Florian Stöckigt

Persistence of iatrogenic atrial septal defect after interventional mitral valve repair with the MitraClip system: a note of caution.

OBJECTIVES The purpose of this study was to investigate the persistence rates of iatrogenic atrial septal defect (iASD) after interventional edge-to-edge repair with serial transesophageal echocardiography examinations and close clinical follow-up (FU). BACKGROUND Transcatheter mitral valve repair (TMVR) with the MitraClip system (Abbott Vascular, Abbott Park, Illinois) is a therapeutic alternative to surgery in selected high-risk patients. Clip placement requires interatrial transseptal puncture and meticulous manipulation of the steerable sheath. The persistence of iASD after MitraClip procedures and its clinical relevance is unknown. METHODS A total of 66 patients (76.7% male, mean age 77.1 ± 7.9 years) with symptomatic mitral regurgitation (MR) at prohibitive surgical risk (EuroSCORE II 10.1 ± 6.1%) underwent MitraClip procedures and completed 6 months of FU. RESULTS Transesophageal echocardiography after FU showed persistent iASD in 50% of cases. Patients with iASD did not significantly differ from patients without ASD concerning baseline characteristics, New York Heart Association functional class, severity of MR, and acute procedural success rates (p > 0.05). When comparing procedural details and hemodynamic measures between groups, MitraClip procedures took longer in patients without iASD (82.4 ± 39.7 min vs. 68.9 ± 45.5 min; p = 0.05), and echocardiography after FU showed less decrease of systolic pulmonary artery pressures in the iASD group (-1.6 ± 14.1 mm Hg vs. 9.3 ± 17.4 mm Hg; p = 0.02). Clinically, patients with iASD presented more often with New York Heart Association functional classes >II after FU (57% vs. 30%; p = 0.04), showed higher levels of N-terminal pro-brain natriuretic peptide (6,667.3 ± 7,363.9 ng/dl vs. 4,835.9 ± 6,681.7 ng/dl; p = 0.05), and had less improvement in 6-min walking distances (20.8 ± 107.4 m vs. 114.6 ± 116.4 m; p = 0.001). Patients with iASD showed higher death rates during 6 months (16.6% vs. 3.3%; p = 0.05). Cox regression analysis found that only persistence of iASD (p = 0.04) was associated with 6-month survival. CONCLUSIONS The persistence rate of 50% iASD after MitraClip procedures is considerably high. Persistent interatrial shunting was associated with worse clinical outcomes and increased mortality. Further studies are warranted to investigate if persistent interatrial shunting is the mediator or marker of advanced disease in these patients.

The Connexin40A96S mutation from a patient with atrial fibrillation causes decreased atrial conduction velocities and sustained episodes of induced atrial fibrillation in mice

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and a major cause of stroke. In the mammalian heart the gap junction proteins connexin40 (Cx40) and connexin43 (Cx43) are strongly expressed in the atrial myocardium mediating effective propagation of electrical impulses. Different heterozygous mutations in the coding region for Cx40 were identified in patients with AF. We have generated transgenic Cx40A96S mice harboring one of these mutations, the loss-of-function Cx40A96S mutation, as a model for atrial fibrillation. Cx40A96S mice were characterized by immunochemical and electrophysiological analyses. Significantly reduced atrial conduction velocities and strongly prolonged episodes of atrial fibrillation were found after induction in Cx40A96S mice. Analyses of the gating properties of Cx40A96S channels in cultured HeLa cells also revealed significantly lower junctional conductance and enhanced sensitivity voltage gating of Cx40A96S in comparison to Cx40 wild-type gap junctions. This is caused by reduced open probabilities of Cx40A96S gap junction channels, while single channel conductance remained the same. Similar to the corresponding patient, heterozygous Cx40A96S mice revealed normal expression levels and localization of the Cx40 protein. We conclude that heterozygous Cx40A96S mice exhibit prolonged episodes of induced atrial fibrillation and severely reduced atrial conduction velocities similar to the corresponding human patient.

Ablation of cyclase-associated protein 2 (CAP2) leads to cardiomyopathy

Cyclase-associated proteins are highly conserved proteins that have a role in the regulation of actin dynamics. Higher eukaryotes have two isoforms, CAP1 and CAP2. To study the in vivo function of CAP2, we generated mice in which the CAP2 gene was inactivated by a gene-trap approach. Mutant mice showed a decrease in body weight and had a decreased survival rate. Further, they developed a severe cardiac defect marked by dilated cardiomyopathy (DCM) associated with drastic reduction in basal heart rate and prolongations in atrial and ventricular conduction times. Moreover, CAP2-deficient myofibrils exhibited reduced cooperativity of calcium-regulated force development. At the microscopic level, we observed disarrayed sarcomeres with development of fibrosis. We analyzed CAP2’s role in actin assembly and found that it sequesters G-actin and efficiently fragments filaments. This activity resides completely in its WASP homology domain. Thus CAP2 is an essential component of the myocardial sarcomere and is essential for physiological functioning of the cardiac system, and a deficiency leads to DCM and various cardiac defects.

The toxic effect of R350P mutant desmin in striated muscle of man and mouse

Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive and sporadic forms of protein aggregation myopathies and cardiomyopathies. We generated R349P desmin knock-in mice, which harbor the ortholog of the most frequently occurring human desmin missense mutation R350P. These mice develop age-dependent desmin-positive protein aggregation pathology, skeletal muscle weakness, dilated cardiomyopathy, as well as cardiac arrhythmias and conduction defects. For the first time, we report the expression level and subcellular distribution of mutant versus wild-type desmin in our mouse model as well as in skeletal muscle specimens derived from human R350P desminopathies. Furthermore, we demonstrate that the missense-mutant desmin inflicts changes of the subcellular localization and turnover of desmin itself and of direct desmin-binding partners. Our findings unveil a novel principle of pathogenesis, in which not the presence of protein aggregates, but disruption of the extrasarcomeric intermediate filament network leads to increased mechanical vulnerability of muscle fibers. These structural defects elicited at the myofiber level finally impact the entire organ and subsequently cause myopathy and cardiomyopathy.

Induction of Atrial Fibrillation by Neutrophils Critically Depends on CD11b/CD18 Integrins

Background Recent observational clinical and ex-vivo studies suggest that inflammation and in particular leukocyte activation predisposes to atrial fibrillation (AF). However, whether local binding and extravasation of leukocytes into atrial myocardium is an essential prerequisite for the initiation and propagation of AF remains elusive. Here we investigated the role of atrial CD11b/CD18 mediated infiltration of polymorphonuclear neutrophils (PMN) for the susceptibility to AF. Methods and Results C57bl/6J wildtype (WT) and CD11b/CD18 knock-out (CD11b−/−) mice were treated for 14 days with subcutaneous infusion of angiotensin II (Ang II), a known stimulus for PMN activation. Atria of Ang II-treated WT mice were characterized by increased PMN infiltration assessed in immunohistochemically stained sections. In contrast, atrial sections of CD11b−/− mice lacked a significant increase in PMN infiltration upon Ang II infusion. PMN infiltration was accompanied by profoundly enhanced atrial fibrosis in Ang II treated WT as compared to CD11b−/− mice. Upon in-vivo electrophysiological investigation, Ang II treatment significantly elevated the susceptibility for AF in WT mice if compared to vehicle treated animals given an increased number and increased duration of AF episodes. In contrast, animals deficient of CD11b/CD18 were entirely protected from AF induction. Likewise, epicardial activation mapping revealed decreased electrical conduction velocity in atria of Ang II treated WT mice, which was preserved in CD11b−/− mice. In addition, atrial PMN infiltration was enhanced in atrial appendage sections of patients with persistent AF as compared to patients without AF. Conclusions The current data critically link CD11b-integrin mediated atrial PMN infiltration to the formation of fibrosis, which promotes the initiation and propagation of AF. These findings not only reveal a mechanistic role of leukocytes in AF but also point towards a potential novel avenue of treatment in AF.

In vitro comparison of platinum-iridium and gold tip electrodes: lesion depth in 4 mm, 8 mm, and irrigated-tip radiofrequency ablation catheters.

AIMS We compared a newly developed irrigated gold tip electrode ablation catheter and a gold tip 4 and 8 mm catheter with the corresponding platinum-iridium (Pt) tip catheters in an in vitro setting. METHODS AND RESULTS In a flow chamber simulating physiological flow conditions, radiofrequency catheter ablation was performed on tissue samples of porcine endomyocardium and liver. Lesion depth, energy and temperature delivery, and popping frequency were determined. Two hundred and fifty-three ablations were conducted. Four and eight millimetre, gold tip electrode catheters produced significantly deeper lesions compared with the Pt tip electrode (liver 4 mm: 4.67 +/- 1.7 vs. 2.9 +/- 1.0 mm, P < 0.0001; endomyocardium 4 mm: 3.88 +/- 1.1 vs. 2.81 +/- 0.7 mm, P < 0.001; liver 8 mm: 3.98 +/- 1.0 vs. 2.03 +/- 1.1 mm, P < 0.001; endomyocardium 8 mm: 4.00 +/- 0.9 vs. 3.39 +/- 0.8 mm, P < 0.001) and correlated with the amount of energy delivery. Popping frequency was significantly higher in gold tip electrodes. In irrigated tip electrodes, there was no difference in the lesion depth comparing gold with Pt (liver: 5.18 +/- 0.7 vs. 5.01 +/- 0.7 mm, P = ns; endomyocardium: 4.89 +/- 0.7 vs. 4.78 +/- 0.8 mm, P = ns). There was a trend towards less popping in the gold tip electrode. CONCLUSION Both 4 and 8 mm not-irrigated gold tip catheters produced deeper lesions than the corresponding Pt tip catheter. In irrigated tip catheters, gold and Pt tip material did not show differences in the lesion depth.

Total beta-adrenoceptor knockout slows conduction and reduces inducible arrhythmias in the mouse heart.

Introduction Beta-adrenoceptors (β-AR) play an important role in the neurohumoral regulation of cardiac function. Three β-AR subtypes (β1, β2, β3) have been described so far. Total deficiency of these adrenoceptors (TKO) results in cardiac hypotrophy and negative inotropy. TKO represents a unique mouse model mimicking total unselective medical β-blocker therapy in men. Electrophysiological characteristics of TKO have not yet been investigated in an animal model. Methods In vivo electrophysiological studies using right heart catheterisation were performed in 10 TKO mice and 10 129SV wild type control mice (WT) at the age of 15 weeks. Standard surface ECG, intracardiac and electrophysiological parameters, and arrhythmia inducibility were analyzed. Results The surface ECG of TKO mice revealed a reduced heart rate (359.2±20.9 bpm vs. 461.1±33.3 bpm; p<0.001), prolonged P wave (17.5±3.0 ms vs. 15.1±1.2 ms; p = 0.019) and PQ time (40.8±2.4 ms vs. 37.3±3.0 ms; p = 0.013) compared to WT. Intracardiac ECG showed a significantly prolonged infra-Hisian conductance (HV-interval: 12.9±1.4 ms vs. 6.8±1.0 ms; p<0.001). Functional testing showed prolonged atrial and ventricular refractory periods in TKO (40.5±15.5 ms vs. 21.3±5.8 ms; p = 0.004; and 41.0±9.7 ms vs. 28.3±6.6 ms; p = 0.004, respectively). In TKO both the probability of induction of atrial fibrillation (12% vs. 24%; p<0.001) and of ventricular tachycardias (0% vs. 26%; p<0.001) were significantly reduced. Conclusion TKO results in significant prolongations of cardiac conduction times and refractory periods. This was accompanied by a highly significant reduction of atrial and ventricular arrhythmias. Our finding confirms the importance of β-AR in arrhythmogenesis and the potential role of unspecific beta-receptor-blockade as therapeutic target.

AMP-activated protein kinase α1-sensitive activation of AP-1 in cardiomyocytes

AMP-activated protein kinase (Ampk) regulates myocardial energy metabolism and plays a crucial role in the response to cell stress. In the failing heart, an isoform shift of the predominant Ampkα2 to the Ampkα1 was observed. The present study explored possible isoform specific effects of Ampkα1 in cardiomyocytes. To this end, experiments were performed in HL-1 cardiomyocytes, as well as in Ampkα1-deficient and corresponding wild-type mice and mice following AAV9-mediated cardiac overexpression of constitutively active Ampkα1. As a result, in HL-1 cardiomyocytes, overexpression of constitutively active Ampkα1 increased the phosphorylation of Pkcζ. Constitutively active Ampkα1 further increased AP-1-dependent transcriptional activity and mRNA expression of the AP-1 target genes c-Fos, Il6 and Ncx1, effects blunted by Pkcζ silencing. In HL-1 cardiomyocytes, angiotensin-II activated AP-1, an effect blunted by silencing of Ampkα1 and Pkcζ, but not of Ampkα2. In wild-type mice, angiotensin-II infusion increased cardiac Ampkα1 and cardiac Pkcζ protein levels, as well as c-Fos, Il6 and Ncx1 mRNA expression, effects blunted in Ampkα1-deficient mice. Pressure overload by transverse aortic constriction (TAC) similarly increased cardiac Ampkα1 and Pkcζ abundance as well as c-Fos, Il6 and Ncx1 mRNA expression, effects again blunted in Ampkα1-deficient mice. AAV9-mediated cardiac overexpression of constitutively active Ampkα1 increased Pkcζ protein abundance and the mRNA expression of c-Fos, Il6 and Ncx1 in cardiac tissue. In conclusion, Ampkα1 promotes myocardial AP-1 activation in a Pkcζ-dependent manner and thus contributes to cardiac stress signaling.

Superiority of Gold versus Platinum Irrigated Tip Catheter Ablation of the Pulmonary Veins and the Cavotricuspid Isthmus: A Randomized Study Comparing Tip Temperatures and Cooling Flow Requirements

Gold versus Platinum Irrigated Tip Ablation Catheters. Introduction: In order to optimize power delivery into the myocardium during radiofrequency ablation (RFA) without overheating the electrode tip, active cooling of the tip electrode as well as electrode tips made of gold have evolved. Recently, an externally irrigated gold tip electrode ablation catheter has been developed to combine the advantages of these 2 technologies. We sought to investigate the procedural parameters tip temperature, delivered power and cooling flow requirements of the irrigated gold tip catheter in comparison to the conventional irrigated platinum iridium (Pt) tip catheter in pulmonary vein isolation (PVI) and cavotricuspid isthmus (CTI) ablation.

Induced and spontaneous heart rate turbulence in mice: influence of coupling interval.

AIMS Heart rate turbulence (HRT) is a prognostic parameter for risk stratification in patients suffering from coronary artery disease. The aims of this study were to demonstrate the feasibility of quantifying HRT in mice, both in long-term electrocardiograms (ECGs) as well as after extrastimulus pacing, and to analyse its characteristics. METHODS AND RESULTS We performed long-term ECG recordings using implanted telemetric chips and electrophysiological (EP) investigations, using transvenously inserted EP catheters, in healthy mice. Heart rate turbulence was calculated using the established turbulence onset (TO) and slope (TS) algorithm. After spontaneous ventricular premature complexes (VPCs), we found a negative TO (-2.2 ± 7.5%) and positive TS (15.5 ± 18.3 ms/RR interval). Electrophysiological investigations revealed positive values for TO (0.6 ± 1.1%) and TS (6.5 ± 2.9 ms/RR interval) after extrastimulus pacing maneuvers. The shortening of the extrastimuli coupling intervals delivered during EP investigations significantly influenced TO (r = 0.57; P = 0.01): shorter coupling intervals provoked more positive TO values. CONCLUSION Mice display both spontaneous and induced HRT. In terms of TO, VPCs generated by extrastimulus pacing are significantly dependent on the coupling interval. Determining HRT in mice is feasible and provides insight into basic mechanisms of blood pressure regulation, which is realized by the baroreflex.