Identifying high-risk asymptomatic diabetic patients who are candidates for screening stress single-photon emission computed tomography imaging

OBJECTIVES: The purpose of this study was to identify which asymptomatic diabetic patients are candidates for screening single-photon emission computed tomography (SPECT) imaging and to examine angiographic findings and mortality in patients according to SPECT imaging categories. BACKGROUND: Previously we reported a high percentage of abnormal and high-risk SPECT imaging scans in asymptomatic diabetic patients. METHODS: We examined the associations between several clinical and laboratory variables and a high-risk stress SPECT imaging scan in 1,427 asymptomatic diabetic patients without known coronary artery disease (CAD). Results of coronary angiography and long-term outcome were also analyzed. RESULTS: An abnormal stress SPECT imaging scan was present in 826 patients (58%) and a high-risk scan in 261 patients (18%). Multivariate analysis demonstrated that seven variables were independently associated with a high-risk scan (model chi-square=107, p <0.0001). The two most important variables were electrocardiogram (ECG) Q waves (adjusted chi-square=38.3, p <0.001) and peripheral arterial disease (PAD) (adjusted chi-square=13.9, p <0.001). Coronary angiography was performed in 127 (49%) high-risk SPECT imaging patients, 61% of whom had angiographic high-risk CAD. Annual mortality rates for patient subsets categorized by SPECT imaging scans were high-risk 5.9%, intermediate-risk 5.0%, and low-risk 3.6% (p <0.001 for differences between groups). CONCLUSIONS: High-risk findings on stress SPECT imaging were present in 18% of asymptomatic diabetic patients without known CAD. Patients with high-risk scans had a high prevalence of severe CAD and a high annual mortality rate. ECG Q waves and/or evidence of PAD identified the most suitable candidates for screening.     

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.     

Preoperative cardiac risk assessment with adenosine stress dual-isotope myocardial single-photon emission computed tomography

Background: Previous studies have demonstrated that pharmacologic stress thallium-201(²⁰¹Tl) myocardial scintigraphy is a useful tool to evaluate preoperative cardiac risk. Hypothesis: The purpose of this study was to assess the utility of adenosine stress dual-isotope [rest ²⁰¹Tl/stress technetium-99m (^99mTc) sestamibi] myocardial single-photon emission computed tomography (SPECT) in predicting the risk of perioperative cardiac events (unstable angina, myocardial infarction, cardiac death) in patients undergoing major noncardiac surgery. Methods: We evaluated 43 consecutive patients (20 men, 23 women, mean age 64 years, range 30-83 years) within 8 weeks prior to major noncardiac surgery requiring general anesthesia. SPECT imaging was performed with 111 MBq (3 mCi)²⁰¹Tl at rest and 925 MBq (25 mCi)^99mTc sestamibi during adenosine stress. Results: Of the 43 patients, 15 (35%) had stress-induced ischemia and 28 (65%) did not. Perioperative cardiac events occurred in 4 (27%) of the 15 patients with stress-induced ischemia (2 unstable angina, 2 nonfatal myocardial infarctions) and in none of the 28 patients without inducible ischemia (p = 0.02). Conclusion: Adenosine stress dual-isotope myocardial SPECT is useful in determining the preoperative cardiac risk of patients undergoing major noncardiac surgery.     

Cardiovascular disease risk stratification with stress single-photon emission computed tomography technetium-99m tetrofosmin imaging in patients with the metabolic syndrome and diabetes mellitus

The metabolic syndrome represents a constellation of risk factors caused by insulin resistance, dyslipidemia, hypertension, and obesity, resulting in elevated coronary disease risk. From a multicenter prospective registry of 7,849 patients, the relation among the metabolic syndrome, diabetes, and risk stratification with stress technetium-99m tetrofosmin single photon-emission computed tomography (SPECT) was evaluated. The percentage of stress myocardial defects was calculated as < or = 5%, 5.1% to 10%, 10.1% to 15%, and > 15%. A Cox proportional-hazards model was used to estimate cardiovascular death or myocardial infarction (n = 752). Of 7,849 patients, 42% had the metabolic syndrome. Patients with the metabolic syndrome had an 84% 2-year event-free survival rate, lower than patients with normal metabolic status (p <0.0001). In patients with the metabolic syndrome, the percentage of moderate to severely abnormal SPECT findings ranged from 11% to 44% for those with 3 to 5 risk factors for the metabolic syndrome. There was an additive relation between the number of risk factors for the metabolic syndrome and the extent and severity of abnormalities in SPECT findings (p <0.0001). Patients with 5 risk factors for the metabolic syndrome were at the greatest risk, with hazard ratios from 7.8- to 14.1-fold for mild to severely abnormal SPECT findings. For diabetic patients requiring combined oral and insulin therapy, relative risk ratios increased from 15 to 21.4 for patients with > 5% to > 15% stress myocardial perfusion defects. In conclusion, cardiovascular prognosis is affected by the degree of metabolic dysfunction, and stress-induced reductions in myocardial perfusion provide an accurate means for near-term risk stratification.     

The use of single-photon emission computed tomography in cardiology

The tomographic distribution of thallium 201 in the myocardium was studied with a gamma camera with 2 detectors (29 cms in diameter) with 37 photo multipliers each. The camera was connected to a PDP computer with a 256 Kbytes memory. Thallium 201 in a dose of about 74 MBq 2 mCi was used in normal subjects, patients with coronary artery disease and with cardiac hypertrophy. Tomographic sections were obtained every 1.2 cms in the sagittal and frontal projections. The distribution of the Thallium was uniform in normal and hypertrophic hearts. Focal defects were seen in C.A.D. Single-photon emission computerized tomography was instrumental in determining the extension of the damage of the myocardium to areas which appeared normal in the regular thallium 201 scintigrams.     

The value of myocardial perfusion single-photon emission computed tomography in screening asymptomatic patients with atrial fibrillation for coronary artery disease.

OBJECTIVES: We sought to determine if screening for coronary artery disease (CAD) with stress single-photon emission computed tomography (SPECT) is of value in patients with atrial fibrillation (AF) who do not have symptoms of chest pain or dyspnea. BACKGROUND: Although noninvasive stress testing is often done to screen for CAD in asymptomatic patients with AF and is considered to be appropriate in selected patients, its potential utility has not been demonstrated. METHODS: A retrospective study was conducted of 374 asymptomatic patients with AF referred for the detection of CAD. Mean follow-up was 5.7 +/- 3.8 years. The study group was compared with a control group of 374 asymptomatic age and gender-matched patients without AF. RESULTS: The mean summed stress score (SSS) was not significantly different between AF patients and control subjects (3.6 +/- 5.3 vs. 3.5 +/- 5.9; p = 0.35). Compared with controls, asymptomatic AF patients had similar rates of abnormal SPECT studies (51.6% vs. 48.4%; p = 0.38) and high-risk studies (14.4% vs. 14.4%; p = 1.0). The SSS was a significant predictor of outcome in both AF patients and control subjects. However, total mortality was significantly greater in AF patients (5-year overall mortality 27% vs. 18%, 10-year overall mortality 47% vs. 40%; p < 0.001), and this difference persisted (p = 0.01) after adjusting for multiple clinical variables and the SSS. CONCLUSIONS: Screening for CAD using stress SPECT in asymptomatic AF patients has a yield similar to age- and gender-matched control patients without AF. Although SSS predicts mortality in patients with and without AF, patients with AF have increased total mortality independent of the findings on stress SPECT. These results suggest that factors other than obstructive CAD are responsible for the increased mortality in AF.     

Impact of stress single-photon emission computed tomography perfusion imaging on downstream resource utilization

This study shows that in patients with intermediate pretest probability of coronary artery disease stress single-photon emission computed tomography perfusion imaging decreases the rate of coronary angiography and coronary revascularization and is economically a superior strategy to routine coronary angiography.     

Ventricular volumes determined by single-photon emission computed tomography

To determine right (RV) and left ventricular (LV) volumes, a new technique was developed using ECG-gated single-photon emission computed tomography (SPECT). RV volumes of nine patients and LV volumes of 22 patients measured by SPECT and biplane contrast cineangiography were compared. In addition, volume and ejection fraction (EF) of the RV and LV were obtained by SPECT for 10 normal controls, 21 patients with old myocardial infarction (OMI), eight patients with hypertrophic cardiomyopathy (HCM) and 12 patients with dilated cardiomyopathy (DCM), and these results were compared. The intracardiac blood pool was labeled with Tc-99m sodium pertechnetate and 32 images were recorded through 180 degrees by a rotating gamma-camera. End-diastolic and end-systolic counts during 50 msec were recorded during 50 or 60 cardiac cycles. These counting data were reconstructed as tomographic images of vertical long-axial slices with thickness of a pixel without any attenuation correction. The numbers of voxels within the % cut-off level were summed, and the sum was multiplied by the one voxel volume. The cut-off level for ventricular delineation was determined as 45% by phantom studies. 1. The values obtained from SPECT and contrast angiography correlated well. 2. In normal controls, LV end-diastolic and end-systolic volumes were significantly less than those of the RV (p less than 0.05, p less than 0.001) and LVEF was significantly greater than the RVEF (p less than 0.001). 3. In OMI (single vessel disease), both end-diastolic and end-systolic volumes of the LV were significantly greater than those of normals (p less than 0.01, p less than 0.001) and LVEF was significantly less. In HCM end-systolic volumes of the RV were significantly less (p less than 0.05) than those of the normals. 4. LV volume was greater and LVEF was extremely low both in DCM and in OMI (multivessel disease) compared to that of the normals. In DCM, RV end-systolic volumes was greater and RVEF was lower than that of OMI (multi-vessel disease), indicating the deterioration of RV contractility , primarily in DCM. From these findings, it was concluded that this noninvasive technique may be useful for estimating left and right ventricular volumes.     

Major advances in single-photon emission computed tomography perfusion imaging

Major advances in single-photon emission computed tomography (SPECT) myocardial perfusion imaging have been realized with the introduction of state-of-the-art imaging equipment and radiopharmaceuticals. Gated tomographic myocardial perfusion imaging with technetium-99m (Tc-99m)-labeled radiopharmaceuticals provides a combined evaluation of both myocardial perfusion and function. Left ventricular ejection fraction can be measured accurately from the gated SPECT images. Recently, hardware and software have been introduced, which minimize the effect of soft tissue attenuation, thereby improving test specificity in the diagnosis of coronary artery disease. Myocardial viability may be assessed with the use of rest/delayed thallium-201 SPECT or F-18 fluorodeoxyglucose SPECT with modified scintillation camera collimation and electronics, or coincidence detection. Imaging patients to assess myocardial infarction or resting ischemia in the emergency department has expedited patient care and improved cost effectiveness. Teleradiography has also facilitated the interpretation of studies performed in the emergency department and at remote facilities, likewise improving cost-effectiveness.     

Simultaneous dobutamine stress echocardiography and 99mTc-tetrofosmin three-head single-photon emission computed tomography in patients with suspected coronary artery disease

OBJECTIVES AND BACKGROUND: Dobutamine stress echocardiography and 99mTc-tetrofosmin single-photon emission computed tomography (T-SPECT) were performed simultaneously in subjects in whom coronary artery disease (CAD) had been proven or excluded at coronary angiography, in order to establish their accuracy and agreement in the diagnosis of CAD, and in localisation and evaluation of the extension of ischaemia. No simultaneous comparison of the two techniques has been performed previously. METHODS: Seventy patients (50 men, mean age 63 +/- 10 years, 21 with previous myocardial infarction) underwent simultaneous dobutamine stress echocardiography and T-SPECT. The response to stress was blindly and independently analysed, adopting a 16-region segmentation and referring to the three major coronary arteries. RESULTS: Sixty-two patients (agreement 89%, kappa = 0.776) and 91% of left ventricular regions (kappa = 0.665) were classified concordantly, independently of the presence or absence of previous myocardial infarction (90%, kappa = 0.740 versus 91%, kappa = 0.589, respectively). At coronary angiography, 47 patients had CAD (disease prevalence 67%). The sensitivity and specificity of stress echocardiography for the diagnosis of anterior descending, circumflex and right coronary artery disease were 62, 78 and 73%, and 79, 79 and 83%, respectively. The corresponding values for T-SPECT were 70, 75 and 78%, and 94, 79 and 90%, respectively. CONCLUSIONS: These data indicate a high concordance between wall motion abnormalities observed using stress echocardiography and perfusion defects observed using T-SPECT; their sensitivity in identifying critical stenoses was similar. Inadequate stressor amounts, and less frequently hyperdynamic regional response may reduce the accuracy of stress echocardiography, while dobutamine effects on coronary flow may prevent T-SPECT from showing subtle flow maldistributions in the presence of worsened wall motion.     

Prevalence and prognostic value of perfusion defects detected by stress technetium-99m sestamibi myocardial perfusion single-photon emission computed tomography in asymptomatic patients with diabetes mellitus and no known coronary artery disease

Coronary artery disease (CAD) is the leading cause of morbidity and mortality in diabetics. Early diagnosis of CAD and identification of high-risk subgroups, followed by appropriate therapy, may therefore enhance survival. This study sought to determine the value of stress myocardial perfusion single-photon emission computed tomography (SPECT) with technetium-99m sestamibi to detect perfusion defects and predict cardiac events in asymptomatic diabetics. One hundred eighty asymptomatic diabetics without known CAD who underwent 2-day stress technetium-99m sestamibi SPECT were followed up for 36 +/- 18 months. End points were defined as hard (myocardial infarction or cardiac death) or total events (myocardial infarction, cardiac death, or late revascularization). Logistic regression analysis evaluated clinical variables, type of stress, exercise treadmill test (ETT), and SPECT as predictors of end points. Perfusion defects were found in 26% of patients (15% reversible, 6% mixed, and 5% fixed). Clinical or ETT variables were not associated with perfusion defect type or with hard events. However, male gender predicted total events (chi-square 3.3; p = 0.01). An abnormal SPECT significantly increased the risk of hard events (chi-square 5.4; p = 0.001) and total events (chi-square 7.4; p = 0.0001). Extensive defects determined the highest risk of total events (chi-square 18.8; p = 0.0001). Event rates increased according to SPECT: 2% of hard events per year and 5% of total events per year in patients with normal SPECT versus 9% per year and 38% per year, respectively, in those with abnormal SPECT. Importantly, a normal SPECT identified a relatively low-risk subgroup of patients. Thus, stress technetium-99m sestamibi SPECT was useful in evaluating asymptomatic diabetics for the presence of CAD, and effectively risk-stratified this population.     

Single-photon emission computed tomography myocardial perfusion imaging in patients with diabetes

Diabetes mellitus has reached epidemic proportions, creating a large population of people at increased risk for cardiac events. Single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI) provides an effective tool to accurately diagnose and risk stratify patients with diabetes, similar to patients without diabetes. Diabetics, however, are at increased risk for coronary events. Diabetics with normal MPI have increased late cardiac events, and even those with mild perfusion defects have increased event rates compared with nondiabetics with similar perfusion abnormalities. Stress MPI can provide valuable risk stratification data for both sexes, with or without diabetes. However, diabetes appears to exert a greater relative impact in women than in men. Despite the absence of symptoms, the incidence and prevalence of coronary artery disease is increased in patients with diabetes. Further studies and research will be needed to define the eventual role of SPECT MPI in asymptomatic diabetics.     

Left ventricular volume determination using single-photon emission computed tomography

A new method for measuring left ventricular (LV) volume based on gated single-photon emission computed tomography (SPECT) is described. Preliminary phantom studies showed an excellent correlation between SPECT and observed volumes (r = 0.99, standard error of the estimate [SEE] = 4.9 ml). SPECT was performed 24 hours after biplane contrast LV angiography in 36 patients. Transaxial blood pool tomograms were reconstructed by filtered back projection and reoriented to views orthogonal to the cardiac axes. Volume was calculated from serial short-axis tomograms by determining the base, apex and lateral borders of the LV blood pool, ascertaining the number of pixels in this volume and multiplying by the known volume of a pixel. Gated SPECT volumes were compared with contrast angiographic volumes. At end-systole, r = 0.96 and SEE = 12 ml; at end-diastole, r = 0.81 and SEE = 27 ml. For ejection fraction, r = 0.85 and SEE = 0.06. To test interobserver variation in processing, count data from 5 patients were processed twice (r = 0.98, SEE = 8.3 ml). There is an excellent correlation between SPECT and contrast angiographic volumes at end-systole; at end-diastole the relation is good. SPECT requires no arbitrary background correction, allows systematic isolation of the left ventricle from other overlapping cardiac chambers and requires no geometric assumptions for volume determination. It has promise as a direct method for measuring LV volume in a minimally invasive manner.     

Comparative ability of myocardial perfusion single-photon emission computed tomography to detect coronary artery disease in patients with and without diabetes mellitus

BACKGROUND: Diabetics generally have more frequent and extensive silent myocardial ischemia than nondiabetics, increasing the importance of noninvasive detection of coronary artery disease (CAD) in this cohort. However, little is known regarding the diagnostic accuracy of myocardial perfusion single-photon emission computed tomography (SPECT) in patients with diabetes. This study was undertaken to compare the diagnostic value of rest thallium-201/stress technetium-99m sestamibi dual-isotope myocardial perfusion SPECT in patients with and without diabetes. METHODS: Of the 203 patients with diabetes and 260 patients without diabetes who underwent dual-isotope myocardial perfusion SPECT with exercise or pharmacologic stress testing, 138 diabetics (12% type 1 diabetics) and 188 nondiabetics had coronary angiography within 6 months of the nuclear test, and 65 diabetics and 72 nondiabetics had a low likelihood (<10%, mean 6% +/- 3% and 6% +/- 3%) of CAD. RESULTS: The angiographic data showed that patients with diabetes had less incidence of 1-vessel disease and a higher incidence of 3-vessel/left main artery disease than patients without diabetes (P <.05). The overall sensitivity and specificity, respectively, of SPECT for detecting CAD with the criterion of >/=50% diameter stenosis were 86% (95 of 111) and 56% (15 of 27) in diabetics, 86% (122 of 142) and 46% (21 of 46) in nondiabetics (P = not significant). With the criterion of >/=70% diameter stenosis the corresponding results were 90% (86 of 96) and 50% (21 of 42) in diabetics, and 91% (108 of 119) and 43% (30 of 69) in nondiabetics, respectively (P = not significant). The normalcy rate for low likelihood patients was 89% (58 of 65) in diabetics and 90% (65 of 72) in nondiabetics (P = not significant). The sensitivity and specificity for individual vessel detection were also similar in patients with and without diabetes (P = not significant) except for a lower sensitivity and a higher specificity for detecting left anterior descending coronary artery disease in the diabetic group (P <.05). CONCLUSION: Dual-isotope myocardial perfusion SPECT has comparable accuracy for the diagnosis of CAD in diabetic and nondiabetic patients.     

Dobutamine stress echocardiography compared with dipyridamole thallium-201 single-photon emission computed tomography in detecting coronary artery disease

To compare the diagnostic value of dobutamine stress echocardiographywith dipyridamole thallium-201 single-photon emission computedtomography (SPECT) in detecting coronary artery disease (CAD),we performed both tests on 54 patients who also underwent coronaryarteriography. Dobutamine was infused at an incremental regimenof 5,10,20,30 and 40 µg. kg^-1. min^-1. Dipyridamole wasinfused at a rate of 0.14 mg. kg^-1. min^-1 over 4 min. Dobutaminestress echocardiography detected 40 (93%) and SPECT 42 (98%,P=ns) of the 43 patients with significant CAD, defined as (greaterthan or equal) 50% diameter stenosis. The specificity was 73%(8 of 11) for both tests. The sensitivity for detecting individualcoronary artery stenosis with dobutamine stress echocardiographywas 81% (30 of 37) for the left anterior descending artery,75% (24 of 32) for the right coronary artery, and 61% (17 of28) for the left circumflex artery. For SPECT it was 89%, 97%(P>0.05 vs dobutamine stress echocardiography) and 75%, respectively. Among the 97 stenotic coronary arteries, 17 had mild to moderatestenosis (50%-69% diameter stenosis) and 80 had severe stenosis($$70% diameter stenosis). With dobutamine stress echocardiography,53% of the arteries with mild to moderate stenosis were identifiedvs 78% of those with severe stenosis (P<0.05). With SPECT,the sensitivity was 82% (14 of 17) in mild to moderate stenosisand 89% (71 of 80) in severe stenosis (P=ns). No major sideeffects occurred during either test. Thus, both dobutamine stressand SPECT are highly sensitive for detection and localizationof CAD. However, the sensitivity of dobutamine stress is affectedby the level of stenosis severity.