Potential added value of three-dimensional reconstruction and display of single photon emission computed tomographic gated blood pool images

Prognostic value of left ventricular dyssynchrony by myocardial perfusion-gated SPECT in patients with normal and abnormal left ventricular functions

BACKGROUND

Left ventricular (LV) dyssynchrony by phase analysis has been studied by myocardial perfusion imaging (MPI)-gated SPECT in patients with LV dysfunction in various clinical settings. We aimed to investigate the routine use of phase analysis with gated SPECT for predicting cardiac outcome.

METHODS

Patients referred to a tertiary medical center in 2010-2011 prospectively underwent a gated SPECT and phase analysis, and follow-up for cardiac events. The values of clinical variables, MPI, LV function, and LV dyssynchrony in predicting cardiac events were tested by univariate and multivariate analyses.

RESULTS

The study group included 787 patients (66.5 ± 11 years, 81% men) followed for a mean duration of 18.3 ± 6.2 months. There were 45 (6%) cardiac events defined as composite endpoint; cardiac death occurred in 26 patients, and the rest had new-onset or worsening heart failure and life-threatening arrhythmias. In multivariate analysis, it was shown that NYHA class, diabetes mellitus, and LVEF <50% were the independent predictors for composite endpoint. However, the independent predictors for cardiac mortality were NYHA class (for each increment in class) and phase standard deviation (SD) (for each 10° increment).

CONCLUSION

Gated SPECT with phase analysis for the assessment of LV dyssynchrony can successfully predict cardiac death together with NYHA class, in patients with LV dysfunction.

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.

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.

The relationship of myocardial contraction and electrical excitation--the correlation between scintigraphic phase image analysis and electrophysiologic mapping

BACKGROUND

Phase imaging derived from equilibrium radionuclide angiography presents the ventricular contraction sequence. It has been widely but only indirectly correlated with the sequence of electrical myocardial activation.

OBJECTIVES

We sought to determine the specific relationship between the sequence of phase progression and the sequence of myocardial activation, contraction and conduction, in order to document a noninvasive method that could monitor both.

METHODS

In 7 normal and 9 infarcted dogs, the sequence of phase angle was correlated with the epicardial activation map in 126 episodes of sinus rhythm and pacing from three ventricular sites.

RESULTS

In each episode, the site of earliest phase angle was identical to the focus of initial epicardial activation. Similarly, the serial contraction pattern by phase image analysis matched the electrical epicardial activation sequence completely or demonstrated good agreement in approximately 85% of pacing episodes, without differences between normal or infarct groups.

CONCLUSIONS

A noninvasive method to accurately determine the sequence of contraction may serve as a surrogate for the associated electrical activation sequence or be applied to identify their differences.

Temporal resolution of multiharmonic phase analysis of ECG-gated myocardial perfusion SPECT studies

BACKGROUND

Multiharmonic phase analysis (MHPA) was developed to assess left-ventricular dyssynchrony from gated myocardial perfusion single-photon emission computed tomography (GSPECT) studies. This study was intended to determine the temporal resolution of MHPA.

METHODS

A reference normal GSPECT study with 128 frames/cycle was simulated using NCAT, a nonuniform rational B-splines-based cardiac torso phantom. It was shifted in the time domain to insert phase delays. Realistic GSPECT studies (8 or 16 frames/cycle) were then obtained by down-sampling the reference and shifted studies. All GSPECT projections were generated with attenuation, scatter, collimator blurring, and Poisson noise. Seventeen regional phases were calculated from the GSPECT reconstructions (filtered back-projection without compensation for physical factors), using linear interpolation for the reference study, and MHPA for the realistic studies. Comparing the regional phases between the realistic studies without and with shifts determined whether MHPA could identify certain phase delays.

RESULTS

When there were enough counts/pixel (>10 counts/pixel), MHPA with either 1, 2, or 3 harmonics could resolve a phase difference of 5.6 degrees , corresponding to 1/64 of the cardiac cycle.

CONCLUSIONS

With clinically equivalent counts, the temporal resolution of MHPA is 1/64 of a cardiac cycle. Achieving this high temporal resolution from data with low temporal resolution demonstrates the benefit of replacing discrete points with continuous harmonic functions.

Assessment of left ventricular mechanical dyssynchrony by phase analysis of ECG-gated SPECT myocardial perfusion imaging

Cardiac resynchronization therapy (CRT) has shown benefits in patients with severe heart failure. However, at least 30% of patients selected for CRT by use of traditional criteria (New York Heart Association class III or IV, depressed left ventricular [LV] ejection fraction, and prolonged QRS duration) do not respond to CRT. Recent studies with tissue Doppler imaging have shown that the presence of LV dyssynchrony is an important predictor of response to CRT. Phase analysis has been developed to allow assessment of LV dyssynchrony by gated single photon emission computed tomography myocardial perfusion imaging. This technique uses Fourier harmonic functions to approximate regional wall thickness changes over the cardiac cycle and to calculate the regional onset-of-mechanical contraction phase. Once the onset-of-mechanical contraction phases are obtained 3-dimensionally over the left ventricle, a phase distribution map is formed that represents the degree of LV dyssynchrony. This technique has been compared with other methods of measuring LV dyssynchrony and shown promising results in clinical evaluations. In this review the phase analysis methodology is described, and its up-to-date validations are summarized.

Left ventricular ejection and filling rate measurement based on the automatic edge detection method of ECG-gated blood pool single-photon emission tomography

The objective of the present investigation was to determine the feasibility of assessing left ventricular systolic ejection and diastolic filling via the automatic edge detection method employing ECG-gated blood pool single-photon emission tomography (SPET GBP) data.

METHODS

Thirty-five patients, who had undergone both SPET GBP and ECG-gated equilibrium blood pool scintigraphy by the planar method (planar GBP), were enrolled in this study. Planar GBP was performed with a single-headed gamma camera. From the left anterior oblique projection, data were acquired at 24 frames/cardiac cycle with ECG-gating during the equilibrium state. SPET GBP was conducted utilizing a triple-headed gamma camera, with 60 projection views over 360 degrees by 60 sec per view, in 16 frames/cardiac cycle. In each frame, left ventricular volume was determined by automatic edge detection employing a quantitative gated SPET program. Additionally, the time-volume curve was fitted by the 4th harmonics of Fourier transform. Ejection fraction (EF, %), peak ejection rate (PER, /sec), peak filling rate (PFR, /sec) and mean filling rate during the initial one-third of diastolic time (1/3 FRm) were calculated from the fitted curve. These parameters were also calculated with planar GBP data.

RESULT

Left ventricular ejection and filling parameters were calculated by SPET GBP with the automatic edge detection program for all patient data. Correlation coefficients of EF, PER, PFR and 1/3 FRm between SPET and planar GBP were 0.91 (p < 0.001), 0.82 (p < 0.001), 0.78 (p < 0.001) and 0.74 (p < 0.001), respectively.

CONCLUSION

Ejection and filling rates can be calculated using SPET GBP with the edge-detection software. These parameters displayed significant correlations with those values obtained via planar GBP. Additional studies are warranted to determine the reliability of parameters with SPET GBP.

Single photon emission computed tomography radionuclide ventriculography in the noninvasive diagnosis and evaluation of a false left ventricular aneurysm (pseudoaneurysm)

An inferior wall false aneurysm (pseudoaneurysm) was diagnosed in a 77-year-old male by single photon emission computed tomography (SPECT) radionuclide ventriculography (RNV). This immediately followed routine planar RNV because the latter did not lead to definitive characterization of the type of aneurysm and did not ideally characterize the location and size of the aneurysm. RNV was followed by false-negative first-pass radionuclide ventriculography, routine echocardiography, and gated magnetic resonance imaging of the heart (cardiac MRI). A definitive diagnosis of a false aneurysm is found at surgery and pathology; however, the patient declined surgery and has done well for 1.5 years after these imaging studies. The first-pass study is limited with relatively small pseudoaneurysms, like in this case. Echocardiography is noninvasive and can show wall motion and aneurysm size. Cardiac MRI is the most expensive noninvasive study but, in addition to revealing the diameters of the neck and body of the aneurysm, MRI is able to characterize the surrounding myocardium. This case report suggests the critical information needed for a confident, noninvasive diagnosis of false aneurysm can be obtained with SPECT RNV. The location of the aneurysm is easily determined, and the relative diameters of the neck to the body of the aneurysm can be easily seen. SPECT RNV is superior to planar RNV and first-pass radionuclide ventriculography in making a diagnosis of false aneurysm. Although RNV might be unable to directly demonstrate the perfusion and thickness of the myocardium, it has an advantage over MRI in terms of ejection fraction (EF) and cost.

Major increase in brain natriuretic peptide indicates right ventricular systolic dysfunction in patients with heart failure

This study sought to investigate whether the presence of right ventricular systolic dysfunction with pre-existing left ventricular systolic dysfunction is associated with higher plasma brain natriuretic peptide (BNP) levels, compared with patients with isolated left ventricular dysfunction. Eighty-five patients referred for evaluation of isotopic ventricular function were prospectively included in the study. Left (LVEF) and right (RVEF) ventricular ejection fractions were evaluated by gated blood pool scintigraphy and compared with plasma BNP levels. BNP correlated negatively with LVEF, except in patients with ischaemic heart disease (P=0.09) and in patients with LVEF<40% (P=0.11). In contrast, BNP levels correlated negatively with RVEF for all subgroups. Among patients with RVEF<40%, no significant BNP difference was found between patients with or without additional left ventricular systolic dysfunction (P=0.51). Among patients with LVEF<40%, plasma BNP levels were significantly higher in patients with RVEF<40% than in patients with RVEF>/=40% (P=0.004) whereas age, renal function, clinical findings, ventricular volumes, LVEF or medication were not significantly different. In conclusion, an important increase in BNP levels in patients with left ventricular systolic dysfunction should be considered by cardiologists as an indication of high risk of right ventricular dysfunction and should justify further investigation.