Delayed response of myocardial flow reserve to lipid-lowering therapy with fluvastatin

Ischemia with Nonobstructive Coronary Artery Disease and Atrial Cardiomyopathy-Two Sides of the Same Story?

Ischemia with nonobstructive coronary artery disease (INOCA) is increasingly recognized as a significant cause of angina, myocardial remodeling, and eventually heart failure (HF). Coronary microvascular dysfunction (CMD) is a major endotype of INOCA, and it is caused by structural and functional alterations of the coronary microcirculation. At the same time, atrial cardiomyopathy (ACM) defined by structural, functional, and electrical atrial remodeling has a major clinical impact due to its manifestations: atrial fibrillation (AF), atrial thrombosis, stroke, and HF symptoms. Both these pathologies share similar risk factors and have a high comorbidity burden. CMD causing INOCA and ACM frequently coexist. Thus, questions arise whether there is a potential link between these pathologies. Does CMD promote AF or the reverse? Which are the mechanisms that ultimately lead to CMD and ACM? Are both part of a systemic disease characterized by endothelial dysfunction? Lastly, which are the therapeutic strategies that can target endothelial dysfunction and improve the prognosis of patients with CMD and ACM? This review aims to address these questions by analyzing the existing body of evidence, offering further insight into the mechanisms of CMD and ACM, and discussing potential therapeutic strategies.

Coronary Microvascular Dysfunction in Diabetes Mellitus: Pathogenetic Mechanisms and Potential Therapeutic Options

Diabetic patients are frequently affected by coronary microvascular dysfunction (CMD), a condition consisting of a combination of altered vasomotion and long-term structural change to coronary arterioles leading to impaired regulation of blood flow in response to changing cardiomyocyte oxygen requirements. The pathogenesis of this microvascular complication is complex and not completely known, involving several alterations among which hyperglycemia and insulin resistance play particularly central roles leading to oxidative stress, inflammatory activation and altered barrier function of endothelium. CMD significantly contributes to cardiac events such as angina or infarction without obstructive coronary artery disease, as well as heart failure, especially the phenotype associated with preserved ejection fraction, which greatly impact cardiovascular (CV) prognosis. To date, no treatments specifically target this vascular damage, but recent experimental studies and some clinical investigations have produced data in favor of potential beneficial effects on coronary micro vessels caused by two classes of glucose-lowering drugs: glucagon-like peptide 1 (GLP-1)-based therapy and inhibitors of sodium-glucose cotransporter-2 (SGLT2). The purpose of this review is to describe pathophysiological mechanisms, clinical manifestations of CMD with particular reference to diabetes, and to summarize the protective effects of antidiabetic drugs on the myocardial microvascular compartment.

Serial changes in the quantitative flow ratio in patients with intermediate residual stenosis after percutaneous coronary intervention

A beneficial surrogate marker for evaluating the effect of medical therapy is warranted to avoid deferred lesion revascularization. Similar to coronary artery imaging for monitoring the effects of medical therapy by analyzing plaque regression and stabilization, we hypothesized that evaluation of serial changes in the quantitative flow ratio (QFR) would serve as a surrogate marker of the effects of medical therapy against deferred lesion revascularization. Here, we investigated serial changes in QFR over time after percutaneous coronary intervention in patients who underwent medical therapy as a secondary prevention. Patients with intermediate stenosis in an untreated vessel observed at the baseline (BL) coronary angiography and follow-up (FU) coronary angiography performed 6-18 months after BL angiography were screened in 2 centers. A total of 52 patients were able to analyze both BL and FU QFR. The median QFR was 0.83 (IQR, 0.69, 0.89) at BL and 0.80 (IQR, 0.70, 0.86) at FU. The number of positive ΔQFR and negative ΔQFR were 21 and 31, respectively. The median ΔQFR was 0.05 (IQR, 0.03, 0.09) in positive ΔQFR and  - 0.05 (IQR,  - 0.07,  - 0.03) in negative ΔQFR (p < 0.0001). Univariate and multivariate analyses revealed that LDL-C at FU predicted improvement in the QFR (OR 0.95, 95% confidence interval [0.91, 0.98], P = 0.001). Assessment of serial changes in the QFR may serve as a surrogate marker for the effects of medical therapy in patients with residual intermediate coronary stenosis.

Elevated serum endothelin-1 is an independent predictor of coronary microvascular dysfunction in non-obstructive territories in patients with coronary artery disease

Endothelin-1 contributes to the constrictor response of the coronary arteries in patients with ischemia with normal coronary arteries. There is thus increasing evidence that endothelin-1 plays a role in coronary microvascular dysfunction (CMD). We investigated whether elevated endothelin-1 is associated with CMD in patients with coronary artery disease (CAD). We prospectively studied 49 consecutive CAD patients with 1- or 2-vessel disease (age 71 ± 10 years, 43 males). Myocardial blood flow (MBF) was measured by ¹⁵O-water PET/CT at rest and during stress, and the coronary flow reserve (CFR) was calculated by dividing the stress MBF by the rest MBF. A CFR of less than 2.0 in non-obstructive regions was defined as a marker of CMD. Eighteen out of 49 (37%) CAD patients had CMD. Endothelin-1 in patients with CMD was significantly higher than in those without CMD (2.27 ± 0.81 vs. 1.64 ± 0.48 pg/mL, P = 0.001). Accordingly, univariate ROC analysis showed that the continuous endothelin-1 levels significantly discriminated between the presence and absence of CMD (area under the curve = 0.746 [95%CI 0.592-0.899]). The dichotomous treatment of elevated endothelin-1 as 1.961 pg/mL or more yielded the optimal discriminatory capacity, with a sensitivity of 72.2% and a specificity of 71.0%. High endothelin-1 was still a significant predictor of CMD after adjusting for diabetes mellitus (odds ratio = 6.64 [1.75-25.22], P = 0.005). Endothelin-1 is associated with CMD in non-obstructive territories in patients with CAD, suggesting that endothelin-1 is a potential target for treating CMD in CAD patients.

Coronary Microvascular Dysfunction and the Role of Noninvasive Cardiovascular Imaging

Patients with coronary microvascular dysfunction (CMD) have significantly higher rates of cardiovascular events, including hospitalization for heart failure, sudden cardiac death, and myocardial infarction (MI). In CMD, several pathophysiological changes lead to functional and structural abnormalities in the coronary microvasculature, which disrupt the ability of the vessels to vasodilate and augment myocardial blood flow in response to increased myocardial oxygen demand, causing ischemia and angina. With the advent of more advanced non-invasive cardiac imaging techniques, the coronary microvasculature has been subjected to more intense study in the past two decades-this has led to further insights into the diagnosis, pathophysiology, treatment, prognosis and follow-up of CMD. This review will highlight and compare the salient features of the currently available non-invasive imaging modalities used in these patients, and discuss the clinical utility of these techniques in the workup and management of these patients.

Coronary Microvascular Disease Pathogenic Mechanisms and Therapeutic Options: JACC State-of-the-Art Review

Coronary microvascular disease (CMD) refers to the subset of disorders affecting the structure and function of the coronary microcirculation, is prevalent in patients across a broad spectrum of cardiovascular risk factors, and is associated with an increased risk of adverse events. Contemporary evidence supports that most patients with CMD also have macrovessel atherosclerosis, which has important implications for their prognosis and management. In this state-of-the-art review, the authors summarize the pathophysiology of CMD, provide an update of diagnostic testing strategies, and classify CMD into phenotypes according to severity and coexistence with atherosclerosis. They examine emerging data highlighting the significance of CMD in specific populations, including obesity and insulin resistance, myocardial injury and heart failure with preserved ejection fraction, and nonobstructive and obstructive coronary artery disease. Finally, they discuss the role of CMD as a potential target for novel interventions beyond conventional approaches, representing a new frontier in cardiovascular disease reduction.

Fluvastatin for lowering lipids

BACKGROUND

Fluvastatin is thought to be the least potent statin on the market, however, the dose-related magnitude of effect of fluvastatin on blood lipids is not known.

OBJECTIVES

Primary objectiveTo quantify the effects of various doses of fluvastatin on blood total cholesterol, low-density lipoprotein (LDL cholesterol), high-density lipoprotein (HDL cholesterol), and triglycerides in participants with and without evidence of cardiovascular disease.Secondary objectivesTo quantify the variability of the effect of various doses of fluvastatin.To quantify withdrawals due to adverse effects (WDAEs) in randomised placebo-controlled trials.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomised controlled trials up to February 2017: the Cochrane Central Register of Controlled Trials (CENTRAL) (2017, Issue 1), MEDLINE (1946 to February Week 2 2017), MEDLINE In-Process, MEDLINE Epub Ahead of Print, Embase (1974 to February Week 2 2017), the World Health Organization International Clinical Trials Registry Platform, CDSR, DARE, Epistemonikos and ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. No language restrictions were applied.

SELECTION CRITERIA

Randomised placebo-controlled and uncontrolled before and after trials evaluating the dose response of different fixed doses of fluvastatin on blood lipids over a duration of three to 12 weeks in participants of any age with and without evidence of cardiovascular disease.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility criteria for studies to be included, and extracted data. We entered data from placebo-controlled and uncontrolled before and after trials into Review Manager 5 as continuous and generic inverse variance data, respectively. WDAEs information was collected from the placebo-controlled trials. We assessed all trials using the 'Risk of bias' tool under the categories of sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting, and other potential biases.

MAIN RESULTS

One-hundred and forty-five trials (36 placebo controlled and 109 before and after) evaluated the dose-related efficacy of fluvastatin in 18,846 participants. The participants were of any age with and without evidence of cardiovascular disease, and fluvastatin effects were studied within a treatment period of three to 12 weeks. Log dose-response data over doses of 2.5 mg to 80 mg revealed strong linear dose-related effects on blood total cholesterol and LDL cholesterol and a weak linear dose-related effect on blood triglycerides. There was no dose-related effect of fluvastatin on blood HDL cholesterol. Fluvastatin 10 mg/day to 80 mg/day reduced LDL cholesterol by 15% to 33%, total cholesterol by 11% to 25% and triglycerides by 3% to 17.5%. For every two-fold dose increase there was a 6.0% (95% CI 5.4 to 6.6) decrease in blood LDL cholesterol, a 4.2% (95% CI 3.7 to 4.8) decrease in blood total cholesterol and a 4.2% (95% CI 2.0 to 6.3) decrease in blood triglycerides. The quality of evidence for these effects was judged to be high. When compared to atorvastatin and rosuvastatin, fluvastatin was about 12-fold less potent than atorvastatin and 46-fold less potent than rosuvastatin at reducing LDL cholesterol. Very low quality of evidence showed no difference in WDAEs between fluvastatin and placebo in 16 of 36 of these short-term trials (risk ratio 1.52 (95% CI 0.94 to 2.45).

AUTHORS' CONCLUSIONS

Fluvastatin lowers blood total cholesterol, LDL cholesterol and triglyceride in a dose-dependent linear fashion. Based on the effect on LDL cholesterol, fluvastatin is 12-fold less potent than atorvastatin and 46-fold less potent than rosuvastatin. This review did not provide a good estimate of the incidence of harms associated with fluvastatin because of the short duration of the trials and the lack of reporting of adverse effects in 56% of the placebo-controlled trials.

Quantitative Assessment of Coronary Microvascular Function: Dynamic Single-Photon Emission Computed Tomography, Positron Emission Tomography, Ultrasound, Computed Tomography, and Magnetic Resonance Imaging

A healthy, functional microcirculation in combination with nonobstructed epicardial coronary arteries is the prerequisite of normal myocardial perfusion. Quantitative assessment in myocardial perfusion and determination of absolute myocardial blood flow can be achieved noninvasively using dynamic imaging with multiple imaging modalities. Extensive evidence supports the clinical value of noninvasively assessing indices of coronary flow for diagnosing coronary microvascular dysfunction; in certain diseases, the degree of coronary microvascular impairment carries important prognostic relevance. Although, currently positron emission tomography is the most commonly used tool for the quantification of myocardial blood flow, other modalities, including single-photon emission computed tomography, computed tomography, magnetic resonance imaging, and myocardial contrast echocardiography, have emerged as techniques with great promise for determination of coronary microvascular dysfunction. The following review will describe basic concepts of coronary and microvascular physiology, review available modalities for dynamic imaging for quantitative assessment of coronary perfusion and myocardial blood flow, and discuss their application in distinct forms of coronary microvascular dysfunction.

Coronary microvascular dysfunction in women with nonobstructive ischemic heart disease as assessed by positron emission tomography

Traditional approaches for risk assessment of ischemic heart disease (IHD) are based on the physiological consequences of an epicardial coronary stenosis. Of note, normal coronary arteries or nonobstructive coronary artery disease (CAD) is a common finding in women with signs and symptoms of ischemia. Therefore, assessment of risk based on a coronary stenosis approach may fail in women. Positron emission tomography (PET) quantifies absolute myocardial blood flow (MBF) which may help to elucidate other mechanisms involved such as endothelial dysfunction and alterations in the smooth muscle cell relaxation responsible for IHD in women. The objective of the present review is to describe the current state of the art of PET imaging in assessing IHD in women with nonobstructive CAD.

Prevalence of coronary macro- and micro-vascular dysfunctions after drug-eluting stent implantation without in-stent restenosis

BACKGROUND

The aim was to examine the prevalence and characteristics of epicardial vasomotor abnormality (EVA) and coronary microvascular dysfunction (CMD) including endothelium-dependent (EDCMD) or -independent (EICMD) in patients following a second-generation drug-eluting stent (second DES) implantation without in-stent restenosis.

METHODS AND RESULTS

In 105 patients who underwent second DES implantation in the left anterior descending coronary artery (74 men; mean age, 67.9±9.6years), and in 105 suspected angina patients without stenting (65 men; mean age 66.4±9.1years), we evaluated EVA using the acetylcholine provocation test, EDCMD and EICMD by measuring the coronary flow reserve and the relationship between myocardial ischemia (intracoronary lactate production between aorta and coronary sinus and ST-T changes) or recurrent angina and vascular function. There was no difference in the incidence of EVA between DES and control (49.5% versus 55.2%; P=0.41). Given that the prevalence of CMD was higher in DES than in control (59.0% versus 29.5%; P<0.001), CMD may be associated with stent placement. Of the CMD patients, EDCMD alone, EICMD alone, and both CMDs were found in 40.3%, 22.6%, and 37.1%, respectively. Myocardial ischemia was detected in 42.4% of patients, and recurrent angina was more common in the presence of both EDCMD and EICMD in patients with EVA or CMD compared to patients with normal vascular function (EVA, 42.9% versus 7.7%, P=0.015: CMD, 39.1% versus 7.7%, P=0.007).

CONCLUSIONS

Myocardial ischemia and recurrent angina may be caused by the presence of both EDCMD and EICMD after a second DES implantation without ISR.

Effect of rosuvastatin on coronary flow reserve in patients with systemic hypertension

Although statins reduce cardiac events in hypertensive patients with cardiovascular risk factors, the effect of statins on coronary flow reserve (CFR) has not been examined. We tried to examine the effect of rosuvastatin on CFR in hypertensive patients at cardiovascular risk. CFR was studied in 56 hypertensive patients (40 men, 61 ± 9 years) with cardiovascular risk factors and without coronary artery disease in a prospective clinical trial. Using Doppler echocardiography, coronary flow velocity in the distal left anterior descending artery was recorded at baseline and during intravenous adenosine infusion, and CFR was defined as the ratio of hyperemic to basal average peak diastolic flow velocity. The primary efficacy measure was defined as the change in CFR after rosuvastatin therapy for 12 months. CFR was measured successfully in 55 of 56 enrolled patients (98%). CFR was 3.16 ± 0.44 at baseline and negatively correlated with age (R = -0.30, p = 0.025). All patients continued rosuvastatin 10 mg/day without any serious adverse events. After rosuvastatin therapy, serum total cholesterol, low-density lipoprotein cholesterol, and high-sensitivity C-reactive protein significantly decreased from 222 ± 18 to 142 ± 20 mg/dl, 148 ± 21 to 85 ± 18 mg/dl, and 1.7 ± 2.9 to 1.2 ± 3.1 mg/L, respectively (all p <0.01). CFR significantly increased from 3.16 ± 0.44 to 3.31 ± 0.42 (p <0.001). The change in CFR correlated with the change in low-density lipoprotein cholesterol (R = -0.28, p = 0.040) but not with the change in high-sensitivity C-reactive protein. In conclusion, CFR was significantly improved after 12 months of rosuvastatin therapy in hypertensive patients at cardiovascular risk and average levels of serum cholesterol.

Four-Dimensional Image Reconstruction Strategies in Cardiac-Gated and Respiratory-Gated PET Imaging

Cardiac and respiratory movements pose significant challenges to image quality and quantitative accuracy in PET imaging. Cardiac and/or respiratory gating attempt to address this issue, but instead lead to enhanced noise levels. Direct four-dimensional (4D) PET image reconstruction incorporating motion compensation has the potential to minimize noise amplification while removing considerable motion blur. A wide-ranging choice of such techniques is reviewed in this work. Future opportunities and the challenges facing the adoption of 4D PET reconstruction and its role in basic and clinical research are also discussed.

[Non-invasive coronary flow reserve is an independent predictor of exercise capacity after acute anterior myocardial infarction]

BACKGROUND

After acute myocardial infarction (MI) coronary microvascular impairment and reduced exercise capacity are both determinant of prognosis.

OBJECTIVE

We tested whether non-invasive coronary flow reserve (CFR) performed after MI predicts post-MI exercise capacity (EC).

METHODS

Fifty consecutive patients (pts) (mean age 56.5±11years, 30% women) with a first reperfused ST-elevation anterior MI, and sustained TIMI 3 flow after mechanical reperfusion, underwent prospectively non-invasive CFR in the distal part of the left anterior descending artery (LAD), using intravenous adenosine infusion (0.14mg/kg per minute, within 2min), within 24h after successful primary coronary angioplasty (CFR 1), and 4±1.6months later after a period of convalescence and a cardiac rehabilitation program (CFR 2). CFR was defined as peak hyperaemic LAD flow velocity divided by baseline flow velocity. All pts also underwent semi-supine exercise stress echocardiography (ESE) the same day of CFR 2. ESE was performed at an initial workload of 25-30watts with a 20watts increase at 2-minute intervals. Beta-blockers were withheld 24h before ESE.

RESULTS

The mean CFR 2 increased significantly when compared to CFR 1 (2.9±0.65 versus 1.9±0.4, P<0.01). During ESE, percentage of maximal predict heart rate achieved was 82±12%, maximal workload 95±30watts, exercise duration 486±155s, the ratio of double product 3.1±0.8, and EC 5.8±1.1 metabolic equivalents. No ischemia was induced during ESE in all pts, and the degree of mitral regurgitation did not differ significantly between rest and exercise. CFR 2 was significantly correlated to all indices related to EC (all, P<0.01), whereas CFR 1 was correlated to LV systolic function at follow-up (P<0.05) but not to EC. In multivariate analysis including age, sex, and body mass index, CFR 2 remained an independent predictor of EC (P<0.01).

CONCLUSION

Contrarily to acute CFR, CFR at follow-up is an independent predictor of EC after reperfused anterior MI. This suggests that the improvement of the coronary microcirculation is closely linked to the physical aptitude after MI.

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

BACKGROUND

Essential hypertension is one of the main risk factors for the development of coronary artery disease (CAD). Hypertension causes endothelial dysfunction which is considered an early sign for the development of CAD. Positron emission tomography is a non-invasive imaging technique that measures myocardial blood flow (MBF), allowing us to identify patients with endothelial dysfunction.

METHODS AND RESULTS

19 patients without comorbidities recently diagnosed hypertensive, as well as 21 healthy volunteers were studied. A three-phase (rest, cold pressor test, and adenosine-induced hyperemia) (13)N-ammonia PET was performed, and MBF was measured. Endothelial-Dependent Vasodilation Index, ΔMBF, and coronary flow reserve (CFR) were calculated for each patient. Hypertensive patients had a significantly higher systolic and diastolic blood pressures compared with the control group (134.6 ± 11.7/86.4 ± 10.6 mm Hg and 106.0 ± 11.8/71.4 ± 6.6 mm Hg, respectively, P < .001). The ENDEVI (1.28 ± 0.26 vs 1.79 ± 0.30, P < .001), the ΔMBF (0.81 ± 0.50 vs 0.25 ± 0.21, P < .001) and the CFR (2.18 ± 0.88 vs 3.17 ± 0.68, P = .001) were significantly lower in the hypertensive patients compared to the control group, 84% of the former group had endothelial dysfunction i.e., ENDEVI < 1.5 and 58% had vasomotor abnormalities, i.e., CFR < 2.5.

CONCLUSIONS

In this study, we showed that recently diagnosed hypertensive patients have coronary endothelial dysfunction and vasomotor disturbances which are early signs for the development of CAD.

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.

Statin therapy and clinical outcomes in myocardial infarction patients complicated by acute heart failure: insights from the EPHESUS trial

AIMS

Several clinical trials have shown that in patients with acute myocardial infarction (MI), statin therapy improves cardiovascular (CV) outcomes, but in these trials patients with acute heart failure (HF) were excluded or only a few were included. In patients with chronic HF, statin therapy does not reduce all-cause or CV mortality. We aimed to assess the association between statin therapy and clinical outcomes in the setting of acute HF with systolic dysfunction complicating acute MI.

METHODS AND RESULTS

We performed a post-hoc analysis in 6632 patients included in the EPHESUS trial. The mean age of patients was 64 years and 71% were male. Overall, 47% of patients had a statin prescribed at baseline. Cox regression models and a secondary analysis using propensity score matching were fit to assess the association between statin prescription and clinical outcomes. During a mean follow-up of 16 ± 7 months, all-cause death occurred in 385 (12%) patients with and in 647 (18%) patients without a statin (P < 0.001). After extensive adjustment, the risk of all-cause death was 20% lower in patients on statin [hazard ratio (HR) 0.80, 95% confidence interval (CI) 0.69-0.92, P = 0.001]. This positive association was mostly due to a lower risk of CV death (HR 0.76, 95% CI 0.65-0.88, P = 0.0002). In contrast, statin use was associated with a higher risk of non-CV hospitalizations (HR 1.16, 95% CI 1.02-1.33, P = 0.02).

CONCLUSION

Our results suggest that patients with acute HF complicating acute MI may benefit from being on statin therapy. Prospective clinical trials are required to validate these findings.

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.

Myocardial perfusion reserve after a PET-driven revascularization procedure: a strong prognostic factor

Not all patients treated on the basis of PET-proven viability benefit from revascularization. Myocardial perfusion reserve (MPR) predicts survival in patients not undergoing revascularization. In the present study, we investigated whether MPR is related to survival in ischemic heart disease (IHD) patients after a PET-driven intervention.

METHODS

Between 1995 and 2003, 119 consecutive patients with chronic IHD underwent a PET-driven revascularization procedure based on ischemia-viability assessment with PET. Patients were followed for all-cause mortality and major cardiovascular events.

RESULTS

One hundred nineteen patients underwent a PET-driven revascularization procedure (67 percutaneous coronary interventions, 52 coronary artery bypass grafts) because of angina complaints. The mean age was 67 ± 11 y (96 men, 23 women); global left ventricle MPR was 1.54 ± 0.43. MPR intertertile boundaries were 1.34 and 1.67. Significantly more cardiac deaths were observed in the lowest and middle MPR tertiles than in the highest tertile. The age- and sex-corrected hazard ratio for the middle tertile was 8.3 (95% confidence interval, 1.02-68.3) and for the lowest tertile 23.6 (95% confidence interval, 3.1-179) (P = 0.002). After left ventricular ejection fraction (LVEF) and viability were added to the model, MPR remained significant, with hazard ratios of 6.5 (0.8-54.4) and 18.5 (2.3-145.5) (P = 0.004), whereas neither LVEF nor viability reached significance in this model. Comparable results were found for major adverse cardiac events, with hazard ratios of 3.15 (0.82-12.0) and 8.24 (2.36-28.8) (P = 0.002).

CONCLUSION

Patients with IHD revascularized on the basis of PET viability assessment who have a low MPR are at risk for cardiac death and subsequent cardiac events. MPR is a more sensitive predictor for cardiac death than LVEF and extent of viability.

PET/CT challenge for the non-invasive diagnosis of coronary artery disease

This review will focus on the clinical potential of PET/CT for the characterization of cardiovascular diseases. We describe the technical challenges of combining instrumentation with very different imaging performance and discuss the clinical applications in the field of cardiology.

Long-term prognostic value of 13N-ammonia myocardial perfusion positron emission tomography added value of coronary flow reserve

OBJECTIVES

The goal of this study was to assess the predictive value of myocardial perfusion imaging with (13)N-ammonia positron emission tomography (PET) and coronary flow reserve (CFR) on long-term prognosis in patients with suspected myocardial ischemia.

BACKGROUND

No prognostic data exist on the predictive value of CFR and (13)N-ammonia PET.

METHODS

Perfusion and CFR were assessed in 256 patients using (13)N-ammonia PET, and follow-up was obtained in 245 (96%) patients. Sixteen early revascularized patients were excluded and 229 were assigned to normal versus abnormal perfusion or normal versus abnormal CFR (<2.0). Major adverse cardiac events (MACE) (cardiac death, nonfatal myocardial infarction, late revascularization, or hospitalization for cardiac reasons) were assessed using the Kaplan-Meier method. Cox proportional hazard regression was used to identify independent predictors for cardiac events.

RESULTS

During follow-up (5.4 +/- 2.2 years), 78 patients had at least 1 cardiac event, including 29 cardiac deaths. Abnormal perfusion (n = 126) was associated with a higher incidence of MACE (p < 0.001) and cardiac death (p < 0.05). In patients with normal perfusion, abnormal CFR was independently associated with a higher annual event rate over 3 years compared with normal CFR for MACE (1.4% vs. 6.3%; p < 0.05) and cardiac death (0.5% vs. 3.1%; p < 0.05). In abnormal perfusion, CFR remained predictive throughout the 10-year follow-up (p < 0.001).

CONCLUSIONS

Perfusion findings in (13)N-ammonia PET and CFR are strong outcome predictors. CFR allows further risk stratification, suggesting a "warranty" period of 3 years if normal CFR is associated with normal perfusion. Conversely, in patients with abnormal perfusion, an impaired CFR has added value for predicting adverse outcomes.

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.

Stress perfusion magnetic resonance imaging of the heart

Extensive research has documented that rapid imaging during the first pass of a magnetic resonance imaging (MRI) contrast agent provides good sensitivity to detect myocardial blood flow deficits caused by coronary disease, cardiomyopathies, or microvascular dysfunction in patients without obstructive lesions in the coronary arteries. The autoregulatory mechanisms of the coronary circulation serve the purpose of maintaining sufficient blood flow at baseline in the presence of flow-obstructing coronary lesions. Stress testing is most commonly used in this setting to determine the hemodynamic effect of coronary lesions in the epicardial arteries when the small-vessel resistance has been minimized by vasodilation. The protocols for perfusion MRI combined with vasodilation have been successfully tested in large patient studies. Besides the absence of any ionizing radiation, MRI offers the advantages of relatively high spatial resolution to detect perfusion defects limited to the inner layer of the heart muscle. Furthermore, MRI can be used for noninvasive quantitative measurements of myocardial blood flow that compare well with invasive measurements with labeled microspheres. Additional useful markers, such as the dynamic distribution volume, the delay in the arrival of the contrast agent in a myocardial region relative to the enhancement in the arterial input, and the capillary permeability-surface area product, may, in the future, further enhance the capabilities to characterize with MRI coronary atherosclerosis, coronary vascular dysfunction, and adaptive mechanisms in the coronary circulation, such as arteriogenesis, that reduce ischemia.

Effects of rosuvastatin on cardiovascular morphology and function in an ApoE-knockout mouse model of atherosclerosis

This study investigated the effects of rosuvastatin on plaque progression and in vivo coronary artery function in apolipoprotein E-knockout (ApoE-KO) mice, using noninvasive high-resolution ultrasound techniques. Eight-week-old male ApoE-KO mice (n = 20) were fed a high-fat diet with or without rosuvastatin (10 micromol.kg(-1).day(-1)) for 16 wk. When compared with control, rosuvastatin reduced total cholesterol levels (P < 0.05) and caused significant retardation of lesion progression in the brachiocephalic artery, as visualized in vivo using an ultrasound biomicroscope (P < 0.05). Histological analysis confirmed the reduction of brachiocephalic atherosclerosis and also revealed an increase in collagen content in the statin-treated group (P < 0.05). Coronary volumetric flow was measured by simultaneous recording of Doppler velocity signals and left coronary artery morphology before and during adenosine infusion. The hyperemic flow in response to adenosine was significantly greater in left coronary artery following 16 wk of rosuvastatin treatment (P < 0.001), whereas the baseline flow was similar in both groups. In conclusion, rosuvastatin reduced brachiocephalic artery atherosclerotic plaques in ApoE-KO mice. Coronary artery function assessed using recently developed in vivo ultrasound-based protocols, also improved.

Determining exercise-induced blood flow reserve in lower extremities using phase contrast MRI

PURPOSE

To study the changes in limb blood flow during lower extremity exercise using phase contrast (PC) MRI in normal volunteers.

MATERIALS AND METHODS

Healthy volunteers performed plantar flexion exercise (<1 W) for four minutes. Flow velocity was measured using cardiac-gated, cine PC-MRI sequences (fast gradient recalled echo [GRE]; multishot echo planar imaging [EPI]) on a 3T scanner at the level of the superficial femoral artery (SFA): 1) preexercise; 2) immediately postexercise; 3) during three minutes recovery; and 4) postrecovery.

RESULTS

At rest there was a triphasic flow waveform in the SFA. During exercise it changed to a monophasic pattern with an increase in total flow; there were variable changes in vessel size and flow velocity. The waveform regained the triphasic pattern during recovery. The exercise-induced flow reserve (FR) was 167 +/- 90%.

CONCLUSION

PC-MRI demonstrates that the resting triphasic flow waveform transforms into a monophasic pattern with submaximal exercise and returns to baseline with recovery. This increase in the regional blood flow allows for measurement of exercise-induced FR in the SFA.

A 6 month randomized, double blind, placebo controlled, multi-center trial of high dose atorvastatin on myocardial perfusion abnormalities by positron emission tomography in coronary artery disease

BACKGROUND

In coronary artery disease (CAD), statins decrease morbidity and mortality but changes in myocardial perfusion abnormalities remain poorly defined.

METHODS

We completed a randomized, double blind, placebo controlled, multi-center trial of 145 patients, 43 to 86 years old, with CAD from seven community and academic centers for cardiac positron emission tomography (PET) randomized to 6 months of atorvastatin 80 mg daily (72 patients) or placebo (73 patients). PET scans were obtained at baseline, 6 weeks and 6 months using N-13 ammonia or Rb-82 at rest and after dipyridamole or adenosine stress, submitted to the core PET laboratory in Houston. Change in stress induced perfusion defects from baseline to follow-up PET scans was scored by two independent, double blinded readers and by automated quantitative software.

RESULTS

Total and LDL cholesterol decreased by 37% and 51%, respectively in atorvastatin but not placebo groups (P < .05). The primary endpoint, quantitative severity (lowest mean quadrant activity), showed no significant difference between treatment and placebo. The secondary endpoint, predefined blinded visual change scores, improved significantly after atorvastatin compared to placebo at six months (P = .02). Ad-hoc subgroup analysis showed interaction between quantitative defect size and treatment response with perfusion defects in the upper tertile of size by automated software improving more in atorvastatin than placebo groups (P = .016).

CONCLUSION

The primary endpoint, quantitative severity of myocardial perfusion abnormalities by PET, did not improve after 6 months of atorvastatin 80 mg daily compared to placebo. The secondary endpoint of predefined blinded visual change scores significantly improved, as did a subgroup in the upper tertile of defect size, compared to placebo.

Quantification of myocardial blood flow with 82Rb dynamic PET imaging

PURPOSE

The PET tracer (82)Rb is commonly used to evaluate regional perfusion defects for the diagnosis of coronary artery disease. There is limited information on the quantification of myocardial blood flow and flow reserve with this tracer. The goal of this study was to investigate the use of a one-compartment model of (82)Rb kinetics for the quantification of myocardial blood flow.

METHODS

Fourteen healthy volunteers underwent rest and dipyridamole stress imaging with both (13)N-ammonia and (82)Rb within a 2-week interval. Myocardial blood flow was estimated from the time-activity curves measured with (13)N-ammonia using a standard two-compartment model. The uptake parameter of the one-compartment model was estimated from the time-activity curves measured with (82)Rb. To describe the relationship between myocardial blood flow and the uptake parameter, a nonlinear extraction function was fitted to the data. This function was then used to convert estimates of the uptake parameter to flow estimates. The extraction function was validated with an independent data set obtained from 13 subjects with documented evidence of coronary artery disease (CAD).

RESULTS

The one-compartment model described (82)Rb kinetics very well (median R-square = 0.98). The flow estimates obtained with (82)Rb were well correlated with those obtained with (13)N-ammonia (r = 0.85), and the best-fit line did not differ significantly from the identity line. Data obtained from the subjects with CAD confirmed the validity of the estimated extraction function.

CONCLUSION

It is possible to obtain accurate estimates of myocardial blood flow and flow reserve with a one-compartment model of (82)Rb kinetics and a nonlinear extraction function.

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

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