The Right Ventricle in Pulmonary Arterial Hypertension: An Organ at the "Heart of the Problem"

Pulmonary Arterial Hypertension (PAH) is a progressive disease with no cure. A major determinant of outcome is the function of the right ventricle (RV). Unfortunately, progressive RV dysfunction and failure can occur despite PAH-specific therapies. While initial adaptive hypertrophic changes occur to maintain cardiac output and preserve contractile function and reserve, maladaptive changes occur in the RV muscle that contribute to RV systolic and diastolic dysfunction and failure. These include impaired angiogenesis / decreased capillary density with ischemia, fibrosis, cardiomyocyte apoptosis and impaired autophagy, inflammation, enhanced oxidative stress, altered metabolism, etc. Of note, there are no therapies currently approved that offset these changes and treatment of RV dysfunction is largely supportive only. Further patients often do not qualify for bilateral lung transplantation because of co-morbidities such as renal impairment. Thus, a dire unmet need exists regarding the management of RV dysfunction and failure in patients with PAH. In this State-of-the-Art review, we comprehensively outline the unique features of the RV compared to the left ventricle (LV) under normal circumstances and highlight the unique challenges faced by the RV when confronted with increased afterload as occurs in PAH. We provide detailed insights into the basis for the adaptive hypertrophic phase as well as detailed commentary into the pathophysiology of the maladapted dysfunctional state as well as the pathobiological aberrations occurring in the RV muscle that underlines the progressive dysfunction and failure that commonly ensues. We also review comprehensively the evaluation of RV function using all currently employed imaging, hemodynamic and other modalities and provide a balanced outline of strengths and limitations of such approaches with the treating clinician in mind. We outline the current approaches, albeit limited to chronic multi-modal management of RV dysfunction and failure. We further outline new possible approaches to treatment that include novel pharmacologic approaches, possible use of cellular/stem cell therapies and mechanical approaches. This review is directed to the treating clinician to provide comprehensive insights regarding the RV in patients with PAH.