Evaluation of the endothelial function in hypertensive patients with 13N-ammonia PET

Segmental cardiac strain assessment by two-dimensional speckle-tracking echocardiography in surviving MIS-c patients: correlations with myocardial flow reserve (MFR) by 13 N-ammonia PET-CT

MIS-c is associated with severe cardiovascular impairment and eventually death. Pathophysiological mechanisms involved in myocardial injury were scarcely investigated and cardiovascular outcomes are uncertain. Autopsy studies suggested that microvascular dysfunction may be relevant to LV impairment. we aimed to evaluate segmental LV longitudinal strain by 2DST echocardiography, as well as myocardial flow reserve (MFR) by 13 N-ammonia PET-CT, in surviving MIS-c patients. each patient generated 34 LV segments for combined 2DST and MRF analysis. MFR was considered abnormal when < 2, borderline when between 2 and 2.5 and normal when > 2.5. From July 2020 to February 2021, six patients were admitted with MIS-c: three males, aged 9.3 (6.6-15.7) years. Time from admission to the follow-up visit was 6.05 (2-10.3) months. Although all patients were asymptomatic and LV EF was ≥ 55%, 43/102 (42.1%) LV segments showed MFR < 2.5. There was a modest positive correlation between segmental peak systolic longitudinal strain and MFR: r = 0.36, p = 0.03 for basal segments; r = 0.41, p = 0.022 for mid segments; r = 0.42, p = 0.021 for apical segments. Median peak systolic longitudinal strain was different among MRF categories: 18% (12%-24%) for abnormal, 18.5% (11%-35%) for borderline and 21% (12%-32%) for normal MFR (p = 0.006). We provided preliminary evidence that surviving MIS-c patients may present subclinical impairment of myocardial microcirculation. Segmental cardiac strain assessment 2DST seems useful for MIS-c cardiovascular follow-up, given its good correlation with 13 N-ammonia PET-CT derived MFR.

Time course of coronary flow capacity impairment in ST-segment elevation myocardial infarction

BACKGROUND

Microvascular dysfunction in the setting of ST-elevated myocardial infarction (STEMI) plays an important role in long-term poor clinical outcome. Coronary flow reserve (CFR) is a well-established physiological parameter to interrogate the coronary microcirculation. Together with hyperaemic average peak flow velocity, CFR constitutes the coronary flow capacity (CFC), a validated risk stratification tool in ischaemic heart disease with significant prognostic value. This mechanistic study aims to elucidate the time course of the microcirculation as reflected by alterations in microcirculatory physiological parameters in the acute phase and during follow-up in STEMI patients.

METHODS

We assessed CFR and CFC in the culprit and non-culprit vessel in consecutive STEMI patients at baseline (n = 98) and after one-week (n = 64) and six-month follow-up (n = 65).

RESULTS

A significant trend for culprit CFC in infarct size as determined by peak troponin T (p = 0.004), time to reperfusion (p = 0.038), the incidence of final Thrombolysis In Myocardial Infarction 3 flow (p = 0.019) and systolic retrograde flow (p = 0.043) was observed. Non-culprit CFC linear contrast analysis revealed a significant trend in C-reactive protein (p = 0.027), peak troponin T (p < 0.001) and heart rate (p = 0.049). CFC improved both in the culprit and the non-culprit vessel at one-week (both p < 0.001) and six-month follow-up (p = 0.0013 and p < 0.001) compared with baseline.

CONCLUSION

This study demonstrates the importance of microcirculatory disturbances in the setting of STEMI, which is relevant for the interpretation of intracoronary diagnostic techniques which are influenced by both culprit and non-culprit vascular territories. Assessment of non-culprit vessel CFC in the setting of STEMI might improve risk stratification of these patients following coronary reperfusion of the culprit vessel.

Warranty period of normal stress myocardial perfusion imaging in hypertensive patients: A parametric survival analysis

BACKGROUND

We evaluated the warranty period of a normal stress myocardial perfusion single-photon emission computed tomography (MPS) in hypertensive patients.

METHODS AND RESULTS

A total of 471 consecutive hypertensive patients with suspected coronary artery disease and normal perfusion at stress MPS were followed for a mean of 76 ± 21 months. Endpoint events were cardiac death or nonfatal myocardial infarction. With Cox analysis, age (hazard ratio 1.1, P < .005) and stress test type (hazard ratio 2.7, P < .005) were independent predictors of events. With parametric Weibull analysis, patients ≤60 years old undergoing exercise stress test remained at low risk for the entire length of follow-up, while the highest probability of events and the major risk acceleration were observed in those > 60 years old who underwent pharmacologic stress test. In patients undergoing exercise test, peak systolic blood pressure (BP; hazard ratio 1.1, P < .005) emerged as predictor of events, and only subjects with peak systolic BP < 160 mmHg remained at low risk for the entire length of follow-up. In contrast, for patients with peak systolic BP ≥180 mmHg, the time to achieve a cumulative cardiac risk level of 3% was 18 months.

CONCLUSIONS

In hypertensive patients, the warranty period of a normal stress MPS varies according to stress type and peak systolic BP. A normal stress MPS can be considered reassuring in subjects ≤60 years old who performed exercise stress test and a peak systolic BP < 160 mmHg.

Uridine Adenosine Tetraphosphate-Induced Coronary Relaxation Is Blunted in Swine With Pressure Overload: A Role for Vasoconstrictor Prostanoids

Plasma levels of the vasoactive substance uridine adenosine tetraphosphate (Up₄A) are elevated in hypertensive patients and Up₄A-induced vascular contraction is exacerbated in various arteries isolated from hypertensive animals, suggesting a potential role of Up₄A in development of hypertension. We previously demonstrated that Up₄A produced potent and partially endothelium-dependent relaxation in the porcine coronary microvasculature. Since pressure-overload is accompanied by structural abnormalities in the coronary microvasculature as well as by endothelial dysfunction, we hypothesized that pressure-overload blunts the coronary vasodilator response to Up₄A, and that the involvement of purinergic receptors and endothelium-derived factors is altered. The effects of Up₄A were investigated using wire-myography in isolated coronary small arteries from Sham-operated swine and swine with prolonged (8 weeks) pressure overload of the left ventricle induced by aortic banding (AoB). Expression of purinergic receptors and endothelium-derived factors was assessed in isolated coronary small arteries using real-time PCR. Up₄A (10^-9 to 10^-5 M) failed to produce contraction in isolated coronary small arteries from either Sham or AoB swine, but produced relaxation in preconstricted arteries, which was significantly blunted in AoB compared to Sham. Blockade of purinergic P1, and P2 receptors attenuated Up₄A-induced coronary relaxation more, while the effect of P2X₁-blockade was similar and the effects of A_2A- and P2Y₁-blockade were reduced in AoB as compared to Sham. mRNA expression of neither A1, A2, A3, nor P2X₁, P2X₇, P2Y₁, P2Y₂, nor P2Y₆-receptors was altered in AoB as compared to Sham, while P2Y₁₂ expression was higher in AoB. eNOS inhibition attenuated Up₄A-induced coronary relaxation in both Sham and AoB. Additional blockade of cyclooxygenase enhanced Up₄A-induced coronary relaxation in AoB but not Sham swine, suggesting the involvement of vasoconstrictor prostanoids. In endothelium-denuded coronary small arteries from normal swine, thromboxane synthase (TxS) inhibition enhanced relaxation to Up₄A compared to endothelium-intact arteries, to a similar extent as P2Y₁₂ inhibition, while the combination inhibition of P2Y₁₂ and TxS had no additional effect. In conclusion, Up₄A-induced coronary relaxation is blunted in swine with AoB, which appears to be due to the production of a vasoconstrictor prostanoid, likely thromboxane A₂.

Hypertension, Left Ventricular Hypertrophy, and Myocardial Ischemia

The risks associated with hypertension emerge through a series of complex interactions. Myocardial ischemia is the major contributor to this risk. The mechanisms driving ischemia reflect many of the key factors in hypertension, including endothelial and neurohumoral factors, fibrosis, and hemodynamics. Left ventricular hypertrophy and fibrosis are of fundamental importance and together with hemodynamics provide an optimal template for myocardial ischemia. Understanding the pathophysiology has aided a more rational management approach but challenges remain which, if surmounted, will have an impact on the morbidity and mortality caused by myocardial ischemia in patients with hypertension.

Impact of time-of-flight on qualitative and quantitative analyses of myocardial perfusion PET studies using (13)N-ammonia

BACKGROUND

The impact of time-of-flight (TOF) in myocardial perfusion (13)N-ammonia positron emission tomography (PET) is unclear.

METHODS AND RESULTS

Twenty consecutive subjects underwent rest and adenosine stress (13)N-ammonia myocardial perfusion PET. Two sets of images were reconstructed using TOF-ordered subset expectation maximization (TOF-OSEM) and 3-dimensional row-action maximum likelihood algorithm (3D-RAMLA). Qualitative and quantitative analyses from the TOF-OSEM and 3D-RAMLA reconstructions were compared. Count profile curves revealed that TOF relatively increased the uptake of (13)N-ammonia at the lateral walls, and apical thinning was emphasized on the TOF images. Both segmental rest and stress myocardial blood flow (MBF) values were higher with TOF-OSEM use than with 3D-RAMLA use (rest MBF: 0.955 ± 0.201 vs 0.836 ± 0.185, P < .001; stress MBF: 2.149 ± 0.697 vs 2.058 ± 0.721, P < .001). The differentiation of MBF between reconstructions was more enhanced under rest conditions. Thus, segmental myocardial flow reserve (MFR) observed using TOF-OSEM reconstruction was lower than that observed using 3D-RAMLA (2.25 ± 0.57 vs 2.46 ± 0.75, P < .001). No remarkable differences were observed between segmental and territorial results.

CONCLUSIONS

TOF increased lateral wall counts and emphasized apical thinning. Quantitatively, TOF reconstruction showed increased MBF, especially under relatively low perfusion conditions.

Novel contributions of multimodality imaging in hypertension: A narrative review

Hypertension is currently one of the most prevalent illnesses worldwide, and is the second most common cause of heart failure, only behind ischemic cardiomyopathy. The development of novel multimodality imaging techniques in recent years has broadened the diagnostic methods, risk stratification and monitoring of treatment of cardiovascular diseases available for clinicians. Cardiovascular magnetic resonance (CMR) has a great capacity to evaluate cardiac dimensions and ventricular function, is extremely useful in ruling-out ischemic cardiomyopathy, the evaluation of the vascular system, in making the differential diagnosis for resistant hypertension and risk stratification for hypertensive cardiomyopathy and constitutes today, the method of choice to evaluate left ventricular systolic function. Computed tomography (CT) is the method of choice for the evaluation of vascular anatomy, including coronary arteries, and is also able to provide both functional and structural information. Finally, nuclear cardiology studies have been traditionally used to evaluate myocardial ischemia, along with offering the capacity to evaluate ventricular, endothelial and cardiac innervation function; information that is key in directing the treatment of the patient. In this narrative review, the most recent contributions of multimodality imaging to the patient with hypertension (CMR, CT and nuclear cardiology) will be reviewed.

Patients with reduced heart rate response to adenosine infusion have low myocardial flow reserve in (13)N-ammonia PET studies

To assess the effect of adenosine infusion by evaluating the relationship between heart rate (HR) response to adenosine and myocardial flow reserve (MFR) of remote regions supplied by normal coronary arteries in ¹³N-ammonia PET. Thirty-one consecutive subjects (20 known coronary artery disease patients, 4 chronic heart failure patients, and 7 normal volunteers) except cases having 3-vessel disease underwent rest and adenosine stress ¹³N-ammonia myocardial perfusion PET. Semi-quantitative, quantitative, and gated analyses were performed. Subjects were divided into two groups with regard to HR response to adenosine. Twenty-two subjects had normal HR response (peak/rest HR > 1.20), while reduced HR response (≤1.20) was observed in nine subjects. There were no differences in rest myocardial blood flow (MBF) of remote regions between the groups. Subjects with reduced HR response had significantly lower stress MBF and MFR of remote regions than those with normal HR response (stress MBF: 1.559 ± 0.517 vs. 2.279 ± 0.530, p = 0.004, MFR: 1.59 ± 0.36 vs. 2.35 ± 0.53, p = 0.001). There were no significant differences between the groups by means of semi-quantitative scoring. Rest and stress ejection fraction (EF) in the reduced HR response group was lower than that in the normal HR response group. In a multiple stepwise regression analysis, HR ratio, dyslipidemia, and Brinkman index were identified as predictors of the change in MFR of remote regions. Subjects with reduced HR response to adenosine had lower stress MBF and MFR of remote regions and lower EF. Moreover, HR response was one of the predictors of the change in MFR of remote regions.

β2-adrenergic stress evaluation of coronary endothelial-dependent vasodilator function in mice using (11)C-acetate micro-PET imaging of myocardial blood flow and oxidative metabolism

Background

Endothelial dysfunction is associated with vascular risk factors such as dyslipidemia, hypertension, and diabetes, leading to coronary atherosclerosis. Sympathetic stress using cold-pressor testing (CPT) has been used to measure coronary endothelial function in humans with positron emission tomography (PET) myocardial blood flow (MBF) imaging, but is not practical in small animal models. This study characterized coronary vasomotor function in mice with [¹¹C]acetate micro-PET measurements of nitric-oxide-mediated endothelial flow reserve (EFR_NOM) (adrenergic-stress/rest MBF) and myocardial oxygen consumption (MVO₂) using salbutamol β₂-adrenergic-activation.

Methods

[¹¹C]acetate PET MBF was performed at rest + salbutamol (SB 0.2, 1.0 μg/kg/min) and norepinephrine (NE 3.2 μg/kg/min) stress to measure an index of MBF response. β-adrenergic specificity of NE was evaluated by pretreatment with α-adrenergic-antagonist phentolamine (PHE), and β₂-selectivity was assessed using SB.

Results

Adjusting for changes in heart rate × systolic blood pressure product (RPP), the same stress/rest MBF ratio of 1.4 was measured using low-dose SB and NE in normal mice (equivalent to human CPT response). The MBF response was correlated with changes in MVO₂ (p = 0.02). Nitric oxide synthase (NOS)-inhibited mice (N^g-nitro-L-arginine methyl ester (L-NAME) pretreatment and endothelial nitric oxide synthase (eNOS) knockout) were used to assess the EFR_NOM, in which the low-dose SB- and NE-stress MBF responses were completely blocked (p = 0.02). With high-dose SB-stress, the MBF ratio was reduced by 0.4 following NOS inhibition (p = 0.03).

Conclusions

Low-dose salbutamol β₂-adrenergic-stress [¹¹C]acetate micro-PET imaging can be used to measure coronary-specific EFR_NOM in mice and may be suitable for assessment of endothelial dysfunction in small animal models of disease and evaluation of new therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-014-0068-9) contains supplementary material, which is available to authorized users.

Advanced tracers in PET imaging of cardiovascular disease

Cardiovascular disease is the leading cause of death worldwide. Molecular imaging with targeted tracers by positron emission tomography (PET) allows for the noninvasive detection and characterization of biological changes at the molecular level, leading to earlier disease detection, objective monitoring of therapies, and better prognostication of cardiovascular diseases progression. Here we review, the current role of PET in cardiovascular disease, with emphasize on tracers developed for PET imaging of cardiovascular diseases.

Cardiac PET: metabolic and functional imaging of the myocardium

Cardiac PET has evolved over the past 30 years to gain wider acceptance as a valuable modality for a variety of cardiac conditions. Wider availability of scanners as well as changes in reimbursement policies in more recent years has further increased its use. Moreover, with the emergence of novel radionuclides as well as further advances in scanner technology, the use of cardiac PET can be expected to increase further in both clinical practice and the research arena. PET has demonstrated superior diagnostic accuracy for the diagnosis of coronary artery disease in comparison with single-photon emission tomography while it provides robust prognostic value. The addition of absolute flow quantification increases sensitivity for 3-vessel disease as well as providing incremental functional and prognostic information. Metabolic imaging using (18)F-fluorodeoxyglucose can be used to guide revascularization in the setting of heart failure and also to detect active inflammation in conditions such as cardiac sarcoidosis and within atherosclerotic plaque, improving our understanding of the processes that underlie these conditions. However, although the pace of new developments is rapid, there remains a gap in evidence for many of these advances and further studies are required.

Review: comparison of PET rubidium-82 with conventional SPECT myocardial perfusion imaging

Nuclear cardiology has for many years been focused on gamma camera technology. With ever improving cameras and software applications, this modality has developed into an important assessment tool for ischaemic heart disease. However, the development of new perfusion tracers has been scarce. While cardiac positron emission tomography (PET) so far largely has been limited to centres with on-site cyclotron, recent developments with generator produced perfusion tracers such as rubidium-82, as well as an increasing number of PET scanners installed, may enable a larger patient flow that may supersede that of gamma camera myocardial perfusion imaging.