Incremental prognostic value of post-stress left ventricular ejection fraction and volume by gated myocardial perfusion single photon emission computed tomography

BACKGROUND

The incremental prognostic value of post-stress left ventricular ejection fraction (EF) and volume over perfusion has not been investigated.

METHODS AND RESULTS

We identified 1680 consecutive patients who underwent rest Tl-201/stress Tc-99m sestamibi gated single photon emission computed tomography (SPECT) and who were followed-up for 569+/-106 days. Receiver-operator characteristics analysis defined an EF<45%, an end-systolic volume (ESV) >70 mL, and an end-diastolic volume >120 mL as optimal thresholds, yielding moderate sensitivity and high specificity in the prediction of cardiac death. Patients with an EF> or = 45% had mortality rates <1%/year, despite severe perfusion abnormalities, whereas patients with an EF<45% had high mortality rates, even with only mild/moderate perfusion abnormalities (9.2%/year; P<0.00001). Similarly, an ESV< or = 70 mL was related to a low cardiac death rate (<1.2%/year), even for patients with severe perfusion abnormalities, whereas patients with an ESV>70 mL and only mild/moderate perfusion abnormalities had high death rates (8.2%/year; P<0.00001). Patients with an EF<45% and an ESV< or = 70 mL had low cardiac death rates (1.7%/year); those with an EF<45% but an ESV>70 mL had high death rates (7.9%/year; P<0.02). Multivariate Cox proportional hazards regression showed that perfusion variables and ESV were independent predictors of overall coronary events, whereas EF and ESV demonstrated incremental prognostic values over prescan and perfusion information in predicting cardiac death and cardiac death or myocardial infarction.

CONCLUSIONS

Post-stress EF and ESV by gated-SPECT have incremental prognostic values over prescan and perfusion information in predicting cardiac death, and they provide clinically useful risk stratification.

The economic consequences of available diagnostic and prognostic strategies for the evaluation of stable angina patients: an observational assessment of the value of precatheterization ischemia. Economics of Noninvasive Diagnosis (END) Multicenter Study Group

OBJECTIVES

The study aim was to determine observational differences in costs of care by the coronary disease diagnostic test modality.

BACKGROUND

A number of diagnostic strategies are available with few data to compare the cost implications of the initial test choice.

METHODS

We prospectively enrolled 11,372 consecutive stable angina patients who were referred for stress myocardial perfusion tomography or cardiac catheterization. Stress imaging patients were matched by their pretest clinical risk of coronary disease to a series of patients referred to cardiac catheterization. Composite 3-year costs of care were compared for two patients management strategies: 1) direct cardiac catheterization (aggressive) and 2) initial stress myocardial perfusion tomography and selective catheterization of high risk patients (conservative). Analysis of variance techniques were used to compare costs, adjusting for treatment propensity and pretest risk.

RESULTS

Observational comparisons of aggressive as compared with conservative testing strategies reveal that costs of care were higher for direct cardiac catheterization in all clinical risk subsets (range: $2,878 to $4,579), as compared with stress myocardial perfusion imaging plus selective catheterization (range: $2,387 to $3,010, p < 0.0001). Coronary revascularization rates were higher for low, intermediate and high risk direct catheterization patients as compared with the initial stress perfusion imaging cohort (13% to 50%, p < 0.0001); cardiac death or myocardial infarction rates were similar (p > 0.20).

CONCLUSIONS

Observational assessments reveal that stable chest pain patients who undergo a more aggressive diagnostic strategy have higher diagnostic costs and greater rates of intervention and follow-up costs. Cost differences may reflect a diminished necessity for resource consumption for patients with normal test results.

Automatic quantitation of regional myocardial wall motion and thickening from gated technetium-99m sestamibi myocardial perfusion single-photon emission computed tomography

OBJECTIVES

We developed an automatic quantitative algorithm for the measurement of regional myocardial wall motion and wall thickening from three-dimensional gated technetium-99m sestamibi myocardial perfusion single-photon emission computed tomographic images.

BACKGROUND

The algorithm measures the motion of the three-dimensional endocardial surface using a modification of the centerline method, as well as wall thickening using both geometry (gaussian fit) and partial volume (counts).

METHODS

The algorithm was tested using a "variable thickness" heart phantom, and the quantitative results were compared with visual segmental assessment of myocardial motion and thickening in 79 clinical patients with a wide range of ejection fractions (6% to 87%).

RESULTS

Phantom measurements of simulated motion and thickening were accurate regardless of the camera used (dual or triple detector), the angular span of reconstructed data (180 degrees or 360 degrees), the amount of motion (3 or 6 mm) or the amount of thickening (33%, 50% or 100%). Quantitative measurements of segmental motion and thickening in the patients were correlated with visual scores (r = 0.668, exact agreement 72.6%, kappa 0.433 and r = 0.550, exact agreement 74.7%, kappa 0.408, respectively). Significant inverse linear relations exist between the global (summed) visual motion score and the average quantitative motion, and between the global (summed) visual thickening score and the average quantitative thickening. Automatic quantitative ejection fraction measurements correlated extremely well with average quantitative motion (r = 0.929) and thickening (r = 0.959).

CONCLUSIONS

Our algorithm is accurate and may be the first automatic technique for the quantitative three-dimensional assessment of regional ventricular function in cardiology.

Incremental prognostic value of myocardial perfusion single photon emission computed tomography in patients with diabetes mellitus

BACKGROUND

Previous studies have shown that myocardial perfusion single photon emission computed tomography (SPECT) provides incremental prognostic information in the general population, but the prognostic efficacy of nuclear testing in patients with diabetes mellitus is unclear.

METHODS

We conducted a study with 1271 consecutively registered patients with diabetes and 5862 patients without diabetes with known or suspected coronary artery disease undergoing rest thallium 201/stress technetium 99m sestamibi dual-isotope myocardial perfusion SPECT with exercise or adenosine pharmacologic testing. Patients were followed up for at least 1 year. The successful follow-up rate was 92.4% for patients with diabetes and 94.0% for subjects without diabetes. The mean follow-up period was 23.7 +/- 7.7 months for the former group and 21.5 +/- 6.1 months for the latter.

RESULTS

Over the follow-up period, patients with diabetes had significantly higher rates of hard events (cardiac death or nonfatal myocardial infarction) (4.3% per year versus 2.3% per year, P <.001) and higher total event rates (hard events and late revascularization) (9.0% per year versus 5.3% per year, P <. 001) compared with rates among patients without diabetes. Cox proportional hazards analysis revealed that nuclear testing added incremental value over clinical and historical variables among patients with diabetes (global chi(2) increased 46% for the exercise group [n = 619] and 88% for the adenosine group [n = 461]; both P <. 001). The event rates rose significantly as a function of summed stress score and summed difference score among both patients with diabetes and patients without diabetes (P <.001). The patients with diabetes with normal scans had relatively low hard event rates (1% to 2% per year), those with mildly abnormal scans had intermediate hard event rates (3% to 4% per year), and those with moderately to severely abnormal scans had relatively high hard event rates (>7% per year).

CONCLUSIONS

The results of this study indicated that exercise and adenosine stress myocardial perfusion SPECT are valuable for risk stratification and management of patients with diabetes.

Comparative prognostic value of automatic quantitative analysis versus semiquantitative visual analysis of exercise myocardial perfusion single-photon emission computed tomography

OBJECTIVES

The purpose of this study was to determine the prognostic value of automatic quantitative analysis in exercise dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT) and to compare the prognostic value of quantitative analysis to semiquantitative visual SPECT analysis.

BACKGROUND

Extent, severity and reversibility of exercise myocardial perfusion defects have been shown to correlate with prognosis. However, most studies examining the prognostic value of SPECT in chronic coronary artery disease (CAD) have been based on visual analysis by experts.

METHODS

We studied 1,043 consecutive patients with known or suspected CAD who underwent rest Tl-201/exercise Tc-99m sestamibi dual-isotope myocardial perfusion SPECT and were followed up for at least 1 year (mean 20.0+/-3.7 months). After censoring 59 patients with early coronary artery bypass grafting or percutaneous transluminal coronary angioplasty, <60 days after nuclear testing, the final population consisted of 984 patients (36% women, mean age 63+/-12 years).

RESULTS

During the follow-up period, 28 hard events (14 cardiac deaths, 14 nonfatal myocardial infarctions) occurred. Patients with higher defect extent (>10%), severity (>150) and reversibility (>5%) by quantitative SPECT defect analysis, as well as those with an abnormal scan (>2 abnormal segments, summed stress score >4 and summed difference score >2) by semiquantitative visual SPECT analysis, had a significantly higher hard event rate compared to patients with a normal scan (p < 0.001). With both visual and quantitative analyses, hard event rates of approximately 1% with normal scans and 5% with abnormal scans (p > 0.05) were observed over the 20-month follow-up period. A Cox proportional hazards regression model showed that chi-square increased similarly with the addition of quantitative defect extent and visual summed stress score variables after considering both clinical and exercise variables (improvement chi-square = 11 for both, p < 0.0007). There were no significant differences in the areas under receiver operating characteristic curves between quantitative and visual analysis (p > 0.70). Linear regression analysis also indicated that quantitative assessments correlated well with visual semiquantitative assessments.

CONCLUSIONS

The findings of this study indicate that automatic quantitative analysis of exercise stress myocardial perfusion SPECT is similar to semiquantitative expert visual analysis for prognostic stratification. These findings may be of particular clinical importance in laboratories with less experienced visual interpreters.

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.

Incremental prognostic value of adenosine stress myocardial perfusion single-photon emission computed tomography and impact on subsequent management in patients with or suspected of having myocardial ischemia

We examined 1,159 consecutive patients who underwent adenosine stress dual isotope single-photon emission computed tomography (SPECT) and had follow-up performed at a mean of 27.5 +/- 9.1 months (94% complete) for hard events (cardiac death and myocardial infarction) and referral to cardiac catheterization after nuclear testing. During follow-up, 120 hard events occurred (11.0% hard event rate; 72 cardiac deaths [6.7% cardiac death rate] and 57 myocardial infarctions [5.3% myocardial infarction rate]). Cox proportional hazards analysis revealed that nuclear testing added incremental value after adjusting for clinical and historical variables (global chi-square increased 13 to 98 for cardiac death as the end point, global chi-square increased 19 to 105 for hard events as the end point; p <0.0001 for both). Kaplan-Meier analysis demonstrated that after clinical risk stratification of the patient population, the results of nuclear testing were further able to significantly stratify both low- and intermediate- to high-risk patients. Patients with both normal and mildly abnormal scans were at low risk of cardiac death (<1% cardiac death per year of follow-up) and the risk of events increased significantly with worsening scan result. Multivariable analysis revealed that the only predictor of referral to catheterization was the extent and severity of reversible defect present on the scan. Referral rates to early catheterization were very low in patients with normal scans and increased significantly as a function of worsening scan results. In patients who underwent myocardial perfusion SPECT using adenosine stress, the results of nuclear testing yielded incremental prognostic information and clinically relevant risk stratification. Referring physicians predominantly utilized nuclear information when referring patients to catheterization after nuclear testing and do so at rates comparable with those after exercise SPECT despite the higher risk of events in patients undergoing pharmacologic stress.

Identification of severe and extensive coronary artery disease by postexercise regional wall motion abnormalities in Tc-99m sestamibi gated single-photon emission computed tomography

Postexercise wall motion abnormality (WMA) in patients with normal resting myocardial perfusion may represent prolonged postischemic stunning, and may be related to the presence of severe angiographic coronary artery disease (CAD). This study assesses the diagnostic value of postexercise WMA by technetium-99m (Tc-99m) sestamibi gated single-photon emission computed tomography (SPECT) in patients with normal resting perfusion. Ninety-nine patients underwent exercise gated Tc-99m sestamibi/resting thallium-201 SPECT and coronary angiography within 90 days of nuclear testing. All patients had normal perfusion at rest. Multivariate logistic regression analysis demonstrated an incremental value of wall motion and perfusion over perfusion data alone in identifying severe and extensive CAD. Sensitivity for identifying any severely stenosed coronary artery by WMA was significantly higher than by severe perfusion defect (78% vs 49%, p <0.0001). Overall specificities of severe perfusion defect and WMA were 91% and 85%, respectively (p = NS). Thus, postexercise WMA detected by gated Tc-99m sestamibi SPECT in patients with normal resting perfusion is a sensitive marker of severe and extensive CAD.

When to stress patients after coronary artery bypass surgery? Risk stratification in patients early and late post-CABG using stress myocardial perfusion SPECT: implications of appropriate clinical strategies

OBJECTIVES

The study compared the prognostic significance of myocardial perfusion single-photon emission computed tomography (SPECT) (MPS) in patients early and late after coronary artery bypass graft surgery (CABG).

BACKGROUND

The long-term effectiveness of CABG is limited by graft stenosis. The greatest incidence of graft occlusion occurs between five and eight years after surgery. However, little is known regarding the appropriate time to stress patients post-CABG with respect to risk stratification.

METHODS

We identified 1,765 patients, who underwent MPS 7.1 +/- 5.0 years post-CABG. All patients underwent rest T1-201/stress Tc-99m sestamibi MPS and were followed up > or =1 year after testing. Patients with early CABG or PTCA (<60 days after MPS) were censored. The prognostic population consisted of 1,544 patients. A semiquantitative visual analysis employing a 20-segment model was used to define summed stress score (SSS), summed rest score (SRS), summed difference score (SDS), and the number of nonreversible segments (NRS).

RESULTS

During follow-up, 53 cardiac deaths (CD) occurred. There was a significant increase in annual CD rates as a function of SSS. A multivariate analysis identified age, ischemia (SDS), and infarct size (NRS) as independent predictors of CD. Nuclear variables added incremental value to prescan information. The annual CD rate was relatively low (1.3%) in patients < or =5 years post-CABG. In this subgroup only age and infarct size (NRS) were predictive of CD.

CONCLUSION

MPS is strongly predictive of subsequent CD in post-CABG patients and adds incremental value over clinical and treadmill test information. Our data suggest that symptomatic patients < or =5 years and all patients >5 years post-CABG may benefit from testing.

Noninvasive strategies for the estimation of cardiac risk in stable chest pain patients. The Economics of Noninvasive Diagnosis (END) Study Group

Effective allocation of medical resources in stable chest pain patients requires the accurate diagnosis of coronary artery disease and the stratification of future cardiac risk. We studied the relative predictive value for cardiac death of 3 commonly applied noninvasive strategies, clinical assessment, stress electrocardiography, and myocardial perfusion tomography, in a large, multicenter population of stable angina patients. The multicenter observational series comprised 7 community and academic medical centers and 8,411 stable chest pain patients. All patients underwent pretest clinical screening followed by stress (exercise 84% or pharmacologic 16%) electrocardiography and myocardial perfusion tomography. Risk-adjusted multivariable Cox proportional hazards models were developed to predict cardiac death. Kaplan-Meier rates of time to cardiac catheterization were also computed. Cardiac mortality was 3% during the 2.5 +/- 1.5 years of follow-up. The number of infarcted vascular territories and pretest clinical risk factors were strong predictors of cardiac mortality, whereas the number of ischemic vascular territories gained increasing importance when determining post-test resource use requirements (i.e., the decision to perform cardiac catheterization). Exertional ST-segment depression in a population with a high frequency of electrocardiographic abnormalities at rest was not a significant differentiator of cardiac death risk. Stable chest pain patients are accurately identified as being at high risk for near-term cardiac events by both physicians' screening clinical evaluation and by the results of stress myocardial perfusion imaging. Disease management strategies for stable chest pain patients aimed at risk reduction should incorporate knowledge of relevant end points in treatment and guideline development.

Incremental prognostic value of rest-redistribution (201)Tl single-photon emission computed tomography

BACKGROUND

The incremental prognostic value of rest-redistribution (201)Tl compared with stress and rest perfusion abnormalities has not been defined.

METHODS AND RESULTS

We identified 458 patients who underwent rest (201)Tl /stress (exercise or adenosine) (99m)Tc sestamibi single-photon emission computed tomography (SPECT) and had late (18 to 24 hours) (201)Tl imaging, were not revascularized within 60 days of SPECT, and were followed up at >1 year. SPECT images were visually analyzed with the use of a 20-segment model on a scale of 0 to 4. Thirty-seven cardiac deaths (CDs) and 17 nonfatal myocardial infarctions occurred. Univariate Cox proportional hazards analysis showed that the presence of a large amount of rest (201)Tl reversibility (rest-late summed difference score [SDS] of >8) was a significant predictor of CD (chi(2) = 5.77, P = 0.02) and CD or myocardial infarction (chi(2) = 5.3, P = 0.02). The CD rate was 9.3% y(-1) in patients with rest-late SDS of >8 compared with 3.6% y(-1) in patients with a mild/moderate amount of rest reversibility (rest-late SDS 3 to 8) and 3.4% y(-1) in patients with no rest reversibility (rest-late SDS <3) (P = 0.029). Kaplan-Meier survival analysis demonstrated significantly lower cumulative survival rates in patients with rest-late SDS of >8 (P = 0.01). Multivariate Cox proportional hazards analysis demonstrated that the presence of a large amount of resting reversibility was an independent and incremental predictor of CD after adjustment for stress and rest perfusion information. Multivariate logistic regression analysis demonstrated that resting reversibility was not an independent predictor of referral to coronary angiography and revascularization.

CONCLUSIONS

The identification of a large amount of resting (201)Tl reversibility is an independent predictor of CD over stress and rest perfusion abnormalities.

Serial changes on quantitative myocardial perfusion SPECT in patients undergoing revascularization or conservative therapy

BACKGROUND

Little is known about changes of myocardial perfusion in patients undergoing coronary revascularization or medical therapy. The purpose of this observational study was to assess the long-term effects of revascularization or conservative therapy on serial quantitative myocardial perfusion single photon emission computed tomography (SPECT).

METHODS AND RESULTS

The study population consisted of 421 patients who underwent serial rest thallium-201/stress technetium-99m sestamibi dual-isotope myocardial perfusion SPECT with at least a 1-year interval between the 2 studies and who had abnormal quantitative scan results on the first stress SPECT. The mean interval between scans was 32.7 +/- 15.9 months. Patients were divided into 3 groups according to stress defect extent: group 1 had small stress defects (4%-10%, n = 145), group 2 had intermediate stress defects (>10%-20%, n = 144), and group 3 had extensive stress defects (>20%, n = 132) at baseline. Forty patients in group 1, 44 in group 2, and 54 in group 3 underwent coronary revascularization between 2 SPECT studies; the others had conservative therapy. In group 3 patients with revascularization, stress defect extent and reversible defect extent were remarkably reduced (14.5% +/- 13.6% and 13.1% +/- 12.5%, respectively; both P <.0001), with greater improvement in those patients reporting increased use of cardiac medications; resting defect extent was slightly reduced (1.9% +/- 6.4%, P <.05). In group 3 patients with conservative therapy, a small reduction in stress defect extent was noted (2.3% +/- 8.3%, P <.05). In group 2, there were modest, similar reductions in reversible defect extent in both the patients with revascularization (2.7% +/- 7.7%, P <.05) and those with conservative therapy (1.8% +/- 7.3%, P <.05), as well as a small but significant reduction in stress defect extent in those with conservative therapy (2.1% +/- 8.2%, P <.05). In group 1 patients, no significant changes in stress, rest, or reversible defect extent were found with either therapy.

CONCLUSIONS

The findings of this study show that improvement in quantitative myocardial perfusion abnormalities over time occurs in some patients with either revascularization or conservative therapy and suggest that, in patients with extensive defects, greater improvement may be seen in those who undergo revascularization.

Comparison of post-stress ejection fraction and relative left ventricular volumes by automatic analysis of gated myocardial perfusion single-photon emission computed tomography acquired in the supine and prone positions

BACKGROUND

We have previously described an automatic method for measuring left ventricular ejection fraction (LVEF) for myocardial perfusion single-photon emission computed tomography (SPECT). The repeatability of this method has not been previously described.

METHODS AND RESULTS

This study compares LVEF and relative end-systolic and end-diastolic volumes assessed from myocardial perfusion SPECT by our automatic method in 180 consecutive patients undergoing gated myocardial perfusion SPECT with injection of 99mTc-labeled sestamibi in whom the acquisitions were performed sequentially in supine and prone positions. The algorithm operated completely automatically in the prone and supine positions in 178 of the 180 patients. Very high correlations were observed for LVEF (r = 0.93), relative left ventricular end-systolic volume (r = 0.98), and relative left ventricular end-diastolic volume (r = 0.97). The mean paired absolute difference between LVEFs in the prone and supine position was 3.8+/-3.2, for left ventricular end-systolic volume was 4.9+/-4.8 ml, and for left ventricular end-diastolic volume was 7.4+/-6.7 ml. When patients were classified by the extent and severity of stress perfusion defect, there was no significant difference in repeatability for the measurements in any category.

CONCLUSIONS

Our algorithm for automatic quantification of LVEF and relative end-systolic and end-diastolic volumes from gated 99mTc sestamibi myocardial perfusion SPECT is repeatable. When performed in the prone position, values of ejection fractions and ventricular volumes are essentially identical to those obtained in the supine position.

Risk stratification in coronary artery disease: implications for stabilization and prevention

Noninvasive nuclear imaging techniques, including dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT), have been employed in the development of strategies for diagnosis and risk stratification of patients with suspected or known coronary artery disease. These risk-stratification strategies are based on studies in which known outcome has been linked to diagnostic and prognostic information provided by myocardial perfusion SPECT. This article describes a validated dual-isotope exercise protocol for assessment of perfusion and function and reviews the evidence on which a cost-effective risk management strategy is based.

Using an outcomes-based approach to identify candidates for risk stratification after exercise treadmill testing

OBJECTIVE

To develop a hierarchical approach to cardiac risk stratification after treadmill testing.

PATIENTS

Clinical and treadmill test data were used to identify a patient population that may be candidates for further risk stratification with stress tomographic myocardial perfusion imaging. A prospective series of 3, 620 medically treated patients (42% female, mean age 63 years) with a 2.5% mortality was identified (follow-up 2.5 +/- SD 1.5 years).

MEASUREMENTS AND MAIN RESULTS

A Cox proportional hazards model was used to estimate a patient's likelihood of cardiac death. Kaplan-Meier survival curves were used to estimate time to cardiac death by nuclear test results. Annual rates of cardiac death were 0. 4% (n = 921), 1% (n = 2,498), and 1% (n = 201) for patients with low, intermediate, and high Duke treadmill scores (DTS). For patients with an intermediate DTS, multivariate estimators of cardiac death included the number of ischemic vascular territories (relative risk per defect 1.4, p =.01), the number of infarcted vascular territories (relative risk per defect 2.4, p =.00001), and the DTS (relative risk per unit 0.97, p =.00001), following adjustment for a patient's pretest risk of coronary disease. For patients with an intermediate DTS, the presence of no, one or two, and three vascular territories with defects was associated with annual rates of cardiac death of 0.5%, 1.4%, and 2.5%, respectively (p <.0001). Kaplan-Meier survival curves exhibited a statistically worsening survival for patients with defects by 1 year after treadmill exercise.

CONCLUSIONS

For symptomatic patients with an intermediate treadmill test score, the exercise myocardial perfusion scan may be used to stratify their risk of cardiac death over 3 years of follow-up. Patient management may be efficiently guided by further outcome assessment, with an exercise nuclear scan for patients whose treadmill test score is intermediate.

Sustained reduction of exercise perfusion defect extent and severity with isosorbide mononitrate (Imdur) as demonstrated by means of technetium 99m sestamibi

BACKGROUND

The impact of long-acting nitrates on the extent and severity of stress-induced myocardial ischemia is not well described, especially after long-term treatment.

METHODS

Forty patients with chronic stable angina and reversible ischemia on an exercise stress myocardial perfusion single photon emission computed tomography (ex-SPECT) were prospectively studied in a 6-week period. At baseline, rest thallium-201/exercise stress technetium 99m sestamibi SPECT was performed, followed by treatment with extended-release isosorbide 5-mononitrate (5-ISMN, Imdur). Follow-up ex-SPECT was performed 5 days and 6 weeks after the initiation of therapy with extended-release 5-ISMN. The exercise treadmill testing (ETT) protocol and exercise duration of the follow-up studies were the same as that of the baseline ETT. Defect extent and severity were analyzed both by means of an automated quantitative method, with CEqual software, and visually, with a 20-segment scoring system (which was also used to derive a summed stress score [SSS]).

RESULTS

In the 6-week study period, significant reductions occurred in both the extent and the severity of exercise-induced ischemia by means of quantitative SPECT (13.8% [P<.0003] and 12.7% [P<.0003], respectively). There was no significant change in these variables between stages 2 (day 5) and 3 (6 weeks), indicating no development of tolerance to the nitrate effect. Similar reductions were noted by means of the visual analysis (SSS reduction of 13.0% [P<.002]) in the entire study period.

CONCLUSIONS

Patients with chronic-stable-angina treated with a long-acting nitrate demonstrate improvement in myocardial perfusion defect extent and severity in an extended period by means of both visual and quantitative analysis of sequential exercise testing to the same rate-pressure product end point.

Transthoracic stress echocardiography with transesophageal atrial pacing for bedside evaluation of inducible myocardial ischemia in patients with new-onset chest pain

To date, there are no data on the feasibility and accuracy of bedside pacing stress echocardiography in patients admitted to the hospital with new-onset chest pain or unstable angina. We evaluated the feasibility of pacing stress echocardiography and examined its correlation with myocardial perfusion stress scintigraphy (rest thallium-201/stress technetium-99m sestamibi dual-isotope myocardial perfusion single-photon emission computerized tomography) performed within 24 hours of the pacing stress echocardiography test. We studied 70 consecutive patients after acute myocardial infarction had been excluded. The bedside pacing stress echocardiography test was performed with 10Fr transesophageal pacing catheters. We found pacing stress echocardiography to be feasible and safe (3% minor adverse event rate) at the patients' bedside. Target heart rate of >85% of the age-predicted heart rate was achieved in 96% of patients, and the mean rate-pressure product was 22,644 +/- 4,520 beats/min/mm Hg. The mean duration of the bedside pacing stress echocardiography test including technical preparations and image interpretation was 41 +/- 7 minutes. Pacing stress echocardiography and myocardial perfusion stress scintigraphy correlated well for identification or exclusion of inducible myocardial ischemia in 63 of 70 patients (90%) (kappa 0.81, p <0.001). The extent of inducible myocardial ischemia by vascular territories correlated with myocardial perfusion stress scintigraphy in 52 of 70 patients (74%) (kappa 0.6, p <0.001). We conclude that bedside pacing stress echocardiography is feasible and safe, and highly correlates with myocardial perfusion stress scintigraphy for identifying inducible myocardial ischemia in patients with new onset of chest pain or unstable angina.

Comparative localization of myocardial ischemia by exercise electrocardiography and myocardial perfusion SPECT

BACKGROUND

Prior angiographic study has shown that the patterns of ST-segment depression during exercise do not provide localizing information of the responsible coronary lesion. However, little is known regarding the ability of exercise-induced ST-segment displacement to localize myocardial perfusion defects.

METHODS AND RESULTS

We studied 552 consecutive patients without prior myocardial infarction who had reversible perfusion defect in one vascular territory on rest 201Tl/exercise 99mTc-labeled sestamibi dual-isotope myocardial perfusion single photon emission computed tomography (SPECT) and ischemic ST depression or elevation during exercise. Of these, 192 patients had angiographically documented coronary artery disease (CAD). Two hundred thirty-two patients had maximal ST depression in anterior leads, 247 patients had maximal ST depression in inferior leads, and 45 patients had similar maximal ST depression in both anterior and inferior leads. Twenty-eight (5%) patients had ST elevation with absent Q waves. In patients with maximal ST depression in anterior leads, perfusion defects were found in the territory of the left anterior descending coronary artery (LAD) in 30%, in the territory of the right coronary artery (RCA) in 52%, and in the territory of the left circumflex coronary artery (LCX) in 18%. In patients with maximal ST depression in inferior leads, perfusion defects were found in RCA territory in 44%, in the LAD territory in 42%, and in the LCX territory in 14%. Compared with exercise ST depression, the less common finding of ST elevation did provide accurate localization of perfusion defects. When ST elevation was greatest in the anterior leads, 96% of patients had LAD territory defects. When ST elevation was most prominent in the inferior leads, 100% patients had RCA territory defects. Data of coronary angiograms demonstrated that myocardial perfusion SPECT correctly identified the most stenotic coronary disease for LAD (94%), LCX (72%), and RCA (75%).

CONCLUSIONS

The findings of this study indicate that the site of maximal ST-segment depression does not identify the localization of myocardial perfusion defects. However, the less common finding of exercise-induced ST-segment elevation does predict localization of myocardial ischemia.

Nuclear cardiology and electron-beam computed tomography: competitive or complementary?

Electron-beam computed tomography (EBCT) and nuclear cardiology techniques are both valuable in the noninvasive assessment of patients with suspected coronary artery disease. The techniques, however, are different in the information they provide about the patient. EBCT provides anatomic information on coronary atherosclerosis, whereas myocardial perfusion single-photon emission computed tomography assesses the physiologic significance of coronary stenosis. Because of these differences, the techniques are highly complementary. In considering the complementary nature of these methods, it is important to clarify the issues being raised. An important question in the consideration of a patient with known or suspected coronary artery disease is, What is the risk in an individual patient of developing clinical coronary artery disease? The answer to this question will determine who needs aggressive medical management. A second question in a suspected coronary artery disease patient is, What is the risk of cardiac death? As will be discussed, this risk, in general, determines the need to consider coronary revascularization. In the former question, EBCT testing and clinical assessment alone is usually sufficient, and in some cases nuclear testing can be of additional value. In answering the second question, on the basis of currently available data, the EBCT and nuclear cardiology studies appear to be operating in a complementary fashion.

Prediction of informativeness for microsatellite markers among progeny of sires used for detection of economic trait loci in dairy cattle

Individual loci affecting economic traits can be located using genetic linkage. Application of either daughter or granddaughter design requires determination of allele origin in the progeny. If only the sires and their progeny are genotyped, the paternal allele origin of progeny having the same genotype as the sire cannot be determined. The expected frequency of informative sons can be predicted for each sire and genetic marker from the allele frequencies in the population. The accuracy of a predictor of the frequency of informative progeny was tested on 103 grandsire x microsatellite combinations. Number of sons per grandsire varied from 24 to 129. Allele frequencies in the population were estimated by genotyping seven sires. The regression of the frequency of informative sons on the predicted frequency was 1.04 with a zero intercept model. Thus, considering the large number of genetic markers available for analysis, predicted informative frequency is a useful criterion for selection of genetic markers.

Achieving sustained improvement in myocardial perfusion: role of isosorbide mononitrate

The efficacy of antianginal agents in the treatment of patients with chronic stable angina has traditionally been evaluated by performance measures, such as the exercise treadmill test (ETT). Although reliable and reproducible, ETT is not a sensitive measure of changes in myocardial ischemia. The effects of antianginal agents on coronary blood flow and myocardial perfusion have been less frequently studied. Angiographic studies have demonstrated that nitrates may operate by preferentially directing blood flow to ischemic regions of the myocardium. These investigations have been limited, however, by the invasive nature of the evaluation. Measurements of regional myocardial perfusion may also be made with noninvasive tests. Both quantitative single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have been employed, but few studies have used these techniques to assess the effects of antianginal drugs (in general) and nitrates (in particular) on changes in reversible myocardial perfusion defects. Studies that have evaluated the direct effects of nitrate treatment on coronary blood flow and myocardial perfusion defects in patients with chronic stable angina are reviewed, and preliminary data from a study of the effects of long-term nitrate treatment on myocardial perfusion are discussed.

Evidence-based risk assessment in noninvasive imaging

Assessment of important clinical and economic outcomes has become central to the evaluation of patient care. Outcome research is deeply rooted in epidemiology, including the use of multivariable, risk-adjusted regression analysis. In our current health care environment, these methods are increasingly being used to assess the quality of care and to profile physicians and laboratories. Nuclear medicine physicians therefore need to better understand outcome methodologies in order to evaluate patient outcomes, develop guidelines, and decide on patient management.

METHODS

This review describes the methods of assessing the diagnostic and prognostic value of nuclear medicine techniques and, briefly, the methodologic limitations of sample size, frequency and type of events, and follow-up periods and the incremental value of imaging. Also described are logistic regression and Cox proportional hazards modeling. Models for risk assessment are designed to identify whether patients require conservative (i.e., low-risk) or aggressive (i.e., high-risk) treatment. Treatment selection is currently based on risk assessment and the formation of an integrated, empiric risk stratification algorithm of care. This review also includes the methods of assessing economic effectiveness and quality-of-life issues for patients examined with nuclear medicine techniques.

CONCLUSION

In this era of constrained resources, low-cost outpatient-based care may be of increasing importance. High-quality evidence of the clinical and economic outcome of nuclear imaging is essential for helping health care providers and payers assess its value.

A new algorithm for the quantitation of myocardial perfusion SPECT. I: technical principles and reproducibility

We have developed a new, completely automatic 3-dimensional software approach to quantitative perfusion SPECT. The main features of the software are myocardial sampling based on an ellipsoid model; use of the entire count profile between the endocardial and epicardial surfaces; independence of the algorithm from myocardial shape, size, and orientation and establishment of a standard 3-dimensional point-to-point correspondence among all sampled myocardial regions; automatic generation of quantitative measurements and 5-point semiquantitative scores for each of 20 myocardial segments and automatic derivation of summed perfusion scores; and automatic generation of normal limits for any given patient population on the basis of data fractionally normalized to minimize hot spot artifacts.

METHODS

The new algorithm was tested on the tomographic images of 420 patients studied with a rest 201TI (111-167 MBq, 35 s/projection)-stress 99mTc-sestamibi (925-1480 MBq, 25 s/projection) separate dual-isotope protocol on a single-detector camera, a dual-detector 90 degrees camera, and a triple-detector camera.

RESULTS

The algorithm was successful in 397 of 420 patients (94.5%) and 816 of 840 image datasets (97.1%), with a statistically significant difference between the success rates of the 201TI images (399/ 420, or 95.0%) and the 99mTc images (417/420, or 99.3%; P < 0.001). Algorithm failure was caused by extracardiac uptake (10/24, or 41.7%) or inaccurate identification of the valve plane because of low count statistics (14/24, or 58.3%) and was obviated by simply limiting the image volume in which the software operates. Reproducibility of measurements of summed perfusion scores (r = 0.999 and 1 for stress and rest, respectively), global defect extent (r = 0.999 and 1 for stress and rest, respectively), and segmental perfusion scores (exact agreement = 99.9%, kappa = 0.998 for stress and 0.997 for rest) was extremely high.

CONCLUSION

Automatic 3-dimensional quantitation of perfusion from 201Tl and 99mTc-sestamibi images is feasible and reproducible. The described software, because it is based on the same sampling scheme used for gated SPECT analysis, ensures intrinsically perfect registration of quantitative perfusion with quantitative regional wall motion and thickening information, if gated SPECT is used.