The prognostic value of ECG-gated SPECT imaging in patients undergoing stress Tc-99m sestamibi myocardial perfusion imaging

Validation of a new automated method for analysis of gated-SPECT images

We recently presented a new method for quantification of CArdiac FUnction--denoted CAFU--as the first step in the development of an automated method for integrated interpretation of gated myocardial perfusion single photon emission computed tomography (SPECT) images. The aim of this study was to validate CAFU in the assessment of global and regional function of the left ventricle. Quantitative gated-SPECT (QGS), the most widely used software package for quantification of gated-SPECT images, was used as reference method for the measurements of ejection fraction (EF) and ventricular volumes, and visual analysis by an experienced physician was used as reference method for the measurements of regional wall motion and thickening. Two different groups of consecutive patients referred for myocardial perfusion scintigraphy were studied. Global function was evaluated in 316 patients and regional function in 49 other patients. The studies were performed using a 2-day stress/rest 99 m-Tc-sestamibi protocol. A good correlation was found between EF values from QGS and CAFU (EF CAFU = 0.84 EF QGS + 13, r = 0.94), but CAFU values were on average 4 EF points higher than QGS values. With CAFU the segments with normal thickening according to the physician showed significantly higher thickening values (in all parts of the myocardium) compared to the segments classified as having abnormal thickening. In conclusion, this study demonstrates that CAFU can be used to quantify global and regional function in gated-SPECT images. This is an important step in our development of an automated method for integrated interpretation of gated-SPECT myocardial perfusion scintigraphy studies.

Left ventricular ejection fraction and volumes on rest gated 201Tl perfusion SPECT: Comparison with two-dimensional echocardiography

BACKGROUND

Rest gated 201Tl images are considered to be of poor count statistics due to lower energy and low photon flux of 201Tl in addition to increased attenuation and low dose that can be administered. We compared the left ventricular ejection fraction (LVEF), end diastolic (EDV) and end systolic volume (ESV) obtained on 4 h gated rest 201Tl myocardial perfusion single photon emission computed tomography (SPECT) with those obtained by two-dimensional echocardiography (2-D ECHO) in patients with known or suspected coronary artery disease (CAD).

METHODS

Eighty-two consecutive patients who underwent gated 201Tl stress-rest myocardial perfusion SPECT and 2-D ECHO were studied. The gated thallium images were processed with Siemens e-soft autocardiac processor and LVEF, EDV and ESV were evaluated using Emory Cardiac Toolbox. The same parameters were also assessed on the 2-D ECHO using the modified Simpson method for comparison.

RESULTS

Out of 82 rest gated images, one study was excluded because of poor count statistics. In 81 (99%) patients there was good linear correlation with 2-D ECHO values and rest gated 201Tl SPECT images for EDV, ESV and LVEF. Pearson's correlation co-efficient (r value) for EDV, ESV and LVEF between the two methods was 0.78, 0.79 and 0.88, respectively. A Bland-Altman plot showed close agreement with LVEF but not for EDV and ESV.

CONCLUSION

These results suggest that the 4 h rest gated 201Tl study gives a reliable value for the LVEF compared to 2-D ECHO and can be used in routine clinical practice.

Combined assessment of left ventricular perfusion and function by gated single-photon emission computed tomography for the risk stratification of high-risk hypertensive patients

OBJECTIVE

This study was aimed at verifying whether combined information on left ventricular perfusion and function by electrocardiogram-gated single-photon emission computed tomography (SPECT) retains its known prognostic value in patients with systemic hypertension.

METHODS

A total of 415 hypertensive patients underwent rest and stress (exercise in 278 and dipyridamole in 137) gated 99mTc-sestamibi SPECT and prospective follow-up for the composite endpoint of death and acute coronary syndrome. Patients undergoing revascularization were censored. The individual effect of clinical and stress imaging data on outcome was evaluated by Cox regression analysis. Model validation was performed using bootstrap methods adjusted by the degree of optimism in estimates. Survival analysis was performed using the product-limit Kaplan-Meier method.

RESULTS

During a median follow-up of 24 months, 12 cardiac deaths and 32 acute coronary syndromes occurred. After adjusting for the most significant covariates, age [hazard ratio (HR) 1.62, 95% confidence interval (CI) 1.02-2.57], diabetes (HR 7.51, 95% CI 1.61-35.2), summed stress score (HR 2.06, 95% CI 1.07-4), and peak end-systolic volume (HR 3.62, 95% CI 1.35-9.69) were multivariable predictors of outcome. The normal perfusion pattern was associated with a low event rate independently of peak end-systolic volume. Conversely, in the case of moderate to severe perfusion abnormalities, a peak end-systolic volume greater than 74 ml was able to identify an increased risk of adverse outcome. Moreover, peak end-systolic volume was significantly higher among patients who died of a cardiac cause compared with those with different outcomes.

CONCLUSION

A combined assessment of left ventricular perfusion and function by gated SPECT significantly improves risk stratification in hypertensive patients.

The role of myocardial perfusion imaging in the diagnosis of patients with coronary artery disease: developments over the past year

PURPOSE OF REVIEW

The role of myocardial perfusion imaging in the diagnosis of coronary artery disease in various patient populations has been expanding. Recent literature from March 2004 to February 2005 has advanced the concept of attenuation correction and electrocardiographic gating in improving the diagnosis of coronary artery disease.

RECENT DEVELOPMENTS

The American Heart Association encourages the use of electrocardiographic-gated single photon emission computerized tomography in women. Asymptomatic diabetic patients may benefit from screening with myocardial perfusion imaging. Dobutamine stress perfusion imaging is an important diagnostic tool in elderly patients who are unable to exercise. In patients with chest pain, acute imaging may decrease unnecessary admissions. Vasodilator stress imaging has high sensitivity and specificity in patients with left bundle branch block. Patients undergoing endovascular stent grafting may benefit from risk stratification with vasodilator myocardial perfusion imaging. The American Society of Nuclear Cardiology and the Society of Nuclear Medicine have recognized the role of attenuation correction in increasing the diagnostic accuracy of myocardial perfusion imaging. Multiple studies emphasize the importance of electrocardiographic gating in myocardial perfusion imaging.

SUMMARY

Recent developments have resulted in an important statement by the American Heart Association that assigns a larger role for myocardial perfusion imaging in the diagnosis of coronary artery disease in women. The role of myocardial perfusion imaging is also expanding in various other patient populations. The literature has validated the concept of attenuation correction for the accurate assessment of attenuation artifacts as well as electrocardiographic gating in enhancing the diagnosis and risk stratification for coronary artery disease.

Imaging techniques in nuclear cardiology for the assessment of myocardial viability

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with sufficient viable myocardium, patients with predominantly scar tissue should be treated medically. Patients with left ventricular dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischemia but at the same time benefit most from revascularization. It is important to identify viable myocardium in these patients, and radionuclide myocardial scintigraphy is an excellent tool for this. Single-photon emission computed tomography perfusion scintigraphy (SPECT), whether using (201)thallium, (99m)Tc-sestamibi, or (99m)Tc-tetrofosmin, in stress and/or rest protocols, has consistently been shown to be an effective modality for identifying myocardial viability and guiding appropriate management. Metabolic and perfusion imaging with positron emission tomography (PET) radiotracers frequently adds additional information and is a powerful tool for predicting which patients will have an improved outcome from revascularization. New techniques in the nuclear cardiology field, like attenuation corrected SPECT, dual isotope simultaneous acquisition (DISA) SPECT and gated FDG PET are promising and will further improve the detection of myocardial viability. Also the combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and non-invasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

A new automated method for analysis of gated-SPECT images based on a three-dimensional heart shaped model

A new automated method for quantification of left ventricular function from gated-single photon emission computed tomography (SPECT) images has been developed. The method for quantification of cardiac function (CAFU) is based on a heart shaped model and the active shape algorithm. The model contains statistical information of the variability of left ventricular shape. CAFU was adjusted based on the results from the analysis of five simulated gated-SPECT studies with well defined volumes of the left ventricle. The digital phantom NURBS-based Cardiac-Torso (NCAT) and the Monte-Carlo method SIMIND were used to simulate the studies. Finally CAFU was validated on ten rest studies from patients referred for routine stress/rest myocardial perfusion scintigraphy and compared with Cedar-Sinai quantitative gated-SPECT (QGS), a commercially available program for quantification of gated-SPECT images. The maximal differences between the CAFU estimations and the true left ventricular volumes of the digital phantoms were 11 ml for the end-diastolic volume (EDV), 3 ml for the end-systolic volume (ESV) and 3% for the ejection fraction (EF). The largest differences were seen in the smallest heart. In the patient group the EDV calculated using QGS and CAFU showed good agreement for large hearts and higher CAFU values compared with QGS for the smaller hearts. In the larger hearts, ESV was much larger for QGS than for CAFU both in the phantom and patient studies. In the smallest hearts there was good agreement between QGS and CAFU. The findings of this study indicate that our new automated method for quantification of gated-SPECT images can accurately measure left ventricular volumes and EF.

Prognostic value of combined perfusion and function by stress technetium-99m sestamibi gated SPECT myocardial perfusion imaging in patients with suspected or known coronary artery disease

The incremental prognostic value of combined regional wall motion and perfusion over perfusion alone by gated single-photon emission computed tomographic myocardial perfusion scintigraphy has not been evaluated. Of the 402 consecutive patients who underwent stress single-photon emission computed tomographic myocardial perfusion scintigraphy for suspected myocardial ischemia, we identified 333 patients (217 men, mean age 63 +/- 10 years; exercise in 249 and dipyridamole adminstered to 84). Visual scoring of perfusion images and regional wall motion used 20 segments and a scale of 0 to 4. Resting and poststress left ventricular ejection fraction was automatically generated. On follow-up (median 13 months), 30 hard cardiac events (17 cardiac deaths, 13 nonfatal acute myocardial infarctions) and 66 total cardiac events (including hard events, 26 with unstable angina, and 10 who underwent late revascularization) occurred. After adjustment for prescan information, the best independent predictors of hard events were summed stress score for wall motion (Wald's chi-square 8.3, p <0.004) and several vascular territories with ischemia by perfusion/function (Wald's chi-square 6.2, p <0.01). The strongest predictors of all cardiac events were the number of ischemias (Wald's chi-square 32.1, p <0.0001) and the number of ischemic vascular territories by perfusion (Wald's chi-square 13.1, p <0.0001). Addition of function data to the combined model of perfusion data yielded an incremental value of 26% for predicting hard events but not for all events. In conclusion, the assessment of combined perfusion/function provides incremental prognostic information for further hard events with perfusion data alone; perfusion data best predict all cardiac events.

The use of nuclear cardiology in clinical decision making

Extensive data exist to support the role of myocardial perfusion single-photon emission computed tomography (MPS) in risk stratification. Normal MPS studies usually are associated with very low risk, and patient risk increase significantly as a function of MPS results. Ventricular function measurements from gated single-photon emission computed tomography further augment risk stratification, particularly with respect to identifying patients at risk of cardiac death. Ancillary findings are prognostically important, particularly in the setting of normal or near-normal MPS results. Recent data suggest that MPS results can identify which patients will benefit from revascularization versus medical therapy and have expanded the understanding of how stress MPS is helpful in the identification of risk, enhanced the means of identifying risk, and improved its use as a means to identify optimal posttest treatment.

Quantitative single-photon emission computed tomography imaging

Over the past decade, quantitation of cardiac single-photon emission computed tomography (SPECT) data, once limited to perfusion assessment, has been extended to global and regional function assessment for both the left and the right ventricle, as well as to measurement of additional cardiac parameters of diagnostic and prognostic interest. A number of commercially available quantitative algorithms exist, based on different mathematic operators and with varying degrees of automation, that are capable of providing accurate and reproducible results. This article describes the many quantitative cardiac SPECT measurements available today, defining them in terms of validation, practical use, and limitations.

[Value of gated SPECT myocardial perfusion imaging for individual cardiac risk assessment]

Myocardial perfusion imaging enables not only accurate diagnosis of disease but also entails prognostic value. Myocardial perfusion SPECT contributes to assessment of future cardiac events independently of other clinical parameters. A normal stress myocardial perfusion scan is associated with a favorable prognosis independent of history, symptoms, and exercise electrocardiography test variables. Cardiac risk and benefit from invasive therapeutic strategies increase in relation to the severity of the abnormality of perfusion and function assessed by gated myocardial perfusion SPECT. Thus, stress myocardial perfusion imaging may serve as a gatekeeper for referral to coronary angiography enabling effective risk stratification in patients with suspected or documented coronary artery disease.