SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Cardiac anatomy

39

The heartbeat originates within the sinoatrial node (SAN), a small structure containing <10,000 genuine pacemaker cells. If the SAN fails, the ∼5 billion working cardiomyocytes downstream of it become quiescent, leading to circulatory collapse in the absence of electronic pacemaker therapy. Here we demonstrate conversion of rodent cardiomyocytes to SAN cells in vitro and in vivo by expression of Tbx18, a gene critical for early SAN specification. Within days of in vivo Tbx18 transduction, 9.2% of transduced, ventricular cardiomyocytes develop spontaneous electrical firing physiologically indistinguishable from that of SAN cells, along with morphological and epigenetic features characteristic of SAN cells. In vivo, focal Tbx18 gene transfer in the guinea-pig ventricle yields ectopic pacemaker activity, correcting a bradycardic disease phenotype. Myocytes transduced in vivo acquire the cardinal tapering morphology and physiological automaticity of native SAN pacemaker cells. The creation of induced SAN pacemaker (iSAN) cells opens new prospects for bioengineered pacemakers.

Concepts: Gene, Cardiology, Heart, Cardiac electrophysiology, Cardiac anatomy, Cardiac pacemaker, Sinoatrial node, Artificial pacemaker

35

Left atrial (LA) remodeling after an acute myocardial infarction (MI) is poorly characterized regarding its determinants or its effect on ischemic mitral regurgitation (MR) development.

Concepts: Myocardial infarction, Heart, Stroke, Necrosis, Mitral regurgitation, Cardiac anatomy

28

A 50-year-old Chinese woman, non-smoker, presented with a 6-month history of increased sweating on the right side of her face, exertional chest tightness and breathlessness. Although the patient presented with increased sweating on the right, further history and examination revealed unilateral, left-sided anhidrosis, left partial ptosis and miosis consistent with Horner’s syndrome. The patient was subsequently investigated with thoracic CT to assess for an apical lung mass (Pancoast tumour). A CT chest ruled out a mediastinal tumour, however, it revealed a large 60×41 mm soft tissue mass arising from the left atrium, protruding across the mitral valve into the left ventricle, suspicious of an intracardiac tumour. The patient was referred urgently for cardiothoracic assessment at a tertiary referral centre and successful open resection was performed. Histology confirmed an atrial myxoma. The patient developed postoperative atrial fibrillation but otherwise made a full recovery.

Concepts: Blood, Heart, Ventricle, Left ventricle, Cardiac anatomy, Miosis, Pancoast tumor, Horner's syndrome

27

The aim of the study is to determine the impact of the underlying etiology (Barlow’s disease or fibroelastic deficiency) on left ventricular function in patients with degenerative mitral valve disease and severe mitral regurgitation.

Concepts: Heart, Mitral valve, Left ventricle, Mitral regurgitation, Mitral valve prolapse, Cardiac anatomy, Regurgitation, Diastole

27

-Risks associated with pediatric reconstructive heart surgery include injury of the sinoatrial node (SAN) and atrioventricular node (AVN), requiring cardiac rhythm management using implantable pacemakers. These injuries are result of difficulties in identifying nodal tissues intraoperatively. Here, we describe an approach based on confocal microscopy and extracellular fluorophores to quantify tissue microstructure and identify nodal tissue.

Concepts: Cardiology, Heart, Cardiac anatomy, Identification, Cardiac pacemaker, Sinoatrial node, Atrioventricular node, Electrical conduction system of the heart

27

KCNE genes encode for a small family of Kv channel ancillary subunits that form heteromeric complexes with Kv channel alpha subunits to modify their functional properties. Mutations in KCNE genes have been found in patients with cardiac arrhythmias such as the long QT syndrome and/or atrial fibrillation. However, the precise molecular pathophysiology that leads to these diseases remains elusive. In previous studies the electrophysiological properties of the disease causing mutations in these genes have mostly been studied in heterologous expression systems and we cannot be sure if the reported effects can directly be translated into native cardiomyocytes. In our laboratory we therefore use a different approach. We directly study the effects of KCNE gene deletion in isolated cardiomyocytes from knockout mice by cellular electrophysiology - a unique technique that we describe in this issue of the Journal of Visualized Experiments. The hearts from genetically engineered KCNE mice are rapidly excised and mounted onto a Langendorff apparatus by aortic cannulation. Free Ca(2+) in the myocardium is bound by EGTA, and dissociation of cardiac myocytes is then achieved by retrograde perfusion of the coronary arteries with a specialized low Ca(2+) buffer containing collagenase. Atria, free right ventricular wall and the left ventricle can then be separated by microsurgical techniques. Calcium is then slowly added back to isolated cardiomyocytes in a multiple step comprising washing procedure. Atrial and ventricular cardiomyocytes of healthy appearance with no spontaneous contractions are then immediately subjected to electrophysiological analyses by patch clamp technique or other biochemical analyses within the first 6 hours following isolation.

Concepts: DNA, Genetics, Blood, Heart, Cardiac muscle, Cardiac electrophysiology, Ventricle, Cardiac anatomy

27

The risk factors for aortic and mitral valve diseases that require surgical repair such as congenital bicuspid aortic valve (BAV) and mitral valve prolapse include acquired clinical factors and genetic influences. Whether race affects the prevalence of certain valvular diseases has not been sufficiently investigated. Through the Cleveland Clinic’s Cardiovascular Information Registry, we evaluated the data from 40,419 patients who had undergone aortic valve surgery, mitral valve surgery, and/or coronary artery bypass grafting from 1993 to 2007. Of these patients, 38,366 were white and 2,053 were black. The prospective evaluation of valvular disease was coded, identifying the etiology and morphology by echocardiographic, surgical, and pathologic inspection. At baseline, compared to white patients, the black patients were younger, more often women, had a greater body mass index, and a greater prevalence of hypertension, diabetes, tobacco use, and renal disease. The prevalence of congenital BAV and mitral valve prolapse was considerably lower in blacks than in whites (9% vs 25%, p <0.001, and 27% vs 52%, p <0.001, respectively), as was the presence of calcific aortic stenosis (14% vs 28%; p <0.001), pathologically determined aortic valve calcium (50% vs 67%; p <0.001), and mitral valve chordal rupture (13% vs 31%; p <0.001). In conclusion, in the present large surgical series, the valve etiologies and morphology differed among blacks and whites. Despite an adverse cardiovascular risk profile, blacks had a significantly lower prevalence of valvular calcium and degeneration than did the whites and a lower prevalence of congenital BAV and mitral valve prolapse. Our findings offer insight into the influence of race on the development of mitral valve disease and congenital BAV.

Concepts: Atherosclerosis, Heart, Left ventricle, Mitral valve prolapse, Cardiac anatomy, Aortic valve, Valvular heart disease, Bicuspid aortic valve

25

Atrial fibrillation (AF) and stroke are important major health problems that share common risk factors and frequently coexist. Left atrial (LA) remodeling is an important underlying substrate for AF and stroke. LA dilation and dysfunction form a prothrombotic milieu characterized by blood stasis and endothelial dysfunction. In addition, alterations of the atrial cardiomyocytes, increase of noncollagen deposits in the interstitial space and fibrosis, favor the occurrence of re-entry that predisposes to AF. Eventually, AF further impairs LA function and promotes LA remodeling, closing a self-perpetuating vicious circle. Multimodality imaging provides a comprehensive evaluation of several aspects of LA remodeling and offers several parameters to identify patients at risk of AF and stroke. How multimodality imaging can be integrated in clinical management of patients at risk of AF and stroke is the focus of the present review paper.

Concepts: Blood, Heart, Atrial fibrillation, Circulatory system, Atrial flutter, Cardiac anatomy, Left atrial appendage occlusion, Left atrial appendage

25

Dual aortic and ventricular thrombi are rare following myocardial infraction. We report the case of a 56-year-old man who initially denied primary percutaneous coronary intervention as a result of psychological phobia. Initial pharmacological management by thrombolysis and heparin was followed by multiple arterial thromboses including those of the left ventricle and right iliac artery with a subsequent diagnosis of heparin-induced thrombocytopaenia. Ensuing surgical management revealed the unanticipated finding of an additional aortic sinus thrombosis that was excised. The left ventricular thrombus was removed endoscopically to prevent ventricular incisions. This case emphasizes the technical advantages of video-endoscopic management of intracardiac thrombi and highlights the unexpected nature of multiple thromboses associated with heparin-induced thrombocytopaenia.

Concepts: Blood, Myocardial infarction, Heart, Thrombosis, Artery, Cardiovascular system, Left ventricle, Cardiac anatomy

22

The transcription factor ISL1 is thought to be key for conveying the multipotent and proliferative properties of cardiac precursor cells. Here, we investigate its function upon cardiac induction of human embryonic stem cells. We find that ISL1 does not stabilize the transient cardiac precursor cell state but rather serves to accelerate cardiomyocyte differentiation. Conversely, ISL1 depletion delays cardiac differentiation and respecifies nascent cardiomyocytes from a ventricular to an atrial identity. Mechanistic analyses integrate this unrecognized anti-atrial function of ISL1 with known and newly identified atrial inducers. In this revised view, ISL1 is antagonized by retinoic acid signaling via a novel player, MEIS2. Conversely, ISL1 competes with the retinoic acid pathway for prospective cardiomyocyte fate, which converges on the atrial specifier NR2F1. This study reveals a core regulatory network putatively controlling human heart chamber formation and also bears implications for the subtype-specific production of human cardiomyocytes with enhanced functional properties.

Concepts: DNA, Developmental biology, Stem cell, Heart, Cardiac muscle, Circulatory system, Embryonic stem cell, Cardiac anatomy