James R. Corbett

Simultaneous Transmission/Emission Myocardial Perfusion Tomography: Diagnostic Accuracy of Attenuation-Corrected 99mTc-Sestamibi Single-Photon Emission Computed Tomography

BACKGROUND The purpose of the present study was to assess the diagnostic performance of attenuation-corrected (AC) stress 99mTc-sestamibi cardiac single-photon emission computed tomography (SPECT) for the identification of coronary heart disease (CHD). METHODS AND RESULTS With a triple-detector SPECT system with a 241Am transmission line source, simultaneous transmission/emission tomography (TCT/ECT) was performed on 60 patients with angiographic coronary disease and 59 patients with < or = 5% likelihood of CHD. Iteratively reconstructed AC stress 99mTc-sestamibi perfusion images were compared with uncorrected (NC) filtered-backprojection images. Normal database polar maps were constructed from AC and NC images for quantitative analyses. From the low-likelihood patients, the visual and quantitative normalcy rates increased from 0.88 and 0.76 for NC to 0.98 and 0.95 for AC (P < .05). For the detection of CHD, the receiver operating characteristic curves for the AC images demonstrated improved discrimination capacity (P < .05), and sensitivity/specificity values increased from 0.78/0.46 (NC) to 0.84/0.82 (AC) with visual analysis and from 0.84/0.46 (NC) to 0.88/0.82 (AC) with quantitative analysis. For localization of stenosed vessels, visual and quantitative sensitivity values were 0.51 and 0.63 for NC and 0.64 and 0.78 for AC images (P < .05), respectively. CONCLUSIONS TCT/ECT myocardial perfusion imaging significantly improves the diagnostic accuracy of cardiac SPECT for the detection and localization of CHD. Clinical use of TCT/ECT imaging deserves serious consideration.

Patient management after noninvasive cardiac imaging: Results from SPARC (Study of myocardial perfusion and coronary anatomy imaging roles in coronary artery disease)

OBJECTIVES This study examined short-term cardiac catheterization rates and medication changes after cardiac imaging. BACKGROUND Noninvasive cardiac imaging is widely used in coronary artery disease, but its effects on subsequent patient management are unclear. METHODS We assessed the 90-day post-test rates of catheterization and medication changes in a prospective registry of 1,703 patients without a documented history of coronary artery disease and an intermediate to high likelihood of coronary artery disease undergoing cardiac single-photon emission computed tomography, positron emission tomography, or 64-slice coronary computed tomography angiography. RESULTS Baseline medication use was relatively infrequent. At 90 days, 9.6% of patients underwent catheterization. The rates of catheterization and medication changes increased in proportion to test abnormality findings. Among patients with the most severe test result findings, 38% to 61% were not referred to catheterization, 20% to 30% were not receiving aspirin, 35% to 44% were not receiving a beta-blocker, and 20% to 25% were not receiving a lipid-lowering agent at 90 days after the index test. Risk-adjusted analyses revealed that compared with stress single-photon emission computed tomography or positron emission tomography, changes in aspirin and lipid-lowering agent use was greater after computed tomography angiography, as was the 90-day catheterization referral rate in the setting of normal/nonobstructive and mildly abnormal test results. CONCLUSIONS Overall, noninvasive testing had only a modest impact on clinical management of patients referred for clinical testing. Although post-imaging use of cardiac catheterization and medical therapy increased in proportion to the degree of abnormality findings, the frequency of catheterization and medication change suggests possible undertreatment of higher risk patients. Patients were more likely to undergo cardiac catheterization after computed tomography angiography than after single-photon emission computed tomography or positron emission tomography after normal/nonobstructive and mildly abnormal study findings. (Study of Perfusion and Anatomys Role in Coronary Artery [CAD] [SPARC]; NCT00321399).

The value and practice of attenuation correction for myocardial perfusion SPECT imaging: A joint position statement from the American Society of Nuclear Cardiology and the Society of Nuclear Medicine

ConclusionDespite advancements in technologies, non-uniform soft tissue attenuation still affects the diagnostic accuracy of single photon emission computed tomography (SPECT) myocardial perfusion imaging. A variety of indirect measures have been used to reduce the impact of attenuation, most notably electrocardiography-gated SPECT imaging. However, all available techniques have limitations, making interpretation in the presence of attenuation difficult. The ultimate solution, similar to positron emission tomography imaging, is to use hardware/software algorithms to eliminate attenuation and provide images that are more uniform and easier to interpret. Several attenuation correction solutions are currently available and more will be available soon. The value of these solutions has been varied, particularly with clinical applications. Guidelines and standards clearly are necessary.In recognition of the importance of this issue, the American Society of Nuclear Cardiology and the Society of Nuclear Medicine convened a joint task force to develop a position statement on attenuation correction. It is being published concurrently in the Journal of Nuclear Cardiology and The Journal of Nuclear Medicine, a first for these societies.The purpose of this position statement is to clarify the role of attenuation correction in SPECT procedures, to provide guidelines for its clinical use, and to provide a basis for the evaluation of published validation. It is hoped that this position statement will provide an important and useful road map to the widespread adoption of attenuation correction into clinical practice.

Scintigraphic assessment of regionalized defects in myocardial sympathetic innervation and blood flow regulation in diabetic patients with autonomic neuropathy.

OBJECTIVES This study sought to evaluate whether regional sympathetic myocardial denervation in diabetes is associated with abnormal myocardial blood flow under rest and adenosine-stimulated conditions. BACKGROUND Diabetic autonomic neuropathy (DAN) has been invoked as a cause of unexplained sudden cardiac death, potentially by altering electrical stability or impairing myocardial blood flow, or both. The effects of denervation on cardiac blood flow in diabetes are unknown. METHODS We studied 14 diabetic subjects (7 without DAN, 7 with advanced DAN) and 13 nondiabetic control subjects without known coronary artery disease. Positron emission tomography using carbon-11 hydroxyephedrine was used to characterize left ventricular cardiac sympathetic innervation and nitrogen-13 ammonia to measure myocardial blood flow at rest and after intravenous administration of adenosine (140 microg/kg body weight per min). RESULTS Persistent sympathetic left ventricular proximal wall innervation was observed, even in advanced neuropathy. Rest myocardial blood flow was higher in the neuropathic subjects (109 +/- 29 ml/100 g per min) than in either the nondiabetic (69 +/- 8 ml/100 g per min, p < 0.01) or the nonneuropathic diabetic subjects (79 +/- 23 ml/100 g per min, p < 0.05). During adenosine infusion, global left ventricular myocardial blood flow was significantly less in the neuropathic subjects (204 +/- 73 ml/100 g per min) than in the nonneuropathic diabetic group (324 +/- 135 ml/100 g per min, p < 0.05). Coronary flow reserve was also decreased in the neuropathic subjects, who achieved only 46% (p < 0.01) and 44% (p < 0.01) of the values measured in nondiabetic and nonneuropathic diabetic subjects, respectively. Assessment of the myocardial innervation/blood flow relation during adenosine infusion showed that myocardial blood flow in neuropathic subjects was virtually identical to that in nonneuropathic diabetic subjects in the distal denervated myocardium but was 43% (p < 0.05) lower than that in the nonneuropathic diabetic subjects in the proximal innervated segments. CONCLUSIONS DAN is associated with altered myocardial blood flow, with regions of persistent sympathetic innervation exhibiting the greatest deficits of vasodilator reserve. Future studies are required to evaluate the etiology of these abnormalities and to evaluate the contribution of the persistent islands of innervation to sudden cardiac death complicating diabetes.

Resting coronary flow and coronary flow reserve in human infants after repair or palliation of congenital heart defects as measured by positron emission tomography

OBJECTIVE Coronary physiology in infants with congenital heart disease remains unclear. Our objective was to better understand coronary physiology in infants with congenital heart disease. METHODS We used positron emission tomography with nitrogen 13-labeled ammonia to measure myocardial perfusion at rest and with adenosine (142 micrograms/kg/min x 6 minutes) in five infants after anatomic repair of a congenital heart lesion (group I), and in five infants after Norwood palliation for hypoplastic left heart syndrome (group II). The groups were matched for age, weight, and time from the operation. RESULTS Resting coronary flow in the left ventricle in group I was 1.8 +/- 0.2 ml/min/gm; resting flow in the right ventricle in group II was 1.0 +/- 0.3 ml/min/gm (p = 0.003). Coronary flow with adenosine was 2.6 +/- 0.5 ml/min/gm in group I and 1.5 +/- 0.7 ml/min/gm in group II (p = 0.02). Absolute coronary flow reserve was the same in both groups (1.5 +/- 0.2 in group I vs 1.6 +/- 0.3 in group II, p = 0.45). Oxygen delivery was reduced in group II compared with group I at rest (16.1 +/- 4.2 ml/min/100 gm vs 28.9 +/- 4.42 ml/min/100 gm, p = 0.02) and with adenosine (25.5 +/- 8.1 ml/min/100 gm vs 42.3 +/- 5.8 ml/min/100 gm, p = 0.02). CONCLUSIONS Infants with repaired heart disease have higher resting flow and less coronary flow reserve than previously reported for adults. After Norwood palliation, infants have less perfusion and oxygen delivery to the systemic ventricle than do infants with a repaired lesion. This may in part explain why the outcome for patients with Norwood palliation is less favorable than for others.

Cardiovascular adaptations to intense swim training in sedentary middle-aged men and women.

Central and peripheral cardiovascular adaptations to 12 weeks of intense swim training were characterized in 12 previously sedentary middle-aged men and women. Peak oxygen uptake (VO2) during upright bicycle exercise improved from 29.2 +/- 5.6 to 34.7 +/- 6.7 ml/kg/min (mean +/- SD, p less than .01) because of similar increases in peak cardiac output (CO) and calculated arteriovenous oxygen difference (both p = .02). Peak supine VO2 was 10% higher after training (p less than .005) solely because of enhanced CO (p = .005). Peak heart rate decreased in both postures; therefore stroke volume at peak exercise was greater by 10% and 18% in the upright and supine postures, respectively (p = .05 and p = .005). There was an identical 18% rise (p = .01) in peak supine left ventricular end-diastolic volume index by radionuclide ventriculography but no change in left ventricular ejection fraction or end-systolic volume index (ESVI). Peak systolic blood pressure (SBP) was unchanged in the upright posture but was 8% higher (p = .002) during recumbency despite a similar total peripheral resistance and SBP/ESVI ratio. Maximal calf conductance (Gmax), assessed separately by venous occlusion plethysmography after local ischemic exercise to fatigue, was augmented 20% (p less than .02) by training, resulting in an 18% greater hyperemic blood flow (p = .05). Peak VO2, CO, and Gmax were unchanged in five nonexercising control subjects. We conclude that in middle-aged humans, intense swim training for 12 weeks produces adaptations that include a greater capacity for vasodilatation in skeletal muscle and an enhanced cardiac pump capacity.

Clinical review of attenuation-corrected cardiac SPECT.

SummaryRather than the introduction of a heralded technologic advancement in cardiac SPECT imaging challenging the accuracy of PET perfusion imaging, the commercial introduction of attenuation correction, has been met with at least as many negative as positive reports. Some studies have reported significant improvements in specificity or specificity and sensitivity, especially for high-risk patterns of coronary artery disease; others have reported no improvement or a decrease in accuracy resulting from the introduction of troublesome artifacts. Although this review has attempted to emphasize the positive aspects of attenuation-corrected cardiac SPECT perfusion imaging and the potential for improved patient care it may provide, several negative reports continue to appear.68,69,108,109 Still there has been sufficient positive data reported to suggest that with fully developed, accurate, and robust correction methods, significant gains in SPECT assessments, of the presence and extent of CHD, patient risk, and myocardial viability can be anticipated. Ultimately attenuation correction for cardiac SPECT should have a positive impact on the management of patients with coronary artery disease with important savings in lives and health care dollars.

Is There a Dose-Response Relationship for Heart Disease With Low-Dose Radiation Therapy?

PURPOSE To quantify cardiac radiation therapy (RT) exposure using sensitive measures of cardiac dysfunction; and to correlate dysfunction with heart doses, in the setting of adjuvant RT for left-sided breast cancer. METHODS AND MATERIALS On a randomized trial, 32 women with node-positive left-sided breast cancer underwent pre-RT stress single photon emission computed tomography (SPECT-CT) myocardial perfusion scans. Patients received RT to the breast/chest wall and regional lymph nodes to doses of 50 to 52.2 Gy. Repeat SPECT-CT scans were performed 1 year after RT. Perfusion defects (PD), summed stress defects scores (SSS), and ejection fractions (EF) were evaluated. Doses to the heart and coronary arteries were quantified. RESULTS The mean difference in pre- and post-RT PD was -0.38% ± 3.20% (P=.68), with no clinically significant defects. To assess for subclinical effects, PD were also examined using a 1.5-SD below the normal mean threshold, with a mean difference of 2.53% ± 12.57% (P=.38). The mean differences in SSS and EF before and after RT were 0.78% ± 2.50% (P=.08) and 1.75% ± 7.29% (P=.39), respectively. The average heart Dmean and D95 were 2.82 Gy (range, 1.11-6.06 Gy) and 0.90 Gy (range, 0.13-2.17 Gy), respectively. The average Dmean and D95 to the left anterior descending artery were 7.22 Gy (range, 2.58-18.05 Gy) and 3.22 Gy (range, 1.23-6.86 Gy), respectively. No correlations were found between cardiac doses and changes in PD, SSS, and EF. CONCLUSIONS Using sensitive measures of cardiac function, no clinically significant defects were found after RT, with the average heart Dmean <5 Gy. Although a dose response may exist for measures of cardiac dysfunction at higher doses, no correlation was found in the present study for low doses delivered to cardiac structures and perfusion, SSS, or EF.

Is anterior ST depression with acute transmural inferior infarction due to posterior infarction?: A vectorcardiographic and scintigraphic study

The hypothesis that anterior ST segment depression represents concomitant posterior infarction was tested in 49 patients admitted with a first transmural inferior myocardial infarction. Anterior ST depression was defined as 0.1 mV or more ST depression in leads V1, V2 or V3 on an electrocardiogram recorded within 18 hours of infarction. Serial vectorcardiograms and technetium pyrophosphate scans were obtained. Eighty percent of the patients (39 of 49) had anterior ST depression. Of these 39 patients, 34% fulfilled vectorcardiographic criteria for posterior infarction, and 60% had pyrophosphate scanning evidence of posterior infarction. Early anterior ST depression was neither highly sensitive (84%) nor specific (20%) for the detection of posterior infarction as defined by pyrophosphate imaging. Of patients with persistent anterior ST depression (greater than 72 hours), 87% had posterior infarction detected by pyrophosphate scan. In patients with inferior myocardial infarction, vectorcardiographic evidence of posterior infarction correlated poorly with pyrophosphate imaging data. Right ventricular infarction was present on pyrophosphate imaging in 40% of patients with pyrophosphate changes of posterior infarction but without vectorcardiographic evidence of posterior infarction. It is concluded that: 1) the majority of patients with acute inferior myocardial infarction have anterior ST segment depression; 2) early anterior ST segment depression in such patients is not a specific marker for posterior infarction; and 3) standard vectorcardiographic criteria for transmural posterior infarction may be inaccurate in patients with concomitant transmural inferior myocardial infarction or right ventricular infarction, or both.

Interpretation of SPECT/CT Myocardial Perfusion Images: Common Artifacts and Quality Control Techniques

Nuclear medicine has long played an important role in the noninvasive evaluation of known or suspected coronary artery disease. The development of single photon emission computed tomography (SPECT) led to improved assessments of myocardial perfusion, and the use of electrocardiographic gating made accurate measurements of ventricular wall motion, ejection fractions, and ventricular volumes possible. With the use of hybrid SPECT/computed tomography (CT) scanning systems, the cardiac functional parameters can be measured in a single imaging session. These recent advances in imaging technology have not only enhanced image quality but also improved diagnostic sensitivity and specificity in the detection of clinically relevant coronary artery disease. The CT-based attenuation maps obtained with hybrid SPECT/CT systems also have been useful for improving diagnostic accuracy. However, when attenuation correction and other advanced image data postprocessing techniques are used, unexpected artifacts may arise. The artifacts most commonly encountered are related to the characteristics either of the technology or of the patient. Thus, close attention to the details of acquisition protocols, processing techniques, and image interpretation is needed to ensure high diagnostic quality in myocardial perfusion studies.