Original Article
Impact of ischemia on left ventricular dyssynchrony by phase analysis of gated single photon emission computed tomography myocardial perfusion imaging

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Abstract

Background

There is increasing awareness of the value of phase analysis of gated tomographic myocardial perfusion imaging in assessing left ventricular (LV) dyssynchrony. A concern repeatedly raised in many studies is whether reversible defects in the stress images “ischemia” could affect the phase-derived standard deviation and bandwidth, the two commonly used dyssynchrony indices. We hypothesized that the stress and rest images should provide comparable information because the images are acquired 1 hour after the tracer injection.

Methods and Results

We studied two groups of patients with normal LV ejection fraction and no fixed perfusion defects. In group-1 (N = 20), the patients had reversible perfusion defects involving > 10% of the LV myocardium and in group-2 (N = 20), the patients had normal images. All patients underwent stress/rest-gated single photon emission computed tomography sestamibi imaging (the stress study was acquired with the lower dose) between January and March 2010. Patients with left bundle branch block or ventricular pacing were excluded. The patients in group-1 had a mean age of 61 ± 9 years, 65% were men, 75% Caucasians, and 70% had known prior coronary artery disease. The size of the reversible perfusion defect was 20 ± 13% (range 11%-50%) of the LV myocardium. The rest and stress phase-derived standard deviation (16 ± 6° vs 18 ± 8° and 16 ± 7° vs. 19 ± 6°) and the rest and stress bandwidth (42 ± 14° vs 46 ± 16° and 45 ± 17° vs 52 ± 12°), respectively, (P= NS for all) were similar in the two groups. The change (stress–rest) in standard deviation and bandwidth in groups 1 and 2 were not statistically significant (0.2 ± 3.1° vs 1.4 ± 4.7°, and 2 ± 13° vs 5 ± 13°, respectively, P= NS). There was no significant change from rest to stress in the standard deviation and the bandwidth in group-1 (P= .8 and .4, respectively) and group-2 (P= .2 and .08, respectively). There was no correlation between the size of the reversible perfusion defect and the change in phase standard deviation or bandwidth (r= 0.07 and 0.12, respectively, P= NS).

Conclusions

The presence of even a large reversible perfusion defect does not alter the indices of mechanical dyssynchrony by phase analysis. Further, comparable information is obtained whether using a low dose or a high dose of the radiotracer.

Introduction

Recently, phase analysis of gated single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) has been introduced as an alternative method to the two-dimensional echocardiography in the evaluation of left ventricular (LV) dyssynchrony.1 The merits of phase analysis have been previously discussed but in summary include the automated nature of the analysis and the high reproducibility.2, 3, 4 In most such studies, the rest images are used to derive the standard deviation and bandwidth. Parenthetically, phase analysis could be performed on previously acquired images as the acquisition technique requires no modification over that used for conventional MPI, another important advantage. There is some concern that the use of stress images may not be reliable especially in the presence of large reversible defects. We hypothesized that since imaging is performed ~1 hour after tracer injection, the stress images should provide comparable information to rest images. A secondary hypothesis tested in the current study is whether the tracer dose affects the phase-derived indices.

Section snippets

Patient Selection

We studied two groups of patients, group-1 (N = 20) had reversible perfusion defects involving > 10% of the LV myocardium and group-2 (N = 20) had normal stress and rest MPI. The other selection criteria were (1) all patients had low dose stress and high dose rest images, (2) both the rest and stress images were obtained with same tracer, (3) all patients had normal LV ejection fraction (EF, >50%) by gated SPECT MPI, (4) none of the patients have any fixed perfusion defects, and (5) none of the

Results

The pertinent data are listed in Table 1. The MPI results are summarized in Table 2. A representative example from group-1 is shown in Figure 1.

The standard deviation and bandwidth were similar in the two groups. The change (stress–rest) in standard deviation and bandwidth in the two groups were not statistically significant (Table 2). There was no significant difference in the rest or stress standard deviation or bandwidth in either group (Table 2 and Figure 2). There was no correlation

Discussion

This is the first study to evaluate changes in mechanical dyssynchrony indices by phase analysis in relation to the presence of reversible perfusion defects. The main findings support our hypothesis that the presence of even a large reversible perfusion defect “ischemia” did not alter the phase-derived standard deviation and histogram bandwidth. Further, comparable data were obtained with use of low dose and high dose of the same radiotracer. This study has important applications, especially in

Conflicts of interest

None.

References (19)

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