Effects of short-term treatment of hyperlipidemia on coronary vasodilator function and myocardial perfusion in regions having substantial impairment of baseline dilator reverse

Coronary circulation: Pressure/flow parameters for assessment of ischemic heart disease

Both invasive and non-invasive parameters have been reported for assessment of the physiological status of the coronary circulation. Fractional flow reserve and coronary (or myocardial) flow reserve may be obtained by invasive or non-invasive means. These metrics of coronary stenosis severity have achieved wide clinical acceptance for guiding revascularization decisions and risk stratification. Other indices are obtained invasively (e.g., instantaneous wave-free ratio, iFR; hyperemic stenosis resistance) or non-invasively (e.g., PET absolute myocardial blood flow (mL/min/g)) and have been used for the same purposes. Both iFR, and whole-cycle distal coronary to aortic mean pressure (Pd/Pa) are measured under basal condition and used for assessment of hemodynamic stenosis severity as is index of basal stenosis resistance (BSR). These metrics typically are dichotomized at an empirically derived cut point into "normal" and "abnormal" categories for purposes of clinical decision making and data analysis. Once dichotomized the indices do not always point in the same direction and so confusion may arise. This review, therefore, will present basic principles relevant to understanding commonly employed metrics of the physiological status of the coronary circulation, potential strengths and weaknesses, and hopefully an improved appreciation of the clinical information provided by each.

Short-term Lipid-Lowering Treatment with Atorvastatin Improves Renal Function But Not Renal Blood Flow Indices in Patients with Peripheral Arterial Disease

Some studies have suggested that lipid lowering with statins exerts favorable effects on the progression of chronic kidney disease. Therefore, the authors assessed the effects of short-term atorvastatin treatment on biochemical markers of renal function and evaluated duplex indices of renal blood flow (RBF) in patients with peripheral arterial disease. Hyperlipidemic claudicants (n=18), aged 44-85 years, were treated for 8 weeks with 20 mg/day atorvastatin. Blood tests at baseline and after 8 weeks included serum fasting lipids, creatinine, urate, and cystatin C (a sensitive indicator of renal function) levels. RBF was also assessed (n=9) by measuring pulsatile and resistance duplex indices. As expected, there was a significant improvement in total cholesterol, low-density lipoprotein cholesterol, and triglycerides. There was also a significant (p<0.0001) fall in serum creatinine from 89 (58-125) to 79 µmol/L (54-119) and an increase in calculated creatinine clearance (CrCl) from 72 (40-129) to 80 mL/minute (47-138; p<0.0001). Serum cystatin C values decreased significantly (p=0.0002) from 1.04 (0.57-1.56) to 0.90 mg/L (0.47-1.47). There were no detectable changes in the RBF duplex indices. Treatment of stable claudicants with atorvastatin for 8 weeks was associated with improved renal function (as assessed by serum creatinine, cystatin C, and calculated CrCl) without changes in RBF. Further studies are required to identify the mechanisms involved in this phenomenon.

The Effect of Short-Term Treatment with Simvastatin on Renal Function in Patients with Peripheral Arterial Disease

The objective of this study was to investigate the effects of lipid-lowering treatment on renal function in patients with peripheral arterial disease (PAD). This was a retrospective study of hyperlipidemic claudicants referred to a vascular surgery and risk modification clinic. Serum creatinine and urate concentrations and the fasting lipid profile were measured pretreatment and after 3-4 months of treatment with 20 mg/day simvastatin. In 103 consecutive patients with PAD (57 men; 46 women), median age 67 years (range: 51 to 83) there was a significant decrease in serum creatinine from a mean (SD) of 87 (12) μmol/L pretreatment to 84 (12) μmol/L post-treatment (p<0.0001). This difference was more marked in the tertile of patients with the highest baseline creatinine levels. There was also a significant reduction in serum urate from 0.37 (0.07) mmol/L to 0.35 (0.07) mmol/L (p<0.0001). Both these effects were independent of the degree of total cholesterol (TC) or low-density lipoprotein (LDL) cholesterol reduction. There was a significant reduction in TC from 6.6 (1.0) to 5.2 (0.8) mmol/L and LDL cholesterol from 4.3 (1.0) to 2.8 (0.7) mmol/L; both p<0.0001. Significant improvement also occurred in the high-density lipoprotein cholesterol and triglyceride levels. Cholesterol lowering with simvas tatin 20 mg/day improved indices of renal function after 3-4 months of treatment in hyper lipidemic patients with PAD. Further studies are needed to establish and define the clinical relevance of these findings, especially in patients with different degrees of renal failure.

Cardiac PET-CT for monitoring medical and interventional therapy in patients with CAD: PET alone versus hybrid PET-CT?

This review focuses on optimal use of PET and PET-CT in monitoring medical and interventional therapy in patients with CAD. PET provides quantitative measurement of absolute myocardial blood flow and thus permits comprehensive physiological assessment of the coronary circulation. Hybrid PET-CT, in particular CCTA, adds anatomical information to maximal MBF measurement and so facilitates distinction of triple vessel focal epicardial disease from coronary microvascular disease or diffuse coronary atherosclerosis without focal stenoses. Hybrid PET-CT also may be of value in determining appropriateness and feasibility of percutaneous interventional therapy for chronic total coronary occlusion. PET alone, however, is the preferred modality to address functional status of the coronary circulation and response over time, if required, to medical or interventional therapy. CT at a minimum provides attenuation correction. More detailed CCTA should be added only when a well-defined need for anatomical information is required to answer the clinical question posed.

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

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

Quantitative cardiac positron emission tomography: the time is coming!

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

Effect of lovastatin therapy and withdrawal on serum uric acid level in people with type 2 diabetic nephropathy

BACKGROUND/AIM

A high uric acid (UA) level is demonstrated as a major risk factor of nephropathy and cardiovascular events in people with type 2 diabetes (T2D). This study aimed to evaluate the lovastatin effect on serum UA levels in people with type 2 diabetic nephropathy (T2DN).

METHODS

Thirty patients completed the study course, out of 38 adult male patients with T2DN who were initially enrolled. Lovastatin, 20 mg/d, was administered for 90 days. Afterwards, lovastatin was withdrawn for the next 30 days. Blood samples were obtained at baseline, after 45 and 90 days of intervention, and 30 days after the withdrawal of lovastatin. The serum level of UA was assessed by the uricase/PAP method. The lipid profile and high-sensitivity C-reactive protein (hs-CRP) were determined using commercial reagents and the ELISA method.

RESULTS

After 90 days of lovastatin intervention, cholesterol (Chol) and low-density lipoprotein cholesterol (LDL-C) levels significantly decreased and the high-density lipoprotein cholesterol (HDL-C) level increased significantly, despite the unchanged level of triglyceride (TG). After withdrawal, Chol, TG, and LDL-C levels were significantly increased, without any change in the HDL-C level. The baseline serum UA level was 5.94 ± 2.02 mg/dL and not changed after the intervention (5.95 ± 2.21 mg/dL; p = 0.969) and withdrawal period (5.80 ± 1.51 mg/dL; p = 0.647). The changes of serum UA levels were not correlated with the changes of serum hs-CRP levels, both after intervention and withdrawal (p = 0.963 & p = 0.835).

CONCLUSIONS

Lovastatin does not have any effect on the serum UA level in people with T2DN. There is no correlation between the anti-lipidemic and anti-inflammatory effects of lovastatin and its effect on serum UA.

PET measurement of adenosine stimulated absolute myocardial blood flow for physiological assessment of the coronary circulation

Considerable awareness has been raised of late of the need to reduce radiation exposure and control costs of x-ray and radionuclide imaging procedures. PET/CT cameras are now widely available and in conjunction with appropriate radionuclides and commercially available software make quantitative measurement of absolute MBF feasible for routine clinical practice. Quantitative measurement of absolute MBF under condition of coronary vasodilation permits independent assessment of the functional status of each of the three major coronary perfusion zones and so obviates the need for rest MBF determination in the great majority of cases. Coronary microvascular function also may be assessed in this same way. Thus, the stress-only protocol with quantitative PET measurement of MBF provides essential information required for clinical decision making related to need for catheterization and intervention for patients with known or suspected ischemic heart disease. Moreover, the single PET determination of maximal MBF in contrast to the usual rest/stress procedure addresses both safety and cost concerns. The present review focuses on: (1) quantitative PET measurements of myocardial blood flow for physiological assessment of the coronary circulation and (2) the value and potential limitations of performing stress only imaging in the clinical context.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effects of three strong statins (atorvastatin, pitavastatin, and rosuvastatin) on serum uric acid levels in dyslipidemic patients

We have retrospectively investigated the effects of three strong statins, atorvastatin, pitavastatin, and rosuvastatin, on serum uric acid (SUA) levels. SUA levels after a few months of statin treatment were compared with those before treatment in 150 outpatients with dyslipidemia. In the atorvastatin (n = 62) and rosuvastatin (n = 45) groups, the SUA levels were reduced by 6.5% (p < 0.0001) and 3.6% (p = 0.03) respectively, but in the pitavastatin group (n = 43), the SUA level increased by 3.7% (p = 0.38). Because uric acid is considered a risk factor for cardiovascular disorders, atorvastatin or rosuvastatin treatment may be recommended when statins are used in patients at high risk for cardiovascular disorders complicated with hyperuricemia.

Short-term exercise training prevents micro- and macrovascular disease following coronary stenting

The purpose of this study was to determine the effects of exercise on coronary blood flow and macrovascular atherosclerosis in response to stent deployment. Male Yucatan swine were placed on a control diet (C); on a high-fat/cholesterol diet (hypercholesterolemic; H); or on a high-fat/cholesterol diet and aerobically exercise trained (HX) starting after 36 wk on the diet. All pigs underwent coronary angiography and intravascular ultrasound (IVUS) guided placement of a bare metal stent in the circumflex coronary artery after 40 wk on diets and 3 wk later pigs underwent repeat angiography and IVUS and coronary blood flow (CBF) measurement. Average peak velocity (APV) was measured under basal conditions and in response to intracoronary application of the endothelium-independent vasodilator adenosine and the endothelium-dependent vasodilator bradykinin. There was a similar approximately 8-fold increase in total cholesterol in H and HX compared with control. Baseline CBF was increased above control and H in HX (P<0.05). At all doses adenosine-induced CBF was impaired in H, but preserved in HX. Similarly, bradykinin-induced CBF was impaired in H vs. control, yet was potentiated in HX. Microvessel density was decreased in H and preserved in HX vs. control. Native atheroma in HX was lower relative to H and control, while in-stent stenosis in HX was not different from H. Hyperlipidemia-induced microvascular dysfunction after stent deployment may be a result of reduction in microvessel density. This is the first report that short-term exercise training near the time of stenting prevents stent-induced microvascular dysfunction and attenuates native atheroma independent of changes in plasma cholesterol in this porcine model.

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

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

Comparison of positron emission tomography measurement of adenosine-stimulated absolute myocardial blood flow versus relative myocardial tracer content for physiological assessment of coronary artery stenosis severity and location

OBJECTIVES

This study tests the hypothesis that absolute measurement of adenosine (Ado)-stimulated myocardial blood flow (MBFado) is superior to measurement of relative tracer uptake for identification of hemodynamically significant coronary artery disease (CAD).

BACKGROUND

Positron emission tomography measurement of absolute myocardial blood flow (MBF) ((13)N-ammonia) with Ado has the capability to more accurately assess hemodynamic severity of CAD than measurement of relative tracer content (TC) (nCi/ml) during Ado, which by definition depends on at least 1 normal zone to which others are compared.

METHODS

A total of 27 patients (20 male, 58 +/- 11 years, mean +/- SD) with known or suspected CAD and 21 normal subjects (13 male, 38 +/- 10 years) were studied. Parametric (K1) MBF images and TC sum images were analyzed. A stenosis > or =70% defined significant CAD. The receiver-operator characteristic curve (ROC) analysis area under the curve (AUC) compared MBF and TC results. Cut-point analysis for sensitivity, specificity, and accuracy showed the best MBF criteria for CAD as MBFado <1.85 ml/min/g and the best TC as <70% maximum. The myocardial blood flow reserve ratio (MBFR) (optimal <2.0x) also was studied.

RESULTS

The ROC analysis of PET parameters showed that MBFado was superior to <70% maximum uptake for CAD detection (n = 144 vessels; AUC 0.900 vs. 0.690, respectively, p < 0.0001) and was marginally greater than MBFR (0.856; p = 0.10). For CAD cut-point analysis, MBFado accuracy exceeded TC (0.84 vs. 0.72, respectively, p = 0.005), as did sensitivity (0.81 vs. 0.48, respectively; p = 0.001). Specificity of MBFado for CAD classification (0.85) was comparable to TC (0.82; p = NS). Sensitivity, specificity, and predictive accuracy for MBFR were 0.62, 0.85, and 0.79, respectively. The difference in specificity was not significant versus MBFado. However, MBFado was more sensitive than MBFR (p = 0.01). The difference in predictive accuracy was borderline (p = 0.06) in favor of MBFado.

CONCLUSIONS

Measurement of Ado-stimulated absolute MBF is superior to relative measurement of myocardial tracer retention for identification of CAD and can be accomplished with a single MBFado measurement.

Preinjury statin use is associated with a higher risk of multiple organ failure after injury: a propensity score adjusted analysis

BACKGROUND

Recent studies suggest that statin use may improve outcome in critically ill patients. This has been attributed to the pleiomorphic effect and modulation of inflammatory mediators that occurs with statin use. We sought to determine whether preinjury statin (PIS) use was associated with improved outcome in severely injured blunt trauma patients.

METHODS

Data were obtained from a multicenter prospective cohort study evaluating outcomes in blunt injured adults with hemorrhagic shock. Patients aged 55 years and older were analyzed. Those with isolated traumatic brain injury, cervical cord injury, and those who survived <24 hours were excluded. A propensity score predicting statin use was created using logistic regression. Cox proportional hazard regression was then used to evaluate the effects of PIS use on mortality and the development of multiple organ failure (MOF, multiple organ dysfunction syndrome >5) and nosocomial infection (NI) after adjusting for important injury characteristics and the propensity of taking PISs.

RESULTS

Overall mortality and MOF rates for the study cohort (n = 295) were 21% and 50%, respectively. Over 24% of patients (n = 71) reported PIS use. Kaplan-Meier analysis revealed no difference in NI or mortality over time but did show a significant higher incidence of MOF in those with PIS use (p = 0.04). Regression analysis verified PIS was independently associated with an 80% higher risk of MOF (hazard ratio: 1.8; 95% confidence interval, 1.1-2.9) and was found to be one of the strongest independent risk factors for the development of MOF.

CONCLUSION

PIS use was independently associated with a higher risk of MOF postinjury. These results are contrary to previous analyses. The protective effect of statins may be lost in the severely injured, and modulation of the inflammatory response may result in higher morbidity. Further studies are required to better understand the impact and potential therapeutic utility of this commonly prescribed medication both before and after injury.

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.

Assessment of regional systolic and diastolic functions affected by atorvastatin in coronary artery disease using tissue Doppler imaging

BACKGROUND

Several studies have shown regional left ventricular (LV) systolic and diastolic changes associated with coronary artery disease (CAD). Statins may have beneficial pleiotropic effects in addition to their lipid-lowering properties.

HYPOTHESIS

We hypothesized that atorvastatin can improve regional LV systolic and diastolic functions in CAD patients using tissue Doppler imaging (TDI).

METHODS

A total of 63 patients with hyperlipemia and CAD were studied. Forty-three patients were given 10 mg daily of atorvastatin and 20 patients were assigned only a low-fat diet. Tissue Doppler imaging was applied to evaluate LV peak systolic velocity (VS), early diastolic velocity (VE), and late diastolic velocity (VA) in 18 segments. The mean value of LV peak systolic velocity (VS(')), the mean value of early diastolic velocity (VE(')), and the mean value of late diastolic velocity (VA(')), in 18 segments were calculated.

RESULTS

Compared with the baseline, VS('), and VE('), increased significantly after the therapy in the atorvastatin group (p < 0.05), while there was no change in the control group (p > 0.05). At 6 mo of therapy, a significant reduction in total cholesterol, triglyceride, and low-density lipoprotein (LDL) cholesterol was observed in the 2 groups (p < 0.05).

CONCLUSIONS

These findings demonstrate that atorvastatin can improve regional LV systolic and diastolic functions in CAD patients independent of its lipid-lowering properties.

Increase in fasting vascular endothelial function after short-term oral L-arginine is effective when baseline flow-mediated dilation is low: a meta-analysis of randomized controlled trials

BACKGROUND

Previous trials suggest that oral l-arginine administration affects endothelial function. However, most of these studies were small, the conclusions were inconsistent, and the precise effects are therefore debatable.

OBJECTIVE

The objective was to assess the effect of oral l-arginine supplementation on endothelial function, as measured with the use of fasting flow-mediated dilation (FMD).

DESIGN

We conducted a meta-analysis of randomized, placebo-controlled l-arginine supplementation trials that evaluated endothelial function. Trials were identified in PubMed, Cochrane Library, Embase, reviews, and reference lists of relevant papers. The weighted mean difference (WMD) was calculated for net changes in FMD by using random-effect models. Previously defined subgroup analyses and meta-regression analyses were performed to explore the influence of study characteristics.

RESULTS

Thirteen trials were included and evaluated. Because there was only one long-term study, we focused on short-term effects of l-arginine (12 studies, 492 participants). In an overall pooled estimate, l-arginine significantly increased FMD (WMD: 1.98%; 95% CI: 0.47, 3.48; P = 0.01). Meta-regression analysis indicated that the baseline FMD was inversely related to effect size (regression coefficient = -0.55; 95% CI: -1.00, -0.1; P = 0.016). A subgroup analysis suggested that l-arginine supplementation significantly increased FMD when the baseline FMD levels were <7% (WMD: 2.56%; 95% CI: 0.87, 4.25; P = 0.003), but had no effect on FMD when baseline FMD was >7% (WMD: -0.27%; 95% CI: -1.52, 0.97; P = 0.67).

CONCLUSION

Short-term oral l-arginine is effective at improving the fasting vascular endothelial function when the baseline FMD is low.

A review of methods for assessment of coronary microvascular disease in both clinical and experimental settings

Obstructive disease of the large coronary arteries is the prominent cause for angina pectoris. However, angina may also occur in the absence of significant coronary atherosclerosis or coronary artery spasm, especially in women. Myocardial ischaemia in these patients is often associated with abnormalities of the coronary microcirculation and may thus represent a manifestation of coronary microvascular disease (CMD). Elucidation of the role of the microvasculature in the genesis of myocardial ischaemia and cardiac damage-in the presence or absence of obstructive coronary atherosclerosis-will certainly result in more rational diagnostic and therapeutic interventions for patients with ischaemic heart disease. Specifically targeted research based on improved assessment modalities is needed to improve the diagnosis of CMD and to translate current molecular, cellular, and physiological knowledge into new therapeutic options.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Methodology for quantifying absolute myocardial perfusion with PET and SPECT

Noninvasive quantitative measurement of myocardial perfusion has played an important role in cardiac research and also has potential applications in clinical imaging. Positron emission tomography (PET) methods for measuring absolute perfusion are well established, although the need for an on-site cyclotron has restricted its use to a limited number of centers. Single-photon emission CT (SPECT) also has potential for quantifying myocardial perfusion and has more widespread availability. In this article we review the basic principles of absolute myocardial perfusion quantification and the radiopharmaceuticals that are available for both PET and SPECT. We also examine the extent to which recent developments in instrumentation have increased the practicality of absolute perfusion quantification in PET and the potential for absolute quantification in SPECT.

Myocardial blood flow and oxygen consumption in patients with Friedreich's ataxia prior to the onset of cardiomyopathy

OBJECTIVES

We tested the hypothesis, in patients with Friedreich's ataxia and no overt structural heart disease, that impairment of cardiac oxidative metabolism may be compensated for either by increased rest myocardial blood flow or more efficient oxygen consumption in performance of external work.

BACKGROUND

Friedreich's ataxia is characterized by a mutant frataxin gene, which causes mitochondrial iron overload and impaired energy production. Further, it is frequently associated with cardiomyopathy. Studies using magnetic resonance spectroscopy, however, suggest impaired cardiac energetics even in the absence of structural heart disease.

METHODS

Positron emission tomography measured rest myocardial blood flow (N-13-ammonia method) and myocardial oxygen consumption (11-C-acetate, Kmono) in Friedreich's ataxia patients (n=8; 31+/-5 years, mean+/-SD, four women) and healthy controls (n=8; 30+/-7 years, five women) matched for stroke work index and age. Stroke work index and power were determined by electrocardiogram gated positron emission tomography N-13-ammonia using modified Simpson's rule to compute left ventricular volumes.

RESULTS

Neither stroke work index nor rest myocardial blood flow differed significantly between the groups. Although myocardial oxygen consumption was lower in Friedreich's ataxia (P<0.001), Kmono/rest myocardial blood flow, an index of myocardial oxygen extraction, did not differ between the groups. Power/Kmono, an index of the efficiency of myocardial oxygen consumption, was greater in Friedreich's ataxia (P<0.04). Rest myocardial blood flow normalized to rate pressure product was lower in Friedreich's ataxia (P<0.05).

CONCLUSIONS

Prior to the onset of cardiomyopathy, selected patients with Friedreich's ataxia may compensate for impaired cardiac energetics through more efficient oxygen consumption rather than increased rest myocardial blood flow. The data illustrate a more general mechanism pertaining to metabolic regulation of myocardial blood flow and myocardial oxygen consumption.

Statin Therapy at Carotid Angioplasty and Stent Placement: Effect on Procedure-related Stroke, Myocardial Infarction, and Death

PURPOSE

To retrospectively determine if preprocedural statin treatment is associated with a reduction of cardiovascular events after carotid angioplasty and stent placement (CAS) in patients with symptomatic carotid stenosis.

MATERIALS AND METHODS

A study resulting in a prospective database was approved by the institutional ethics review board; written informed consent was obtained. The approval and informed consent included future retrospective analysis. Consecutive patients (n = 180) from the prospective database underwent CAS for high-grade symptomatic carotid disease. The frequency of cardiovascular complications (composite of stroke, myocardial infarction, and death within 30 days after CAS) between 127 patients without preprocedural statin treatment and that of 53 patients with preprocedural statin treatment at CAS were compared with chi2 and multivariate logistic regression analysis.

RESULTS

The overall 30-day myocardial infarction rate was two of 180 (1%) patients, the minor stroke rate was 16 of 180 (9%) patients, the major stroke rate was one of 180 (0.5%) patients, and the death rate was two of 180 (1%) patients. The incidence of cardiovascular events (composite of stroke, myocardial infarction, and death within 30 days after CAS) was significantly different between patients with preprocedural treatment (4%) and those without preprocedural statin treatment (15%) (P < .05). These higher complication rates among patients without preprocedural statin treatment were not mediated by adjustment for age, sex, other baseline characteristics, degree of carotid stenosis, use of cerebral protection devices, or the year in which CAS was performed.

CONCLUSION

Preprocedural statin therapy appears to reduce the incidence of stroke, myocardial infarction, and death within 30 days after CAS. Future prospective randomized trials are warranted to further assess this potential protective effect of statin drugs during carotid interventions.

Myocardial flow reserve is influenced by both coronary artery stenosis severity and coronary risk factors in patients with suspected coronary artery disease

PURPOSE

Myocardial flow reserve (MFR) measurement has an important role in assessing the functional severity of coronary artery stenosis. However, a discrepancy between the anatomical severity of coronary artery stenosis and MFR is often observed. Such a discrepancy may be explained by coronary risk factors. In this study, we aimed to investigate the influence of coronary artery stenosis severity and risk factors on MFR.

METHODS

Seventy-four patients suspected to have coronary artery disease and seven age-matched healthy volunteers were enrolled. Myocardial blood flow (MBF) and MFR were measured using 15O-labelled water PET. Regional MFR was calculated in regions with significant coronary artery stenosis (stenotic regions) and in regions without significant stenosis (remote regions). The contributions of coronary artery stenosis severity and coronary risk factors were assessed using univariate and multivariate analyses.

RESULTS

In stenotic regions, MFR correlated inversely with coronary artery stenosis severity (r=-0.50, p<0.01). Univariate analysis did not show any significant difference in MFR between the patients with and the patients without each risk factor. In remote regions, however, MFR was significantly decreased in the diabetes and smoking groups (each p<0.05). By multivariate analysis, diabetes and smoking were independent predictors of MFR (each p<0.05). In the group with more than one risk factor, MFR was significantly lower (2.78+/-0.79) than in the other group (3.40+/-1.22, p<0.05).

CONCLUSION

MFR is influenced not only by coronary stenosis severity but also by coronary risk factors. In particular, the influence of risk factors should be considered in regions without severe coronary stenosis.

Effect of simvastatin on coronary flow reserve in patients with atherosclerosis and hypercholesterolemia: an intracoronary Doppler study

BACKGROUND

Early stages of coronary atherosclerosis are accompanied by a functional impairment of coronary vasodilator capacity and endothelial dysfunction. Reduced coronary flow reserve has been reported in patients with hypercholesterolemia, despite angiographically normal coronary arteries. The aim of the study was to evaluate the effect of simvastatin on coronary flow reserve.

METHODS

The study was an open non-placebo-controlled serial investigation in which every patient acted as his own control: 36 male patients with hypercholesterolemia and a non-significant coronary artery lesion in a not previously revascularized coronary artery. Intracoronary Doppler measurements were performed. Coronary flow reserve, relative coronary flow reserve and average peak velocity were performed at baseline, after 3 months on a lipid-lowering diet (control period), and after another 12 months of simvastatin 40 mg/day. In the same patient cohort, significant reduction in lesion plaque plus media has been demonstrated by intravascular ultrasound.

RESULTS

Changes in coronary flow reserve were not influenced by either diet or simvastatin (2.5+/-0.6 vs. 2.6+/-0.5 vs. 2.6+/-0.6, P=ns). Maximum hyperemic flow (34.8+/-12.2 vs. 36.7+/-12.5 vs. 42.5+/-13.1, P<0.001) as well as resting flow (14.3+/-5.3 vs. 14.5+/-4.4 vs. 16.6+/-4.6, P<0.001) increased significantly after 12 months simvastatin therapy.

CONCLUSION

Despite plaque plus media, regression simvastatin therapy for 12 months does not affect coronary flow reserve obtained using serial intracoronary Doppler studies. Simvastatin, however, increases the hyperemic flow velocity.

Endothelial function and its assessment

Endothelial dysfunction is a characteristic aspect of most of the conditions associated with atherosclerosis and is commonly found as an early feature in atherothrombotic vascular disease. An appreciation of the underlying mechanisms of endothelial function, as well as dysfunction, is essential as this has critical influence on the different methods in the assessment of endothelial function and effects of various treatments on its quantification. Furthermore, endothelial dysfunction is recognised as a type of 'target organ damage' in common cardiovascular conditions (e.g., hypertension) and the area is of increasing interest for new drug development, as therapies that modulate the endothelium will have added advantages; thus, for the development of new/experimental drugs, an awareness of ways to assess the endothelium is necessary. In this review, an overview of different methods including biochemical markers, and invasive and non-invasive tools, to determine endothelial function is presented as well as their clinical relevance. Furthermore, the effects of various treatments on endothelial dysfunction and their underlying mechanisms are elucidated.

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.

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.

How aggressive should lipid lowering be among patients with acute coronary syndromes?

Results from recent clinical trials have advanced our understanding of the role of HMG-CoA reductase inhibitors (statins) in the management of patients following acute coronary syndrome (ACS) episodes. In aggregate, these trials have demonstrated the safety and efficacy associated with initiation of intensive statin therapy prior to hospital discharge following an ACS episode, independent of baseline low-density lipoprotein (LDL) cholesterol concentrations. Based on the results of these trials, there is now compelling evidence to support intensive lipid lowering with high-dose statins initiated prior to hospital discharge for all patients suffering ACS episodes with a target for LDL cholesterol of 70 mg/dL or lower, recommendations that have been incorporated into clinical practice guideline recommendations in the most recent position statement from the National Cholesterol Education Panel.

Early effects of statin therapy on endothelial function and microvascular reactivity in patients with coronary artery disease

BACKGROUND

Recent data suggest an early outcome benefit with reduction in cholesterol using statin therapy in patients with coronary artery disease (CAD). This may be caused by effects of low-density lipoprotein cholesterol (LDL-C) reduction on endothelial function and vascular reactivity in the coronary bed. The aim of this randomized placebo-controlled study was to examine the early effects of important reductions in LDL-C on myocardial perfusion and peripheral endothelial function.

METHODS AND RESULTS

Seventy-two patients with CAD and LDL-C between 3.0 and 5.9 mmol/L (116-228 mg/dL) were randomized to receive simvastatin 20 mg daily, pravastatin 40 mg daily, or placebo for 8 weeks. At baseline, 2 weeks, and 8 weeks, patients underwent dynamic positron emission tomography perfusion imaging to quantify the retention of rubidium-82 as a measure of myocardial flow at rest and after dipyridamole stress. Patients also underwent brachial artery ultrasound to measure endothelium-dependent flow-mediated vasodilatation. At 2 and 8 weeks, the simvastatin and pravastatin groups showed a significant reduction (P < .001) in LDL-C compared with placebo. At 8 weeks, simvastatin led to an improvement in flow-mediated vasodilatation compared with placebo (6.86% +/- 4.4% vs 3.44% +/- 4.0%, P < .05), whereas pravastatin was not significantly different than placebo (5.62% +/- 4.1% vs 3.44% +/- 4.0%, P = NS). Despite this improvement in peripheral endothelial function with simvastatin, there were no significant differences observed in global stress flow and coronary flow reserve at 8 weeks with either drug.

CONCLUSIONS

Short-term LDL reduction with simvastatin therapy improves peripheral endothelial function in patients with stable CAD, although an early effect on coronary vascular reactivity could not be demonstrated.

High-dose folic acid acutely improves coronary vasodilator function in patients with coronary artery disease

OBJECTIVES

We investigated the acute effect of orally administered high-dose folic acid on coronary dilator function in humans.

BACKGROUND

Folic acid and its active metabolite, 5-methyltetrahydrofolate, increase endothelium-dependent vasodilation in human peripheral circulation. However, the acute effect on coronary circulation is not known.

METHODS

Fourteen patients with ischemic heart disease, age 62 +/- 12 years (mean +/- SD), were enrolled in a double-blind, placebo-controlled crossover trial. Basal and adenosine-stimulated myocardial blood flow (MBF) were determined by positron emission tomography, and myocardial flow reserve was calculated. Each patient was studied after ingestion of placebo and after ingestion of 30 mg folic acid. Myocardial zones were prospectively defined physiologically as "normal" versus "abnormal" on the basis of MBF response to adenosine 140 microg/kg/min (normal = MBF >1.65 ml/min/g). Abnormal and normal zones were analyzed separately in a patient-based analysis.

RESULTS

Folate was associated with a reduction in mean arterial pressure (100 +/- 12 mm Hg vs. 96 +/- 11 mm Hg, placebo vs. folate, p < 0.03). Despite the fall in mean arterial pressure, folic acid significantly increased the MBF dose response to adenosine (p < 0.001 using analysis of variance) in abnormal zones, whereas MBF in normal zones did not change. In abnormal segments, folic acid increased peak MBF by 49% (1.45 +/- 0.59 ml/min/g vs. 2.16 +/- 1.01 ml/min/g, p < 0.02). Furthermore, folate increased dilator reserve by 83% in abnormal segments (0.77 +/- 0.59 vs. ml/min/g 1.41 +/- 1.08 ml/min/g, placebo vs. folate, p < 0.05), whereas dilator reserve in normal segments remained unchanged (2.00 +/- 0.61 ml/min/g vs. 2.12 +/- 0.69 ml/min/g, placebo vs. folate, p = NS).

CONCLUSIONS

The data demonstrate that high-dose oral folate acutely lowers blood pressure and enhances coronary dilation in patients with coronary artery disease.

Cardiac positron emission tomography imaging

Cardiac positron emission tomography (PET) imaging has advanced from primarily a research tool to a practical, high-performance clinical imaging modality. The widespread availability of state-of-the-art PET gamma cameras, the commercial availability of perfusion and viability PET imaging tracers, reimbursement for PET perfusion and viability procedures by government and private health insurance plans, and the availability of computer software for image display of perfusion, wall motion, and viability images have all been a key to cardiac PET imaging becoming a routine clinical tool. Although myocardial perfusion PET imaging is an option for all patients requiring stress perfusion imaging, there are identifiable patient groups difficult to image with conventional single-photon emission computed tomography imaging that are particularly likely to benefit from PET imaging, such as obese patients, women, patients with previous nondiagnostic tests, and patients with poor left ventricular function attributable to coronary artery disease considered for revascularization. Myocardial PET perfusion imaging with rubidium-82 is noteworthy for high efficiency, rapid throughput, and in a high-volume setting, low operational costs. PET metabolic viability imaging continues to be a noninvasive standard for diagnosis of viability imaging. Cardiac PET imaging has been shown to be cost-effective. The potential of routine quantification of resting and stress blood flow and coronary flow reserve in response to pharmacologic and cold-pressor stress offers tantalizing possibilities of enhancing the power of PET myocardial perfusion imaging. This can be achieved by providing assurance of stress quality control, in enhancing diagnosis and risk stratification in patients with coronary artery disease, and expanding diagnostic imaging into the realm of detection of early coronary artery disease and endothelial dysfunction subject to risk factor modification. Combined PET and x-ray computed tomography imaging (PET-CT) results in enhanced patient throughput and efficiency. The combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and noninvasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.

The effect of statins versus untreated dyslipidaemia on renal function in patients with coronary heart disease. A subgroup analysis of the Greek atorvastatin and coronary heart disease evaluation (GREACE) study

BACKGROUND

Little is known about statins in the prevention of dyslipidaemia induced renal function decline. The secondary coronary heart disease (CHD) prevention GREACE study suggested that dose titration with atorvastatin (10-80 mg/day, mean dose 24 mg/day) achieves the national cholesterol educational programme treatment goals and significantly reduces morbidity and mortality, compared with usual care.

AIMS

To report the effect of statin on renal function compared with untreated dyslipidaemia in both treatment groups.

METHODS/RESULTS

All patients had plasma creatinine values within the reference range < 115 micro mol/litre (13 mg/litre). The on study creatinine clearance (CrCl), as estimated (for up to 48 months) by the Cockroft-Gault formula, was compared within and between treatment groups using analysis of variance to assess differences over time. Patients from both groups not treated with statins (704) showed a 5.2% decrease in CrCl (p < 0.0001). Usual care patients on various statins (97) had a 4.9% increase in CrCl (p = 0.003). Structured care patients on atorvastatin (783) had a 12% increase in CrCl (p < 0.0001). This effect was more prominent in the lower two quartiles of baseline CrCl and with higher atorvastatin doses. After adjustment for 25 predictors of all CHD related events, multivariate analysis revealed a hazards ratio of 0.84 (confidence interval 0.73 to 0.95; p = 0.003) with every 5% increase in CrCl.

CONCLUSIONS

In untreated dyslipidaemic patients with CHD and normal renal function at baseline, CrCl declines over a period of three years. Statin treatment prevents this decline and significantly improves renal function, potentially offsetting an additional factor associated with CHD risk.

Effect of statins versus untreated dyslipidemia on serum uric acid levels in patients with coronary heart disease: a subgroup analysis of the GREek Atorvastatin and Coronary-heart-disease Evaluation (GREACE) study

BACKGROUND

Little is known about the effect of dyslipidemia on serum uric acid (SUA) levels, and less is known about the effect of statin treatment on them. The GREek Atorvastatin and Coronary-heart-disease Evaluation study suggested that a mean atorvastatin dose of 24 mg/d achieves the National Cholesterol Educational Program treatment goals and significantly reduces morbidity and mortality in patients with coronary heart disease (CHD) in comparison to the usual care. Here, we report the time course of SUA levels in usual-care patients undertreated for their dyslipidemia (12% were administered statins) in comparison to structured-care patients treated with atorvastatin in the vast majority (98%).

METHODS

Mean on-study SUA levels (up to 48 months) were compared with those at baseline by using analyses of variance to assess differences over time within and between treatment groups. Cox multivariate analysis was used to investigate whether changes in SUA levels during the study were clinically relevant.

RESULTS

All patients had normal renal function at baseline; serum creatinine (SCr) levels less than 1.3 mg/dL (<115 micromol/L) and moderately elevated SUA levels (mean, 7.1 +/- 0.9 [SD] mg/dL [425 +/- 52 micromol/L]; upper normal limit, 7.0 mg/dL [415 micromol/L]). Usual-care patients (n = 800) showed an increase in SUA levels by 3.3% ( P < 0.0001). Structured-care patients (n = 800) had an 8.2% reduction in SUA levels ( P < 0.0001). In all patients not administered diuretics (n = 1,407), SUA level changes showed a positive correlation with changes in SCr levels ( r = 0.82; P < 0.0001) and an inverse correlation with estimated glomerular filtration rate ( r = -0.77; P < 0.0001). After adjustment for 19 predictors of all CHD-related events, Cox multivariate analysis involving backward stepwise logistic regression showed a hazard ratio (HR) of 0.89 (95% confidence interval [CI], 0.78 to 0.96; P = 0.03) with every 0.5-mg (30-micromol/L) reduction in SUA level, an HR of 0.76 (95% CI, 0.62 to 0.89; P = 0.001) with every 1-mg (60-micromol/L) reduction, an HR of 1.14 (95% CI, 1.03 to 1.27; P = 0.02) with every 0.5-mg increase, and an HR of 1.29 (95% CI, 1.17 to 1.43; P = 0.001) with every 1-mg increase in SUA levels.

CONCLUSION

Data suggest that SUA level is an independent predictor of CHD recurrent events. Atorvastatin treatment significantly reduces SUA levels in patients with CHD, thus offsetting an additional factor associated with CHD risk.

Relation of coronary vasoreactivity and coronary calcification in asymptomatic subjects with a family history of premature coronary artery disease

Electron-beam computed tomography (EBCT) allows non-invasive imaging of coronary calcification and has been promoted as a screening tool for coronary artery disease (CAD) in asymptomatic high-risk subjects. This study assessed the relation of coronary calcifications to alterations in coronary vascular reactivity by means of positron emission tomography (PET) in asymptomatic subjects with a familial history of premature CAD. Twenty-one subjects (mean age 51+/-10 years) underwent EBCT imaging for coronary calcifications expressed as the coronary calcium score (CCS according to Agatston) and rest/adenosine-stress nitrogen-13 ammonia PET with quantification of myocardial blood flow (MBF) and coronary flow reserve (CFR). The mean CCS was 237+/-256 (median 146, range 0-915). The CCS was <100 in eight subjects and >100 units in 13. As defined by age-related thresholds, 15 subjects had an increased CCS (>75th percentile). Overall mean resting and stress MBF and CFR were 71+/-16 ml 100 g(-1) min(-1), 218+/-54 ml 100 g(-1) min(-1) and 3.20+/-0.77, respectively. Three subjects with CCS ranging from 114 to 451 units had an abnormal CFR (<2.5). There was no relation between CCS and resting or stress MBF or CFR ( r=0.17, 0.18 and 0.10, respectively). In asymptomatic subjects a pathological CCS was five times more prevalent than an abnormal CFR. The absence of any close relationship between CCS and CFR reflects the fact that quantitative myocardial perfusion imaging with PET characterises the dynamic process of vascular reactivity while EBCT is a measure of more stable calcified lesions in the arterial wall whose presence is closely related to age.