alpha-adrenergic coronary vasoconstriction and myocardial ischemia in humans

Dronedarone prevents microcirculatory abnormalities in the left ventricle during atrial tachypacing in pigs

BACKGROUND AND PURPOSE

Atrial fibrillation induces ischaemic microcirculatory flow abnormalities in the ventricle, contributing to the risk for acute coronary syndromes. We evaluated the effect of dronedarone on ventricular perfusion during rapid atrial pacing (RAP).

EXPERIMENTAL APPROACH

Coronary and fractional flow reserve (CFR/FFR) were measured in the left anterior descending artery in 29 pigs. Six received RAP, six received RAP with dronedarone (RAP/D), seven received dronedarone alone, four received RAP with amiodarone (RAP/A), and six received neither (sham). In ventricular tissue, oxidative stress/ischaemia-related gene and protein expression was evaluated by RT-PCR and Western blotting; Isoprostanes were measured by GC-MS procedures.

KEY RESULTS

CFR was decreased in the RAP group, compared with other groups. FFR was not different between groups. Effective refractory period was reduced in RAP compared with RAP/D. RAP-activated PKC phosphorylation tended to be decreased by dronedarone (P= 0.055) RAP induced NOX-1 and NOX-2 protein and the mRNA for hypoxia-inducible factor-1α (HIF-1α). Dronedarone reduced the pacing-dependent increase in the expression of NOX-2 protein and of HIF-1α mRNA. The oxidative stress marker, F(2)-isoprostane, was increased by RAP and this increase was attenuated by dronedarone. Other oxidative stress/ischaemia-related genes were induced by RAP compared with sham and were decreased by dronedarone treatment. In HL1 cells, dronedarone significantly inhibited the increased phosphorylation of PKCα after oxidative stress, with an almost significant effect (P= 0.059) on that after RAP.

CONCLUSIONS AND IMPLICATIONS

Dronedarone abolished RAP-induced ventricular microcirculatory abnormalities by decreasing oxidative stress/ischaemia-related gene and protein expression in the ventricle.

Heart of the matter: coronary dysfunction in metabolic syndrome

Metabolic syndrome (MetS) is a collection of risk factors including obesity, dyslipidemia, insulin resistance/impaired glucose tolerance, and/or hypertension. The incidence of obesity has reached pandemic levels, as ~20-30% of adults in most developed countries can be classified as having MetS. This increased prevalence of MetS is critical as it is associated with a two-fold elevated risk for cardiovascular disease. Although the pathophysiology underlying this increase in disease has not been clearly defined, recent evidence indicates that alterations in the control of coronary blood flow could play an important role. The purpose of this review is to highlight current understanding of the effects of MetS on regulation of coronary blood flow and to outline the potential mechanisms involved. In particular, the role of neurohumoral modulation via sympathetic α-adrenoceptors and the renin-angiotensin-aldosterone system (RAAS) are explored. Alterations in the contribution of end-effector K(+), Ca(2+), and transient receptor potential (TRP) channels are also addressed. Finally, future perspectives and potential therapeutic targeting of the microcirculation in MetS are discussed. This article is part of a Special Issue entitled "Coronary Blood Flow".

Efficacy of ivabradine in combination with Beta-blocker versus uptitration of Beta-blocker in patients with stable angina

PURPOSE

The antianginal and anti-ischemic efficacy of the selective I (f) inhibitor ivabradine is established in patients with stable angina in monotherapy and in combination with other antianginals, including beta-blocker. This pilot study compared the antianginal and anti-ischemic efficacy and hemodynamic profile of ivabradine plus 5 mg bisoprolol versus those of 10 mg bisoprolol in patients with stable angina.

PATIENTS AND METHODS

Twenty-nine patients with stable angina and moderate left ventricular systolic dysfunction already on bisoprolol 5 mg od were randomized into 2 groups. Group 1 (n = 17) received ivabradine (5-7.5 mg bid) in addition to bisoprolol 5 mg od, while in group 2 (n = 12) bisoprolol was uptitrated first to 7.5 mg and then 10 mg od. Patients underwent a treadmill test, 6-minute walking test, and echocardiography at baseline and after 2 months.

RESULTS

Mean resting heart rate decreased in both groups, from 76.6 ± 4.6 bpm to 59.3 ± 2.5 bpm (P < 0.001) in group 1 and from 75.9 ± 3.0 bpm to 60.5 ± 2.3 bpm (P = 0.002) in group 2. The effect on resting heart rate did not differ significantly between the two groups. However, more patients became asymptomatic in group 1 than in group 2. Addition of ivabradine also improved exercise capacity, as shown by the results of the 6-minute walking and exercise tolerance tests, whereas in group 2 neither parameter was significantly affected. Chronotropic reserve significantly improved with ivabradine, but not with bisoprolol 10 mg.

CONCLUSIONS

These results suggest that combining ivabradine with low dose bisoprolol in stable angina patients produces additional antianginal and anti-ischemic benefits and improves chronotropic reserve.

Dexmedetomidine: applications for the pediatric patient with congenital heart disease

This study aimed to provide a general description of the cardiovascular and hemodynamic effects of dexmedetomidine and an evidence-based review of the literature regarding its use in infants and children with congenital heart disease (CHD). A computerized bibliographic search of the literature on dexmedetomidine use in infants and children with CHD was performed. The cardiovascular effects of dexmedetomidine have been well studied in animal and adult human models. Adverse cardiovascular effects include occasional episodes of bradycardia, with rare reports of sinus pause or cardiac arrest. Both hypotension and hypertension also have been reported. The latter is related to peripheral α(2B) agonism leading to vasoconstriction. No adverse effects on the pulmonary vasculature have been noted even in patients with preexisting pulmonary hypertension. Although there are no direct effects on myocardial function, decreased cardiac output may result from changes in heart rate or increases in afterload. Although not currently Food and Drug Administration (FDA)-approved for the pediatric population, findings have shown dexmedetomidine to be effective in various clinical scenarios of patients with CHD including sedation during mechanical ventilation, prevention of procedure-related anxiety, prevention of emergence delirium and shivering after anesthesia, and treatment of withdrawal. Although dexmedetomidine may have limited utility for painful or invasive procedures, preliminary data suggest that the addition of ketamine to the regimen may offer benefits. When used during the perioperative period, additional benefits include blunting of the sympathetic stress response with a reduction of endogenous catecholamine release, a decrease in intraoperative anesthetic requirements, and a limitation of postoperative opioid requirements.

Reduction of myocardial infarct size by dronedarone in pigs--a pleiotropic action?

Purpose

Dronedarone is a first-line drug to prevent the recurrence of atrial fibrillation according to ESC guidelines. In the recent ATHENA trial, dronedarone reduced mortality and also hospitalization for acute coronary syndrome in patients with atrial fibrillation. This beneficial effect suggests that dronedarone might have also an impact on events associated with ischemia/reperfusion injury.

Methods

Fourteen anesthetized pigs received either dronedarone (2.5 mg/kg) or placebo. Effects of dronedarone on heart rate and blood pressure were reversed by atrial pacing and aortic constriction before pigs were subjected to 90 min regional low-flow myocardial ischemia and 2 h reperfusion. Regional myocardial blood flow was measured with microspheres and infarct size determined by TTC staining.

Results

With comparable heart rate and left ventricular pressure during ischemia, dronedarone reduced infarct size from 34 ± 3% to 22 ± 4% (p < 0.05) of the area at risk. Subendocardial blood flow during ischemia was not different between groups. The relationship between ischemic subendocardial blood flow in the area at risk and infarct size was displaced downwards, reflecting a direct cardioprotective action of dronedarone.

Conclusion

The beneficial effect of dronedarone is attributed to cardioprotective properties, possibly through attenuation of calcium overload during myocardial ischemia/reperfusion.

Coronary β2-adrenoreceptors mediate endothelium-dependent vasoreactivity in humans: novel insights from an in vivo intravascular ultrasound study

AIMS

The interaction between coronary β(2)-adrenoreceptors and segmental plaque burden is complex and poorly understood in humans. We aimed to validate intracoronary (IC) salbutamol as a novel endothelium-dependent vasodilator utilizing intravascular ultrasound (IVUS), and thus assess relationships between coronary β(2)-adrenoreceptors, regional plaque burden and segmental endothelial function.

METHODS AND RESULTS

In 29 patients with near-normal coronary angiograms, IVUS-upon-Doppler Flowire imaging protocols were performed. Protocol 1: incremental IC salbutamol (0.15, 0.30, 0.60 μg/min) infusions (15 patients, 103 segments); protocol 2: salbutamol (0.30 μg/min) infusion before and after IC administration of N(G)-monomethyl-L-arginine (L-NMMA) (10 patients, 82 segments). Vehicle infusions (IC dextrose) were performed in 4 patients (21 segments). Macrovascular response [% change segmental lumen volume (ΔSLV)] and plaque burden [per cent atheroma volume (PAV)] were studied in 5-mm coronary segments. Microvascular response [per cent change in coronary blood flow (ΔCBF)] was calculated following each infusion. Intracoronary salbutamol demonstrated significant dose-response ΔSLV and ΔCBF from baseline, respectively (0.15 μg/min: 3.5 ± 1.3%, 28 ± 14%, P = 0.04, P = NS; 0.30 μg/min: 5.5 ± 1.4%, 54 ± 17%, P = 0.001, P < 0.0001; 0.60 μg/min: 4.8 ± 1.6%, 66 ± 15%, P = 0.02, P < 0.0001), with ΔSLV responses further exemplified in low vs. high plaque burden groups. Salbutamol vasomotor responses were suppressed by l-NMMA, supporting nitric oxide-dependent mechanisms. Vehicle infusions resulted in no significant ΔSLV or ΔCBF. Multivariate analysis including conventional cardiovascular risk factors, PAV, segmental remodelling and plaque eccentricity indices identified PAV as the only significant predictor of a ΔSLV to IC salbutamol (coefficient -0.18, 95% CI -0.32 to -0.044, P = 0.015). Conclusions Intracoronary salbutamol is a novel endothelium-dependent epicardial and microvascular coronary vasodilator. Intravascular ultrasound-derived regional plaque burden is a major determinant of segmental coronary endothelial function.

Peri-interventional coronary vasomotion

A percutaneous coronary intervention (PCI) is a unique condition to study the effects of ischemia and reperfusion in patients with severe coronary atherosclerosis when coronary vasomotor function is compromised by loss of endothelial and autoregulatory vasodilation. We studied the effects of intracoronary non-selective α-, as well as selective α(1)- and α(2)-blockade in counteracting the observed vasoconstriction in patients with stable and unstable angina and in patients with acute myocardial infarction. Coronary vasoconstriction in our studies was a diffuse phenomenon and involved not only the culprit lesion but also vessels with angiographically not visible plaques. Post-PCI vasoconstriction was reflected by increased coronary vascular resistance and associated with decreased LV-function. α (1)-Blockade with urapidil dilated epicardial coronary arteries, improved coronary flow reserve and counteracted LV dysfunction. Non-selective α-blockade with phentolamine induced epicardial and microvascular dilation, while selective α(2)-blockade with yohimbine had only minor vasodilator and functional effects. Intracoronary α-blockade also attenuated the no-reflow phenomenon following primary PCI. This article is part of a Special Issue entitled "Coronary Blood Flow".

Cardioprotection by Ivabradine Through Heart Rate Reduction and Beyond

The present review summarizes the experimental and clinical evidence for the anti-ischemic action of the selective bradycardic agent ivabradine. Improvements in myocardial blood flow and contractile function during experimental myocardial ischemia and the clinical anti-anginal effect are largely mediated by heart rate reduction. However, a significant reduction in infarct size by ivabradine persists in the absence of heart rate reduction, and such protection can also be recruited when ivabradine is given only during early reperfusion. The mechanisms for such pleiotropic action of ivabradine remain to be resolved.

Effects of verbal suggestion on coronary arteries: results of a randomized controlled experimental investigation during coronary angiography

BACKGROUND

Decrease of chest pain perception under placebo conditions has been frequently observed. The aim of this study was to examine whether placebo-induced chest pain improvement could be the result of changes in coronary blood flow. We, therefore, performed an experiment to investigate whether a verbal suggestion (VS) integrated in a cardiologic procedure has an impact on diameters of coronary arteries.

METHODS

A total of 30 chest pain patients with normal diagnostic angiograms were assigned to a VS or a control group (CG). Saline solution was administered intracoronarily to both groups. The VS group received a standardized VS, implying coronary vasodilation. The CG remained without VS. Coronary end points were the changes in percentage diameter stenosis, Minimal lumen diameter and reference diameter of the index coronary segment before and 60 seconds after the administration of saline. Furthermore, changes in hemodynamics, psychological distress, and chest pain perception were recorded.

RESULTS

The VS led to coronary vasoconstriction in comparison with CG (change in mean percentage diameter stenosis ± SD 3.2% ± 6.3% vs -1.7% ± 6.8%, P = .062; change in mean minimal lumen diameter ± SD -0.18 ± 0.32 mm vs 0.06 ± 0.23 mm, P = .029, no relevant change in the reference diameter). At the same time, the degree of chest pain perception was significantly reduced in the VS group (-0.7 ± 1.3) compared with the CG (0.3 ± 1.3), P = .024.

CONCLUSION

The findings of this study suggest that a VS results in a biological alteration within coronary arteries. Contrary to expectation, the VS led to vasoconstriction, whereas chest pain perception decreased.

Effect of Carvedilol, Ivabradine or their combination on exercise capacity in patients with Heart Failure (the CARVIVA HF trial)

AIM

Patients with heart failure (HF) have reduced exercise capacity. The beneficial effect of beta-blocker on prognosis is not matched by an impact on exercise capacity and quality of life. We performed a randomised open blinded endpoint study to assess the effect of heart rate reduction with carvedilol, ivabradine, and their combination on exercise capacity in HF patients receiving maximal dose of ACE inhibitor.

METHODS AND RESULTS

After a run-in phase patients were randomly allocated to 3 groups: carvedilol up to 25mg bid (n=38); ivabradine up to 7.5mg bid (n=41); and carvedilol/ivabradine up to 12.5/7.5mg bid (n=42). The maximal dose of study treatment was more frequently tolerated in patients receiving ivabradine (36/41) than in those receiving carvedilol (18/38) or combination therapy (32/42) (P<0.01 ivabradine versus carvedilol). Heart rate was reduced in all three groups, but to a greater extent by the combination. The distance walked on the 6-min walking test and the exercise time on MVO(2) test significantly improved in the ivabradine and combination groups (both P<0.01 versus baseline), as did peak VO(2) and VAT (P<0.01 for ivabradine and P<0.03 for combination versus carvedilol, respectively). No changes in these parameters were found with carvedilol. The patients receiving ivabradine or the combination had better quality of life (P<0.01 versus baseline for ivabradine and P<0.02 for combination), versus no change with carvedilol.

CONCLUSION

Ivabradine alone or in combination with carvedilol is more effective than carvedilol alone at improving exercise tolerance and quality of life in HF patients.

Lessons from human coronary aspirate

The interventional implantation of a stent into an atherosclerotic coronary artery is a unique and paradigmatic scenario of plaque rupture in humans. The use of protection devices not only prevents the released plaque particles and the superimposed thrombotic material from being washed and embolized into the coronary microcirculation of the individual patient, but permits also the retrieval and ex vivo analysis of particulate plaque debris and soluble substances. The particulate debris comprises typical cholesterol crystals, foam cells, hyalin material and calcium deposits from the atheroma as well as platelets and coagulation material; soluble substances include vasoconstrictors, such as serotonin and thromboxane, as well as inflammatory mediators, such as TNFα which amplifies vasoconstriction by inducing endothelial dysfunction. The vasoconstriction observed in a bioassay ex vivo correlates to clinical symptoms, angiographic stenosis and plaque burden, as assessed by intravascular ultrasound. The release of TNFα into the aspirate correlates to restenosis. Detailed analysis of the human coronary aspirate may promote a better understanding of the pathophysiology of the vulnerable atherosclerotic plaque and help to better antagonize the microvascular consequences of coronary microembolization, including the no reflow phenomenon. This article is part of a Special Issue entitled "Coronary Blood Flow."

The impact of adenosine pharmacologic stress combined with low-level exercise in patients undergoing myocardial perfusion imaging (BIWAKO adenosine-Ex trial)

BACKGROUND

The combination of adenosine infusion with low-level exercise has become a common approach for inducing stress during stress myocardial perfusion imaging (MPI). We investigated stress MPI performed by combined low-level exercise and adenosine infusion. This combined protocol can decrease adverse reactions and reduce the effect of scattered rays from the liver.

METHODS AND RESULTS

Subjects were clinically referred for a 53-min rest-stress Tc-99m Sestamibi MPI procedure using BIWAKO PROTOCOL. Ninety-eight patients (44.5%) underwent adenosine infusion with ergometer exercise testing and 122 patients (55.5%) underwent adenosine infusion without exercise testing. We evaluated the liver/heart (L/H) uptake ratio, background activity in the upper mediastinum, and adverse reactions.

RESULTS

The L/H ratio and background activity were lower in the adenosine-exercise group than in the adenosine-non-exercise group (1.8 ± 0.54 vs. 2.1 ± 0.62, P < 0.0056; 43.1 ± 12.2 vs. 61.5 ± 15.4, P < 0.0001). The adenosine-exercise group had fewer adverse reactions than the adenosine-non-exercise group (11.2 vs. 19.7%). All of the adverse reactions were minor, with the exception of severe back pain in one case. The incidence of adverse reactions in our study was lower than that in previous studies for unknown reason.

CONCLUSION

Adenosine infusion in combination with low-level exercise seems to result in higher-quality images and fewer adverse reactions than adenosine infusion without exercise. The combined protocol decreases adverse reactions and improves the quality of myocardial perfusion images by decreasing background activity.

Heart rate: a forgotten link in coronary artery disease?

A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.

Effects of high thoracic epidural anesthesia on atrial electrophysiological characteristics and sympathetic nerve sprouting in a canine model of atrial fibrillation

High thoracic epidural anesthesia (HTEA) blocks the afferent and efferent cardiac sympathetic nerve fibers and may affect atrial electrophysiological characteristics and nerve sprouting in patients with atrial fibrillation (AF). In this study, 18 dogs were randomly divided into a control group (n = 6), in which dogs were atrially paced at 400 beats/min for 6 weeks; an HTEA group (n = 6), in which dogs underwent atrial pacing and HTEA for 6 weeks; and a sham-operated group (n = 6), in which dogs underwent the operation but did not receive atrial pacing or HTEA. Electrophysiological examinations were performed in all groups. Cardiac nerves were immunocytochemically stained with anti-growth-associated protein 43 (GAP43) and anti-tyrosine hydroxylase (TH) antibodies. The protein expressions of nerve growth factor (NGF), GAP43 and TH in atrial myocardium were also studied by western blot. In addition, the plasma levels of C-reactive protein (CRP) and norepinephrine, as well as atrial production of superoxide anion (O(2)(·-)) and malondialdehyde, were measured. In the HTEA group, atrial effective refractory period increased (P < 0.05) and AF maintenance decreased (P < 0.01) significantly compared with the control group. The densities of GAP43-positive nerves and TH-positive nerves were significantly lower in the HTEA group compared with the control group. The protein levels of NGF, GAP43 and TH were also lower in the HTEA group compared with the control group. A significant positive correlation between the expressions of NGF and GAP43 (P < 0.01) was observed. A similar correlation was demonstrated for NGF and TH (P < 0.01) in our study. Furthermore, the plasma levels of CRP and norepinephrine, as well as the amount of O(2)(·-) and malondialdehyde produced from myocardium, decreased in the HTEA group compared with the control group. In conclusion, HTEA inhibited electrical and nerve remodeling and reduced the maintenance of AF in a canine AF model, in which process HTEA exhibited anti-inflammatory and antioxidant effects, indicating that, in addition to the efferent cardiac sympathetic nerve, afferent fibers also play an important role in the initiation and/or maintenance of AF.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Functional alpha-1B adrenergic receptors on human epicardial coronary artery endothelial cells

Alpha-1-adrenergic receptors (α1-ARs) regulate coronary arterial blood flow by binding catecholamines, norepinephrine (NE), and epinephrine (EPI), causing vasoconstriction when the endothelium is disrupted. Among the three α1-AR subtypes (α1A, α1B, and α1D), the α1D subtype predominates in human epicardial coronary arteries and is functional in human coronary smooth muscle cells (SMCs). However, the presence or function of α1-ARs on human coronary endothelial cells (ECs) is unknown. Here we tested the hypothesis that human epicardial coronary ECs express functional α1-ARs. Cultured human epicardial coronary artery ECs were studied using quantitative real-time reverse transcription polymerase chain reaction, radioligand binding, immunoblot, and (3)H-thymidine incorporation. The α1B-subtype messenger ribonucleic acid (mRNA) was predominant in cultured human epicardial coronary ECs (90-95% of total α1-AR mRNA), and total α1-AR binding density in ECs was twice that in coronary SMCs. Functionally, NE and EPI through the α1B subtype activated extracellular signal-regulated kinase (ERK) in ECs, stimulated phosphorylation of EC endothelial nitric oxide synthase (eNOS), and increased deoxyribonucleic acid (DNA) synthesis. These results are the first to demonstrate α1-ARs on human coronary ECs and indicate that the α1B subtype is predominant. Our findings provide another potential mechanism for adverse cardiac effects of drug antagonists that nonselectively inhibit all three α1-AR subtypes.

Oxidant sensing by protein kinases a and g enables integration of cell redox state with phosphoregulation

The control of vascular smooth muscle contractility enables regulation of blood pressure, which is paramount in physiological adaptation to environmental challenges. Maintenance of stable blood pressure is crucial for health as deregulation (caused by high or low blood pressure) leads to disease progression. Vasotone is principally controlled by the cyclic nucleotide dependent protein kinases A and G, which regulate intracellular calcium and contractile protein calcium sensitivity. The classical pathways for activation of these two kinases are well established and involve the formation and activation by specific cyclic nucleotide second messengers. Recently we reported that both PKA and PKG can be regulated independently of their respective cyclic nucleotides via a mechanism whereby the kinases sense cellular oxidant production using redox active thiols. This novel redox regulation of these kinases is potentially of physiological importance, and may synergise with the classical regulatory mechanisms.

The alpha-1D Is the predominant alpha-1-adrenergic receptor subtype in human epicardial coronary arteries

OBJECTIVES

The goal was to identify alpha-1-adrenergic receptor (AR) subtypes in human coronary arteries.

BACKGROUND

The alpha1-ARs regulate human coronary blood flow. The alpha1-ARs exist as 3 molecular subtypes, alpha1A, alpha1B, and alpha1D, and the alpha1D subtype mediates coronary vasoconstriction in the mouse. However, the alpha1A is thought to be the only subtype in human coronary arteries.

METHODS

We obtained human epicardial coronary arteries and left ventricular (LV) myocardium from 19 transplant recipients and 6 unused donors (age 19 to 70 years; 68% male; 32% with coronary artery disease). We cultured coronary rings and human coronary smooth muscle cells. We assayed alpha1- and beta-AR subtype messenger ribonucleic acid (mRNA) by quantitative real-time reverse transcription polymerase chain reaction and subtype proteins by radioligand binding and extracellular signal-regulated kinase (ERK) activation.

RESULTS

The alpha1D subtype was 85% of total coronary alpha1-AR mRNA and 75% of total alpha1-AR protein, and alpha1D stimulation activated ERK. In contrast, the alpha1D was low in LV myocardium. Total coronary alpha1-AR levels were one-third of beta-ARs, which were 99% the beta2 subtype.

CONCLUSIONS

The alpha1D subtype is predominant and functional in human epicardial coronary arteries, whereas the alpha1A and alpha1B are present at very low levels. This distribution is similar to the mouse, where myocardial alpha1A- and alpha1B-ARs mediate beneficial functional responses and coronary alpha1Ds mediate vasoconstriction. Thus, alpha1D-selective antagonists might mediate coronary vasodilation, without the negative cardiac effects of nonselective alpha1-AR antagonists in current use. Furthermore, it could be possible to selectively activate beneficial myocardial alpha1A- and/or alpha1B-AR signaling without causing coronary vasoconstriction.

Insertion/deletion polymorphism in alpha2-adrenergic receptor gene is a genetic risk factor for sudden cardiac death

BACKGROUND

Adrenoceptors mediate contraction of vascular smooth muscle and induce coronary vasoconstriction in humans. A deletion variant of the human alpha(2B)-adrenoreseptor of glutamic acid residues has been associated with impaired receptor desensitization. This receptor variant could, therefore, be involved in cardiovascular diseases associated with enhanced vasoconstriction. Our aim was to study whether an insertion/deletion (I/D) polymorphism in the alpha(2B)-adrenoceptor gene is associated with the risk for sudden cardiac death.

METHODS

This was a prospective population-based study investigating risk factors for cardiovascular diseases in middle-aged men from 42 to 60 years from eastern Finland. The study is based on 1,606 men with complete data on DNA observed for an average time of 17 years.

RESULTS

In this study population, 338 men (21%) had the D/D genotype, 467 (29%) had the I/I genotype, and 801 (50%) had a heterozygous genotype. There were 76 sudden cardiac deaths during follow-up (0.81 deaths/1,000 persons per year). In a Cox model adjusting for other coronary risk factors (age, systolic blood pressure, smoking, diabetes, serum low-density lipoprotein and high-density lipoprotein cholesterol, body mass index, and exercise-induced myocardial ischemia), men with the D/D or I/D genotype had 1.97 times (95% CI 1.08-3.59, P = .026) higher risk to experience sudden cardiac death (20 events for D/D genotype, 13 events for I/I genotype, and 43 events for I/D genotype) compared with men carrying the I/I genotype. In addition, the alpha(2B)-adrenoceptor D/D genotype was associated with the risk of coronary heart disease death and acute coronary events, after adjusting for risk factors.

CONCLUSIONS

The genetic polymorphism of the alpha(2B)-adrenoreceptor is genetic risk predictor for sudden cardiac death.

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.

Coronary microvascular resistance: methods for its quantification in humans

Coronary microvascular dysfunction is a topic that has recently gained considerable interest in the medical community owing to the growing awareness that microvascular dysfunction occurs in a number of myocardial disease states and has important prognostic implications. With this growing awareness, comes the desire to accurately assess the functional capacity of the coronary microcirculation for diagnostic purposes as well as to monitor the effects of therapeutic interventions that are targeted at reversing the extent of coronary microvascular dysfunction. Measurements of coronary microvascular resistance play a pivotal role in achieving that goal and several invasive and noninvasive methods have been developed for its quantification. This review is intended to provide an update pertaining to the methodology of these different imaging techniques, including the discussion of their strengths and weaknesses.

High thoracic epidural analgesia improves left ventricular function in patients with ischemic heart

BACKGROUND

In patients with ischemic heart disease, high thoracic epidural analgesia (HTEA) has been proposed to improve myocardial function. Tissue Doppler Imaging (TDI) is a tool for quantitative determination of myocardial systolic and diastolic velocities and a derivative of TDI is tissue tracking (TT), which allows quantitative assessment of myocardial systolic longitudinal displacement during systole. The purpose of this study was to evaluate the effect of thoracic epidural analgesia on left ventricular (LV) systolic and diastolic function by means of two-dimensional (2D) echocardiography and TDI in patients with ischemic heart disease.

METHODS

The effect of a high epidural block (at least Th1-Th5) on myocardial function in patients (N=15) with ischemic heart disease was evaluated. Simpson's 2D volumetric method was used to quantify LV volume and ejection fraction. Systolic longitudinal displacement was assessed by the TT score index and the diastolic function was evaluated from changes in early (E'') and atrial (A'') peak velocities during diastole.

RESULTS

After HTEA, 2D measures of left ventricle function improved significantly together with the mean TT score index [from 5.87 +/- 1.53 to 6.86 +/- 1.38 (P<0.0003)], reflecting an increase in LV global systolic function and longitudinal systolic displacement. The E''/A'' ratio increased from 0.75 +/- 0.27 to 1.09 +/- 0.32 (P=0.0026), indicating improved relaxation.

CONCLUSION

A 2D-echocardiography in combination with TDI indicates both improved systolic and diastolic function after HTEA in patients with ischemic heart disease.

Vascular control in humans: focus on the coronary microcirculation

Myocardial perfusion is regulated by a variety of factors that influence arteriolar vasomotor tone. An understanding of the physiological and pathophysiological factors that modulate coronary blood flow provides the basis for the judicious use of medications for the treatment of patients with coronary artery disease. Vasomotor properties of the coronary circulation vary among species. This review highlights the results of recent studies that examine the mechanisms by which the human coronary microcirculation is regulated in normal and disease states, focusing on diabetes. Multiple pathways responsible for myogenic constriction and flow-mediated dilation in human coronary arterioles are addressed. The important role of endothelium-derived hyperpolarizing factors, their interactions in mediating dilation, as well as speculation regarding the clinical significance are emphasized. Unique properties of coronary arterioles in human vs. other species are discussed.

Review of the If selective channel inhibitor ivabradine in the treatment of chronic stable angina

Coronary heart disease is the major cause of morbidity and mortality in industrialized countries, and its prevalence is predicted to grow as the population ages. Current drugs for chronic stable angina (such as beta-blockers, calcium-channel blockers, long- and short-acting nitrates, and potassium-channel activators) are often effective, either as monotherapy or in combination, but side effects and contraindications may limit their use. The "I(f)" (for "funny") channel, discovered in 1979, is expressed mainly in the membrane of pacemaker cells present in the sinus node, the atrioventricular node, the ventricular conduction pathways, and ventricular myocytes. By determining the slope of diastolic depolarization, which in turn controls action potential frequency, it is a key determinant of heart rate and so provides a new therapeutic target for controlling angina symptoms. A new antiangina drug, ivabradine, has been developed and licensed for clinical use. It exclusively reduces the heart rate by selectively blocking the I(f) channel of the sino-atrial node. As clinical trials have shown it to be remarkably well-tolerated, ivabradine offers an alternative for patients who cannot take, or are intolerant of, beta blockade. This review provides an insight into this new agent, its historical background, mechanism of action, and pathophysiologic basis, and provides up-to-date evidence-based information on its optimum use in stable angina.

Increased diastolic time fraction as beneficial adjunct of α1-adrenergic receptor blockade after percutaneous coronary intervention

The effect of α1-receptor blockade with urapidil on coronary blood flow and left ventricular function has been attributed to relief of diffuse coronary vasoconstriction following percutaneous coronary intervention (PCI). We hypothesized that an increase in diastolic time fraction (DTF) contributes to the beneficial action of urapidil. In eleven patients with a 63% (SD 13) diameter stenosis, ECG, aortic pressure (Pa) and distal intracoronary pressure (Pd), and blood flow velocity were recorded at baseline and throughout adenosine-induced hyperemia. Measurements were obtained before and after PCI and after subsequent α1-receptor blockade with urapidil (10 mg ic). DTF was determined from the ECG and the Pa waveform. Functional parameters such as coronary flow velocity reserve, fractional flow reserve, and an index of hyperemic microvascular resistance (HMR) were assessed. Urapidil administration after PCI induced an upward shift in the DTF-heart rate relationship, resulting in a 3.1% (SD 2.7) increase in hyperemic DTF at a constant heart rate ( P < 0.005) due to a shorter duration of systole. Hyperemic Pa and Pd decreased, respectively, by 6.1% (SD 6.6; P < 0.05) and 5.7% (SD 5.8; P < 0.01) after α1-blockade. Although epicardially measured functional parameters were on average not altered by α1-blockade due to concurrent changes in pressure and heart rate, HMR decreased by urapidil in those patients where coronary pressure remained constant. In conclusion, α1-receptor blockade after PCI produced a modest but significant prolongation of DTF at a given heart rate, thereby providing an adjunctive beneficial mechanism for improving subendocardial perfusion, which critically depends on DTF.

Adrenergic receptor polymorphisms in patients with stress (tako-tsubo) cardiomyopathy

BACKGROUND

Stress (tako-tsubo) cardiomyopathy (SC) is a newly reported condition afflicting older women, characterized by acute left ventricular (LV) systolic dysfunction, triggered by emotionally and physically stressful events, and occurring without significant coronary obstruction. Sympathetic nervous system hyperactivity has been implicated in the pathophysiology of SC. Single nucleotide polymorphisms involving the adrenergic receptors (AR) might result in susceptibility to SC.

METHODS

Forty-one female SC patients were identified aged 34-89 years (mean 65) and were compared with 43 control females of similar age with respect to AR genotype frequencies for B1 receptor (amino acid positions 389 and 49) and alpha 2c receptor (deletion 322-325).

RESULTS

For SC patients, initial LV ejection fraction was 32 ± 10% vs. 62 ± 11% in control patients, p < 0.05. Genotype frequencies for SC patients vs. controls were B1 389 Arg/Arg (0.49 vs. 0.51), B1 389 Arg/Gly (0.49 vs. 0.49), B1 389 Gly/Gly (0.02 vs. 0), B1 49 Ser/Ser (0.88 vs. 0.81), B1 49 Ser/Gly (0.12 vs. 0.16), B1 49 Gly/Gly (0 vs. 0.02), alpha 2c Wt/Wt (0.93 vs. 0.86), and alpha 2c Wt/Del 322-325 (0.07 vs. 0.14); p = ns for all comparisons.

CONCLUSIONS

Genotype polymorphism frequencies for B1 receptor (amino acid positions 389 and 49) and alpha 2c receptor (deletion 322-325) are not significantly different in SC patients compared to female controls. These data suggest that these AR polymorphisms do not mediate the sympathetic nervous system hyperactivity in SC patients.

Pleiotropic action(s) of the bradycardic agent ivabradine: cardiovascular protection beyond heart rate reduction

The bradycardic agent ivabradine has proved to be of benefit in experimental models with the end points of ischaemic myocardial blood flow and contractile function, infarct size, post-infarct remodelling and atherosclerosis. The benefits to ischaemic myocardial blood flow and contractile function are strictly heart rate dependent; those on infarct size are partly heart rate independent. The heart rate dependency of ivabradine's benefit for atherosclerotic vascular function is contradictory, and that on post-infarct remodelling is entirely unclear.

Regulation of Coronary Blood Flow During Exercise

Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (∼5-fold), as hemoglobin concentration and oxygen extraction (which is already 70–80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of α- and ß-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases extravascular compressive forces at rest and at comparable levels of exercise, mainly because of a decrease in heart rate. Impedance to coronary inflow due to an epicardial coronary artery stenosis results in marked redistribution of myocardial blood flow during exercise away from the subendocardium towards the subepicardium. However, in contrast to the traditional view that myocardial ischemia causes maximal microvascular dilation, more recent studies have shown that the coronary microvessels retain some degree of vasodilator reserve during exercise-induced ischemia and remain responsive to vasoconstrictor stimuli. These observations have required reassessment of the principal sites of resistance to blood flow in the microcirculation. A significant fraction of resistance is located in small arteries that are outside the metabolic control of the myocardium but are sensitive to shear and nitrovasodilators. The coronary collateral system embodies a dynamic network of interarterial vessels that can undergo both long- and short-term adjustments that can modulate blood flow to the dependent myocardium. Long-term adjustments including recruitment and growth of collateral vessels in response to arterial occlusion are time dependent and determine the maximum blood flow rates available to the collateral-dependent vascular bed during exercise. Rapid short-term adjustments result from active vasomotor activity of the collateral vessels. Mature coronary collateral vessels are responsive to vasodilators such as nitroglycerin and atrial natriuretic peptide, and to vasoconstrictors such as vasopressin, angiotensin II, and the platelet products serotonin and thromboxane A2. During exercise, ß-adrenergic activity and endothelium-derived NO and prostanoids exert vasodilator influences on coronary collateral vessels. Importantly, alterations in collateral vasomotor tone, e.g., by exogenous vasopressin, inhibition of endogenous NO or prostanoid production, or increasing local adenosine production can modify collateral conductance, thereby influencing the blood supply to the dependent myocardium. In addition, vasomotor activity in the resistance vessels of the collateral perfused vascular bed can influence the volume and distribution of blood flow within the collateral zone. Finally, there is evidence that vasomotor control of resistance vessels in the normally perfused regions of collateralized hearts is altered, indicating that the vascular adaptations in hearts with a flow-limiting coronary obstruction occur at a global as well as a regional level. Exercise training does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. In addition to ischemia, the pressure gradient between vascular beds, which is a determinant of the flow rate and therefore the shear stress on the collateral vessel endothelium, may also be important in stimulating growth of collateral vessels.

Dexmedetomidine sedation leading to refractory cardiogenic shock

Dexmedetomidine is frequently used for deep sedation during electrophysiology procedures. We report a case where, presumably, the use of dexmedetomidine resulted in a patient's death. The patient developed unexplained and refractory cardiogenic shock and could not be resuscitated. Autopsy failed to demonstrate any abnormality or cause of death. We postulate that, in certain susceptible individuals, dexmedetomidine may lead to terminal complications. We therefore urge caution about using dexmedetomidine in the electrophysiology laboratory.

Effects of α-adrenoreceptor antagonists on apoptosis and proliferation of pancreatic cancer cells in vitro

AIM: To discuss the expression of α-adrenoreceptors in pancreatic cancer cell lines PC-2 and PC-3 and the effects of α₁- and α₂-adrenoreceptor antagonists, yohimbine and urapidil hydrochloride, on the cell lines in vitro.

METHODS: We cultured the human ductal pancreatic adenocarcinoma cell lines PC-2 and PC-3 and analyzed the mRNA expression of α₁- and α₂-adrenergic receptors by reverse transcription polymerase chain reaction (RT-PCR). The effects of yohimbine and urapidil hydrochloride on cell proliferation were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,4,-diphenyltetrazolium bromide (MTT) assay. Apoptosis was detected using the terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) assay and flow cytometry (FCM).

RESULTS: PC-2 expressed mRNA in α₁- and α₂-adrenoreceptors. MTT assays showed that urapidil hydrochloride had no effect on PC-3 cell lines. However, exposure to urapidil hydrochloride increased DNA synthesis in PC-2 cell lines as compared to the control group. PC-2 cell lines were sensitive to both drugs. The proliferation of the 2 cell lines was inhibited by yohimbine. Cell proliferation was inhibited by yohimbine via apoptosis induction.

CONCLUSION: The expression of α₁- and α₂-adrenoreceptors is different in PC-2 and PC-3 cell lines, which might be indicative of their different functions. The α₂-adrenoceptor antagonist, yohimbine, can inhibit the proliferation of both cell lines and induce their apoptosis, suggesting that yohimbine can be used as an anticancer drug for apoptosis of PC-2 and PC-3 cells.