Pulmonary arterial hypertension (PAH) is a term used to classify a variety of conditions that share in common an injury to the pulmonary vasculature that produces elevations in pulmonary arterial pressure. However, it is the integrity of right ventricular function, rather than the degree of vascular injury, that is the major determinant of symptoms and survival in PAH. The article will review the normal structure and function of the right ventricle and summarize the impact of PAH and its treatments on right ventricular function.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a progressive disease with poor prognosis if not treated. The treatment of choice is surgery with pulmonary endarterectomy. However, a significant percentage of patients are deemed non-operable due to distal distribution of the disease and arteriopathy in the non-occluded areas that is indistinguishable from pulmonary arterial hypertension (PAH). The overlap in clinical presentation, pathological features and pathogenesis between PAH and CTEPH provides a compelling rationale for exploring the efficacy of PAH-targeted therapies in CTEPH. These therapies are often considered for non-operable patients and are also used in operable patients as a bridge to surgery or as post-pulmonary endarterectomy therapy for persistent pulmonary hypertension, despite the fact they are not licensed for CTEPH.Two randomised clinical trials have been performed in non-operable CTEPH patients. The BENEFiT study, with the endothelin receptor antagonist bosentan, did not show improvement in walking distance. Recently, the CHEST-1 trial, with the soluble guanylate cyclase stimulator riociguat, met study end-point and demonstrated significant improvement in walking distance in patients with non-operable CTEPH.There is an urgent need for more randomised clinical trials designed to clarify whether administration of PAH-targeted therapies improves clinically meaningful end-points in various CTEPH populations. KEYWORDS: Drug therapy, pulmonary arterial hypertension, pulmonary vasculature, thromboembolism, vascular remodelling C hronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH) are dyspnoea-fatigue syndromes caused by an increase in pulmonary vascular resistance (PVR) leading to right ventricular failure [1]. CTEPH and PAH have historically been associated with a poor prognosis, but in the majority of cases, CTEPH can now be cured surgically with pulmonary endarterectomy (PEA) [2]. CTEPH is a rare disease with an estimated incidence of 2,500 new cases per year in the USA [3]. Recent follow-up studies in patients presenting with acute pulmonary embolism suggest that CTEPH develops in 0.6-9% of patients having experienced an acute pulmonary embolism [4][5][6][7][8]. However, a significant number of CTEPH patients (25-75%) have no history of acute pulmonary embolism [9][10][11][12]. Therefore, the true incidence of CTEPH is likely to be underestimated by studies

Pulmonary endarterectomy surgery (PEA) offers the possibility of a cure for patients suffering from chronic thromboembolic pulmonary hypertension (CTEPH). Despite growing experience worldwide, the approach and criteria for patient selection remain variable and center- or expert-dependent. A significant proportion of patients with CTEPH may be turned down for PEA for a number of reasons, most frequently over concerns of distal or inaccessible disease. Although traditional preoperative testing and currently available tools are adequate in identifying the presence of proximal disease in CTEPH, they provide only limited information on the status of the microvasculature. Because persistent pulmonary hypertension is the most important determinant of post-PEA outcome, the preoperative identification of patients with CTEPH with concomitant small-vessel disease and/or microvascular disease is crucial. Pulmonary vascular resistance (PVR) is a useful parameter for assessing potential concomitant small-vessel disease. By assessing the relative contribution of small vessels to the PVR, the pulmonary artery occlusion technique represents a promising tool for determining the risk of surgery in patients with high PVR. More information is required regarding the potential value or risk of preoperative medical therapies. Although traditional surgical classification of CTEPH takes place intraoperatively, there is a need for a preoperative classification system and consensus on operability. A preliminary preoperative classification system has been proposed.

Background-Pulmonary thromboendarterectomy (PTE) is the preferred treatment for chronic thromboembolic pulmonary hypertension (CTEPH), but persistent pulmonary hypertension after PTE, as a result of either inaccessible distal thrombotic material or coexistent intrinsic small-vessel disease, remains a major determinant of poor outcome. Conventional preoperative evaluation is unreliable in identifying patients at risk for persistent pulmonary hypertension or predicting postoperative hemodynamic outcome. We postulated that pulmonary arterial occlusion pressure waveform analysis, a technique that has been used for partitioning pulmonary vascular resistance, might identify CTEPH patients with significant distal, small-vessel disease. Methods and Results-Twenty-six patients underwent preoperative right heart catheterization before PTE. Pulmonary artery occlusion waveform recordings were performed in triplicate. Postoperative hemodynamics after PTE were compared with preoperative partitioning of pulmonary vascular resistance derived from the occlusion data.

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