Selective left bundle branch pacing for pediatric complete heart block

Traditionally Right Ventricle has been the preferred site of pacing for the management of symptomatic brady-arrhythmias. The deleterious effect of chronic RV pacing has been shown by several studies. This has generated interest into a novel pacing strategy called physiological pacing wherein the His bundle or the left bundle is paced directly with 4.1 F pacing lead. Herewith we are reporting a case of congenital complete heart block in a 13-year-old child for whom selective left bundle branch pacing was done. This physiological pacing will ensure a synchronized contraction of the ventricles thereby avoiding the deleterious effect of RV pacing.     

Cardiomyopathy induced by incessant ventricular tachycardia originating in the vicinity of the His bundle

A 04-year-old boy was referred to our institution with severe, progressive heart failure of 4-months duration associated with a persistent wide QRS tachycardia with left bundle branch block and severe left ventricular dysfunction. Because of incessant wide QRS tachycardia refractory to antiarrhythmic drugs, he was referred for electrophysiological study. The ECG was suggestive of VT arising from the right ventricle near the His area. Electrophysiological study revealed that origin of tachycardia was septum of the right ventricle, near His bundle, however the procedure was not successful and an inadvertent complete atrioventricular conduction block occurred. The same ventricular tachycardia recurred. A second procedure was performed with a retrograd aortic approach to map the left side of the interventricular septum. The earliest endocardial site for ablation was localized in the anterobasal region of left ventricle near His bundle. In this location, one radiofrequency pulse interrupted VT and rendered it not inducible. The echocardiographic evaluation showed partial reversal of left ventricular function in the first 3 months. The diagnosis was idiopathic parahisian left ventricular tachycardia leading to a tachycardia mediated cardiomyopathy, an extremely rare clinical picture in children.     

The early development of the atrioventricular node and bundle of His in the embryonic chick heart. An electrophysiological and morphological study

The development of the atrioventricular node and bundle of His of embryonic chick hearts was studied by electrophysiological and morphological techniques. The dorsal wall of the AV canal and the interatrial septum were explored to determine if they contribute to the formation of the AV node and bundle of His. The resting membrane and action potentials of the interatrial septum cells were systematically analyzed and found to undergo progressive differentiation with development. The earliest identification of the AV node and upper bundle of His group of cells was achieved at 5 1/2-6 days of development by the electrical recording of their corresponding characteristic action potentials, from a circumscribed area located in the lowest and dorsal segment of the interatrial septum. The morphological and anatomical characterization of the cells was made following electrical recording and labelling with charcoal particles. The earlier AV node and bundle of His responses had similar characteristics to those of the adult heart. It is concluded that the AV node and upper bundle of His cells derive from the low interatrial septum. The possibility that AV canal cells contribute to this event was discarded. The functional relationship of the Av node and bundle of His with other cardiac tissues during the early development of the heart is discussed.     

Selective His-bundle pacing in an adult with atrioventricular canal defect via retrograde His localization

Adult congenital heart disease patients may undergo numerous fluoroscopically guided procedures including pacemaker implantation during their lifetime. One alternative to traditional pacemaker setup which may improve long-term pacing outcomes is His bundle pacing. Given the altered His-bundle location, and given increased radiation exposure over a lifetime, we used 3-dimensional mapping to locate the His and to minimize fluoroscopy for placement of a His-bundle pacemaker system in a 31-year old patient with atrioventricular canal defect and complete heart block with 100% RV pacing and epicardial lead fracture.MethodsAn Octapolar Livewire catheter (Abbott, Minneapolis, USA) was used for mapping and location of the His bundle from a right femoral venous access on the EnSite Precision system 3-dimensional mapping system (Abbott Medical, Abbott Park, IL). The same map was used to guide 3830 lead placement into the posterior-inferior His-bundle position.ResultsSuccessful placement of a His-bundle pacing system with thresholds of 1Volt@0.4ms for both the atrial and ventricular leads with selective His-bundle pacing noted. Ten-month follow-up demonstrated His-bundle capture at 0.75V@0.4ms with stable impedance, sensing and with 100% right ventricular pacing a projected longevity of 12 years total.ConclusionsSuccessful placement of selective His-bundle pacing can be achieved in an adult patient with atrioventricular canal defect using 3-dimensional mapping.     

A morphometric analysis of the structure of the atrioventricular node of the sheep heart]

The work deals with the geometry of the structure of different sections of the atrio-venticular (A-V) node of the sheep's heart and measurement of the diameter of fibres in its three zones: atrio-nodal (A-N), the node proper (N) and transition of the node into His bundle (NH). The revealed difference in the diameter of contacting fibres of N and NH areas under worse conditions of conducting may contribute to block of excitation. The geometrical features of A-N and N areas contribute to prolonged delay of excitation and geometrical parameters of the site of contact between N and NH zones to its block.     

Unusual Pauses In Sinus rhythm And Intermittent 2 to 1 AV Block In A Patient With Concealed His Extra Systoles - A Rare Cause Of Bradycardia

A 56 year old male with a past medical history of hypertension and dyslipidemia presented with recurrent dizziness. Routine EKG was performed, which suggested frequent junctional extra systoles with compensatory pauses. During telemetry periods of 2:1 block with effective ventricular rate of 34 bpm was observed. His bundle study suggested frequent His extra systoles causing functional AV block. Treatment with anti-arrhythmic medication, paradoxically improved AV block and symptoms in our patient.     

Types of anatomic correspondence between the conducting system and the heart

The principles of a quantitative determination of characteristics concerning the types of anatomical correspondence between the conduction system and the heart at its congenital malformations are presented. This makes it possible to establish that the topographoanatomical type of the conduction system depends on the peculiarities of the heart structure at its congenital malformations rather than from changes in the structure and position of the parts of the conduction system, or the conduction system as a whole according to the types of congenital heart malformations. The mechanism of the left-sided position of the atrioventricular bundle (His bundle) in some congenital malformations of the heart is explained.     

Development of a model of complete heart block in rats

Atrioventricular(AV) block is a useful substrate for the study of cardiacphysiology. The objective of this investigation was todevelop a straightforward and reproducible model of permanent AV blockin rats. Working through a sternotomy, we used an epicardial fat padbetween the aortic root and the right atrial wall of the rat as alandmark for the site for injection of 70% ethanol (5-10 µl)into the myocardium 3 mm below the epicardial surface. Stable, completeheart block was produced in 23 of 28 rats (82%) with a success rate of100% in the last 16 rats of the series. Saline injection produced noheart block in 15 rats. A separate group of 14 animals was allowed torecover. Chronic heart block was achieved in all ethanol-injectedanimals for up to 7 days before death. The survival rate in therecovered rats was 90% in the ethanol-injected group and 100% in thesaline-injected control group. Acute hemodynamic changes following theproduction of heart block consisted of an increase in central venouspressure, a decrease in systolic blood pressure, a decrease in leftventricular pressure, and a decrease in change in pressure overtime. Chronic hemodynamic changes demonstrated a return tobaseline of the central venous pressure, a persistent decrease insystolic blood pressure, and a decrease in left ventricular pressure.After the rats were killed and the hearts were dissected, discreteareas of myocardial damage were identified histologically in the atrialseptum near the AV conduction axis tissue in the ethanol-injectedhearts. Complete heart block was associated only with lesions extendinginto the specialized muscle of the AV node or His bundle. Focal mildhemorrhage, inflammation, and damaged myocardial fibers were observedin the acute stage, whereas healing lesions were characterized bygranulation tissue and fibrosis replacing conduction tissue. The simpletechnique described provides a reproducible model for permanent,complete heart block and the study of cardiac function.

     

Therapy-related myelodysplastic syndrome presenting as fulminant heart failure secondary to myeloid sarcoma

Rapidly progressive heart failure is commonly caused by an extensive myocardial infarction, a mechanical complication of infarction, myocarditis, or acute valvular insufficiency. We present an unusual case that was caused by a diffuse infiltration of the myocardium with leukemic cells (myeloid sarcoma). The patient presented with episodic shortness of breath, he was anemic and thrombocytopenic, and his bone marrow biopsy revealed myelodysplastic syndrome from treatment for oligodendroglioma. His clinical course was characterized by a chronic leak of cardiac enzymes, a new right bundle branch block, and a large pericardial effusion causing tamponade and death from fulminant heart failure and ventricular arrhythmias within 2 weeks. At autopsy, the heart was massively infiltrated with myeloblasts and other immature myeloid cells. There was no evidence of acute leukemia in the bone marrow or peripheral blood. Cardiac infiltration in a patient with myelodysplastic syndrome is extremely rare, especially in the absence of bone marrow involvement by blasts. The recognition of this entity is becoming increasingly important as the incidence of cardiac myeloid sarcoma may be on the rise as the number of patients receiving chemotherapy increases.     

The conduction system of the heart in mice chronically infected with Trypanosoma cruzi: histopathological lesions and electrocardiographic correlations

Chronic focal and diffuse myocarditis with interstitial fibrosis developed in Swiss outbred mice and in the inbred AKR and A/J strains of mice which were chronically infected with several Trypanosoma cruzi strains belonging to three biological types (Type I, II and III). High incidence of electrocardiographic changes with predominance of intraventricular conduction disturbances, 1st. and 2nd. degree AV block, arrhythmias, comparable with those found in human Chagas' disease, were also present. Morphological study of the conduction tissue of the heart revealed inflammatory and fibrotic changes. The presence of inflammation in the inter-atrial septum almost always coincided with the inflammatory involvement of the ventricular conduction system. Focal inflammation was associated with vacuolization and focal necrosis of the specific fibers. Most of the lesions were seen affecting the His bundle (76.3% of the cases), the right bundle branch (73.3%), AV node (43.9%) and left bundle branch (37.5%). Correlation between morphological changes in the conduction tissue and electrocardiographic alteration occurred in 53.0 to 62.5% of the cases, according to the experimental groups.     

Computer-assisted morphometric study of the innervation of the guinea pig heart

A computer-assisted method is introduced for the morphometric analysis of immunoreactive markers of the innervation of the heart, such as synaptophysin, neuropeptide Y (NPY), neurotensin (NT), substance P (SP), and calcitonin gene-related peptide (CGRP). Video images of stained sections were digitalized and the area density (AD) of the immunoreactive structures was measured by discrimination for grey levels within the myocardium of the right atrium, the perivascular region of epicardial arteries, and the trunk of the bundle of His. Synaptophysin immunoreactivity (IR), which served as a marker for presynaptic vesicles, indicated a dense innervation of the conductive system (AD 1.5241). Marked differences in the pattern of distribution were found between the neuropeptides. The AD of NPY-IR (0.5073) and SP-IR (0.1352) was highest in the perivascular tissue, while NT-IR (0.1628) and CGRP-IR (0.5161) exhibited maximal values in the bundle of His. The computer-assisted morphometric measurement of the AD of immunoreactive markers is suggested to be a suitable method for quantitative studies of the innervation of the heart under normal and experimental conditions.     

Bundle branch reentrant ventricular tachycardia

Bundle branch reentrant (BBR) tachycardia is an uncommon form of ventricular tachycardia (VT) incorporating both bundle branches into the reentry circuit. The arrhythmia is usually seen in patients with an acquired heart disease and significant conduction system impairment, although patients with structurally normal heart have been described. Surface ECG in sinus rhythm (SR) characteristically shows intraventricular conduction defects. Patients typically present with presyncope, syncope or sudden death because of VT with fast rates frequently above 200 beats per minute. The QRS morphology during VT is a typical bundle branch block pattern, usually left bundle branch block, and may be identical to that in SR. Prolonged His-ventricular (H-V) interval in SR is found in the majority of patients with BBR VT, although some patients may have the H-V interval within normal limits. The diagnosis of BBR VT is based on electrophysiological findings and pacing maneuvers that prove participation of the His- Purkinje system in the tachycardia mechanism. Radiofrequency catheter ablation of a bundle branch can cure BBR VT and is currently regarded as the first line therapy. The technique of choice is ablation of the right bundle. The reported incidence of clinically significant conduction system impairment requiring implantation of a permanent pacemaker varies from 0% to 30%. Long-term outcome depends on the underlying cardiac disease. Patients with poor systolic left ventricular function are at risk of sudden death or death from progressive heart failure despite successful BBR VT ablation and should be considered for an implantable cardiovertor-defibrillator.     

Reformative cannula electrodes for His bundle electrogram recording in isolated rat hearts

His bundle electrogram (HBE) recording is an important method for the study of the atrioventricular conduction system. However, the current HBE recording methods in isolated animal hearts have some disadvantages, such as unstable recording due to the difficulty in fixing electrodes as a result of intense heart beat, the small amplitude of the His signal or the possibility to destroy the integrity of heart structure. To overcome these disadvantages, we designed and manufactured reliable, inexpensive and easy-made bipolar cannula electrodes, which combine the functions of Langendorff-perfusion aortic cannula and recording electrodes. With the cannula electrodes, the operation of HBE recording becomes easier and clearer; hence, more stable recordings can be obtained in isolated rat hearts.     

Computer-assisted morphometric study of the innervation of the guinea pig heart

Summary A computer-assisted method is introduced for the morphometric analysis of immunoreactive markers of the innervation of the heart, such as synaptophysin, neuropeptide Y (NPY), neurotensin (NT), substance P (SP), and calcitonin gene-related peptide (CGRP). Video images of stained sections were digitalized and the area density (AD) of the immunoreactive structures was measured by discrimination for grey levels within the myocardium of the right atrium, the perivascular region of epicardial arteries, and the trunk of the bundle of His. Synaptophysin immunoreactivity (IR), which served as a marker for presynaptic vesicles, indicated a dense innervation of the conductive system (AD 1.5241). Marked differences in the pattern of distribution were found between the neuropeptides. The AD of NPY-IR (0.5073) and SP-IR (0.1352) was highest in the perivascular tissue, while NT-IR (0.1628) and CGRP-IR (0.5161) exhibited maximal values in the bundle of His. The computer-assisted morphometric measurement of the AD of immunoreactive markers is suggested to be a suitable method for quantitative studies of the innervation of the heart under normal and experimental conditions.Dedicated to Professor Dr. T. H. Schiebler on the occasion of his 65th birthday     

Cryoablation of Anteroseptal Accessory Pathways with a His Bundle Electrogram on the Ablation Catheter

Background

Radiofrequency catheter ablations of anteroseptal (AS) accessory pathways (AP) in pediatric patients have higher incidence of atrioventricular (AV) block than other AP locations. We report our experience using cryoablation in pediatric patients where a His bundle electrogram was noted on the ablation catheter at the site of the successful ablation.

Methods and Results

We retrospectively reviewed all patients ≤21 years that underwent cryoablation for an AS AP from 2005 to 2012 at our institution (n=70). Patients with a His bundle electrogram noted on the cryoablation catheter at the location of the successful lesion were identified (n=6, 8.5%). All six patients had ventricular preexcitation. Median age of 15.9 years (7.2 - 18.2). AV nodal function was monitored during the cryoablation with intermittent rapid atrial pacing conducted through the AV node (n=2), with atrial extra-stimulus testing (n=2), or during orthodromic reentrant tachycardia (n=2). Acute success occurred in all patients. Two patients had early recurrence of AP conduction. Both patients underwent a second successful cryoablation, again with a His bundle electrogram on the cryoablation catheter. At a median follow-up of 13 months (3 to 37 months) there was no recurrence of accessory pathway conduction and AVN function was normal.

Conclusion

In a small number of pediatric patients with AS AP with a His bundle electrogram seen on the ablation catheter, the use of cryotherapy was safe and effective for elimination of AP conduction without impairment of AV nodal conduction.     

Connexin45 (alpha 6) expression delineates an extended conduction system in the embryonic and mature rodent heart

We previously demonstrated that alpha 6 (Cx45), one of the three connexins of the mammalian myocardium, is preferentially expressed in the peripheral portion of the ventricular conduction system in rats and mice. Here we report that alpha 6 is also prominently immunolocalized in the atrioventricular node and His bundle of these species. The distribution of immunolocalized alpha 6 reveals that the node and bundle form part of an extended central conductive network circumscribing the AV and outflow junctional regions of the fetal, and less continuously, the adult heart. Of the three cardiac connexins, alpha 6 is the isoform most continuously expressed by conduction tissues, and may thus account for the recently reported viability of the alpha 5 (Cx40) knockout mouse. It is concluded that alpha 6 expression is a defining feature of the heterogenous tissues comprising the atrioventricular conduction system of the rodent heart.     

猫冠状动脉缺血与再灌注对房室传导的影响

急性下壁心肌梗塞常引起房室传导功能障碍,然而这种障碍与心肌缺血的内在联系并不很清楚,本实验在去植物性神经传出纤维的猫上进行,通过模板匹配方法从Ｈｉｓ束电图检测Ａ,Ｈ,Ｖ波并测量两心房间期（ＡＡ）,心房波与Ｈｉｓ波间期（ＡＨ）,Ｈｉｓ波与心室波间期（ＨＶ）和心房波与心室波间期（ＡＶ）。结果如下：结扎右冠状动脉后,２０只动物的ＡＨ间期１４只出现增加（Ａ组）６只未出现增加（Ｂ组）对Ｂ组进行快速心房起博和     

Cardiac neural crest ablation inhibits compaction and electrical function of conduction system bundles

Retroviral and transgenic lineage-tracing studies have shown that neural crest cells associate with the developing bundles of the ventricular conduction system. Whereas this migration of cells does not provide progenitors for the myocardial cells of the conduction system, the question of whether neural crest affects the differentiation and/or function of cardiac specialized tissues continues to be of interest. Using optical mapping of voltage-sensitive dye, we determined that ventricles from chick embryos in which the cardiac neural crest had been laser ablated did not progress to apex-to-base activation by the expected stage [i.e., Hamburger and Hamilton (HH) 35] but instead maintained basal breakthroughs of epicardial activation consistent with immature function of the conduction system. In direct studies of activation, waves of depolarization originating from the His bundle were found to be uncommon in control hearts from HH34 and HH35 embryos. However, activations propagating from septal base, at or near the His bundle, occurred frequently in hearts from HH34 and HH35 neural crest-ablated embryos. Consistent with His bundle cells maintaining electrical connections with adjacent working myocytes, histological analyses of hearts from neural crest-ablated embryos revealed His bundles that had not differentiated a lamellar organization or undergone a process of compaction and separation from surrounding myocardium observed in controls. Furthermore, measurements on histological sections from optically mapped hearts indicated that, whereas His bundle diameter in control embryos thinned by almost one-half between HH30 and HH34, the His bundle in ablated embryos underwent no such compaction in diameter, maintaining a thickness at HH30, HH32, and HH34 similar to that observed in HH30 controls. We conclude that the cardiac neural crest is required in a novel function involving lamellar compaction and electrical isolation of the basally located His bundle from surrounding myocardium.     

Electrophysiological effects of the aqueous extract of Averrhoa carambola L. leaves on the guinea pig heart

This work aims to describe some electrophysiological changes promoted by the aqueous extract (AEx) from Averrhoa carambola leaves in guinea pig heart. The experiments were carried out on isolated heart or on right atrium-ventricle preparations. In 6 hearts, the extract induced many kinds of atrioventricular blocks (1st, 2nd, and 3rd degrees); increased the QT interval from 229+/-23 to 264+/-19 ms; increased the QRS complex duration from 27+/-3.1 to 59+/-11 ms, and depressed the cardiac rate from 136+/-17 to 89+/-14b pm. Furthermore, it decreased the conduction velocity of atrial impulse (17+/-3%); reduced the intraventricular pressure (86+/-6%), and increased the conduction time between the right atrium and the His bundle (27+/-6.5%). The conduction time from the His bundle to the right ventricle was not altered. Atropine sulfate did not change either the electrocardiographic parameters or the intraventricular pressure effects promoted by the A. carambola AEx. Based on these results, the popular use of such extracts should be avoided because it can promote electrical and mechanical changes in the normal heart.     

降钙素基因相关肽在豚鼠冠脉血流量和心脏传导系统作用的比较

本文目的在于深入研究降钙素基因相关肽（ＣＧＲＰ）对豚鼠冠状血流量以及心脏传导系统各部分的作用。采用Ｌａｎｇｅｎｄｏｒｆｆ法灌流心脏,同步记录心脏表面电图和希氏束电活动。观察应用ＣＧＲＰ前后的冠脉流量、自主心率、在相同心房周期下的房室结（ＡＨ）及希浦系传导时间（ＨＶ）、心脏出现３：２文氏传导及２：１房室传导阻滞所需的最长起搏周期（ＰＣＬ３：２,ＰＣＬ２：１）。ＣＧＲＰ（３－３０ｎｍｏｌ／Ｌ）可显著增