Original ArticlePrediction of all-cause mortality from gated-SPECT global myocardial wall thickening: Comparison with ejection fraction and global longitudinal 2D-strain
Introduction
The prognostic value of myocardial perfusion single photon emission computed tomography (SPECT) for stratification of risk of cardiac deaths and myocardial infarction is well described in patients with suspected or proven coronary artery disease.1, 2, 3, 4 Gated techniques improve SPECT performance and bring additive prognostic value by permitting evaluation of left ventricular volumes and ejection fraction (EF).5, 6, 7 Even in the absence of stress-induced perfusion abnormalities, increase of left ventricular volumes and decrease of EF detected by gated-SPECT provide additional prognostic value.8 Most of these studies were focused on myocardial ischemia or its consequences; and even if normal myocardial perfusion SPECT provided a favorable prognosis value, long-term survival was not free of cardiac events.9 Echocardiographic studies showed that tissue deformation evaluated by two-dimensional strain (automated and quantitative technique from gray-scale images) provides a reliable and reproducible measurement of regional and global left ventricular systolic function.10,11 The three components of myocardial deformation are evaluated by frame-by-frame tracking of individual speckles throughout the cardiac cycle. Recent studies have shown that two-dimensional strain can detect early myocardial impairment in prehypertension 12 or subclinical drug cardiac toxicity,13, 14, 15, 16 even in the absence of alteration of the EF. These findings suggest that EF alteration is a delayed process during myocardial dysfunction and could explain that two-dimensional strain is a superior predictor of outcome to EF.17 Gated-SPECT analysis provides high objectivity, reproducibility, and automatic scoring of wall thickening (WT),18 which has a good correlation and agreement with longitudinal strain (LS) measured by echocardiography.19 WT obtained from gated-SPECT can also predict functional recovery after coronary artery revascularization in patients with ischemic cardiomyopathy.20,21 A recent study has shown, similar to echocardiography, that WT abnormalities can be an early sign of chemotherapeutic cardiac toxicity.22 These results suggest that WT abnormalities, as strain abnormalities, could be an early marker of left ventricular function impairment.
The objectives of the study were to correlate WT by gated-SPECT with echocardiographic measures, including EF, LS, and LRS and to assess their respective value for all-cause mortality.
Section snippets
Study Population
Patients that were referred for myocardial perfusion gated-SPECT with or without known coronary artery disease from March to September 2011 were prospectively included in the study. All patients underwent complete physical exam before inclusion. Exclusion criteria included the following: documented allergies to dipyridamole, asthma, systolic blood pressure <90 mm Hg, decompensated heart failure or acute angina, significant valvular disease, hypertrophic cardiomyopathy, and the possibility to
Baseline Characteristics
Eighty-nine patients were screened for the study. Nine patients (10%) were excluded due to poor acoustic window, 5 (6%) were excluded from the analysis due to poor resolution of 2D echocardiography that did not allow speckle-tracking imaging, and 1 (1%) was excluded due to refusal of gated-SPECT after echocardiography. Baseline characteristics of the 74 patients included are presented in Table 1. Mean SSS was 2.8 ± 5.7. Twelve (16%) patients had myocardial perfusion gated-SPECT ischemia with a
Discussion
This study is the first to demonstrate the prognostic significance of GWT obtained from myocardial perfusion gated-SPECT on all-cause mortality and to compare it with commonly used echocardiographic techniques. We show good overall correlation and agreement of GWT with GLS and GLSR, which are accurate tools for myocardial functional exploration and prognosis evaluation. We show that GWT is an independent prognosticator for all-cause mortality regardless of age and EF, and has a greater
Limitations
Despite the theoretical and intuitive correlation between radial strain and WT, we deliberately studied LS rather than radial strain because LS is more commonly evaluated, sensitive, and reproducible than radial strain.33 Furthermore, GLS was assessed immediately after the peak of stress whereas GWT was assessed 20-30 minutes after the stress, leading to a possible discrepancy in data. However, we find a strong correlation between GWT and echocardiographic measures suggesting that the timing of
New Knowledge Gained
The goal of the majority of the new tools exploring the myocardium is to detect early myocardial injury before macroscopic changes, usually assessed by the left ventricular EF. GWT is well correlated with GLS and GLRS, and is a sensitive tool to provide prognostic information for the prediction of all-cause mortality, even in the absence of myocardial ischemia.
Conclusion
GWT assessed by gated-SPECT is an easy, reproducible, and objective method of exploration of left ventricular systolic function. It is a highly sensitive tool to detect early myocardial systolic dysfunction and brings additional prognostic information, over myocardial ischemia.
Acknowledgments
Authors thank Bernard Estivals and the staff of the department of nuclear medicine of Rangueil for their technical support.
Disclosure
Doctor Lairez has received research support (equipment and software) from Kontron for studies of 2D strain. However, the current study was not supported by those grants.
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