Relationship between the location of the most severe myocardial perfusion defects, the most severe coronary artery stenosis, and the site of subsequent myocardial infarction.

This study evaluated the relationship between the location of the most severe myocardial perfusion defects, the most severe coronary artery stenosis, and the site of subsequent acute myocardial infarction (AMI). METHODS: Of 3,180 patients who were admitted with a diagnosis of AMI, we identified 44 patients who had undergone previous myocardial perfusion SPECT. Thirty-one of them also had previous coronary angiography. The relationship between the location of the myocardial perfusion defects, the coronary artery stenosis, and the site of subsequent AMI was studied in these patients. RESULTS: The concordance between the location of the most severe reversible defects detected by SPECT and the site of subsequent AMI was 71% (kappa = 0.499). The concordance between the most severe stenosis detected by coronary angiography and the site of subsequent AMI was 64% (kappa = 0.451). However, kappa values for SPECT and coronary angiography were good when the interval between these investigations and subsequent AMI was <3 mo (0.724 and 0.661, respectively), for moderate to severe perfusion defects (0.719), and for 90%-99% coronary stenosis (0.626). CONCLUSION: The culprit lesion is not always the one that is manifested by the most severe reversible perfusion defect or the most critical coronary artery stenosis. Myocardial SPECT and coronary angiography can predict the location of a future AMI in 71% and 64% of patients, respectively. The percentage is higher when the interval between investigations and subsequent AMI is <3 mo, for moderate to severe perfusion defects, and for 90%-99% coronary stenosis.     

Myocardial perfusion reserve in spared myocardium: correlation with infarct size and left ventricular ejection fraction

Purpose

Left ventricular ejection fraction (LVEF) after myocardial infarction is considered to be determined by the size of the infarction and residual function of the spared myocardium. Myocardial perfusion reserve (MPR) has been shown to be a strong prognostic factor in patients with ischaemic heart failure, even stronger than LVEF. In the present study, the interrelationship between MPR, LVEF and infarct size was investigated.

Methods

In total, 102 patients with a prior history of myocardial infarction were included. All underwent rest and stress ¹³N-ammonia and gated ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) for evaluation of myocardial ischaemia and viability. FDG polar maps were used to determine the size of the infarction. The LVEF was obtained by gated ¹⁸F-FDG PET or another available method within 3 months of the PET scan. MPR was obtained per segment in the spared myocardium.

Results

The mean age of the subjects was 68?±?12 years. Global MPR was 1.63?±?0.51. The mean LVEF was 36?±?10 % and mean infarct size 23.72?±?14.8 %. A linear regression model was applied for the analysis considering the LVEF as a dependent variable. All risk factors, mean stress flow, infarct size and MPR were entered as variables. The infarct size (p?<?0.001) and MPR (p?=?0.04) reached statistical significance. In a multivariate model MPR had a stronger correlation with LVEF than infarct size.

Conclusion

In patients with a prior history of myocardial infarction, LVEF is not just related to infarct size but also to MPR in the spared myocardium.     

Myocardial perfusion scintigraphy: the evidence

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.Abbreviations Acc Diagnostic accuracy - ACS Acute coronary syndromes - BCS British Cardiac Society - BNCS British Nuclear Cardiology Society - BNMS British Nuclear Medicine Society - CABG Coronary artery bypass grafting - CHD Coronary heart disease - CT Computed X-ray tomography - LBBB Left bundle branch block - MI Myocardial infarction - MIBI Technetium-99m 2-methoxy-isobutyl-isonitrile - MPS Myocardial perfusion scintigraphy - NSF National Service Framework for Cardiovascular Disease - NSTEMI Non-ST segment elevation myocardial infarction - PCI Percutaneous coronary intervention - Q Quantitative analysis - QALY Quality-adjusted life-year - RCP Royal College of Physicians of London - RCR Royal College of Radiologists - Sens Sensitivity - Spec Specificity - SPET Single-photon emission tomography - STEMI ST segment elevation myocardial infarction - Tetro or tetrofosmin Technetium-99m 1,2-bis[bis(2-ethoxyethyl) phosphino] ethane - 201Tl or thallium Thallium-201 thallous chloride - UA Unstable angina - V Visual analysis     

Radio-iodobenzylguanidine for the scintigraphic location and therapy of adrenergic tumors

Radioiodinated meta-iodobenzylguanidine, a recently developed radiopharmaceutical, has been shown to permit safe, noninvasive, sensitive, and specific scintigraphic location of pheochromocytomas of all types. The technique is especially efficacious in the case of extraadrenal primary lesions and locally recurrent and metastatic tumors. In addition to being taken up by pheochromocytomas, meta-iodobenzylguanidine may be used to image neuroblastomas, nonfunctioning paragangliomas, and carcinoid tumors. Lesions with high 131I-meta-iodobenzylguanidine uptake may respond to treatment with large doses of this radiopharmaceutical.     

Brain perfusion defect size in SPECT predicts outcome in cerebral infarction

The results of previous reports on the usefulness of brain perfusion single photon emission computed tomography (SPECT) in predicting the outcome of patients with acute cerebral infarction are conflicting. We therefore studied brain perfusion in 64 patients with a single supratentorial infarction. Contradictory to previous results the perfusion defect volume estimated from transversal and coronal slices correlated significantly with both presenting clinical findings and outcome. Although the clinical status at admission also correlated well with outcome, there was a subgroup of patients in which the favourable outcome was predicted only by SPECT and not by physical or any other examination at admission.     

Myocardial perfusion and perfusion reserve in endurance-trained men

PURPOSE: This study was undertaken to determine whether endurance training is associated with changes in myocardial perfusion in humans. METHODS: Myocardial perfusion was measured in eleven trained and nine sedentary men at rest and during adenosine-stimulated hyperemia using positron emission tomography (PET). Left ventricular (LV) dimensions and mass were measured using echocardiography. Myocardial work per gram of tissue was calculated as (cardiac output. mean arterial blood pressure)/LV mass. RESULTS: LV mass was significantly higher and myocardial work per gram of tissue lower in the trained than in the untrained subjects. Basal (0.78 +/- 0.10 and 0.76 +/- 0.15 mL. min-1. g-1, P = NS) and adenosine-stimulated perfusion (3.46 +/- 0.91 and 3.14 +/- 0.70 mL. min-1. g-1, P = NS) were similar between trained and untrained men, respectively. Consequently, myocardial perfusion reserve was similar in both groups (4.4 +/- 1.2 and 4.1 +/- 0.7, P = NS). In addition, coronary resistance at baseline (115 +/- 17 vs 119 +/- 22, mm Hg. mL. min-1. g-1, P = NS) and during adenosine infusion (28 +/- 8 vs 30 +/- 8, mm Hg. mL. min-1. g-1, P = NS) were similar in both groups. Resting myocardial work correlated with resting myocardial perfusion in both groups, but the relationship between perfusion and work was different between the groups so that perfusion for a given myocardial work was significantly higher in trained subjects (0.56 +/- 0.04 and 0.34 +/- 0.05 mL. (mm Hg. L)-1, P < 0.001). CONCLUSIONS: These findings suggest that endurance trained subjects do not have different resting or adenosine-stimulated myocardial perfusion. However, the relationship between myocardial perfusion and work appears altered in the athletes.     

Myocardial kinetics of radiolabeled perfusion agents: Basis for perfusion imaging

The myocardial deposition of radiolabeled perfusion agents permits the noninvasive assessment of regional coronary blood flow. The design of imaging protocols and the optimal interpretation of clinical perfusion studies are based on an understanding of the kinetics of blood-tissue exchange for these compounds. Thallium 201 and the technetium 99m-labeled compounds sestamibi, teboroxime, and tetrofosmin show differing myocardial extraction and retention. This review focuses on studies that used cell culture, isolated heart, and intact animal models that form the basis of our current understanding of the myocardial kinetics of these imaging agents.     

Myocardial perfusion imaging agents: SPECT and PET

The advent of myocardial perfusion imaging 30 years ago was a major landmark, which heralded the emergence of the field of nuclear cardiology into clinical practice. Over the years, the different tracers cited in this review have been used with SPECT or PET imaging technologies for the noninvasive evaluation of regional myocardial blood flow, which has enhanced our ability to diagnose CAD, assess prognosis, detect viable myocardium, and evaluate the efficacy of therapies aimed at improving myocardial blood flow. In the future, new SPECT perfusion agents should be developed and validated in the experimental laboratory for feasibility in the clinical setting. Hopefully, such new radiolabeled perfusion agents will have a high first-pass extraction, will be more linear with flow increases in the hyperemic range, and will be labeled with Tc-99m. The clearance rates from the myocardium after initial uptake should be slow enough, as with Tl-201, to acquire high-quality poststress gated SPECT images. Ideally, such perfusion agents should also be extracted intracellularly with quantitative uptake reflecting the degree of viability (eg, as with Tl-201). Absolute quantitation of myocardial blood flow in milliliters per minute per gram by use of SPECT technology would be highly desirable, particularly to increase the detection rate of multivessel disease in which flow reserve is uniformly diminished. This is often categorized as balanced ischemia. Absolute quantitation is a major strength of PET perfusion tracers, as is the ability to accurately correct for attenuation, thereby providing high sensitivity and specificity for CAD detection. The roll-off or plateau in myocardial uptake with hyperemia is also seen with the PET perfusion tracers such as N-13 ammonia and Rb-82. Despite the advent of molecular imaging and the introduction of new imaging agents by which to noninvasively evaluate biologic processes such as apoptosis and angiogenesis in vivo, myocardial perfusion imaging will remain the mainstay of nuclear cardiology in the near future. Continued research and development for this imaging technique are warranted for the reasons cited in this review.     

Myocardial infarction: optimization of inversion times at delayed contrast-enhanced MR imaging

Seventeen patients underwent magnetic resonance (MR) imaging for myocardial viability with a protocol approved by the institutional review board and gave written informed consent. Breath-hold cine inversion-recovery segmented k-space true fast imaging with steady-state precession sequence, referred to as inversion time (TI) mapping, was performed to determine optimal TI for myocardial infarction inversion-recovery imaging. From TI mapping, optimal TI was 180-315 msec 10-15 minutes after administration of 0.15 mmol/kg of gadolinium-based contrast material. At that optimal TI, relative signal intensity of infarcted myocardium compared with uninfarcted myocardium was maximal (mean +/- standard deviation, 297.8% +/- 86.5), whereas signal-to-noise ratio of uninfarcted myocardium was minimal (4.5 +/- 1.2). When applied to conventional myocardial infarction inversion-recovery imaging, optimal TI resulted in nulling of signal intensity of uninfarcted myocardium in all patients and in excellent conspicuity of infarcted myocardium in all nine patients with visible infarction.