Effect of short-term cardiovascular conditioning and low-fat diet on myocardial blood flow and flow reserve

Use of a Single-item Exercise Questionnaire Predicts Prognostic Risk among Patients undergoing Stress PET-MPI

BACKGROUND

Exercise activity reduces mortality and favorably influences mediators of risk, including myocardial flow reserve (MFR) and chronotropic responsiveness. Comprehensive research regarding the relationship between exercise activity, MFR, and chronotropic response to pharmacological stress, as assessed by heart rate response (HRR) among patients undergoing PET myocardial perfusion imaging (MPI) has not been performed. Thus, we aimed to evaluate the relationship between exercise activity as assessed by a practical single-item questionnaire, MFR and HRR, and longitudinal clinical risk.

METHODS

We studied outpatients who underwent pharmacological stress rubidium-82. PET-MPI and answered a self-reported one-item exercise activity questionnaire (0-10 scale) at the time of PET-MPI. HRR was calculated by the following equation: (stress HR-rest HR)/rest HR*100 (%). The primary outcome was death or myocardial infarction.

RESULTS

Of 1,686 patients, 221 (13%) patients had hard events during our mean follow up of 3.8 years. Patients were divided into four groups: no/minimal exercise (n=551), low exercise (n=468), moderate exercise (n=485), and high exercise (n=182) based on the questionnaire. MFR and HRR increased with exercise activity in a stepwise manner. By Cox analysis adjusted for clinical and PET-MPI variables including MFR and HRR, exercise activity was independently associated with hard events (HR [95%CI] per activity scale, 0.95 [0.91-0.99]; p=0.028).

CONCLUSIONS

Patients with higher exercise activity assessed by a practical single-item questionnaire had higher MFR and HRR. Exercise activity was an independent predictor of hard events in patients undergoing PET-MPI. Because of its ease of use, this single-item questionnaire should be applied among patients undergoing stress MPI.

Chemokine Fractalkine and Non-Obstructive Coronary Artery Disease-Is There a Link?

Non-obstructive coronary artery disease (NO-CAD) constitutes a heterogeneous group of conditions collectively characterized by less than 50% narrowing in at least one major coronary artery with a fractional flow reserve (FFR) of ≤0.80 observed in coronary angiography. The pathogenesis and progression of NO-CAD are still not fully understood, however, inflammatory processes, particularly atherosclerosis and microvascular dysfunction are known to play a major role in it. Chemokine fractalkine (FKN/CX3CL1) is inherently linked to these processes. FKN/CX3CL1 functions predominantly as a chemoattractant for immune cells, facilitating their transmigration through the vessel wall and inhibiting their apoptosis. Its concentrations correlate positively with major cardiovascular risk factors. Moreover, promising preliminary results have shown that FKN/CX3CL1 receptor inhibitor (KAND567) administered in the population of patients with ST-elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI), inhibits the adverse reaction of the immune system that causes hyperinflammation. Whereas the link between FKN/CX3CL1 and NO-CAD appears evident, further studies are necessary to unveil this complex relationship. In this review, we critically overview the current data on FKN/CX3CL1 in the context of NO-CAD and present the novel clinical implications of the unique structure and function of FKN/CX3CL1 as a compound which distinctively contributes to the pathomechanism of this condition.

Targeted Therapies for Microvascular Disease

Coronary microvascular dysfunction (CMD) is a common cause of ischemia but no obstructive coronary artery disease that results in an inability of the coronary microvasculature to meet myocardial oxygen demand. CMD is challenging to diagnose and manage due to a lack of mechanistic research and targeted therapy. Recent evidence suggests we can improved patient outcomes by stratifying antianginal therapies according to the diagnosis revealed by invasive assessment of the coronary microcirculation. This review article appraises the evidence for management of CMD, which includes treatment of cardiovascular risk, antianginal therapy and therapy for atherosclerosis.

Targeted Therapies for Microvascular Disease

Coronary microvascular dysfunction (CMD) is a common cause of ischemia but no obstructive coronary artery disease that results in an inability of the coronary microvasculature to meet myocardial oxygen demand. CMD is challenging to diagnose and manage due to a lack of mechanistic research and targeted therapy. Recent evidence suggests we can improved patient outcomes by stratifying antianginal therapies according to the diagnosis revealed by invasive assessment of the coronary microcirculation. This review article appraises the evidence for management of CMD, which includes treatment of cardiovascular risk, antianginal therapy and therapy for atherosclerosis.

Short-term Intensive Lifestyle Therapy in a Worksite Setting Improves Cardiometabolic Health in People With Obesity

Context

The Pritikin Program, which provides intensive lifestyle therapy, has been shown to improve cardiometabolic outcomes when provided as a residential program.

Objective

The purpose of the present study was to conduct a short-term, randomized, controlled trial to evaluate the feasibility and clinical efficacy of treatment with the Pritikin Program in an outpatient worksite setting.

Methods

Cardiometabolic outcomes were evaluated in people with overweight/obesity and ≥2 metabolic abnormalities (high triglycerides, low high-density lipoprotein (HDL) cholesterol, high blood pressure, HbA1c > 5.7%), before and after they were randomized to 6 weeks of standard care (n = 26) or intensive lifestyle therapy, based on the Pritikin Program (n = 28). Participants in the lifestyle intervention group were provided all food as packed-out meals and participated in group nutrition, behavioral education, cooking classes, and exercise sessions 3 times per week at a worksite location.

Results

Compared with standard care, intensive lifestyle therapy decreased body weight (-5.0% vs -0.5%), HbA1c (-15.5% vs +2.3%), plasma total cholesterol (-9.8% vs +7.7%), low-density lipoprotein cholesterol (-10.3% vs +9.3%) and triglyceride (-21.7% vs +3.0%) concentrations, and systolic blood pressure (-7.0% vs 0%) (all P values < .02), and increased exercise tolerance (time to exhaustion walking on a treadmill by +23.7% vs +4.5%; P < .001).

Conclusion

This study demonstrates the feasibility and clinical effectiveness of short-term, intensive outpatient lifestyle therapy in people with overweight/obesity and increased risk of coronary heart disease when all food is provided and the intervention is conducted at a convenient worksite setting.

Targeted Therapies for Microvascular Disease

Coronary microvascular dysfunction (CMD) is a common cause of ischemia but no obstructive coronary artery disease that results in an inability of the coronary microvasculature to meet myocardial oxygen demand. CMD is challenging to diagnose and manage due to a lack of mechanistic research and targeted therapy. Recent evidence suggests we can improved patient outcomes by stratifying antianginal therapies according to the diagnosis revealed by invasive assessment of the coronary microcirculation. This review article appraises the evidence for management of CMD, which includes treatment of cardiovascular risk, antianginal therapy and therapy for atherosclerosis.

Effects of cardiac rehabilitation with and without meditation on myocardial blood flow using quantitative positron emission tomography: A pilot study

BACKGROUND

Psychosocial stress is recognized as a risk factor for coronary heart disease (CHD). High rates of CHD in African-Americans may be related to psychosocial stress. However, standard cardiac rehabilitation (CR) usually does not include a systematic stress-reduction technique. Previous studies suggest that the Transcendental Meditation (TM) technique may reduce CHD risk factors and clinical events. This pilot study explored the effects of standard CR with and without TM on a measure of CHD in African-American patients.

METHODS

Fifty-six CHD patients were assigned to CR, CR + TM, TM alone, or usual care. Testing was done at baseline and after 12 weeks. The primary outcome was myocardial flow reserve (MFR) assessed by 13N-ammonia positron emission tomography (PET). Secondary outcomes were CHD risk factors. Based on guidelines for analysis of small pilot studies, data were analyzed for effect size (ES).

RESULTS

For 37 patients who completed posttesting, there were MFR improvements in the CR + TM group (+20.7%; ES = 0.64) and the TM group alone (+12.8%; ES = 0.36). By comparison, the CR-alone and usual care groups showed modest changes (+ 5.8%; ES = 0.17 and - 10.3%; ES = - 0.31), respectively. For the combined TM group, MFR increased (+ 14%, ES = 0.56) compared to the combined non-TM group (- 2.0%, ES = - 0.08).

CONCLUSIONS

These pilot data suggest that adding the TM technique to standard cardiac rehabilitation or using TM alone may improve the myocardial flow reserve in African-American CHD patients. These results may be applied to the design of controlled clinical trials to definitively test these effects.

TRIAL REGISTRATION

ClinicalTrials.gov registration # NCT01810029.

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

The use of cardiac PET, and in particular of quantitative myocardial perfusion PET, has been growing during the last years, because scanners are becoming widely available and because several studies have convincingly demonstrated the advantages of this imaging approach. Therefore, there is a need of determining the procedural modalities for performing high-quality studies and obtaining from this demanding technique the most in terms of both measurement reliability and clinical data. Although the field is rapidly evolving, with progresses in hardware and software, and the near perspective of new tracers, the EANM Cardiovascular Committee found it reasonable and useful to expose in an updated text the state of the art of quantitative myocardial perfusion PET, in order to establish an effective use of this modality and to help implementing it on a wider basis. Together with the many steps necessary for the correct execution of quantitative measurements, the importance of a multiparametric approach and of a comprehensive and clinically useful report have been stressed.

Treatment strategies in coronary microvascular dysfunction: A systematic review of interventional studies

CMD has been associated with a wide spectrum of diseases and conditions, and it has proven to be a strong prognostic marker of morbidity and mortality. Despite increased attention, guideline-based treatment recommendations are lacking. We performed a systematic review of pharmacological and nonpharmacological interventions to improve coronary perfusion, assessed by IC Doppler, TTDE, PET, CMRI, transthoracic contrast perfusion echocardiography, and dilution techniques. No restrictions were made regarding the study design (randomized, placebo-controlled/randomized with active comparators/nonrandomized with or without a control group), the cardiac condition studied, or the coronary microvascular function at baseline. An electronic database search yielded 4485 records of which 80 studies met our inclusion criteria. Included studies were sorted according to intervention and study design. Studies were small and heterogeneous in methodology, and only few were placebo-controlled. Although some treatments looked promising, we found that no specific treatment was sufficiently well documented to be recommended in any patient groups. There is a need for larger well-designed clinical trials, and we suggest that future studies stratify study populations according to pathogenic mechanisms, thereby investigating whether an individualized treatment approach would be more successful.

Cardiac perfusion and function after high-intensity exercise training in late premenopausal and recent postmenopausal women: an MRI study

We examined the influence of recent menopause and aerobic exercise training in women on myocardial perfusion, left ventricular (LV) dimension, and function. Two groups (n = 14 each) of healthy late premenopausal (50.2 ± 2.1 yr) and recent postmenopausal (54.2 ± 2.8 yr) women underwent cardiac magnetic resonance imaging (cMRI) at baseline and after 12 wk of high-intensity aerobic training. Measurements included LV morphology, systolic function, and myocardial perfusion at rest and during an adenosine stress test. At baseline, resting myocardial perfusion was lower in the postmenopausal than the premenopausal group (77 ± 3 vs. 89 ± 3 ml·100 g^-1·min^-1; P = 0.01), while adenosine-induced myocardial perfusion was not different (P = 0.81). After exercise training, resting myocardial perfusion was lower in both groups (66 ± 2; P = 0.002 vs. 81 ± 3 ml·100 g^-1·min^-1; P = 0.03). The adenosine-induced change in myocardial perfusion was lower in the groups combined (by 402 ± 17 ml·100 g^-1·min^-1; P = 0.02), and the adenosine-induced increase in heart rate was 10 ± 2 beats/min lower (P < 0.0001) in both groups after training. Normalization of myocardial perfusion using an estimate of cardiac work eliminated the differences in perfusion between the premenopausal and postmenopausal groups and the effect of training. Left ventricle mass was higher in both groups (P = 0.03; P = 0.006), whereas LV end-diastolic (P = 0.02) and stroke (P = 0.045) volumes were higher in the postmenopausal group after training. Twelve weeks of exercise training increased left ventricle mass and lowered resting and adenosine-induced myocardial perfusion, an effect that was likely related to cardiac work. The current data also suggest that the early menopausal transition has limited impact on cardiac function and structure. NEW & NOTEWORTHY This study provides for the first time estimates of myocardial perfusion in late premenopausal and recent postmenopausal women before and after a period of intense aerobic training. Resting myocardial perfusion was lower in postmenopausal than premenopausal women. Training lowered myocardial resting and stress perfusion in both groups, an effect that was likely influenced by the lower heart rate.

Positron Emission Tomography-Determined Hyperemic Flow, Myocardial Flow Reserve, and Flow Gradient-Quo Vadis?

Positron emission tomography/computed tomography (PET/CT) applied with positron-emitting flow tracers such as ¹³N-ammonia and ⁸²Rubidium enables the quantification of both myocardial perfusion and myocardial blood flow (MBF) in milliliters per gram per minute for coronary artery disease (CAD) detection and characterization. The detection of a regional myocardial perfusion defect during vasomotor stress commonly identifies the culprit lesion or most severe epicardial narrowing, whereas adding regional hyperemic MBFs, myocardial flow reserve (MFR), and/or longitudinal flow decrease may also signify less severe but flow-limiting stenosis in multivessel CAD. The addition of regional hyperemic flow parameters, therefore, may afford a comprehensive identification and characterization of flow-limiting effects of multivessel CAD. The non-specific origin of decreases in hyperemic MBFs and MFR, however, prompts an evaluation and interpretation of regional flow in the appropriate context with the presence of obstructive CAD. Conversely, initial results of the assessment of a longitudinal hyperemic flow gradient suggest this novel flow parameter to be specifically related to increases in CAD caused epicardial resistance. The concurrent assessment of myocardial perfusion and several hyperemic flow parameters with PET/CT may indeed open novel avenues of precision medicine to guide coronary revascularization procedures that may potentially lead to a further improvement in cardiovascular outcomes in CAD patients.

Characteristics of anginal patients with high resting myocardial blood flow measured with N-13 ammonia PET/CT

OBJECTIVES

We hypothesized that anginal patients with low coronary flow reserve (CFR) could have variable clinical features according to resting myocardial blood flow (MBF). Therefore, we analyzed the clinical and imaging characteristics according to resting MBF in anginal patients.

METHODS

We enrolled 70 patients who underwent N-13 ammonia PET-computed tomography (CT) for evaluation of angina. Resting and stress MBF values were obtained and resting MBF was corrected with rate-pressure product to exclude the effect of heart rate and blood pressure on resting MBF. Clinical and imaging characteristics were compared on the basis of MBF and CFR.

RESULTS

Among patients with CFR less than 2.0, those with high resting MBF (≥1.0 ml/min/g) had significantly fewer number of smokers, were younger, had lower Agatston calcium scores, and had less coronary stenosis compared with those with low resting MBF (<1.0 ml/min/g). In contrast, there was no significant difference in clinical or imaging findings according to resting MBF when compared among all patients or within those with CFR greater than or equal to 2.0. The subgroup analysis of patients with CFR less than 2.0 revealed lower Agatston calcium score and less coronary stenosis in patients with high resting MBF regardless of stress MBF.

CONCLUSION

High resting MBF is associated with a lower rate of smoking, younger age, less coronary calcium burden, and less coronary stenosis compared with low resting MBF in anginal patients with low CFR. Moreover, in these patients, favorable angiographic features were mainly associated with high resting MBF, irrespective of stress MBF. Therefore, resting MBF should be reviewed to validate the clinical significance of low CFR measured by N-13 ammonia PET/CT especially in anginal patients showing low CFR.

Coronary microvascular dysfunction, microvascular angina, and treatment strategies

Angina without coronary artery disease (CAD) has substantial morbidity and is present in 10% to 30% of patients undergoing angiography. Coronary microvascular dysfunction (CMD) is present in 50% to 65% of these patients. The optimal treatment of this cohort is undefined. We performed a systematic review to evaluate treatment strategies for objectively-defined CMD in the absence of CAD. We included studies assessing therapy in human subjects with angina and coronary flow reserve or myocardial perfusion reserve <2.5 by positron emission tomography, cardiac magnetic resonance imaging, dilution methods, or intracoronary Doppler in the absence of coronary artery stenosis ≥50% or structural heart disease. Only 8 papers met the strict inclusion criteria. The papers were heterogeneous, using different treatments, endpoints, and definitions of CMD. The small sample sizes severely limit the power of these studies, with an average of 11 patients per analysis. Studies evaluating sildenafil, quinapril, estrogen, and transcutaneous electrical nerve stimulation application demonstrated benefits in their respective endpoints. No benefit was found with L-arginine, doxazosin, pravastatin, and diltiazem. Our systematic review highlights that there is little data to support therapies for CMD. We assess the data meeting rigorous inclusion criteria and review the related but excluded published data. We additionally describe the next steps needed to address this research gap, including a standardized definition of CMD, routine assessment of CMD in studies of chest pain without obstructive CAD, and specific therapy assessment in the population with confirmed CMD.

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.

Quantitation of myocardial blood flow and myocardial flow reserve with 99mTc-sestamibi dynamic SPECT/CT to enhance detection of coronary artery disease

PURPOSE

Conventional dual-head single photon emission computed tomography (SPECT)/CT systems capable of fast dynamic SPECT (DySPECT) imaging have a potential for flow quantitation. This study introduced a new method to quantify myocardial blood flow (MBF) and myocardial flow reserve (MFR) with DySPECT scan and evaluated the diagnostic performance of detecting coronary artery disease (CAD) compared with perfusion using invasive coronary angiography (CAG) as the reference standard.

METHODS

This study included 21 patients with suspected or known CAD who had received DySPECT, ECG-gated SPECT (GSPECT), and CAG (13 with ≥ 50% stenosis in any vessel; non-CAD group: 8 with patent arteries or < 50% stenosis). DySPECT and GSPECT scans were performed on a widely used dual-head SPECT/CT scanner. The DySPECT imaging protocol utilized 12-min multiple back-and-forth gantry rotations during injections of (99m)Tc-sestamibi (MIBI) tracer at rest or dipyridamole-stress stages. DySPECT images were reconstructed with full physical corrections and converted to the physical unit of becquerels per milliliter. Stress MBF (SMBF), rest MBF (RMBF), and MFR were quantified by a one-tissue compartment flow model using time-activity curves derived from DySPECT images. Perfusion images were processed for GSPECT scan and interpreted to obtain summed stress score (SSS) and summed difference score (SDS). Receiver-operating characteristic (ROC) analyses were conducted to evaluate the diagnostic performance of flow and perfusion.

RESULTS

Using the criteria of ≥ 50% stenosis as positive CAD, areas under the ROC curve (AUCs) of flow assessment were overall significantly greater than those of perfusion. For patient-based analysis, AUCs for MFR, SMBF, SSS, and SDS were 0.91 ± 0.07, 0.86 ± 0.09, 0.64 ± 0.12, and 0.59 ± 0.13. For vessel-based analysis, AUCs for MFR, SMBF, SSS, and SDS were 0.81 ± 0.05, 0.76 ± 0.06, 0.62 ± 0.07, and 0.56 ± 0.08, respectively.

CONCLUSION

The preliminary data suggest that MBF quantitation with a conventional SPECT/CT system and the flow quantitation method is a clinically effective approach to enhance CAD detection.

Impact of diet and exercise on lipid management in the modern era

Unfortunately, many patients as well as the medical community, continue to rely on coronary revascularization procedures and cardioprotective medications as a first-line strategy to stabilize or favorably modify established risk factors and the course of coronary artery disease. However, these therapies do not address the root of the problem, that is, the most proximal risk factors for heart disease, including unhealthy dietary practices, physical inactivity, and cigarette smoking. We argue that more emphasis must be placed on novel approaches to embrace current primary and secondary prevention guidelines, which requires attacking conventional risk factors and their underlying environmental causes. The impact of lifestyle on the risk of cardiovascular disease has been well established in clinical trials, but these results are often overlooked and underemphasized. Considerable data also strongly support the role of lifestyle intervention to improve glucose and insulin homeostasis, as well as physical inactivity and/or low aerobic fitness. Accordingly, intensive diet and exercise interventions can be highly effective in facilitating coronary risk reduction, complementing and enhancing medications, and in some instances, even outperforming drug therapy.

PET tracers and techniques for measuring myocardial blood flow in patients with coronary artery disease

Assessment of the relative distribution of myocardial flow with myocardial perfusion imaging (MPI) is methodologically limited to predict the presence or absence of flow-limited coronary artery disease (CAD). This limitation may often occur, when obstructive lesions involve multiple epicardial coronary arteries or disease-related disturbances of the coronary circulation coexist at the microvascular level. Non-invasive assessment of myocardial blood flow in absolute units with position emission tomography (PET) has been positioned as the solution to improve CAD diagnosis and prediction of patient outcomes associated with risks for cardiac events. This article reviews technical and clinical aspects of myocardial blood flow quantitation with PET and discusses the practical consideration of this approach toward worldwide clinical utilization.

Journey in evolution of nuclear cardiology: will there be another quantum leap with the F-18-labeled myocardial perfusion tracers?

The field of nuclear cardiac imaging has evolved from being rather subjective, more "art than a science," to a more objective, digital-based quantitative technique, providing insight into the physiological processes of cardiovascular disorders and predicting patient outcome. In a mere 4 decades of its clinical use, the technology used to image myocardial perfusion has made quantum leaps from planar to single-photon emission computed tomography (SPECT) and now to a more contemporary rapid SPECT, positron emission tomography (PET), and hybrid SPECT-computed tomography (CT) and PET-CT techniques. Meanwhile, radiotracers have flourished from potassium-43 and red blood cell-tagged blood pool imaging to thallium-201 and technetium-99m-labeled SPECT perfusion tracers along with rubidium-82, ammonia N-13, and more recently F-18 fluorine-labeled PET perfusion tracers. Concurrent with this expansion is the introduction of new quantitative methods and software for image processing, evaluation, and data interpretation. Technical advances, particularly in obtaining quantitative data, have led to a better understanding of the physiological mechanisms underlying cardiovascular diseases beyond discrete epicardial coronary artery disease to coronary vasomotor function in the early stages of the development of coronary atherosclerosis, hypertrophic cardiomyopathy, and dilated nonischemic cardiomyopathy. Progress in the areas of molecular and hybrid imaging are equally important areas of growth in nuclear cardiology. However, this paper focuses on the past and future of nuclear myocardial perfusion imaging and particularly perfusion tracers.

Inflammation and microvascular dysfunction in cardiac syndrome X patients without conventional risk factors for coronary artery disease

OBJECTIVES

The aim of this study was to ascertain whether coronary microvascular dysfunction (CMD) and inflammation are related in cardiac syndrome X (CSX).

BACKGROUND

CMD can lead to CSX, defined as typical angina and transient myocardial ischemia despite normal coronary arteriograms. Inflammation has been suggested to play a role in the pathogenesis of myocardial ischemia in CSX.

METHODS

We assessed 21 CSX patients (age 52 ± 10 years; 17 women) without traditional cardiovascular risk factors and 21 matched apparently healthy control subjects. Positron emission tomography was used to measure myocardial blood flow (MBF) and coronary flow reserve (CFR) in response to intravenous adenosine, whereas high-sensitivity C-reactive protein (CRP) was measured to assess inflammation. Patients were subdivided a priori into 2 groups according to CRP concentrations at study entry (i.e., ≤3 or >3 mg/l).

RESULTS

There were no differences in resting (1.20 ± 0.23 ml/min/g vs. 1.14 ± 0.20 ml/min/g; p = 0.32) or hyperemic MBF (3.28 ± 1.02 ml/min/g vs. 3.68 ± 0.89 ml/min/g; p = 0.18) between CSX patients and the control group, whereas CFR was mildly reduced in CSX patients compared with the control group (2.77 ± 0.80 vs. 3.38 ± 0.80; p = 0.02). Patients with CRP >3 mg/l had more severe impairment of CFR (2.14 ± 0.33 vs. 3.16 ± 0.76; p = 0.001) and more ischemic electrocardiographic changes during adenosine administration than patients with lower CRP, and a negative correlation between CRP levels and CFR (r = -0.49, p = 0.02) was found in CSX patients.

CONCLUSIONS

CSX patients with elevated CRP levels had a significantly reduced CFR compared with the control group, which is indicative of CMD. Our study thus suggests a role for inflammation in the modulation of coronary microvascular responses in patients with CSX.

Quantitative cardiac positron emission tomography: the time is coming!

In the last 20 years, the use of positron emission tomography (PET) has grown dramatically because of its oncological applications, and PET facilities are now easily accessible. At the same time, various groups have explored the specific advantages of PET in heart disease and demonstrated the major diagnostic and prognostic role of quantitation in cardiac PET. Nowadays, different approaches for the measurement of myocardial blood flow (MBF) have been developed and implemented in user-friendly programs. There is large evidence that MBF at rest and under stress together with the calculation of coronary flow reserve are able to improve the detection and prognostication of coronary artery disease. Moreover, quantitative PET makes possible to assess the presence of microvascular dysfunction, which is involved in various cardiac diseases, including the early stages of coronary atherosclerosis, hypertrophic and dilated cardiomyopathy, and hypertensive heart disease. Therefore, it is probably time to consider the routine use of quantitative cardiac PET and to work for defining its place in the clinical scenario of modern cardiology.

Matching between regional coronary vasodilator capacity and corresponding circumferential strain in individuals with normal and increasing body weight

BACKGROUND

To define the relationship between regional coronary vasodilator capacity and myocardial circumferential strain at rest in normal weight, overweight, and obese individuals with normal global left-ventricular function.

METHODS AND RESULTS

Myocardial blood flow at rest and during pharmacologic vasodilation was measured with (13)N-ammonia PET/CT in mL/g/minute in normal weight control (CON, n = 12), overweight (OW, n = 10), and obese individuals (OB, n = 10). In addition, resting myocardial function was evaluated as circumferential strain (Єc, %) by MRI. Global myocardial flow reserve (MFR) did not differ significantly between CON and OW (2.98 ± 0.96 vs 2.70 ± 0.66, P = .290), whereas it declined significantly in OB (1.98 ± 1.04, P = .030). Further, global Єc (%) was comparable between CON, OW, and OB (-0.24 ± 0.03, -0.23 ± 0.02, and -0.23 ± 0.04) but it was lowest in OB when normalized to the rate-pressure product (NЄc: -0.31 ± 0.06, -0.32 ± 0.05, and -0.26 ± 0.08). When MFR of the three major coronary territories was correlated with corresponding Єc, a positive association was observed in CON (r = 0.36, P = .030), in OW (r = 0.54, P = .002), and also in OB when relating NЄc to coronary vascular resistance during pharmacologic vasodilation (r = -0.46, P = .010).

CONCLUSIONS

Higher coronary vasodilator capacity is related to corresponding regional circumferential strain at rest in non-obese individuals, while this is also observed for reduced MFR in obesity.

Impaired global myocardial flow dynamics despite normal left ventricular function and regional perfusion in chronic kidney disease: a quantitative analysis of clinical 82Rb PET/CT studies

Impaired global myocardial flow reserve (MFR) may be associated with increased risk for cardiac events and coronary artery disease progression. Chronic kidney disease (CKD) is also considered a risk factor for cardiovascular disease. We sought to investigate the effect of CKD on the myocardial microcirculation in patients referred for clinical (82)Rb PET/CT, who had normal left ventricular (LV) function and no flow-limiting coronary artery disease.

METHODS

Estimated glomerular filtration rate (eGFR) was available for 230 patients who had undergone rest and pharmacologic stress (82)Rb PET/CT for suspected coronary artery disease. CKD was defined as an eGFR less than 60 mL/min/1.73 m(2). After patients with hemodialysis, a renal transplant, abnormal regional perfusion (summed stress score > 4), or reduced LV function (LV ejection fraction < 45%) were excluded, 40 CKD patients remained. Those were compared with a control group without CKD, which was matched for age, sex, coronary risk factors, and systemic hemodynamics (n = 42). List-mode acquisition of PET enabled quantification of myocardial blood flow (MBF) and MFR using a previously validated retention model with correction for (82)Rb extraction. Rest MBF was normalized to rate-pressure product.

RESULTS

Mean eGFR in the CKD group was reduced (44 ± 14 vs. 99 ± 28 mL/min/1.73 m(2); P < 0.0001), and creatinine was significantly elevated, compared with controls (1.9 ± 1.1 vs. 0.8 ± 0.2 mg/dL; P < 0.0001). MFR was significantly reduced in CKD (2.2 ± 1.0 vs. 3.0 ± 1.2 for controls; P = 0.027). This reduction was mainly due to increased rest MBF (1.1 ± 0.4 in CKD vs. 0.8 ± 0.2 mL/min/g in controls; P = 0.007). Stress myocardial flow was comparable between both groups (2.3 ± 0.9 vs. 2.3 ± 0.8 mL/min/g; P = 0.08). Overall, MFR was significantly correlated with eGFR (r = 0.41; P = 0.0005). Stress MBF did not correlate with eGFR (r = 0.002; P = 0.45), but rest MBF showed an inverse correlation (r = -0.49; P < 0.0001). Rest MBF was also inversely correlated with hemoglobin (r = -0.28; P = 0.014), but only eGFR was an independent correlate at multivariate analysis.

CONCLUSION

MFR is impaired in patients with renal insufficiency with normal regional perfusion and LV function, mostly because of elevated rest flow. Absolute quantification of flow may be useful to identify microvascular dysfunction as a precursor of clinically overt coronary disease in this specific risk group.

Coronary vasoreactivity in subjects with thyroid autoimmunity and subclinical hypothyroidism before and after supplementation with thyroxine

BACKGROUND

The association of subclinical hypothyroidism (SCH) with increased risk for cardiovascular disease is still controversial. This study aimed to examine coronary vascular reactivity by positron emission tomography (PET) in asymptomatic patients with SCH before and after levothyroxine (LT4) supplementation.

METHODS

Ten patients (7 women and 3 men; mean age 43±15 years) with untreated autoimmune SCH, defined by elevated levels of thyroid-stimulating hormone (mean TSH: 16.9±11.3 μU/mL), normal levels of free thyroxine (0.9±0.1 μg/mL), free triiodothyronine (3.2±0.4 pg/mL), and positive thyroid peroxidase antibodies were studied. Eight euthyroid subjects with similar low-risk cardiovascular risk profile served as controls. Myocardial blood flow (MBF) and coronary flow reserve (CFR) were quantitatively assessed with rest/stress N-13 ammonia PET at baseline and after 6 months of LT4 replacement therapy (given only to patients).

RESULTS

At baseline, stress MBF and CFR corrected (c) for rate pressure product (RPP) and myocardial vascular resistance (MVR) during stress were significantly reduced in SCH compared with controls (stress MBF: 2.87±0.93 vs. 4.79±1.16 mL/g/min, p=0.003; CFR: 2.6±0.73 vs. 4.66±1.38, p=0.004; MVR: 40.14±18.76 vs. 20.47±6.24 mmHg/mL/min, p=0.02). Supplementation therapy with LT4 normalized TSH in all subjects and was associated with an increase in CFR (2.6±0.73 vs. 3.81±1.19, p=0.003) and with a tendency toward a decrease in MVR. Differences in CFR between SCH and controls were also seen after correction of resting MBF for RPP.

CONCLUSIONS

In asymptomatic subjects with SCH due to thyroid autoimmunity, coronary microvascular function is impaired and improves after supplementation with LT4. This may partially explain the increased cardiovascular risk attributed to SCH.

PET and PET/CT in cardiovascular disease

The present review provides an overview of the role of cardiac positron emission tomography in the diagnosis and management of cardiovascular disease. It expands on the relative advantages and disadvantages over other imaging modalities as well as the available evidence supporting its value in the diagnosis and management of patients with coronary artery disease, the assessment of myocardial viability, and evaluation of the cardiac sympathetic nervous system. Furthermore, the recent developments, such as the implementation of high-end computed tomography devices to form hybrid systems, and the advances of molecular imaging probes in experimental applications are briefly discussed.

Coronary Flow Reserve of the Non-Ischemia Related Coronary Artery During Dobutamine Stress Echocardiography

Background

Incorporation of analysis of coronary velocities in stress studies adds diagnostic value to both clinical variables and dobutamine echocardiography. Micorcirculatory abnormalities may precede obstructive corornary disease. Therefore the aim of this study was to assess Doppler derived coronary velocity and flow of the left anterior descending coronary artery (LAD) during dobutamine stress echocardiography (DSE) in patients without LAD-related ischemia.

Methods

Sixty nine patients with chest pain underwent DSE studies to evaluate myocardial ischemia. All had trans-thoracic Doppler interrogation of the distal LAD before and just after termination of the DSE. Coronary velocity reserves (CFR) were calculated as the ratios of post-DSE/baseline diastolic velocities. Volumetric flow in the distal LAD was calculated from the diameter of LAD color jet and velocity integral. Volumetric flow reserve was calculated as the ratio of post-DSE baseline LAD flows.

Results

At rest all subjects had left ventricular wall motion score index (WMSI) = 1, while in 28, wall motion abnormality appeared in non-LAD territory with WMSI = 1.17 ± 0.08. Peak diastolic velocity after DSE increased form 28.5 ± 13.6 to 52.4 ± 23.7 cm/sec, P = 9.5 × 10^-11, and velocity-CFR was 2.08 ± 0.7. Diastolic LAD flow increased from 36.5 ± 23.8 to 75.75 ± 48.7 mL/min, P = 1.21 × 10^-7 and volumetric-CFR was 2.6 ± 2.8. Peak diastolic velocity-CFR in patients without LV wall motion abnormality was 2.4 ± 0.7 while in those with motion abnormality 1.77 ± 0.56, P = 0.00008. Flow-derived LAD-CFR was 3.3 ± 3.7 in those without compared to 1.88 ± 0.57 in patients with wall motion abnormality, P < 0.05.

Conclusion

LAD velocity and flow reserves are reduced in patients with remote myocardial ischemia, which may indicate early atherosclerotic involvement.

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.

Quantification of myocardial blood flow: what is the clinical role?

Quantification of regional myocardial blood flow and of its responses to targeted physiologic and pharmacologic interventions, which is now available with positron emitting tracers of blood flow and positron emission tomography (PET), extends the diagnostic potential of standard myocardial perfusion imaging. These noninvasive flow measurements serve as tools for quantifying functional consequences of epicardial coronary artery disease, as well as of impairments in microcirculatory reactivity that escape detection by standard perfusion imaging. Flow measurements are clinically useful for more comprehensively assessing the extent and severity of coronary vascular disease or impairments in microcirculatory function in noncoronary cardiac disease. Flow estimates in these disorders contain independent or unique prognostic information about future major cardiac events. Flow measurements are also useful for assessing the coronary risk, for predicting long-term cardiovascular events, and for monitoring the effectiveness of risk reduction strategies.

Effects of exercise training and hypercholesterolemia on adenosine activation of voltage-dependent K+ channels in coronary arterioles

Coronary arterioles from hypercholesterolemic swine display attenuated adenosine-mediated vasodilatation that is attributable to the elimination of voltage-dependent K(+) (Kv) channel stimulation. For the present study, we tested the hypotheses that exercise training would correct impaired adenosine-induced dilatation in coronary arterioles from hypercholesterolemic pigs through restoration of adenosine activation of Kv channels and that vasodilatation to the receptor-independent adenylyl cyclase activator, forskolin, would also be attenuated in arterioles from hypercholesterolemic pigs. Pigs were randomly assigned to a control (NC) or high-fat, high-cholesterol (HC) diet for 20 wk. Four weeks after the diet was initiated, pigs from both groups were assigned to exercise training (Ex; 5 days/wk for 16 wk) or sedentary (Sed) protocols, resulting in four groups of pigs: NC-Sed, NC-Ex, HC-Sed, and HC-Ex. Arterioles ( approximately 150 mum) from both HC-Sed and HC-Ex pigs displayed impaired adenosine-mediated dilatation that was attributable to the elimination of 4-aminopyridine (4-AP; 1 mM)-sensitive Kv channel activation compared with NC counterparts. Arteriolar smooth muscle whole cell Kv currents were significantly reduced in HC-Sed compared with NC-Sed, although HC-Ex and NC-Ex did not differ. Forskolin-mediated dilatation was attenuated by 4-AP (1 mM) and in a concentration-dependent manner by tetraethylammonium (TEA; 0.1-1 mM) in NC-Sed but not HC-Sed. Further, TEA-sensitive Kv currents were diminished in cells of HC-Sed compared with NC-Sed pigs. Quantitative RT-PCR revealed similar expression levels of Kv3.1 and 3.3 in arterioles of NC-Sed and HC-Sed swine with undetectable expression of Kv1.1, 3.2, and 3.4. Taken together, these results suggest that hypercholesterolemia-mediated attenuation of adenosine-induced vasodilatation in coronary arterioles is not corrected by exercise training and is likely attributable to an impairment in the pathway coupling adenylyl cyclase with a highly TEA-sensitive Kv channel isoform(s).