TAPSE and Tricuspid Annular Longitudinal Velocity by DTI S′

TAPSE and DTI S′ are the most widely used parameters in the routine evaluation of RV systolic function. They represent a measure of RV longitudinal shortening that accounts for the majority of global RV systolic function, and they are easy to obtain, are highly reproducible, and showed good correlation with cardiac magnetic resonance (CMR) RV ejection fraction (RVEF) ( Table 1 ). However, they quantify the displacement and the longitudinal velocity of excursion of the tricuspid annulus, respectively, predominantly reflecting the function of the basal segment of the RV free wall and assuming it as representative of RV global function; this assumption may not be valid when regional dysfunction is involved. Despite the prognostic value that is established, this element limits the sensitivity and prognostic efficacy in some settings, such as RV myocardial infarction (MI), compared with other parameters that allow a global evaluation of RV function, such as 3D ejection fraction and strain. More important, they are angle and load dependent. Thus, these parameters are valid screening tools for the evaluation of RV systolic function, but because of their limitations, they should be used in conjunction with other measurements for accurate interpretation of RV function.

Right-sided Index of Myocardial Performance

RIMP, also known as the Tei index, gives a global estimate of both systolic and diastolic function. It is defined as the ratio between isovolumic time (including both contraction and relaxation time) and RV ejection time; these intervals can be obtained using continuous-wave Doppler or tissue Doppler of the tricuspid annulus. Although its efficacy has been demonstrated in different clinical settings, use of RIMP in daily practice is limited by the need to quantify multiple intervals; this may require acquiring multiple images and require beats with similar R-R intervals. This limit can be overcome by using tricuspid annular tissue Doppler. However, its accuracy can be influenced by loading conditions, elevated right atrial pressures, or atrial fibrillation. Therefore, RIMP should be considered a possible tool for the initial assessment of RV systolic function in certain patients, but always in complement with other parameters.

Fractional Area Change

FAC is considered a useful measurement for the assessment of RV systolic function. It has shown a good correlation with RVEF by CMR, although weaker than strain ( Table 1 ), and it is an independent predictor of adverse outcomes. The reasons for using FAC are that it is a 2D method, it is not affected by angle dependency, and it encompasses both the longitudinal and radial components of RV contraction. Its main limitation is the dependency on image quality, as incorrect tracing of RV area can lead to under- or overestimation of RV function that can be overcome in some patients using echocardiographic contrast agents. Therefore, FAC could be considered a valid and reliable method for the study of patients with suspected or known disease involving RV function, but only when image quality allows a good tracing of endocardial border.

TAPSE and Tricuspid Annular Longitudinal Velocity by DTI S′

TAPSE and DTI S′ are the most widely used parameters in the routine evaluation of RV systolic function. They represent a measure of RV longitudinal shortening that accounts for the majority of global RV systolic function, and they are easy to obtain, are highly reproducible, and showed good correlation with cardiac magnetic resonance (CMR) RV ejection fraction (RVEF) ( Table 1 ). However, they quantify the displacement and the longitudinal velocity of excursion of the tricuspid annulus, respectively, predominantly reflecting the function of the basal segment of the RV free wall and assuming it as representative of RV global function; this assumption may not be valid when regional dysfunction is involved. Despite the prognostic value that is established, this element limits the sensitivity and prognostic efficacy in some settings, such as RV myocardial infarction (MI), compared with other parameters that allow a global evaluation of RV function, such as 3D ejection fraction and strain. More important, they are angle and load dependent. Thus, these parameters are valid screening tools for the evaluation of RV systolic function, but because of their limitations, they should be used in conjunction with other measurements for accurate interpretation of RV function.

Right-sided Index of Myocardial Performance

RIMP, also known as the Tei index, gives a global estimate of both systolic and diastolic function. It is defined as the ratio between isovolumic time (including both contraction and relaxation time) and RV ejection time; these intervals can be obtained using continuous-wave Doppler or tissue Doppler of the tricuspid annulus. Although its efficacy has been demonstrated in different clinical settings, use of RIMP in daily practice is limited by the need to quantify multiple intervals; this may require acquiring multiple images and require beats with similar R-R intervals. This limit can be overcome by using tricuspid annular tissue Doppler. However, its accuracy can be influenced by loading conditions, elevated right atrial pressures, or atrial fibrillation. Therefore, RIMP should be considered a possible tool for the initial assessment of RV systolic function in certain patients, but always in complement with other parameters.

Fractional Area Change

FAC is considered a useful measurement for the assessment of RV systolic function. It has shown a good correlation with RVEF by CMR, although weaker than strain ( Table 1 ), and it is an independent predictor of adverse outcomes. The reasons for using FAC are that it is a 2D method, it is not affected by angle dependency, and it encompasses both the longitudinal and radial components of RV contraction. Its main limitation is the dependency on image quality, as incorrect tracing of RV area can lead to under- or overestimation of RV function that can be overcome in some patients using echocardiographic contrast agents. Therefore, FAC could be considered a valid and reliable method for the study of patients with suspected or known disease involving RV function, but only when image quality allows a good tracing of endocardial border.

PH and Thromboembolic Disease

PH is the common end result in the pathophysiology of a complex cluster of cardiac and noncardiac diseases that result in an increase in flow, resistance, or both in the pulmonary circulation. Two-dimensional STE strain has proved to be the most sensitive tool for the detection of subtle systolic abnormalities in these particular patient populations. In patients with PH, RV 2D STE strain is reduced and shows a great correlation with B-type natriuretic peptide levels, 6-min walking distance, and invasive hemodynamic parameters of RV performance. Similar results have been obtained in patients with acute and chronic thromboembolism, in whom RV strain showed the best correlation with hemodynamic and laboratory parameters compared with conventional measurements. Furthermore, RV strain has been found to represent a powerful predictor of outcomes in these settings. It is a strong predictor of cardiovascular events and death with high sensitivity and specificity ( Supplemental Table 2 , available at www.onlinejase.com ), with the advantage of not being invasive like cardiac catheterization. In further support of the above, in patients who undergo various therapies and who remain free of adverse cardiovascular events, strain values usually improve during follow-up ( Supplemental Figures 1 and 2 and Videos 1 and 2 , available at www.onlinejase.com ), but when low RV strain values persist, this correlates significantly with unfavorable outcomes. Therefore, there is a strong role for strain in the serial assessment of RV systolic function in patients with PH and those with thromboembolic disease, and it could successfully replace other more invasive and costly tests.

Heart Failure

The role of RV systolic dysfunction in the pathogenesis of HF has been recently pointed out. Indeed, in patients with HF with reduced ejection fraction, RV dysfunction has been shown to predict shorter survival. Conventional parameters show a good results in predicting adverse outcomes, especially DTI S′ and a significant correlation with RVEF by CMR, but RV strain has emerged as the most accurate and sensitive tool for evaluation of RV function ( Supplemental Figure 3 and Video 3 , available at www.onlinejase.com ), with a great capability of subclinical RV dysfunction detection. More so, correlation with invasive hemodynamic and clinical functional parameters allows strain to provide an overall better estimation of RV systolic performance. RV strain is a powerful predictor of prognosis, too, and lower values have been associated with death, need for emergency transplantation, and acute HF admissions on short-term follow-up. Furthermore, RV strain provides an incremental prognostic value to left ventricular (LV) ejection fraction in patients with chronic systolic HF. The latter reinforces the fundamental role RV function holds in the natural history of HF and the necessity to detect subtle RV systolic dysfunction as accurately and as early as possible.

However, evidence of RV systolic dysfunction has been obtained not only in patients with HF with reduced ejection fraction, who more frequently show RV involvement, but also in a significant percentage of patients with HF with preserved ejection fraction. It could be due to an increase in RV afterload secondary to chronic pulmonary venous hypertension or to the same comorbidities responsible for the fibrotic processes that alter LV longitudinal function, such as type 2 diabetes, obesity, hypertension, and others, as recently suggested by Morris et al ., who showed that RV strain was reduced in patients with HF with preserved EF compared with asymptomatic control subjects with LV diastolic dysfunction. Conventional parameters showed good results in this subgroup of patients but, as in those with HF with reduced ejection fraction, 2D STE strain obtained better results in detecting subclinical RV alterations, being impaired also in a significant proportion of patients with normal TAPSE, DTI S′, and FAC.

Last, strain is an important tool in risk stratification for RV failure in patients eligible for LV assist device implantation, a fundamental element in the treatment of end-stage HF. Indeed, RV failure is one of the most frequent and dreaded complications of LV assist device placement, and significantly reduced RV strain values obtained before or immediately after implantation can identify those patients who are at higher risk, whereas patients at low risk show higher RV strain at baseline and an improvement of its value at follow-up.

Myocardial Infarction

RV dysfunction is an important determinant of outcomes in patients with MI, even when overt RV infarction is not apparent. Recently, clues of RV involvement in patients with not only inferior but also anterior LV infarcts have been provided by CMR ; these pieces of evidence suggest that RV function should always be evaluated in patients with coronary disease.

In an interesting state-of-the-art review article, Rallidis et al . showed that TAPSE and DTI S′ have moderately good diagnostic and prognostic results in the assessment of RV function in this setting, whereas Møller et al . found that a higher RIMP was a strong predictor of cardiac events, and Anavekar et al . reported that decreased FAC was independently associated with increased risk for poor outcomes. However, all conventional measurements of RV systolic function except FAC have shown weak correlations with CMR RVEF in this setting, whereas RV strain has proved to be the best tool for RV evaluation, as it provides information about global and targeted regional function, with good feasibility and reproducibility. The better performance of 2D strain and FAC could be explained by the fact that TAPSE and DTI S′ quantify the displacement of the basal segment of RV free wall, considered representative of the function of the entire right ventricle, but they are not able to assess the presence of regional wall motion abnormalities; on the other hand, FAC and, even more so, 2D strain provide the evaluation of regional alterations and are representative of all the components of RV systolic function. ( Supplemental Figure 4 and Video 4 , available at www.onlinejase.com ). Last, RV strain was a strong predictor of death, reinfarction, and hospitalization for HF in patients with acute MI, confirming its fundamental role in the evaluation of these subjects.

Arrhythmogenic RV Dysplasia/Cardiomyopathy and Other Cardiomyopathies

Arrhythmogenic RV dysplasia/cardiomyopathy (ARVD/C) is a rare disease, characterized by myocardial atrophy and fibrofatty replacement of the RV myocardium and clinically by a high incidence of ventricular tachycardia or ventricular fibrillation, mostly in young people and athletes. For a definite diagnosis of ARVD/C, current diagnostic criteria include structural features detectable by 2D echocardiography and CMR, the latter considered the gold-standard technique. However, the accuracy of these criteria is not very high, especially in the first stages of the disease. TAPSE and DTI S′ proved to be quite accurate in the diagnosis of RV dysfunction in these patients, but ARVD/C is characterized by inhomogeneous loss of function, so a regional approach to quantitative analysis could be more sensitive to local changes in myocardial function. Indeed, 2D STE strain seems to be superior to conventional parameters in this setting, reaching sensitivity and specificity that in some studies are >90% for a cutoff value <−18%. Reduced strain seems to be able to reveal subtle RV systolic dysfunction in patients with initial stages of ARVD/C and to detect subclinical RV functional abnormalities in asymptomatic carriers of pathogenic ARVD/C mutations, improving the current diagnostic criteria specificity and sensitivity. Unfortunately, as further discussed, authors do not agree about the real feasibility and reproducibility of strain measurements: very high in some studies, significantly lower in others. These discrepancies could be partly explained by differences between groups in the severity of disease; however, further studies are needed to better understand the real limitations of strain measurements.

Recently the role of RV systolic dysfunction has been investigated in other cardiomyopathies, in which the role of RV was previously misunderstood. Hypertrophic cardiomyopathy, for example, is characterized by inhomogeneous myocardial hypertrophy that can be found not only in the left ventricle but quite frequently in the right ventricle too. Between the conventional 2D echocardiography parameters, RIMP and TAPSE have solid evidence for the evaluation of RV function, and higher RIMP and lower TAPSE values have been reported in patients with hypertrophic cardiomyopathy compared with control subjects. On the other hand, some authors reported lower correlation of conventional parameters in this population and suggested the use of 2D STE strain, which was reduced compared with control subjects and had good feasibility (80%) and acceptable reproducibility. Interestingly, as demonstrated in the evaluation of the left ventricle, RV 2D STE strain differentiated between hypertrophic cardiomyopathy and hypertrophy secondary to hypertension, with high sensitivity and specificity. Similar data have been obtained in patients with dilated cardiomyopathy, one of the most common causes of HF. Two-dimensional STE strain is reduced in patients with dilated cardiomyopathy and seems to be able to differentiate between patients with idiopathic dilated cardiomyopathy, in whom the strain values were lower, and ischemic dilatation, whereas the conventional parameters did not differ significantly.

Valvular Heart Diseases

It is well known that mitral and aortic valve diseases involve RV function, causing chronic pulmonary venous congestion, which leads to PH and increased RV afterload, with the subsequent RV dysfunction. Evidence of more or less subtle RV systolic dysfunction has been obtained by several authors by conventional parameters, especially TAPSE, and in recent years by 2D strain. RV dysfunction has been quite prevalent in severe aortic stenosis, with both normal and low gradients, and to have a significant prognostic value, with a severe increase of mortality in patients with TAPSE < 17 mm. Similar results have been obtained in patients with asymptomatic moderate to severe mitral regurgitation and asymptomatic moderately severe to severe aortic regurgitation, in whom RV function quantified at rest by 2D RV strain and during exercise by TAPSE turned out to be a strong predictor of valve surgery.

Between valvular heart diseases, mitral stenosis is the alteration that mostly involves the right ventricle. RV function quantified by conventional parameters was decreased in these patients, whereas 2D STE strain seems to show a peculiar regional pattern, with a significantly lower segmental strain at the septum and basal RV free wall but normal strain values at the mid and apical RV free wall. There is not a widely shared explanation for these characteristic asymmetric regional abnormalities. Because RV dysfunction is related to RV overload and not to reduced RV contractility, some authors have suggested that the septum is affected by moderate degrees of PH, while severe degrees of PH are required to affect the RV free wall; the moderate PH reported in these subjects may not be enough to reduce strain in all segments of the RV free wall, affecting only the basal segment, more sensitive to RV overload. This theory seems to be further supported by the evidence that balloon mitral valvuloplasty significantly improves RV GLS within 24 hours, probably because the relief of the LV inflow obstruction and consequently the decrease in the RV afterload represents a major contributing factor in the improvement of the RV function. On the other hand, some other authors that studied mild mitral stenosis suggested that RV systolic dysfunction could be due to rheumatic process directly affecting interventricular septum that is in continuity to mitral apparatus, whereas RV free wall contractility is spared. However, this theory does not seem to explain the significant changes in RV function after balloon mitral valvuloplasty. From the above, it seems quite clear that RV function is an important element in patients with valvular heart diseases and it has to take into account in the management of these subjects. Moreover, RV function was a strong predictor of outcomes after cardiac surgery. However, although conventional parameters seem to be equivalent to deformation measurements in the assessment of risk for mortality or need of valve surgery, among RV systolic indices, only 2D free wall longitudinal strain was strongly associated with patient outcomes after mitral or aortic valve surgery or coronary artery bypass graft. This evidence is of particular interest, because the authors found that the 34% of patients with normal FAC but abnormal RV longitudinal strain were at higher risk for postoperative mortality, demonstrating that conventional parameters are less effective in this setting compared with 2D strain.

An important issue that must be considered in the assessment of RV function is the characteristic changes of RV longitudinal function reported after cardiac surgery. The peculiar element is that despite the reductions in all the parameters estimating longitudinal function, including conventional parameters and 2D longitudinal strain, global RV function quantified by 3D ejection fraction or by CMR ejection fraction seems to be normal. Different causes have been proposed to explain the impairment of RV longitudinal function, including intraoperative ischemia, poor protection during cardiopulmonary bypass, and postoperative adherence of the right ventricle to the thoracic wall; however, the evidence that pulmonary pressures are usually reduced after surgery and, in patients, no signs or symptoms of RV failure are usually present both before and after surgery seem to be coherent with the finding of a normal RVEF and suggests the hypothesis that the loss in RV performance could be due to geometric changes in the RV chamber after pericardial disruption and not to a true dysfunction; it would mean that 2D indices may be inadequate for the postoperative assessment of RV function. By now, this latter statement is quite widely shared, and the current 2015 recommendations suggest the use of 3D RVEF in this particular setting, defining the other parameters “no longer representative of overall RV performance.”

RV 2D STE Strain: A Technique with Many Pitfalls

Although many authors have expressed an increased interest in using 2D strain analysis for the assessment of RV systolic function, this technique has several limitations that should be kept in mind.

First, 2D strain software currently used was originally created for the assessment of LV systolic function and only later adapted for the right ventricle. However, LV geometry and spatial orientation are different from RV ones: RV chamber shape is more complex, with the inflow and outflow portions in different planes and a thin RV wall that makes it difficult to limit the width of the region of interest to the myocardium, excluding the pericardium, and to track speckles from frame to frame, especially when the images are not excellent. The image quality is a fundamental requirement to consider the evaluation by 2D STE strain reliable, and this is one of the most common limitations in the everyday routine, in which a substantial percentage of patients are affected by obesity, lung diseases, and so on, that can substantially reduce 2D strain feasibility ( Figure 3 ). Furthermore, software originally designed for analysis of LV strain must be “tricked” to calculate RV strain, as the images are inverted compared with LV assessment; as a result, the bull’s-eye figures are not relevant, because they are designed for the LV, and it makes the evaluation of regional alterations of systolic function less immediate and easy.

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