemodynamics, RV function and exercise tolerance [84, 85, 86, 87, 88]. The off-label use of these medications is common in group 2 PH [89]. However, there is no proven specific medications for these patients [90]. The main treatment remains managing the underlying LHD and treatment of resultant RVF (e.g., diuretics and inotropes) [91].

Due to the lack of sufficient evidence, current guidelines do not recommend any of the pulmonary vasodilators for the treatment of group 2 PH [91, 92]. A single-center study on 11 patients with LHD-PH showed that sildenafil lowers mPAP and PVR and increases cardiac output (CO) in these patients [93]. Other small studies have replicated the same findings [94, 95, 96]. The PDE5 inhibition to improve clinical status and exercise capacity in HFpEF (RELAX) trial has shown that sildenafil does not improve exercise capacity in patients with HFpEF compared to placebo. RHC hemodynamics were not measured in this trial [97].

Soluble guanylate cyclase (sGC) stimulators and ET receptor antagonists were also studied in patients with group 2 PH. Riociguat, a sGC stimulator, was shown to improve PVR, cardiac index, and stroke volume without reducing mPAP [98]. Randomized controlled trials (RCTs) did not show reduction in clinical adverse events with ET receptor antagonists (bosentan, darusentan or macitentan) [99, 100, 101, 102]. While prostacyclins are considered an acceptable treatment option for group 1 PH, A RCT on epoprostenol use in group 2 PH showed an increased mortality in these patients [103].

Severe PH in patients with LHD is considered a contraindication to isolated HT due to increased risk of RV failure, and the definitive treatment is heart-lung transplantation. Due to the limitations in donor organs, LVADs have been increasingly used for these patients [104, 105, 106, 107, 108].

With the increased use of LVAD for HF patients and PH, several pulmonary vasodilator drugs, including agents used for the treatment of group 1 PH, have been studied for use in post LVAD patients with persistent PH. They can be used either to wean LVAD patients from inotropes or mechanical RV support during the early postoperative period, or as long-term therapy to prevent late RVF. However, there is institutional variation in their use, and no consensus on their benefits versus risks [109]. The 2013 International Society for Heart and Lung Transplantation guidelines for mechanical circulatory support recommend the use of pulmonary vasodilators for the treatment of postoperative RVF after LVAD. The medications include NO, inhaled prostacyclin (Class I, Level of evidence C), and PDE5I (Class IIb, Level of evidence C). These recommendations are mainly based on low quality evidence from small studies and expert opinions [110]. LVAD speed should also be optimized to maximally unload the LV and this can subsequently reduce the PA pressure over time [63, 64, 65, 66].

With the assistance of an experienced librarian, we executed systematic searches of the following databases; PubMed, Ovid Medline, Embase, and Web of Science from January 1995 through December 2021. We used a combination of text words for the main concepts of HF, PH, and LVAD. Studies were limited to those including only patients above the age of 18 with HF who underwent LVAD implantation and received pulmonary vasodilator medications postoperatively. These included RCTs, prospective or retrospective observational cohort studies, and abstracts from major cardiovascular meetings.

We excluded studies that were performed in pediatrics, case reports, studies with less than 10 patients, studies conducted in animals, and studies that are not in English. All abstracts and full-text articles were maintained on the Covidence platform. Two reviewers (MS and FA) independently screened titles and abstracts to determine if they meet the inclusion criteria. The search results included 654 citations including 196 duplicates. A total of 458 were screened. 342 citations were irrelevant and 116 full articles were assessed. 13 studies were included (Fig. 2, Table 1 (Ref. [69, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122])).

Fig. 2.

PRISMA flowchart of pulmonary vasodilators in LVAD study selection. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses; LVAD, left ventricular assist device.

Treatment of RVF post-LVAD implantation is mainly directed toward supportive measures. Pharmacologic treatments include inotropes, diuretics to decrease preload, and pulmonary vasodilators that can reduce RV afterload by decreasing PVR as described above. Arrhythmias should be managed properly to maintain atrial-ventricular synchrony. LVAD speed should be optimized to allow proper positioning of the interventricular septum which helps RV contractility [135]. Despite medical treatment, 4–6% of patients with RVF post-LVAD are unresponsive and these patients require temporary right ventricular assist device support (RVAD) [83, 136]. Options include single lumen cannula RVAD (Biomedicus or TandemLife) or double-lumen cannula RVAD (ProtekDuo® TandemLife), other percutaneous devices (Impella RP® Abiomed), and TandemHeart (TH-RVAD). Biventricular temporary mechanical circulatory support device (veno-arterial extracorporeal membrane oxygenation) may be considered for crashing patients [137, 138]. Renal replacement therapy should be instituted for volume removal in case of concomitant renal failure and unresponsiveness to diuretics [135].

In conclusion, persistent PH and RVF after LVAD implantation have gained increasing interest in literature due to their significant impact on the outcome of these HF patients. Multiple pulmonary vasodilators, either immediately after surgery or in the following months, have shown therapeutic efficacy by offloading the RV, however there is paucity of supporting evidence. Further prospective RCTs are warranted to evaluate the most potent and safest options for these patients, particularly for long-term therapy.

Shelley Hall – advisory board for Abbott, Abiomed, Medtronic, CareDx, Natera.

MS—article conception, design, data collection, and writing. FA—article conception, design, review and editing. SH—article conception, review, editing, and final approval. All authors have read and approved the final version of the manuscript.

Not applicable.

Authors would like to thank Sudha Ramakrishnan, MSIS for her assistance with the literature search.

This research received no external funding.

The authors declare no conflict of interest.