RV dysfunction is associated with reduced systemic parasympathetic activity in patients with PAH, with an inadequate adaptive response of the cholinergic system in the RV. Enhancing parasympathetic activity by PYR improved survival, RV function, and pulmonary vascular remodeling in experimental PH.

While beta-blockers are considered contraindicated in pulmonary arterial hypertension (PAH), the prognostic significance of sympathetic nervous system over-activity suggests a potential benefit of beta-blocker therapy. The aim of this randomised, placebo-controlled, crossover, single centre study was to determine the effects of bisoprolol on right ventricular ejection fraction (RVEF) in idiopathic PAH (iPAH) patients. Additional efficacy and safety parameters were explored.Patients with optimally treated, stable iPAH (New York Heart Association functional class II/III) were randomised to placebo or bisoprolol. Imaging and functional measurements were performed at baseline, crossover and end of study.18 iPAH patients were included, because inclusion faltered before enrolment of the targeted 25 patients. 17 patients completed 6 months of bisoprolol, 15 tolerated bisoprolol, one patient required intravenous diuretics. Bisoprolol was associated with a lower heart rate (17 beats per minute, p=0.0001) but RVEF remained unchanged. A drop in cardiac index (0.5 L·min(-1)·m(-2), p=0.015) was observed, along with a trend towards a decreased 6-min walking distance (6MWD).Although careful up-titration of bisoprolol was tolerated by most patients and resulted in a decreased heart rate, no benefit of bisoprolol in iPAH was demonstrated. Decreases in cardiac index and 6MWD suggest a deteriorated cardiac function. The results do not favour the use of bisoprolol in iPAH patients.

In pulmonary arterial hypertension (PAH), right ventricular (RV) adaptation is essential to overcome the chronic increases in RV pressure overload. Ultimately, RV compensatory mechanisms are not sufficient and patients succumb to RV failure. The processes underlying the transition of RV adaptation to RV failure are not well understood. In this review, we propose that important insights in RV adaptation processes can be obtained by comparing different etiologies of PAH, namely patients with PAH secondary to Eisenmenger syndrome, patients with PAH secondary to systemic sclerosis and patients where no cause is identified: idiopathic PAH. Although the amount of RV afterload does not differ between these patient groups, their prognosis is distinctly different. We will show that an adaptive RV phenotype, as is observed in Eisenmenger patients, coincides with RV hypertrophy, increased RV contractility, low RV fibrosis and low RV diastolic stiffness. Whereas a phenotype of RV failure, as is observed in patients with PAH-secondary to systemic sclerosis, is characterized by impaired contractile reserve, RV fibrosis and RV diastolic stiffness.

Although RVFAC, TAPSE, FTWM, and FLWM were significantly correlated to CMRI-derived-RVEF, all four echo parameters showed a low sensitivity for predicting a deterioration in CMRI-derived RVEF during follow-up. Therefore, RVFAC, TAPSE, FTWM, and FLWM are not suitable parameters for the serial assessment of RV systolic function in patients with precapillary PH.

Right ventricular (RV) function and autonomic dysfunction are important determinants of morbidity and mortality in patients with pulmonary arterial hypertension (PAH). Although successful in animal studies, effects of beta-blocker therapy on RV function in clinical trials were disappointing. To understand this discrepancy, we studied whether beta-blocker therapy changes RV sympathetic activity. Idiopathic PAH (IPAH) patients received beta-blocker therapy (uptitrated to a maximal tolerated dose) and underwent cardiac magnetic resonance imaging, right heart catheterization, and a [ 11 C]-hydroxyephedrine positron emission tomography ([ 11 C]HED PET) scan at baseline to determine, respectively, RV ejection fraction (RVEF), RV pressures, and sympathetic activity.[ 11 C]HED, a norepinephrine analogue, allows determination of sympathetic innervation of the RV. [ 11 C]HED retention index reflects norepinephrine transporter activity. As a consequence of excessive catecholamine levels in the synaptic cleft, this transporter may be downregulated. Therefore, low [ 11 C]HED retention index indicates high sympathetic activity. 13 IPAH patients underwent [ 11 C]HED PET scans at baseline and after bisoprolol treatment. Although heart rate was reduced, systemic modulation of autonomic activity by bisoprolol did not affect local RV sympathetic nerve activity, RV function, or RV wall tension. In PAH patients, RV [ 11 C]HED retention index was lower compared to LV tracer uptake (p<0.01) and was related to systolic wall tension (R 2 ¼ 0.4731, p<0.01) and RV function (R 2 ¼ 0.44, p ¼ 0.01). In RV failure, the tolerated dosage of bisoprolol did not result in an improvement of RV function nor in a reduction in RV sympathetic activity.

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