Influence of nitric oxide synthase and adrenergic inhibition on adenosine-induced myocardial hyperemia

Coronary microvascular reactivity to adenosine predicts adverse outcome in women evaluated for suspected ischemia results from the National Heart, Lung and Blood Institute WISE (Women's Ischemia Syndrome Evaluation) study

OBJECTIVES

We investigated whether coronary microvascular dysfunction predicts major adverse outcomes during follow-up among women with signs and symptoms of ischemia.

BACKGROUND

Altered coronary reactivity occurs frequently in women evaluated for suspected ischemia, and the endothelium-dependent component is linked with adverse outcomes. Possible links between endothelium-independent microvascular coronary reactivity and adverse outcomes remain uncertain.

METHODS

As part of the National Heart, Lung and Blood Institute-sponsored WISE (Women's Ischemia Syndrome Evaluation), we investigated relationships between major adverse outcomes and baseline coronary flow reserve (CFR) after intracoronary adenosine in 189 women referred to evaluate suspected ischemia.

RESULTS

At a mean of 5.4 years, we observed significant associations between CFR and major adverse outcomes (death, nonfatal myocardial infarction, nonfatal stroke, or hospital stay for heart failure). An exploratory receiver-operator characteristic analysis identified CFR <2.32 as the best discriminating threshold for adverse outcomes (event rate 26.7%; and >or=2.32 event rate 12.2%; p = 0.01). Lower CFR was associated with increased risk for major adverse outcomes (hazard ratio: 1.16, 95% confidence interval: 1.04 to 1.30; p = 0.009). This held true among the 152 women without obstructive coronary artery disease (CAD) (hazard ratio: 1.20, 95% confidence interval: 1.05 to 1.38; p = 0.008). The CFR significantly improved prediction of adverse outcomes over angiographic CAD severity and other risk conditions.

CONCLUSIONS

Among women with suspected ischemia and atherosclerosis risk factors, coronary microvascular reactivity to adenosine significantly improves prediction of major adverse outcomes over angiographic CAD severity and CAD risk factors. These findings suggest that coronary microvessels represent novel targets for diagnostic and therapeutic strategies to predict and limit adverse outcomes in women. (Women's Ischemia Syndrome Evaluation [WISE]; NCT00000554).

Systemic nitric oxide clamping in normal humans guided by total peripheral resistance

AIM

We wanted to stabilize the availability of nitric oxide (NO) at levels compatible with normal systemic haemodynamics to provide a model for studies of complex regulations in the absence of changes in NO levels.

METHODS

Normal volunteers (23-28 years) were infused i.v. with the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) at 0.5 mg kg(-1) h(-1). One hour later, the NO donor sodium nitroprusside (SNP) was co-infused in doses eliminating the haemodynamic effects of l-NAME. Haemodynamic measurements included blood pressure (MABP) and cardiac output (CO) by impedance cardiography.

RESULTS

l-NAME increased MABP and total peripheral resistance (TPR, 1.02 + or - 0.05 to 1.36 + or - 0.07 mmHg s mL(-1), mean + or - SEM, P < 0.001). With SNP, TPR fell to a stable value slightly below control (0.92 + or - 0.05 mmHg s mL(-1), P < 0.05). CO decreased with l-NAME (5.8 + or - 0.3 to 4.7 + or - 0.3 L min(-1), P < 0.01) and returned to control when SNP was added (6.0 + or - 0.3 L min(-1)). A decrease in plasma noradrenaline (42%, P < 0.01) during l-NAME administration was completely reversed by SNP. Plasma renin activity decreased during l-NAME administration and returned towards normal after addition of SNP. In contrast, plasma aldosterone was increased by l-NAME and remained elevated.

CONCLUSIONS

Concomitant NOS inhibition and NO donor administration can be adjusted to maintain TPR at control level for hours. This approach may be useful in protocols in which stabilization of the peripheral supply of NO is required. However, the dissociation between renin and aldosterone secretion needs further investigation.

Impaired myocardial blood flow reserve in subjects with metabolic syndrome analyzed using positron emission tomography and N-13 labeled ammonia

PURPOSE

Coronary vasomotor response might be impaired in metabolic syndrome (MS); however, the precise abnormality has not been elucidated. The aim of this study was to assess coronary-vasomotor response in MS subjects using N-13 labeled ammonia and positron emission tomography.

METHODS AND RESULTS

Myocardial blood flow (MBF) was measured at rest and during adenosine infusion in MS subjects (n = 13, MS group) with no definite evidence of heart disease and in subjects without MS (n = 14, non-MS group). Coronary vascular resistance (CVR) was calculated by dividing the mean aortic blood pressure by MBF. Myocardial blood flow reserve (MFR) was calculated as the ratio of the MBF during adenosine infusion to that during rest. Blood chemical parameters were measured to evaluate their relationship with MFR. During adenosine infusion, MBF was lower (p = 0.0085) and CVR higher (p = 0.0128) in the MS group than in the non-MS group and MFR was significantly lower in the MS group than in the non-MS group (2.13 +/- 0.99 vs. 3.38 +/- 0.95, p = 0.0027). Multivariate analysis demonstrated that the homeostasis model assessment-insulin resistance (p < 0.05) and the presence of hypertension (p < 0.05) were independent determinants of MFR.

CONCLUSIONS

The results indicate that MFR was impaired in MS subjects, suggesting that an abnormal coronary microvascular response occurred in these subjects. This abnormality may have been partially due to insulin resistance and hypertension.

Improvement of myocardial blood flow by lipid‐lowering therapy with pravastatin is modulated by apolipoprotein E genotype

OBJECTIVE

Apolipoprotein E (apoE) polymorphism affects the risk of advanced coronary artery disease, but its role in early atherosclerosis remains unknown. We used positron emission tomography (PET) to study whether coronary reactivity or its response to pravastatin is related to the apoE genotype.

MATERIAL AND METHODS

Samples from 44 mildly hypercholesterolaemic men (aged 35 +/- 4 years) of an earlier trial were re-analysed according to apoE genotype. Subjects were randomized to receive either 40 mg/day pravastatin or placebo for 6 months. To assess coronary reactivity, myocardial blood flow was measured by PET at rest and during adenosine infusion. PET studies and lipid analyses were done at baseline and after 6 months of therapy.

RESULTS

There were no differences between apoE epsilon3/3 and epsilon4/3 genotypes in basal or adenosine-stimulated flow or in coronary flow reserve (CFR) at baseline. There was a significant apoE genotype-by-treatment group interaction regarding the change in adenosine-stimulated flow (ANCOVA; p = 0.018) and CFR (p = 0.020) at the end of the study. In the pravastatin group, the adenosine-stimulated flow increased by 32.5 % in subjects with epsilon3/3 (n = 9), but decreased non-significantly (-14.4 %) in subjects with epsilon4/3 (n = 9) (p = 0.0009). The corresponding changes in CFR were +17.8 % for epsilon3/3 and (-11.9 % for epsilon4/3 (p = 0.05). There were no significant changes from the baseline values in placebo recipients. After pravastatin treatment, both genotype groups showed a similar decrease in serum total and low-density lipoprotein cholesterol (p<0.0001 for both).

CONCLUSIONS

Coronary function improves by 6 months of pravastatin in subjects with the apoE epsilon3/3 genotype, but not in those with the epsilon4/3.

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.

Vascular endothelial function predicts mortality risk in patients with advanced ischaemic chronic heart failure

AIMS

Endothelial function is impaired in advanced chronic heart failure (ACHF) patients. We explored a possible association between endothelial function and subsequent mortality risk in ACHF.

METHODS AND RESULTS

We prospectively assessed brachial flow-mediated dilation (FMD) in 82 consecutive New York Heart Association class IV ischaemic ACHF patients with a mean left ventricular ejection fraction (LVEF) of 22 +/- 3%. Following overnight fasting and discontinuation of all medications for > or = 12 h, percent increase in FMD (%FMD) and nitroglycerin-mediated vasodilation were assessed using linear array ultrasound. All patients were followed for 14 +/- 2 months for adverse cardiovascular events, including death, hospitalization for CHF exacerbation, or myocardial infarction. Patients were divided into two groups: those with an FMD lesser than or equal to the median %FMD of 4.6% (n = 41) and those with an FMD above the median (n = 41). Both groups were comparable regarding cardiovascular risk factors, LVEF, and concomitant medications. During follow-up, 22 (53.6%) patients with FMD lesser than or equal to the median had composite adverse cardiovascular events compared with only eight patients (19.5%) with FMD above the median (P < 0.01). Furthermore, fiver deaths (12.1%) occurred in patients with FMD lesser than or equal to the median, compared with no deaths in patients with FMD above the median (P < 0.03). Cox regression analyses revealed that FMD was an independent predictor for these events.

CONCLUSION

Flow-mediated dilation is associated with increased mortality risk in ischaemic ACHF patients.

Increased basal myocardial perfusion in patients with chronic kidney disease without symptomatic coronary artery disease

BACKGROUND

Even minor renal dysfunction is a powerful cardiovascular risk factor. The abnormalities in coronary and peripheral artery function in different stages of chronic kidney disease (CKD) remain poorly understood. Our aim was to test by a positron emission tomography (PET)-based method whether microvascular dysfunction, an early marker of coronary dysfunction, exists already in early stages of CKD.

METHODS

Myocardial blood flow was measured at baseline and during dipyridamole-induced hyperaemia by PET. Peripheral artery endothelial function was examined by measuring flow-mediated dilatation (FMD) of the brachial artery at rest and during reactive hyperaemia. Twenty-two patients with moderate to severe kidney failure and 10 healthy controls were investigated. Diabetic patients were excluded. Baseline characteristics were similar between the groups with the exception of antihypertensive medication in all CKD patients.

RESULTS

The basal myocardial perfusion was statistically significantly higher in CKD patients than observed values in similarly aged controls. There was a statistically significant negative correlation between the baseline myocardial perfusion and the estimated glomerular filtration rate. Coronary flow reserve was comparable to healthy controls in all patients. FMD was significantly reduced in all patients with CKD regardless of the stage of kidney failure.

CONCLUSIONS

Coronary flow reserve was normal although baseline myocardial blood flow was increased in all CKD patients as compared to healthy controls. Peripheral endothelial dysfunction was detected in all patients. Our findings suggest that coronary perfusion and peripheral vascular function are disturbed by different mechanisms in patients with CKD.

Endothelial dysfunction in recently diagnosed type 2 diabetic patients evaluated by PET

PURPOSE

To demonstrate the presence of endothelial dysfunction (ED) in asymptomatic patients with type 2 diabetes mellitus (DM) by using (13)N-ammonia-positron emission tomography (PET). PET can identify ED by quantifying myocardial blood flow (MBF) during rest, cold pressor test (CPT), and pharmacologic stress. The endothelial-dependent vasodilation index (EDVI), myocardial flow reserve (MFR), and the percentage of the change between rest and CPT (%DeltaMBF) are markers of endothelial function.

PROCEDURES

Thirty-nine subjects were studied (19 women and 20 men); 22 recently diagnosed type 2 diabetic patients and 17 healthy controls (HC). A three-phase (13)N-ammonia-PET was performed.

RESULTS

Mean EDVI was 1.208 +/- 0.34 vs. 1.55 +/- 0.37 (diabetic vs. HC group, respectively) (p = 0.002), MFR was 2.803 +/- 1.39 vs. 3.27 +/- 0.72 (p = NS), and the %DeltaMBF was 20 +/- 34% vs. 55 +/- 37% (p = 0.002). Rest MBF and CPT MBF were normalized to the rate pressure product (RPP). EDVI' and %DeltaMBF' were calculated using the corrected values for the RPP. Mean EDVI' was (0.864 +/- 0.250 vs. 1.110 +/- 0.238, p = 0.004) and mean %DeltaMBF' was (-8.2 +/- 14.7% vs. 4.5 +/- 12.1%, p = 0.005).

CONCLUSIONS

Asymptomatic, recently diagnosed type 2 diabetes patients present ED that can be quantified by (13)N-ammonia-PET.

Transient impairment of coronary flow reserve in tako-tsubo cardiomyopathy is related to left ventricular systolic parameters

AIMS

Recent studies suggest that coronary flow reserve (CFR) is transiently impaired in tako-tsubo cardiomyopathy (TTC). Mechanisms by which such impairment occurs are still unknown. To assess the relationship between CFR obtained by transthoracic Doppler echocardiography (TDE) and parameters of left ventricular (LV) performance in patients with TTC.

METHODS AND RESULTS

A total of 20 consecutive patients in sinus rhythm, with TTC (mean age 70+/-9 years, 19 women) underwent serial evaluation of TDE-CFR, in the distal part of the left anterior descending coronary artery (LAD), at the acute phase and after recovery using intravenous adenosine infusion (140 microg/kg/min over 2 min). CFR was calculated as hyperaemic to basal mean diastolic coronary flow velocity (CFV). Average of the septal and lateral mitral annulus early diastolic (Ea) and systolic (Sa) tissue velocity, early (E) and late (A) diastolic transmitral velocity, the ratio E/Ea, wall motion score (WMS, 16 segment model), LV end-systolic volume index (ESV/m(2)) and LV end-diastolic volume index (EDV/m(2), biplane-Simpson method) were serially measured by TDE. Basal CFV, LV mass index and haemodynamics parameters did not differ between acute phase and recovery, whereas hyperaemic CFV increased significantly after recovery (P<0.01) leading to a greater CFR (2.9+/-0.3 vs. 2.1+/-0.4, P<0.0001). At the acute phase, hyperaemic CFV was significantly correlated to WMS, ESV/m(2), but not to E/Ea, whereas at recovery, hyperaemic CFV was not correlated to LV parameters. The improvement of CFR was closely correlated to the decrease of ESV/m(2), of WMS, but not to diastolic parameters. No significant correlation was found between CFR and E/Ea or LV mass index at each stage.

CONCLUSION

There is a transient impairment of CFR at the acute phase of TTC, which is due to a reduced vasodilating capacity. This impairment is closely correlated to LV systolic parameters. Diastolic compressive forces to the coronary microcirculation do not appear to play a critical role.

Effect of angiotensin-converting enzyme inhibitor on serum asymmetric dimethylarginine and coronary circulation in patients with type 2 diabetes mellitus

Measurements of serum asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, and coronary flow velocity reserve (CFVR) using transthoracic Doppler echocardiography were performed at baseline and after 4 weeks of temocapril therapy (2 mg/day) in 18 patients with type 2 diabetes. Although blood pressure, fasting blood sugar and lipid profiles remained unchanged, serum ADMA concentrations decreased significantly (0.51+/-0.08 to 0.46+/-0.07 micromol/l, p<0.01) and CFVR increased significantly (2.78+/-0.36 to 3.35+/-0.46, p<0.001) after the treatment. Moreover, a strong correlation was observed between the difference of ADMA and that of CFVR (r=-0.80, p<0.001). Temocapril reduced serum ADMA concentrations, improved CFVR beyond its blood pressure lowering effect. Our results suggest that decrease in ADMA by temocapril treatment is related to improvement of coronary circulation as determined by CFVR in patients with type 2 diabetes.

Noninvasive assessment of coronary microvascular function in women at risk for ischaemic heart disease

The primary objective of the current review is to describe the assessment of coronary microvascular function by noninvasive imaging techniques in women at risk for and with ischaemic heart disease (IHD). The search criteria were the analyses of the related bibliography published in PUBMED database. Normal or minimal obstructive coronary artery disease (CAD) at angiography is a common finding in women with signs of ischaemia. Up to 50% of them will have coronary microvascular dysfunction, suggesting that the mechanism of ischaemia may be localised at coronary microcirculation level. Noninvasive measurements of coronary microvascular function can be performed by radionuclide techniques. In particular, positron emission tomography (PET) measures myocardial blood flow (MBF) not only relatively but also in absolute units. Thus, PET offers the possibility to uncover microvascular dysfunction even in patients without obstructive CAD. PET-derived estimates of MBF showed an abnormal coronary microvascular function in women with chest pain and non-obstructive CAD and in women with high-risk conditions for CAD. Interestingly, there is a relationship between an abnormal coronary vascular function and adverse cardiovascular outcomes. In particular, this significant relationship was observed with measurements related to endothelial function. Recent evidence suggests that vascular dysfunction plays a central role as an estimator of outcomes in women at risk for or with IHD. Therefore, assessment of coronary vascular function in these women appears to be of clinical relevance. Whether such evaluation may have an impact to reduce cardiac events needs further investigation.

Diagnostic value of PET-measured heterogeneity in myocardial blood flows during cold pressor testing for the identification of coronary vasomotor dysfunction

BACKGROUND

We aimed to evaluate the diagnostic value of a positron emission tomography (PET)-measured heterogeneity in longitudinal myocardial blood flow (MBF) during cold pressor testing (CPT) and global MBF response to CPT from rest (DeltaMBF) for identification of coronary vasomotor dysfunction.

METHODS AND RESULTS

In 35 patients CPT-induced alterations in epicardial luminal area were determined with quantitative angiography as the reference. MBF was assessed over the whole left ventricle as global MBF and regionally in the mid and mid-distal myocardium as MBF difference or MBF heterogeneity with nitrogen-13 ammonia and PET. The sensitivity and specificity of a longitudinal MBF difference during CPT in the identification of epicardial vasomotor dysfunction were significantly higher than the global DeltaMBF to CPT (88% vs 79% and 82% vs 64%, respectively; P < .05). Combining both parameters resulted in an optimal sensitivity of 100% at the expense of an intermediate specificity of 73%. The diagnostic accuracy was higher for the combined analysis than that for the MBF difference alone and global DeltaMBF alone (91% vs 86% and 74%, respectively; P < .05).

CONCLUSIONS

The combined evaluation of a CPT-induced heterogeneity in longitudinal MBF and the change in global MBF from rest may emerge as a new promising analytic approach to further optimize the identification and characterization of coronary vasomotor dysfunction.

Altered coronary vasomotor function in young patients with systemic lupus erythematosus

OBJECTIVE

Accelerated atherosclerosis is an important cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Altered coronary microvascular function may act as a marker of changes that predispose to the development of significant coronary vascular disease. The purpose of this study was to compare coronary flow reserve (CFR) in a group of premenopausal women with SLE and a group of age-, sex-, and race-matched healthy control subjects.

METHODS

Coronary flow velocity in 18 premenopausal women with SLE (mean +/- SD age 29.4 +/- 5.9 years) and 19 matched healthy controls (mean +/- SD age 28.2 +/- 4.3 years) was assessed by transthoracic Doppler echocardiography after an overnight fast. The CFR was calculated as the ratio of hyperemic to baseline coronary blood flow velocity in the left anterior descending coronary artery. Hyperemia was induced by intravenous administration of adenosine triphosphate.

RESULTS

The mean +/- SD duration of SLE was 8.2 +/- 7.2 years (range 0.25-25 years), and the mean +/- SD score on the Systemic Lupus Erythematosus Disease Activity Index was 11.0 +/- 5.3 (range 4.0-21.0). Adequate recordings of flow velocity in the left anterior descending artery under both conditions were obtained using an ultrasound procedure in all study subjects. CFR was significantly lower in SLE patients as compared with control subjects (mean +/- SD 3.4 +/- 0.8 versus 4.5 +/- 0.5; P < 0.0001).

CONCLUSION

These findings provide evidence that coronary vasomotor function is impaired in patients with SLE and support the notion that many of these young patients have subclinical coronary artery disease.

Endothelial dysfunction in patients with antiphospholipid syndrome assessed with positron emission tomography

BACKGROUND

There is limited knowledge about endothelial dysfunction in patients with primary antiphospholipid syndrome (PAPS). The purpose of this study was to evaluate endothelial function in patients with PAPS assessed by positron emission tomography.

METHODS AND RESULTS

A 3-phase protocol--rest, cold pressor test (CPT), and adenosine positron emission tomography with nitrogen 13 ammonia--was used in 18 patients with PAPS and 18 healthy volunteers (HVs). Myocardial blood flow (MBF) was measured in each phase, with calculation of the endothelial-dependent vasodilation index, the increase in the MBF in response to CPT, and the myocardial flow reserve. An important trend was found in the myocardial flow reserve (2.76 +/- 1.04 in PAPS group vs 3.27 +/- 0.72 in HV group, P > .05), in the endothelial-dependent vasodilation index (1.19 +/- 0.31 in PAPS group vs 1.55 +/- 0.37 in HV group, P < .05), and in the percent change in the MBF in response to CPT (from rest) (19% +/- 31% in PAPS group vs 55% +/- 37% in HV group, P < .05).

CONCLUSION

The CPT results obtained in this study showed that the PAPS patients studied have endothelial dysfunction.

From hypertension to heart failure: role of nitric oxide-mediated endothelial dysfunction and emerging insights from myocardial contrast echocardiography

There is growing evidence that nitric oxide (NO)-mediated endothelial dysfunction occurs in hypertension and may represent the earliest stage of target organ damage, which ultimately leads to hypertensive heart disease and heart failure (HF). An understanding of how impaired myocardial microvascular function and flow reserve relate to early remodeling during the transition to HF in patients with hypertension may lead to new therapeutic insights. The hypertrophied heart, which is a feature of the adverse structural remodeling in hypertensive heart disease, may be accompanied by impaired coronary flow reserve (CFR). Reduced CFR could potentially cause subendocardial ischemia during conditions of high metabolic demand, such as uncontrolled hypertension and tachycardia. Such vulnerability of the subendocardium to abnormal perfusion or ischemia may accelerate the progression from compensated hypertrophy to HF. In this review, we discuss preliminary evidence that altered NO balance may contribute to cardiac hypertrophy-mediated myocardial ischemia. We also describe early results with myocardial contrast echocardiography in the postulated transition from compensated hypertrophy to cardiac failure. These data support further evaluation of NO mediators as potential targets for novel therapies in hypertensive heart disease.

Variable response of conductance and resistance coronary arteries to endothelial stimulation in patients with heart failure due to nonischemic dilated cardiomyopathy

Attenuation of endothelial-dependent coronary vasodilation has been reported in idiopathic dilated cardiomyopathy and anatomically normal coronaries; however, data are insufficient for understanding the incidence and extent of this finding. The response of conductance and resistance coronary arteries to endothelial stimulation with acetylcholine was examined in 25 patients. Coronary blood flow had a variable response to acetylcholine and suggested coronary endothelial dysfunction in approximately half of the patients. Abnormal endothelial dysfunction involved the large conductance epicardial coronary arteries and the small resistance vessels. Abnormal endothelial response of coronary blood flow to acetylcholine could not be predicted by demographic and hemodynamic data.

CONCLUSIONS

Coronary artery endothelial function is heterogeneous in patients with idiopathic dilated cardiomyopathy. Endothelial dysfunction is present in approximately half of the cases and involves both resistance as well as conductance coronary blood vessels. Furthermore, coronary endothelial function cannot be predicted by demographic and hemo-dynamic parameters or left ventricular ejection fraction.

Impact of type 2 diabetes on nitric oxide and adrenergic modulation of myocardial perfusion

Type 2 diabetic patients are characterized by a reduced adenosine-induced hyperemic myocardial perfusion, which may contribute to their increased cardiovascular morbidity. We hypothesized that the reduced hyperemia can be explained by functional changes in endothelial or autonomic nervous regulation. In 12 type 2 diabetic patients without signs of ischemic heart disease and 14 age-matched control subjects, myocardial perfusion was measured at rest, during adenosine, and during adenosine and alpha-receptor blockade (phentolamine) using positron emission tomography on two separate days: 1) with, and 2) without nitric oxide (NO) inhibition with N(G)-nitro-L-arginine methyl ester. Myocardial perfusion during adenosine was lower in type 2 diabetic patients compared with control subjects (P = 0.05). No significant effect of NO inhibition on myocardial perfusion during adenosine was found in any of the groups. In control subjects, alpha-receptor blockade increased hyperemic myocardial vascular resistance during NO inhibition, whereas no effect was observed in type 2 diabetic patients. At rest, a significant correlation was observed between rate-pressure product and myocardial perfusion in control subjects. NO inhibition and type 2 diabetes abolished this correlation. Endothelial and cardiac autonomic nerve function seems to play only a minimal role in the reduced hyperemic myocardial perfusion in type 2 diabetic patients. However, the linear correlation between resting perfusion and cardiac work appears to be abolished in type 2 diabetes and during NO synthase inhibition.

Effects of long-term treatment with carvedilol on myocardial blood flow in idiopathic dilated cardiomyopathy

OBJECTIVE

To assess whether chronic treatment with carvedilol can increase myocardial blood flow (MBF) and MBF reserve in idiopathic dilated cardiomyopathy (IDC).

STUDY DESIGN

In a double-blind, placebo-controlled trial, 16 consecutive patients with IDC were randomised to treatment with either carvedilol up to 25 mg twice a day (n = 8, 7 men, mean (SD) age 60 (9) years, mean (SD) left ventricular ejection fraction (LVEF) 30% (5%)), or placebo (n = 8, 6 men, mean (SD) age 62 (9) years, mean (SD) LVEF 28% (6%), NS vs carvedilol group). Before and 6 months after treatment, regional MBF was measured at rest and after intravenous injection of dipyridamole (Dip; 0.56 mg/kg in 4 min) by positron emission tomography and using (13)N-ammonia as a flow tracer. Exercise capacity was assessed as the time duration in a maximal bicycle exercise stress test.

RESULTS

Carvedilol induced a significant decrease in heart rate at rest and during maximal exercise, and an increase in exercise capacity. Absolute MBF values did not significantly change after carvedilol or placebo treatment, either at rest or during Dip injection, although Dip-MBF tended to improve after treatment. Coronary flow reserve significantly increased following carvedilol treatment (from 1.67 (0.63) to 2.58 (1.04), p<0.001), whereas it remained unchanged following the placebo treatment (from 1.80 (0.84) to 1.77 (0.60), NS). Stress-induced regional perfusion defects decreased after carvedilol treatment (from 38% to 15%).

CONCLUSIONS

Long-term treatment with carvedilol can significantly increase coronary flow reserve and reduce the occurrence of stress-induced perfusion defects, suggesting a favourable effect of the drug on coronary microvascular function in patients with IDC.

Assessment of coronary flow reserve by sestamibi imaging in patients with typical chest pain and normal coronary arteries

PURPOSE

We assessed coronary flow reserve (CFR) by sestamibi imaging in patients with typical chest pain, positive exercise stress test and normal coronary vessels.

METHODS

Thirty-five patients with typical chest pain and normal angiogram and 12 control subjects with atypical chest pain underwent dipyridamole/rest (99m)Tc-sestamibi imaging. Myocardial blood flow (MBF) was estimated by measuring first transit counts in the pulmonary artery and myocardial counts from SPECT images. Estimated CFR was expressed as the ratio of stress to rest MBF. Rest MBF and CFR were corrected for rate-pressure product (RPP) and expressed as normalised MBF (MBF(n)) and normalised CFR (CFR(n)). Coronary vascular resistances (CVR) were calculated as the ratio between mean arterial pressure and estimated MBF.

RESULTS

At rest, estimated MBF and MBF(n) were lower in controls than in patients (0.98 +/- 0.4 vs 1.30 +/- 0.3 counts/pixel/s and 1.14 +/- 0.5 vs 1.64 +/- 0.6 counts/pixel/s, respectively, both p < 0.02). Stress MBF was not different between controls and patients (2.34 +/- 0.8 vs 2.01 +/- 0.7 counts/pixel/s, p=NS). Estimated CFR was 2.40 +/- 0.3 in controls and 1.54 +/- 0.3 in patients (p < 0.0001). After correction for the RPP, CFR(n) was still higher in controls than in patients (2.1 +/- 0.5 vs 1.29 +/- 0.5, p < 0.0001). At baseline, CVR values were lower (p < 0.01) in patients than in controls. Dipyridamole-induced changes in CVR were greater (p < 0.0001) in controls (-63%) than in patients (-35%). In the overall study population, a significant correlation between dipyridamole-induced changes in CVR and CFR was observed (r = -0.88, p < 0.0001).

CONCLUSION

SPECT might represent a useful non-invasive method for assessing coronary vascular function in patients with angina and a normal coronary angiogram.

Vardenafil increases coronary flow response to hypercapnic acidosis in isolated guinea pig heart

The hypothesis was tested that vardenafil, a PDE5 inhibitor, specifically enhances coronary vasodilation during acidosis. In isolated constant pressure perfused guinea pig hearts, infusion of vardenafil (<or= 1 microM) increased coronary flow concentration-dependently 34 % above baseline. In parallel, cGMP release increased (0.44 +/- 0.094 vs. 0.14 +/- 0.017 pmol/min x g at 0.5 microM vardenafil vs. baseline). Flow increases occurred in the absence of changes in heart function (LVP, heart rate, dP/dt(max), heart rate - pressure product). Infusion of the NO synthase blocker L-NMMA (100 microM) caused a rightward shift of the dose-response curve of vardenafil. To test whether vardenafil treatment may enhance metabolic coronary vasodilation, arterial pCO(2) was raised from 38 to 61 mmHg, which resulted in a steady state flow increase of 18.8 +/- 4.5%. Infusion of vardenafil, given at a threshold flow enhancing concentration, doubled the coronary flow response during hypercapnic acidosis to 38.4 +/- 4.2 % (p=0.004). This flow amplification during acidosis was not shared by the K(ATP) channel opener cromakalim, indicating a specific effect of vardenafil on flow control during myocardial acidosis. We conclude that vardenafil specifically relaxes coronary resistance vessels through NO/cGMP-dependent pathways and increases the coronary flow response toward hypercapnic acidosis. This finding further supports the importance of the NO-cGMP axis in mediation of this flow response.

Positive family history of coronary artery disease is associated with reduced myocardial vasoreactivity in healthy men

OBJECTIVE

Positive family history as a risk factor for coronary artery disease seems to be most important in subjects who otherwise are at low risk. We examined the association between family history of coronary artery disease and myocardial vasoreactivity in healthy men.

METHODS

35 non-smoking healthy men (age 35+/-7 years) were studied: 16 had positive family history of coronary artery disease and 19 had negative family history. The myocardial blood flow measurements were performed basally and during adenosine infusion (140 mug/kg/min) with and without simultaneous physiological hyperinsulinemia (insulin infusion at a rate of 1 mU/kg/min) using positron emission tomography and O-15-water.

RESULTS

Basal myocardial blood flow was similar between the subjects with positive and negative family history of coronary artery disease (0.79+/-0.19 and 0.79+/-0.21 mL g(-1) min(-1), NS). Adenosine stimulated flow was significantly reduced in subjects with positive family history (3.0+/-0.5 vs 4.0+/-1.2 mL g(-1) min(-1), respectively, p=0.003). During physiological hyperinsulinemia adenosine stimulated flow was further enhanced in both groups but significantly blunted in subjects with positive family history (3.7+/-0.9 vs 5.2+/-1.5 mL g(-1) min(-1), respectively, p=0.001). These differences remained significant after simultaneous controlling for age, BMI, HbA1c, LDL-cholesterol, HDL-cholesterol and blood pressure (p=0.002).

CONCLUSIONS

Healthy non-smoking men with positive family history of coronary artery disease are characterized by impaired myocardial vasoreactivity.

Structural and functional changes in peripheral vasculature of Fabry patients

OBJECTIVE

Fabry disease is a lysosomal storage disorder due to deficient alpha-galactosidase A activity, which leads to glycosphingolipid accumulation especially in vascular smooth-muscle and endothelial cells. Little is known about the effects of Fabry disease on peripheral artery function and structure. Therefore, we aimed to further characterize the peripheral vascular structural and functional changes in Fabry disease.

METHODS AND RESULTS

We measured structural and functional vascular parameters, including intima-media thickness (IMT) of brachial and carotid arteries and abdominal aorta, carotid and aortic compliance, and brachial artery flow-mediated dilatation (FMD) in 17 Fabry patients and 34 healthy controls matched for age, sex and smoking. Carotid IMT (0.64 +/- 0.15 vs 0.57 +/- 0.12 mm), brachial IMT (1.02 +/- 0.25 vs 0.74 +/- 0.18 mm), and aortic IMT (0.31 +/- 0.09 vs 0.26 +/- 0.04 mm) were significantly increased, and brachial FMD was significantly impaired (6.3 +/- 5.0 vs 9.7 +/- 3.9%) in Fabry patients compared to healthy controls (p < 0.05 in all comparisons after adjustments for age, LDL-cholesterol, and systolic blood pressure). No differences were observed in arterial compliance between the groups.

CONCLUSIONS

These data suggest that Fabry disease affects arterial function and structure by disturbing peripheral endothelial function and promoting intima-media thickening.

Basal and hyperaemic myocardial blood flow in regionally denervated canine hearts: an in vivo study with positron emission tomography

PURPOSE

Positron emission tomography (PET) studies in patients with diabetic autonomic neuropathy (DAN) have demonstrated the impact of this disease on cardiac sympathetic innervation and myocardial blood flow (MBF). To investigate the effects of selective partial sympathetic denervation of the left ventricle (LV) on baseline and hyperaemic MBF, we measured myocardial presynaptic catecholamine re-uptake (uptake-1), beta-adrenoceptor (beta-AR) density and MBF non-invasively by means of PET in a canine model of regional sympathetic denervation.

METHODS

In 11 anaesthetised dogs, the sympathetic nerves of the free wall and septum of the LV were removed by means of dissection and phenol painting. Three weeks later, the animals were studied with PET. MBF was measured at baseline and following i.v. adenosine (140 microg kg(-1) min(-1)) and dobutamine (20 microg kg(-1) min(-1)) using(15)O-labelled water. Sympathetic denervation was confirmed by an 80+/-12% decrease in the volume of distribution (V(d)) of [(11)C]hydroxyephedrine (HED) compared with innervated regions. Myocardial beta-AR density was measured using [(11)C]CGP12177.

RESULTS

Innervated and denervated regions showed no differences in MBF at baseline and during adenosine or dobutamine. [(11)C]HED V(d)was inversely correlated with MBF in both regions at baseline, and the correlation was lost during hyperaemia in denervated regions. However, for any given value of MBF, [(11)C]HED V(d)was significantly lower in the denervated regions. beta-AR density was comparable in denervated and innervated regions (17.9+/-4.2 vs 18.4+/-3.3 pmol g(-1); p=NS).

CONCLUSION

In this experimental model, selective, regional sympathetic denervation of the LV, which results in a profound reduction in [(11)C]HED V(d), did not affect baseline or hyperaemic MBF. In addition, we demonstrated that, under baseline conditions, there was a significant inverse correlation between [(11)C]HED V(d)and MBF in both denervated and innervated regions.

Effect of exercise training on myocardial blood flow in patients with stable coronary artery disease

BACKGROUND

The mechanisms by which exercise training benefits patients with coronary artery disease (CAD) are unclear but may include improved myocardial circulation. The aim of this study was to investigate the effect of exercise training on myocardial blood flow (MBF) and coronary flow reserve (CFR) in patients with stable CAD.

METHODS

Twelve patients with documented CAD and ischemic ST-segment depression during exercise testing were randomized to exercise training (n = 7) or sedentary life style (control; n = 5) and underwent rubidium-82 positron emission tomography pre- and postintervention. Global left ventricle MBF and regional MBF in 17 left ventricular segments were calculated. Segments with <75% uptake (2 SD below normal) on stress uptake images were defined as abnormal.

RESULTS

Exercise training increased global CFR by 20.8% +/- 27.9% versus control (10.5 +/- 24.1%, P = .0001). In normal segments (exercise training: n = 91; control: n = 46), exercise training did not change resting MBF (-14.1% +/- 16.3% vs -8.8% +/- 15.6%) and hyperemic MBF (-1.93% +/- 19.1% vs 2.86% +/- 20.5%, P = NS) and increased in CFR compared to control (17.0% +/- 25.5% vs 11.3% +/- 23.5%, P = .01). In abnormal segments, the change in resting MBF was not significantly different (-12.6% +/- 18.5% exercise [28 segments] vs -2.9% +/- 18.0% control [39 segments], P = NS). A significant increase was seen in hyperemic MBF with exercise (12.5% +/- 22.1% vs 2.6% +/- 16.3%, P = .02) and CFR (32.8% +/- 32.3% vs 9.5% +/- 24.8%, P = .001).

CONCLUSIONS

Exercise training increased CFR in normal and diseased segments, and increased hyperemic flow in diseased segments. These data provide preliminary evidence in support of a favorable effect of exercise training on blood flow to ischemic myocardium.

PET-measured heterogeneity in longitudinal myocardial blood flow in response to sympathetic and pharmacologic stress as a non-invasive probe of epicardial vasomotor dysfunction

PURPOSE

We investigated whether a myocardial perfusion gradient during pharmacologically induced hyperemia also occurred during sympathetic stimulation with cold pressor testing (CPT), which commonly induces a paradoxical coronary vasoconstriction in individuals with coronary risk factors.

METHODS

Myocardial blood flow (MBF) was measured in absolute units (ml/g/min) with 13N-ammonia and PET at rest, during CPT, and during pharmacologic vasodilation in 59 participants with coronary risk factors ("at risk") and in 43 healthy individuals (controls). MBF was assessed globally as mean MBF, and in the mid and mid-distal myocardium of the left ventricle (LV). A decrease in MBF from mid to mid-distal LV myocardium was defined as MBF difference indicative of a perfusion gradient.

RESULTS

The change in mean MBF to CPT (DeltaMBF) in the at-risk group was significantly reduced compared with controls (0.05+/-0.19 vs 0.31+/-0.20 ml/g/min, p<0.0001), whereas mean MBF during pharmacologic vasodilation in the at-risk group tended to be lower than in controls (1.72+/-0.71 vs 2.00+/-0.64 ml/g/min, p=NS). Absolute MBFs during CPT and pharmacologic vasodilation were significantly lower in the mid-distal than in the mid LV myocardium, resulting in a significant MBF difference in the at-risk group (0.15+/-0.06 and 0.27+/-0.12 ml/g/min, p<0.0001) that was not observed in controls (0.007+/-0.05 and 0.014+/-0.10 ml/g/min, p=NS). In the at-risk group there was a significant correlation between the difference of mid to mid-distal MBF during CPT and that during pharmacologic vasodilation (r=0.43, p<0.004), suggesting functional alterations of epicardial vessels as the predominant cause for the observed MBF difference.

CONCLUSION

The relative decrease in MBF from the mid to the mid-distal left-ventricular myocardium suggests an intracoronary pressure decline during CPT and pharmacologic vasodilation, which is likely to reflect an impairment of flow-mediated epicardial vasomotor function.

Effect on coronary flow velocity reserve in patients with type 2 diabetes mellitus: comparison between angiotensin-converting enzyme inhibitor and angiotensin II type 1 receptor antagonist

BACKGROUND

The effects of angiotensin antagonists on coronary circulation in type 2 diabetes are unclear. We aimed to assess whether 4 weeks of treatment with angiotensin-converting enzyme inhibitor or angiotensin II type 1 receptor antagonist improves coronary flow velocity reserve (CFVR) in patients with type 2 diabetes.

METHODS

Twenty-four asymptomatic patients with type 2 diabetes were randomly assigned to temocapril (2 mg/d) or candesartan (8 mg/d). Coronary flow velocity reserve, calculated as the ratio of adenosine-induced hyperemic to basal coronary flow velocity, was measured with transthoracic Doppler echocardiography. Coronary flow velocity reserve measurement and venous blood sampling were performed before and after 4 weeks of treatment. We also obtained CFVR and venous blood data in the 8 healthy controls.

RESULTS

Coronary flow velocity reserve was significantly lower in patients than controls (temocapril group 2.74 +/- 0.28, candesartan group 2.65 +/- 0.30, controls 3.53 +/- 0.23, P < .0001 for both, respectively). Blood pressure was reduced in both diabetic groups (n = 12 each) similarly 4 weeks after treatment. There were no significant differences between the 2 groups in venous blood data before or after treatment. However, CFVR increased significantly in the temocapril group (2.74 +/- 0.28 to 3.31 +/- 0.36, P < .0001), but not in the candesartan group (2.65 +/- 0.30 to 2.71 +/- 0.43, P = ns).

CONCLUSIONS

Coronary flow velocity reserve in patients with type 2 diabetes improved after treatment with temocapril but not with candesartan, suggesting that angiotensin-converting enzyme inhibitor, but not angiotensin II type 1 receptor antagonist, might have beneficial effects on coronary microangiopathy associated with type 2 diabetes.

Insulin improves myocardial blood flow in patients with type 2 diabetes and coronary artery disease

Insulin infusion improves myocardial blood flow (MBF) in healthy subjects. Until now, the effect of insulin on myocardial perfusion in type 2 diabetic subjects with coronary artery disease (CAD) has been unknown. We studied the effects of insulin on MBF in ischemic regions evaluated by single-photon emission-computed tomography and coronary angiography and in nonischemic regions in 43 subjects (ages 63 +/- 7 years) with type 2 diabetes (HbA(1c) 7.1 +/- 0.9%). MBF was measured at fasting and during a euglycemic-hyperinsulinemic clamp at rest (n = 43) and during adenosine-induced (140 mug . kg(-1) . min(-1) for 7 min) hyperemia (n = 26) using positron emission tomography and (15)O-labeled water. MBF was significantly attenuated in ischemic regions as compared with in nonischemic regions (P < 0.0001) and was increased by insulin as compared with in the fasting state (P < 0.0001). At rest, insulin infusion increased MBF by 13% in ischemic regions (P = 0.043) and 22% in nonischemic regions (P = 0.003). During adenosine infusion, insulin enhanced MBF by 20% (P = 0.018) in ischemic regions and 18% (P = 0.045) in nonischemic regions. In conclusion, insulin infusion improved MBF similarly in ischemic and nonischemic regions in type 2 diabetic subjects with CAD. Consequently, in addition to its metabolic effects, insulin infusion may improve endothelial function and thus increase the threshold for ischemia and partly contribute to the beneficial effects found in clinical trials in these subjects.

Effect of phentolamine on the hyperemic response to adenosine in patients with microvascular disease

For accurate measurement of the fractional flow reserve (FFR) of the myocardium, the presence of maximum hyperemia is of paramount importance. It has been suggested that the hyperemic effect of the conventionally used hyperemic stimulus, adenosine, could be submaximal in patients who have microvascular dysfunction and that adding alpha-blocking agents could augment the hyperemic response in these patients. We studied the effect of the nonselective alpha-blocking agent phentolamine, which was administered in addition to adenosine after achieving hyperemia, in patients who had microvascular disease and those who did not. Thirty patients who were referred for percutaneous coronary intervention were selected. Of these 30 patients, 15 had strong indications for microvascular disease and 15 did not. FFR was measured using intracoronary adenosine, intravenous adenosine, and intracoronary papaverine before and after intracoronary administration of the nonselective alpha blocker phentolamine. In patients who did not have microvascular disease, no differences in hyperemic response to adenosine were noted, whether or not alpha blockade was given before adenosine administration; FFR levels before and after phentolamine were 0.76 and 0.75, respectively, using intracoronary adenosine (p = 0.10) and 0.75 and 0.74, respectively, using intravenous adenosine (p = 0.20). In contrast, in patients who had microvascular disease, some increase in hyperemic response was observed after administration of phentolamine; FFR levels decreased from 0.74 to 0.70 using intracoronary adenosine (p = 0.003) and from 0.75 to 0.72 using intravenous adenosine (p = 0.04). Although statistically significant, the observed further decrease in microvascular resistance after addition of phentolamine was small and did not affect clinical decision making in any patient. In conclusion, when measuring FFR, routinely adding an alpha-blocking agent to adenosine does not affect clinical decision making.

Evaluation of Left Anterior Descending Coronary Artery Stenosis of Intermediate Severity Using Transthoracic Coronary Flow Reserve and Dobutamine Stress Echocardiography

BACKGROUND

The physiologic significance of left anterior descending coronary artery (LAD) stenosis of intermediate angiographic severity is of clinical importance and difficult to assess. Assessment of coronary flow reserve (CFR) by Doppler transthoracic echocardiography (TTE) is a new tool and could allow rapid, noninvasive evaluation of stenosis severity in this setting.

OBJECTIVE

We sought to evaluate the value of CFR measurement determined by TTE, compared with dobutamine stress echocardiography (DSE), in the setting of LAD stenosis of intermediate angiographic severity.

METHODS

A total of 51 consecutive stable patients in sinus rhythm (33 men; age 65 +/- 12 years; left ventricular ejection fraction 59 +/- 7%) with no previous anterior myocardial infarction and with an angiographic proximal LAD stenosis of intermediate severity (56 +/- 8% quantitative coronary angioplasty) were prospectively studied. Coronary flow velocity was measured in the distal part of the LAD by TTE at rest and during continuous infusion of 0.14 mg/kg/min of adenosine over 2 minutes, using a multifrequency transducer, in the modified parasternal or 3-apical view. CFR was calculated as the ratio of hyperemic to basal mean (mean CFR) and peak (peak CFR) diastolic flow velocity. DSE was performed immediately after the adenosine test to assess ischemia in the LAD territory (percent maximum predicted heart rate = 94 +/- 8).

RESULTS

Adequate recording of CFR was possible in 46 patients. Of the 35 patients with a CFR of 2 or more (peak CFR = 2.7 +/- 0.6), DSE was normal in 34. Of the 11 patients with a CFR less than 2 (peak CFR = 1.7 +/- 0.2), 7 had an abnormal response with DSE in the LAD territory. In this range of intermediate stenosis, there was a poor correlation between percent LAD diameter stenosis and CFR. For patients with positive DSE, CFR was 1.6 +/- 0.2 compared with 2.7 +/- 0.6 for patients with normal DSE (P < .05). The sensitivity, specificity, and the positive and negative predictive values of TTE CFR for detecting ischemia on DSE were 88%, 89%, 64%, and 97%, respectively, with an overall agreement of 89% between the two tests.

CONCLUSION

Given its high negative predictive value, noninvasive CFR could be a useful aid in reaching clinical decisions promptly at the bedside in patients with moderately severe lesions of the proximal LAD.

Short-term changes in inflammatory response protein (hsCRP) do not parallel with changes in coronary vasoreactivity in obese men

AIM

Obese subjects are characterized by increased high-sensitivity C-reactive protein (hsCRP) and coronary vascular resistance. Clucocorticoids suppress inflammation, a possible cardioprotective effect. We tested the short-term anti-inflammatory effect of dexamethasone (dx) on these parameters in obese subjects.

METHODS

Coronary vascular resistance was quantitated basally and during adenosine infusion with or without simultaneous euglycemic hyperinsulinemic clamp (insulin infusion rate of 1 mU/kg/min) in 11 obese and 19 age-matched nonobese males using positron emission tomography and (15)O-water. Each subject was studied both with and without previous dx treatment for 2 days (2 mg/day).

RESULTS

Before dx treatment, hsCRP concentration was significantly higher in obese than in nonobese subjects (1.55+/-1.73 vs 0.32+/-0.32 mg/l, P = 0.005). In addition, coronary vascular resistances were higher (P < 0.05) in obese than in nonobese subjects at baseline (139+/-36 vs 117+/-22) and during adenosine infusion without (32+/-7 vs 26+/-7) or with simultaneous clamp (26+/-8 vs 21+/-5 mmHg min g/ ml). Dx treatment decreased significantly hsCRP concentration in obese but not in nonobese subjects, leading to similar hsCRP concentrations between the groups (0.45+/-0.43 vs 0.26+/-0.42 mg/l, respectively, P = 0.3). Dx had no effect on coronary vascular resistances (NS).

CONCLUSIONS

Obese subjects are characterized by high hsCRP, which can be normalized by dx. However, despite this, coronary vascular resistances did not decrease in obese subjects. Short-term changes in inflammatory response protein appear not to parallel with changes in coronary vasoreactivity in obese men.

Effects of sildenafil on myocardial blood flow in humans with ischemic heart disease

BACKGROUND

We tested the hypothesis that sildenafil increases myocardial dilator reserve in humans with ischemic heart disease.

METHODS

Positron emission tomography measured myocardial blood flow in 14 patients with ischemic heart disease. Patients were studied twice, in double-blind, placebo-control, cross-over design with sildenafil (or placebo) given approximately 2-3 h before measurements of hemodynamics and myocardial blood flow: at rest, with cold pressor stress and with adenosine. All myocardial segments of each patient with myocardial blood flow <1.65 ml/min per g with adenosine under placebo conditions were combined into one abnormal zone for that patient. Segments with myocardial blood flow >1.65 ml/min per g were averaged and combined into a normal zone for that patient.

RESULTS

At rest, rate pressure product (heart rate x systolic arterial pressure, mmHg/min) was comparable, as was abnormal zone myocardial blood flow (ml/min per g; 0.76+/-0.48 placebo versus 0.64+/-0.20 sildenafil, both P=NS; mean+/-SD). Both rate pressure product and myocardial blood flow increased (P<0.01) with cold pressor stress (11+/-3 K and 1.14+/-0.59 placebo versus 10+/-3 K and 1.21+/-0.62 sildenafil). However, sildenafil failed to improve the myocardial blood flow response to cold pressor stress in abnormal or normal zones. In contrast, abnormal zone myocardial blood flow reserve with adenosine and sildenafil (2.6+/-0.7) exceeded that with adenosine and placebo (2.0+/-1.3, P<0.04, paired sign test).

CONCLUSION

Sildenafil improves myocardial blood flow dilator response to adenosine in abnormal zones, possibly by augmenting nitric oxide-mediated increases in cGMP because adenosine response in part is nitric oxide dependent. Failure to improve myocardial blood flow response to cold pressor stress suggests that alpha-adrenergic constriction may offset enhanced nitric oxide effects. Clinically, the data suggest sildenafil may exert an anti-ischemic effect in patients with coronary artery disease.

Physical exercise capacity is associated with coronary and peripheral vascular function in healthy young adults

Short-term exercise training has been shown to improve cardiovascular function, whereas long-term effects of a physically active lifestyle, on coronary artery function in particular, are still not well studied. We explored possible relationships between physical exercise capacity and coronary and peripheral vascular function in healthy young adults. Twenty-nine healthy young male and female volunteers participated in the study. They underwent 1) basic clinical and echocardiographic characterization, 2) coronary flow velocity reserve (CFVR) measurement of the left anterior descending coronary artery (LAD), 3) common carotid artery (CCA) intima-media thickness (IMT) measurement, 4) assessment of CCA stiffness index (SI), 5) forearm flow-mediated vasodilation (FMD), and 6) submaximal exercise test. The calculated weight-adjusted maximal oxygen uptake capacity (V̇o2 maxc) was positively correlated to LAD CFVR and inversely correlated to IMT and SI. Also, subjects with high compared with moderate exercise capacity had higher FMD. In addition, subjects with LAD CFVR in the upper median had greater ratios between endothelium-dependent and -independent vasodilation in the forearm and lower SI in CCA. High exercise capacity due to a physically active lifestyle is associated with high coronary and peripheral artery function, indicating an early protective role of physical exercise for cardiovascular health.

Beneficial effects of atorvastatin on myocardial regions with initially low vasodilatory capacity at various stages of coronary artery disease

PURPOSE

The aim of this study was to analyse non-invasively the regional effect of therapy with an HMG-CoA reductase inhibitor on myocardial blood flow in patients with coronary artery disease (CAD) with special reference to segments with initially substantially impaired vasodilation.

METHODS

The study included 26 patients with untreated hypercholesterolaemia. Coronary angiography revealed CAD in nine patients with stenosis >50% and wall irregularities or minimal stenosis <30% in 17 patients. Before and 4.6+/-1.8 months after atorvastatin therapy, ( 13)N-ammonia positron emission tomography (PET) studies were performed at rest and under pharmacological stress. Minimum coronary vascular resistance (MCR) and coronary flow reserve (CFR) were determined. Segments were divided into those with normal or near-normal (MBF during adenosine > or =2.0 ml/min/g) and those with abnormal (MBF<2.0 ml/min/g) vasodilator flow response. In CAD patients, 156 segments were analysed, 85 of which had abnormal MBF; in the non-obstructive group, 59 of 297 segments had abnormal MBF.

RESULTS

LDL cholesterol decreased after atorvastatin therapy from 186+/-43 mg/dl to 101+/-26 mg/dl (p<0.001). In normal segments no significant changes in MBF, CFR and MCR were found. However, initially abnormal segments showed significant improvements in MCR (15%, p<0.0001) and MBF during adenosine (30%, p<0.0001) after therapy.

CONCLUSION

The improvement in regional coronary vasodilator function after atorvastatin in patients with coronary atherosclerosis may be caused, at least in part, by increased flow-mediated (endothelium-dependent) dilation of the total arteriolar and arterial vascular system. These data further support the concept of non-invasive management of stable CAD by statin therapy and life-style modification guided by PET.

Voluntary physical exercise and coronary flow velocity reserve: a transthoracic colour Doppler echocardiography study in spontaneously hypertensive rats

In the present study, we have developed and demonstrated a coronary artery imaging protocol in rats using transthoracic high-frequency CDE (colour Doppler echocardiography) to investigate the potential direct effects of exercise on CFVR (coronary flow velocity reserve). SHR (spontaneously hypertensive rats) performed voluntary exercise for 6 weeks. Rats were then submitted to ultrasonographic examination and CFVR measurements. The LAD (left anterior descending coronary artery) was visualized using transthoracic CDE in a modified parasternal long-axis view. Doppler measurement was made in mid-LAD during baseline and adenosine-induced hyperaemic condition. Gene and protein expression in cardiac tissue were studied using real-time PCR and immunohistochemistry. Adenosine infusion significantly (P<0.001, as determined by ANOVA) decreased HR, without affecting blood pressure in anaesthetized SHR. A significantly greater adenosine dose-dependent response was seen in exercised rats compared with controls (P=0.02, as determined by ANOVA). The baseline flow velocity in mid-LAD was 0.33±0.06 and 0.41±0.14 m/s in the exercised and control animals respectively (P value was not significant). The maximum adenosine-induced response was reached at a dose of 140 μg·kg−1 of body weight·min−1, and CFVR averaged at 2.6±0.53 and 1.5±0.24 in exercised and control animals respectively (P<0.01). Gene expression of CuZnSOD was up-regulated by 21% in exercised animals compared with controls (1.1±0.16 compared with 0.89±0.09; P<0.01), whereas eNOS expression was unchanged. In conclusion, CFVR in rats can be non-invasively assessed using CDE with high feasibility. Physical exercise is associated with improved CFVR and antioxidative capacity in SHR.

Functional and Morphologic Imaging of Coronary Atherosclerosis in Living Mice Using High-Resolution Color Doppler Echocardiography and Ultrasound Biomicroscopy

OBJECTIVES

This study aimed to establish non-invasive methods of assessing coronary artery morphology in normal and atherosclerotic mice in vivo.

BACKGROUND

Coronary flow velocity reserve (CFVR) has been shown to correlate with coronary minimal lumen diameter (MLD) in patients with coronary artery stenosis. In mice, there are no existing non-invasive imaging techniques allowing quantitative measurement of the coronary artery morphology and function.

METHODS

Systemic hemodynamic effects of adenosine were studied in seven C57BL/6 mice. In 17 C57BL/6 mice, CFVR was measured in the mid left coronary artery (LCA) using either hypoxia- or adenosine-induced coronary hyperemia. Further, in another 10 atherosclerotic low-density lipoprotein receptor (LDLR)-/- mice, the hypoxia-induced CFVR was performed and proximal LCA MLD was measured using ultrasound biomicroscopy (UBM). Histologic sections of the LCA were collected.

RESULTS

The adenosine dose of 160 microg/kg/min induced maximal coronary hyperemia without any systemic hemodynamic effects. Adenosine and hypoxia-induced CFVR values averaged at 2.0 +/- 0.1 and 1.9 +/- 0.3, respectively, in C57BL/6 mice (p = NS). In LDLR-/- mice, CFVR and MLD ranged between 1.4 to 2.9 microm and 190 to 370 microm, respectively. Histology revealed proximal lumen-narrowing plaques in the LCA. Significant correlation was found between hypoxia-induced CFVR and the MLD (p < 0.005, R2 = 0.8707).

CONCLUSIONS

The CDE and UBM technique can be used to measure atherosclerosis-related lumen narrowing of the LCA in living mice. These non-invasive techniques may provide us with novel tools for following up disease status in mouse coronary arteries in a quantitative manner.

Weight changes and obesity predict impaired resting and endothelium-dependent myocardial blood flow in postmenopausal women

BACKGROUND

Obesity has been associated with impaired endothelial function, but the influence of lifetime weight patterns on endothelial function has not been studied.

HYPOTHESIS

We hypothesized that coronary vascular reactivity would be diminished in postmenopausal women with a history of obesity and frequent weight swings.

METHODS

We performed dynamic N-13 ammonia positron emission tomography in 18 postmenopausal women with cardiac risk factors. Myocardial blood flow (MBF) was measured at rest, after the cold pressor test (CPT), and after adenosine infusion in order to determine baseline and endothelium-dependent and -independent flows, respectively. Myocardial blood flow was corrected for cardiac work by normalizing to the rate-pressure product. Weight history was obtained by standardized questionnaire.

RESULTS

Normalized rest (n-rest) MBF correlated negatively with current weight (r = -0.52, p = 0.026) and weight at age 18 (r = -0.47, p = 0.047). Normalized CPT (n-CPT) MBF correlated inversely with current weight (r = -0.55, p = 0.018), weight at age 18 (r = -0.605, p = 0.008), and highest weight (r = -0.62, p = 0.006). Higher waist circumference predicted lower n-rest MBF (r = -0.52, p = 0.028) and n-CPT MBF (r = -0.48, p = 0.04). The same association was found with hip circumference (r = -0.52, p = 0.028; r = -0.49, p = 0.038, respectively), whereas higher body mass index (BMI) predicted lower n-CPT MBF (r = -0.53, p = 0.02). Women with at least four significant weight swings had lower MBF during rest, CPT, and n-CPT (0.88 vs. 1.19 ml/g/min, p = 0.008; 0.76 vs. 1.23 ml/g/min, p < 0.001; 0.74 vs. 1.10 ml/g/min, p = 0.009, respectively).

CONCLUSIONS

Increased waist and hip circumference, weight, and frequent weight swings are associated with impaired resting and endothelium-dependent MBF in postmenopausal women. These data suggest that lifetime weight patterns may influence cardiovascular risk in women.

Effect of a peroxisome proliferator-activated receptor-gamma agonist on myocardial blood flow in type 2 diabetes

OBJECTIVE

The relationship between coronary endothelial function and insulin resistance remains speculative. We sought to determine whether pioglitazone, an insulin-sensitizing peroxisome proliferator-activated receptor (PPAR)-gamma agonist, improves cardiac endothelial function in individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Sixteen subjects with insulin-treated type 2 diabetes and without overt cardiovascular disease were randomly assigned to receive either 45 mg of pioglitazone or matching placebo for 3 months. Rest and adenosine-stimulated myocardial blood flow (MBF) were quantified with [(13)N]ammonia and positron emission tomography at baseline and study conclusion.

RESULTS

After 3 months, HbA(1c) levels dropped by 0.68% in the pioglitazone group and increased by 0.17% in the placebo group (P = 0.009 for difference between groups). Triglyceride (-93 vs. -39 mg/dl, P = 0.026) and HDL concentrations (+4.8 vs. -6.0 mg/dl, P = 0.014) improved significantly in the pioglitazone group compared with placebo. Despite these favorable changes, there was no demonstrable change in baseline MBF (-0.05 +/- 0.24 vs. -0.09 +/- 0.24 ml . min(-1) . g(-1), P = 0.45), adenosine-stimulated MBF (0.10 +/- 0.75 vs. 0.14 +/- 0.31 ml . min(-1) . g(-1), P = 0.25), or coronary flow reserve (0.45 +/- 1.22 vs. 0.35 +/- 0.72 ml . min(-1) . g(-1), P = 0.64) after 12 weeks of exposure to pioglitazone or placebo, respectively. Regression analysis revealed that lower glucose concentration at the time of the study was associated with higher coronary flow reserve (P = 0.012).

CONCLUSIONS

Pioglitazone treatment for 12 weeks in subjects with insulin-requiring type 2 diabetes had no demonstrable effect on coronary flow reserve despite metabolic improvements. Higher ambient glucose levels contribute to impaired vascular reactivity in individuals with diabetes.

Quantitative relation between hemodynamic changes during intravenous adenosine infusion and the magnitude of coronary hyperemia: implications for myocardial perfusion imaging

OBJECTIVES

The goal of this study was to determine the relationship between changes in cardiac hemodynamics during intravenous adenosine (ADO) infusion, and myocardial blood flow (MBF).

BACKGROUND

The relationship between changes in MBF and the peripheral hemodynamic effects during peak adenosine infusion is unknown.

METHODS

We studied 348 (age 57 +/- 11 years; 106 females) without evidence of obstructive coronary artery disease by positron emission tomography (PET). Patients underwent [(13)N]ammonia PET imaging to measure MBF and coronary vascular resistance (CVR) at rest and during a standard 6-min ADO infusion. Changes in heart rate (HR) and mean arterial pressure (MAP) were measured at baseline and during peak hyperemia.

RESULTS

During ADO, HR increased (delta: 24 +/- 11 beats/min) and MAP decreased (delta: -2 +/- 10 mm Hg). Overall, delta HR correlated poorly with hyperemic MBF (R = 0.10, p = 0.06) and with CVR (R = 0.11, p = 0.04). Delta MAP also showed a weak correlation with hyperemic MBF (R = 0.04, p = 0.44) and with CVR (R = 0.11, p = 0.04). Patients in the lowest tertile for delta HR showed a 7% lower hyperemic MBF (1.84 +/- 0.6 ml/min/g vs. 1.98 +/- 0.6 ml/min/g, p = 0.022) and an 8% higher CVR (54 +/- 20 mm Hg/ml/min/g vs. 50 +/- 17 mm Hg/ml/min/g, p = 0.056) compared with those in the highest tertile. Patients in the lowest tertile for delta MAP (i.e., greatest decline) showed similar hyperemic MBF, and an 8% lower CVR compared with those in the highest tertile (p = NS for both). These small differences between tertiles remain, even after adjusting for differences in age, gender, smoking status, and lipid profile.

CONCLUSIONS

Changes in cardiac hemodynamics during intravenous ADO are generally poor predictors of changes in MBF and CVR during peak hyperemia, and, thus, they should not be used to assess the effectiveness of vasodilator stress in myocardial perfusion imaging.

Increased lipoprotein(a) is associated with reduced myocardial vasoreactivity in young healthy men

OBJECTIVES AND BACKGROUND

We examined the association between lipoprotein(a) and myocardial vasoreactivity in healthy men.

METHODS

Thirty non-smoking healthy men (age 34+/-6 years) were studied: 9 had increased lipoprotein(a) (>200 mg/L) concentrations (lipoprotein(a) 317 (range 218-550) mg/L) and 21 had normal lipoprotein(a) (<200 mg/L) concentrations (lipoprotein(a) 57 (range 13-156) mg/L). The myocardial blood flow measurements were performed basally and during adenosine infusion (140 microg/kg/min) with or without simultaneous physiological hyperinsulinemia (insulin infusion at a rate of 1 mU/kg/min) using positron emission tomography and [(15)O]H(2)O.

RESULTS

Basal myocardial blood flow was similar between the subjects with increased and normal lipoprotein(a) (0.76+/-0.20 and 0.79+/-0.20 mLg(-1) min(-1), NS). Adenosine-stimulated flow tended to be reduced in subjects with increased lipoprotein(a) (3.1+/-0.7 mLg(-1) min(-1) versus 3.7+/-1.1 mLg(-1) min(-1), respectively, p=0.1). During physiological hyperinsulinemia adenosine-stimulated flow was further enhanced in both groups but significantly blunted in subjects with increased lipoprotein(a) (3.7+/-0.8 mLg(-1) min(-1) versus 4.8+/-1.4 mLg(-1) min(-1), respectively, p=0.03). This difference remained significant after simultaneous controlling for BMI, HbA1c, LDL-cholesterol, HDL-cholesterol and blood pressure (p=0.04).

CONCLUSIONS

Already young healthy men with lipoprotein(a) concentrations greater than 200mg/L are characterized by impaired myocardial vasoreactivity.

Effects of nateglinide on myocardial microvascular reactivity in Type 2 diabetes mellitus--a randomized study using positron emission tomography

AIMS

To evaluate effects of the oral antidiabetic insulinotropic agent nateglinide on myocardial blood flow (MBF) and microvascular reactivity in Type 2 diabetic patients.

METHODS

Forty-seven Type 2 diabetic patients were randomly assigned 2 : 1 to nateglinide 120 mg (t.i.d., n = 33) or placebo (n = 14). At baseline and after 16 weeks of treatment, MBF was quantified using positron emission tomography with N-13 ammonia at rest, during endothelial-dependent stimulation by cold pressor test and during adenosine-mediated vasodilation. Additional blood samples were taken to assess glycaemic control and lipid profile.

RESULTS

MBF at rest and during adenosine did not change during the study. The percentage of flow increase from rest during cold pressor test did not improve significantly in the nateglinide group vs. placebo (from 26.1 +/- 37.2% to 29.1 +/- 27.8% between week 0 to week 16 for nateglinide vs. 14.9 +/- 37.1% to 18.1 +/- 28.4% for placebo; P = 0.07 for nateglinide when adjusted for higher baseline values). Nateglinide decreased HbA1c by 0.4% (from 7.6 +/- 0.9% to 7.2 +/- 1.3%) compared to an increase of 0.5% in the placebo group (from 7.9 +/- 0.8% to 8.4 +/- 1.7%; P = 0.02 for nateglinide). No differences between the two groups were observed in insulin levels and lipid status.

CONCLUSIONS

Nateglinide neither improved, nor impaired myocardial blood flow in Type 2 diabetic patients. Potential effects on endothelial-dependent myocardial blood flow remain to be investigated further. Positron emission tomography is a sensitive approach to assess the effects of therapeutic agents on myocardial blood flow in patients with diabetes.

Myocardial blood flow in patients with dilated cardiomyopathy: Quantitative assessment with velocity-encoded cine magnetic resonance imaging of the coronary sinus

PURPOSE

To quantify global myocardial perfusion using magnetic resonance imaging (MRI) in patients with heart failure due to idiopathic dilated cardiomyopathy (IDC) and to compare myocardial perfusion and microvascular reactivity with healthy subjects.

MATERIALS AND METHODS

A total of 19 subjects (healthy volunteers (N = 12) and IDC patients (N = 7)) were studied using cine MRI to measure left ventricular (LV) mass and a velocity-encoded cine MRI technique to measure coronary sinus flow at rest and after dipyridamole-induced hyperemia. Absolute values of total myocardial blood flow (MBF) were calculated from coronary sinus flow and LV mass.

RESULTS

At baseline, MBF was not significantly different in patients with IDC (0.48 +/- 0.07 mL/minute/g) and healthy subjects (0.55 +/- 0.19 mL/minute/g, P= 0.41). After dipyridamole administration, MBF in IDC patients increased to a level significantly less than that in normal volunteers (1.05 +/- 0.35 mL/minute/g vs. 1.99 +/- 1.05 mL/minute/g, P < 0.05). Consequently, MBF reserve was impaired in patients with IDC (2.19 +/- 0.77) compared to that in healthy subjects (3.51 +/- 1.29, P < 0.05). A moderate correlation was found between MBF reserve and LV ejection fraction (r = 0.48, P < 0.05).

CONCLUSION

MBF reserve is reduced in patients with IDC, indicating that coronary microcirculatory flow is impaired. This integrated MRI approach allows quantitative measurement of global MBF in humans and may have the potential to study the effects of pharmacological interventions on myocardial perfusion.

Tetrahydrobiopterin restores impaired coronary microvascular dysfunction in hypercholesterolaemia

PURPOSE

Tetrahydrobiopterin (BH4) is an essential co-factor for the synthesis of nitric oxide (NO), and BH4 deficiency may cause impaired NO synthase (NOS) activity. We studied whether BH4 deficiency contributes to the coronary microcirculatory dysfunction observed in patients with hypercholesterolaemia.

METHODS

Myocardial blood flow (MBF; ml min(-1) g(-1)) was measured at rest, during adenosine-induced (140 microg kg(-1) min(-1) over 7 min) hyperaemia (mainly non-endothelium dependent) and immediately after supine bicycle exercise (endothelium-dependent) stress in ten healthy volunteers and in nine hypercholesterolaemic subjects using 15O-labelled water and positron emission tomography. Measurements were repeated 60 min later, after intravenous infusion of BH4 (10 mg kg(-1) body weight over 30 min). Adenosine-induced hyperaemic MBF is considered to represent (near) maximal flow. Flow reserve utilisation was calculated as the ratio of exercise-induced to adenosine-induced hyperaemic MBF and expressed as percent to indicate how much of the maximal (adenosine-induced) hyperaemia can be achieved by bicycle stress.

RESULTS

BH4 increased exercise-induced hyperaemia in controls (2.96+/-0.58 vs 3.41+/-0.73 ml min(-1) g(-1), p<0.05) and hypercholesterolaemic subjects (2.47+/-0.78 vs 2.70+/-0.72 ml min(-1) g(-1), p<0.01) but had no influence on MBF at rest or during adenosine-induced hyperaemia in controls (4.52+/-1.10 vs 4.85+/-0.45 ml min(-1) g(-1), p=NS) or hypercholesterolaemic subjects (4.86+/-1.18 vs 4.53+/-0.93 ml min(-1) g(-1), p=NS). Flow reserve utilisation remained unchanged in controls (70+/-17% vs 71+/-19%, p=NS) but increased significantly in hypercholesterolaemic subjects (53+/-15% vs 66+/-14%, p<0.05).

CONCLUSION

BH4 restores flow reserve utilisation of the coronary microcirculation in hypercholesterolaemic subjects, suggesting that BH4 deficiency may contribute to coronary microcirculatory dysfunction in hypercholesterolaemia.