Comparison of left ventricular contraction homogeneity index using SPECT gated blood pool imaging and planar phase analysis

Development and evolution of nuclear cardiology and cardiac PET in Canada

Gated radionuclide angiography and myocardial perfusion imaging were developed in the United States and Europe in the 1970's and soon adopted in Canadian centers. Much of the early development of nuclear cardiology in Canada was in Toronto, Ontario and was quickly followed by new programs across the country. Clinical research in Canada contributed to the further development of nuclear cardiology and cardiac PET. The Canadian Nuclear Cardiology Society (CNCS) was formed in 1995 and became the Canadian Society of Cardiovascular Nuclear and CT Imaging (CNCT) in 2014. The CNCS had a major role in education and advocacy for cardiovascular nuclear medicine testing. The CNCS established the Dr Robert Burns Lecture and CNCT named the Canadian Society of Cardiovascular Nuclear and CT Imaging Annual Achievement Award for Dr Michael Freeman in memoriam of these two outstanding Canadian leaders in nuclear cardiology. The future of nuclear cardiology in Canada is exciting with the expanding use of SPECT imaging to include Tc-99m-pyrophosphate for diagnosis of transthyretin cardiac amyloidosis and the ongoing introduction of cardiac PET imaging.

Assessment of left ventricular ejection fraction with cardiofocal collimators: Comparison between IQ-SPECT, planar equilibrium radionuclide angiography, and cardiac magnetic resonance

BACKGROUND

IQ-SPECT has been shown to significantly reduce acquisition time and administered dose while preserving image quality in myocardial perfusion imaging. Whether IQ-SPECT provides accurate left ventricular ejection fractions (LVEF) with gated blood pool SPECT (GBPS) remains unknown.

METHODS

Sixty patients underwent IQ-SPECT GBPS and planar imaging. Among those patients, 11 underwent both cMRI and GBPS. GBPS LVEF, LVEDV, and LVESV were calculated using 2 validated software; QBS (Cedars-Sinai Medical Center, Los Angeles, USA) and MHI (Montreal Heart Institute, Montreal, Canada). LVEF, LVEDV, and LVESV obtained with the different modalities were compared.

RESULTS

Average planar LVEF was 48 ± 11% (mean ± SD), average LVEDV was 177 ± 59 mL (range 63 to 342 mL), and average LVESV was 96 ± 46 mL (range 16 to 234 mL). GBPS LVEF and their correlation coefficient with planar LVEF were 40 ± 12% (r = 0.70) and 44 ± 12% (r = 0.83) with QBS and MHI, respectively. Correlation coefficient between cMRI and planar LVEF was 0.65 and were 0.69 and 0.52 between cMRI and GBPS using QBS and MHI, respectively.

CONCLUSIONS

LVEF calculated with GBPS using IQ-SPECT correlates with planar measurements. Correlation is best using the MHI method and variation is independent of LVEDV.

Phase analysis of gated blood pool SPECT for multiple stress testing assessments of ventricular mechanical dyssynchrony in a tachycardia-induced dilated cardiomyopathy canine model

BACKGROUND

Stress-induced dyssynchrony has been shown to be independently correlated with clinical outcomes in patients with dilated cardiomyopathy (DCM) and narrow QRS complexes. However, the extent to which stress levels affect inter- and intraventricular dyssynchrony parameters remains unknown.

METHODS

Ten large dogs were submitted to tachycardia-induced DCM by pacing the right ventricular apex for 3-4 weeks to reach a target ejection fraction (EF) of 35% or less. Stress was then induced in DCM dogs by administering intravenous dobutamine up to a maximum of 20 μg·kg-1·min-1. Hemodynamic and ventricular dyssynchrony data were analyzed by left ventricular (LV) pressure measurements and gated blood pool SPECT (GBPS) imaging. In order to assess mechanical dyssynchrony in DCM subjects and compare it with that of 8 normal counterparts, we extracted the following data: count-based indices of LV contraction homogeneity index (CHI), entropy and phase standard deviation, and interventricular dyssynchrony index.

RESULTS

A significant LV intraventricular dyssynchrony (CHI: 96.4 ± 1.3% in control vs 78.6% ± 10.9% in DCM subjects) resulted in an intense LV dysfunction in DCM subjects (EF: 49.5% ± 8.4% in control vs 22.6% ± 6.0% in DCM), compared to control subjects. However, interventricular dyssynchrony did not vary significantly between the two groups. Under stress, DCM subjects showed a significant improvement in ventricular functional parameters at each level (EF: 22.6% ± 6.0% at rest vs 48.1% ± 5.8% at maximum stress). All intraventricular dyssynchrony indices showed a significant increase in magnitude of synchrony from baseline to stress levels of greater than or equal to 5 μg·kg-1·min-1 dobutamine. There were individual differences in the magnitude and pattern of change in interventricular dyssynchrony during the various levels of stress.

CONCLUSIONS

Based on GBPS analyses, different levels of functional stress, even in close intervals, can have a significant impact on hemodynamic and intraventricular dyssynchrony parameters in a DCM model with narrow QRS complex.

Value of mechanical dyssynchrony as assessed by radionuclide ventriculography to predict the cardiac resynchronization therapy response

AIMS

To assess the value of mechanical dyssynchrony measured by equilibrium radionuclide angiography (ERNA) in predicting long-term outcome in cardiac resynchronization therapy (CRT) patients.

METHODS AND RESULTS

We reviewed 146 ERNA studies performed in heart failure patients between 2001 and 2011 at our institution. Long-term follow-up focused on death from any cause or heart transplantation. Phase images were computed using the first harmonic Fourier transform. Intra-ventricular dyssynchrony was calculated as the delay between the earliest and most delayed 20% of the left ventricular (LV) (IntraV-20/80) and inter-ventricular dyssynchrony as the difference between LV- and right ventricular (RV)-mode phase angles (InterV). Eighty-three patients (57%) were implanted with a CRT device after ERNA. Median follow-up was 35 [21-50] months. Twenty-four events were observed during the first 41 months. Median baseline ERNA dyssynchrony values were 28 [3 to 46] degrees for intraV-20/80 and 9 [-6 to 24] degrees for interV. Comparing survival between CRT and non-CRT patients according to dyssynchrony status, log-rank tests showed no difference in survival in patients with no ERNA dyssynchrony (P = 0.34) while a significant difference was observed in ERNA patients with high level of mechanical dyssynchrony (P = 0.004).

CONCLUSION

ERNA mechanical dyssynchrony could be of value in CRT patient selection.

The effects of dobutamine stress on cardiac mechanical synchrony determined by phase analysis of gated SPECT myocardial perfusion imaging in a canine model

BACKGROUND

Precise identification of left ventricular (LV) systolic mechanical dyssynchrony may be useful in optimizing the response to cardiac resynchronization therapy in heart failure (HF) patients. However, LV dyssynchrony is mostly measured at rest; patients often suffer from the HF symptoms during exercise.

OBJECTIVES

Our objective was to examine the impacts of stress on LV synchronism with phase analysis of gated SPECT myocardial perfusion imaging (GMPS) within a normal animal cohort.

METHODS

Stress was induced with different levels of dobutamine infusion in six healthy canine subjects. Hemodynamic properties were assessed by LV pressure measurements. Also, LV mechanical synchronism (coordination of LV septal and lateral wall at the time of contraction) was determined by phase analysis of GMPS using commercially available QGS software and in-house MHI4MPI software, with the thickening- and displacement-based method. Synchrony indexes in MHI4MPI included the septal-to-lateral delay and homogeneity index, derived from each of the two methods. Also, bandwidth, SD, and entropy (synchrony indexes) of the QGS software were assessed.

RESULTS

LVEF increased from 36.7% ± 8.7% at rest to 53.67% ± 12.34% at 20 μg · kg(-1) · minute(-1) (P < .001). Also, cardiac output increased from 3.67 ± 1.0 L · minute(-1) at rest to 8.4 ± 2.6 L · minute(-1) at 10 μg · kg(-1) · minute(-1) (P < .001). The same trend was observed for dP/dt max which increased from 1,247 ± 382.7 at rest to 5,062 ± 1,800 mm Hg · s(-1) at 10 μg · kg(-1) · minute(-1) (P < .01). Entropy decreased from 55.2% ± 8% at baseline to 43.5% ± 8.5% at 5 and 43.0% ± 3.7% at 10 μg · kg(-1) · minute(-1) dobutamine (P < .01). Thickening homogeneity index showed a difference from 91.7% ± 5.53% at rest to 98.2% ± 0.75% at 20 μg · kg(-1) · minute(-1) (P < .05).

CONCLUSIONS

Dobutamine stimulation could amplify the ventricular synchronism, and the thickening-based approach is more accurate than wall displacement for assessment of mechanical dyssynchrony in GMPS.

Effects of dobutamine stress on cardiac contraction synchronism in a canine model

In cardiac resynchronization therapy, many devices need to be optimized to take into account the magnitude and characteristics of patients' ventricular mechanical dyssynchrony. The optimization process is mostly performed at rest; however, mechanical resynchronization might be more important under stress, while patients need to improve their cardiac efficiency. The objective of this study was to observe if levels of cardiac stress could modify the ventricular contraction synchronism. Cardiac stress was induced with dobutamine infusion in eight healthy canine subjects. Hemodynamic and ventricular synchronism assessments were performed by left ventricular pressure measurements and radionuclide tomographic-gated blood pools. Cardiac output increased from 2.8 ± 1.0 at rest to 5.7 ± 2.2 L min(-1) at 20 µg kg(-1) min(-1), while the ventricular performance (dP/dtmax) increased from 1588 ± 374 to 8004 ± 710 mmHg s(-1). At baseline, the interventricular delay (in degrees) was -6.3 ± 2.6°, the left ventricle contraction preceding the right. The delay significantly increased to -21.6 ± 3.1° with dobutamine stress (p < 0.0001). On assessment of the left intraventricular synchrony, septal-to-lateral delay was -6.9 ± 5.1° at baseline which revealed a preceded contraction of the left lateral wall from the septum. Cardiac stress produced a significant modulation (p = 0.01), with an inversion of the contraction pattern, the septum contraction preceding the lateral wall contraction by 15.5 ± 5.6° at maximum dobutamine infusion; a significant linear trend (p < 0.001) was found between cardiac stress levels and septal-to-lateral delays. Cardiac activity levels modified the ventricular synchronism supporting the fact that optimizations of cardiac resynchronization devices could be improved by taking cardiac stress into account.

LV dyssynchrony as assessed by phase analysis of gated SPECT myocardial perfusion imaging in patients with Wolff-Parkinson-White syndrome

PURPOSE

The purpose of this study was to evaluate left ventricular (LV) mechanical dyssynchrony in patients with Wolff-Parkinson-White (WPW) syndrome pre- and post-radiofrequency catheter ablation (RFA) using phase analysis of gated single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI).

METHODS

Forty-five WPW patients were enrolled and had gated SPECT MPI pre- and 2-3 days post-RFA. Electrophysiological study (EPS) was used to locate accessory pathways (APs) and categorize the patients according to the AP locations (septal, left and right free wall). Electrocardiography (ECG) was performed pre- and post-RFA to confirm successful elimination of the APs. Phase analysis of gated SPECT MPI was used to assess LV dyssynchrony pre- and post-RFA.

RESULTS

Among the 45 patients, 3 had gating errors, and thus 42 had SPECT phase analysis. Twenty-two patients (52.4%) had baseline LV dyssynchrony. Baseline LV dyssynchrony was more prominent in the patients with septal APs than in the patients with left or right APs (p < 0.05). RFA improved LV synchrony in the entire cohort and in the patients with septal APs (p < 0.01).

CONCLUSION

Phase analysis of gated SPECT MPI demonstrated that LV mechanical dyssynchrony can be present in patients with WPW syndrome. Septal APs result in the greatest degree of LV mechanical dyssynchrony and afford the most benefit after RFA. This study supports further investigation in the relationship between electrical and mechanical activation using EPS and phase analysis of gated SPECT MPI.

SPECT myocardial perfusion imaging for the assessment of left ventricular mechanical dyssynchrony

Phase analysis of gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is an evolving technique for measuring LV mechanical dyssynchrony. Since its inception in 2005, it has undergone considerable technical development and clinical evaluation. This article reviews the background, the technical and clinical characteristics, and evolving clinical applications of phase analysis of gated SPECT MPI in patients requiring cardiac resynchronization therapy or implantable cardioverter defibrillator therapy and in assessing LV diastolic dyssynchrony.

The use of nuclear imaging for cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) has shown benefits in patients with end-stage heart failure, depressed left ventricular (LV) ejection fraction (≤ 35%), and prolonged QRS duration (≥ 120 ms). However, based on the conventional criteria, 20% to 40% of patients fail to respond to CRT. Studies have focused on important parameters for predicting CRT response, such as LV dyssynchrony, scar burden, LV lead position, and site of latest activation. Phase analysis allows nuclear cardiology modalities, such as gated blood-pool imaging and gated myocardial perfusion single photon emission computed tomography (GMPS), to assess LV dyssynchrony. Most importantly, GMPS with phase analysis has the potential of assessing LV dyssynchrony, scar burden, and site of late activation from a single acquisition, so that this technique may provide a one-stop shop for predicting CRT response. This article provides a summary on the role of nuclear cardiology in selecting patients for CRT, with emphasis on GMPS with phase analysis.

SPECT blood pool phase analysis can accurately and reproducibly quantify mechanical dyssynchrony

OBJECTIVES

Phase analysis of SPECT blood pool imaging has the potential to assess mechanical dyssynchrony (MD). However, wall motion of the left ventricle (LV) from SPECT images can be based on either time-activity or time-distance curves. In this paper, these two techniques were compared using receiver-operator characteristics (ROC) analysis at detecting MD patients from a population of normal subjects.

METHODS

SPECT phase analysis was performed on 48 normal subjects (LVEF > 55%, normal wall motion, QRS < 120 ms), and 55 MD patients (LVEF < 35%, QRS > 120 ms). ROC analysis was individually performed on each of three phase parameters (phase standard deviation, synchrony, and entropy) for each LV wall motion technique. ROC area differences were assessed using the Student t-test. Intra- and inter-observer reproducibilities were investigated using regression analysis.

RESULTS

Time-activity-based phase analysis produced excellent ROC areas of .93 or better for all three phase parameters. The time-distance techniques produced significantly (P < .05) lower ROC areas in the range of .53-.76. Time-activity-based phase analysis had excellent intra- and inter-observer reproducibility with correlation coefficients >.96, compared to values of ~.85 for the time-distance methods.

CONCLUSION

SPECT time-activity-based phase analysis had excellent sensitivity and specificity at detecting MD patients with very high intra- and inter-observer reproducibility.

Gated blood-pool SPECT versus cardiac magnetic resonance imaging for the assessment of left ventricular volumes and ejection fraction

BACKGROUND

We evaluated the accuracy of planar radionuclide angiography and different count-based and space-based electrocardiogram (ECG)-gated blood-pool single-photon emission computed tomography (GBPS) algorithms for assessment of left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF) compared with the gold standard of cardiac magnetic resonance imaging (cMRI). The goal is to assess the accuracy of a recently developed GBPS algorithm.

METHODS AND RESULTS

Subjects had planar, GBPS, and cMRI sequentially. Datasets were processed by QBS software (Cedar-Sinai) and by MHI software (Montreal Heart Institute). Space-based approaches were used to compute LVEDV, LVESV, and LVEF. Count-based techniques were also used to assess LVEF. All results were compared to cMRI. Fifty-five patients (85% male; mean age 63 +/- 9 years) completed the study. LVEFs and their correlations to cMRI values were 43 +/- 12% (r = .82), 39 +/- 14% (r = .82), and 39 +/- 13% for MHI(space), QBS(space), and cMRI methodologies, respectively. LVEF by count-based methods also demonstrated good correlation to LVEF provided by cMRI (42 +/- 13%, r = .88 for MHI(count) and 46 +/- 15%, r = .84 for QBS(count)). Strong correlations were obtained for LVEDV (r = .96 for MHI and r = .92 for QBS) and for LVESV (.97 for MHI and r = .94 for QBS).

CONCLUSIONS

All Gated blood-pool SPECT algorithms had significant variation in estimating LVEF. Nevertheless our software provides good estimates of LV volumes and LVEF. Such software may, therefore, be applied to assess LV morphology and function.

Evaluation of ventricular synchrony with equilibrium radionuclide angiography: assessment of variability and accuracy

BACKGROUND AND AIMS

Equilibrium radionuclide angiography (ERNA) has become an established method for assessing cardiac function. However, limited data are available to evaluate ventricular synchrony with ERNA. The aim of this study was to assess the variability and accuracy of ERNA to evaluate ventricular synchrony by means of phase images in healthy individuals and to compare them with a group of subjects with left bundle-branch block (interventricular dyssynchrony, LBBB) and with a group of patients with nonischemic, dilated cardiomyopathy (DCM) (inter- and intraventricular dyssynchrony).

METHODS

The population was divided into groups as follows: group 1 included 22 healthy subjects, group 2 included 11 patients with LBBB and normal left ventricular ejection fraction (LVEF), and group 3 included 14 DCM patients with LVEF <35% and LBBB. Interventricular synchrony was measured as the difference between LV mean phase angle (mPA) and RV mPA (LV-RV mPA). Intraventricular synchrony for each ventricle was measured as the standard deviation (SD) of the RV mPA and LA mPA blood pools.

RESULTS

Intra- and interobserver correlation coefficients were high for both inter- and intraventricular synchrony parameters. Area under the curve (AUC) was 0.98 for LV-RV mPA (p <0.001; 95% CI: 0.947-1.0). A cutoff value of 10 degrees yielded 96% sensitivity and 99% specificity to identify interventricular dyssynchrony. AUC was high for SD RV mPA and SD LV mPA (AUC = 1.0, p <0.001; 95% CI: 1.0-1.0 and AUC = 0.99, p <0.001; 95% CI: 0.979-1.0). A cutoff value of 22 degrees for SD LV mPA yielded 100% sensitivity and 100% specificity to identify LV intraventricular dyssynchrony. A cutoff value of 20 degrees for SD RV mPA yielded 100% sensitivity and 99% specificity to identify RV intraventricular dyssynchrony.

CONCLUSIONS

ERNA is an accurate and highly reproducible technique for evaluation of ventricular function and synchrony.

Patient assessment for cardiac resynchronization therapy: Past, present and future of imaging techniques

It has been proposed that dyssynchrony assessment before cardiac resynchronization therapy (CRT) implantation could help predict response to CRT. It is known that up to 40% of patients who receive a CRT device for established indications do not respond to CRT. Great expectations came from the Predictors of Response to Cardiac Resynchronization Therapy (PROSPECT) study, which would finally identify the ultimate echocardiographic dyssynchrony criteria to help select responders. The recently published PROSPECT trial failed to identify an ideal parameter of dyssynchrony. Patient selection for CRT should involve a multimodal approach, and new promising tools are being investigated in that view. The present review integrated new data coming from the exciting field of imaging with currently available evidence to generate a stepwise approach to patient selection.

Evaluation of mechanical dyssynchrony and myocardial perfusion using phase analysis of gated SPECT imaging in patients with left ventricular dysfunction

BACKGROUND

Using phase analysis of gated single photon emission computed tomography (SPECT) imaging, we examined the relation between myocardial perfusion, degree of electrical dyssynchrony, and degree of SPECT-derived mechanical dyssynchrony in patients with left ventricular (LV) dysfunction.

METHODS AND RESULTS

We retrospectively examined 125 patients with LV dysfunction and ejection fraction of 35% or lower. Fourier analysis converts regional myocardial counts into a continuous thickening function, allowing resolution of phase of onset of myocardial thickening. The SD of LV phase distribution (phase SD) and histogram bandwidth describe LV phase dispersion as a measure of dyssynchrony. Heart failure (HF) patients with perfusion abnormalities have higher degrees of dyssynchrony measured by median phase SD (45.5 degrees vs 27.7 degrees, P < .0001) and bandwidth (117.0 degrees vs 73.0 degrees, P = .0006). HF patients with prolonged QRS durations have higher degrees of dyssynchrony measured by median phase SD (54.1 degrees vs 34.7 degrees, P < .0001) and bandwidth (136.5 degrees vs 99.0 degrees, P = .0005). Mild to moderate correlations exist between QRS duration and phase analysis indices of phase SD (r = 0.50) and bandwidth (r = 0.40). Mechanical dyssynchrony (phase SD >43 degrees) was 43.2%.

CONCLUSIONS

HF patients with perfusion abnormalities or prolonged QRS durations have higher degrees of mechanical dyssynchrony. Gated SPECT myocardial perfusion imaging can quantify myocardial function, perfusion, and dyssynchrony and may help in evaluating patients for cardiac resynchronization therapy.