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Simplified three-dimensional spatial approach for improving confidence in reliably measuring left ventricular linear internal dimensions

Nicolosi, Gian Luigia; Antonini-Canterin, Francescob; Pavan, Danielac; Piazza, Ritad

Journal of Cardiovascular Medicine: June 2019 - Volume 20 - Issue 6 - p 367–371
doi: 10.2459/JCM.0000000000000775
Editorial
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aCardiologia, ARC, Policlinico San Giorgio, Pordenone

bCardiologia, Ospedale Riabilitativo di Alta Specializzazione, Motta di Livenza

cCardiologia, ARC, Ospedale Civile, San Vito al Tagliamento

dCardiologia, ARC, Ospedale Civile, Pordenone, Italy

Correspondence to Gian Luigi Nicolosi, MD, Cardiologia, ARC, Policlinico San Giorgio, Pordenone 33170, Italy E-mail: gianluigi.nicolosi@alice.it

Received 16 October, 2018

Revised 18 December, 2018

Accepted 15 January, 2019

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Introduction

Current guidelines indicate that surgery should be considered in asymptomatic patients with chronic severe aortic or primary mitral regurgitation with severe left ventricular dilatation, and specifically when indicated cut-offs are reached or overcome. For asymptomatic severe aortic regurgitation with resting ejection fraction more than 50%, such cut-offs are left ventricular end-diastolic diameter (LVEDD) more than 70 mm or left ventricular end-systolic diameter (LVESD) more than 50 mm (or LVESD >25 mm/m2 body surface area (BSA) in patients with small body size), Class of Recommendation IIa, Level of evidence B.1–4

For asymptomatic severe primary mitral regurgitation, surgery is indicated in patients with left ventricular dysfunction (LVESD ≥45 mm and/or LVEF ≤60%), Class of Recommendation I, Level of evidence B.1,2,5,6 For both types of valvular heart disease, levels of evidence have been updated from C of the 2012 Guidelines2 to B of the 2017 Guidelines.1

Both indications are based on left ventricular linear internal dimensions. The precise, reproducible and reliable measurement of these minor-axis diameters, in diastole and systole, is then critical for clinical decision making and for the follow-up of such patients. Methodological standardization for measuring such diameters is essential for reaching a better confidence in the reliability of such measurements.

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From current guidelines to an integrated simplified three-dimensional spatial approach for left ventricular linear minor-axis internal dimensions measurements

The 2015 Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults recommend that linear internal measurements of the left ventricle (LV) be performed in the parasternal long-axis view.7–10 Values should be carefully obtained perpendicular to the left ventricular long axis and measured at or immediately below the level of the mitral valve leaflet tips.7–10 In this regard, the electronic callipers should be positioned on the interface between the myocardial wall and cavity. Internal dimensions can be obtained with a two-dimensional (2D) echocardiography (2DE)-guided M-mode approach, although linear measurements obtained from 2D echocardiographic images are preferred to avoid oblique sections of the ventricle.7–10 We have, however, to also taken into account some suggestions coming from the 2005 Recommendations for Cardiac Chamber Quantification.9 In fact, it should be recognized that even with 2D guidance, it may not be possible to align the M-mode cursor perpendicular to the long axis of the ventricle, which is mandatory to obtain a true minor-axis.9 This is mostly true when the normal angulation between the LV and the aorta tends to increase. Alternatively then, chamber dimension can be acquired from the parasternal short-axis view using direct 2D measurements or targeted M-mode echocardiography, provided that the M-mode cursor can be positioned perpendicular to the septum and left ventricular posterior wall.9 Measurement of LVEDD and LVESD from M-mode can be guided by parasternal short-axis image, by optimizing the round section of the LV and the medial-lateral beam orientation.9 To reach a better confidence in reliably measuring left ventricular linear internal dimensions such as short-axis diameters, both in diastole and in systole, with the same rules and internal anatomical markers, could be measured not only from the parasternal short-axis view but also from the optimized subcostal short-axis view and from the apical four-chamber view (Fig. 1). In any of the three situations, measurements should be performed, as indicated by the guidelines,7–10 at or immediately below the level of the mitral valve leaflet tips (Fig. 1). These standardized imaging planes in the parasternal (long-axis and short-axis) and the apical four-chambers views were also used previously for quantifying chamber dimensions, according to the guidelines for chamber quantification of the American Society of Echocardiography Recommendations9 and to compare to dual-source computed tomography (DSCT) corresponding measurements.11 This study has revealed a good agreement regarding quantitative assessment of left ventricular dimensions between the two techniques and different views.11

Fig. 1

Fig. 1

The three left ventricular linear internal diameters, measured in this way from the three views (Fig. 1), which are angled around 60° one from the other, allow, in some way, a simplified three-dimensional spatial description of the short-axis internal dimension of the LV, which is symmetrically and uniformly remodelled and dilated in severe chronic aortic and primary mitral regurgitation.12–15

The best reproducibility of measurements of left ventricular diameters in diastole and systole, from M-mode tracings, is obtained at the onset of the QRS of the Electrocardiogram with the leading edge methodology.16 Because of its closer timing relationship to end-systole, it is recommended that the left ventricular systolic dimension be measured at the nadir of septal motion in patients whose septal motion is normal.16 In patients in whom septal motion is abnormal, left ventricular systolic dimension should be measured at the peak of the posterior wall motion.16

Taken in this way, the three diameters should be then very similar, with expected only very small millimetric difference one from the other. Then, the absolute agreement among the three diameters, internal to the same echocardiographic examination, allows one to reach a great quality control and confidence in the reliability of such measurements at any single time of each serial echocardiographic examination. Possible encountered variations of those same dimensions of at least 3 to 5 mm during follow-up, for all three diameters, are usually easily identified, because they are concordant and consistent. The observed variations can then be trusted, considered as reliable and assessed accordingly for clinical decision making.

In fact, interreader and intrareader reproducibility of LVEDD and LVESD have been shown to be good, even in the paediatric population with dilated cardiomyopathy, with the smallest median % error for left ventricular internal short-axis dimensions measurements in diastole and systole.17 In fact, in children with dilated cardiomyopathy, a median % error of 2–3% for interreader and less than 2% intrareader have been reported for LVEDD and LVESD.17

Another important study compared the measurements in the paediatric population obtained in the same individuals by 2D and M-mode techniques in two imaging planes, that is in the parasternal long-axis view and in the parasternal short-axis view.18 Due to the age range of the paediatric population under study (114 healthy individuals aged from 1 to 18 years with a mean age 8.9 ± 4.2 years), the absolute values of LVEDD and LVESD were wide (maximal dimensions for LVEDD were 39.8 ± 6.5 mm, while minimal dimensions for LVESD were 23.9 ± 4.8 mm by the different methods).18 The magnitude of differences among the measurement methods did not vary with individual age, BSA, heart rate or SBP.18 Intraclass correlation coefficients were very high for both intraobserver (≥0.997) and interobserver (≥0.976) reproducibility comparisons between measurements.18 Bland–Altman analysis showed good agreements for 2D and M-mode methods.18 Temporal resolution, however, is limited in 2D methodology and may account for the relatively smaller LVEDD and larger LVESD observed in the study.18 Long-axis methodology may predispose to off-centre or nonperpendicular data acquisition and the potential for dimensional underestimation, particularly in diastole.18 Consistency in methods for assessment of left ventricular dimensions is an important factor for serial comparisons.

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Serial testing and the confidence in assessing significant changes

Current guidelines indicate that all asymptomatic patients with severe aortic regurgitation and normal left ventricular function should be seen for follow-up at least every year.1 In patients with a first diagnosis, or if left ventricular diameter and/or ejection fraction show significant changes or come close to thresholds for surgery, follow-up should be continued at 3- to 6-month intervals.1 Patients with mild to moderate aortic regurgitation can be reviewed on a yearly basis and echocardiography performed every 2 years.1

If small changes are encountered or if there is any doubt on the consistency of measurements of left ventricular internal diameters, a short-term echo control study should be programmed, to confirm the encountered variation and improve the confidence in assessing the observed changes.

From our 20-year database, we identified all asymptomatic patients with severe aortic regurgitation and left ventricular ejection fraction more than 50% and at least two echocardiograms at least 1 year apart.19 The study included 84 patients (52 ± 18 years, 61 men) followed-up for 7.1 ± 5.1 years. Left ventricular diameters were measured by 2D echocardiography-guided M-mode from the parasternal short-axis view at the mitral chordae level.19,20 The rate of change of left ventricular diameters was very small (0.5 ± 2.4 mm/year for LVEDD and 0.4 ± 2.8 mm/year for LVESD) and similar both in individuals with and without severe left ventricular dilatation at baseline.19 Moreover, in all 32 patients who underwent surgery during follow-up, postoperative left ventricular dimensions recovered and were not significantly different between the two subgroups with and without severe left ventricular dilatation at baseline.19 Our findings failed to confirm previous results that have identified the increased dimensions of LV as a predictor of worse postoperative outcome, giving more importance to the stability of serial assessment of left ventricular dimensions and to the derived individual clinical decision.19 Intraobserver variability of LVEDD and LVESD was, respectively, 1.1 ± 2.2, and 1.2 ± 2.5%. The interobserver variability for LVEDD and LVESD was, respectively, 2.8 ± 4.6 and 6.1 ± 8.6%.19

Current guidelines indicate that asymptomatic patients with severe primary mitral regurgitation and LVEF more than 60% should be followed clinically and echocardiographically every 6 months, ideally in the setting of a Heart Valve Center.1 Closer follow-up is indicated if no previous evaluation is available and when measured variables show significant dynamic changes or are close to the thresholds.1 Asymptomatic patients with moderate mitral regurgitation and preserved left ventricular function can be followed on a yearly basis and echocardiography should be performed every 1–2 years.1

If small changes are encountered or if there is any doubt on the consistency of measurements of left ventricular internal diameters, a short-term echo control study should be programmed to confirm the encountered variation and improve the confidence in assessing the observed changes.

Serial measurements obtained analysing pre- and postoperative echocardiograms (n = 454) acquired from 108 consecutive patients with chronic mitral regurgitation who underwent mitral valve surgery allowed demonstrating that the left ventricular diastolic diameter was 4 mm smaller on postoperative than preoperative examinations.21 This further supports our contention that even small changes of left ventricular internal diameters can be assessed in serial examination.

We realize that what is lacking is the formal proof of this concept in a prospective study, even though the daily personal experience of the authors is supporting this approach. This should be clearly considered as a limitation. On the contrary, it is clear from the published guidelines and comparison between computed tomography (CT) and echocardiographic techniques7–11 that all the three short-axis dimensions are strictly related and considered somewhat interchangeable, if measured following reported standardized rules and optimized approach, due to the symmetrical and uniform dilatation and spherical changes of the geometry of the LV in chronic aortic regurgitation and mitral regurgitation.12,13 We have also to remember that the reproducibility of linear M-mode measurements following guidelines is very good, allowing even long-term follow-up and comparison between subsequent examination.19,21 Furthermore, measuring absolute values and looking at variability for each of the three described diameters from the different three windows (Fig. 1) during the same echocardiographic examination can generate an immediate direct internal comparison within the same LV, allowing an outstanding quality control of the same measurements.

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Conclusion

Current guidelines indicate that surgery should be considered in asymptomatic patients with chronic severe aortic or primary mitral regurgitation with severe left ventricular dilatation, and specifically when indicated cut-offs are reached or overcome. Both indications are based on left ventricular linear internal dimensions. The precise, reproducible and reliable measurement of these minor-axis diameters, in diastole and systole, is then critical for clinical decision making and for the follow-up of such patients. Methodological standardization for measuring such diameters is essential for reaching a better confidence in the reliability of such measurements.

To reach a better quality control and confidence in reliably measuring left ventricular linear internal dimensions, such minor-axis diameters, both in diastole and in systole, could be measured not only from the parasternal short-axis view but also from the optimized subcostal short-axis view and from the apical four-chamber view. The three left ventricular linear internal minor-axis diameters, measured in this way from the three views, which are angled around 60° one from the other, allow a reliable simplified three-dimensional spatial description of the minor-axis dimension of the LV, which is symmetrically and uniformly remodelled in severe chronic aortic and primary mitral regurgitation. Immediate direct comparison can be made among the three diameters. Possible variations of those dimensions during follow-up can then be more easily and consistently identified with the described methodology. Furthermore, those changes can be considered as reliable and assessed accordingly for clinical decision making. The assessment of serial echocardiogram in the same patient by the same observer should reduce variability and improve reliability of the observed changes.

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Acknowledgements

Conflicts of interest

All authors have made substantial contributions to all of the following: the conception and design of the study, the analysis and interpretation of data, drafting the article and/or revising it critically for important intellectual content and final approval of the version to be submitted.

No funding was required for the present study nor any conflict of interest was present for each one of the authors.

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