Treadmill Exercise Produces Larger Perfusion Defects Than Dipyridamole Stress N-13 Ammonia Positron Emission Tomography

Development and evolution of nuclear cardiology and cardiac PET in Canada

Gated radionuclide angiography and myocardial perfusion imaging were developed in the United States and Europe in the 1970's and soon adopted in Canadian centers. Much of the early development of nuclear cardiology in Canada was in Toronto, Ontario and was quickly followed by new programs across the country. Clinical research in Canada contributed to the further development of nuclear cardiology and cardiac PET. The Canadian Nuclear Cardiology Society (CNCS) was formed in 1995 and became the Canadian Society of Cardiovascular Nuclear and CT Imaging (CNCT) in 2014. The CNCS had a major role in education and advocacy for cardiovascular nuclear medicine testing. The CNCS established the Dr Robert Burns Lecture and CNCT named the Canadian Society of Cardiovascular Nuclear and CT Imaging Annual Achievement Award for Dr Michael Freeman in memoriam of these two outstanding Canadian leaders in nuclear cardiology. The future of nuclear cardiology in Canada is exciting with the expanding use of SPECT imaging to include Tc-99m-pyrophosphate for diagnosis of transthyretin cardiac amyloidosis and the ongoing introduction of cardiac PET imaging.

Noninvasive Multimodality Imaging for the Assessment of Anomalous Coronary Artery

PURPOSE OF REVIEW

Anomalous aortic origin of a coronary artery (AAOCA) is a rare congenital coronary anomaly with the potential to cause myocardial ischemia and adverse cardiac events. The presence of AAOCA anatomy itself does not necessarily implicate a need for revascularization. Therefore, the purpose of this review is to assess how noninvasive comprehensive anatomic- and physiologic evaluation may guide patient management.

RECENT FINDINGS

The assessment of AAOCA includes an accurate description of the anomalous origin/vessel course including anatomical high-risk features such as a slit-like ostium, proximal narrowing, elliptic vessel shape, acute take-off angle, intramural course, and possible concomitant coronary atherosclerosis and hemodynamics. Various cardiac imaging modalities offer unique advantages and capabilities in visualizing these anatomical and functional aspects of AAOCA. This review explored the role of noninvasive multimodality imaging in the characterization of AAOCA by highlighting the strengths, limitations, and potential applications of the current different cardiac imaging methods, with a focus on the pathophysiology of myocardial ischemia and stress testing protocols.

Review of cardiovascular imaging in the Journal of Nuclear Cardiology 2022: positron emission tomography, computed tomography, and magnetic resonance

In 2022, the Journal of Nuclear Cardiology® published many excellent original research articles and editorials focusing on imaging in patients with cardiovascular disease. In this review of 2022, we summarize a selection of articles to provide a concise recap of major advancements in the field. In the first part of this 2-part series, we addressed publications pertaining to single-photon emission computed tomography. In this second part, we focus on positron emission tomography, cardiac computed tomography, and cardiac magnetic resonance. We specifically review advances in imaging of non-ischemic cardiomyopathy, cardio-oncology, infectious disease cardiac manifestations, atrial fibrillation, detection and prognostication of atherosclerosis, and technical improvements in the field. We hope that this review will be useful to readers as a reminder to articles they have seen during the year as well as ones they have missed.

Feasibility of exercise treadmill 13N-ammonia positron emission tomography myocardial perfusion imaging using an off-site cyclotron

BACKGROUND

Myocardial perfusion imaging with treadmill exercise nitrogen-13 (13N)-ammonia positron emission tomography (PET) presents a logistical challenge. We investigated the feasibility of exercise treadmill (GXT) 13N-ammonia PET MPI using an off-site cyclotron for production of 13N-ammonia.

METHODS

Thirty-three patients underwent GXT 13N-ammonia PET MPI over 23 months. 13N-ammonia doses were prepared at an off-site cyclotron. Patients underwent 13N-ammonia resting and 13N-ammonia GXT emission and transmission scans at our facility. Image quality, perfusion data, and clinical variables were evaluated.

RESULTS

We analyzed 33 patients (7/26 female/male). Mean age was 63 ± 12 years and mean BMI was 33.7 ± 6.9. GXT PET was feasible in all patients. Image quality was good in 29 patients, adequate in 3, and severely compromised in 1 patient. Summed stress score was 4.5 ± 5.7. Resting and GXT left ventricular ejection fractions were 63.7 ± 10.9% and 66.3 ± 13.1%. TID ratio was 1.0 ± 0.1.

CONCLUSIONS

Treadmill exercise 13N-ammonia PET is feasible in a large medical center without access to an on-site cyclotron. This technique requires close coordination with an off-site cyclotron but expands the role of PET to patients for whom exercise is more appropriate than pharmacologic stress imaging.

Development, diagnostic performance, and interobserver agreement of a 18F-flurpiridaz PET automated perfusion quantitation system

BACKGROUND

Computerized methodologies standardize the myocardial perfusion imaging (MPI) interpretation process.

METHODS

To develop an automated relative perfusion quantitation approach for 18F-flurpiridaz, PET MPI studies from all phase III trial participants of 18F-flurpiridaz were divided into 3 groups. Count distributions were obtained in N = 40 normal patients undergoing pharmacological or exercise stress. Then, N = 90 additional studies were selected in a derivation group. Following receiver operating characteristic curve analysis, various standard deviations below the mean normal were used as cutoffs for significant CAD, and interobserver variability determined. Finally, diagnostic performance was compared between blinded visual readers and blinded derivations of automated relative quantitation in the remaining N = 548 validation patients.

RESULTS

Both approaches yielded comparable accuracies for the detection of global CAD, reaching 71% and 72% by visual reads, and 72% and 68% by automated relative quantitation, when using CAD ≥ 70% or ≥ 50% stenosis for significance, respectively. Similar results were observed when analyzing individual coronary territories. In both pharmacological and exercise stress, automated relative quantitation demonstrated significantly more interobserver agreement than visual reads.

CONCLUSIONS

Our automated method of 18F-flurpiridaz relative perfusion analysis provides a quantitative, objective, and highly reproducible assessment of PET MPI in normal and CAD subjects undergoing either pharmacological or exercise stress.

Cardiac perfusion by positron emission tomography

Myocardial perfusion imaging (MPI) with positron emission tomography (PET) is an established tool for evaluation of obstructive coronary artery disease (CAD). The contemporary 3-dimensional scanner technology and the state-of-the-art MPI radionuclide tracers and pharmacological stress agents, as well as the cutting-edge image reconstruction techniques and data analysis software, have all enabled accurate, reliable and reproducible quantification of absolute myocardial blood flow (MBF), and henceforth calculation of myocardial flow reserve (MFR) in several clinical scenarios. In patients with suspected coronary artery disease, both absolute stress MBF and MFR can identify myocardial territories subtended by epicardial coronary arteries with haemodynamically significant stenosis, as defined by invasive coronary fractional flow reserve measurement. In particular, absolute stress MBF and MFR offered incremental prognostic information for predicting adverse cardiac outcome, and hence for better patient risk stratification, over those provided by traditional clinical risk predictors. This article reviews the available evidence to support the translation of the current techniques and technologies into a useful decision-making tool in real-world clinical practice.

Association between vertebral bone mineral density, myocardial perfusion, and long-term cardiovascular outcomes: A sex-specific analysis

BACKGROUND

Sexual dimorphism in the manifestation of coronary artery disease (CAD) has unleashed a call to reconsider cardiovascular risk assessment. Alterations of bone mineral density (BMD) have been associated with congestive heart failure and appear to be modified by sex. However, the sex-specific association between BMD, myocardial perfusion, and cardiovascular outcomes is currently unknown.

METHODS

A total number of 491 patients (65.9 ± 10.7 years, 32.4% women) underwent 13N-ammonia positron emission tomography/computed tomography for evaluation of CAD, and were tracked for major adverse cardiac events (MACEs).

RESULTS

Event-free survival (median follow-up time of 4.3 ± 2.0 years) was significantly reduced in patients with low (≤ 100 Hounsfield units) compared to those with higher BMD (log-rank P = .037). Accordingly, reduced BMD was chosen as significant predictor of MACE in a fully adjusted proportional hazards regression model (P = .015). Further, a first-order interaction term consisting of sex and BMD was statistically significant (P = .007). BMD was significantly lower in patients with abnormal myocardial perfusion or impaired left ventricular ejection fraction (P < .05). This difference, however, was noticed in men, but not in women.

CONCLUSIONS

The association between low BMD and cardiovascular disease is sex dependent. Our data suggest that quantification of BMD during myocardial perfusion imaging for evaluation of CAD may be particularly useful in men.

Diagnostic accuracy of 13N-ammonia myocardial perfusion imaging with PET-CT in the detection of coronary artery disease

Background

¹³N-ammonia positron emission tomography-computed tomography (PET-CT) is being increasingly used as a non-invasive imaging modality for evaluating patients with known or suspected coronary artery disease (CAD), but information about the diagnostic accuracy of PET-MPI is sparse. Objectives: Our objective was to determine the accuracy of ¹³N-ammonia PET-CT myocardial perfusion imaging (MPI) for detecting CAD.

Methods

We retrospectively evaluated 383 patients with suspected CAD who underwent rest-stress ¹³N- ammonia PET-CT MPI. Invasive coronary angiography (ICA) was performed within 60 days for all patients with abnormal PET-MPI findings and for selected patients with normal PET-MPI findings.

Results

The mean age of the patients was 64±11 years, and the mean body mass index was 32±7 kg/m². Stress perfusion defects were identified in 147 (34%) out of a total of 383 patients. ICA was performed in 213 patients (145 patients with abnormal PET and 68 patients with normal PET). The sensitivity of PET-MPI for detection of obstructive CAD based on ≥50% stenosis was 90%; specificity, 90%; positive predictive value, 96%; negative predictive value, 76%; and diagnostic accuracy, 80%.

Conclusions

PET-MPI with ¹³N-ammonia affords high sensitivity and overall accuracy for detecting CAD. The addition of coronary artery calcium score (CACS) can improve CAD risk stratification.

Benefits of adding coronary calcium score scan to stress myocardial perfusion positron emission tomography imaging

There have been little and conflicting data regarding the relationship between coronary artery calcification score (CACS) and myocardial ischemia on positron emission tomography myocardial perfusion imaging (PET MPI). The aims of this study were to investigate the relationship between myocardial ischemia on PET MPI and CACS, the frequency and severity of CACS in patients with normal PET MPI, and to determine the optimal CACS cutoff point for abnormal PET. This retrospective study included 363 patients who underwent same-setting stress PET perfusion imaging and CACS scan because of clinically suspected coronary artery disease (CAD). Fifty-five (55%) of the 363 patients had abnormal PET perfusion. There was an association between sex, diabetes mellitus (DM), smoking, and CACS and PET perfusion abnormities with P = 0.003, 0.05, 0.005, and 0.001, respectively. However, there was no association between PET perfusion abnormalities with age, body mass index, hypertension, and hypercholesterolemia. There was association between CACS and age, sex, and DM with P = 0.000, 0.014, and 0.052, respectively, and stepwise increase in the frequency of myocardial ischemia and CACS groups. Receiver-operating characteristic analysis showed that a CACS ≥304 is the optimal cutoff for predicting perfusion abnormalities with sensitivity of 64% and specificity of 69%. In conclusion, the frequency of CAC in patients with normal PET MPI is 49%, it is highly recommended to combine CACS with PET MPI in patients without a history of CAD. PET MPI identifies myocardial ischemia and defines the need for coronary revascularization, but CAC reflects the anatomic burden of coronary atherosclerosis. Combining CACS to PET MPI allows better risk stratification and identifies high-risk patients with PET, and it may change future follow-up recommendations. CACS scan is readily available and easily acquired with modern PET-computed tomography (CT) and single-photon emission CT (SPECT)-CT with modest radiation exposure.

Positron Emission Tomography in the Diagnosis and Management of Coronary Artery Disease

Cardiac positron emission tomography (PET) and positron emission tomography/computed tomography (PET/CT) are encouraging precise non-invasive imaging modalities that allow imaging of the cellular function of the heart, while other non-invasive cardiovascular imaging modalities are considered to be techniques for imaging the anatomy, morphology, structure, function and tissue characteristics. The role of cardiac PET has been growing rapidly and providing high diagnostic accuracy of coronary artery disease (CAD). Clinical cardiology has established PET as a criterion for the assessment of myocardial viability and is recommended for the proper management of reduced left ventricle (LV) function and ischemic cardiomyopathy. Hybrid PET/CT imaging has enabled simultaneous integration of the coronary anatomy with myocardial perfusion and metabolism and has improved characterization of dysfunctional areas in chronic CAD. Also, the availability of quantitative myocardial blood flow (MBF) evaluation with various PET perfusion tracers provides additional prognostic information and enhances the diagnostic performance of nuclear imaging.

Risk stratification with exercise N(13)-ammonia PET in adults with anomalous right coronary arteries

Objective

In adults with an interarterial and intramural course of an anomalous right coronary artery from the left sinus (AAORCA), surgical unroofing is recommended in the setting of myocardial ischaemia. However, data regarding functional testing are limited, and the management of adults without ischaemia is unclear. To evaluate these patients, we employed an exercise N¹³-ammonia positron emission tomography (PET) protocol. We hypothesised that patients with typical angina and exertional dyspnoea would be more likely to have ischaemia and that patients without ischaemia could be managed conservatively.

Methods

Between July 2008 and December 2014, we retrospectively identified 27 consecutive patients >18 years old with an interarterial and intramural course of an AAORCA who had exercise N¹³-ammonia PET.

Results

The majority of patients had anatomic delineation with cardiac CT (25, 93%), and most patients had chest pain (24, 89%). Myocardial ischaemia with PET was common (13, 48%), and ischaemia was more likely in patients with typical angina and exertional dyspnoea (p<0.05). Surgery was performed in 12 patients including 11 patients with ischaemia. At a median follow-up of 245 days, there were no deaths in patients with surgery or in patients managed conservatively.

Conclusions

In patients with an interarterial and intramural course of an AAORCA, typical angina and exertional dyspnoea are associated with ischaemia on exercise N¹³-ammonia PET. Referral for surgical unroofing in symptomatic patients with ischaemia on exercise N¹³-ammonia PET and initial conservative management in patients without ischaemia seems appropriate, though larger studies with long-term follow-up are needed.

SPECT and PET imaging of angiogenesis and arteriogenesis in pre-clinical models of myocardial ischemia and peripheral vascular disease

Purpose

The extent of neovascularization determines the clinical outcome of coronary artery disease and other occlusive cardiovascular disorders. Monitoring of neovascularization is therefore highly important. This review article will elaborately discuss preclinical studies aimed at validating new nuclear angiogenesis and arteriogenesis tracers. Additionally, we will briefly address possible obstacles that should be considered when designing an arteriogenesis radiotracer.

Methods

A structured medline search was the base of this review, which gives an overview on different radiopharmaceuticals that have been evaluated in preclinical models.

Results

Neovascularization is a collective term used to indicate different processes such as angiogenesis and arteriogenesis. However, while it is assumed that sensitive detection through nuclear imaging will facilitate translation of successful therapeutic interventions in preclinical models to the bedside, we still lack specific tracers for neovascularization imaging. Most nuclear imaging research to date has focused on angiogenesis, leaving nuclear arteriogenesis imaging largely overlooked.

Conclusion

Although angiogenesis is the process which is best understood, there is no scarcity in theoretical targets for arteriogenesis imaging.

Feasibility and diagnostic accuracy of exercise treadmill nitrogen-13 ammonia PET myocardial perfusion imaging of obese patients

BACKGROUND

Treadmill exercise nitrogen-13 ((13)N)-ammonia positron emission tomography (PET) has logistical challenges and limited literature. We aimed to assess its feasibility, image quality, and diagnostic accuracy in obese and nonobese patients.

METHODS AND RESULTS

Between 2009 and 2012, 10,804 patients were referred for myocardial perfusion imaging, including 300 for treadmill PET, of whom 265 were included in this study. Treadmill testing and PET were performed using standard procedures. Image quality, perfusion, and summed stress score (SSS) were assessed. Invasive coronary angiography was performed within 90 days of PET in 43 patients. Mean ± SD body mass index (BMI) was 35.7 ± 7.7 kg/m(2) (range 19.5-63.5 kg/m(2)). Feasibility of treadmill (13)N-ammonia PET was 100%. Exercise duration was less for obese patients than nonobese patients (P < .001). Image quality was rated good for 96.9% of obese and 100% of nonobese patients. For all patients, sensitivity was 86.4% and specificity was 74.4%. Diagnostic accuracy did not change significantly with increasing BMI. SSS remained significant in predicting angiographic coronary artery disease after adjustment for age, sex, and Duke treadmill score.

CONCLUSIONS

Treadmill (13)N-ammonia PET is highly feasible, yields good image quality, and has moderately high diagnostic accuracy in a small subset of obese and nonobese patients who are deemed able to perform treadmill exercise.

Clinical PET Myocardial Perfusion Imaging and Flow Quantification

Cardiac PET imaging is a powerful tool for the assessment of coronary artery disease. Many tracers with different advantages and disadvantages are available. It has several advantages over single photon emission computed tomography, including superior accuracy and lower radiation exposure. It provides powerful prognostic information, which can help to stratify patients and guide clinicians. The addition of flow quantification enables better detection of multivessel disease while providing incremental prognostic information. Flow quantification provides important physiologic information, which may be useful to individualize patient therapy. This approach is being applied in some centers, but requires standardization before it is more widely applied.

Cardiac PET perfusion tracers: current status and future directions

PET myocardial perfusion imaging (MPI) is increasingly being used for noninvasive detection and evaluation of coronary artery disease. However, the widespread use of PET MPI has been limited by the shortcomings of the current PET perfusion tracers. The availability of these tracers is limited by the need for an onsite ((15)O water and (13)N ammonia) or nearby ((13)N ammonia) cyclotron or commitment to costly generators ((82)Rb). Owing to the short half-lives, such as 76 seconds for (82)Rb, 2.06 minutes for (15)O water, and 9.96 minutes for (13)N ammonia, their use in conjunction with treadmill exercise stress testing is either not possible ((82)Rb and (15)O water) or not practical ((13)N ammonia). Furthermore, the long positron range of (82)Rb makes image resolution suboptimal and its low myocardial extraction limits its defect resolution. In recent years, development of an (18)F-labeled PET perfusion tracer has gathered considerable interest. The longer half-life of (18)F (109 minutes) would make the tracer available as a unit dose from regional cyclotrons and allow use in conjunction with treadmill exercise testing. Furthermore, the short positron range of (18)F would result in better image resolution. Flurpiridaz F 18 is by far the most thoroughly studied in animal models and is the only (18)F-based PET MPI radiotracer currently undergoing clinical evaluation. Preclinical and clinical experience with Flurpiridaz F 18 demonstrated a high myocardial extraction fraction, high image and defect resolution, high myocardial uptake, slow myocardial clearance, and high myocardial-to-background contrast that was stable over time-important properties of an ideal PET MPI radiotracer. Preclinical data from other (18)F-labeled myocardial perfusion tracers are encouraging.

Positron-emitting myocardial blood flow tracers and clinical potential

Positron-emitting myocardial flow radiotracers such as (15)O-water, (13)N-ammonia and (82)Rubidium in conjunction with positron-emission-tomography (PET) are increasingly applied in clinical routine for coronary artery disease (CAD) detection, yielding high diagnostic accuracy, while providing valuable information on cardiovascular (CV) outcome. Owing to a cyclotron dependency of (15)O-water and (13)N-ammonia, their clinical use for PET myocardial perfusion imaging is limited to a few centers. This limitation could be overcome by the increasing use of (82)Rubidium as it can be eluted from a commercially available (82)Strontium generator and, thus, is independent of a nearby cyclotron. Another novel F-18-labeled myocardial flow radiotracer is flurpiridaz which has attracted increasing interest due to its excellent radiotracer characteristics for perfusion and flow imaging with PET. In particular, the relatively long half-life of 109 minutes of flurpiridaz may afford a general application of this radiotracer for PET perfusion imaging comparable to technetium-99m-labeled single-photon emission computed tomography (SPECT). The ability of PET in conjunction with several radiotracers to assess myocardial blood flow (MBF) in ml/g/min at rest and during vasomotor stress has contributed to unravel pathophysiological mechanisms underlying coronary artery disease (CAD), to improve the detection and characterization of CAD burden in multivessel disease, and to provide incremental prognostic information in individuals with subclinical and clinically-manifest CAD. The concurrent evaluation of myocardial perfusion and MBF may lead to a new era of a personalized, image-guided therapy approach that may offer potential to further improve clinical outcome in CV disease patients but needing validation in large-scale clinical trials.

Stress myocardial CT perfusion: an update and future perspective

Coronary computed tomography angiography (CTA) has been shown by several multicenter trials to have excellent diagnostic accuracy in the detection and exclusion of significant coronary stenosis. However, a major limitation of coronary CTA is that the physiological significance of stenotic lesions identified is often unknown. Stress myocardial computed tomography perfusion (CTP) is a novel examination that provides both anatomic and physiological information (i.e., myocardial perfusion). Multiple single-center studies have established the feasibility of stress myocardial CTP. Furthermore, it has been illustrated that a combined CTA/CTP protocol improves the diagnostic accuracy to detect hemodynamic significant stenosis as compared with CTA alone; this combined protocol can also be accomplished at a radiation dose comparable to nuclear myocardial perfusion imaging exams. Although initial results hold some promise, stress myocardial CTP is a modality in its infancy. Further research is required to define, validate, and optimize this new technique. However, it is a modality with significant potential, particularly in the evaluation of chest pain patients, given the advantages of short exam time and comprehensive data acquisition. This review highlights how to perform and interpret stress myocardial CTP, summarizes the current literature, and discusses some future directions.

Advances in PET myocardial perfusion imaging: F-18 labeled tracers

Coronary artery disease and its related cardiac disorders represent the most common cause of death in the USA and Western world. Despite advancements in treatment and accompanying improvements in outcome with current diagnostic and therapeutic modalities, it is the correct assignment of these diagnostic techniques and treatment options which are crucial. From a diagnostic standpoint, SPECT myocardial perfusion imaging (MPI) using traditional radiotracers like thallium-201 chloride, Tc-99m sestamibi or Tc-99m tetrofosmin is the most utilized imaging technique. However, PET MPI using N-13 ammonia, rubidium-82 chloride or O-15 water is increasing in availability and usage as a result of the growing number of medical centers with new-generation PET/CT systems taking advantage of the superior imaging properties of PET over SPECT. The routine clinical use of PET MPI is still limited, in part because of the short half-life of conventional PET MPI tracers. The disadvantages of these conventional PET tracers include expensive onsite production and inconvenient on-scanner tracer administration making them unsuitable for physical exercise stress imaging. Recently, two F-18 labeled radiotracers with longer radioactive half-lives than conventional PET imaging agents have been introduced. These are flurpiridaz F 18 (formerly known as F-18 BMS747158-02) and F-18 fluorobenzyltriphenylphosphonium. These longer half-life F-18 labeled perfusion tracers can overcome the production and protocol limitations of currently used radiotracers for PET MPI.

Cardiac PET/CT for the evaluation of known or suspected coronary artery disease

Positron emission tomography (PET) is increasingly being applied in the evaluation of myocardial perfusion. Cardiac PET can be performed with an increasing variety of cyclotron- and generator-produced radiotracers. Compared with single photon emission computed tomography, PET offers lower radiation exposure, fewer artifacts, improved spatial resolution, and, most important, improved diagnostic performance. With its capacity to quantify rest-peak stress left ventricular systolic function as well as coronary flow reserve, PET is superior to other methods for the detection of multivessel coronary artery disease and, potentially, for risk stratification. Coronary artery calcium scoring may be included for further risk stratification in patients with normal perfusion imaging findings. Furthermore, PET allows quantification of absolute myocardial perfusion, which also carries substantial prognostic value. Hybrid PET-computed tomography scanners allow functional evaluation of myocardial perfusion combined with anatomic characterization of the epicardial coronary arteries, thereby offering great potential for both diagnosis and management. Additional studies to further validate the prognostic value and cost effectiveness of PET are warranted.

Cardiac PET imaging for the detection and monitoring of coronary artery disease and microvascular health

Positron emission tomography (PET) myocardial perfusion imaging in concert with tracer-kinetic modeling affords the assessment of regional myocardial blood flow (MBF) of the left ventricle in absolute terms (milliliters per gram per minute). Assessment of MBF both at rest and during various forms of vasomotor stress provides insight into early and subclinical abnormalities in coronary arterial vascular function and/or structure, noninvasively. The noninvasive evaluation and quantification of MBF and myocardial flow reserve (MFR) extend the scope of conventional myocardial perfusion imaging from detection of end-stage, advanced, and flow-limiting, epicardial coronary artery disease (CAD) to early stages of atherosclerosis or microvascular dysfunction. Recent studies have shown that impaired hyperemic MBF or MFR with PET, with or without accompanying CAD, is predictive of increased relative risk of death or progression of heart failure. Quantitative approaches that measure MBF with PET identify multivessel CAD and offer the opportunity to monitor responses to lifestyle and/or risk factor modification and to therapeutic interventions. Whether improvement or normalization of hyperemic MBF and/or the MFR will translate to improvement in long-term cardiovascular outcome remains clinically untested. In the meantime, absolute measures of MBF with PET can be used as a surrogate marker for coronary vascular health, and to monitor therapeutic interventions. Although the assessment of myocardial perfusion with PET has become an indispensable tool in cardiac research, it remains underutilized in clinical practice. Individualized, image-guided cardiovascular therapy may likely change this paradigm in the near future.

Prognostic value of treadmill exercise and dobutamine stress positron emission tomography

BACKGROUND

Although positron emission tomography (PET) is routinely performed using vasodilator stress, exercise and dobutamine stress are available alternatives. Evidence suggests that vasodilator PET myocardial perfusion imaging (MPI) has prognostic value, but the prognostic value of treadmill exercise and dobutamine PET MPI is unknown.

OBJECTIVE

To determine the potential prognostic value of nonvasodilator stress PET MPI.

METHODS

Patients underwent treadmill exercise or dobutamine PET MPI. Images were assessed qualitatively and semiquantitatively. PET results were categorized as normal (summed stress score [SSS] of less than 4), abnormal (SSS of 4 or greater) or inconclusive (SSS of less than 4 and submaximal peak stress heart rate). Patient follow-up (cardiac death, nonfatal myocardial infarction [MI] and/or late revascularization) was performed.

RESULTS

Of the 124 patients (mean follow-up period of 2.3+/-1.6 years), 46 patients (37%) had a normal study, 15 patients (12%) had an inconclusive study and 63 (51%) had an abnormal PET. Patients with a normal PET had no deaths or nonfatal MI. One patient with a normal PET underwent late revascularization (annual event rate of 1.7%). Patients with an abnormal PET had 15 cardiac events (one cardiac death, four nonfatal MIs and 10 late revascularizations), with an annual event rate of 13.0% (P=0.002).

CONCLUSIONS

Although small, the present study suggests that defects seen on PET myocardial perfusion, resulting from stressors (treadmill exercise and dobutamine) that increase myocardial oxygen demand, may have prognostic value.

Cardiac positron emission tomography: current clinical practice

In the last two decades, the field of nuclear cardiology has experienced significant progress. The introduction of positron emission tomography (PET) imaging represented a major breakthrough that has significantly contributed to a better understanding of physiology and pathophysiology of several heart diseases. Currently, PET imaging is recognized as a well-established method to assess cardiac perfusion, function, metabolism, and viability. This article summarizes the main clinical applications of state-of-the art cardiac PET technology.

Will 3-dimensional PET-CT enable the routine quantification of myocardial blood flow?

Quantification of myocardial blood flow (MBF) and flow reserve has been used extensively with positron emission tomography (PET) to investigate the functional significance of coronary artery disease. Increasingly, flow quantification is being applied to investigations of microvascular dysfunction in early atherosclerosis and in nonatherosclerotic microvascular disease associated with primary and secondary cardiomyopathies. Fully three-dimensional (3D) acquisition is becoming the standard imaging mode on new equipment, bringing with it certain challenges for cardiac PET, but also the potential for MBF to be measured simultaneously with routine electrocardiography (ECG)-gated perfusion imaging. Existing 3D versus 2D comparative studies support the use of 3D cardiac PET for flow quantification, and these protocols can be translated to PET-CT, which offers a virtually noise-free attenuation correction. This technology combines the strengths of cardiac CT for evaluation of anatomy with cardiac PET for quantification of the hemodynamic impact on the myocardium. High throughput clinical imaging protocols are needed to evaluate the incremental diagnostic and prognostic value of this technology.