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Assessment of right ventricular function
  1. Lynne Williams,
  2. Michael Frenneaux
  1. Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham, UK
  1. Dr L Williams, Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham, B15 2TT UK; L.K.Williams{at}bham.ac.uk

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The right ventricle has traditionally received less consideration than the left ventricle. In recent years this interest has increased with the recognition of the critical role of right ventricular performance in determining the clinical outcome and decision-making in patients with both clinical heart failure and congenital heart disease. In this issue of Heart, Missant et al1 (see online only article on p e15) propose a non-invasive method for assessment of RV contractility that is less load-dependent than currently used techniques and that correlates with invasive pressure–volume assessment of RV function.

The right ventricle is a structurally and functionally complex chamber, with a shape less amenable to geometric simplification for the purpose of volume estimation than the left ventricle, and a heavily trabeculated endocardial surface. In addition, its substernal position makes echocardiographic assessment of its size and function difficult. When assessing RV function, it is necessary to bear in mind that the ventricular septum is an important architectural component of the right ventricle, and myocardial fibre orientation in both the free wall and the septum plays a major role in determining ejection. The RV free wall predominantly contains transverse fibres, whereas the septum contains oblique fibres.2 The oblique orientation of fibres in the LV free wall and septum allows the wringing or twisting required to eject blood into high systemic vascular resistance, whereas the compressive force generated by transverse fibres in the RV free wall is sufficient to eject blood in the low-resistance pulmonary vascular bed under normal conditions. When pulmonary vascular resistance is raised the oblique fibres of the septum assume an increasing importance in determining overall right ventricular function.3 This becomes important in situations of septal hypokinesia/dysfunction or when biventricular dilatation causes a reduction in the obliquity of these fibres. In this setting right ventricular failure may supervene due to loss of function of the oblique septal fibres.4

Echocardiography remains the most widely available tool for assessing RV function. Systolic function can be assessed by both geometric and non-geometric methods. Volumetric ejection fraction based on the area–length or Simpson’s methods can be improved by the use of agitated saline or dedicated ultrasound agents. Echocardiographic ejection fractions correlate well with radionuclide-measured RVEF,5 but tend to systematically underestimate RV volumes as they do not take into account the intense trabeculation of the RV. However, volumetric methods are time-consuming and few patients have images of sufficient quality to allow accurate measurement. The advent of real-time three-dimensional scanning for the calculation of RVEF shows results that compare favourably with MRI,6 but image quality and the availability of 3-D echocardiography limit this technique. Non-geometric methods of assessment do not rely on geometric assumptions and are thus more reproducible. The tricuspid annular plane systolic excursion (TAPSE) provides a simple method for global functional assessment, which, if reduced, is very specific, and an excellent correlation exists between the TAPSE and RVEF as assessed by radionuclide angiography.7 In addition, the advent of tissue velocity imaging allows assessment of peak systolic velocity at the lateral tricuspid annulus as a measure of RV function. The sensitivity of tricuspid annular motion for the detection of early right ventricular dysfunction may be superior to conventional imaging techniques, and it appears that reduced systolic annular velocity is highly predictive of RV dysfunction as measured by radionuclide ventriculography.8 In heart failure patients, the reduction of tricuspid annular systolic velocity is associated with severity of right ventricular dysfunction.8 Systolic time intervals have been used as a measure of both global systolic and diastolic function, most notably in the form of the Tei index or index of myocardial performance,9 which has been validated in congenital heart disease,10 11 primary pulmonary hypertension12 and chronic respiratory disease13 14 and been shown to have prognostic relevance.12 13 All of the above, however, are load-dependent indices of RV function.

Magnetic resonance imaging of the heart does not rely on geometric assumption,1517 provides a method of accurately visualising the complex internal architecture of the right ventricular cavity18 and offers fast data acquisition. Advantages include improved cardiac imaging in patients with poor echocardiographic windows, and improved reproducibility with less variability when compared with echocardiography.19 Time volume curves of the right ventricle can be used to assess both systolic and diastolic function.20 It is now generally accepted that MRI measurements are the gold standard for non-invasive estimation of RV volume, wall mass and function,2125 but, unfortunately, availability is an issue and data is lacking on its prognostic value and use for serial assessment of RV function.

Although strain rate imaging is widely used in experimental and clinical studies as an indicator of both LV and RV function, little data is available on the effect of loading conditions on this measure. Several groups have claimed that strain rate is a strong index of contractility,26 although this has been based on data on the effects of inotropic and chronotropic status only, with no comment on the effects of loading conditions. Vogel et al were the first to put forward the concept that isovolumic indices should be less sensitive to altered loading conditions than ejection phase indices.27 The article by Missant et al in the current issue of this journal appears to support the concept that isovolumic indices are superior to ejection phase indices for the study of RV function. In this study the authors evaluate the sensitivity of myocardial tissue deformation to changes in inotropic state, heart rate and loading conditions in the right ventricle in an animal model, using pressure–volume analysis as the reference method. By utilising inferior vena cava occlusion it is possible to reduce preload and thereby measure stroke work over a range of preloads. It is then possible to generate a ‘preload recruitable stroke work relationship’, the slope of which quantifies contractility of the right ventricle. Data was acquired in the steady state, and during a brief period of IVC occlusion, for assessment of the slope of the preload recruitable stroke work relation. Inotropic state was altered by means of esmolol and subsequently dobutamine infusions. Sensitivity to alterations in preload and afterload were then assessed by means of inferior vena cava occlusion and partial occlusion of the main pulmonary artery respectively. In order to assess the effects of altered heart rate, data was acquired during periods of rapid atrial pacing over a range of heart rates. The authors conclude that both maximum strain rate and isovolumic strain acceleration correlate directly with global contractility of the right ventricle (as quantified by the slope of the preload recruitable stroke work). However, isovolumic strain acceleration appears in this model to be less sensitive to acute changes in loading conditions. This observation is in keeping with previous data which suggests that isovolumic indices of tissue deformation may be a more robust index of global RV function.

In conclusion, echocardiography remains the most widely available non-invasive tool for serial assessment of RV function, albeit with the limitation that the majority of echocardiographic measures are load-dependent. Measures of RV function that are less load-dependent would therefore present an attractive diagnostic option in patients in whom loading conditions vary dramatically over time, making serial assessment more accurate.

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Footnotes

  • Competing interests: None declared.

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