Advertisement

Journal of Nuclear Cardiology

, Volume 26, Issue 1, pp 233–235 | Cite as

Assessing LV remodeling in nuclear cardiology

  • Guido GermanoEmail author
  • Piotr J. Slomka
Editorial
  • 470 Downloads

The concept of “cardiac remodeling” was first introduced in the 1970s to describe the structural changes in left ventricular (LV) volume subsequent to a large myocardial infarction,1 but can also be related to other processes, particularly congestive heart failure (CHF) caused by diabetes mellitus, hypertension, valvular disease, kidney disease, or advanced age.2-4 Considering that about 50% of heart failure patients (HFP) have preserved LV ejection fraction (EF)5 and that many have normal myocardial perfusion, it makes sense for nuclear imaging techniques aimed at the diagnostic assessment and monitoring of such patients to also evaluate alternative cardiac parameters, such as diastolic function and ventricular shape/size.

Most imaging approaches to measuring LV geometry have been reported in echocardiography, often for the purposes of monitoring post-infarction remodeling and assessing response to therapy with angiotensin-converting enzyme inhibitors, beta blockers, and angiotensin receptor blockers.6-10 However, almost all echocardiographic descriptions of geometric changes have been two-dimensional (2D), failing to take into account the actual three-dimensional (3D) nature of the LV.11-14 In contrast, myocardial perfusion imaging using SPECT or PET is an intrinsically 3D technique, and is ideally suited to accurately, reproducibly and automatedly measure parameters of LV size and shape.15,16 The paper published in this issue of the Journal by Gimelli et al.17 investigates the usefulness of a specific parameter of LV shape as a potential additional marker of multivessel coronary artery disease (CAD), in a population of 343 patients with normal EF undergoing gated 99mTc-tetrofosmin SPECT on a new-generation, Cadmium-Zinc-Telluride (CZT) cardiac camera.

The measurement of LV eccentricity (eccentricity index, EI) used by Gimelli et al. is three-dimensional, but global in nature—in other words, the 3D maximal count mid-myocardial surface of the LV is fit to an ellipsoid, whose major axis b and minor axes a and c are used to compute the index according to the equation:
$$ {\text{EI}} = \sqrt {1 - \frac{a*c}{{b^{2} }}.} $$
(1)
If the minor axes have the same length, the ellipsoid can be considered as an “ellipsoid of revolution” obtained via a rotation around its major axis, and the previous equation can be simplified as
$$ {\text{EI}} = \sqrt {1 - \frac{{a^{2} }}{{b^{2} }}.} $$
(2)
This type of ellipsoid is also called a spheroid, and is in fact closer to a sphere the closer a is to b (Fig. 1)—for a perfectly spherical LV, a = b and EI = 0.
Figure 1

Best-fit ellipse to a horizontal long-axis image from a Flurpiridaz F-18 PET study. The ellipsoid obtained by rotating the ellipse around b is usually prolate since b > a, but becomes more spherical the closer in length a is to b

Figure 2

Calculation of the LV’s SI by use of the maximum short-axis (A) and long-axis (B) dimensions of the LV cavity, automatically and independently calculated by software18 (Reproduced with permission)

Another parameters measuring LV eccentricity, the shape index (SI or LVSI) is more regional in nature, as it is defined as the ratio of the maximum short-axis dimension A of the LV cavity to the long-axis dimension B, from the endocardial apex to the center of the valve plane (Fig. 2).18
$$ {\text{SI}} = \frac{{A_{\hbox{max} } }}{B} $$
(3)

Thus, local “bulging” of the LV can be captured and will be reflected in a higher SI, whose numeric value (contrary to the EI) will be closest to 1 when the LV is most spherical. While this approach could be potentially affected by perfusion defects, the myocardial surface-estimating algorithm’s ability to ensure the continuity of surface gradients even in the complete absence of myocardial uptake makes it less of a concern.15

Of note, both the EI and the SI can be calculated for ungated images as well as for the individual phases of gated acquisitions, with the end-systolic measurement having been reported as most significantly correlated with hospitalization for CHF in subgroups with and without LV dysfunction.18 The investigation by Gimelli et al. presumably focused on the ungated EI, but since all acquisitions were gated it should be straightforward to extend the analysis to the end-systolic and end-diastolic frames, perhaps using both EI and SI.

Employing EI or SI as a marker of severe and extensive, multivessel CAD would be most useful in cases of triple-vessel disease with balanced reduction of flow, since SPECT is a technique that assesses myocardial hypoperfusion relative to the LV’s highest uptake region. The specific CZT SPECT camera used in Gimelli’s study is potentially capable of overcoming this limitation and directly measure coronary flow reserve (CFR) via “dynamic acquisition,” but that protocol is still not generally used in clinical practice, and remains at this time most commonly done with PET. As far as SPECT is concerned, however, other parameters (such as summed perfusion scores, LV cavity volumes, and transient dilatation (TID)) could have been helpful in identifying multivessel CAD, and it would have been interesting to see if EI or SI had incremental value over them.

As mentioned before, LV remodeling has been traditionally measured with echocardiographic techniques in order to assess serial changes in LV geometry, either in conjunction with clinical trials of new therapies for heart failure and other cardiovascular diseases, or post-infarction. Echocardiographic classifications of remodeling make ample use of the ratio of LV myocardial thickness to cavity radius, also termed relative wall thickness (RWT), as well as the end-diastolic cavity volume and the LV myocardial mass.2 The relatively low spatial resolution of nuclear cardiology images is not particularly well suited to measuring “small” structures such as myocardial thickness and mass,16 but LV cavity volumes as well as TID, shape, and diastolic function can be quantified with a high degree of precision. In this context, LV parameters such as the eccentricity index and the shape index can be an important addition to the armamentarium of highly diversified quantitative measurements provided by nuclear cardiology techniques, with potential future application to patient subpopulations (diabetics, hypertensives, etc.) in which early LV remodeling may be of particular interest and significance.

Notes

Disclosure

The authors receive royalties from Cedars-Sinai Medical Center for algorithms incorporated in commercially distributed software that performs automatic quantification of perfusion, function and other cardiac parameters, including LV shape.

References

  1. 1.
    Eaton LW, Weiss JL, Bulkley BH, Garrison JB, Weisfeldt ML. Regional cardiac dilatation after acute myocardial infarction: recognition by two-dimensional echocardiography. N Engl J Med 1979;300:57-62.CrossRefGoogle Scholar
  2. 2.
    Gaasch WH, Zile MR. Left ventricular structural remodeling in health and disease with special emphasis on volume, mass, and geometry. J Am Coll Cardiol 2011;58:1733-40.CrossRefGoogle Scholar
  3. 3.
    Paulus WJ, Tschope C. A novel paradigm for heart failure with preserved ejection fraction comorbidities drive myocardial dysfunction and remodeling through coronary microvascular endothelial inflammation. J Am Coll Cardiol 2013;62:263-71.CrossRefGoogle Scholar
  4. 4.
    Morgan S, Smith H, Simpson I, Liddiard GS, Raphael H, Pickering RM, et al. Prevalence and clinical characteristics of left ventricular dysfunction among elderly patients in general practice setting: Cross sectional survey. Br Med J 1999;318:368-72.CrossRefGoogle Scholar
  5. 5.
    Maeder MT, Kaye DM. Heart failure with normal left ventricular ejection fraction. J Am Coll Cardiol 2009;53:905-18.CrossRefGoogle Scholar
  6. 6.
    McKay RG, Pfeffer MA, Pasternak RC, Markis JE, Come PC, Nakao S, et al. Left-ventricular remodeling after myocardial-infarction—a corollary to infarct expansion. Circulation 1986;74:693-702.CrossRefGoogle Scholar
  7. 7.
    Lamas GA, Vaughan DE, Parisi AF, Pfeffer MA. Effects of left ventricular shape and captopril therapy on exercise capacity after anterior wall acute myocardial infarction. Am J Cardiol 1989;63:1167-73.CrossRefGoogle Scholar
  8. 8.
    Konstam MA, Kronenberg MW, Rousseau MF, Udelson JE, Melin J, Stewart D, et al. Effects of the angiotensin-converting enzyme-inhibitor enalapril on the long-term progression of left-ventricular dilatation in patients with asymptomatic systolic dysfunction. Circulation 1993;88:2277-83.CrossRefGoogle Scholar
  9. 9.
    Lowes BD, Gill EA, Abraham WT, Larrain JR, Robertson AD, Bristow MR, et al. Effects of carvedilol on left ventricular mass, chamber geometry, and mitral regurgitation in chronic heart failure. Am J Cardiol 1999;83:1201-5.CrossRefGoogle Scholar
  10. 10.
    Konstam MA, Kramer DG, Patel AR, Maron MS, Udelson JE. Left ventricular remodeling in heart failure current concepts in clinical significance and assessment. JACC-Cardiovasc Imag 2011;4:98-108.CrossRefGoogle Scholar
  11. 11.
    Wyatt HL, Meerbaum S, Heng MK, Gueret P, Corday E. Cross-sectional echocardiography. III. Analysis of mathematic models for quantifying volume of symmetric and asymmetric left-ventricles. Am Heart J 1980;100:821-8.CrossRefGoogle Scholar
  12. 12.
    Thomson HL, Basmadjian AJ, Rainbird AJ, Razavi M, Avierinos JF, Pellikka PA, et al. Contrast echocardiography improves the accuracy and reproducibility of left ventricular remodeling measurements: A prospective, randomly assigned, blinded study. J Am Coll Cardiol 2001;38:867-75.CrossRefGoogle Scholar
  13. 13.
    Knapp WH, Bentrup A, Schmidt U, Ohlmeier H. Myocardial scintigraphy with thallium-201 and technetium-99m-hexakis-methoxyisobutylisonitrile in left bundle branch block: A study in patients with and without coronary artery disease. Eur J Nucl Med 1993;20:219-24.Google Scholar
  14. 14.
    Lessick J, Fisher Y, Beyar R, Sideman S, Marcus ML, Azhari H. Regional three-dimensional geometry of the normal human left ventricle using cine computed tomography. Ann Biomed Eng 1996;24:583-94.CrossRefGoogle Scholar
  15. 15.
    Germano G, Kiat H, Kavanagh PB, Moriel M, Mazzanti M, Su HT, et al. Automatic quantification of ejection fraction from gated myocardial perfusion SPECT. J Nucl Med 1995;36:2138-47.Google Scholar
  16. 16.
    Germano G, Kavanagh PB, Slomka PJ, Van Kriekinge SD, Pollard G, Berman DS. Quantitation in gated perfusion SPECT imaging: The cedars-sinai approach. J Nucl Cardiol 2007;14:433-54.CrossRefGoogle Scholar
  17. 17.
    Gimelli A, Liga R, Giorgetti A, Casagranda M, Marzullo P. Stress-induced alteration of left ventricular eccentricity: An additional marker of multivessel CAD. J Nucl Cardiol 2017. doi: 10.1007/s12350-017-0862-7.Google Scholar
  18. 18.
    Abidov A, Slomka PJ, Nishina H, Hayes SW, Kang XP, Yoda S, et al. Left ventricular shape index assessed by gated stress myocardial perfusion SPECT: Initial description of a new variable. J Nucl Cardiol 2006;13:652-9.CrossRefGoogle Scholar

Copyright information

© American Society of Nuclear Cardiology 2017

Authors and Affiliations

  1. 1.Department of MedicineCedars-Sinai Medical CenterLos AngelesUSA
  2. 2.David Geffen School of MedicineUCLALos AngelesUSA

Personalised recommendations