The ASE has highlighted the importance of accurate and reproducible LV and RV measurements with the publication of two recent guidelines. The first provides recommendations for quantitative methods during a pediatric echocardiogram, and the second covers the assessment of the right heart in adults. Taken together, the guidelines provide an excellent review of the available methods for quantitative ventricular function assessment. In the management of congenital heart disease, the evaluation of ventricular performance is frequently complicated by the presence of atypical ventricular morphology. A brief consideration of this problem is provided below using the Who What Where When Why How (WWWWWH) approach to problem analysis.
Who: In pediatric studies, measurement of LV dimensions is recommended as part of a complete examination. Other measures of ventricular function are performed if clinically indicated. In adult studies, the routine assessment of systolic and diastolic function in both the LV and RV is now recommended.
What: No single ventricular performance measurement has been prescribed, and the protocols of pediatric echocardiography laboratories vary. The aforementioned pediatric quantitative guidelines recommend 2D shortening fraction or ventricular volumes for ejection fraction using the biplane Simpson or 5/6 area x length methods. In our clinical laboratory, we routinely report M-mode shortening fraction and 2D or 3D ejection fractions. We regularly measure, but do not usually report, annular tissue Doppler velocities and mitral E/e’ ratio. On the RV, we use tricuspid annular plane systolic excursion (TAPSE) to quantitatively evaluate systolic function.
Where: Whenever possible, we direct quantitative function studies to our main laboratory, which primarily services outpatients. The staffing of this “outpatient” laboratory provides for a greater degree of attending physician supervision and involvement in imaging.
When: Our standard protocol, as described above, is performed as part of all complete studies. When LV ventricular function is the primary indication, we expand our protocol to include imaging for LV myocardial performance index; speckle tracking for longitudinal and circumferential strain and strain rate; 3D ejection fraction, and biplane LA volume. These studies are performed on patients with cardiomyopathy (dilated or hypertrophic), myocarditis, chemotherapy, HIV rheumatic fever, sickle cell anemia, and transplantation (including liver). When our study is focused on RV function—such as those for patients with repaired tetralogy of Fallot or pulmonary hypertension—we will image from a modified apical window for TAPSE, RV fractional area change, RV strain (including parasternal imaging), and biplane RA volume. These additional LV and RV imaging techniques are often analyzed only for research purposes.
Why: The ideal imaging technique for measuring ventricular function should be accurate, reproducible, load-independent, and easy to perform. These measurements should have normal values available for comparison, and multi-center studies should show a correlation between these measures and clinical outcomes.
The advantages and disadvantages of each measurement of ventricular performance were reviewed in the ASE pediatric quantitative guidelines. A limited discussion of these measurements is provided here. Shortening fraction has the advantages of extensive experience, ease of performance, and abundant normative pediatric data. Its disadvantages include load dependence, reliance on normal LV shape, and requirement of a good blood-endocardium border. Ejection fraction is less sensitive to abnormal LV shape, but suffers from the lack of normal pediatric data. The velocity of circumferential fiber shortening is preload independent and can be adjusted for heart rate and after-load. However, it is inappropriate for abnormal LV shape and is time consuming.
Tissue Doppler imaging is reproducible, has good temporal resolution, and benefits from having normal pediatric data. Its disadvantages include angle dependence, load dependence, and inability to differentiate between regional and global wall motion abnormalities. TAPSE is simple, reproducible, and correlates well to RV function in certain clinical situations. However, it is load dependent and has not been fully evaluated in children with congenital heart disease. RV fractional area change has been shown to correlate modestly with ejection fraction by MRI, but not in patients with congenital heart disease. It is also very sensitive to technical limitations in blood-endocardium border detection.
More what: What about the single ventricle? The techniques commented upon can also be used to assess single ventricles, but the disadvantage of abnormal ventricular shape becomes a primary concern. For patients who have undergone a Fontan procedure, diastolic function is more important than systolic function. Systolic and diastolic tissue Doppler velocities have been shown to be abnormal in patients with single ventricles, but the clinical benefit of these measurements has not been demonstrated. Ventricular volumes by 3D echocardiography tend to be smaller than MRI-derived volumes, but 3D ejection fraction correlates well with MRI ejection fraction. DP/dt is geometry independent and relatively after-load independent; but it requires the presence of valvular regurgitation, and is preload and angle dependent. The myocardial performance index, a measure of combined systolic and diastolic function, is geometry independent and has been shown to correlate mildly with functional status in Fontan patients. Its potential to guide clinical care requires additional study.
How: In-depth discussions of these technical factors, i.e., on how to best perform these measurements, are readily available in the literature. Regardless of the preferred technique, clinical usefulness can be best achieved with image optimization and quality assurance. Improvements in accuracy and reproducibility will provide the clinician with confidence that a difference in the measurement is due to a change in ventricular performance rather than technical issues.