Long-Term Follow-Up of Outcomes With F-18-Fluorodeoxyglucose Positron Emission Tomography Imaging–Assisted Management of Patients With Severe Left Ventricular Dysfunction Secondary to Coronary Disease

Background—

Whether viability imaging can impact long-term patient outcomes is uncertain. The PARR-2 study (Positron Emission Tomography and Recovery Following Revascularization) showed a nonsignificant trend toward improved outcomes at 1 year using an F-18-fluorodeoxyglucose positron emission tomography (PET)–assisted strategy in patients with suspected ischemic cardiomyopathy. When patients adhered to F-18-fluorodeoxyglucose PET recommendations, outcome benefit was observed. Long-term outcomes of viability imaging–assisted management have not previously been evaluated in a randomized controlled trial.

Methods and Results—

PARR-2 randomized patients with severe left ventricular dysfunction and suspected CAD being considered for revascularization or transplantation to standard care (n= 195) versus PET-assisted management (n=197) at sites participating in long-term follow-up. The predefined primary outcome was time to composite event (cardiac death, myocardial infarction, or cardiac hospitalization). After 5 years, 105 (53%) patients in the PET arm and 111 (57%) in the standard care arm experienced the composite event (hazard ratio for time to composite event =0.82 [95% confidence interval 0.62–1.07]; P =0.15). When only patients who adhered to PET recommendations were included, the hazard ratio for the time to primary outcome was 0.73 (95% confidence interval 0.54–0.99; P =0.042).

Conclusions—

After a 5-year follow-up in patients with left ventricular dysfunction and suspected CAD, overall, PET-assisted management did not significantly reduce cardiac events compared with standard care. However, significant benefits were observed when there was adherence to PET recommendations. PET viability imaging may be best applied when there is likely to be adherence to imaging-based recommendations.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00385242.

The role of nuclear imaging in pulmonary hypertension

Pulmonary hypertension (PH) is a disease characterized by a chronic elevation of pulmonary artery pressure from various causes. Pulmonary artery hypertension (PAH) is one of subtype which results in premature death often as a result of right ventricular (RV) dysfunction. In spite of the recent progress in novel cardiac imaging techniques and new drugs for PAH, there remain significant unresolved issues including a need for earlier diagnosis, refinement of risk stratification, and monitoring the effects of treatment. Cardiac and pulmonary imaging with transthoracic echocardiography (TTE) with Doppler, magnetic resonance imaging (MRI), and computed tomography (CT) are done routinely in many clinical centers. However, routine and emerging nuclear techniques may have a pivotal role of assessment of the patient with PH, and is currently the subject of significant research. Potential Roles for Nuclear Imaging in the Evaluation of the PH Patient: (1) Evaluation of cardiac structure and function (RNA) (non-nuclear techniques would include TTE, CT, and MRI). (2) Functional imaging. This includes the use of ventilation-perfusion scintigraphy (V/Q scan) to diagnose chronic thromboembolic pulmonary hypertension (CTEPH), 123l-metaiodobenzylguanidine (MIBG) imaging to evaluate the cardiac sympathetic nervous system (non-nuclear techniques include invasive right heart catheterization and TTE). (3) Measurement of RV perfusion (with gated SPECT studies). (4) Evaluation of cardiac and pulmonary metabolism (PET scans). This review article will summarize the pathophysiology, classification, natural history, and diagnostic approach of PH. Current and emerging nuclear techniques will be discussed under the four themes of evaluation of structure, functional imaging, flow, and metabolism. These will be compared to current and emerging nuclear and non-nuclear diagnostic tests in the evaluation and management of patients with PH. We will also discuss research applications exploring new insights into flow and metabolism in the right heart and lung and the application of new radioligands.

The role of F(18)-fluorodeoxyglucose positron emission tomography in guiding diagnosis and management in patients with known or suspected cardiac sarcoidosis

Cardiac sarcoidosis (CS) has gained significant interest in recent years with the emergence of advanced imaging modalities such as MRI and F(18)-fluorodeoxyglucose-positron emission tomography (FDG-PET) as modalities to aid in the diagnosis of this condition. CS remains a difficult condition to diagnose, particularly in cases of isolated cardiac involvement and it can present with a broad spectrum of clinical syndromes. Furthermore, the appropriate management of these patients remains controversial. FDG-PET has a potential role not only in diagnosis of CS but also in directing further therapies, facilitating the decision to start immunosuppression and monitoring the response to it. In this article, we discuss when to consider FDG-PET, outline the current optimal patient preparation and scanning protocols and then, using case examples, discuss the use of FDG-PET in follow-up of patients with known or suspected CS. We also outline how PET can influence management decisions in these patients.

Relation Between Right Ventricular Function and Increased Right Ventricular [ 18 F]Fluorodeoxyglucose Accumulation in Patients With Heart Failure

Background—

Left heart failure is characterized by alterations in metabolic substrate utilization, and metabolic modulation may be a future strategy in the management of heart failure. Little is known about cardiac metabolism in the right ventricle and how it relates to other measures of right ventricular (RV) function. This study was designed to measure glucose metabolism in the right ventricle, as estimated by [ 18 F]fluorodeoxyglucose (FDG) positron emission tomography imaging and to determine the relation between RV function and FDG uptake in patients with heart failure.

Methods and Results—

A total of 68 patients underwent cardiac [ 18 F]FDG positron emission tomography scanning with measurement of RV FDG uptake as a standardized uptake value. Perfusion imaging was acquired at rest with rubidium-82 or [ 13 N]ammonia. RV function was determined by equilibrium radionuclide ventriculography. Relative RV FDG uptake was determined as the ratio of RV to LV standardized uptake value. Fifty-five percent of these patients had ischemic cardiomyopathy. The mean LV and RV ejection fractions were 21±7% and 35±10%, respectively. There was a correlation between RV ejection fraction and the ratio of RV to LV FDG uptake whether the entire LV myocardium ( r =−0.40, P <0.001) or LV free wall ( r =−0.43, P <0.001) was used. This relation persisted in the subgroup with nonischemic cardiomyopathy ( r =−0.37, P =0.04). RV FDG uptake was weakly related to increased RV systolic pressure but not related to LV size, function, or FDG uptake. The correlation between RV ejection fraction and RV/LV FDG was maintained after partial-volume correction ( r =−0.68, P <0.001).

Conclusions—

RV dysfunction is associated with an increase in RV FDG uptake, the magnitude of which may be correlated with severity.

Kinetic model-based factor analysis of dynamic sequences for 82-rubidium cardiac positron emission tomography

PURPOSE

Factor analysis has been pursued as a means to decompose dynamic cardiac PET images into different tissue types based on their unique temporal signatures to improve quantification of physiological function. In this work, the authors present a novel kinetic model-based (MB) method that includes physiological models of factor relationships within the decomposition process. The physiological accuracy of MB decomposed (82)Rb cardiac PET images is evaluated using simulated and experimental data. Precision of myocardial blood flow (MBF) measurement is also evaluated.

METHODS

A gamma-variate model was used to describe the transport of (82)Rb in arterial blood from the right to left ventricle, and a one-compartment model to describe the exchange between blood and myocardium. Simulations of canine and rat heart imaging were performed to evaluate parameter estimation errors. Arterial blood sampling in rats and (11)CO blood pool imaging in dogs were used to evaluate factor and structure accuracy. Variable infusion duration studies in canine were used to evaluate MB structure and global MBF reproducibility. All results were compared to a previously published minimal structure overlap (MSO) method.

RESULTS

Canine heart simulations demonstrated that MB has lower root-mean-square error (RMSE) than MSO for both factor (0.2% vs 0.5%, p < 0.001 MB vs MSO, respectively) and structure (3.0% vs 4.7%, p < 0.001) estimations, as with rat heart simulations (factors: 0.2% vs 0.9%, p < 0.001 and structures: 3.0% vs 6.7%, p < 0.001). MB blood factors compared to arterial blood samples in rats had lower RMSE than MSO (1.6% vs 2.2%, p =0.025). There was no difference in the RMSE of blood structures compared to a (11)CO blood pool image in dogs (8.5% vs 8.8%, p =0.23). Myocardial structures were more reproducible with MB than with MSO (RMSE=3.9% vs 6.2%, p < 0.001), as were blood structures (RMSE=4.9% vs 5.6%, p =0.006). Finally, MBF values tended to be more reproducible with MB compared to MSO (CV= 10% vs 18%, p =0.16). The execution time of MB was, on average, 2.4 times shorter than MSO (p < 0.001) due to fewer free parameters.

CONCLUSIONS

Kinetic model-based factor analysis can be used to provide physiologically accurate decomposition of (82)Rb dynamic PET images, and may improve the precision of MBF quantification.

Precision control of eluted activity from a Sr/Rb generator for cardiac positron emission tomography

A rubidium-82 (/sup 82/Rb) elution system is described for use with clinical positron emission tomography. The system is self-calibrating with 1.4% repeatability, independent of generator activity and elution flow rate. Saline flow is switched between a /sup 82/Sr//sup 82/Rb generator and a bypass line to achieve a constant activity elution of /sup 82/Rb. In the present study, pulse width modulation (PWM) of a solenoid valve is compared to simple threshold control as a means to simulate a proportional valve. A predictive-corrective control algorithm is developed which produces a constant activity elution within the constraints of long feedback delay and short elution time. Accurate constant-activity elutions of 10-70% of the total generator activity were demonstrated using the threshold comparison control. The adaptive-corrective control of the PWM valve provided a substantial improvement in precision of the steady-state output.

Precision-controlled elution of a 82Sr/82Rb generator for cardiac perfusion imaging with positron emission tomography

A rubidium-82 ((82)Rb) elution system is described for use with positron emission tomography. Due to the short half-life of (82)Rb (76 s), the system physics must be modelled precisely to account for transport delay and the associated activity decay and dispersion. Saline flow is switched between a (82)Sr/(82)Rb generator and a bypass line to achieve a constant-activity elution of (82)Rb. Pulse width modulation (PWM) of a solenoid valve is compared to simple threshold control as a means to simulate a proportional valve. A predictive-corrective control (PCC) algorithm is developed which produces a constant-activity elution within the constraints of long feedback delay and short elution time. The system model parameters are adjusted through a self-tuning algorithm to minimize error versus the requested time-activity profile. The system is self-calibrating with 2.5% repeatability, independent of generator activity and elution flow rate. Accurate 30 s constant-activity elutions of 10-70% of the total generator activity are achieved using both control methods. The combined PWM-PCC method provides significant improvement in precision and accuracy of the requested elution profiles. The (82)Rb elution system produces accurate and reproducible constant-activity elution profiles of (82)Rb activity, independent of parent (82)Sr activity in the generator. More reproducible elution profiles may improve the quality of clinical and research PET perfusion studies using (82)Rb.

Treating the right patient at the right time: access to cardiovascular nuclear imaging

Cardiovascular nuclear medicine uses agents labelled with radioisotopes that can be imaged with cameras (single-photon emission tomography [SPECT] or positron emission tomography [PET]) capable of detecting gamma photons to show physiological parameters such as myocardial perfusion, myocardial viability or ventricular function. There is a growing body of literature providing guidelines for the appropriate use of these techniques, but there are little data regarding the appropriate timeframe during which the procedures should be accessed. An expert working group composed of cardiologists and nuclear medicine specialists conducted an Internet search to identify current wait times and recommendations for wait times for a number of cardiac diagnostic tools and procedures, including cardiac catheterization and angioplasty, bypass grafting and vascular surgery. These data were used to estimate appropriate wait times for cardiovascular nuclear medicine procedures. The estimated times were compared with current wait times in each province. Wait time benchmarks were developed for the following: myocardial perfusion with either exercise or pharmacological stress and SPECT or PET imaging; myocardial viability assessment with either fluorodeoxyglucose SPECT or PET imaging, or thallium-201 SPECT imaging; and radionuclide angiography. Emergent, urgent and nonurgent indications were defined for each clinical examination. In each case, appropriate wait time benchmarks were defined as within 24 h for emergent indications, within three days for urgent indications and within 14 days for nonurgent indications. Substantial variability was noted from province to province with respect to access for these procedures. For myocardial perfusion imaging, mean emergent/urgent wait times varied from four to 24 days, and mean nonurgent wait times varied from 15 to 158 days. Only Ontario provided limited access to viability assessment, with fluorodeoxyglucose available in one centre. Mean emergent/urgent wait times for access to viability assessment with thallium-201 SPECT imaging varied from three to eight days, with the exception of Newfoundland, where an emergent/urgent assessment was not available; mean nonurgent wait times varied from seven to 85 days. Finally, for radionuclide angiography, mean emergent/urgent wait times varied from two to 20 days, and nonurgent wait times varied from eight to 36 days. Again, Newfoundland centres were unable to provide emergent/urgent access. The publication of these data and proposed wait times as national targets is a step toward the validation of these recommendations through consultation with clinicians caring for cardiac patients across Canada.

Diagnostic and clinical perspectives of fusion imaging in cardiology: is the total greater than the sum of its parts?

Positron emission tomography, cardiovascular magnetic resonance and multislice computed tomography have contributed to changing our pathophysiological understanding of many conditions. Clinically, they have provided new tools for the identification of preclinical disease and a better understanding of how disease progresses. The application of these imaging modalities to preclinical disease and the use of these techniques in patients with overt cardiovascular disease are reviewed.

Myocardial glucose utilization and optimization of (18)F-FDG PET imaging in patients with non-insulin-dependent diabetes mellitus, coronary artery disease, and left ventricular dysfunction

In patients with non-insulin-dependent diabetes mellitus (NIDDM), FDG PET imaging is often problematic because of poor uptake of FDG. Different protocols have been used; however, these have not been directly compared in patients with NIDDM who have both coronary artery disease (CAD) and severe left ventricular (LV) dysfunction, for which defining viability is most relevant. The aim of this study was to better define the optimal means of FDG PET imaging, assessed by image quality and myocardial glucose utilization rate (rMGU), among 3 imaging protocols in patients with NIDDM, CAD, and severe LV dysfunction.

METHODS

Ten patients with NIDDM, CAD, and severe LV dysfunction (mean ejection fraction, 29.8% +/- 7.1%) underwent dynamic FDG PET scanning using 3 different protocols: the standard protocol, consisting of oral glucose loading or a supplemental insulin bolus based on fasting glucose; the niacin protocol, consisting of pretreatment with niacin to lower free fatty acids; and the insulin clamp protocol, consisting of hyperinsulinemic euglycemic clamp. Image quality was satisfactory with at least 1 approach in 8 patients, who formed the primary analysis group.

RESULTS

Myocardium-to-blood-pool ratios were significantly higher with the insulin clamp (standard, 1.7 +/- 1.2; niacin, 1.6 +/- 1.0; insulin clamp, 3.4 +/- 2.5 [P < 0.05 vs. standard and niacin]). Values for rMGU were higher with the insulin clamp (standard, 0.11 +/- 0.07 micromol/g/min; niacin, 0.12 +/- 0.11 micromol/g/min; insulin clamping, 0.22 +/- 0.12 micromol/g/min [P = 0.004 vs. standard and 0.07 vs. niacin]).

CONCLUSION

The hyperinsulinemic euglycemic clamp yielded the highest FDG PET image quality and the highest rMGU in a comparison with the standard and niacin protocols in this difficult group of patients with NIDDM, CAD, and severe LV dysfunction. The hyperinsulinemic euglycemic clamp may be the preferred method for FDG PET viability imaging in this population. Larger clinical trials are needed to assess whether accuracy is greater with this approach.

Stenting versus thrombolysis in acute myocardial infarction trial (STAT)

OBJECTIVES

We sought to directly compare primary stenting with accelerated tissue plasminogen activator (t-PA) in patients presenting with acute ST-elevation myocardial infarction (AMI).

BACKGROUND

Thrombolysis remains the standard therapy for AMI. However, at some institutions primary angioplasty is favored. Randomized trials have shown that primary angioplasty is equal or superior to thrombolysis, while recent studies demonstrate that stent implantation improves the results of primary angioplasty.

METHODS

Patients presenting with AMI were randomly assigned to primary stenting (n = 62) or accelerated t-PA (n = 61). The primary end point was the composite of death, reinfarction, stroke or repeat target vessel revascularization (TVR) for ischemia at six months.

RESULTS

The primary end point was significantly reduced in the stent group compared with the accelerated t-PA group, 24.2% versus 55.7% (p < 0.001). The event rates for other outcomes in the stent group versus the t-PA group were as follows: mortality: 4.8% versus 3.3% (p = 1.00); reinfarction: 6.5% versus 16.4% (p = 0.096); stroke: 1.6% versus 4.9% (p = 0.36); recurrent unstable ischemia: 9.7% versus 26.2% (p = 0.03) and repeat TVR for ischemia: 14.5% versus 49.2% (p < 0.001). The median length of the initial hospitalization was four days in the stent group and seven days in the t-PA group (p < 0.001).

CONCLUSIONS

Compared with accelerated t-PA, primary stenting reduces death, reinfarction, stroke or repeat TVR for ischemia. In centers where facilities and experienced interventionists are available, primary stenting offers an attractive alternative to thrombolysis.

The effects of beta(1)-blockade on oxidative metabolism and the metabolic cost of ventricular work in patients with left ventricular dysfunction: A double-blind, placebo-controlled, positron-emission tomography study

BACKGROUND

The mechanism for the beneficial effect of beta-blocker therapy in patients with left ventricular (LV) dysfunction is unclear, but it may relate to an energy-sparing effect that results in improved cardiac efficiency. C-11 acetate kinetics, measured using positron-emission tomography (PET), are a proven noninvasive marker of oxidative metabolism and myocardial oxygen consumption (MVO(2)). This approach can be used to measure the work-metabolic index, which is a noninvasive estimate of cardiac efficiency.

METHODS AND RESULTS

The aim of this study was to determine the effect of metoprolol on oxidative metabolism and the work-metabolic index in patients with LV dysfunction. Forty patients (29 with ischemic and 11 with nonischemic heart disease; LV ejection fraction <40%) were randomized to receive metoprolol or placebo in a treatment protocol of titration plus 3 months of stable therapy. Seven patients were not included in analysis because of withdrawal from the study, incomplete follow-up, or nonanalyzable PET data. The rate of oxidative metabolism (k) was measured using C-11-acetate PET, and stoke volume index (SVI) was measured using echocardiography. The work-metabolic index was calculated as follows: (systolic blood pressure x SVI x heart rate)/k. No significant change in oxidative metabolism occurred with placebo (k=0.061+/-0.022 to 0.054+/-0.012 per minute). Metoprolol reduced oxidative metabolism (k=0.062+/-0. 024 to 0.045+/-0.015 per minute; P:=0.002). The work-metabolic index did not change with placebo (from 5.29+/-2.46 x 10(6) to 5.14+/-2. 06 x 10(6) mm Hg. mL/m(2)), but it increased with metoprolol (from 5. 31+/-2.15 x 10(6) to 7.08+/-2.36 x 10(6) mm Hg. mL/m(2); P:<0.001).

CONCLUSIONS

Selective beta-blocker therapy with metoprolol leads to a reduction in oxidative metabolism and an improvement in cardiac efficiency in patients with LV dysfunction. It is likely that this energy-sparing effect contributes to the clinical benefits observed with beta-blocker therapy in this patient population.

Detection of serial changes in absolute myocardial perfusion with 82Rb PET

Serial changes in myocardial perfusion may represent an important marker of disease progression or regression or the effects of therapy for patients with coronary artery disease (CAD). Quantitative methods have not been developed for the assessment of serial changes in perfusion. The objective of this study was to use receiver operator characteristic (ROC) analysis to determine the sensitivity and specificity of direct paired comparisons (DPCs) to detect changes in absolute myocardial perfusion measured with 82Rb PET.

METHODS

Repeated dynamic 82Rb PET scans were obtained on 8 dogs at rest and during hyperemia induced with dobutamine (n = 4) or atrial pacing (n = 4). Radiolabeled microspheres were used to verify perfusion changes. Polar maps of absolute 82Rb retention and associated SD were estimated from the dynamic images. Paired comparisons were then performed using a t test on each of the 532 polar map sectors. Rest-rest and stress-stress differences were used to assess specificity and reproducibility, and stress-rest differences were used to assess sensitivity.

RESULTS

82Rb retention differences of 20% over baseline were detected with 85%-90% sensitivity and specificity, using the optimal DPC probability value and image smoothness. The average 82Rb retention differences correlated well with microspheres (r = 0.74; P = 0.001). Reproducibility of the mean retention values was 4.7% +/- 2.1%. As reproducibility varies, the DPC probability value can be adjusted to maintain specificity. These ROC results are directly applicable to other image modalities that produce measurements with similar SEs (3.7% +/- 0.9%).

CONCLUSION

The developed method of DPCs is sensitive and specific for the detection of changes in absolute myocardial perfusion measured with 82Rb PET.

Stress perfusion/metabolism imaging: a pilot study for a potential new approach to the diagnosis of coronary disease in women

BACKGROUND

The diagnosis of coronary artery disease (CAD) in women continues to be a challenge. F-18 deoxyglucose (FDG) positron emission tomography (PET) has been used for detection of myocardial ischemia at rest. Little has been reported about FDG stress imaging. The aim of this pilot study was to assess stress FDG PET imaging for defining CAD in a group of women referred for chest pain.

METHODS

Stress FDG imaging was performed in 19 women (mean age 59 +/- 10 years). All had abnormal stress testing before entering the study. FDG and 2-methoxy-2-methylpropyl isonitrile were injected at peak stress (treadmill n = 8, dipyridamole n = 11) followed by PET and single photon emission computed tomography image acquisitions. Myocardial ischemia was defined by regions that demonstrated both a defect on perfusion imaging and increased FDG uptake relative to uptake in normal perfusion zones. Defect/normal zone FDG ratios were also determined. Coronary angiography was performed on all patients.

RESULTS

Average, or mean, body mass index was high at 29.2 +/- 5 kg/m2. Nine of 19 patients had significant CAD. Eight of 9 with CAD had FDG-defined ischemia. Nine of the 10 without CAD had negative FDG images (sensitivity 89%, specificity 90%). The average defect/normal zone FDG ratio was greater in patients with CAD than in those without (2.4 +/- 1.9 vs 0.9 +/- 0.4, P < .05).

CONCLUSIONS

Regional FDG uptake in areas of perfusion defects with stress increased in this group with CAD. These pilot data suggest that stress FDG PET may be diagnostically helpful in obese female patients. This novel approach may complement current methods of CAD detection in women and warrants further study.

Establishing an approach for patients with recent coronary occlusion: identification of viable myocardium

BACKGROUND

Revascularization of occluded coronary arteries after myocardial infarction (MI) may restore flow to viable myocardium and improve ventricular function. The aim of this pilot study was to determine the potential utility of thallium-201 viability imaging for the prediction of recovery of regional ventricular function in patients undergoing revascularization of total or subtotal occlusion of infarct-related arteries (TIMI 0-2 flow) during the convalescent period after MI.

METHODS

Twenty-three patients were identified < 6 weeks after MI and underwent Tl-201 viability imaging (rest imaging, n = 16; stress/reinjection imaging, n = 7) and radionuclide angiography. Patients were revascularized with percutaneous transluminal coronary artery in 10, stent in 10, and bypass in 3. Follow-up radionuclide angiography at 3 months was used to assess recovery of regional wall motion.

RESULTS

Among 41 abnormal wall motion segments in the infarct territories, the sensitivity, specificity, and accuracy for Tl-201 imaging in the prediction of recovery of regional function were 89% (25/28), 54% (7/13), and 78% (32/41), respectively. When 8 segments supplied by vessels with restenosis to >70% were excluded, specificity improved to 70%. Wall motion scores improved in those with adequate revascularization (1.6+/-1.4 vs 2.7+/-1.6; P < .001) but not in those with restenosis or occlusion (1.8+/-1.0 vs 2.0+/-1.6; P = NS).

CONCLUSIONS

In patients with an occluded artery after MI, Tl-201 viability imaging can detect recoverable myocardium with reasonable accuracy and may help select which patients will most benefit from revascularization.

Delay in revascularization is associated with increased mortality rate in patients with severe left ventricular dysfunction and viable myocardium on fluorine 18-fluorodeoxyglucose positron emission tomography imaging

BACKGROUND

The identification of high-risk patients who require early revascularization has become increasingly important with the present emphasis on reducing health care resources. This is particularly relevant to health care systems with prolonged waiting times for interventions. Myocardial viability imaging with the use of fluorine 18-fluorodeoxyglucose (FDG) PET may help to identify high-risk patients with severe left ventricular dysfunction. The aim of this study was to evaluate the consequences of prolonged waiting time on cardiac outcomes in patients with left ventricular dysfunction directed to revascularization based on FDG PET imaging.

METHODS AND RESULTS

Forty-six patients with coronary disease and an ejection fraction of < or = 35% were considered candidates for revascularization based on FDG PET viability imaging. Thirty-five of 46 patients were subsequently accepted for revascularization. Patients were divided into 2 groups based on the median waiting time after PET: an early group (< 35 days; n = 18) and a late group (> or = 35 days; n = 17). Preoperative mortality rates were significantly increased in the late group (4 of 17 [24%] versus 0 of 18 in the early group; P < 0.05). In postoperative follow-up (17 +/- 7 months), cardiac events occurred in 2 of 18 (11%) and 1 of 13 (7.8%) patients in the early and late groups, respectively. Left ventricular ejection fraction increased after early revascularization (24 +/- 7% to 29 +/- 8%, P < 0.001, baseline versus 3 months) but not in the late group (27 +/- 5% to 28 +/- 6%, P = NS).

CONCLUSIONS

Preoperative FDG PET can be used to identify a high-risk group of patients who may benefit from early revascularization. A long waiting time for revascularization is associated with a high mortality rate and suggests that early revascularization is desirable after the identification of hibernating viable myocardium.

Late clinical and angiographic follow-up after stenting in evolving and recent myocardial infarction

OBJECTIVES

This study sought to assess the late clinical and angiographic outcomes of patients who received stents within the first week of acute myocardial infarction (AMI).

BACKGROUND

Recent studies have demonstrated that stenting of the infarct-related artery is a useful adjunct to balloon angioplasty in patients with AMI. However, there are limited data on the late clinical and angiographic outcomes of these patients.

METHODS

Between January 1994 and September 1995, 32 patients at our institution underwent stenting of the infarct-related artery within 1 week of AMI: 13 within 14 hours (evolving group) and 19 between days 2 and 7 (recent AMI group). Late clinical follow-up was obtained on all survivors. Quantitative angiographic measurements were recorded on the stented segments before stenting, immediately after stenting, and on the follow-up angiograms.

RESULTS

At 13.1+/-6.4 months from the time of stenting, three patients died and three required repeat angioplasty, but no patient had reinfarction or required bypass surgery. At follow-up 26 (81%) of 32 patients remained free of major cardiac events; of these, 24 (92%) were free of angina. Repeat angiography performed at 10.8+/-7.5 months in 26 (87%) of 30 discharged patients showed that all infarct-related arteries were patent and the restenosis rate was low: 22% in the 13 patients with evolving AMI (<14 hours) and 12% in the 19 patients with recent AMI (days 2 through 7).

CONCLUSION

In this study stenting of the infarct-related artery in patients with evolving and recent AMI was associated with a favorable late clinical outcome. Patency of the infarct-related artery was well maintained, and the restenosis rate was low.

Assessment of diagnostic performance of quantitative flow measurements in normal subjects and patients with angiographically documented coronary artery disease by means of nitrogen-13 ammonia and positron emission tomography

OBJECTIVES

Regional myocardial blood flow (MBF) and flow reserve measurements using nitrogen-13 (N-13) ammonia positron emission tomography (PET) were compared with quantitative coronary angiography to determine their utility in the detection of significant coronary artery disease (CAD).

BACKGROUND

Dynamic PET protocols using N-13 ammonia allow regional quantification of MBF and flow reserve. To establish the diagnostic performance of this method, the sensitivity and specificity must be known for varying decision thresholds.

METHODS

MBF and flow reserve for three coronary territories were determined in 20 normal subjects and 31 patients with angiographically documented CAD by means of dynamic PET and a three-compartment model for N-13 ammonia kinetics. Ten normal subjects defined the normal mean and SD of MBF and flow reserve, and 10 normal subjects were compared with patients. PET flow obtained in the territory with the most severe stenosis in each patient was correlated with the angiographic assessment of the stenosis (severity > or = 50%, > or = 70%, > or = 90%). Receiver operating characteristic (ROC) curve analysis was performed for 1.5, 2.0, 2.5, 3.0 and 4.0 SD of flow abnormalities.

RESULTS

MBF and flow reserve values from the normal subjects and from territories with documented stenoses > or = 50% were significantly different (p < 0.05). A significant difference was found between normal subjects and angiographically normal territories of patients with CAD. High diagnostic accuracy and sensitivity, with moderately high specificity, were demonstrated for detection of all stenoses.

CONCLUSIONS

Quantification of myocardial perfusion using dynamic PET and N-13 ammonia provides a high performance level for the detection and localization of CAD. The specificity of dynamic PET was excellent in patients with a low likelihood of CAD, whereas an abnormal flow reserve in angiographically normal territories was postulated to represent early functional abnormalities of vascular reactivity.

Differentiation of myocardial ischemia and necrosis by technetium 99m glucaric acid kinetics

BACKGROUND

Current clinical approaches may not always be helpful in the early differentiation of necrotic tissue from ischemic viable myocardium in patients with acute myocardial infarction. Tc-99m-glucaric acid is a carbohydrate ligand that may permit differentiation of necrosis from ischemia. However, the myocardial kinetics of Tc-99m-glucaric acid have not been well defined early after myocardial injury. The aim of this study was to evaluate the effect of necrosis in comparison to postischemic injury alone on the kinetics of Tc-99m-glucaric acid with the use of an isolated perfused rat heart model.

METHODS AND RESULTS

Three groups of hearts were studied: group I: control (n = 6); group II: postischemia (15 minutes of no flow with complete reperfusion, n = 6); and group III: necrosis (90 minutes of no flow to induce necrosis with complete reperfusion, n = 6). Tc-99m-glucaric acid (1.3 +/- 0.6 mCi/L of buffer) was perfused for 30 minutes to evaluate tracer accumulation. Then tracer-free buffer was perfused for 45 minutes to evaluate clearance. The peak accumulation relative to the control group mean was significantly increased (p < 0.01) in group III (necrosis) (254% +/- 75%) compared with control (100% +/- 10%) and compared with postischemia (108% +/- 26%). On kinetic data analysis, the monoexponential clearance rate constant: (kc) was significantly reduced with necrosis (control: kc = 20.2 +/- 14.0 x 10(-4) sec-1; postischemia: kc = 22.3 +/- 15.2 x 10(-4) sec-1; and necrosis: kc = 1.2 +/- 0.3 x 10(-4) sec-1; p < 0.05). A retention fraction was calculated from the activity after 45 minutes of clearance corrected for the peak activity for each group. The necrotic group had significant myocardial retention in comparison to control and postischemia (control: 12% +/- 8%; postischemia: 14% +/- 16%; necrosis: 64% +/- 10%; p < 0.01).

CONCLUSIONS

The accumulation and retention of Tc-99m-glucaric acid is markedly increased in the presence of myocardial necrosis in comparison to control and postischemic myocardial injury. In this model, Tc-99m-glucaric acid is capable of defining the presence of necrotic myocardial injury in comparison to postischemic injury alone. This agent may have potential application for the early differentiation of ischemic from necrotic myocardium in acute myocardial infarction.

Comparison of Tc-99m sestamibi perfusion imaging and echocardiography using an arbutamine infusion for the detection of coronary artery disease

Arbutamine, a synthetic catecholamine, coupled with a closed-loop, computerized delivery system was evaluated in conjunction with technetium-99m sestamibi scintigraphy and echocardiography for the detection of coronary artery disease. Concordance between the imaging methods was 68%, with a similar sensitivity for coronary disease using echocardiography (78%) and technetium-99m sestamibi (76%), although more arbutamine-induced ischemia was noted with perfusion imaging.

F-18-fluorodeoxyglucose PET imaging alters clinical decision making in patients with impaired ventricular function

The effect of F-18-fluorodeoxyglucose positron emission tomography imaging on decision making in the selection of patients with impaired ventricular function for revascularization was determined in 87 patients. In 57% of patients, positron emission tomography data influenced management decisions, indicating an important effect of myocardial viability determination on difficult therapy decisions in these patients.

Can nitrogen-13 ammonia kinetic modeling define myocardial viability independent of fluorine-18 fluorodeoxyglucose?

OBJECTIVES

The hypothesis of this study was that evaluation of myocardial flow and metabolism using nitrogen-13 (N-13) ammonia kinetic modeling with dynamic positron emission tomographic (PET) imaging could identify regions of myocardial scar and viable myocardium as defined by fluorine-18 fluorodeoxyglucose (F-18 FDG) PET.

BACKGROUND

Uptake of most perfusion tracers depends on both perfusion and metabolic retention in tissue. This characteristic has limited their ability to differentiate myocardial scar from viable tissue. The kinetic modeling of N-13 ammonia permits quantification of blood flow and separation of the metabolic component of its uptake, which may permit differentiation of scar from viable tissue.

METHODS

Sixteen patients, > 3 months after myocardial infarction, underwent dynamic N-13 ammonia and F-18 FDG PET imaging. Regions of reduced and normal perfusion were defined on static N-13 ammonia images. Patients were classified into two groups (group I [ischemic viable], n = 6; group II [scar], n = 10) on the basis of percent of maximal F-18 FDG uptake in hypoperfused segments. Nitrogen-13 ammonia kinetic modeling was applied to dynamic PET data, and rate constants were determined. Flow was defined by K1; volume of distribution (VD = K1/k2) of N-13 ammonia was used as an indirect indication of metabolic retention.

RESULTS

Fluorine-18 FDG uptake was reduced in patients with scar compared with normal patients with ischemic viable zones (ischemic viable 93 +/- 27% [mean +/- SD]; scar 37 +/- 16%, p < or = 0.01). Using N-13 ammonia kinetic modeling, flow and VD were reduced in the hypoperfused regions of patients with scar (ischemic viable flow: 0.65 +/- 0.20 ml/min per g, scar: 0.36 +/- 0.16 ml/min per g, p < or = 0.01; VD: 3.9 +/- 1.3 and 2.0 +/- 1.07 ml/g, respectively, p < or = 0.01). For detection of viable myocardium in these patients, the sensitivity and specificity were 100% and 80% for N-13 ammonia PET flow > 0.45 ml/min per g; 100% and 70% for VD > 2.0 ml/g; and 100% and 90% for both flow > 0.45 ml/min per g and VD > 2.0 ml/g, respectively. The positive and negative predictive values for the latter approach were 86% and 100%, respectively.

CONCLUSIONS

In this cohort, patients having regions with flow < or = 0.45 ml/min per g or VD < or = 2.0 ml/g had scar. Viable myocardium had both flow > 0.45 ml/min per g and VD > 2.0 ml/g. Nitrogen-13 ammonia kinetic modeling permits determination of blood flow and metabolic integrity in patients with previous myocardial infarction and can help differentiate between scar and ischemic but viable myocardium.

Myocardial kinetics of technetium-99m teboroxime in the presence of postischemic injury, necrosis and low flow reperfusion

OBJECTIVES

This study evaluated technetium-99m (Tc-99m) teboroxime kinetics in postischemic and partially necrotic myocardium with complete and low flow reperfusion using an isolated perfused rat heart model.

BACKGROUND

Technetium-99m teboroxime has been proposed for use in the early diagnosis of reperfusion after thrombolysis on the basis of models of myocardial necrosis with complete reperfusion. Clinically, however, reperfusion is frequently incomplete, resulting in a mixture of necrotic, ischemic and postischemic tissue.

METHODS

Hearts were classified into five groups: group 1 (n = 8, control); group 2 (n = 7, 30 min of no flow with complete reperfusion); group 3 (n = 12, 60 min of no flow to induce partial necrosis, followed by complete reperfusion); group 4 (n = 8, continuous low flow without flow interruption); and group 5 (n = 9, 60 min of no flow with low flow reperfusion). Buffer containing Tc-99m teboroxime was perfused for 15 min, followed by tracerfree buffer for 35 min, to evaluate uptake and clearance, respectively.

RESULTS

Uptake slopes for groups 1 to 5 were (mean +/- SD) 3.0 +/- 0.7, 2.6 +/- 0.8, 2.1 +/- 0.5, 0.8 +/- 0.2 and 0.8 +/- 0.3, respectively (p < or = 0.0005 for groups 1, 2 and 3 vs. groups 4 and 5, and p = 0.003 for group 3 vs. groups 1 and 2). Clearance curves from groups 1 to 3 were best fit by a biexponential function (p < 0.001); those from groups 4 and 5 were monoexponential. In groups 1, 2 and 3, the initial clearance rate constants (ki) (0.9 +/- 0.5 x 10(-3); 1.0 +/- 0.2 x 10(-3); 1.1 +/- 0.5 x 10(-3) s-1, respectively) and the monoexponential rate constants (Kmono) (2.0 +/- 0.3 x 10(-4); 2.2 +/- 0.4 x 10(-4); 2.1 +/- 0.2 x 10(-4) s-1, respectively) were significantly greater than those in groups 4 and 5 (0.9 +/- 0.5 x 10(-4); 1.2 +/- 0.3 x 10(-4) s-1, respectively, p < or = 0.005).

CONCLUSIONS

The uptake and initial clearance kinetics of Tc-99m teboroxime depend mainly on myocardial flow in this model. The presence of partial necrosis and postischemic injury has little effect on the initial clearance but leads to some reduction in uptake at normal flow rates. Evaluation of Tc-99m teboroxime kinetics may permit early noninvasive detection of inadequate reperfusion in acute myocardial infarction.

Usefulness of intracoronary stenting in acute myocardial infarction

Data on the feasibility, safety, and clinical outcome of intracoronary stenting in acute myocardial infarction (AMI) are limited. This study examined the immediate angiographic results and the early and late outcomes in 32 patients who had stenting during AMI. Coronary angiograms recorded at the time of stenting were reviewed with quantitative measurements obtained on the "target" coronary lesion before and after stenting. Immediate angiographic success was achieved in 30 patients (94%). The minimal luminal diameter increased from 0.36 +/- 0.37 to 2.58 +/- 0.41 mm (p<0.0001). Two patients died in the hospital. Of the remainder, none had reinfarction or required bypass surgery, whereas 2 required repeat coronary angioplasty for recurrent ischemia. Although thrombus at the infarct-related coronary lesion was initially detected in 41% of the patients, its presence was not associated with adverse procedural outcome. Only 1 patient had persistent thrombus after stenting, which resolved with intracoronary urokinase. At a mean follow-up of 6.1 +/- 4.1 months, there was 1 additional cardiac death, and no patient had AMI or required repeat coronary angioplasty or bypass; among the 29 survivors, 86% were free of angina. Thus, intracoronary stenting of the infarct-related artery in the setting of AMI is associated with excellent immediate angiographic success and a favorable clinical outcome, and remains an option even in the presence of thrombus.

Improvement of ventricular function after atrioventricular junction ablation in a patient with atrial flutter after Mustard's operation

Arrhythmias are common problems following Mustard's operation for D-transposition of the great arteries. A 19-year-old male is presented who was diagnosed at birth with D-transposition of the great arteries and a right aortic arch and underwent a Mustard procedure at 12 months of age. He developed sinus node dysfunction and atrial flutter unresponsive to antiarrhythmic drugs and dual chamber pacing. Following complete heart block with radiofrequency catheter ablation of the atrioventricular junction, the patient's heart was paced in VVIR mode. Ventricular function improved after the ablation and persisted in two years' follow-up.