Two dimensional global longitudinal strain of right ventricle using transthoracic echocardiography can detect right ventricular fibrosis confirmed by 320 slice CT in pulmonary hypertension

Right Ventricular Fibrosis

The role of right ventricular (RV) fibrosis in pulmonary hypertension (PH) remains a subject of ongoing discussion. Alterations of the collagen network of the extracellular matrix may help prevent ventricular dilatation in the pressure-overloaded RV. At the same time, fibrosis impairs cardiac function, and a growing body of experimental data suggests that fibrosis plays a crucial role in the development of RV failure. In idiopathic pulmonary arterial hypertension and chronic thromboembolic PH, the RV is exposed to a ≈5 times increased afterload, which makes these conditions excellent models for studying the impact of pressure overload on RV structure. With this review, we present clinical evidence of RV fibrosis in idiopathic pulmonary arterial hypertension and chronic thromboembolic PH, explore the correlation between fibrosis and RV function, and discuss the clinical relevance of RV fibrosis in patients with PH. We postulate that RV fibrosis has a dual role in patients with pressure-overloaded RVs of idiopathic pulmonary arterial hypertension and chronic thromboembolic PH: as part of an adaptive response to prevent cardiomyocyte overstretch and to maintain RV shape for optimal function, and as part of a maladaptive response that increases diastolic stiffness, perturbs cardiomyocyte excitation-contraction coupling, and disrupts the coordination of myocardial contraction. Finally, we discuss potential novel therapeutic strategies and describe more sensitive techniques to quantify RV fibrosis, which may be used to clarify the causal relation between RV fibrosis and RV function in future research.

Detection of right ventricular myocardial fibrosis using quantitative CT attenuation of the right ventricular myocardium in the late phase on 320 slice CT in subjects with pulmonary hypertension

PURPOSE

Right ventricular myocardial (RVM) fibrosis may be a significant indicator of prognosis in pulmonary hypertension (PH). To detect the presence of RVM fibrosis in PH subjects, we employed ECG gated 320-slice CT.

METHODS

62 confirmed PH subjects (16 males; 55±16years; 45 chronic thromboembolic PH (CTEPH) who underwent conventional non-surgical medical therapy; and 17 pulmonary arterial hypertension (PAH)) underwent ECG-gated 320-slice CT. On CT, RV fibrosis was defined as contrast defect in the early phase and conversely abnormal enhancement in the late phase.

RESULTS

RVM fibrosis was observed in 14 subjects (23%) on CT (CTEPH 22%; PAH 29%; P=0.91). CT attenuation of RVM in the late phase was significantly greater in subjects with RVM fibrosis than in those without (P=0.025). ROC curves of CT attenuation of RVM in the early and late phase, and ratio of CT attenuation of RVM in the early phase/late phase showed AUCs of 0.55, 0.70, and 0.65, respectively. The best cutoff points of 79.5 HU (sensitivity of 50% and specificity of 69% for CT attenuation of RVM in the early phase, P=0.59), 99.5 HU (sensitivity of 50% and specificity of 88% for CT attenuation of RVM in the late phase, P=0.025), and 1.416 (sensitivity of 29% and specificity of 94% for ratio of CT attenuation of RVM in the early phase/late phase, P=0.092) were used to distinguish subjects±RVM fibrosis.

CONCLUSION

Quantitative-measurement of CT attenuation of RVM in the late phase may be able to detect presence of RVM fibrosis in PH subjects.

Echocardiographic assessment of the right ventricle: Impact of the distinctly load dependency of its size, geometry and performance

Right ventricular (RV) size, shape and function are distinctly load-dependent and pulmonary load is an important determinant of RV function in patients with congestive heart failure (CHF) due to primary impaired left ventricular function and in those with pre-capillary pulmonary hypertension (PH). In a pressure overloaded RV, not only dilation and aggravation of tricuspid regurgitation, but also systolic dysfunction leading to RV failure (RVF) can occur already before the development of irreversible alterations in RV myocardial contractility. This explains RV ability for reverse remodeling and functional improvement in patients with post-capillary and pre-capillary PH of a different etiology, after normalization of loading conditions. There is increasing evidence that RV evaluation by echocardiography in relation with its loading conditions can improve the decision-making process and prognosis assessments in clinical praxis. Recent approaches to evaluate the RV in relation with its actual loading conditions by echo-derived composite variables which either incorporate a certain functional parameter (i.e. tricuspid annulus peak systolic excursion, stroke volume, RV end-systolic volume index, velocity of myocardial shortening) and load, or incorporate measures which reflect the relationship between RV load and RV dilation, also taking the right atrial pressure into account (i.e. "load adaptation index"), appeared particularly suited and therefore also potentially useful for evaluation of RV contractile function. Special attention is focused on the usefulness of RV echo-evaluation in relation to load for proper decision making before ventricular assist-device implantation in patients with CHF and for optimal timing of listing procedures to transplantation in patients with end-stage pre-capillary PH.

Modulators of right ventricular apoptosis and contractility in a rat model of pulmonary hypertension

AIMS

Right ventricular (RV) failure is the major cause of death among patients with pulmonary arterial hypertension (PAH). However, the mechanism of RV failure has not been defined.

METHODS AND RESULTS

This study examined mechanisms and consequences of RV myocyte apoptosis and fibrosis in response to PAH. Rats were injected with SU5416 (vascular endothelial growth factor inhibitor), followed by hypoxia for 3 weeks, and subsequently maintained in normoxia for 2, 5, or 14 weeks (5-, 8-, and 17-week time points after the SU5416 injection, respectively). RV systolic pressure (RVSP) was elevated to >70 mmHg at 5-week time point, and this pressure was sustained thereafter. Significant RV myocyte apoptosis and fibrosis were observed at 8- and 17-week time points. Apoptosis was associated with downregulated Bcl-xL (anti-apoptotic protein), downregulated GATA4 (transcriptional regulator of Bcl-xL), and upregulated p53 (negative regulator of GATA4 gene transcription). PAH-mediated RV apoptosis and fibrosis were attenuated in p53 knock-out rats. Despite the major loss of cardiomyocytes, RV contractility was enhanced, suggesting that the remaining myocytes can perform improved contractile functions. Improved RV contractility is associated with the increased expression of contractile and sarcoplasmic reticulum Ca(2+) uptake proteins. In contrast, the expression of calsequestrin 2 (CSQ2) was downregulated. The siRNA knockdown of CSQ2 improved RV contractility and increased the expression of contractile and Ca(2+) uptake proteins.

CONCLUSION

These results suggest that RV decompensation is associated with the death of cardiomyocytes, resulting in fibrosis. However, the remaining myocytes are capable of sustaining RV contractility through the mechanism that involves CSQ2.