Nicholas A. Boon

Diesel Exhaust Inhalation Causes Vascular Dysfunction and Impaired Endogenous Fibrinolysis

Background— Although the mechanisms are unknown, it has been suggested that transient exposure to traffic-derived air pollution may be a trigger for acute myocardial infarction. The study aim was to investigate the effects of diesel exhaust inhalation on vascular and endothelial function in humans. Methods and Results— In a double-blind, randomized, cross-over study, 30 healthy men were exposed to diluted diesel exhaust (300 &mgr;g/m3 particulate concentration) or air for 1 hour during intermittent exercise. Bilateral forearm blood flow and inflammatory factors were measured before and during unilateral intrabrachial bradykinin (100 to 1000 pmol/min), acetylcholine (5 to 20 &mgr;g/min), sodium nitroprusside (2 to 8 &mgr;g/min), and verapamil (10 to 100 &mgr;g/min) infusions 2 and 6 hours after exposure. There were no differences in resting forearm blood flow or inflammatory markers after exposure to diesel exhaust or air. Although there was a dose-dependent increase in blood flow with each vasodilator (P<0.0001 for all), this response was attenuated with bradykinin (P<0.05), acetylcholine (P<0.05), and sodium nitroprusside (P<0.001) infusions 2 hours after exposure to diesel exhaust, which persisted at 6 hours. Bradykinin caused a dose-dependent increase in plasma tissue plasminogen activator (P<0.0001) that was suppressed 6 hours after exposure to diesel (P<0.001; area under the curve decreased by 34%). Conclusions— At levels encountered in an urban environment, inhalation of dilute diesel exhaust impairs 2 important and complementary aspects of vascular function in humans: the regulation of vascular tone and endogenous fibrinolysis. These important findings provide a potential mechanism that links air pollution to the pathogenesis of atherothrombosis and acute myocardial infarction.

Adverse cardiovascular effects of air pollution

Air pollution is increasingly recognized as an important and modifiable determinant of cardiovascular disease in urban communities. Acute exposure has been linked to a range of adverse cardiovascular events including hospital admissions with angina, myocardial infarction, and heart failure. Long-term exposure increases an individuals lifetime risk of death from coronary heart disease. The main arbiter of these adverse health effects seems to be combustion-derived nanoparticles that incorporate reactive organic and transition metal components. Inhalation of this particulate matter leads to pulmonary inflammation with secondary systemic effects or, after translocation from the lung into the circulation, to direct toxic cardiovascular effects. Through the induction of cellular oxidative stress and proinflammatory pathways, particulate matter augments the development and progression of atherosclerosis via detrimental effects on platelets, vascular tissue, and the myocardium. These effects seem to underpin the atherothrombotic consequences of acute and chronic exposure to air pollution. An increased understanding of the mediators and mechanisms of these processes is necessary if we are to develop strategies to protect individuals at risk and reduce the effect of air pollution on cardiovascular disease.

Impaired Coronary Tissue Plasminogen Activator Release Is Associated With Coronary Atherosclerosis and Cigarette Smoking Direct Link Between Endothelial Dysfunction and Atherothrombosis

BackgroundThe aim of the study was to establish the influence of proximal coronary artery atheroma and smoking habit on the stimulated release of tissue plasminogen activator (tPA) from the heart. Methods and ResultsAfter diagnostic coronary angiography in 25 patients, the left anterior descending coronary artery (LAD) was instrumented, and the proximal LAD plaque volume was determined by use of intravascular ultrasound (IVUS). Blood flow and fibrinolytic responses to selective LAD infusion of saline, substance P (10 to 40 pmol/min; endothelium-dependent), and sodium nitroprusside (5 to 20 &mgr;g/min; endothelium-independent) were measured by intracoronary IVUS and Doppler, combined with arterial and coronary sinus blood sampling. Mean plaque burden was 5.5±0.8 mm3/mm vessel (range 0.6 to 13.7 mm3/mm vessel). LAD blood flow increased with both substance P and sodium nitroprusside (P <0.001), although coronary sinus plasma tPA antigen and activity concentrations increased only during substance P infusion (P <0.006 for both). There was a strong inverse correlation between the LAD plaque burden and release of active tPA (r =−0.61, P =0.003). Cigarette smoking was associated with impaired coronary release of active tPA (current smokers, 31±23 IU/min; ex-smokers, 50±33 IU/min; nonsmokers 202±73 IU/min;P <0.05). ConclusionsWe found that both the coronary atheromatous plaque burden and smoking habit are associated with a reduced acute local fibrinolytic capacity of the heart. These important findings provide evidence of a direct link between endogenous fibrinolysis, endothelial dysfunction, and atherothrombosis in the coronary circulation and may explain the greater efficacy of thrombolytic therapy for myocardial infarction in cigarette smokers.

Coronary Arterial 18F-Sodium Fluoride Uptake : A Novel Marker of Plaque Biology

OBJECTIVES With combined positron emission tomography and computed tomography (CT), we investigated coronary arterial uptake of 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) as markers of active plaque calcification and inflammation, respectively. BACKGROUND The noninvasive assessment of coronary artery plaque biology would be a major advance particularly in the identification of vulnerable plaques, which are associated with specific pathological characteristics, including micro-calcification and inflammation. METHODS We prospectively recruited 119 volunteers (72 ± 8 years of age, 68% men) with and without aortic valve disease and measured their coronary calcium score and 18F-NaF and 18F-FDG uptake. Patients with a calcium score of 0 were used as control subjects and compared with those with calcific atherosclerosis (calcium score >0). RESULTS Inter-observer repeatability of coronary 18F-NaF uptake measurements (maximum tissue/background ratio) was excellent (intra-class coefficient 0.99). Activity was higher in patients with coronary atherosclerosis (n = 106) versus control subjects (1.64 ± 0.49 vs. 1.23 ± 0.24; p = 0.003) and correlated with the calcium score (r = 0.652, p < 0.001), although 40% of those with scores >1,000 displayed normal uptake. Patients with increased coronary 18F-NaF activity (n = 40) had higher rates of prior cardiovascular events (p = 0.016) and angina (p = 0.023) and higher Framingham risk scores (p = 0.011). Quantification of coronary 18F-FDG uptake was hampered by myocardial activity and was not increased in patients with atherosclerosis versus control subjects (p = 0.498). CONCLUSIONS 18F-NaF is a promising new approach for the assessment of coronary artery plaque biology. Prospective studies with clinical outcomes are now needed to assess whether coronary 18F-NaF uptake represents a novel marker of plaque vulnerability, recent plaque rupture, and future cardiovascular risk. (An Observational PET/CT Study Examining the Role of Active Valvular Calcification and Inflammation in Patients With Aortic Stenosis; NCT01358513).

Diesel exhaust inhalation increases thrombus formation in man

AIMS Although the mechanism is unclear, exposure to traffic-derived air pollution is a trigger for acute myocardial infarction (MI). The aim of this study is to investigate the effect of diesel exhaust inhalation on platelet activation and thrombus formation in men. METHODS AND RESULTS In a double-blind randomized crossover study, 20 healthy volunteers were exposed to dilute diesel exhaust (350 microg/m(3)) and filtered air. Thrombus formation, coagulation, platelet activation, and inflammatory markers were measured at 2 and 6 h following exposure. Thrombus formation was measured using the Badimon ex vivo perfusion chamber. Platelet activation was assessed by flow cytometry. Compared with filtered air, diesel exhaust inhalation increased thrombus formation under low- and high-shear conditions by 24% [change in thrombus area 2229 microm(2), 95% confidence interval (CI) 1143-3315 microm(2), P = 0.0002] and 19% (change in thrombus area 2451 microm(2), 95% CI 1190-3712 microm(2), P = 0.0005), respectively. This increased thrombogenicity was seen at 2 and 6 h, using two different diesel engines and fuels. Diesel exhaust also increased platelet-neutrophil and platelet-monocyte aggregates by 52% (absolute change 6%, 95% CI 2-10%, P = 0.01) and 30% (absolute change 3%, 95% CI 0.2-7%, P = 0.03), respectively, at 2 h following exposure compared with filtered air. CONCLUSION Inhalation of diesel exhaust increases ex vivo thrombus formation and causes in vivo platelet activation in man. These findings provide a potential mechanism linking exposure to combustion-derived air pollution with the triggering of acute MI.

Calcific Aortic Stenosis: A Disease of the Valve and the Myocardium

Although aortic stenosis is a common condition associated with major morbidity, mortality, and health economic costs, there are currently no medical interventions capable of delaying or halting its progression. Re-evaluation of the underlying pathophysiology is therefore required so that novel therapeutic strategies can be developed. Aortic stenosis is characterized by progressive aortic valve narrowing and secondary left ventricular hypertrophy. Both processes are important because in combination they drive the development of symptoms and adverse events that characterize the latter stages of the disease. In this review, the authors examine the pathophysiology of aortic stenosis with respect to both the valve and the myocardium. In particular, the authors focus on the role of inflammation, fibrosis, and calcification in progressive valve narrowing and then examine the development of left ventricular hypertrophy, its subsequent decompensation, and the transition to heart failure. Finally the authors discuss potential therapeutic strategies on the basis of similarities aortic stenosis shares with other pathological conditions.

Assessment of Valvular Calcification and Inflammation by Positron Emission Tomography in Patients With Aortic Stenosis

Background— The pathophysiology of aortic stenosis is incompletely understood, and the relative contributions of valvular calcification and inflammation to disease progression are unknown. Methods and Results— Patients with aortic sclerosis and mild, moderate, and severe stenosis were compared prospectively with age- and sex-matched control subjects. Aortic valve severity was determined by echocardiography. Calcification and inflammation in the aortic valve were assessed by 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) uptake with the use of positron emission tomography. One hundred twenty-one subjects (20 controls; 20 aortic sclerosis; 25 mild, 33 moderate, and 23 severe aortic stenosis) were administered both 18F-NaF and 18F-FDG. Quantification of tracer uptake within the valve demonstrated excellent interobserver repeatability with no fixed or proportional biases and limits of agreement of ±0.21 (18F-NaF) and ±0.13 (18F-FDG) for maximum tissue-to-background ratios. Activity of both tracers was higher in patients with aortic stenosis than in control subjects (18F-NaF: 2.87±0.82 versus 1.55±0.17; 18F-FDG: 1.58±0.21 versus 1.30±0.13; both P<0.001). 18F-NaF uptake displayed a progressive rise with valve severity (r2=0.540, P<0.001), with a more modest increase observed for 18F-FDG (r2=0.218, P<0.001). Among patients with aortic stenosis, 91% had increased 18F-NaF uptake (>1.97), and 35% had increased 18F-FDG uptake (>1.63). A weak correlation between the activities of these tracers was observed (r2=0.174, P<0.001). Conclusions— Positron emission tomography is a novel, feasible, and repeatable approach to the evaluation of valvular calcification and inflammation in patients with aortic stenosis. The frequency and magnitude of increased tracer activity correlate with disease severity and are strongest for 18F-NaF. Clinical Trial Registration— http://www.clinicaltrials.gov. Unique identifier: NCT01358513.

State-of-the-Art PaperCalcific Aortic Stenosis: A Disease of the Valve and the Myocardium

Although aortic stenosis is a common condition associated with major morbidity, mortality, and health economic costs, there are currently no medical interventions capable of delaying or halting its progression. Re-evaluation of the underlying pathophysiology is therefore required so that novel therapeutic strategies can be developed. Aortic stenosis is characterized by progressive aortic valve narrowing and secondary left ventricular hypertrophy. Both processes are important because in combination they drive the development of symptoms and adverse events that characterize the latter stages of the disease. In this review, the authors examine the pathophysiology of aortic stenosis with respect to both the valve and the myocardium. In particular, the authors focus on the role of inflammation, fibrosis, and calcification in progressive valve narrowing and then examine the development of left ventricular hypertrophy, its subsequent decompensation, and the transition to heart failure. Finally the authors discuss potential therapeutic strategies on the basis of similarities aortic stenosis shares with other pathological conditions.

Heart muscle disease related to HIV infection : prognostic implications

Abstract Objectives: To determine the natural course of heart muscle disease in patients infected with HIV. Design: Prospective echocardiographic survey and observational study over four years. Setting: Edinburgh. Subjects—296 adults infected with HIV (mean age 32.7 years (range 21.5 to 67.6) drawn from all the major groups at risk of HIV infection in Britain. Main outcome measures: Detection of myocardial dysfunction and time to death from index echocardiogram in serial echocardiography. Results: Cardiac dysfunction was identified in 44 subjects (dilated cardiomyopathy, 13; isolated right ventricular dysfunction, 12; borderline left ventricular dysfunction, 19). Dilated cardiomyopathy was strongly associated with a CD4 cell count of <100 × 106/l, in contrast with the other forms of cardiac dysfunction. During the study 12/13 (92%) subjects with dilated cardiomyopathy, 5/12 (42%) with right ventricular dysfunction, and 8/19 (42%) with borderline left ventricular function died of conditions related to AIDS. Survival was significantly reduced in the subjects with dilated cardiomyopathy compared with those with normal hearts (P<0.001). The median survival from the index echocardiogram was 101 days (95% confidence interval 42 to 146) for the subjects with cardiomyopathy compared with 472 days (383 to 560) for those with normal hearts and a CD4 cell count of <20 × 106/l. No significant difference existed in survival for subjects with borderline left or isolated right ventricular dysfunction. Conclusion: Even after adjustment for the significantly reduced CD4 cell count with which dilated cardiomyopathy is associated, the outlook for patients with HIV infection and dilated cardiomyopathy is poor. Isolated right and borderline left ventricular dysfunction are not associated with reduced CD4 cells counts and do not carry adverse prognostic implications.

Progressive coronary calcification despite intensive lipid-lowering treatment: a randomised controlled trial

Objectives: To evaluate the effect of intensive lipid-lowering treatment on coronary artery calcification in a substudy of a trial recruiting patients with calcific aortic stenosis. Methods: In a double blind randomised controlled trial, 102 patients with calcific aortic stenosis and coronary artery calcification were randomly assigned by the minimisation technique to atorvastatin 80 mg daily or matched placebo. Coronary artery calcification was assessed annually by helical computed tomography. Results: 48 patients were randomly assigned to atorvastatin and 54 to placebo with a median follow up of 24 months (interquartile range 24–30). Baseline characteristics and coronary artery calcium scores were similar in both groups. Atorvastatin reduced serum low density lipoprotein cholesterol (−53%, p < 0.001) and C reactive protein (−49%, p < 0.001) concentrations whereas there was no change with placebo (−7% and 17%, p > 0.95 for both). The rate of change in coronary artery calcification was 26%/year (0.234 (SE 0.037) log arbitrary units (AU)/year; n  =  39) in the atorvastatin group and 18%/year (0.167 (SE 0.034) log AU/year; n  =  49) in the placebo group, with a geometric mean difference of 7%/year (95% confidence interval −3% to 18%, p  =  0.18). Serum low density lipoprotein concentrations were not correlated with the rate of progression of coronary calcification (r  =  0.05, p  =  0.62). Conclusion: In contrast to previous observational studies, this randomised controlled trial has shown that, despite reducing systemic inflammation and halving serum low density lipoprotein cholesterol concentrations, statin treatment does not have a major effect on the rate of progression of coronary artery calcification.