Transient complete AV block in Lyme disease. Electrophysiologic observations

The findings in a patient with complete AV block and intra-atrial conduction disturbances due to Lyme disease are presented. The electrocardiographic follow-up and serial EP findings suggest that complete AV block in Lyme disease may signify a more extensive affection of the AV conduction system (with eventually attendant intra-atrial conduction disturbances) than described in earlier reports. An almost complete resolution of the considerable damage to the conduction system occurred within two weeks.     

An autopsy case of rheumatoid arthritis with an involvement of the cardiac conduction system

A case of rheumatoid arthritis with an involvement of the cardiac conduction system was described. The patient was a 65-year-old man who had a 15-year history of classical rheumatoid arthritis combined with an advanced atrioventricular (AV) block resulting in Adams-Stokes seizure. Prior to the occurrence of the AV block, a complete right bundle branch block with a left axis deviation and a first-degree AV block were found on an electrocardiogram (ECG). The histological examination of the conduction system according to the serial sectioning method disclosed that the branching portion of the His bundle and anterior fascicle of the left bundle branch were replaced by the scarring tissue and that the penetrating portion of the His bundle, the AV node and the right bundle branch had rheumatoid granulomatous lesions. The extent and localization of the lesions in the conduction system were well correlated with the findings on the ECG.     

Exercise-induced distal atrioventricular block

Three patients with 1:1 atrioventricular (AV) conduction at rest developed fixed 2:1 or 3:1 AV block during treadmill exercise testing. Electrophysiologic study documented block distal to the AV node in all three patients, and suggested that the exercise-induced block occurred because of increased atrial rate and abnormal refractoriness of the His-Purkinje conduction system. The findings in these three patients suggest that high grade AV block appearing during exercise reflects conduction disease of the His-Purkinje system rather than of the AV node, even in the absence of bundle branch block. Patients with this diagnosis should be considered for permanent cardiac pacing.     

Complete atrioventricular block in experimental murine myocarditis

BACKGROUND: There were few reports on the pathological characteristics of the conduction system in myocarditis. This study was aimed to clarify the pathological characteristics of complete atrioventricular (AV) block in myocarditis. METHODS AND RESULTS: We studied serial electrocardiograms in experimental myocarditis in mice and also examined their cardiac pathology. After taking baseline electrocardiograms, mice were inoculated intraperitoneally with the encephalomyocarditis virus. Electrocardiograms were serially recorded until day 360. Serial electrocardiograms revealed the appearance of complete AV block. Myocardial lesions were found in the hearts of mice with these ectopic beats. Mononuclear cell infiltrations into the His bundle and necrotic lesions of the conduction system were found in 10.7% (18/168) of mice with complete AV block. However, 17.3% (29/168) of mice showed no evident pathological lesions except the edematous changes of AV node. CONCLUSIONS: The appearance of complete AV block in myocarditis may suggest not only significantly comparable pathological lesions of the conduction system but also the trivial edematous changes; in clinical settings, in the former case, permanent pacing therapy is necessary, and in the latter case, the disease may be transient and could be recovered from complete AV block. This study may shed light on the pathological characteristics of complete AV block in myocarditis.     

Retrograde conduction in complete atrioventricular block Study using His bundle recordings.

Using His bundle recordings and ventricular stimulation retrograde conduction was studied in 57 cases of complete AV block. VA conduction was observed in 13 patients. Of the 13, 12 had AV block distal to H, and during cardiac pacing 5 of them showed a retrograde His bundle potential. In all cases the AV node-His pathway was implicated in the transmission of the retrograde impulse. There was no retrograde atrial response in the remaining patients. VA block usually occurred at the same level as AV block. Nevertheless, two cases of AV block distal to H were associated with concealed retrograde conduction which stopped within the AV node.     

Transvenous ablation of the atrioventricular conduction system in dogs: Electrophysiologic and histologic observations

The correlation of histologic and electrophysiologic findings in dogs undergoing transvenous ablation of atrioventricular (AV) conduction has not been described. The creation of complete AV block in 10 dogs was attempted by delivering a direct-current shock transvenously through a standard tripolar electrode catheter. The catheter was positioned to record the largest unipolar atrial and His bundle electrograms. A 280 J shock was delivered to the recording electrode by a standard cardioversion unit. After 1 shock, all dogs were in complete AV block refractory to isoproterenol (1 to 4 μg/min) and atropine (0.5 to 2.0 mg). Four weeks later, 5 dogs remained in complete AV block, 1 had first-degree block, and 4 had resumed normal AV conduction. Each dog with complete heart block had histologic evidence of severe damage to the AV node, His bundle, or both. On gross examination, these dogs were found to have discrete scars at the base of the septal leaflet of the tricuspid valve. Of the 5 dogs that had resumption of AV conduction, only 1 had histologic evidence of significant damage to the AV conduction system. That animal manifested a marked increase in the P-R interval (100 to 210 ms). Although temporary heart block occurred in each animal, chronic interruption of AV conduction was more difficult. Catheter location, atrial and His bundle electrogram relations, and the electrode used for delivery of energy were factors determining the effectiveness of this technique.     

Transient complete atrioventricular block provoked by ventricular pacing in a patient with nonsustained ventricular tachycardia.

A 75-year-old woman with complete left bundle branch block underwent electrophysiological study (EPS) to assess the conduction in the His-Purkinje conduction system and to further investigate the electrical instability in the ventricle, which was suggestive by the findings of nonsustained ventricular tachycardia in ambulatory monitoring. Transient complete atrioventricular (AV) block was provoked by ventricular pacing, and the intracardiac recordings proved that the site of AV block was distal to the His bundle. This phenomenon was not related to the rate or the duration of the ventricular pacing. The transient impairment of the conduction appeared to be due to the fatigue phenomenon in the His-Purkinje system.     

Complete AV Block Following Mediastinal Radiation Therapy: Electrocardiographic and Pathologic Correlation and Review of the World Literature

The clinical, features, serial electrocardiograms, and autopsy findings of a patient with symptomatic complete AV block, who had received mediastinal radiation therapy 81/2 years previously, are presented. The cardiac histopathology disclosed immense fibrosis of the conduction system and of the atria and ventricles. The enormous amount of fibrosis was similar in location and intensity to that observed in our previously reported patient (Cohen et al., Arch Intern Med 1981;141:676-679) who had undergone mediastinal radiation. We conclude that the severe fibrosis was primarily due to radiation, rather than secondary to atherosclerotic coronary artery disease, which also has been described as a consequence of mediastinal radiotherapy. This patientÆs serial electrocardiograms disclosed evidence of complete block both in the AV nodal area and infra His system, which correlated well with the histopathology. The characteristic clinical features of patients with symptomatic complete AV block post mediastinal radiation therapy are presented, along with a review of the world literature.     

Atrioventricular block in Kearns-Sayre syndrome: a case report

The Kearns-Sayre (K-S) syndrome which includes the triad of progressive external ophthalmoplegia, pigment retinopathy, and disorder of cardiac conduction was first described in 1958. The mitochondria disorder is believed to be the cause of this syndrome. Involvement of the cardiac conduction system is the most importent prognostic factor in K-S syndrome. A 34-year-old male K-S syndrome patient, manifesting as ptosis and weakness of limbs since the age of 15 years, suffered from dizziness and weakness. Twelve-lead eletrocardiography (ECG) showed a 2:1 atrioventricular (AV) block with slow ventricular rate. Intermittent complete AV block, complete left bundle branch block and torsades de pointes were noted in Holter ECG. The electrophysiology study demonstrated prolonged HV interval (85 ms) on conduction beat and infra-His block on non-conduction beat. A VVIR mode of permanent pacemaker was implanted and the patient's condition was stable during this period of follow-up.     

QRS Alternans with 2:1 Atrioventricular Conduction Block: What Is the Mechanism?

An 81‐year‐old woman was admitted for symptomatic bradycardia. On admission, the ECG exhibited QRS alternans, narrow QRS complex and left bundle branch block with 2:1 AV block. The patient soon had complete AV block and underwent a pacemaker implantation. An appropriate mechanism for explaining those ECG findings might be 4:1 conduction over the left bundle branch and 2:1 conduction over the right bundle branch. An ECG pattern exhibiting QRS alternans with a narrow QRS complex and bundle branch block with 2:1 AV block may suggest the coexistence of both bundle branch blocks and a high risk of complete AV block.     

Sudden death caused by benign tumor of the atrioventricular node.

Histologic study of the conduction system of the heart of a 16-year-old girl who died suddenly demonstrated a benign mesothelioma of the AV node, with almost complete replacement of the structure by the tumor. Teh past history was unremarkable, except for few syncopal episodes at 9 and 11 years of age and during pregnancy. Immediately postpartum, she developed a 2:1 AV block and intermittent complete AV block. Six weeks later, during diagnostic work-up in the cardiac catheterization laboratory, she died suddenly. Electrophysiological studies during this work-up disclosed complete AV dissociation, with normal QRS complexes. The block was proximal to the His-bundle recording site, with a normal H-V interval. Occasional syncopal attacks in young adults should alert the physician to the possibility of this diagnosis and lead to pacemaker insertion.     

Cardiac manifestations of Lyme disease

Three cases of Lyme's disease with cardiac involvement are reported. One patient had myocarditis complicated by symptomatic complete AV block and two patients had asymptomatic 1st degree AV block. There were no abnormalities on echocardiography. The cardiac changes occurred between the 18th and 40th day after the onset of the disease and persisted 10 days: however these conduction defects may vary within a few hours. A rapid and complete cure was obtained with antibiotic therapy.     

Conduction disorders after cardiac surgery with extracorporeal circulation

Two-hundred-fifty-eight patients who had cardiac surgery with extracorporeal circulation were studied to determine the frequency and significance of conduction disturbances. Fifty-eight (34%) developed new postoperative conduction defects. Seventeen patients developed new conduction alterations after coronary artery bypass graft. The most common disturbance was transient bifascicular block (right bundle branch block and anterior subdivision block of the left bundle branch of His) (p less than 0.01). After valvular surgery twenty-one patients developed conduction defects. Of those the most common disturbance was high degree AV block (57%). The authors found no relation between the AV block and the number of valves operated on or type of valvular surgery. After congenital heart surgery, twenty patients developed conduction defects. The most common defect was high degree AV block. The frequency of complete heart block was higher after the closure of atrial septal defects (P less than 0.01). None of the conduction defects were related to the amount of time the patient was exposed to extracorporeal circulation or to postoperative myocardial infarction. All conduction defects were transient except complete heart block in some patients with ventricular septal defect surgery. In this study there were no hemodynamic complications or mortality associated with the conduction disturbances.     

Congenital atrioventricular block in right atrial isomerism (asplenia). A case due to atrionodal discontinuity

The association of complex congenital heart disease with asplenia syndrome and congenital AV block is described in a newborn. Cardiovascular lesions were right atrial isomerism, d-loop, discordant ventriculoarterial connection, pulmonary stenosis, total anomalous pulmonary venous drainage, absent right pulmonary artery, and bilateral superior vena cava. The ECG recording disclosed complete AV block with narrow QRS (suprahisian block). The histology of the conduction system revealed two AV nodes, one anterior and one posterior, none of which connected with the atrial myocardium; only the posterior node was continuous with a penetrating and bifurcating bundle. The histologic findings were consistent with the suprahisian AV block due to lack of connection between the atria and the regular posterior AV specialized junction.     

A complete atrioventricular block during exertion]

Exercise-induced atrioventricular (AV) block in patients with normal electrocardiogram at rest is uncommon. We report the clinical features of two patients with AV block during treadmill test. The first patient was a woman of 54 years of age with presyncope on exercise. She developed complete AV block during exercise testing without evidence of ischemic myocardial disease. Electrophysiologic study documented distal AV block. The second patient was a man 31 years old who developed angina and third-degree AV block with depression of ST segment during treadmill test. Myocardial perfusion study suggested ischemic heart disease. He received anti-ischemic drugs with improvement of symptoms. A control exercise testing demonstrated normal AV conduction and electrophysiologic study was normal. In the first case, exercise AV block was probably due to abnormal His Purkinje conduction system refractoriness to autonomic modulation, while in second case AV block was secondary to ischemic heart disease. Third-degree AV block at exercise can be present in patients without conduction system abnormalities at rest. Exercise-induced infra-Hisian AV block must be treated with pacing until ischemic heart disease has been ruled out.     

Selective experimental chelation of calcium in the AV node and His bundle

There are P cells in the human and canine AV (atrioventricular) node which are virtually devoid of gap junctions. All other components of myocardial cellular connections are calcium-dependent except the gap junction. Direct perfusion of disodium EDTA through the AV node artery of 16 anaesthetized dogs produced three immediate effects: complete AV block, a rapid irregular atrial rhythm and a separate rapid irregular ventricular rhythm. The atrial arrhythmia was short in duration and sinus rhythm resumed, initially with complete AV and VA block; both waned until normal AV conduction returned in each dog. In 3 of the 16 dogs there was transient complete AV block during which two independent His potentials were separately associated with the atrial and ventricular complexes. When conducted sinus rhythm resumed, there was initially A-H prolongation (but not H-V). Atropine, propranolol and reserpine had no influence on any electrophysiologic effect of EDTA. Both tachycardias probably originate in P cells of the AV node, the irregularity being attributable to varying enhancement of automaticity plus functional disaggregation of P cells. AV block is attributed to failure of conduction between disaggregated P cells, which in turn must be an obligatory pathway for normal AV conduction, because of their anatomic interposition. The findings further suggest that the AV nodal P cells are the site of the normal 40 ms delay in AV conduction, and that they may be the site of origin of the His potential.     

Atrioventricular block complicating amiodarone-induced hypothyroidism in a patient with pre-excitation and rate-dependent bilateral bundle branch block

As a clinical entity atrioventricular (AV) block due to hypothyroidism is rare. Such a case induced by hypothyroidism complicating long-term therapy with amiodarone in a 45 year old woman with pre-excitation is presented. Electrophysiologic data obtained before and during thyroxine replacement therapy showed that hypothyroidism lengthens the effective refractory period of the atria, AV node, bypass tract and His-Purkinje system (that in the ventricle not being measured); this lengthening resembles the effects of long-term administration of amiodarone. These observations suggest that depressed thyroid function may be protective against arrhythmias but a patient with preexisting conduction system disease may develop AV block. The tendency to develop AV block in a patient who is euthyroid was reduced by bypass tract conduction. These findings are significant not only in monitoring amiodarone effects during chronic prophylactic drug therapy but also in providing further insight into the complex interrelation between the action of the drug and the thyroid hormones on cardiac muscle.     

Acute myocarditis associated with cardiac amyloidosis manifesting as transient complete atrioventricular block and slow ventricular tachycardia

This is the first report of conduction system disturbances and slow ventricular tachycardia (VT), related to acute myocarditis associated with cardiac amyloidosis. A 57-year-old female was presented with chest pain and pre-syncope after flu-like symptoms, and was promptly diagnosed with acute myocarditis. The initial electrocardiogram (ECG) revealed complete atrioventricular (AV) block, and transient slow VT was observed after an atropine injection (0.5 mg). This AV conduction disturbance persisted for 12 days, and spontaneously resolved. Left ventricular function was relatively well preserved, and an endomyocardial biopsy revealed acute myocardial inflammation and underlying amyloid deposits. A His-bundle recording, taken 6 weeks after the initial manifestation, indicated normal AV nodal conduction. Endomyocardial biopsies have proven helpful with regard to the diagnosis of acute myocarditis superimposed on amyloidosis, in patients who present with conduction disorder and relatively preserved ventricular function, as was seen in this case.     

Sudden death after catheter-induced atrioventricular junctional ablation

Atrioventricular (AV) junctional ablation was performed in a 59-year-old woman with recurrent atrial fibrillation refractory to treatment with digoxin, beta-blockers, verapamil, quinidine, procainamide, and amiodarone. She received two shocks of 500 J which produced complete AV block. After six weeks, both 24-hour ECG recordings and an exercise tolerance test showed infrequent premature ventricular complexes, 3 degrees AV block, and paced ventricular rhythm with 100 percent capture. She suddenly collapsed and was found to be in ventricular fibrillation and could not be resuscitated. Serial sections of the conduction system showed marked fatty infiltration of the approaches to the AV node with almost complete separation from the node. A partially fibrosed atrioHisian connection was also present. Fibroelastosis with chronic inflammatory changes was present in the AV node, bundle of His, and right and left bundle branches. In addition, marked inflammatory changes with fibrosis were present in the atrial septum, in the summit of the ventricular septum, with degenerative changes in the tricuspid and aortic valves. The sequelae of these findings outside the conduction system in other patients remains to be determined.     

Cardiac arrhythmias and conduction disturbances in autoimmune rheumatic diseases

Rhythm and conduction disturbances and sudden cardiac death (SCD) are important manifestations of cardiac involvement in autoimmune rheumatic diseases (ARDs). In patients with rheumatoid arthritis (RA), a major cause of SCD is atherosclerotic coronary artery disease, leading to acute coronary syndrome and ventricular arrhythmias. In systemic lupus erythematosus (SLE), sinus tachycardia, atrial fibrillation and atrial ectopic beats are the major cardiac arrhythmias. In some cases, sinus tachycardia may be the only manifestation of cardiac involvement. The most frequent cardiac rhythm disturbances in systemic sclerosis (SSc) are premature ventricular contractions (PVCs), often appearing as monomorphic, single PVCs, or rarely as bigeminy, trigeminy or pairs. Transient atrial fibrillation, flutter or paroxysmal supraventricular tachycardia are also described in 20-30% of SSc patients. Non-sustained ventricular tachycardia was described in 7-13%, while SCD is reported in 5-21% of unselected patients with SSc. The conduction disorders are more frequent in ARD than the cardiac arrhythmias. In RA, infiltration of the atrioventricular (AV) node can cause right bundle branch block in 35% of patients. AV block is rare in RA, and is usually complete. In SLE small vessel vasculitis, the infiltration of the sinus or AV nodes, or active myocarditis can lead to first-degree AV block in 34-70% of patients. In contrast to RA, conduction abnormalities may regress when the underlying disease is controlled. In neonatal lupus, 3% of infants whose mothers are antibody positive develop complete heart block. Conduction disturbances in SSc are due to fibrosis of sinoatrial node, presenting as abnormal ECG, bundle and fascicular blocks and occur in 25-75% of patients.