Myocardial perfusion and viability by positron emission tomography in infants and children with coronary abnormalities: correlation with echocardiography, coronary angiography, and histopathology

Image Quality of Cardiac Silicon Photomultiplier PET/CT Using an Infant Phantom of Extremely Low Birth Weight

The lack of pediatrics-specific equipment for nuclear medicine imaging has resulted in insufficient diagnostic information for newborns, especially low-birth-weight infants. Although PET offers high spatial resolution and low radiation exposure, its use in newborns is limited. This study investigated the feasibility of cardiac PET imaging using the latest silicon photomultiplier (SiPM) PET technology in infants of extremely low birth weight (ELBW) using a phantom model. Methods: The study used a phantom model representing a 500-g ELBW infant with brain, cardiac, liver, and lung tissues. The cardiac tissue included a 3-mm-thick defect mimicking myocardial infarction. Organ tracer concentrations were calculated assuming 18F-FDG myocardial viability scans and 18F-flurpiridaz myocardial perfusion scans and were added to the phantom organs. Imaging was performed using an SiPM PET/CT scanner with a 5-min acquisition. The data acquired in list mode were reconstructed using 3-dimensional ordered-subsets expectation maximization with varying iterations. Image evaluation was based on the depiction of the myocardial defect compared with normal myocardial accumulation. Results: Increasing the number of iterations improved the contrast of the myocardial defect for both tracers, with 18F-flurpiridaz showing higher contrast than 18F-FDG. However, even at 50 iterations, both tracers overestimated the defect accumulation. A bull's-eye image can display the flow metabolism mismatch using images from both tracers. Conclusion: SiPM PET enabled cardiac PET imaging in a 500-g ELBW phantom with a 1-g heart. However, there were limitations in adequately depicting these defects. Considering the image quality and defect contrast,18F-flurpiridaz appears more desirable than 18F-FDG if only one of the two can be used.

Anomalous Coronary Arteries: A State-of-the-Art Approach

Congenital coronary anomalies are not an infrequent occurrence and their clinical presentation typically occurs during early years, though may be manifested only in adulthood. In the setting of anomalous aortic origin of a coronary artery, this is particularly concerning as it inflicts sudden loss of healthy young lives. Risk stratification remains a challenge and so does the best management decision-making in these patients, particularly if asymptomatic. Standardized approach to evaluation and management, with careful data collection and collaboration among centers, will likely impact future outcomes in this patient population, thus allowing for exercise participation and healthier lives.

Anomalous Coronary Arteries: A State-of-the-Art Approach

Congenital coronary anomalies are not an infrequent occurrence and their clinical presentation typically occurs during early years, though may be manifested only in adulthood. In the setting of anomalous aortic origin of a coronary artery, this is particularly concerning as it inflicts sudden loss of healthy young lives. Risk stratification remains a challenge and so does the best management decision-making in these patients, particularly if asymptomatic. Standardized approach to evaluation and management, with careful data collection and collaboration among centers, will likely impact future outcomes in this patient population, thus allowing for exercise participation and healthier lives.

Myocardial Functional Imaging in Pediatric Nuclear Cardiology

The role of nuclear medicine in pediatric cardiology has grown rapidly over the years, providing useful functional and prognostic information and playing a complementary role to morphological imaging in the evaluation of myocardial perfusion, cardiovascular inflammation and infections, and cardiac sympathetic innervation. The aim of this narrative review is to summarize and highlight the most important evidence on pediatric nuclear cardiology, describing clinical applications and the possibilities, advantages, and limitations of nuclear medicine techniques. Moreover, a special focus will be given to the minimization of radiation exposure in pediatric nuclear cardiology imaging, a critical topic in children.

The Use of Stress Cardiovascular Imaging in Pediatric Population

Although not frequent in the pediatric population, ischemia could occur in children due to several congenital and acquired disease. Stress imaging is key for the non-invasive evaluation of myocardial abnormalities and perfusion defect in this clinical setting. Moreover, beyond ischemia assessment, it can provide complementary diagnostic and prognostic information in valvular heart disease and cardiomyopathies. When performed using cardiovascular magnetic resonance, it could detect, in addition, myocardial fibrosis and infarction, increasing the diagnostic yield. Several imaging modalities are currently available for the evaluation of stress myocardial perfusion. Advances in technologies have also increased the feasibility, safety and availability of these modalities in the pediatric age group. However, despite the established role of stress imaging and its increasing use in daily clinical practice, there are currently no specific guidelines, and little data are available in the literature on this topic. The aim of this review is to summarize the most recent evidence on pediatric stress imaging and its clinical application with a focus on the advantages and limitations of each imaging modality currently available.

Preserved myocardial viability in patients with chronic total occlusion of a single coronary artery

OBJECTIVE

To assess the benefits of coronary collateral circulation on myocardial perfusion, viability and function in patients with total occlusion of a single coronary artery using the 99mTc-sestamibi SPECT and 18F-fluorodeoxyglucose PET.

METHODS

164 Consecutive patients were included who underwent coronary angiography results exhibited total occlusion of a single coronary artery and received 99mTc-MIBI SPECT and 18F-FDG PET within 90 days of angiography. Myocardial perfusion and viability in patients with collateral circulation and those without it were compared. Long-term follow-up was performed through a review of patient clinical records.

RESULTS

Collateral circulation was present in 56 patients (34%) and absent in 108 patients (66%). The total perfusion defect size in patients with collateral circulation decreased when compared to those without (30% ± 13% to 35% ± 14%, P < .05). The myocardial viability was 22% ± 12% in patients with collateral circulation, and 12% ± 9% in those without (P < .001). The left ventricular ejection fraction was higher, and the end-diastolic and end-systolic left ventricular volumes were lower in patients with collateral circulation (39% ± 11%, 138 ± 66, 89 ± 57) compared to patients without collateral circulation (31% ± 9%, 177 ± 55, 125 ± 48, all P < .001, respectively). Multi-factor logistic regression identified that concerning the variables of sex, age, viable myocardium, collateral circulation, treatment type and others, only treatment type was significantly associated with therapeutic effects (OR 3.872, 95% CI 1.915-7.830, P < .001).

CONCLUSION

Collateral circulation can preserve resting myocardial blood perfusion and myocardial viability, and help maintain the function of the left ventricular myocardium. The appropriate treatment strategy will have a substantial impact on the therapeutic outcome.

Myocardial Perfusion in Hypoplastic Left Heart Syndrome

BACKGROUND

The status of the systemic right ventricular coronary microcirculation in hypoplastic left heart syndrome (HLHS) is largely unknown. It is presumed that the systemic right ventricle's coronary microcirculation exhibits unique pathophysiological characteristics of HLHS in Fontan circulation. The present study sought to quantify myocardial blood flow by cardiac magnetic resonance imaging and evaluate the determinants of microvascular coronary dysfunction and myocardial ischemia in HLHS.

METHODS

One hundred nineteen HLHS patients (median age, 4.80 years) and 34 healthy volunteers (median age, 5.50 years) underwent follow-up cardiac magnetic resonance imaging ≈1.8 years after total cavopulmonary connection. Right ventricle volumes and function, myocardial perfusion, diffuse fibrosis, and late gadolinium enhancement were assessed in 4 anatomic HLHS subtypes. Myocardial blood flow (MBF) was quantified at rest and during adenosine-induced hyperemia. Coronary conductance was estimated from MBF at rest and catheter-based measurements of mean aortic pressure (n=99).

RESULTS

Hyperemic MBF in the systemic ventricle was lower in HLHS compared with controls (1.89±0.57 versus 2.70±0.84 mL/g per min; P<0.001), while MBF at rest normalized by the rate-pressure product, was similar (1.25±0.36 versus 1.19±0.33; P=0.446). Independent risk factors for a reduced hyperemic MBF were an HLHS subtype with mitral stenosis and aortic atresia (P=0.017), late gadolinium enhancement (P=0.042), right ventricular diastolic dysfunction (P=0.005), and increasing age at total cavopulmonary connection (P=0.022). The coronary conductance correlated negatively with systemic blood oxygen saturation (r, -0.29; P=0.02). The frequency of late gadolinium enhancement increased with age at total cavopulmonary connection (P=0.014).

CONCLUSIONS

The coronary microcirculation of the systemic ventricle in young HLHS patients shows significant differences compared with controls. These hypothesis-generating findings on HLHS-specific risk factors for microvascular dysfunction suggest a potential benefit from early relief of frank cyanosis by total cavopulmonary connection.

Pediatric Cardiac PET/CT Imaging

With the routine availability of PET/CT imaging for oncologic purposes, there has been renewed interest in and acceptance of cardiac and neurologic applications of PET/CT. As our understanding of the pathophysiology underlying various pediatric heart diseases has improved, there has been a parallel advance in imaging modalities. Cardiac MR imaging and cardiac PET continue to improve in the pediatric domain. Molecular imaging holds promise to provide a more robust assessment of the cardiac pathophysiology in a 1-stop setting with less radiation exposure to the patient, an important consideration for the pediatric patient population.

Preoperative Evaluation and Midterm Outcomes after the Surgical Correction of Anomalous Origin of the Left Coronary Artery from the Pulmonary Artery in 50 Infants and Children

Background:

Anomalous origin of the left coronary artery (LCA) from the pulmonary artery (ALCAPA) is a rather rare congenital anomaly that has a profound effect on heart function. This study aimed to retrospectively illustrate the perioperative clinical features, therapy experience, and midterm outcomes after surgical correction, and to determine the value of left ventricular ejection fraction (LVEF) and myocardial viability in differentiating critically ill patients among infants and children with ALCAPA.

Methods:

From April 1999 to March 2013, infants and children patients diagnosed with ALCAPA in Beijing Fuwai Hospital were analyzed. Clinical data of patients were summarized and retrospectively analyzed. All patients were divided into two groups according to LVEF level (Group 1: LVEF >50%, or Group 2: LVEF ≤50%) to compare perioperative and follow-up variables. Effect of myocardial viability evaluated according to myocardial perfusion/¹⁸F-fluorodeoxyglucose (FDG) imaging on the clinical variables was also analyzed.

Results:

A total of 50 patients with ALCAPA (male/female: 29/21; median age: 3.1 years [range: 4 months to 18 years]) were included. Younger age, lower weight, intercoronary collaterals (ICC) dysplasia, ratio of the proximal right coronary artery diameter to the aortic root diameter <0.2, and larger cardiothoracic ratio (CTR) were more frequently found in Group 2 than those in Group 1. Forty-seven patients underwent cardiac surgery. The times of cross-clamp and cardiopulmonary bypass were not different between the two groups; however, the duration of mechanical ventilation and postoperative Intensive Care Unit stay were longer in Group 2 than those in Group 1. Follow-ups were possible in 38 patients (80.9%); median time: 84.5 months (range: 49 months to 216 months). There was one late sudden death with simple ligation of the LCA at 8 months after surgery. No severe complications and reoperation occurred. The relationship of the grades of myocardial viability and clinical features was analyzed in 15 patients with myocardial perfusion/¹⁸F-FDG imaging, and the results showed that myocardial viability correlated well with LVEF, CTR, abnormal Q waves, and left ventricular end-diastolic dimension. It was not correlated with age, mitral regurgitation, and ICC. Heart implantation was decided in one patient with little viable myocardium; however, this patient died 2 months after the diagnosis while waiting for transplantation. Two patients with no viable myocardium in the area of aneurysm had aneurysmectomy concomitantly.

Conclusions:

In infants and children with ALCAPA, heart function and myocardial viability are closely related to clinical features. LVEF and the grades of myocardial viability can differentiate high-risk patients before surgery and in the early stage of recovery after surgery. The area and extent of myocardial infarction are also crucial in making preoperative clinical decisions. However, even in patients with depressed ventricular function and severe myocardial infarction, the midterm follow-up showed satisfactory recovery of cardiac function after the successful restoration of a dual-coronary arterial system.

Low-dose computed tomography scans with automatic exposure control for patients of different ages undergoing cardiac PET/CT and SPECT/CT

PURPOSE

This study aimed to evaluate the efficacy of automatic exposure control (AEC) in order to optimize low-dose computed tomography (CT) protocols for patients of different ages undergoing cardiac PET/CT and single-photon emission computed tomography/computed tomography (SPECT/CT).

METHODS

One PET/CT and one SPECT/CT were used to acquire CT images for four anthropomorphic phantoms representative of 1-year-old, 5-year-old and 10-year-old children and an adult. For the hybrid systems investigated in this study, the radiation dose and image quality of cardiac CT scans performed with AEC activated depend mainly on the selection of a predefined image quality index. Multiple linear regression methods were used to analyse image data from anthropomorphic phantom studies to investigate the effects of body size and predefined image quality index on CT radiation dose in cardiac PET/CT and SPECT/CT scans.

RESULTS

The regression relationships have a coefficient of determination larger than 0.9, indicating a good fit to the data. According to the regression models, low-dose protocols using the AEC technique were optimized for patients of different ages. In comparison with the standard protocol with AEC activated for adult cardiac examinations used in our clinical routine practice, the optimized paediatric protocols in PET/CT allow 32.2, 63.7 and 79.2% CT dose reductions for anthropomorphic phantoms simulating 10-year-old, 5-year-old and 1-year-old children, respectively. The corresponding results for cardiac SPECT/CT are 8.4, 51.5 and 72.7%.

CONCLUSION

AEC is a practical way to reduce CT radiation dose in cardiac PET/CT and SPECT/CT, but the AEC settings should be determined properly for optimal effect. Our results show that AEC does not eliminate the need for paediatric protocols and CT examinations using the AEC technique should be optimized for paediatric patients to reduce the radiation dose as low as reasonably achievable.

Myocardial stress perfusion magnetic resonance: initial experience in a pediatric and young adult population using regadenoson

BACKGROUND

Dipyridamole and adenosine are traditional pharmacological stressors for myocardial perfusion. Regadenoson, a selective adenosine A2A agonist, has a lower side effect profile with lower incidence of bronchospasm and bradycardia. There is a growing need for myocardial perfusion assessment within pediatrics. There is no report on the utility of regadenoson as a stress agent in children.

OBJECTIVE

To observe the safety and feasibility of regadenoson as a pharmacologic stressor for perfusion cardiac MR in a pilot cohort of pediatric patients weighing more than 40 kg who have congenital heart disease and pediatric acquired heart disease.

MATERIALS AND METHODS

We reviewed our initial experience with regadenoson stress cardiac MR in 31 pediatric patients 15.8 ± 1.7 years (range 12-22 years) with congenital heart disease and acquired heart disease. Mean patient weight was 60 ± 15 kg (range of 40-93 kg). All patients underwent cardiac MR because of concern for ischemia. The cohort included a heterogeneous group of patients at a pediatric institution with potential risk for ischemia. Subjects' heart rate and blood pressure were monitored and pharmacologic stress was induced by injection of 400 mcg of regadenoson. We evaluated their hemodynamic response and adverse effects using changes in vital signs and onset of symptoms. A pediatric cardiologist and radiologist qualitatively assessed myocardial perfusion and viability images.

RESULTS

One child was unable to complete the stress perfusion portion of the examination, but did complete the remaining portion of the CMR. Resting heart rate was 72 ± 14 beats per minute (bpm) and rose to peak of 124 ± 17 bpm (95 ± 50% increase, P < 0.005) with regadenoson. Image quality was considered good or diagnostic in all cases. Three patients had irreversible perfusion defects. Four patients had reversible perfusion defects. Nine of the patients underwent cardiac catheterization with angiography and the findings showed excellent agreement.

CONCLUSION

Regadenoson might be a safe and feasible pharmacologic stress agent for use in cardiac MR in older pediatric patients with congenital heart disease and acquired heart disease. The ease of use as a bolus and the advantage of a prolonged hyperemia make its use appealing in pediatrics. In a limited number of cases, regadenoson stress perfusion showed excellent agreement with cardiac catheterization. Regadenoson might be a viable pharmacologic stress agent in this population.

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.

Clinical applications of radionuclide imaging in the evaluation and management of patients with congenital heart disease

Non-invasive testing of children with congenital heart disease (CHD) began in the 1950s with the introduction of radionuclide studies to assess shunt fractions, pulmonary blood flow, and ventricular contractile function. Echocardiography and cardiac magnetic resonance imaging have since replaced radionuclide imaging in many of these roles. Concurrently, percutaneous and surgical repairs of complex CHD evolved, creating new roles for radionuclide imaging. In this paper on applications of radionuclide imaging in CHD, we review the multiple mechanisms for myocardial ischemia in CHD. We critically compare optimal radionuclide imaging techniques to other imaging modalities for assessing ischemia in CHD. We present the current role of nuclear imaging for assessing viability and pulmonary blood flow. We highlight the value added by advances in dedicated cardiac SPECT scanners, novel reconstruction software, and cardiac PET in performing low-dose radionuclide imaging in CHD. Finally, we discuss the emerging clinical indications for radionuclide imaging in CHD including coronary flow reserve assessment and evaluation of cardiovascular prosthesis and device infections.

Anomalous origination of a coronary artery from the opposite sinus

Anomalous origination of a coronary artery from the opposite sinus (ACAOS) is estimated to be present in 0.2-2.0% of the population. In the majority of individuals, ACAOS has no hemodynamic or prognostic implications, but in a minority of cases, typically where the anomalous coronary artery takes an interarterial course to reach its correct myocardial territory, it can precipitate ischemia and sudden cardiac death (SCD). With the growing use of CT coronary angiography (CTCA) in the investigation of ischemic heart disease, we can expect increasing rates of incidental detection of this anomaly. Although CTCA and magnetic resonance coronary angiography can effectively characterize these lesions anatomically, they fail to describe and quantitatively assess the basic defect that leads to coronary insufficiency, such as mural intussusception. The key challenge lies in the identification of which patients are at risk of SCD and, therefore, who should be offered corrective surgical or (potentially) percutaneous intervention. Conventional, noninvasive stress testing has limited sensitivity, but emerging, invasive stress tests, which utilize intravascular ultrasonography and measurements of fractional flow reserve, show the potential to provide more-accurate hemodynamic and prognostic assessment.

Feasibility of perfusion cardiovascular magnetic resonance in paediatric patients

AIMS

As coronary artery disease may also occur during childhood in some specific conditions, we sought to assess the feasibility and accuracy of perfusion cardiovascular magnetic resonance (CMR) in paediatric patients.

METHODS AND RESULTS

First-pass perfusion CMR studies were performed under pharmacological stress with adenosine and by using a hybrid echo-planar pulse sequence with slice-selective saturation recovery preparation. Fifty-six perfusion CMR examinations were performed in 47 patients. The median age was 12 years (1 month-18 years), and weight 42.8 kg (2.6-82 kg). General anaesthesia was required in 18 patients. Mean examination time was 67 +/- 19 min. Diagnostic image quality was obtained in 54/56 examinations. In 23 cases the acquisition parameters were adapted to patient's size. Perfusion CMR was abnormal in 16 examinations. The perfusion defects affected the territory of the left anterior descending coronary artery in 11, of the right coronary artery in 3, and of the circumflex coronary artery in 2 cases. Compared to coronary angiography, perfusion CMR showed a sensitivity of 87% (CI 52-97%) and a specificity of 95% (CI 79-99%).

CONCLUSION

In children, perfusion CMR is feasible and accurate. In very young children (less than 1 year old), diagnostic image quality may be limited.

Cardiac positron emission tomography

Positron emission tomography (PET) is a powerful, quantitative imaging modality that has been used for decades to noninvasively investigate cardiovascular biology and physiology. Due to limited availability, methodologic complexity, and high costs, it has long been seen as a research tool and as a reference method for validation of other diagnostic approaches. This perception, fortunately, has changed significantly within recent years. Increasing diversity of therapeutic options for coronary artery disease, and increasing specificity of novel therapies for certain biologic pathways, has resulted in a clinical need for more accurate and specific diagnostic techniques. At the same time, the number of PET centers continues to grow, stimulated by PET's success in oncology. Methodologic advances as well as improved radiotracer availability have further contributed to more widespread use. Evidence for diagnostic and prognostic usefulness of myocardial perfusion and viability assessment by PET is increasing. Some studies suggest overall cost-effectiveness of the technique despite higher costs of a single study, because unnecessary follow-up procedures can be avoided. The advent of hybrid PET-computed tomography (CT), which enables integration of PET-derived biologic information with multislice CT-derived morphologic information, and the key role of PET in the development and translation of novel molecular-targeted imaging compounds, have further contributed to more widespread acceptance. Today, PET promises to play a leading diagnostic role on the pathway toward a future of high-powered, comprehensive, personalized, cardiovascular medicine. This review summarizes the state-of-the-art in current imaging methodology and clinical application, and outlines novel developments and future directions.

Preliminary data on the diagnostic accuracy of rubidium-82 cardiac PET perfusion imaging for the evaluation of ischemia in a pediatric population

Evaluation of myocardial perfusion is sometimes necessary in children with congenital heart disease or acquired coronary artery abnormalities. Limited information is available regarding the clinical utility of myocardial perfusion imaging in children. PET imaging with rubidium-82 may provide a convenient clinical means of assessing regional circulatory compromise in pediatric patients with small hearts, due to its improved spatial resolution. Clinically indicated cardiac PET studies obtained in 22 pediatric patients were reviewed by two blinded observers and assigned myocardial perfusion scores using a standard 17-segment model. PET results were correlated with coronary angiography, available in 15 cases, to determine the accuracy of PET scanning for evaluating compromise of the myocardial circulation. Reversible defects consistent with myocardial ischemia were present in 6 of 15 (40%) PET cases. The sensitivity and specificity of cardiac PET for the detection of significant coronary artery disease were 100% and 82%, respectively. The positive predictive value of cardiac PET was 67%, while the negative predictive value was 100%. Cardiac PET imaging with rubidium-82 appears promising for the noninvasive assessment of myocardial perfusion in the pediatric population. The findings from this small series suggest that prospective study in a larger patient cohort merits consideration.

Segmental Wall-Motion Abnormalities After an Arterial Switch Operation Indicate Ischemia

We prospectively studied 29 consecutive neonates undergoing an arterial switch operation to determine if segmental wall motion abnormalities (SWMA) represented myocardial ischemia. Intraoperative transesophageal echocardiogram was recorded at baseline and twice after cardiopulmonary bypass. Cardiac troponin I (cTnI) levels were measured before sternal incision and 3, 6, 12, 24, 48, and 72 h after removal of the aortic cross-clamp. Immediate postoperative Holter and 15-lead electrocardiograms (ECG) were evaluated for ischemia. Transthoracic echocardiograms were obtained before hospital discharge. At bypass termination, immediately after protamine administration, segmental wall motion was normal in nine neonates and abnormal in 20. SWMA were transient in five and present at the time of chest closure in 15 neonates. Neonates in whom SWMA were present at chest closure had more segments involved than those in whom SWMA were transient (P > 0.001). Neonates with SWMA at chest closure had higher cTnI levels postoperatively versus neonates with normal wall motion (P = 0.02). Postoperative ECG data were available in 26 neonates. There was ECG evidence of myocardial ischemia in two of eight neonates with normal wall motion, one of five with transient SWMA, and nine of 13 with SWMA at chest closure. CTnI levels at 12, 24, and 48 h and intraoperative SWMA were predictive of postoperative SWMA. We believe these data indicate that SWMA, which persist at the completion of an arterial switch operation, and which are present in multiple myocardial segments, correlate with myocardial ischemia. Further follow-up of these patients is needed to determine if increased intraoperative myocardial ischemia correlates with long-term outcomes.

Assessment of left ventricular function long term after arterial switch operation for transposition of the great arteries by dobutamine stress echocardiography

OBJECTIVES

To use dobutamine stress echocardiography to determine left ventricular (LV) function and wall motion of children long term after arterial switch operation (ASO) for transposition of the great arteries.

DESIGN AND PATIENTS

31 patients (24 boys) with ASO performed at a mean (SD) of 15.5 (4.3) days of life were studied at an age of 9.4 (2.0) years. All had normal coronary angiographic findings. LV echocardiographic indexes, including fractional shortening, ejection fraction, rate corrected velocity of circumferential fibre shortening (VCFc), and wall stress, as well as LV wall motion abnormalities were determined at rest and under dobutamine stress. The results were compared with those of 20 healthy age matched control participants.

SETTING

Tertiary paediatric cardiac centre.

RESULTS

Fractional shortening, ejection fraction, and VCFc were significantly lower in patients than in controls at rest (all with p < 0.001). Stress-velocity index detected impaired LV contractility in 19 (61%) patients at rest. An older age at operation (p = 0.01), longer bypass (p = 0.01) and circulatory arrest times (p = 0.045), and an unusual coronary artery pattern (p = 0.059) were associated with impaired resting LV contractility. Dobutamine stress echocardiography unmasked wall motion abnormalities in 23 (74%) patients. Exercise myocardial perfusion scan, performed in 22 patients, showed reversible myocardial perfusion defects in 17. These defects corresponded to segments of hypokinesia as detected by dobutamine stress echocardiography.

CONCLUSION

A significant proportion of children, albeit asymptomatic, had impaired baseline LV contractility and reversible myocardial perfusion defects and mild wall motion abnormalities on stress after ASO.

Cardiac positron emission tomography imaging

Cardiac positron emission tomography (PET) imaging has advanced from primarily a research tool to a practical, high-performance clinical imaging modality. The widespread availability of state-of-the-art PET gamma cameras, the commercial availability of perfusion and viability PET imaging tracers, reimbursement for PET perfusion and viability procedures by government and private health insurance plans, and the availability of computer software for image display of perfusion, wall motion, and viability images have all been a key to cardiac PET imaging becoming a routine clinical tool. Although myocardial perfusion PET imaging is an option for all patients requiring stress perfusion imaging, there are identifiable patient groups difficult to image with conventional single-photon emission computed tomography imaging that are particularly likely to benefit from PET imaging, such as obese patients, women, patients with previous nondiagnostic tests, and patients with poor left ventricular function attributable to coronary artery disease considered for revascularization. Myocardial PET perfusion imaging with rubidium-82 is noteworthy for high efficiency, rapid throughput, and in a high-volume setting, low operational costs. PET metabolic viability imaging continues to be a noninvasive standard for diagnosis of viability imaging. Cardiac PET imaging has been shown to be cost-effective. The potential of routine quantification of resting and stress blood flow and coronary flow reserve in response to pharmacologic and cold-pressor stress offers tantalizing possibilities of enhancing the power of PET myocardial perfusion imaging. This can be achieved by providing assurance of stress quality control, in enhancing diagnosis and risk stratification in patients with coronary artery disease, and expanding diagnostic imaging into the realm of detection of early coronary artery disease and endothelial dysfunction subject to risk factor modification. Combined PET and x-ray computed tomography imaging (PET-CT) results in enhanced patient throughput and efficiency. The combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and noninvasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

PET in pediatric diseases

FDG-PET is being increasingly applied to pediatric conditions, particularly in oncology. PET and PET/CT scanning in children are not currently supported by Centers for Medicare and Medicaid Services unless the disease condition coincides with a reimbursed adult condition. The recent merger of the Children's Cancer Group and the Pediatric Oncology Group to form the Children's Oncology Group creates an opportunity to examine the use of FDG-PET in the management of childhood tumors in multi-institutional, cooperative efforts. The interest in incorporating PET imaging technology in pediatric medicine has been evidenced by several recent review articles summarizing the ongoing progress in this area. Future data will show that FDG-PET provides useful diagnostic information and can play a pivotal role in the clinical management and care of children with disease.