Matthias Hammwöhner

Angiotensin II Receptor Blockade Reduces Tachycardia-Induced Atrial Adhesion Molecule Expression

Background— Increased levels of inflammatory markers are predictors of thromboembolic events during atrial fibrillation (AF). Increased endocardial expression of adhesion molecules (ie, vascular cell adhesion molecule [VCAM] and intercellular adhesion molecule [ICAM]) could be an important link between initiation of inflammatory and prothrombogenic mechanisms responsible for thrombus development at the atrial endocardium (endocardial remodeling). Methods and Results— Tissue microarrays were used to screen right atrial tissue specimens obtained from 320 consecutive patients for differences in atrial expression of the prothrombogenic proteins VCAM-1, ICAM-1, thrombomodulin, plasminogen activator inhibitor-1, and von Willebrand factor. An in vitro organotypic human atrial tissue model and a pig model of rapid atrial pacing were used to determine the therapeutic impact of angiotensin II receptor blockade. Immunohistochemical analyses showed that all prothrombogenic proteins are expressed by endocardial cells. Using multivariable analysis, only the intensity of VCAM-1 expression was increased in patients with AF (P=0.03). Increased atrial VCAM-1 expression was confirmed by Western blotting in patients with persistent and paroxysmal AF (persistent AF 207±42% versus sinus rhythm 100±16%, P=0.028; paroxysmal AF 193±42%, P=0.024 versus sinus rhythm). In vitro pacing of ex vivo human atrial tissue slices confirmed that rapid activation causes VCAM-1 upregulation (mRNA and protein levels). Pacing-induced VCAM-1 expression was abolished by olmesartan. To confirm this finding in vivo, VCAM-1 expression was determined in 14 pigs after rapid atrial pacing (600 bpm). Atrial tachycardia caused an upregulation of VCAM-1 expression, which was prevented by irbesartan, consistent with the observed increase in plasma levels of angiotensin II. Alterations in the in vivo VCAM-1 expression were more pronounced in the left atrium (>5-fold compared with sham) than in the right atrium (3.5-fold compared with sham). Conclusions— AF and rapid atrial pacing both increase endocardial VCAM-1 expression, which can be attenuated by angiotensin II receptor blockade. This provides evidence that angiotensin II plays a pathophysiological role in prothrombotic endocardial remodeling.

The impact of rapid atrial pacing on ADMA and endothelial NOS

BACKGROUND The endothelial nitric oxide synthase (eNOS) inhibitor asymmetric dimethylarginine (ADMA) is a well-established risk factor for oxidative stress, vascular dysfunction, and congestive heart failure. The aim of the present study was to determine the impact of rapid atrial pacing (RAP) on ADMA levels and eNOS expression. METHODS AND RESULTS ADMA levels were studied in 60 age- and gender-matched patients. Thirty five patients had persistent atrial fibrillation (AF)≥ 4months. In AF-patients, parameters were studied before and 24h after electrical cardioversion. Moreover, ADMA, eNOS expression, and calcium-handling proteins were studied in pigs subjected to RAP as well as in endothelial cell (EC) cultures. ADMA level was significantly higher in AF compared to sinus rhythm patients (p=0.024). ADMA was highest in AF-patients, who also showed elevated troponin T (TnT) levels. Moreover, ADMA showed a significant linear correlation to TnT (r=0.47; p<0.01). After electrical cardioversion ADMA returned to normal within 24h. In pigs, RAP for 7h increased ADMA levels (p=0.018) and TnI (p<0.05), and reduced mRNA expression of ventricular and aortic eNOS (-80%; p<0.05) compared to sham-control. However, ADMA per se did not affect eNOS mRNA level in EC cultures. CONCLUSION The current study shows that acute and persistent episodes of atrial tachyarrhythmia are associated with elevated ADMA levels accompanied by increased ischemic myocardial markers. Moreover, RAP increases ADMA and down-regulates eNOS expression in an ADMA-independent manner. We conclude that the combination of these two separate and potentially synergistic mechanisms may contribute to long-term vascular injury during atrial tachyarrhythmia.

G‐CSF‐Induced Mobilization of CD34+ Progenitor Cells and Proarrhythmic Effects in Patients with Severe Coronary Artery Disease

Aim: Granulocyte colony stimulating factor (G‐CSF) therapy has been reported to be proarrhythmic. The in vivo mobilization of endothelial progenitor cells (EPCs) and the possible proarrhythmic effects in patients with severe coronary artery disease (CAD) and inducible ischemia have not been described.

Neue Antiarrhythmika in der Therapie des Vorhofflimmerns

SummaryThe therapeutic approach to atrial fibrillation is difficult and challenging. The effect of “classical” antiarrhythmic agents is based on their inhibitory effects on various ion channels. However, therapeutic benefit of these agents is often limited. The primary goal of this article is to discuss new therapeutic approaches using non-ion channel blocking drugs in the treatment of atrial fibrillation. Some of the substances discussed in this article have been used already in the clinical practice. Others, for example gentherapeutic approaches, are still in the experimental state. In contrast to ion channel blocking agents their efficacy is based on the suppression of structural remodeling. Hence, it can be assumed that due to these effects they may also be beneficial in the primary prevention of atrial fibrillation.ZusammenfassungDie Behandlung des Vorhofflimmerns (VHF) ist schwierig und für den behandelnden Arzt eine Herausforderung. Die medikamentöse Therapie mit den „klassischen“ ionenkanalblockierenden Substanzen ist in der Effektivität limitiert und birgt insbesondere das Risiko der Proarrhythmie. Ziel dieses Artikels ist es, alternative Behandlungsstrategien mit „Nicht-Ionenkanalblockern“ aufzuzeigen, welche zum Teil schon Einzug in den klinischen Alltag gefunden haben und zum Teil, wie einige gentherapeutische Ansätze, noch im experimentellen Stadium sind. Anders als klassische Antiarrhythmika besteht ihr Wirkprinzip vor allem in der Beeinflussung des strukturellen Remodeling der Vorhöfe. Daher kommt ihnen auch eine Bedeutung im Rahmen der Primärprävention des VHF zu.

Will warfarin soon be passé? New approaches to stroke prevention in atrial fibrillation.

Atrial fibrillation (AF) is the most common cause for thromboembolic stroke. Oral anticoagulation with warfarin is still the most effective therapy in patients with AF, who are at an increased risk for stroke. Nevertheless, warfarin therapy has several limitations; therefore, new anticoagulants like warfarin analogs, thrombin inhibitors, or factor Xa inhibitors have been developed. Some of them are currently being tested in phase III trials in patients with AF. Furthermore, the pathophysiology of prothrombotic endocardial remodeling in fibrillating atria suggests that angiotensin II increases prothrombotic expression of vascular adhesion molecules at the atrial endocardium. Thus, novel anticoagulants or hybrid therapy with a combination of anticoagulants with inhibitors of endocardial remodelling like angiotensin II receptor blockers appear to be attractive future perspective approaches.

New Pharmacologic Approaches to Prevent Thromboembolism in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is associated with a 6 fold increased risk for ischemic stroke. Observational studies suggest that one in four to five strokes is due to AF. Depending on the risk profile of an individual patient, the yearly risk for ischemic stroke is between 2% and 14%. AF is accompanied by an increased propensity for atrial clot formation due to a combination of decreased atrial blood flow, increased activity of the platelet/plasmatic coagulation system and prothrombotic changes at the atrial endocardium. This review summarizes the current guidelines for thromboembolic prevention in patients with AF. In many cases, continuous oral anticoagulation therapy (OAT) with vitamin K antagonists (VitKAs) is indicated if AF is accompanied by more than one additional risk factor for thromboembolic complications. However, therapeutic range of VitKAs (Phenprocoumon, Warfarin, and others), the most commonly used oral anticoagulants, is narrow and their use requires regular anticoagulation monitoring. Possibly due to these limitations, about one third of eligible patients are not treated with VitKAs. Furthermore, in many treated patients OAT is not well controlled. Thus, in clinical practice anticoagulation therapy in AF is suboptimal. Therefore, new and more convenient pharmacologic approaches to prevent thromboembolism with i.e. direct thrombin inhibitors (DTI), synthetic polysaccharides (factor Xa Inhibitors), and others are discussed, and their possible future role in the treatment of AF is evaluated.

[New antiarrhythmic drugs for therapy of atrial fibrillation: II. Non-ion channel blockers].

SummaryDuring the last ten years we have made substantial progress in our understanding of the underlying mechanisms of atrial fibrillation. The high rate associated alterations in electrical and structural properties of the atria, referred to as atrial remodeling, promote the progression of atrial fibrillation. The development of new therapeutic approaches addresses three different directions: (i) prevention of atrial remodeling, especially of structural remodeling; (ii) increase of long-term efficacy of currently used drugs and improvement of their side-effect profile; and (iii) design of atria- and pathology-specific antiarrhythmic drugs without concomitant proarrhythmic effects in the ventricles. The current review outlines the pathophysiology of atrial fibrillation and focuses on electrical remodeling. The properties of new antiarrhythmic drugs for atrial fibrillation are discussed in detail.ZusammenfassungDie vergangenen zehn Jahre haben einen rasanten Zuwachs in unserem Verständnis von den Mechanismen, die dem Vorhofflimmern zugrunde liegen, gebracht. Nach dem Einsetzen von Vorhofflimmern treten bereits innerhalb kurzer Zeit elektrophysiologische und strukturelle Veränderungen (Remodeling) auf, die die Progredienz dieser Rhythmusstörung maßgeblich verstärken. Die Entwicklung neuer Therapieansätze verfolgt drei Ziele, nämlich 1. Verhinderung von Remodeling, insbesondere von strukturellem Remodeling, 2. Verbesserung von zugelassenen Antiarrhythmika hinsichtlich Wirksamkeit und Nebenwirkungsprofil, und 3. Entwicklung von Vorhof- bzw. Pathologie-selektiven Antiarrhythmika, um ventrikuläre proarrhythmische Effekte zu vermeiden. In der vorliegenden Übersicht werden die Pathophysiologie und das elektrische Remodeling bei Vorhofflimmern erörtert. Nachfolgend werden die Eigenschaften neuer, speziell für die Therapie des Vorhofflimmerns entwickelter antiarrhythmischer Substanzen im Einzelnen diskutiert.

Atrial expression of endothelial nitric oxide synthase in patients with and without atrial fibrillation

BACKGROUND Atrial fibrillation (AF) is associated with oxidative stress within the fibrillating atrial myocardium. Experimental studies suggest that reduced levels of nitric oxide (NO) caused by down-regulation of the NO synthase (eNOS) contribute to the development of prothrombotic endocardial remodeling in AF. This study was designed to determine the endocardial expression of eNOS in atrial tissue samples from patients with and without AF. METHODS Tissue microarrays were used to analyze right atrial tissue specimens obtained from 234 patients (38 with AF; 196 with sinus rhythm) for differences in atrial eNOS expression. In selected patients, immunohistological results were confirmed by Western blotting. RESULTS Immunohistochemical analyses showed that eNOS is expressed by endocardial cells and myocytes. However, endocardial expression of eNOS was not independently related to AF per se. There was no difference between paroxysmal and persistent AF. Clinical factors like gender (P=.05) and coronary artery disease (P=.06) were associated with down-regulation of eNOS. Interestingly, diabetes mellitus (P=.02) was associated with an up-regulation of endocardial eNOS, whereas other risk factors for thromboembolic events did not influence eNOS levels. Multivariable analysis showed that eNOS expression is influenced by interactions between diabetes mellitus and AF (P=.09) as well as by interactions between gender and AF (P=.04). Lowest levels of eNOS were found in women with AF. CONCLUSION AF does not independently effect atrial eNOS expression in humans. Due to the nonuniform regulation of endocardial eNOS expression, it appears unlikely that down-regulation of eNOS is a final common pathway for the development of prothrombotic endocardial remodeling, since classical risk factors for thromboembolic events do not reduce endocardial eNOS protein.

Enzymatic activity of DPIV and renin–angiotensin system (RAS) proteases in patients with left ventricular dysfunction and primary prevention implantable cardioverter/defibrillator (ICD)

BACKGROUND Patients (pts) with severely decreased left ventricular ejection fraction (LV-EF ≤ 35%) are at high risk for sudden cardiac death (SCD). We sought to investigate, if pts with primary prevention ICD hold alterations in enzyme-activities of the dipeptidyl-aminopeptidase IV (DPIV) and the renin-angiotensin system (RAS) before VT/VF occurrence. METHODS 57 Pts (53 male, mean age 64.9 [42-84] years, mean LV-EF 26 ± 5%) with ischemic (n=49) or non-ischemic cardiomyopathy (n=8) who had received an ICD/CRT-D for primary prevention, were included. Pts were assessed for appropriate ICD intervention for VT/VF during a mean follow-up of 365 ± 90 days. Serum levels of dipeptidyl-aminopeptidase IV (DPIV), aminopeptidase N (APN), aminopeptidase B (APB), insulin-regulated aminopeptidase (IRAP), and angiotensin-converting enzyme 2 (ACE2) were determined. RESULTS Pts with appropriate ICD intervention (n=16) had higher serum activities of IRAP (mean difference=12.681 pkat/mL; p=0.007), and DPIV (mean difference=117.557 pkat/mL; p=0.032) than pts without appropriate ICD intervention. Furthermore, ACE2 activity was significantly higher (median: 223.7 RFU/smL vs. 169.10 RFU/smL; p=0.037). A Cox regression analysis indicated DPIV activity >50th centile to have a hazard ratio (HR) of 5.955 (CI 95%: 1.670-21.241; p=0.006) for prediction of appropriate ICD intervention. In a multivariate Cox regression model, DPIV and IRAP >50th centile remained predictive for appropriate ICD intervention. CONCLUSION Our prospective study shows that pts with primary prevention ICD, who receive appropriate ICD intervention during follow-up, can be identified by elevated activities of DPIV and several RAS proteases. Hence, theses biomarkers seem to be of prognostic relevance in a primary prevention collective. Our data has to be proven in larger cohorts.

Aortic thrombus and pulmonary embolism in a patient with hyperhomocysteinemia

Background A 32-year-old man presented at hospital with persistent pain, hypothermia and paraesthesia in his right leg, caused by embolic occlusion of all three large arteries as a result of massive thrombi in the abdominal aorta. Previously, the patient had been diagnosed with pulmonary embolism and admitted at least a 6-month history of alcohol abuse. Laboratory assessment of the patients lipid levels, platelet function and coagulation factors yielded normal results. Duplex ultrasound revealed substantial media thickening of the carotid and femoral arteries, without evidence of calcification. Further laboratory tests revealed elevated plasma levels of homocysteine, asymmetric dimethylarginine, symmetric dimethylarginine and 8-isoprostaglandin F2α.Investigations Physical examination, laboratory analyses, bronchoscopy, duplex ultrasonography, CT scan and CT angiographyDiagnosis Severe hyperhomocysteinemia associated with acute aortic thrombi and peripheral emboliManagement Diet supplementation with folic acid, vitamin B6 and vitamin B12, low-molecular-weight heparin and L-arginine.