The cardiac conduction system in situs ambiguus.

The cardiac specialized conduction tissue was studied by serial sectioning in 13 cases of situs ambiguus. In four cases of right isomerism, we found paired sinus nodes in relation to a crista terminalis, and in each case a sling of conduction tissue between two atrioventricular nodes was present regardless of the ventricular morphology or cardiac position. In the cases with left isomerism, the sinus node was hypoplastic and abnormally located. We saw two types of atrioventricular conduction systems. In the three cases in which the morphologically right ventricle lay to the right of the morphologically left ventricle (presumed d-loop), a single atrioventricular bundle arose from a normally located atrioventricular node. In the five cases in which the morphologically right ventricle lay to the left of the morphologically left ventricle (presumed l-loop) and in the one case with a univentricular heart, paired atrioventricular nodes were present, linked or potentially linked by a sling of conduction tissue.     

Atrioventricular conduction tissues in univentricular hearts of left ventricular type.

Univentricular heart of left ventricular type is defined as the condition in which the entirety of atrial inputs is committed to a main chamber exhibiting trabecular pattern of left ventricular type, usually in the presence of another chamber in the ventricular mass which has a right ventricular trabecular pattern. This condition can occur with two atrioventricular valves, a common atrioventricular valve, a straddling atrioventricular valve or with absence of the right or left atrioventricular connexions. The hallmark of univentricular heart of left ventricular type is absence of the inlet septum, which normally separates the inlet portions of the two ventricles and which in the normal heart carries the atrioventricular conduction bundle. In univentricular heart of the left ventricular type, as a consequence of its absence, an abnormal disposition of the atrioventricular conduction tissues is found. An anterior or lateral atrioventricular node is present from which the prenetrating bundle descends onto the trabecular septum separating main chamber from rudimentray chamber. The topographical relationship of the bundle particularly with respect to the outflow tract of the posterior great artery from the main chamber, depends on the position of the rudimentary chamber. In atrial situs solitus, a left-sided rudimentary chamber will be associated with a long bundle in close proximity to the ostium of the posterior great artery from the main chamber. In contrast, in the heart with a right-sided rudimentary chamber the bundle will stay remote from the posterior outflow tract. The position of the rudimentary chamber will also alter the site of the ventriculotomy for any proposed corrective surgery and, hence,, alter the relationship of the bundle relative to the outlet foremen, as viewed by the surgeon. The general disposition of the atrioventricular conduction system in univentricular heart of left ventricular type is not altered by the type or mode of the atrioventricular connexion, nor by the type of the arterial connexion.     

Persisting zones of slow impulse conduction in developing chicken hearts.

We performed a correlative electrophysiological and immunohistochemical study of embryonic chicken hearts during the septational period (Hamburger and Hamilton stages 13-31 [2-7 days of incubation]). The analyses yield conclusive evidence for slow conduction, up to 7 days of development, in the outflow tract, in the atrioventricular canal, and in the sinoatrial junction. The conduction velocity remains approximately 1 cm/sec in the outflow tract and increases in the ventricle 20-fold to approximately 20 cm/sec between 2 and 7 days of development. Transmembrane potentials of myocytes in the outflow tract and atrioventricular canal slowly rise (less than 5 V/sec), whereas in the atrium and ventricle, the upstroke velocity is eightfold to 13-fold higher. In the outflow tract, repolarization is completed only after the start of the next cycle. Because of the persistence of slow conduction, the myocardium flanking the developing atria and ventricle is thought to represent segments of persisting "primary" myocardium, whereas the more rapidly conducting "working" myocardium of the ventricle and atria is thought to represent more advanced stages of myocardial differentiation. The persisting primary myocardium was characterized by a continued coexpression of both the atrial and ventricular isoforms of myosin heavy chain. The developing atria and ventricle could be demarcated morphologically from the primary myocardium because the free walls of these segments only express their respective isoforms of myosin heavy chain. The slowly conducting myocardial zones appear to be essential for the function of the embryonic heart because 1) they provide the septating heart with alternating segments of slow and relatively fast conduction necessary for consecutive contraction of the atrial and ventricular segments and 2) their sphincterlike prolonged peristaltic contraction pattern can substitute for the adult type of one-way valves that start to develop at the end of septation.     

The right ventricle of transplanted hearts at 2,640 meters above sea level. A latin-american experience

Background:High-altitude cardiovascular adaptations increase lung pressure. This effect on the right ventricle (RV) of transplanted hearts at altitudes above 2,500 meters above sea level (masl) has not been described.Objective:The objective of the study was to describe echocardiography RV behavior in the immediate post-operative period (Days 1-7 post-Heart transplant [HTx]), 3, 6, 12, and 24 months after HTx in patients at 2,640 masl.Methods:Historical cohort of HTx patients in the period between 2005 and 2019, in a hospital located in Bogotá, Colombia. Socio-demographic, clinical, and echocardiographic evaluation data of the RV at 5 follow-up moments were analyzed.Results:91 patients underwent HTx, 64% remained at a height > 2,500 masl in the post-operative period. Transthoracic echo was available in 37 patients (40.6%). Right ventricular dysfunction was found in 95% of patients, which was predominantly moderate (43%), with improvement 3 months after transplant. The immediate post-operative Tricuspid annular plane systolic excursion was 8.9 ± 4.9 mm, with recovery from the 3^rd post-operative month (15.1 ± 3.6 mm) and without significant changes in month 24 (15.8 ± 4.9 mm). Immediate post-operative systolic pulmonary artery pressure (sPAP) was 39.2 ± 8.2 mmHg, showing a decrease at 24 post-operative months (31.0 ± 5.0 mmHg). The 5-year survival was 78% Confidence Interval 95% 60-85.Conclusion:After HTx, most patients present right ventricular dysfunction, improving at the 3^rd month of transplant. There were no significant differences between patients living at more than 2,500 masl and < 2,500 masl.     

Noninvasive mapping of ventricular activation in patients with transplanted hearts

This is the first reported study of ventricular activation patterns after cardiac transplantation, using electrocardiographic imaging (ECGI), a noninvasive method for electrophysiologic mapping. This study of ten patients reveals that transplanted hearts have unique ventricular activation patterns in sinus rhythm, activating early in the epicardial aspect of the anterior or inferior septum, with intact right and left bundle branch conduction. They have late activation with slowing of conduction near the right ventricular (RV) basal free wall, causing a mild QRS prolongation and an rSr’ pattern in lead V1 of the ECG. PVCs arise from both endocardial and epicardial locations in both ventricles.     

Evidence for cardiomyocyte repopulation by extracardiac progenitors in transplanted human hearts

Human myocardium has long been considered to have essentially no intrinsic regenerative capacity. Recent studies in rodent models, however, have suggested the presence of an extracardiac stem cell population, perhaps in bone marrow, that is capable of some reconstitution of cardiomyocytes after injury. To determine whether similar mechanisms exist in the human heart, we evaluated human female allograft hearts transplanted into male patients. The presence of Y chromosomes in cardiomyocytes would indicate these cells arose from the recipient, rather than the donor heart. We identified 5 male patients who had retained a female heart at least 9 months before death and necropsy. Remarkably, in each case, the transplanted heart contained a minute but readily detectable fraction of Y chromosome-positive cardiomyocytes. The mean percentage of cardiomyocytes arising from the host was estimated to be 0.04% with a median of 0.016%. Most Y-positive cardiomyocytes were associated with regions of acute rejection, suggesting such chimerism involves an injury event. Furthermore, the sole patient whose immediate cause of death was allograft rejection showed a much higher percentage of host-derived cardiomyocytes, up to 29% in local, 1-mm(2) "hot spots." Thus, adult humans have extracardiac progenitor cells capable of migrating to and repopulating damaged myocardium, but this process occurs at very low levels.     

The atrioventricular conduction system in dissecting aneurysm of the aorta.

In dissecting aneurysm of the ascending aorta the hemorrhage may spread into the interatrial septum and into the area of the specialized atrioventricular junctional tissue. A clinicopathologic investigation has been performed in 48 cases with classical complete dissecting aneurysm in order to evaluate whether such hemorrhage may lead to conduction disturbances. Among 42 cases with aortic dissection originating in the ascending aorta, eight hearts (19 per cent) presented with hemorrhagic infiltration of the atrial septum, extended to the coronary sinus. Histologic examination of the atrioventricular conduction tissues was performed in six of these hearts and in five without such gross evidence (“controls”). In the former the hemorrhage had spread between the transitional cell zone of the atrioventricular junctional area, but never actually penetrated the compact node. In none of the “controls” was there any histological evidence for hemorrhage. The correlation between the histologic data and the available electrocardiographic findings disclosed that atrioventricular conduction disturbances, including atrioventricular dissociation, were present only in cases with hemorrhage of the atrial septum. It is suggested that: (a) hematoma of the interatrial septum is not at all infrequent in cases with dissection of the ascending aorta, (b) this complication leads to atrioventricular conduction disturbances, (c) the hemorrhage preserves a large part of the atrioventricular junctional tissues, thus explaining the occurrence of the atrioventricular dissociation with junctional rhythm and eventual restoration of the normal conduction.     

The conduction system in rheumatoid arthritis with complete atrioventricular block.

Rheumatoid arthritis, of the peripheral type, or the ankylosing spondylitis type, with complete atrioventricular (A-V) block^1–11 or other conduction disturbances^12–18 has been sporadically reported. Very few conduction system studies have been done in these cases.^{3, 7–9, 17, 18} The present report deals with a comprehensive serial section study of the conduction system in a case of the peripheral type of rheumatoid arthritis with complete A-V block.     

The conduction system in hypoplasia of the aortic tract complex.

This is a study of the course of the conduction system in two cases of hypoplasia of the aortic tract complex, one with mitral stenosis and the other with mitral atresia. In both there was a posterior atrioventricular (AV) node which formed the AV bundle. In case 1 the bundle was short and bifurcated early. The branching bundle gave off a large left bundle branch (LBB), many Mahaim fibers to the septum and a small right bundle branch (RBB). In case 2 the AV node was divided into two parts which formed two posterior bundles which joined together to form a short branching bundle. Instead of a LBB there were profuse Mahaim fibers passing from the branching bundle to the depths of the ventricular septum. The RBB was large. The abnormalities seen in the conduction system particularly in the LBB are discussed from the embryologic stand-point.     

胚胎干细胞移植到大鼠梗死心脏后的分化研究

目的研究胚胎下细胞在梗死心脏微环境下向心肌细胞、成纤维细胞的分化情况。方法将大鼠分为两组,梗死组为正常大鼠通过结扎左前降支(LAD)制备,对照组为正常大鼠。将4,6-二氨基(DAPI)标记的具有伞能分化能力的鼠胚胎干细胞(mESCs)注射人急性心肌梗死大鼠(18只)或对照绀大鼠(16只)的心脏,观察胚胎干细胞在休内的分化情况。结果 DAPI标记的移植mESCs在对照和梗死心脏均能成活并形成稳定的移植岛,同时在移植区有巨噬细胞浸润。mESCs移植2～4周后,心脏特异性肌钙蛋白T(cTnT)阳性的移植mESCs比例在正常心脏较梗死心脏高(2.67%±0.79%比1.06%±0.52%,P0.01),但4周后cTnT阳性的DAP1标记细胞在正常和梗死心脏的比例差异无统计学意义(1.17%±0.98%比1.07±1,02%,P0.05)。mESCs在埘照组和梗死组心脏都能分化为成纤维细胞。结论移植mESCs不仪能仔活,还可分化进入大鼠梗死心肌细胞。但是,梗死心脏的微环境不能选择性促进mESCs分化进入心肌细胞。