Comparative effects of ajmaline on intermittent bundle branch block and the Wolff-Parkinson-White syndrome

Phase 4 or phase 3 block or both occurred in the His bundle branch system of 11 patients with intermittent bundle branch block and in the anomalous bundle of 6 of 46 patients with the Wolff-Parkinson-White syndrome (13%). Administration of a single dose of ajmaline (50 mg intravenously) in these patients caused a similar response: expansion of the range of phase 3 and phase 4 block at the expense of the intermediate normal conduction range and total interruption of conduction in the affected fascicle when the effect of the drug was maximal. The great similarity in physiologic behavior and pharmacologic response in these groups of patients suggests that the anomalous bundle was probably diseased or abnormal in the six patients with Wolff-Parkinson-White conduction. In addition, ajmaline caused the first appearance of phase 4 or phase 3 block, or both, but not total interruption of conduction in 26 of the 46 patients with Wolff-Parkinson-White conduction (56.5%). Ajmaline does not cause fascicular block in normal subjects; thus this finding suggests either that the anomalous bundle is diseased or that the safety margin for conduction in the anomalous bundle is much narrower than in the bundle branch system. The conduction-depressing action of ajmaline may be greater at relatively rapid or relatively slow rates of stimulation, and smaller or absent at intermediate rates.     

Altered electrocardiogram during general anesthesia in a patient with intermittent Wolff-Parkinson-White conduction

A delta wave, which had not been detected in the preoperative electrocardiogram (ECG), was observed just before induction of anesthesia in a 53-year-old male scheduled for partial pancreatectomy. His ECG, diagnosed as intermittent Wolff-Parkinson-White (WPW) conduction, varied markedly displaying different wide QRS complexes with a short PR interval, and then returned abruptly to normal during anesthesia. WPW syndrome belongs to the category of pre-excitation syndromes, which is characterized by the accelerated abnormal conduction to the ventricle and paroxysmal tachyarrhythmias caused by an accessory pathway. We should consider the influence of anesthesia-related agents on atrioventricular conduction, and aim at preventing and managing tachyarrhythmias caused by this syndrome.     

Congenitally corrected transposition with atrioventricular septal defect

We describe 4 cases of congenitally corrected transposition associated with atrioventricular septal defect, diagnosed by echocardiography and angiocardiography. Two had usual atrial arrangement and two had mirror imaged atrial arrangement . All cases were associated with subpulmonary valvar stenosis. All patients presented with cyanosis and were in sinus rhythm. Atrioventricular septal defect with common atrioventricular junction was easily diagnosed on the basis of a common atrioventricular valve permitting interatrial and interventricular communications. All patients had balanced right and left ventricles. The echocardiographic recognition of the ventricles was based on the presence of the moderator band within the morphologically right ventricle, the characteristics of the apical septal trabeculations, and the shape of the ventricles. Angiocardiographic recognition of the ventricles was achieved on the basis of right and left ventriculography. In one case with usual atrial arrangement, we recorded two His bundle potentials, one anteriorly and another posteriorly. Atrial stimulation revealed blocked atrioventricular conduction at the level of the posterior bundle, and normal atrioventricular conduction through the anterior bundle. In both cases with atrial mirror-imagery, only a posterior His bundle potential was found, with normal atrioventricular conduction revealed by atrial stimulation The clinical course with this combination depends on the other lesions present in addition to the common atrioventricular valve. Our electrophysiological studies show that the conduction system in presence of a common atrioventricular valve is as expected for congenitally corrected transposition with two atrioventricular valves.     

Evidence for a distinct gap-junctional phenotype in ventricular conduction tissues of the developing and mature avian heart

The gap-junctional proteins connexin43 and connexin42 have been shown to be expressed in the developing and mature avian heart, but their respective spatiotemporal distributions are unknown. In the present study, we have immunolocalized connexin42 in the conduction tissues of the adult avian heart (nonbranching bundle, bundle branches, and Purkinje fibers) and vascular endothelial cells. Connexin43 immunolabeling was confined to vascular smooth muscle. A novel microwave-based method was used to label connexin42 and connexin43 in the same tissue section. Neither connexin42 nor connexin43 was immunolocalized in working myocardium, atrioventricular node, and atrioventricular ring tissue of the bird heart. Although connexin42 first appeared in periarterial conduction myocytes and vascular endothelium at 9-10 embryonic days, the central conduction tissues, including the nonbranching bundle and proximal branches, remained immunonegative for connexin42 up until hatching (approximately 20 embryonic days). During the early postnatal period (1-14 days), connexin42 immunolabeling progressively spread up the bundle branches toward the nonbranching bundle. Connexin42 appeared uniformly distributed along the left bundle branch by 14 postnatal days. The distribution and spread of connexin42 immunoreactivity suggest that the emergence of specialized junctional contacts along ventricular fascicles occurs relatively late in heart development and coincides with the emergence of the chick from incubation within the egg.     

Dispersion of junctional tissue and its consequences in a case of sudden infant death

This article reports a case of sudden infant death syndrome in a 1-month-old male. Some important abnormalities of the cardiac conduction system were found, consisting of persistent fetal dispersion of the atrioventricular node and His bundle, accessory atrioventricular pathways of Mahaim type and resorptive degeneration. These changes could be considered as a morphological substrate for cardiac arrhythmias.     

Advances in the understanding of conduction disturbances

The interest towards intraventricular conduction defects started some 10 yr after the introduction of the string galvanometer by Einthoven. As early as 1910, it was known that conduction blockade could occur along either branch of the intraventricular conducting pathway. It took some 20 yr to identify properly the electrocardiographic manifestations of right and left bundle branch blocks. A further 30 yr were needed to obtain a sound correlation between these functional disorders and the presence of anatomical lesions. The more recent introduction of the concept of left hemiblocks further improved our understanding of intraventricular conduction defects. The latter concept is based on the hypothesis of the anatomical and functional bifascicularity of the left bundle branch, a hypothesis which cannot be accepted without some reservations. Later developments indicated that left hemiblocks associated with right bundle branch block represent manifestations of bilateral conduction disturbances (incomplete bilateral bundle branch block). Such an association may constitute a forerunner of complete atrioventricular block, or an indicator of the possibility of sudden death. Whether these complications occur frequently or unfrequently in the setting of incomplete bilateral bundle branch block remains an unsettled question.     

A quantitative assessment of innervation in the conduction system of the calf heart

BACKGROUND: The aim of the present investigation was to determine the relative distribution of autonomic and sensory nerves in the cardiac conduction tissues of calves. METHODS: A quantitative immunohistochemical and histochemical technique was adopted. RESULTS: Immunoreactivity to the general neuronal marker protein gene product 9.5 (PGP 9.5) demonstrated that all regions of the conduction system possessed a higher relative density of total nerves when compared with the surrounding myocardial tissues. Unlike myocardial innervation, the conduction system did not display an atrial-to-ventricular gradient in nerve density. PGP 9.5-immunoreactive nerve trunks and varicose nerve fibres were more numerous in the transitional atrioventricular node and the penetrating atrioventricular bundle than in either the sinus node, compact atrioventricular node, or bundle branches. The Purkinje network of the ventricular conduction tissues possessed a rich supply of PGP 9.5-immunoreactive nerve trunks and varicose nerve fibres. Acetylcholinesterase (AChE)-positive nerves were the main subtype identified in the sinus and atrioventricular nodes and in the ventricular conduction tissues, representing 50-80% of the area occupied by PGP 9.5-immunoreactive nerves. The compact atrioventricular node possessed AChE-positive and tyrosine hydroxylase (TH)-immunoreactive nerves in similar proportions (45%), although, in general, TH-immunoreactive nerves had a lower relative nerve density than AChE-positive nerves. Neuropeptide Y (NPY)-immunoreactive nerves represented the main peptide-containing subpopulation and occurred throughout the conduction system, displaying a similar pattern of distribution and relative density to those demonstrating TH immunoreactivity. Nerve fibres immunoreactive for somatostatin, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide formed relatively minor subpopulations. CONCLUSIONS: The general innervation of the bovine conduction tissues exhibits significant regional variation. Throughout all regions of the conduction system, AChE-positive nerve represented the dominant subtype when compared with TH- and NPY-immunoreactive nerves. The distribution and relative density of nerve subtypes in the tissues of the bovine conduction system are similar to those observed in man, whereas differences were observed in other regions, such as the atrioventricular bundle and bundle branches. This finding must be considered by those making interspecies comparisons.     

Double-chamber right ventricle: a case report

The double-chamber right ventricle is a congenital cardiac malformation usually associated with other cardiac defects, seldom isolated and in adult subject. It is characterized by the presence of an anomalous bundle that divides the right ventricle into two chambers. The clinical and electrocardiographic signs of isolated double-chamber right ventricle are few and not specific. An echocardiographic diagnosis of isolated double-chamber right ventricle is reported. In a 18-year-old asymptomatic male with systolic murmur 2/6 at third space over the left sternal border, right ventricular hypertrophy and intraventricular conduction delay at ECG, two-dimensional echo showed an anomalous transversal muscle bundle that divided the right ventricle into two chambers, superior and inferior. Color Doppler showed a diastolic tricuspidal-like flow through a paraseptal discontinuity of the bundle and a systolic jet that reached the right atrium, with a pressure gradient of 30.9 mmHg. The absence of symptoms and other cardiopathy, without significant right outflow tract obstruction, was considered as an index of a good prognosis; therefore cardiac catheterization was not advised.     

"The athlete's heart": most common electrocardiographic findings

The morphological and functional cardiac adaptations induced by physical training may be reflected in several athlete's electrocardiographic variants. Rhythm and heart rate disturbances are the most common findings, and sinus bradycardia is the most frequent adaptation. Non-specific intraventricular conduction delay and incomplete right bundle branch block are also frequent, but other bundle branch and fascicular blocks are extremely rare. While the atrioventricular conduction may be prolonged, the occurrence of first degree and type I second degree atrioventricular blocks depends on the individual's susceptibility. Advanced second and third degree atrioventricular blocks are exceptional, and when present, the possibility of underlying heart disease must be excluded. High QRS voltage is more frequent in male athletes, but its correlation with left ventricular hypertrophy is low. The ST segment elevation in the so called "early repolarization" pattern is typical of the athlete's electrocardiogram. Vagotonic or high T wave voltages and U waves are also frequent when sinus bradycardia is present. Tachyarrhythmias and increased automatism arrhythmias are rare and usually benign. The increased vagal tone is responsible for the suppression of the physiological and ectopic pacemakers. While Wolff-Parkinson-White syndrome per se does not exclude an athlete from sports activity, the risk of a sudden death makes it mandatory to perform an exhaustive cardiac evaluation. We may conclude that no sport can be considered arrhythmogenic or as a predisposing factor for malignant ventricular arrhythmias.     

Development of the cardiac conduction tissue in human embryos using HNK-1 antigen expression: possible relevance for understanding of abnormal atrial automaticity

BACKGROUND: Abnormal atrial automaticity in young patients with structurally normal hearts is often located around the pulmonary veins and in sinus venosus-related parts of the right atrium. We hypothesize that these ectopic pacemaker sites correspond to areas of embryonic myocardium with an early phenotypic differentiation, as indicated by differences in antigen expression during normal cardiac development. METHODS AND RESULTS: In human embryos ranging in age from 42 to 54 days of gestation, the development of the cardiac conduction system was studied with the use of HNK-1 immunohistochemistry. HNK-1 stains the developing atrioventricular conduction system, ie, the bundle branches, His bundle, right atrioventricular ring, and retroaortic ring. In addition, the myocardium around the common pulmonary vein showed transient HNK-1 antigen expression. In the right atrium, 3 HNK-1-positive connections were demonstrated between the sinoatrial node and the right atrioventricular ring. An anterior tract through the septum spurium connects the sinoatrial node with the anterior right atrioventricular ring, and 2 posterior tracts connect the sinoatrial node with the posterior right atrioventricular ring through the right venous valve (future crista terminalis) and sinus septum, encircling the coronary sinus. The medioposterior part of the right atrioventricular ring connected to the His bundle and the medioanterior part form 2 node-like structures. CONCLUSIONS: In patients with abnormal atrial automaticity, the distribution of left and right atrial pacemaker foci correspond to areas of the embryonic myocardium that temporarily express the HNK-1 antigen.     

Multiple accessory pathways in patients with the pre-excitation syndrome

We have studied 135 patients with the pre-excitation syndrome and have demonstrated evidence of multiple accessory pathways in 20 patients. Five patients had two distinct accessory atrioventricular (A-V) connections, associated with enhanced A-V node conduction in one patient. Twelve patients had a single accessory A-V connection associated with enhanced A-V conduction. In one of these there was an additional fasciculo-ventricular connection. One patient had an accessory A-V connection associated with a nodoventricular bundle. Two patients had fasciculo-ventricular connections combined with enhanced A-V conduction. The latter two patients had electrocardiograms suggestive of a complete accessory A-V connection. Patients with enhanced A-V conduction had shorter cycle lengths during reciprocating tachycardia, primarily because of a short A-H during the dysrhythmia, than those without such conduction. In addition, patients with enhanced A-V conduction demonstrated more rapid conduction from atrium to His bundle during induced atrial fibrillation and two developed life-threatening ventricular responses during atrial fibrillation. A nodo-ventricular pathway was documented to participate in reciprocating tachycardia in one patient. Surgery was undertaken in 13 patients. In 11, the intraoperative mapping studies confirmed the preoperative predictions. In two patients, the presence of a second accessory A-V connection was documented after ablation of one.     

Cyclin A1 is predominantly expressed in hematological malignancies with myeloid differentiation

OBJECTIVE: To document the frequency of conduction defects and their influence on prognosis in a large series of patients with acute myocardial infarction who underwent coronary care during a period when thrombolytic therapy was in common usage. BACKGROUND: Conduction defects have been associated with an adverse prognosis following acute myocardial infarction, but there are few data on the incidence and outcome of conduction defects since the introduction of thrombolytic therapy. PATIENTS AND METHODS: The study group comprised 1225 consecutive patients with acute myocardial infarction treated in the coronary care unit from 1 January 1988 to 31 December 1994. Conduction defects were recorded prospectively and were classified as follows: complete atrioventricular node block associated with narrow complex escape rhythms; left or right bundle branch block; bifascicular block; complete heart block involving both bundle branches. RESULTS: Electrocardiographic data were available in 1220 patients. Complete atrioventricular node block occurred in 65 (5.3%), left and right bundle branch block in 29 (2.4%) and 44 (3.6%) bifascicular block in 36 (2.9%) and complete heart block involving both bundle branches in 20 (1.6%). The more advanced degrees of block in the bundle branches occurred more commonly in patients with diabetes, previous infarction. Q-wave infarction, anterior infarction and left ventricular failure. Survival analysis showed an increased short- and long-term cardiac mortality in patients with conduction defects, prognosis worsening as the severity of the conduction defect increased. CONCLUSION: Conduction defects complicated acute myocardial infarction in 16% of cases and had a graded impact on the short- and long-term prognosis, patients with advanced bundle branch involvement faring worst. The data showed a small decline in the rate of severe conduction defects compared with previous studies, possibly reflecting the beneficial effects of thrombolytic therapy on infarct size.     

Electrophysiologic effects of anterior septal arterial occlusion

The effect of reduction in anterior septal arterial flow on the conduction system was studied in seven anesthetized dogs. After 2 hours of occlusion P-Q, A-H, and H-V intervals as well as atrioventricular nodal effective and functional refractory periods were significantly prolonged, sinoatrial conduction time was prolonged and the heart rate was decreased. The duration of the His bundle electrogram was significantly prolonged and the configuration altered. However, QRS duration did not prolong significantly. Fifteen minutes after reperfusion, A-H interval, duration of the His bundle electrogram, effective refractory period and functional refractory period returned toward control values. However, the H-V and QRS intervals as well as sinoatrial conduction time were unchanged after reperfusion. Thus, reduction of anterior septal arterial flow influences not only the distal but also the proximal portion of the conduction system; the most vulnerable part is probably the His bundle. The distal portion of the conduction system is directly influenced by ischemia itself, whereas the proximal portion is influenced through other mechanisms induced by reduction of anterior septal arterial flow.     

Sinus node dysfunction after complete correction of tetralogy of Fallot. Report of a case

Atrioventricular conduction defects after complete correction of tetralogy of Fallot are well known and their prevalence is decreasing with improved operative techniques. On the other hand, sinus node dysfunction has not been described after this type of surgery. The authors report the case of a 24 year old patient operated at the age of 2 for a favourable form of tetralogy of Fallot. In the long-term, this patient had a minimal anatomical sequel (mild pulmonary insufficiency) and first degree AVB with complete right bundle branch block with sinus bradycardia on the surface ECG. A recent aggravation of the patient's functional status led to rhythmological investigation which showed chronotropic atrial incompetence with nodal atrioventricular delay. The patient was implanted with a permanent DDD cardiac pacemaker programmed in the DDDR mode with a good outcome. Atrial chronotropic incompetence is one of the modes of expression of sinus node dysfunction. This has not been previously described in this context. This form of sinus node dysfunction should be systematically excluded after surgical cure of tetralogy of Fallot by exercise stress testing and 24 hour Holter ECG. Symptomatic patients are greatly improved by permanent cardiac pacing with hysteresis.     

Severe atrioventricular block in 2 cases with pre-excitation syndrome

In two patients with WPW syndrome Type A suffering from syncopes and dizziness intermittent high degree A-V block was observed. The analysis of the surface Ecg revealed in the first case a complete A-V block within the normal conduction system at the level of the A-V node. In the second case there was a constant left bundle branch block with intermittent block in the right fascicle (intermittent trifascicular block). In both cases the preexcitation syndromes could be best explained by accessory tracts bypassing the normal nodal system left side. One-to-one conduction through the bypass occurred only at a distinct range of cycle lengths, at lower frequencies the accessory tracts were refractory and a IInd or IIIrd degree A-V block occurred. However, outside this frequency zone some P waves were conducted through the accessory tracts without changes in cycle lengths. The findings support the thesis of at least two functionally different atrioventricular pathways in patients with preexcitation syndrome.     

Wolff-Parkinson-White syndrome type B with tachycardia-dependent (phase 3) block in the accessory pathway and in left bundle-branch coexisting with rate-unrelated right bundle-branch block

A patient with Wolff-Parkinson-White syndrome type B developed 2:1 atrioventricular block resulting from the association of persistent right bundle-branch block with tachycardia-dependent (phase 3) left bundle-branch block. Electrophysiological studies disclosed the coexistence of a tachycardia-dependent (phase 3) block in the accessory pathway. This conduction disturbance was exposed, not by carotid sinus massage as in previous studies, but by pacing-induced prolongation of the interval between two consecutively conducted atrial impulses. Furthermore, the surface electrocardiogram showed, at different times, ventricular complexes resulting from: (1) exclusive atrioventricular conduction through the normal pathway without bundle-branch block; (2) predominant, or exclusive, atrioventricular conduction through a right-sided accessory pathway; (3) exclusive atrioventricular conduction through the normal pathway with right bundle-branch block; (4) exclusive conduction through the normal pathway, with left bundle-branch block; (5) fusion between (1) and (2); and finally, (6) fusion between (2) and (3) However, QRS complexes resulting from simultaneously occurring Wolff-Parkinson-White syndrome type B and left bundle-branch block could not be identified. Future electrophysiological investigations should re-evaluate the criteria used to diffrentiate between true and false patterns of Wolff-Parkinson-White syndrome type B coexisting with left bundle-branch block.     

Cryosurgical ablation of accessory atrioventricular connections: a method for correction of the pre-excitation syndrome

Cryothermia, a new technique for definitive treatment of the pre-excitation syndrome, is described in two patients. The first patient presented with a normal P-R interval with a delta wave and reciprocating tachycardia. Preoperative electrophysiologic study suggested a free-wall atrioventricular connection on the left posterior atrioventricular (A-V) groove. At surgery, epicardial mapping confirmed the site of pre-excitation on the posterior left ventricular (LV) wall. An electrogram arising from the accessory pathway (AP) was recorded at the site of earliest ventricular activation. Interatrial delay combined with an apparently long accessory pathway to the ventricle caused the P-R interval to appear normal. Local pressure abolished pre-excitation. The site of early ventricular activation was cooled to -60 degrees C with a specially designed cryoprobe. All evidence of pre-excitation and arrhythmias disappeared. The second patient presented with a refractory reciprocating tachycardia and was found to have an AP in the septum capable of only retrograde conduction. Retrograde conduction was abolished by applying a temperature of 0 degrees C to the anulus at this site during tachycardia. Conduction over the AP and reciprocating tachycardia returned with rewarming. Ablation of the AP was obtained by applying a temperature of -60 degrees C for 90 seconds on two occasions to the same area. The His bundle was not injured.     

Correlative studies on electrocardiogram and histopathology of the conduction system. (1) Right bundle branch block with left axis deviation and prolonged P-R interval

The conduction system was examined histologically in three cases whose electrocardiograms showed right bundle branch block and left axis deviation with or without PR prolongation. In two cases histological lesions were found in the right bundle branch and anterior division of the left bundle branch. In the third case histological lesions were found in the right bundle branch and anterior and posterior divisions of the left bundle branch. This case sufferred an Adams-Stokes attack. In the two patients with right bundle branch block and left axis deviation with PR prolongation, the PR prolongation was attributed to delay in atrioventricular node or His bundle in one case and to delay in left bundle branch in the other.     

A study of methods for surgical interruption of the His bundle

The relationship of the atrioventricular (AV) node and His bundle to surrounding structures is described from the viewpoint of the surgeon. A series of experiments were carried out for interruption of atrial to ventricular conduction that included electrocauterization of the His bundle, incision just above the tricuspid annulus to attempt to divide the His bundle, and finally excision of the right atrial wall and the insertion of the atrial septum into the right fibrous trigone to remove all connections from the AV node and atrium to the His bundle. The last procedure was the most satisfactory method, as judged by the certainty of accomplishing both His bundle interruption and interruption at its highest possible point.     

Transient complete left bundle branch block during epidural anesthesia with mepivacaine

A 65-year-old woman with ovarian tumor was scheduled for abdominal total hysterectomy and bilateral adnexectomy under epidural anesthesia. Preoperative examinations revealed no abnormalities including ECG. Twenty minites after the epidural injection of mepivacaine, widened QRS complexes, which were diagnosed as complete left bundle branch block (CLBBB) later, appeared on ECG. At that time, heart rate (HR) was 150.min-1. CLBBB disappeared when HR decreased to 110.min-1 following the administration of pindolol and verapamil. The operation was postponed. Exercise-treated ECG showed neither CLBBB nor ischemic change even when HR increased to 160.min-1. Two weeks later the operation was attempted again. CLBBB appeared again twenty minites after the epidural injection of mepivacaine. The CLBBB disappeared 5 minites after the induction of general anesthesia when HR decreased to 100.min-1. The operation was performed uneventfully. The effective refractory period (ERP) is shortened with the increase in HR, but the shortning of ERP varies in different part of the cardiac conduction system. In tachycardia, ERP of left bundle branch is longer than that of right one. Because the cardiac conduction system is depressed by local anesthetics, it is speculated that ERP of left bundle branch is elongated further by mepivacaine and CLBBB appeared in this case.