Ventricular dyssynchrony assessed by gated myocardial perfusion SPECT using a geometrical approach: a feasibility study

Simultaneous assessment of left ventricular mechanical dyssynchrony using integrated 13N-ammonia PETMR system: direct comparison of PET phase analysis and MR feature tracking

BACKGROUND

To compare phase analysis with positron emission tomography (PA) and magnetic resonance feature tracking derived myocardial strain (FT) for left ventricular (LV) mechanical dyssynchrony using PETMR system in patients with ischemic heart disease.

METHODS AND RESULTS

Patients who underwent rest-pharmacological stress 13N ammonia PETMR were enrolled. Histogram bandwidth (BW) and phase standard deviation (PSD) were compared to global longitudinal, long axis radial, short axis circumferential, and radial strain (GLS, GRS, SA Circ, and SA Rad) obtained from FT. LV dyssynchrony index (SDI) derived from PA and FT were compared. BW and PSD showed significant correlations with FT (a Pearson's coefficient r = 0.64, P < .0001, and r = 0.51, P < .0001 for SA Circ; r = 0.67, P < .0001, and r = 0.74, P < .0001 for GLS; r = - 0.60, P < .0001, r = - 0.61, P < .0001 for SA Rad; r = - 0.62, P < .0001, and r = - 0.68, P < .0001 for GRS, respectively). Bland-Altman plots for SDI showed a preferable agreement (95% limit of agreement - 0.12 to 0.075, - 0.20 to 0.098, - 0.38 to 0.077, and - 0.37 to 0.032; bias 0.0068 ± 0.056, 0.026 ± 0.068, 0.11 ± 0.088, and 0.13 ± 0.079 for SA Circ, SA Rad, GLS, and GRS, respectively).

CONCLUSION

In simultaneous acquisition using PETMR, comparison of PET phase analysis and MR strain showed a good correlation.

Are SPECT MPI measures of dyssynchrony dyssynchronous?

BACKGROUND

Assessment of left ventricular mechanical dyssynchrony (LVMD) from gated SPECT myocardial perfusion imaging (MPI) aims to aid selection of patients for cardiac resynchronization therapy (CRT), using either the standard deviation of left ventricular phase (PSD) ≥ 43° or phase histogram bandwidth (HBW) of > 38° and > 30.6° in males and females, respectively. We observed dyssynchrony parameters might be affected by test type and alignment.

METHODS

We reviewed 242 patients who underwent gated SPECT MPI with use of the Emory Cardiac Toolbox comparing PSD and HBW at rest and stress for Pearson correlation, and substitutability with Bland-Altman analysis.

RESULTS

There is statistically significant difference in the mean PSD and HBW during rest vs stress (33.4 ± 17.4° vs 20.7 ± 13.5° and 97.7 ± 59.6° vs 59.4 ± 45.4°, respectively, P < 0.001). Proper valve plane alignment rendered smaller values (i.e., less dyssynchrony) in both phase SD and HBW (16.8 ± 13.5) vs (22.2 ± 14.7) (P = 0.011), and (47.0 ± 38.2) vs (60.7 ± 48.0) (P = 0.023), respectively.

CONCLUSION

Proper alignment and test type, particularly low-dose rest vs high-dose stress, should be considered when assessing LVMD using SPECT MPI.

Determinants of left ventricular mechanical dyssynchrony in patients submitted to myocardial perfusion imaging: A cardiac CZT study

BACKGROUND

An interaction between coronary anatomy, myocardial perfusion, and left ventricular (LV) functional parameters in the development of mechanical LV dyssynchrony (LVD) has been suggested. This study examined the correlates of LVD in a large sample size of patients with known or suspected coronary artery disease (CAD) using cadmium-zinc-telluride camera.

METHODS

Six-hundred and fifty-seven consecutive patients who underwent myocardial perfusion imaging (MPI) and coronary angiography were included. Coronary stenosis >70% was considered significant. LV perfusion and functional parameters were computed from MPI images. The presence of significant LVD was evaluated by phase standard deviation and histogram bandwidth.

RESULTS

415/657 (63%) patients had significant CAD. LVD was present in 247 (38%) patients and was associated with the presence of a higher CAD burden (P < .001), more impaired measures of LV perfusion (P < .001), contractile function (P < .001), and larger LV volumes (P < .001). By multivariate analysis, the LV end-systolic volume index (P < .001) and ischemic burden (P < .001) were the strongest predictors of LVD independent of CAD extent and LV systolic dysfunction.

CONCLUSIONS

LVD is frequent in patients undergoing MPI for suspected or known CAD. Its presence is independent of CAD burden and LV systolic dysfunction, but is dependent on the presence of myocardial perfusion abnormalities and LV end-systolic volume.

Comparison between a count-based and geometrical approach for the assessment of left ventricular dyssynchrony using myocardial perfusion scintigraphy

OBJECTIVE

There are two distinct approaches for the assessment of left ventricular (LV) dyssynchrony by myocardial perfusion scintigraphy (MPS). The aim of this study was to compare the performance of the count-based and geometrical approach in clinical data using gated single photon emission computed tomography MPS.

MATERIAL AND METHODS

Group 1 consisted of 113 patients (49 men, 64 women) with normal perfusion [summed rest score (SRS)≤3], normal LV ejection fraction (≥55%), and normal QRS duration (QRSd<120 ms). Group 2 consisted of 89 heart failure patients (79 men, 10 women) with no restriction for SRS, LV ejection fraction ≤35%, and QRSd ≥120 ms. All MPS parameters were obtained from the software Corridor4DM. Dyssynchrony parameters used were time to peak contraction, SD, and bandwidth (BW).

RESULTS

SD and BW were estimated higher (difference group 1: SD 3.0±2.3 and BW 11.3±9.3, P-values <0.001; difference group 2: SD 2.4±4.3 and BW 1.3±17.0, P-value <0.001 and 0.479 respectively) using the count-based approach in comparison with the geometrical method. A significant and good correlation was found between these two methods (R=0.763, 0.902, 0.896 for time to peak contraction, SD, and BW respectively, P-values ≤0.001). SD and BW in both approaches were equally good parameters for differentiating heart failure patients (area under the curve: 0.995-0.998), although using different cut-off values.

CONCLUSION

The count-based approach generally provides a wider phase distribution and subsequently greater SD and BW estimates compared with the geometrical algorithm. These differences result in clinically relevant deviations in normal and cut-off values that have to be recognized when evaluating patients.

Dependence of left ventricular functional parameters on image acquisition time in cardiac-gated myocardial perfusion SPECT

BACKGROUND

Reduction of image acquisition time in single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) examinations has been considered. However, association between left ventricular (LV) functional parameters and acquisition time is unclear.

METHODS

Twenty-four patients referred to one-day stress/rest SPECT MPI examinations were imaged at rest with dual-headed gamma camera. List-mode emission data were processed into sets of cardiac-gated images corresponding to different acquisition times: 20%, 30%, 40%, 50%, 60%, 80%, and 100% of total acquisition time (30 seconds per projection). Image quality was quantitatively evaluated by computing contrast-to-noise ratio. LV volumes, wall motion, wall thickening, and mechanical dyssynchrony were quantified with automatic clinical software (QGS; Cedars-Sinai Medical Center).

RESULTS

A significant negative dependence was found between phase analysis parameter values and image acquisition time. Differences in LV volume parameters were small but statistically significant at relative acquisition times of less than 50%. LV wall motion and wall thickening were found to be robust to the increase of noise.

CONCLUSIONS

Image acquisition time of gated SPECT MPI examination can be reduced to 15 seconds per projection without significantly affecting LV volumes, wall motion, or wall thickening. However, reduction of acquisition time has a significant effect on phase analysis results.

Role of nuclear cardiology for guiding device therapy in patients with heart failure

Heart failure is a dynamic condition with high morbidity and mortality and its prognosis should be reassessed frequently, particularly in patients for whom critical treatment decisions may depend on the results of prognostication. In patients with heart failure, nuclear cardiology techniques are useful to establish the etiology and the severity of the disease, while fewer studies have explored the potential capability of nuclear cardiology to guide cardiac resynchronization therapy (CRT) and to select patients for implantable cardioverter defibrillators (ICD). Left ventricular synchrony may be assessed by radionuclide angiography or gated single-photon emission computed tomography myocardial perfusion scintigraphy. These modalities have shown promise as predictors of CRT outcome using phase analysis. Combined assessment of myocardial viability and left ventricular dyssynchrony is feasible using positron emission tomography and could improve conventional response prediction criteria for CRT. Preliminary data also exists on integrated positron emission tomography/computed tomography approach for assessing myocardial viability, identifying the location of biventricular pacemaker leads, and obtaining left ventricular functional data, including contractile phase analysis. Finally, cardiac imaging with autonomic radiotracers may be useful in predicting CRT response and for identifying patients at risk for sudden cardiac death, therefore potentially offering a way to select patients for both CRT and ICD therapy. Prospective trials where imaging is combined with image-test driven therapy are needed to better define the role of nuclear cardiology for guiding device therapy in patients with heart failure.

On the importance of image gating for the assay of left ventricular mechanical dyssynchrony using SPECT

The potential of SPECT for quantifying left ventricular mechanical dyssynchrony is increasingly appreciated. We sought to examine the incidence and impact of image gating errors on this quantification and to test a possible solution for affected studies.

METHODS

First, to establish whether and how gating error alone could affect the measurement of dyssynchrony, we performed a prospective study in which patients with pacemakers were studied twice: during normal rhythm without gating error and with gating error caused by pacemaker-induced dysrhythmia. Second, to understand the pattern and magnitude of gating error during our typical imaging practice, we retrospectively examined studies from a separate cohort of 64 patients who were referred for dyssynchrony evaluation. Third, to understand whether studies with gating error could be repaired for the purpose of quantifying dyssynchrony, we tested a correction algorithm on the pacemaker-induced dysrhythmia image set to see whether it repaired this set so as to approximate the patients' normal rhythm image data. We subsequently applied this algorithm to the 64-patient cohort.

RESULTS

Pacemaker-induced gating error caused a spurious decrease in dyssynchrony magnitude. Among the 64-patient cohort, similar gating errors were common, and an inverse exponential relationship between gating-error magnitude and dyssynchrony magnitude was observed. The correction algorithm accurately repaired the pacemaker-induced dysrhythmia image set; when it was applied to the 64-patient cohort, the magnitude of the postcorrection increase in dyssynchrony magnitude was proportional to the magnitude of the gating error.

CONCLUSION

Gating errors cause a spurious reduction in SPECT assay of dyssynchrony magnitude. In our standard imaging practice, gating errors were common. Post hoc correction appears to be feasible.

A CMR study of the effects of tissue edema and necrosis on left ventricular dyssynchrony in acute myocardial infarction: implications for cardiac resynchronization therapy

BACKGROUND

In acute myocardial infarction (AMI), both tissue necrosis and edema are present and both might be implicated in the development of intraventricular dyssynchrony. However, their relative contribution to transient dyssynchrony is not known. Cardiovascular magnetic resonance (CMR) can detect necrosis and edema with high spatial resolution and it can quantify dyssynchrony by tagging techniques.

METHODS

Patients with a first AMI underwent percutaneous coronary interventions (PCI) of the infarct-related artery within 24 h of onset of chest pain. Within 5-7 days after the event and at 4 months, CMR was performed. The CMR protocol included the evaluation of intraventricular dyssynchrony by applying a novel 3D-tagging sequence to the left ventricle (LV) yielding the CURE index (circumferential uniformity ratio estimate; 1 = complete synchrony). On T2-weighted images, edema was measured as high-signal (> 2 SD above remote tissue) along the LV mid-myocardial circumference on 3 short-axis images (% of circumference corresponding to the area-at-risk). In analogy, on late-gadolinium enhancement (LGE) images, necrosis was quantified manually as percentage of LV mid-myocardial circumference on 3 short-axis images. Necrosis was also quantified on LGE images covering the entire LV (expressed as % LV mass). Finally, salvaged myocardium was calculated as the area-at-risk minus necrosis (expressed as % of LV circumference).

RESULTS

After successful PCI (n = 22, 2 female, mean age: 57 ± 12y), peak troponin T was 20 ± 36ug/l and the LV ejection fraction on CMR was 41 ± 8%. Necrosis mass was 30 ± 10% and CURE was 0.91 ± 0.05. Edema was measured as 58 ± 14% of the LV circumference. In the acute phase, the extent of edema correlated with dyssynchrony (r2 = -0.63, p < 0.01), while extent of necrosis showed borderline correlation (r2 = -0.19, p = 0.05). PCI resulted in salvaged myocardium of 27 ± 14%. LV dyssynchrony (=CURE) decreased at 4 months from 0.91 ± 0.05 to 0.94 ± 0.03 (p < 0.004, paired t-test). At 4 months, edema was absent and scar %LV slightly shrunk to 23.7 ± 10.0% (p < 0.002 vs baseline). Regression of LV dyssynchrony during the 4 months follow-up period was predicted by both, the extent of edema and its necrosis component in the acute phase.

CONCLUSIONS

In the acute phase of infarction, LV dyssynchrony is closely related to the extent of edema, while necrosis is a poor predictor of acute LV dyssynchrony. Conversely, regression of intraventricular LV dyssynchrony during infarct healing is predicted by the extent of necrosis in the acute phase.