Concealed Paroxysmal Atrioventricular Block: Diffuse Congenital Atrioventricular Conduction System Disorder with Nonpropagated His Bundle Depolarizations

A 2 1/2-year-old girl with bradycardia and left bundle branch block at birth began to experience "night cries" when deeply asleep. Electrophysiological study demonstrated congenital diffuse atrioventricular conduction disease with concealed paroxysmal atrioventricular block, nonpropagated His bundle depolarizations, severe sinus node abnormality, and a low atrioventricular junctional escape rhythm with probable reciprocation. After pacemaker implant, the "night cries" ceased.     

Pacemaker Dependence in Transient High-grade Atrioventricular Block

In a prospective study 16 patients who had been given a pacemaker because of symptomatic high-grade atrioventricular block and whose conduction had been recovered were checked for their dependence on the pacemaker. During a follow-up time ranging from 32 to 158 months (median 62 months) six patients proved to be dependent on the device owing to the development of recurrent stable high-grade atrioventricular block. The subsequent return of atrioventricular block was evidently not associated with etiology, age, sex, ECG-pattern or length of follow-up period. Five additional patients equipped with a bradycardia-indicating pacemaker all proved to be pacemaker-dependent after a follow-up time ranging from 1-20 months (median 7 months), even though atrioventricular conduction had recovered and its presence had been confirmed at regular outpatient checks. It is thus evident that the conventional clinical methods are of limited value for examining the course of conduction defect and assessing the prognosis for patients whose spontaneous cardiac activity has returned after periods of symptomatic high-grade atrioventricular block. When a bradycardia-indicating pacemaker was furnished, pacemaker dependence was demonstrated in most of the patients whose atrioventricular conduction had recovered. This confirms that pacing introduced because of symptomatic high-grade atrioventricular block should not be discontinued even if a conducted heart rhythm has been established and maintained for long periods.     

Pacemaker Treatment in Familial Amyloidosis with Polyneuropathy

Involvement of the heart is common in familial amyloidosis with polyneuropathy (FAP) and is manifested by disturbances of atrioventricular and intraventricular conduction and dysfunction of the sinus node. Pacemaker implantation was performed in 20 patients with FAP in northern Sweden between 1968 and 1983 for the following indications: complete heart block (11), second degree heart block (1), sinus node dysfunction (5), and atrial fibrillation with a slow ventricular rate (3). There was a prompt improvement of symptoms attributable to a slow heart rate. Dislodgement of the electrode occurred in four patients; no other serious complications were observed. From our experience we conclude that at least one out of ten patients with FAP will eventually require pacemaker treatment. Cardiac pacing is an effective adjunct in the symptomatic treatment of FAP, although the ultimate prognosis depends mainly on the underlying disease.     

家兔房室交界区的形态学观察及其意义

目的:观察家兔心房室结周围的纤维联系,探讨结间传导及折返机制。方法:选20只家兔心脏做房室交界区水平面及矢状面连续切片,HE染色光学显微镜下观察并拍照。结果:房间隔主要观察到3种形态的细胞,P细胞、T细胞和普通心房肌细胞。房室结由致密结和后延伸两部分组成。致密结分浅、深两层。房室结周围有3条纤维与之相连。后方为两束过渡纤维,分别源于冠状窦口及其下方,上方通过普通房肌与下房间隔相连。各肌纤维之间形成回路。结论:结间传导存在着形态学证据,肌纤维形成的回路很可能成为兴奋发生转折的部位。     

Laser Induced Fluorescence Identification of Sinoatrial and Atrioventricular Nodal Conduction Tissue

Transcatheter ahlation of nodal tissue is used for the treatment of arrhythmia resistant to medical therapy. We have investigated the use of laser induced fluorescence spectroscopy for the in vitro recognition of nodal conduction tissue. Twelve fresh human necropsy specimens (< 48 hours)were obtained from sinoatrial node and atrioventricular node areas. Spectra were recorded during excitation at 308 nm (XeCl excimer iaser, 1.5–2.0 mJ/puJse, 10 Hz). Each area examined was marked for subsequent histoiogic examination. Four hundred eleven spectra were obtained, of which 37 contained nodai conduction tissue (21 sinoatrial, 16 atrioventricular node). Normalized fluorescence emission intensity from these areas was compared with that of surrounding endomyocardial tissue at 18 wavelengths and 35 ratios of fluorescence intensity at selected wavelengths. Spectra recorded from nodal tissue could be clearly distinguished hy a visible decrease in fluorescence emission intensity at wavelengths from 440 to 500 nm (P < 0.0006 at 450 nm), peak area, and peak width when compared to that of adjacent atrial endomyocardial tissue. Nodal conduction tissue was also distinguished from ventricular endocardium (14 spectra) by an increase in fluorescence emission at 430 to 550 nm (P < 0.0001). The specificity was 73% and 88% and the sensitivity was 73% and 60% for sinus nodal and atrioventricular nodal conduction tissue identification, respectively. A ratio of fluorescence emission intensity > 1.3 for 380/475 nm was able to detect nodal conducfion tissue (P < 0.001). Conclusion. Laser induced fluorescence can differentiate nodal conduction tissue from atrial and ventricular endocardium and may provide a new diagnostic tool for the recognition and subsequent ablation of nodal conduction tissue.     

Atrioventricular Block Occurring Late After Heart Transplantation: Presentation of Three Cases and Literature Review

Sinus node dysfunction is a well-known occurrence following orthotopic heart transplantation, but atrioventricular block is rarely described. We compare the incidence and clinical presentation of atrioventricular block and sin us node dysfunction among the first 200 consecutive patients receiving heart transplantation at the University of Utah. Two of 200 patients (1%) required pacemaker implantation for symptomatic atrioventricular block compared to 13 of 200 (6.5%) who required pacemaker for symptomatic sinus node dysfunction. Of the patients with atrioventricular block, one had intermittent Mobitz II second-degree atrioventricular block and one had high grade atrioventricular block without ventricular escape. The most striking difference between the patients with atrioventricular block and those with sinus node dysfunction was the interval between transplantation and pacemaker implantation; time to pacemaker implantation in the atrioventricular block patients was 955 and 810 days compared to a median time of 26 days for sinus node dysfunction patients (P = 0.037). The patients requiring permanent pacemaker implantation were similar to those not requiring pacemaker implantation with respect to age, sex, ischemic time, and donor age. None of the patients requiring permanent pacemaker implantation was on amiodarone therapy within 2 months of transplant.     

Response of an Abnormal Sinus Node to Intravenous Flecainide Acetate

A patient with sinus node disease underwent provocative testing with flecainide, a new Vaughan Williams class IC antiarrhythmic agent. There were dramatic increases in sinus node recovery times and in Sinoatrial conduction times, and the magnitude of the response could only be witnessed because of the emergence of a subsidiary junctional pacemaker without retrograde conduction to the atria.     

Fatigue of the His-Purkinje System During Routine Electrophysiologic Studies

In this report we describe fatigue of the His-Purkinje system during retrograde stimulation of the His bundle by ventricular programmed stimulation. The patient underwent electrophysiologic evaluation for syncope. Antegrade conduction and supraventricular studies were normal with the exception of baseline left bundle branch block. During programmed ventricular stimulation, the patient developed intra-Hisian and infra-Hisian block with symptomatic 3:1 atrioventricular heart block requiring insertion of a permanent pacemaker. This case demonstrates the need for careful study of both antegrade and retrograde conduction properties of the His bundle and atrioventricular node when performing standard His bundle studies in evaluation of syncope.     

Pacemakers of the 1980s. An overview

Methods and devices for permanent cardiac pacing remained relatively stable for over two decades with use of the single-chamber ventricular demand (VVI) pacemaker. However, changes have occurred in the 1980s and are expected to continue with the availability of more advanced technology and with increasing knowledge about cardiac pacing. The physiologic benefit of the newer dual-chamber atrial synchronous (VDD) and fully automatic, universal (DDD) pacemakers over the VVI pacemaker in patients with permanent complete heart block and normal sinus node function has been established. These newer units not only reestablish atrioventricular synchrony but also are physiologically rate-responsive. The VDD pacemaker is expected to be phased out in favor of the DDD pacemaker. When the atrial rate or interval is lower than the lower rate limit, the VDD pacemaker functions as a VVI, whereas the DDD pacemaker functions as an atrioventricular sequential (DVI) pacemaker to maintain continuous atrioventricular synchrony. Contrary to general belief, patients with complete heart block and normal sinus node function may gain very little physiologic benefit, if any, from DVI pacing. The sinus node will compete with the pacemaker's atrial stimulation when the sinus rate is faster than the DVI pacemaker rate (which usually occurs during activity). Also, the ventricular pacing rate will not vary with physiologic change. The DVI and atrial demand (AAI) pacemakers have been used in some patients with sinus node dysfunction. Increasing exercise tolerance should not be expected in the majority of patients because they are not pacemaker-dependent during activity, ie, their heart rate is higher than the pacemaker rate. However, these pacemakers appear to help in eliminating pacemaker syndrome, which does not infrequently occur with VVI pacemakers. Patients with sinus node dysfunction but without atrioventricular block do not gain more physiologic benefit with a DDD than with a DVI pacemaker. Whether these patients have severe sinus node dysfunction all the time or adequate sinus node function most of the time during follow-up, the DDD pacemaker will function as a noncommitted DVI with atrial sensing (DDI). The early report of DVI pacemaker-induced atrial fibrillation during follow-up has been refuted by more recent works. If the DDD pacemaker is significantly more expensive than the DVI pacemaker, the latter type may be a good alternative for this condition.     

Radiofrequency Catheter Atrioventricular Node Ablation in Patients with Permanent Cardiac Pacing Systems

Following successful BF ablation of the atrioventricular node (AVN), temporary pacing is necessary prior to insertion of a permanent pacemaker. The risks and inconvenience of temporary pacing could be avoided if a permanent pacemaker is already in place. This study reports the feasibility of RF ablation of the AVN in 27 patients (age 55 ± 17 years, 15 males) with hypertrophic cardiomyopathy and pacemakers, Indications for AVN ablation were drug refractory atrial fibrillation in 24 patients, and rapid AVN conduction preventing septal pre-excitation by DDD pacemaker, inserted for relief of left ventricular outflow obstruction, in three cases. Sixteen patients had DDD devices and 11 patients had VVI devices. During RF ablation, each pacemaker was programmed to VVI at 50 beats/min. The ablation catheter was manipulated with fluoroscopic control to avoid close contact with or disturbance of the pacing leads. In 16 patients, RF ablation was performed immediately following pacemaker implantation but in the remaining patients, the AVN was ablated 6–32 months after pacemaker implantation. The power applied was 25–50 watts for a duration of 15–60 seconds. AV block was achieved in all cases but required 34 ± 36 applications for 16.5 ± 17.8 min/case. RF ablation consistently caused reversion to magnet rate in one patient and temporarily inhibited appropriate pacemaker discharge in another. However, no other pacemaker or lead malfunction was detected so that temporary pacing was not required in any case. At 6 ± 3 months follow-up, all pacemakers were functioning normally without alteration in pacing parameters from baseline. Thus. RF ablation of the AVN can be performed safely in the presence of a recently implanted permanent pacemaker, without temporary pacing.     

心肌缺血对大鼠房室交界区的形态学影响

目的 :在大鼠心肌缺血模型上研究房室交界区 (房室结及房室束 )的形态学变化。方法 :SD大鼠 2 0只 ,分为 2 4h实验组、48h实验组、72h实验组和对照组 ,实验组皮下注射去甲肾上腺素 5mg/Kg。取材心房室交界区 ,常规石蜡切片 ,HE或Masson三色染色 ,光镜下观察和照相。结果 :3个缺血实验组一般心肌光镜下的形态学改变均已出现 ;72h实验组的房室交界区表现为传导细胞边界不清 ,胞浆嗜酸性增强 ,细胞核染色加深 ,传导细胞间的毛细血管扩张 ,而且房室束区的缺血变化比房室结区严重。结论 :心肌缺血时 ,传导系统缺血的情况没有一般心肌严重 ,没有一般心肌反应快 ,分布也不均匀 ,从房室结后部到房室束逐渐加重     

Unusual Sinus Node Response Curves in Two Cardiac Transplant Recipients

We describe unusual responses of the sinus node to programmed atrial stimulation in two asymptomatic cardiac transplant recipients. In one patient the sinoatrial conduction time, calculated using the revised method of Strauss, is extremely short (5 ms), and in the other it is extremely long (460 ms). The various mechanisms that might be involved in these atypical responses to atrial extrastimulation are discussed. These include sinus node suppression, shift of pacemaker, direct stimulation of the sinus node and shortening of the sinus node action potential duration.     

Cardiac Involvement by Non-Hodgkin's Lymphoma: An Unusual Presentation of Heart Conduction Disturbances

A 57-year-old man with non-Hodgkin's lymphoma presented with solitary sinus node dysfunction. Superior vena cava syndrome and progressive disturbance of the conduction system requiring dual chamber pacemaker implantation later appeared. Combination chemotherapy and radiation reversed abnormal sinus node function and the AV conduction disturbance, as demonstrated during electrophysiological evaluation.     

A 2:1 AV rhythm: an adverse effect of a long AV delay during DDI pacing and its prevention by the ventricular intrinsic preference algorithm in DDD mode

A 91-year-old woman received a dual-chamber pacemaker for sick sinus syndrome and intermittently abnormal atrioventricular (AV) conduction. The pacemaker was set in DDI mode with a 350-ms AV delay to preserve intrinsic ventricular activity. She complained of palpitation during AV sequential pacing. The electrocardiogram showed a 2:1 AV rhythm from 1:1 ventriculoatrial (VA) conduction during ventricular pacing in DDI mode with a long AV interval. After reprogramming of the pacemaker in DDD mode with a 250-ms AV interval and additional 100-ms prolongation of the AV interval by the ventricular intrinsic preference function, VA conduction disappeared and the patient's symptom were alleviated without increasing unnecessary right ventricular pacing.     

Transvenous Atrial Pacing in the Management of Sick Sinus Syndrome Following Surgical Treatment of the Univentricular Heart: Case Report and Review

An 11-year-old boy with univentricular heart type A-III underwent surgical treatment at age 10 with a modified Fontan operation. Six months postoperatively he developed intermittent periods of cyanosis and fatigue associated with profound sinus bradycardia and nodal escape. After demonstrating normal atrioventricular conduction, a transvenous atrial pacemaker was implanted. This produced a marked clinical improvement. Transvenous atrial pacing is a satisfactory method of treating sinus node dysfunction in patients with univentricular heart following the Fontan operation provided that there is normal AV conduction.     

Sunao Tawara: a father of modern cardiology

Knowledge of the conduction system of the heart was greatly advanced by Tawara's work carried out in Aschoff's laboratory in Marburg at the beginning of this century. In his monograph, The Conduction System of the Mammalian Heart, published in 1906, Tawara indicated that the treelike structure of specific muscle fibers comprising the atrioventricular node, His bundle, bundle branches, and Purkinje fibers served as the pathway for atrioventricular conduction of excitation in the mammalian heart. From his own anatomic and histological findings of the conduction system, he assumed precisely that the conduction velocity of excitation in the system, except in the atrioventricular node, would be fast and that contraction as the result of excitation would take place at the various sites of the ventricles almost simultaneously. According to Tawara, a long pathway to each contracting unit and a fast conduction velocity of excitation would be a prerequisite for the effective contraction of the ventricles. Tawara's findings and assumptions provided Einthoven the theoretical basis for interpreting the electrocardiogram, resulting in rapid popularization of electrocardiography. This century has witnessed the rapid progress of cardiology, including cardiac pacing and its related sciences. This progress has its roots in the discovery of the conduction system and the development of electrocardiography that took place almost in the same period at the beginning of this century. Tawara's pioneering work on the conduction system still serves as an invaluable reference for basic and clinical research.     

Resumption of atrioventricular conduction by levosimendan after radiofrequency ablation of the AV node:

We report the case of a patient in whom radiofrequency catheter ablation of the AV node was initially successfully performed for persistent atrial fibrillation with fast ventricular rate, but in whom atrioventricular conduction transiently resumes following therapy with levosimendan. Plausible hypothesis are discussed as well as potential implications.     

Selection and pharmacological characterisation of Procoralan, a selective inhibitor of the pacemaker If current

The screening of a series of benzocycloalkane derivatives led to the selection of Procoralan (ivabradine), the first selective inhibitor of the depolarizing If (funny) current of the sinus node, for the treament of myocardial ischaemia. In vitro, this compound reduces the spontaneous beating rate of isolated right rat atria and the firing rate of the action potential of rabbit sinus node preparations. This effect is explained by a reduction in the diastolic depolarisation slope of the action potential and underlies a selective inhibition of the pacemaker If current. In vivo, it induces a selective reduction in heart rate both at rest and during exercise. It preserves myocardial contractility, atrioventricular conduction and ventricular repolarisation duration. Ivabradine exerts a similar anti-ischaemic activity in exercise-induced myocardial ischaemia in pigs to that of a beta-blocker and, furthermore, it limits to a greater extent ischaemic myocardial contractile dysfunction.     

A Degenerative Lesion of the Approach to the Atrioventricular Node Producing Second-Degree and Third-Degree Atrioventricular Block

We report a case of a degenerative approach lesion in an 83-year-old male with diabetes mellitus, hypertension, and ischemic heart disease. His ECGs changed from first-degree atrioventricular (AV) block 14 years ago, to third-degree AV (A-H) block. A pacemaker was implanted for bradycardia. He died 4 years later from heart and renal failure. Serial sections through the conduction system revealed total depletion and fatty replacement of the atrial muscle at the approaches to the AV node.     

Use of DDDRP pacing device in prevention and treatment of tachy-brady syndrome after Mustard procedure

A 13-year-old male patient, who underwent Mustard operation for a very complex congenital heart disease (CHD), after palliation presented a decrease of the sinus node function, developing a tachy-brady syndrome and a mild dysfunction of atrioventricular (AV) conduction. He was successfully treated using a DDDRP pacemaker, which ensured a suitable atrial rhythm and was able to interrupt supraventricular tachycardia episodes. Until now, hospitalization related to episodes of heart failure or symptomatic arrhythmia, has not been necessary.