Coronary flow reserve is reduced in young men with IDDM

Measurement of coronary vasomotor function: getting to the heart of the matter in cardiovascular research

Measurement of endothelial function in patients has emerged as a useful tool for cardiovascular research. Although no gold standard for the measurement of endothelial function exists, the measurement of flow-mediated dilation in the brachial artery, assessed with Doppler ultrasonography, is the most studied method. However, the assumption that endothelial dysfunction detected in brachial arteries is a manifestation of systemic endothelial dysfunction including the coronary circulation may not be entirely valid. Brachial and myocardial circulations differ in terms of the microvascular architecture, the pattern of blood flow and vascular resistance (e.g. shunt vessels occur in the hand but not in the myocardium), their metabolic regulation, type of receptors that contribute to humoral regulation and the pathways that are activated to induce hyperaemia. In this context, measuring coronary vasomotor function may be more useful than brachial artery measures to predict and assess potential myocardial damage related to limited vascular responsiveness. This review aims to provide an overview of the basic concept of coronary flow reserve and its different modalities of measurement, as well as its utility in cardiovascular research.

Coronary flow velocity and coronary flow velocity reserve in children with ventricular septal defect

To assess coronary flow characteristics in congenital heart defect with left ventricular (LV) volume overload, we examined 24 children (mean 12.1 +/- 7.1 months) with ventricular septal defect. The pulmonary to systemic flow ratio ranged from 1.1 to 3.0. Control group consisted of 10 age-matched children who had a history of Kawasaki disease with angiographically normal coronary artery in the acute phase. LV end-diastolic volume and LV mass were measured by left ventriculogram. With Doppler flow guide wire (0.014-inch), average peak flow velocity (APV) in left anterior descending coronary artery was recorded at rest and during hyperemia (0.16 mg/kg/min adenosine infusion intravenously). Coronary flow velocity reserve (CFVR) was calculated as the ratio of hyperemic/baseline APV. Seven patients were also studied 5-7 months after surgery. Compared with control subjects, CFVR was significantly reduced in patients with LVvolume overload (1.78 +/- 0.24 vs. 2.66 +/- 0.42, p < .0001) because baseline APV was significantly greater (30 +/- 8 vs. 23 +/- 5 cm/sec, p = 0.0027). Significant correlations were observed between CFVR and Qp/Qs, baseline APV, LV end-diastolic volume, or LVmass. Stepwise regression analysis showed that baseline APV and Qp/Qs were important determinants of CFVR (CFVR = 2.64-0.202 [Qp/Qs]-0.015 [APV] r = 0.83, p < 0.0001). In 7 patients with LVvolume overload, CFVR improved significantly after surgery because of reduction of baseline APV. CFVR is limited in patients with LV volume overload because of the elevation of baseline resting APV. LAD flow pattern is dependent on LV volume overload level and its changes after surgery.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.

Effect of Pravastatin on Low-Density Lipoprotein Oxidation and Myocardial Perfusion in Young Adults With Type 1 Diabetes

OBJECTIVE

Diabetes has been associated with increased oxidative stress and impaired vascular function. Statins have been shown to reduce low-density lipoprotein (LDL) oxidizability and improve myocardial perfusion in hypercholesterolemic nondiabetic subjects. We studied whether pravastatin decreases LDL oxidation and improves myocardial perfusion in normocholesterolemic subjects with type 1 diabetes.

METHODS AND RESULTS

In this randomized, double-blind study, myocardial perfusion was measured at rest and during dipyridamole stimulation with positron emission tomography and [15O]H2O during hyperinsulinemic euglycemia in 42 patients (age 30+/-6 years; LDL cholesterol 2.48+/-0.57 mmol/L) before and after 4-month treatment with pravastatin 40 mg/d or placebo. In addition, 12 healthy nondiabetic subjects were studied. LDL oxidation was measured by determining the level of baseline diene conjugation in lipids extracted from LDL. The level of LDL oxidation was similar in the pravastatin and placebo groups before treatment (23.9+/-4.6 versus 25.6+/-9.5 micromol/L, respectively) and decreased significantly during pravastatin treatment to 19.5+/-5.0 micromol/L (P<0.005). Myocardial perfusion reserve was significantly lower in diabetic patients compared with controls (4.15+/-1.29 versus 5.31+/-1.86, P<0.05) and did not change after treatment. Glycemic control and insulin sensitivity remained unchanged during treatment.

CONCLUSIONS

Pravastatin treatment, resulting in decreased LDL oxidation, did not improve myocardial perfusion reserve in subjects with type 1 diabetes.

Black tea increases coronary flow velocity reserve in healthy male subjects

Epidemiologic studies suggest that tea consumption decreases the risk for cardiovascular events. However, there has been no clinical report examining the effects of tea consumption on coronary circulation. The purpose of this study was to evaluate the effects of black tea on coronary flow velocity reserve (CFVR) using transthoracic Doppler echocardiography (TTDE). This was a double-blind crossover study of 10 healthy male volunteers conducted to compare the effects of black tea and caffeine on coronary circulation. The coronary flow velocity of the left anterior descending coronary artery was measured at baseline and at hyperemia during adenosine triphosphate infusion by TTDE to determine CFVR. The CFVR ratio was defined as the ratio of CFVR after beverage consumption to CFVR before beverage consumption. All data were divided into 2 groups according to beverage type: group T (black tea) and group C (caffeine). Two-way analysis of variance showed a significant group effect and interaction in CFVR before and after beverage consumption (p = 0.001). CFVR significantly increased after tea consumption in group T (4.5 +/- 0.9 vs 5.2 +/- 0.9, p <0.0001). The CFVR ratio of group T was larger than that of group C (1.18 +/- 0.07 vs 1.04 +/- 0.08, p = 0.002). Acute black tea consumption improves coronary vessel function, as determined by CFVR.

Coronary flow reserve abnormalities in patients with diabetes mellitus who have end-stage renal disease and normal epicardial coronary arteries

BACKGROUND

Diabetic nephropathy is associated with increased cardiovascular events. Coronary atherosclerosis is responsible for many of these events, but other mechanisms such as impaired flow reserve may be involved. The purpose of this study was to define the prevalence and mechanism of abnormal coronary velocity reserve (CVR) in patients with diabetes mellitus who have nephropathy and a normal coronary artery.

METHODS

Patients undergoing catheterization for clinical purposes were enrolled. CVR was measured with a Doppler ultrasound scanning wire in a normal coronary in 32 patients without diabetes mellitus, 11 patients with diabetes mellitus who did not have renal failure, and 21 patients with diabetes mellitus who had nephropathy. A CVR <2.0 was considered to be abnormal.

RESULTS

Patients with diabetes mellitus who had renal failure had a higher incidence of hypertension and left ventricular hypertrophy. The average peak velocity (APV) at baseline was higher in patients with diabetes mellitus who had renal failure. At peak hyperemia, APV increased in all 3 groups, with no difference between groups. The mean CVR for patients without diabetes was 2.8 +/- 0.8 and was not different from that in patients with diabetes mellitus who did not have renal failure (2.7 +/- 0.7), but was lower than that in patients with diabetes mellitus who had renal failure (1.6 +/- 0.5; P < 0.001). Abnormal CVR was observed in 9% of patients without diabetes mellitus, 18% of patients with diabetes mellitus who did not have renal failure, and 57% of patients with diabetes mellitus who had renal failure, and abnormal CVR was caused by an elevation of baseline APV in 66% of these cases. The baseline heart rate and the presence of diabetes mellitus with renal failure were independent predictors of abnormal CVR by multivariable analysis.

CONCLUSIONS

Patients with diabetic nephropathy have abnormalities in CVR in the absence of angiographically evident coronary disease.

Peroxisome Proliferator Activator Receptors (PPAR), Insulin Resistance, and Cardiomyopathy

Diabetes is a risk factor for coronary atherosclerosis, myocardial infarction, and ischemic cardiomyopathy. Insulin resistance is associated with left ventricular (LV) hypertrophy and hypertensive cardiomyopathy. Even in the absence of coronary artery disease or hypertension, "diabetic cardiomyopathy" can develop because of myocardial autonomic dysfunction or impaired coronary flow reserve. The relationship between insulin resistance and cardiomyopathy is bidirectional. Systemic and myocardial glucose uptake is compromised in heart failure independent of etiology. These abnormalities are associated with cellular deficits of insulin signaling. Insulin resistance in heart failure can be detrimental, because transcriptional shifts in metabolic gene expression favor glucose over fat as a substrate for high-energy phosphate production. Although preexisting diabetes accelerates this process of "metabolic death," insulin resistance can also develop secondary to cardiomyopathy-associated overabundance of neurohormones and cytokines. Insulin resistance and fatty acid excess are potential therapeutic targets in heart failure, striving for efficient myocardial substrate utilization. Peroxisome proliferator activator receptor gamma (PPARgamma) agonists are antidiabetic agents with antilipemic and insulin-sensitizing activity. Experimental studies suggest salutary effects in limiting infarct size, attenuating myocardial reperfusion injury, inhibiting hypertrophic signaling and vascular antiinflammatory actions through cytokine inhibition. However, clinical applicability in diabetic patients experiencing heart failure has been hampered because of increased edema and even fewer reports of exacerbation associated with these compounds. Evidence to date argues for peripheral mechanisms of edema unrelated to central hemodynamics. Nevertheless, they are currently contraindicated in New York Heart Association (NYHA) III-IV patients, particularly in combination with insulin. Investigations are underway to decipher mechanisms, risks, and benefits of PPARgamma agonists, as well as the role of the structurally related PPARalpha receptor on cardiovascular metabolism and function.

Insulin induced increase in coronary flow reserve is abolished by dexamethasone in young men with uncomplicated type 1 diabetes

OBJECTIVE

To examine the role of the sympathetic nervous system in regulating insulin's action on coronary perfusion in uncomplicated type 1 diabetes by blocking centrally mediated sympathetic activity with dexamethasone.

METHODS

Positron emission tomography and oxygen 15 labelled water were used to quantify myocardial blood flow basally and during adenosine infusion with or without simultaneous euglycaemic physiological hyperinsulinaemia in nine non-smoking men with type 1 diabetes and 12 healthy non-diabetic men. Each patient was studied both with and without previous dexamethasone treatment for two days (2 mg/day).

RESULTS

Insulin increased coronary flow reserve in diabetic (from 4.3 (0.7) to 5.1 (0.6), p < 0.05) and non-diabetic (from 4.3 (0.3) to 5.4 (0.4), p < 0.05) patients. In contrast to non-diabetic patients dexamethasone pretreatment abolished the insulin induced increase in coronary flow reserve in diabetic patients (p < 0.05) leading to lower coronary flow reserve in diabetic than in non-diabetic patients (3.9 (0.6) v 7.1 (0.9), p < 0.05).

CONCLUSIONS

These results show that insulin's ability to modulate coronary perfusion is sustained in young patients with type 1 diabetes without microvascular complications or autonomic neuropathy. Dexamethasone treatment abolished the insulin induced increase in coronary flow reserve in diabetic patients but not in healthy study participants, suggesting that sympathetic activation plays an important part in regulating insulin's effects on myocardial perfusion in patients with type 1 diabetes.

Association between vascular dysfunction and reduced myocardial flow reserve in patients with hypertension: a LIFE substudy

Impaired myocardial flow reserve (MFR) has been demonstrated in hypertension, and has been associated with peripheral vascular changes. We investigated whether MFR was impaired and associated with structural and/or functional vascular changes in hypertensive patients without evidence of coronary artery disease (CAD). We measured left ventricular (LV) mass index by echocardiography and MFR by positron emission tomography in 33 unmedicated, hypertensive patients with electrocardiographic LV hypertrophy without CAD, and 15 age- and gender-matched normotensive subjects. We also measured 24-h ambulatory blood pressure, minimal forearm vascular resistance (MFVR) by plethysmography, media:lumen ratio in isolated, subcutaneous resistance arteries by myography, intima-media cross-sectional area of the common carotid artery, and flow-mediated (FMD) and nitroglycerin-induced dilatation (NID) of the brachial artery by ultrasound. Compared to the controls, the patients had impaired MFR (2.4 (95% CI 1.95-2.8) vs 3.4 (2.7-4.2), P<0.01) due to increased resting myocardial blood flow (MBF) (0.82 (0.73-0.91) vs 0.65 (0.56-0.75) ml/g min), and decreased dipyridamole-stimulated MBF (1.80 (1.55-2.1) vs 2.3 (1.80-2.8) ml/g min, both P<0.05). The difference in resting MBF disappeared (80 (74-87) vs 86 (74-97) microl/kg mmHg, NS) when normalized for blood pressure and heart rate. MFR correlated negatively to median 24-h systolic blood pressure (r=-0.50, P<0.01) as well as to LV mass index (r=-0.45, P<0.05) and MFVR in men (r=-0.47, P<0.05), and positively to FMD (r=0.44, P<0.05) and NID (r=0.40, P<0.05). Hypertensive patients with electrocardiographic LV hypertrophy without CAD had impaired MFR associated with cardiovascular hypertrophy and vasodilatory dysfunction. This suggests that MFR is impaired by LV hypertrophy and structural/functional vascular damage in the coronary and noncoronary circulation.

Molecular imaging in nuclear cardiology

State-of-the-art techniques have been used to measure key aspects of cardiovascular pathophysiology from the birth of radionuclide cardiovascular imaging. However, during the last 30 years, there have been few innovative imaging advances to further our understanding of the complex physiologic processes. Molecular imaging now offers an array of tools to develop advanced diagnostic approaches and therapies for patients with coronary artery disease and heart failure. For example, the enhanced understanding of the pathophysiology of atheroma makes it possible to identify vulnerable plaque based on its metabolic signature or the presence of excessive apoptosis. Because the metabolic and apoptotic signals are large, it is likely that even small lesions will be visible. Of the many approaches that are being developed, 2 tracers appear most likely to be tested in the near future: (1) [18F]-fluorodeoxyglucose, to determine macrophage metabolism; and (2) radiolabeled annexin, to measure apoptosis of the inflammatory cells. Using existing techniques such as perfusion imaging, appropriate patients can be selected for treatment with novel therapies, such as stem cell transplantation or vascular gene therapy. Using positron tomography in place of single photon imaging adds the capability for the measurement of absolute perfusion and perfusion reserve to the information on regional perfusion. Flow reserve detects global decreases in perfusion and refines the determination of lesion severity available from perfusion imaging.

C-peptide improves adenosine-induced myocardial vasodilation in type 1 diabetes patients

Patients with type 1 (insulin-dependent) diabetes show reduced skeletal muscle blood flow and coronary vasodilatory function despite intensive insulin therapy and good metabolic control. Administration of proinsulin C-peptide increases skeletal muscle blood flow in these patients, but a possible influence of C-peptide on myocardial vasodilatory function in type 1 diabetes has not been investigated. Ten otherwise healthy young male type 1 diabetic patients (Hb A1c 6.6%, range 5.7-7.9%) were studied on two consecutive days during normoinsulinemia and euglycemia in a double-blind, randomized, crossover design, receiving intravenous infusion of C-peptide (5 pmol.kg-1.min-1) for 120 min on one day and saline infusion on the other day. Myocardial blood flow (MBF) was measured at rest and during adenosine administration (140 microg.kg-1.min-1) both before and during the C-peptide or saline infusions by use of positron emission tomography and [15O]H2O administration. Basal MBF was not significantly different in the patients compared with an age-matched control group, but adenosine-induced myocardial vasodilation was 30% lower (P < 0.05) in the patients. During C-peptide administration, adenosine-stimulated MBF increased on average 35% more than during saline infusion (P < 0.02) and reached values similar to those for the healthy controls. Moreover, as evaluated from transthoracal echocardiographic measurements, C-peptide infusion resulted in significant increases in both left ventricular ejection fraction (+5%, P < 0.05) and stroke volume (+7%, P < 0.05). It is concluded that short-term C-peptide infusion in physiological amounts increases the hyperemic MBF and left-ventricular function in type 1 diabetic patients.

Application of Pressure-Derived Myocardial Fractional Flow Reserve in Assessing the Functional Severity of Coronary Artery Stenosis in Patients With Diabetes Mellitus

BACKGROUND

Although the development of a coronary guidewire mounted with a pressure sensor has facilitated the measurement of pressure-derived fractional flow reserve (FFR) to assess the functional severity of coronary artery stenoses, the theoretical limitations include diabetes mellitus because of the associated microvascular abnormalities.

METHODS AND RESULTS

In the present study 304 vessels and their coronary territories in 96 diabetic and 149 nondiabetic patients were evaluated by pressure-derived FFR and thallium-201 single photon emission computed tomography (SPECT) to determine the applicability of measuring FFR in diabetic subjects. The best cut-off value for FFR to detect myocardial ischemia, as demonstrated by (201)Tl SPECT, was 0.725 in the diabetic and 0.745 in the nondiabetic patients. Sensitivity and specificity were similar for the 2 groups (83% and 75% (diabetic) vs 79% and 83%). However, diabetic patients with homoglobin (Hb) A(1c) >or=7.0% showed lower specificity in comparison with those having HbA(1c) <7.0% (64 vs 88%; p=0.045); however, sensitivities were similar (83 vs 83%; p=NS).

CONCLUSIONS

The cut-off value of 0.75 for FFR can detect myocardial ischemia in diabetic patients, although the adequacy of glycemic control should be taken into consideration when assessing the FFR measurements.

Myeloperoxidase gene variation and coronary flow reserve in young healthy men

Chronic inflammation may lead to endothelial dysfunction, which manifests as an impaired coronary reactivity. Impairment in coronary flow reserve (CFR), preceding the clinical symptoms of coronary artery disease, can be measured noninvasively by positron emission tomography. Myeloperoxidase (MPO) is an oxidative enzyme present in phagocytes and atherosclerotic lesions. The MPO gene has a promoter polymorphism (-463G/A) which affects gene transcription. Whether these variants associate with coronary artery function is not known. Myocardial blood flow at rest and during adenosine-induced hyperemia was assessed in 49 healthy young men with normal or slightly elevated serum total cholesterol. These subjects were divided into high (G/G) and low (A/G, A/A) MPO expression groups and effect of MPO genotype on myocardial blood flow was evaluated. We found a significant difference between MPO genotypes in CFR after adjusting for age, body mass index, smoking and family history of cardiovascular disease (p = 0.019). Men with G/G genotype had 18.1% lower CFR than subjects with low-expression genotypes (A/G and A/A). This was due to an 11.5% lower adenosine-stimulated flow of the G/G genotype carriers (p = 0.049). These findings provide evidence that MPO polymorphism is associated with coronary artery reactivity. However, the number of individuals investigated was low and our observation should be confirmed by a larger number of subjects.

Cut-off value of coronary flow velocity reserve by transthoracic Doppler echocardiography for diagnosis of significant left anterior descending artery stenosis in patients with coronary risk factors

The purpose of this study was to evaluate the adequate cut-off value of coronary flow velocity reserve (CFVR) with transthoracic Doppler echocardiography for diagnoses of significant left anterior descending (LAD) artery stenosis in a large study population with various coronary risk factors. CFVR, which has been used for evaluation of significant coronary artery stenosis, can be reduced despite angiographically normal coronary arteries in patients with various coronary risk factors. However, the adequate cut-off value of CFVR for diagnosing significant LAD stenosis has not been fully established in patients with coronary risk factors. We examined 138 consecutive patients who underwent coronary angiography. Clinical histories of coronary risk factors were determined from interviews or medical records. CFVR assessment in the LAD artery by transthoracic Doppler echocardiography was performed in all patients. Of the 138 patients, 30 had significant stenosis, and the remainder had no stenotic lesions in the LAD artery. Receiver-operating characteristic curves for detection of significant LAD stenosis showed that a cut-off value of <2.0 was extremely precise. A cut-off value <2.0 of CFVR had a sensitivity of 90%, a specificity of 93%, a positive predictive value of 77%, and a negative predictive value of 97% for the presence of significant LAD stenosis. A cut-off value <2.0 of CFVR by transthoracic Doppler echocardiography was adequate for the diagnosis of significant LAD stenosis in a population that included patients with coronary risk factors.

Cardiac autonomic dysinnervation and myocardial blood flow in long-term Type 1 diabetic patients

AIMS

The aim of the study was to assess scintigraphically the relationship between myocardial blood flow response and sympathetic dysinnervation in long-term Type 1 diabetic patients. Effects of the iron chelator deferoxamine on myocardial blood flow were studied and they were investigated according to the presence of cardiac sympathetic dysfunction.

METHODS

Myocardial blood flow (MBF) was assessed with N-13 ammonia positron emission tomography in 13 long-term Type 1 diabetic patients and 13 control subjects at rest and in response to sympathetic stimulation (cold pressor test (CPT)). In diabetic patients, the study was repeated after preinfusion with deferoxamine. Furthermore, 123I metaiodobenzylguanidine (MIBG) scintigraphy was applied to assess regional cardiac sympathetic dysinnervation (uptake score 1 = normal, homogeneous uptake em leader 6 = no uptake).

RESULTS

In diabetic patients, MBF increased in response to CPT from 78 +/- 18 ml/100 g/min to 84 +/- 26 ml/100 g (8%, P < 0.001). Control subjects demonstrated an increase from 63 +/- 17 ml/100 g to 84 +/- 26 ml/100 g (33%, P < 0.001), respectively. Resting MBF was higher in diabetic patients than in control subjects (P < 0.001). In diabetic patients, increase in MBF in response to CPT was significant in regions with a MIBG uptake score of <or= 3. Regions with a MIBG uptake score of > 3 did not exhibit a significant increase in MBF in response to CPT. After administration of deferoxamine, the increase in MBF in response to CPT was 23% and the magnitude of increase was related to the MIBG uptake score (r = 0.40, P < 0.0001).

CONCLUSIONS

Myocardial blood flow response to sympathetic stimulation is significantly impaired in long-term Type 1 diabetes. After preinfusion with deferoxamine the impairment is partially reversed and a relationship between myocardial blood flow and the extent of cardiac sympathetic dysfunction is observed.

Role of chronic hyperglycemia in the pathogenesis of coronary microvascular dysfunction in diabetes

OBJECTIVES

We sought to determine the differences in coronary microvascular function between patients with type 1 (insulin-deficient) and type 2 (insulin-resistant) diabetes mellitus (DM).

BACKGROUND

Coronary vascular function is impaired in patients with DM. However, it is unclear whether the type and/or severity of this vascular dysfunction are similar in patients with type 1 and type 2 DM.

METHODS

We studied 35 young subjects with DM (18 with type 1 and 17 with type 2), who were free of overt cardiovascular complications, and 11 age-matched healthy controls. Positron emission tomography imaging was used to measure myocardial blood flow (MBF) at rest, during adenosine-induced hyperemia (reflecting primarily endothelium-independent vasodilation), and in response to cold pressor test (CPT) (reflecting primarily endothelium-dependent vasodilation).

RESULTS

The two groups of diabetics were similar with respect to age and glycemic control. The duration of diabetes was longer and high-density lipoprotein cholesterol levels were higher in type 1 than in type 2 diabetics. Basal MBF was similar in the three groups studied. The increase (from baseline) in MBF with adenosine was similar in the subjects with type 1 (161 +/- 18%) and type 2 (185 +/- 19%) DM, but lower than in the controls (351 +/- 43%) (p < 0.001 for the comparison with both groups of diabetics). Similarly, the increase in MBF during the CPT was comparable in the subjects with type 1 (23 +/- 4%) and type 2 (19 +/- 3%) DM, but lower compared with the controls (66 +/- 12%) (p < 0.0001 for the comparison with both groups of diabetics). These differences persisted after adjusting for the duration of diabetes, insulin treatment, metabolic abnormalities, and autonomic neuropathy.

CONCLUSIONS

These results demonstrate markedly reduced and similar endothelium-dependent and -independent coronary vasodilator function in subjects with both type 1 and type 2 DM. These results suggest a key role of chronic hyperglycemia in the pathogenesis of vascular dysfunction in diabetes.

Optimum Hypoglycemic Therapy can Improve Coronary Flow Velocity Reserve in Diabetic Patients-Demonstration by Transthoracic Doppler Echocardiography-

The purpose of this study was to determine whether the elimination or the alleviation of hyperglycemia would improve coronary flow velocity reserve (CFVR) using transthoracic Doppler echocardiography (TTDE). CFVR was measured by TTDE in the left anterior descending coronary artery in 49 poorly controlled diabetic patients before and after antidiabetic treatment and 15 well controlled diabetic patients also underwent the same measurements. The fasting blood glucose level in the poorly controlled patients reduced from 270 +/-106 mg/dl to 116+/-39 mg/dl at 20+/-15 days after the intensive treatment. Although baseline coronary flow velocity (CFV) did not change between the 2 measurements (19.9+/-6.9 cm/s vs 19.0+/-5.4 cm/s, p=NS), the hyperemic CFV increased significantly after the treatment (47.3+/-13.4 cm/s vs 55.4+/-13.2 cm/s, p<0.001). Thus, the CFVR improved significantly after the treatment (2.47+/-0.55 vs 2.98+/-0.56, p<0.001). Although there was minimal improvement in the control group (2.37+/-0.38 vs 2.50+/-0.37, p<0.05), the improvement in CFVR was significantly greater in the poorly controlled patients with intensive treatment (0.51+/-0.33 vs 0.12+/-0.19, p<0.001) than that in the control group. These results suggest that optimal hypoglycemic therapy is important to improve the CFVR in poorly controlled diabetic patients.

High oxidized LDL and elevated plasma homocysteine contribute to the early reduction of myocardial flow reserve in healthy adults

BACKGROUND

Impairment of coronary blood flow reserve has been shown to be an early manifestation of atherosclerosis and coronary artery disease (CAD). We studied more closely the contribution of various risk factors on early deterioration of coronary function.

MATERIALS AND METHODS

Fifty-one young, apparently healthy adults, with normal or mildly elevated serum cholesterol levels but without other major risk factors for CAD, such as diabetes or hypertension, underwent positron emission tomography (PET) studies. Coronary flow reserve (CFR) was measured using O15-water. In addition to the classical risk factors, the role of several new risk indicators, such as low-density lipoprotein (LDL) oxidation, infection (Chlamydia pneumoniae antibodies), and inflammation parameters (adhesion molecules, ICAM, VCAM, selectin, and C-reactive protein), homocysteine and body iron stores were investigated.

RESULTS

Elevated lipid and lipoprotein levels were not associated with reduced coronary reactivity. However, high autoantibody titers against oxidized LDL (oxLDL) were associated with 21% lower CFR than low oxLDL (P < 0.05). Furthermore, high homocysteine levels predicted low CFR (P < 0.05). The other measured parameters, Chlamydia pneumoniae antibody levels, C-reactive protein and adhesion molecule concentrations did not associate with myocardial blood flow. In a stepwise regression model, oxLDL (P = 0.03), homocysteine (P = 0.04) and triglycerides (P = 0.018) were significant predictors of CFR.

CONCLUSIONS

The present study suggests an important role for oxidized LDL and plasma homocysteine on early impairment of coronary reactivity in young adults.

Hypertension attenuates the efficacy of hypoglycemic therapy for preserving coronary flow reserve in patients with type 2 diabetes

Impairment of coronary flow reserve (CFR) in patients with type 2 diabetes has been generally demonstrated; however, there have been few studies investigating CFR in cases of relatively well-controlled diabetes, in distinction to the influence of hypertension. The purpose of the present study was to evaluate the influence of diabetes and hypertension upon CFR in relatively well-controlled patients. This study included 12 healthy controls (C group) and 57 patients with type 2 diabetes (DM) and/or essential hypertension who were divided into three groups as follows: patients with DM (DM group; n = 24), patients with essential hypertension (HT group; n = 15), and patients with both DM and essential hypertension (DM+HT group; n = 18). We excluded patients with evidence of coronary artery disease and/or left ventricular hypertrophy. We performed transthoracic Doppler recording of diastolic coronary flow velocity (CFV) in the left anterior descending coronary artery at rest and after maximal vasodilation by adenosine infusion (140 microg/kg/min for 3 min) CFR was defined as the ratio of hyperemic to averaged basal peak CFV. The CFR (2.92 +/- 0.46) of the DM group was not decreased compared to that of the C group (2.96 +/- 0.58), although the CFR of the HT (2.33 +/- 0.25) and DM+HT (2.35 +/- 0.25) groups were significantly reduced. Left ventricular mass index, relative wall thickness, and diastolic function were worse in the HT and DM+HT groups than in the C and DM groups. Subjects with concentric left ventricular remodeling had a lower CFR than those with normal left ventricular geometry. In conclusion, adequate hyperglycemic control prevented the progression of coronary microcirculatory disturbance, but concomitant hypertension attenuated the effect.

Plasma asymmetric dimethylarginine and hyperemic myocardial blood flow in young subjects with borderline hypertension or familial hypercholesterolemia

OBJECTIVE

The goal of this study was to examine the relationship between plasma asymmetric dimethylarginine (ADMA) level and hyperemic myocardial blood flow (MBF) in subjects with borderline hypertension (BHT) and familial hypercholesterolemia (FH).

METHODS

Asymmetric dimethylarginine is an endogenous competitive inhibitor of nitric oxide synthase that may modulate vascular function. We measured plasma ADMA levels and myocardial flow in 77 young men (mean age 35 +/- 5 years), including 47 healthy controls, 16 men with BHT, and 14 men with FH. Basal and dipyridamole-induced myocardial flow was measured using positron emission tomography. Plasma ADMA levels were measured using high-pressure liquid chromatography.

RESULTS

Asymmetric dimethylarginine levels were significantly elevated in the BHT group compared with controls (0.59 +/- 0.13 micromol/l vs. 0.43 +/- 0.12 micromol/l, p < 0.001), and they had significantly lower dipyridamole flow (2.85 +/- 1.20 ml/min/g vs. 3.69 +/- 1.68 ml/min/g, p < 0.05). In a multivariate regression model adjusted for the study group, dipyridamole flow was inversely associated with ADMA (p < 0.05), age (p < 0.05), and apolipoprotein B concentration (p < 0.05).

CONCLUSIONS

We conclude that plasma ADMA concentration is related to dipyridamole-induced vasodilatory function in young men, independently of blood pressure elevation and hypercholesterolemia. Subjects with BHT have significantly increased plasma ADMA levels, which may partly explain the impaired hyperemic MBF in this condition.

Coronary flow reserve assessment by Doppler echocardiography in children with and without congenital heart defect: comparison with invasive technique

To evaluate whether transthoracic Doppler echocardiography can reliably measure coronary flow velocity (CFV) and CFV reserve (CFVR) in the left anterior descending coronary artery (LAD) in children, we examined 12 patients who had a history of Kawasaki disease without stenosis or aneurysm formation of coronary artery and 9 patients who had congenital heart disease (ventricular septal defect in 6, patent ductus arteriosus in 2, tricuspid atresia in 1). The pulmonary-to-systemic flow ratio ranged from 1.7 to 2.8. CFV in the proximal LAD was measured by transthoracic Doppler echocardiography at the time of Doppler guidewire examination. CFV in the proximal LAD was measured at baseline and hyperemic conditions by both transthoracic Doppler echocardiography and Doppler guidewire techniques. CFVR was defined as "the ratio of peak hyperemic to basal CFV in the proximal LAD." Clear envelopes of basal and hyperemic CFV in the proximal LAD were obtained in 19 of 21 patients by transthoracic Doppler echocardiography. There was a significant correlation between transthoracic Doppler echocardiography and Doppler guidewire methods for the measurements of CFV (r = 0.84, P <.0001). The mean difference between the 2 methods was -0.5 +/- 5.9 cm/s. CFVR from transthoracic Doppler echocardiography correlated well with that from Doppler guidewire examinations (r = 0.83, P <.0001). The mean difference between the 2 methods was 0.06 +/- 0.24. Noninvasive measurement of CFV and CFVR in the proximal LAD using transthoracic Doppler echocardiography accurately reflects invasive measurement of CFV and CFVR by Doppler guidewire method in pediatric patients with various heart diseases.

Oestrogen receptor gene variation is a determinant of coronary reactivity in healthy young men

BACKGROUND

Oxidised low-density lipoprotein (ox-LDL) is a determinant of impaired coronary function and oestrogens inhibit its formation probably throughout genetically-variable oestrogen receptor 1 (ESR1) in artery wall. We hypothesized that the ESR1 polymorphism might influence coronary function and reactivity as measured by positron emission tomography (PET), which allows the detection of coronary dysfunction before appearance of angiographic lesions.

MATERIALS AND METHODS

Fifty-one healthy young men (aged 35 +/- 4 years), with normal or slightly-elevated serum cholesterol, underwent PET with intravenous adenosine. ESR1 PvuII genotypes P/P, P/p, and p/p in addition to the plasma autoantibody titre against ox-LDL, a marker of in vivo oxidation, were determined.

RESULTS

The ESR1 genotype persisted as the only significant predictor of adenosine stimulated coronary flow (P = 0.035) after adjustment for other coronary risk factors. Subjects with P/P genotype had 33.4 and 41.8% lower adenosine-stimulated flow values than subjects with P/p and p/p genotypes (P = 0.030). Furthermore, plasma levels of ox-LDL titre were on average 59 and 77% higher in subjects with P/P genotype than in subjects with P/p or p/p genotypes (P = 0.049).

CONCLUSIONS

These tentative findings from our pilot study provide evidence that genetic variation in ESR1 may modify coronary reactivity and LDL oxidation and reflect differences in the early pathogenesis of coronary dysfunction in these healthy young men.

Myocardial perfusion and perfusion reserve in endurance-trained men

PURPOSE

This study was undertaken to determine whether endurance training is associated with changes in myocardial perfusion in humans.

METHODS

Myocardial perfusion was measured in eleven trained and nine sedentary men at rest and during adenosine-stimulated hyperemia using positron emission tomography (PET). Left ventricular (LV) dimensions and mass were measured using echocardiography. Myocardial work per gram of tissue was calculated as (cardiac output. mean arterial blood pressure)/LV mass.

RESULTS

LV mass was significantly higher and myocardial work per gram of tissue lower in the trained than in the untrained subjects. Basal (0.78 +/- 0.10 and 0.76 +/- 0.15 mL. min-1. g-1, P = NS) and adenosine-stimulated perfusion (3.46 +/- 0.91 and 3.14 +/- 0.70 mL. min-1. g-1, P = NS) were similar between trained and untrained men, respectively. Consequently, myocardial perfusion reserve was similar in both groups (4.4 +/- 1.2 and 4.1 +/- 0.7, P = NS). In addition, coronary resistance at baseline (115 +/- 17 vs 119 +/- 22, mm Hg. mL. min-1. g-1, P = NS) and during adenosine infusion (28 +/- 8 vs 30 +/- 8, mm Hg. mL. min-1. g-1, P = NS) were similar in both groups. Resting myocardial work correlated with resting myocardial perfusion in both groups, but the relationship between perfusion and work was different between the groups so that perfusion for a given myocardial work was significantly higher in trained subjects (0.56 +/- 0.04 and 0.34 +/- 0.05 mL. (mm Hg. L)-1, P < 0.001).

CONCLUSIONS

These findings suggest that endurance trained subjects do not have different resting or adenosine-stimulated myocardial perfusion. However, the relationship between myocardial perfusion and work appears altered in the athletes.

Early impairment of coronary flow reserve is not associated with Chlamydia pneumoniae antibodies

BACKGROUND

Chlamydia pneumoniae infection has been associated with atherosclerosis by sero-epidemiological, histopathological and interventional studies, and animal experiments. We hypothesized that if chlamydial infection is causative of atherosclerosis, the occurrence of antibodies against C. pneumoniae should be associated with coronary vasomotor dysfunction - an early sign of atherosclerosis.

AIM

To study the association between C. pneumoniae infection and coronary vasomotor function in young men without signs of ischemic heart disease.

METHODS

Serum IgG and IgA antibody concentrations against C. pneumoniae were determined in 125 clinically healthy subjects undergoing positron emission tomography (PET) studies. Myocardial blood flow was measured at rest and during pharmacologically induced hyperemia using [15O]H2O Coronary flow reserve was calculated as the ratio of hyperemic blood flow to resting blood flow.

RESULTS

No association was found between serum C. pneumoniae antibody concentrations and myocardial blood flow parameters. In contrast, more conventional risk factors for coronary artery disease, such as total cholesterol and apolipoprotein B, were inversely associated with hyperemic flow and flow reserve.

CONCLUSIONS

We found no association between C. pneumoniae antibodies and coronary vasomotor function in subjects without ischemic heart disease. Thus, these results do not support the role of C. pneumoniae infection as an early phase risk factor for coronary artery disease.

Modulation of coronary flow velocity reserve by gender, menstrual cycle and hormone replacement therapy

OBJECTIVES

The purpose of this study was twofold: 1) to examine the relationship between menstrual cycle and coronary flow velocity reserve (CFVR) in young healthy women, and 2) to evaluate the effect of hormone replacement therapy by estrogen on CFVR in postmenopausal women, using transthoracic color Doppler echocardiography (TTCDE).

BACKGROUND

Although the incidence of cardiovascular disease is lower in women before menopause compared with men, postmenopausal women have an incidence of coronary artery disease similar to that of men of the same age. This is mainly dependent upon estrogen deficiency. However, no clinical report has yet examined the effect of estrogen on CFVR, which is one index of coronary microcirculation.

METHODS

We examined 15 male and both 15 premenopausal and 10 postmenopausal female healthy volunteers. We measured coronary flow velocity of the left anterior descending coronary artery at baseline and hyperemic conditions during adenosine triphosphate infusion by TTCDE and determined CFVR. Each premenopausal woman was studied two times (menstrual [M] and follicular [F] phases) in one menstrual cycle. Fifteen men were also studied at a time corresponding to women's menstrual cycle. The postmenopausal women were studied before and two hours after oral administration of conjugated estrogen (CE).

RESULTS

Serum 17beta-estradiol level in premenopausal women increased in the F phase and decreased to the same levels as in men, as in the M phase and as in postmenopausal women (123 +/- 9 pg/ml vs. 28 +/- 6 pg/ml, 25 +/- 9 pg/ml and 19 +/- 11 pg/ml; p < 0.0001, respectively). The CFVR increased in the F phase compared with that in the M phase (4.8 +/- 0.4 vs. 3.7 +/- 0.8, p < 0.0001). We found that CFVR in men remained unchanged (3.7 +/- 0.6 vs. 3.8 +/- 0.5). After CE administration, CFVR increased compared with baseline in postmenopausal women (4.1 +/- 0.8 vs. 3.4 +/- 0.8, p < 0.005).

CONCLUSIONS

In premenopausal women, CFVR determined by TTCDE varied during the menstrual cycle, and in postmenopausal women, CFVR increased after acute estrogen replacement.

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

BACKGROUND

Myocardial perfusion during adenosine-induced hyperemia is used both in clinical diagnosis of coronary heart disease and for scientific investigations of the myocardial microcirculation. The objective of this study was to clarify whether adenosine-induced hyperemia is dependent on endothelial NO production or is influenced by adrenergic mechanisms.

METHODS AND RESULTS

In 12 healthy men, myocardial perfusion was measured with PET in 2 protocols performed in random order, each including 3 perfusion measurements. First, perfusion was measured at rest. Second, either saline or the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 4 mg/kg) was infused, and perfusion during adenosine-induced hyperemia was determined. Last, in both protocols, the alpha-receptor blocker phentolamine was infused, and perfusion during adenosine-induced hyperemia was determined again. Resting perfusion was similar in the 2 protocols (0.69+/-0.14 and 0.66+/-0.18 mL. min(-1). g(-1)). L-NAME increased mean arterial blood pressure by 12+/-7 mm Hg (P<0.01) and reduced heart rate by 16+/-7 bpm (P<0.01). Adenosine-induced hyperemia (1.90+/-0.33 mL. min(-1). g(-1)) was attenuated by L-NAME (1.50+/-0.55 mL. min(-1). g(-1), P<0.01). The addition of phentolamine had no effect on the adenosine-induced hyperemia (2.10+/-0.34 mL. min(-1). g(-1), P=NS). In the presence of L-NAME, however, when the adenosine response was attenuated, phentolamine was able to increase hyperemic perfusion (2.05+/-0.44 mL. min(-1). g(-1), P<0.05).

CONCLUSIONS

Inhibition of endogenous NO synthesis attenuates myocardial perfusion during adenosine-induced hyperemia, indicating that coronary vasodilation by adenosine is partly endothelium dependent. alpha-Adrenergic blockade has no effect on adenosine-induced hyperemia unless NO synthesis is inhibited.

Assessing coronary sinus blood flow in patients with coronary artery disease: a comparison of phase-contrast MR imaging with positron emission tomography

OBJECTIVE

This study was performed to determine whether MR imaging can be used to reliably measure global myocardial blood flow and coronary flow reserve in patients with coronary artery disease as compared with such measurements obtained by positron emission tomography (PET).

SUBJECTS AND METHODS

We measured myocardial blood flow first at baseline and then after dipyridamole-induced hyperemia in 20 patients with coronary artery disease. Myocardial blood flow as revealed by MR imaging was calculated by dividing coronary sinus flow by the left ventricular mass. Coronary flow reserve was calculated by dividing the rate of hyperemic flow by the rate of baseline flow.

RESULTS

Using MR imaging, myocardial blood flow at baseline was 0.73 +/- 0.23 mL x min(-1) x g(-1), and at hyperemia the blood flow was 1.43 +/- 0.37 mL x min(-1) x g(-1), yielding an average coronary flow reserve of 1.99 +/- 0.47. Using PET, myocardial blood flow was 0.89 +/- 0.21 mL x min(-1) x g(-1) at baseline and 1.56 +/- 0.42 mL x min(-1) x g(-1) at hyperemia, yielding an average coronary flow reserve of 1.77 +/- 0.36. The correlation of myocardial blood flow and coronary flow reserve measurements for these two methods was an r of 0.80 (p < 0.01) and an r of 0.50 (p < 0.05), respectively.

CONCLUSION

This study shows that myocardial blood flow measurements obtained using MR imaging have a good correlation with corresponding PET measurements. Coronary flow reserve measurements obtained using MR imaging had only moderate correlation with PET-obtained measurements. Our results suggest that MR imaging flow quantification could potentially be used for measuring global myocardial blood flow in patients in whom interventional treatment for coronary artery disease is being evaluated.

Hepatic lipase gene variation is related to coronary reactivity in healthy young men

BACKGROUND

Impaired coronary flow reserve (CFR) can be used to indicate vascular dysfunction before the appearance of angiographic lesions. The hepatic lipase (HL) gene has a functional promoter polymorphism at position C-480T, which affects transcription and leads to high activity (C/C) and low activity (C/T, T/T) genotypes. These genotypes modulate HL activity, but their role in coronary artery disease is controversial and the effect on coronary function has not been studied. We investigated whether HL genotypes are associated with coronary artery function in healthy young men.

MATERIALS AND METHODS

We studied 49 healthy, mildly hypercholesterolemic men (aged 35 +/- 4 years). Myocardial blood flow was measured at rest and during adenosine induced hyperaemia with positron emission tomography using [15O] H2O. HL genotype was determined by PCR and Nla III enzyme digestion.

RESULTS

Resting myocardial blood flow was not statistically different in subjects with high and low activity HL genotypes. However, CFR (the ratio of adenosine flow to resting flow) was 24% higher (4.62 +/- 1.52 vs. 3.73 +/- 1.08 mL g-1 min-1, P = 0.024) in men with the high activity genotype (n = 26) than in those with low activity (n = 23). In multivariate analysis, the HL genotype remained a significant predictor of CFR (P = 0.038) after adjusting for age, body mass index, serum lipids and smoking.

CONCLUSIONS

The findings of our preliminary study suggest that the C-480T polymorphism of the HL gene may modify coronary reactivity and reflect differences in the early pathogenesis of coronary dysfunction in these healthy young men. If the association between HL polymorphism and impaired CFR is also present in subjects with other dyslipoproteinemias, the HL polymorphism could be a new risk factor for cardiovascular disease.

Reduced myocardial flow reserve relates to increased carotid intima-media thickness in healthy young men

Increased carotid artery wall thickness and lipoprotein oxidation are key early events in atherosclerosis. To test the hypothesis that reduced myocardial flow reserve is a marker of subclinical atherosclerosis, we examined the relationships between flow reserve and carotid artery intima-media thickness (IMT) in young men free from coronary heart disease. Basal and dipyridamole stimulated coronary blood flow was measured using positron emission tomography (PET) in 55 healthy men aged 36+/-4 years. Myocardial flow reserve was calculated as the ratio of stimulated flow to basal flow. The mean carotid artery IMT was measured using high-resolution ultrasound. Oxidised LDL was measured as baseline LDL diene conjugation. Myocardial flow reserve decreased across the quartiles of increasing IMT (P=0.006), and was 5.2+/-1.9 in the lowest quartile for IMT and 3.7+/-1.2 in the highest (P=0.04, I vs. IV quartile). In univariate analysis, oxidised LDL correlated inversely with flow reserve (r=-0.35, P=0.01) and directly with IMT (r=0.51, P<0.001). The association between flow reserve and IMT remained significant (P< or =0.01) in multivariate regression model including age, blood pressure, left ventricular mass, ox-LDL, total cholesterol, HDL-cholesterol and triglycerides as covariates. These data support the concept that reduced myocardial flow reserve reflects subclinical atherosclerosis in asymptomatic subjects, and suggest that increased lipoprotein oxidation is directly related to early structural and functional atherosclerotic vascular changes.

Coronary microvascular dysfunction is highly prevalent in women with chest pain in the absence of coronary artery disease: results from the NHLBI WISE study

BACKGROUND

Chest pain in the absence of obstructive coronary artery disease (CAD) is common in women; it is frequently associated with debilitating symptoms and repeated evaluations and may be caused by coronary microvascular dysfunction. However, the prevalence and determinants of microvascular dysfunction in these women are uncertain.

METHODS

We measured coronary flow velocity reserve (coronary velocity response to intracoronary adenosine) to evaluate the coronary microvasculature and risk factors for atherosclerosis in 159 women (mean age, 52.9 years) with chest pain and no obstructive CAD. All women were referred for coronary angiography to evaluate their chest pain as part of the Women's Ischemia Syndrome Evaluation (WISE) study.

RESULTS

Seventy-four (47%) women had subnormal (<2.5) coronary flow velocity reserve suggestive of microvascular dysfunction (mean, 2.02 +/- 0.38); 85 (53%) had normal reserve (mean, 3.13 +/- 0.64). Demographic characteristics, blood pressure, ventricular function, lipid levels, and reproductive hormone levels were not significantly different between women with normal and those with abnormal microvascular function. Postmenopausal hormone use within 3 months was significantly less prevalent among those with microvascular dysfunction (40% vs 60%, P =.032). Age and number of years past menopause correlated with flow velocity reserve (r = -0.18, P =.02, and r = -0.30, P <.001, respectively). No significant associations were identified between flow velocity reserve and lipid and hormone levels, blood pressure, and left ventricular ejection fraction.

CONCLUSIONS

Coronary microvascular dysfunction is present in approximately one half of women with chest pain in the absence of obstructive CAD and cannot be predicted by risk factors for atherosclerosis and hormone levels. Therefore, the diagnosis of coronary microvascular dysfunction should be considered in women with chest pain not attributable to obstructive CAD.

Global myocardial blood flow and global flow reserve measurements by MRI and PET are comparable

Coronary flow reserve (CFR) measurements have been widely used in assessing the functional significance of coronary artery stenosis because they are more sensitive in predicting major cardiac events than angiographically detected reductions of coronary arteries. Myocardial blood flow can be determined by measuring coronary sinus (CS) flow with velocity-encoded cine magnetic resonance imaging (VEC-MRI). The purpose of this study was to compare global myocardial blood flow (MBF) and CFR measured using VEC-MRI with MBF and CFR measured using positron emission tomography (PET). We measured MBF at baseline and after dipyridamole-induced hyperemia in 12 male volunteers with VEC-MRI and PET. With VEC-MRI, MBF was 0.64 +/- 0.09 (ml/min/g) at baseline and 1.59 +/- 0.79 (ml/min/g) at hyperemia, which yielded an average CFR of 2.51 +/- 1.29. With PET, MBF was 0.65 +/- 0.20 (ml/min/g) at baseline and 1.78 +/- 0.72 (ml/min/g) at hyperemia, which yielded an average CFR of 2.79 +/- 0.97. The correlation of MBFs between these two methods was good (r = 0.82, P < 0.001). The CFRs measured by MRI correlated well with those measured using PET (r = 0.76, P < 0.004). These results suggest that MRI is a useful and accurate method to measure global MBF and CFR. Therefore, it would be suitable for studying risk factor modifications of vascular function at an early stage in healthy volunteers.

Peripheral flow response to transient arterial forearm occlusion does not reflect myocardial perfusion reserve

BACKGROUND

Ultrasonographic evaluation of systemic arterial function is widely available, and a close relation of endothelial function in the coronary and brachial arteries has been documented. It is unknown, however, whether a similar correlation exists for their 2 microcirculatory territories and thus whether assessment of the systemic microcirculation can be used similarly as a surrogate marker of myocardial perfusion.

METHODS AND RESULTS

Twenty-three patients with documented coronary artery disease (CAD; 66+/-9 years old, 18 men), 16 patients with syndrome X (SX; 56+/-5 years old, 13 women), and 45 healthy control subjects (C; 34+/-9 years old, 22 men) were studied. Myocardial perfusion was measured at rest and after dipyridamole (0.56 mg. kg(-1). min(-1) over 4 minutes) by PET, and brachial artery blood flow was measured at rest and after transient forearm ischemia by standard Doppler ultrasound techniques. Dipyridamole increased myocardial perfusion in all groups (mL. g(-1). min(-1): CAD, 0.89+/-0.27 versus 1.62+/-0.67, P:<0.001; SX, 0.82+/-0.16 versus 1.67+/-0.49, P:<0.001; and C, 0.82+/-0.15 versus 2.32+/-0.64, P:<0.001). Postocclusion forearm flow increased similarly in all groups (CAD, 52+/-18 versus 174+/-77 mL/min, P:<0.001; SX, 49+/-29 versus 202+/-82 mL/min, P:<0.001; and C, 61+/-34 versus 229+/-108 mL/min, P:<0.001). No significant correlations were found between peripheral and myocardial microcirculatory beds for either resting flow, hyperemic flow, or flow reserve in any of the groups (r(2)<0.1, P:=NS).

CONCLUSIONS

The peripheral perfusion responses to transient forearm ischemia do not correlate with dipyridamole-induced myocardial hyperemia. The lack of correlation indicates different mechanisms of microvascular activation or regulation and confirms that extrapolations between findings in the 2 vascular beds are not suitable.

Coronary flow reserve: measurement with transthoracic Doppler echocardiography is reproducible and comparable with positron emission tomography

Detection of early vascular changes indicated by lowered coronary flow reserve (CFR) would allow early treatment and prevention of atherosclerosis. The purpose of this study was to test whether it is possible to reproducibly measure CFR with transthoracic Doppler echocardiography (TTE) in healthy volunteers. We measured CFR using dipyridamole infusion in ten healthy male volunteers with two methods: TTE and positron emission tomography (PET) with oxygen-15-labelled water (group A). However, CFR was assessed twice with TTE in eight healthy male volunteers (group B) to study the reproducibility of this method. We compared CFRs obtained using TTE flow measurements in the left anterior descending coronary artery (LAD) and PET flow measurements in the corresponding myocardial area. Coronary flow in LAD could be measured in all subjects using TTE. By TTE, an average CFR based on peak diastolic flow velocity (PDV) was 2.72 +/- 1.16, mean diastolic flow velocity (MDV) 2.56 +/- 1.06 and velocity time integral (VTI) 1.87 +/- 0.49. The results were reproducible in two repeated TTE studies (coefficient of variation in MDV 6.1 +/- 4.3%, n=8). By PET, CFR was 2.52 +/- 0.84. CFR assessed by TTE correlated closely with that measured by PET (MDV r=0.942, P<0.001; PDV r=0.912, P<0.002 and VTI r=0.888, P<0.006) and intraclass correlation was 0.929 (MDV) and tolerance limits for differences of CFRs was -0.78 to 0.72. We show that CFR measured by TTE has an excellent correlation with CFR measured by PET. We also found that TTE measurements of CFR were highly reproducible.

Role of relative myocardial perfusion reserve for evaluating stenosis severity in patients with single-vessel coronary artery disease using

A statistically significant correlation was observed between the severity of anatomic stenosis and coronary flow reserve in experimental animals. A similar correlation in human coronary artery disease (CAD) was shown using positron emission tomography (PET) and pharmacologic vasodilator stress. The present study tested whether the concept of relative myocardial perfusion reserve (MPR) might be superior to absolute MPR in correlating coronary stenosis determined by quantitative coronary arteriography in patients with single vessel CAD using [13N]ammonia and PET. The study group comprised 21 patients (62 +/-10 years old; 15 men, 6 women) with normal left ventricular function who underwent angioplasty for isolated left anterior descending coronary artery stenosis. Absolute MPR, the ratio of dipyridamole-induced hyperemic blood flow to baseline blood flow by [13N]ammonia PET, and relative MPR, the ratio of MPR in regions supplied by stenosed coronary arteries to MPR in remote regions, were measured before and 3 months after angioplasty. The percent diameter stenosis was also quantified on coronary arteriograms just before the angioplasty and again at 3 months after. The study found that absolute MPR (r=0.755; p<0.0001) and relative MPR (r=0.814; p<0.0001) were inversely and nonlinearly correlated with the percent stenosis on angiography. The fitting curve of the correlation between relative MPR and coronary stenosis on angiography was identical to that observed in animal models. Therefore, relative MPR measured by [13N]ammonia PET more accurately and specifically describes stenosis severity in patients with CAD compared with absolute MPR, probably because of its independence from hemodynamic variations and the effects of coronary risk factors.

Testing for endothelial dysfunction

Endothelial health is a key factor in normal cardiovascular homeostasis, and recent studies have revealed several important functions of the vascular endothelium that protect against atherothrombosis. These include control over arterial tone, coagulation, fibrinolysis, and vascular growth. Consequently, endothelial dysfunction has been implicated as an important event in the pathogenesis of atherosclerosis, coronary vasoconstriction, hypertension, and myocardial ischaemia. Therefore, there has been considerable research interest in diagnostic assays for the assessment of endothelium. This review outlines the current status of markers of endothelial dysfunction, particularly those related to vasomotor control, as well as circulating markers of vascular health.

Reverse cholesterol transport in diabetes mellitus

There are epidemiological data and experimental animal models relating the development of premature atherosclerosis with defects of the reverse cholesterol transport (RCT) system. In this regard, the plasma concentrations of the high density lipoprotein (HDL) subfractions, of cholesteryl ester transfer protein (CETP), as well as the activity of the enzyme lecithin-cholesterol acyl transferase (LCAT) play critical roles. However, there has been plenty of evidence that atherosclerosis in diabetes mellitus (DM) is ascribed to a greater arterial wall cell uptake of modified apoB-containing lipoproteins whereas a primary or predominant defect of the RCT system is still a subject of debate. In other words, in spite of the fact that in DM the composition and rates of metabolism of the HDL particles are greatly altered and display a diminished in vitro efficiency to remove cell cholesterol, definitive in vivo demonstration of the importance of this fact in atherogenesis is lacking. Furthermore, the roles played by LCAT and CETP in RCT in DM are difficult to interpret because the in vitro procedures of measurement utilized have either been inadequate, or inappropriately interpreted. Knock-out or transgenic mice are much needed models to investigate the roles of LCAT, CETP, phospholipid transfer protein (PLTP), and of a CETP inhibitor in the development of atherosclerosis of experimental DM.

Impaired coronary microvascular function in diabetics

Global and regional myocardial uptake was determined with technetium-99m tetrofosmin and a 4 hour exercise (370 MBq i.v.) and rest (740 MBq i.v.) protocol, in 24 patients with non-insulin dependent diabetes mellitus and in 22 control subjects. The purpose of this study was to evaluate impaired coronary microvascular function in diabetics by measurement of % uptake increase in myocardial counts. The parameter of % uptake increase (deltaMTU) was calculated as the ratio of exercise counts to rest myocardial counts with correction of myocardial uptake for dose administered and physical decay between the exercise study and the rest study. Global deltaMTU was significantly lower in the diabetics than in control subjects (14.4 +/- 5.4% vs. 21.7 +/- 8.5%, p < 0.01). Regional deltaMTU in each of 4 left ventricular regions (anterior, septal, inferior, posterolateral) was significantly lower in the diabetic group than in the control group (p < 0.01) respectively, but there were no significant differences between deltaMTU in the 4 left ventricular regions in the same group. deltaMTU was useful as a non-invasive means of evaluating impaired coronary microvascular function in diabetics.

PET as a cardiovascular and metabolic research tool

Positron emission tomography (PET) represents the most advanced scintigraphic imaging technology. It can be employed for cardiovascular research as well as for clinical applications in patients with various cardiovascular diseases. PET allows the noninvasive functional assessment of myocardial perfusion, substrate metabolism and cardiac innervation as well as the study of skeletal muscle metabolism and perfusion in vivo. The large number of existing tracers and the flexibility of the PET technique that allows it to be combined with many other methods, such as the insulin clamp technique, increase its potential as a research tool. In the detection of myocardial viability PET is regarded as the golden standard, and it is the only method available for the quantitative assessment of myocardial blood flow.

Reduced myocardial flow reserve does not impair exercise capacity in asymptomatic men

We examined whether impaired coronary flow reserve in healthy men is associated with changes in cardiac performance and exercise-induced ischemia. A comparison between 7 asymptomatic men with low flow reserve (<3.5) and 8 men with normal flow reserve (>3.5) showed no differences in these parameters, suggesting that the mechanisms that control myocardial blood flow during exercise remain normal despite the alterations in the mechanisms that control the vasodilatory reaction to dipyridamole.

Effects of autonomic neuropathy on coronary blood flow in patients with diabetes mellitus

BACKGROUND

C ardiac sympathetic signals play an important role in the regulation of myocardial perfusion. We hypothesized that sympathetically mediated myocardial blood flow would be impaired in diabetics with autonomic neuropathy.

METHODS AND RESULTS

We studied 28 diabetics (43+/-7 years old) and 11 age-matched healthy volunteers. PET was used to delineate cardiac sympathetic innervation with [(11)C]hydroxyephedrine ([(11)C]HED) and to measure myocardial blood flow at rest, during hyperemia, and in response to sympathetic stimulation by cold pressor testing. The response to cardiac autonomic reflex tests was also evaluated. Using ultrasonography, we also measured brachial artery reactivity during reactive hyperemia (endothelium-dependent dilation) and after sublingual nitroglycerin (endothelium-independent dilation). Based on [(11)C]HED PET, 13 of 28 diabetics had sympathetic-nerve dysfunction (SND). Basal flow was regionally homogeneous and similar in the diabetic and normal subjects. During hyperemia, the increase in flow was greater in the normal subjects (284+/-88%) than in the diabetics with SND (187+/-80%, P=0.084) and without SND (177+/-72%, P=0.028). However, the increase in flow in response to cold was lower in the diabetics with SND (14+/-10%) than in those without SND (31+/-12%) (P=0.015) and the normal subjects (48+/-24%) (P<0.001). The flow response to cold was related to the myocardial uptake of [(11)C]HED (P<0.001). Flow-mediated brachial artery dilation was impaired in the diabetics compared with the normal subjects, but it was similar in the diabetics with and without SND.

CONCLUSIONS

Diabetic autonomic neuropathy is associated with an impaired vasodilator response of coronary resistance vessels to increased sympathetic stimulation, which is related to the degree of SND.

Improvement of impaired myocardial vasodilatation due to diffuse coronary atherosclerosis in hypercholesterolemics after lipid-lowering therapy

BACKGROUND

Diminished myocardial vasodilatation (MVD) in hypercholesterolemics without overt coronary stenosis has been reported. However, whether the diminished MVD of angiographically normal coronary arteries in hypercholesterolemics can be reversed after lipid-lowering therapy is not known.

METHODS AND RESULTS

A total of 27 hypercholesterolemics and 16 age-matched controls were studied. All patients had >1 normal coronary artery, and those segments that were perfused by anatomically normal coronary arteries were studied. Myocardial blood flow (MBF) was measured during dipyridamole loading and at baseline using positron emission tomography and 13N-ammonia, after which MVD was calculated before and after lipid-lowering therapy. Total cholesterol was significantly higher in hypercholesterolemics (263+/-33.8) than in controls (195+/-16.6), and it normalized after lipid-lowering therapy (197+/-19.9). Baseline MBF (ml. min-1. 100 g-1) was comparable among hypercholesterolemics (both before and after therapy) and controls. MBF during dipyridamole loading was significantly lower in hypercholesterolemics before therapy (189+/-75.4) than in controls (299+/-162, P<0.01). However, MBF during dipyridamole loading significantly increased after therapy (226+/-84.7; P<0.01). MVD significantly improved after therapy in hypercholesterolemics (2.77+/-1.35 after treatment [P<0.05] versus 2. 02+/-0.68 before treatment [P<0.01]), but it remained significantly higher in controls (3.69+/-1.13, P<0.01). There was a significant relationship between the percent change of total cholesterol and the percent change of MVD before and after lipid-lowering therapy (r=-0. 61, P<0.05).

CONCLUSIONS

Diminished MVD of anatomically normal coronary arteries in hypercholesterolemics can be reversed after lipid-lowering therapy.

Coronary flow reserve in young men with familial combined hyperlipidemia

BACKGROUND

Familial combined hyperlipidemia (FCHL) is a common hereditary disorder of lipoprotein metabolism estimated to cause 10% to 20% of premature coronary heart disease. We investigated whether functional abnormalities exist in coronary reactivity in asymptomatic patients with FCHL.

METHODS AND RESULTS

We studied 21 male FCHL patients (age, 34.8+/-5.4 years) and a matched group of 21 healthy control subjects. Myocardial blood flow (MBF) was measured at baseline and during dipyridamole-induced hyperemia with PET and 15O-labeled water. The baseline MBF was similar in patients and control subjects (0.79+/-0.19 versus 0.88+/-0.20 mL. g-1. min-1, P=NS). An increase in MBF was seen in both groups after dipyridamole infusion, but MBF at maximal vasodilation was lower in FCHL patients (3.54+/-1.59 versus 4.54+/-1.17 mL. g-1. min-1, P=0.025). The difference in coronary flow reserve (CFR) was not statistically significant (4.7+/-2.2 versus 5.3+/-1.6, P=NS, patients versus control subjects). Considerable variability in CFR values was detected within the FCHL group. Patients with phenotype IIB (n=8) had lower flow during hyperemia (2.5+/-1.2 versus 4.2+/-1.5 mL. g-1. min-1, P<0.05) and lower CFR (3.4+/-2.1 versus 5.4+/-2.0, P<0.05) compared with phenotype IIA (n=13).

CONCLUSIONS

Abnormalities in coronary flow regulation exist in young asymptomatic FCHL patients expressing phenotype IIB (characterized by abnormalities in both serum cholesterol and triglyceride concentrations). This is in line with previous observations suggesting that the metabolic abnormalities related to the pathophysiology of FCHL are associated with the phenotype IIB.