A study of heart block in man using His bundle recordings

Reflections on the early invasive clinical cardiac electrophysiology era through fifty manuscripts: 1967-1992

In 1967, researchers in The Netherlands and France independently reported a new technique, later called programmed electrical stimulation. The ability to reproducibly initiate and terminate arrhythmias heralded the beginning of invasive clinical cardiac electrophysiology as a medical discipline. Over the next fifty years, insights into the pathophysiologic basis of arrhythmias would transform the field into an interventional specialty with a tremendous armamentarium of procedures. In 2015, the variety and complexity of these procedures were major reasons that led to the recommendation for an increase in the training period from one year to two years. The purpose of this manuscript is to present fifty manuscripts from the early invasive clinical cardiac electrophysiology era, between 1967 and 1992, to serve as an educational resource for current and future electrophysiologists. It is our hope that reflection on the transition from a predominantly noninvasive discipline to one where procedures are commonly utilized will lead to more thoughtful patient care today and to inspiration for innovation tomorrow. In the words of the late Dr. Mark E. Josephson, "It is only by getting back to the basics that the field of electrophysiology will continue to grow instead of stagnate."

Human His-Purkinje System: Normal Electrophysiologic Behavior

The His-Purkinje system (HPS) plays a significant role in human pathophysiology, but knowledge is scattered. This article highlights some of the relevant concepts, phenomena, and mechanisms; clarifies, expands, confirms, or modifies commonly encountered clinical events; and adds new information, which is often available but obscure. Also included are the essentials of HPS anatomy and physiology. It is important to abandon inaccurate concepts that are still taught and occasionally appear in text books.

Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model

Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias.

Computational modeling of pathophysiologic responses to exercise in Fontan patients

Reduced exercise capacity is nearly universal among Fontan patients. Although many factors have emerged as possible contributors, the degree to which each impacts the overall hemodynamics is largely unknown. Computational modeling provides a means to test hypotheses of causes of exercise intolerance via precisely controlled virtual experiments and measurements. We quantified the physiological impacts of commonly encountered, clinically relevant dysfunctions introduced to the exercising Fontan system via a previously developed lumped-parameter model of Fontan exercise. Elevated pulmonary arterial pressure was observed in all cases of dysfunction, correlated with lowered cardiac output (CO), and often mediated by elevated atrial pressure. Pulmonary vascular resistance was not the most significant factor affecting exercise performance as measured by CO. In the absence of other dysfunctions, atrioventricular valve insufficiency alone had significant physiological impact, especially under exercise demands. The impact of isolated dysfunctions can be linearly summed to approximate the combined impact of several dysfunctions occurring in the same system. A single dominant cause of exercise intolerance was not identified, though several hypothesized dysfunctions each led to variable decreases in performance. Computational predictions of performance improvement associated with various interventions should be weighed against procedural risks and potential complications, contributing to improvements in routine patient management protocol.

Neurocardiogenic syncope in chronic atrioventricular block

We report a 37-year-old man with type I second-degree atrioventricular (AV) block (atypical Wenckebach's periodicity) referred to our department for pacemaker implantation because of an episode of syncope. After exhaustive evaluation, including electrophysiological test, in which Wenckebach's cycles with block within the AV node was demonstrated, syncope was considered to be neurally mediated. Head-up tilt testing with sublingual isosorbide dinitrate was positive. The decrease in atrial rate at the beginning of the vasovagal reaction was not immediately accompanied by a depressed AV node conduction. Only at the moment of syncope did incomplete AV block appear. This observation illustrates (1) a neurally mediated origin of syncope in a patient with chronic AV block, and (2) the different time-course responses of the sinus and AV nodes to autonomic tone.

Function follows form: cardiac conduction system defects in Nkx2-5 mutation

Mutations of Nkx2-5 cause congenital heart disease and atrioventricular block in man. The altered expression of an electrophysiologic protein regulated by Nkx2-5 was originally presumed to cause the conduction defect, but when no such protein was found, an alternative hypothesis was considered. In pediatric patients, the association of certain cardiac malformations with congenital atrioventricular block suggests that errors in specific developmental pathways could cause both an anatomic and a physiologic defect. We therefore hypothesized that Nkx2-5 insufficiency perturbs the conduction system during development, which in turn manifests as a postnatal conduction defect. Experimental results from Nkx2-5 knockout mouse models support the developmental hypothesis. Hypoplasia of the atrioventricular node, His bundle, and Purkinje system can explain in whole or in part specific conduction and electrophysiologic defects present in Nkx2-5 haploinsufficiency.

Electrocardiographic manifestations: diagnosis of atrioventricular block in the Emergency Department

Patients with bradycardia are commonly encountered by the Emergency Physician. Of the possible bradydysrhythmias, atrioventricular blocks (AVB) represent a significant portion of these presentations. In this article, we provide four illustrative cases of patients presenting to the Emergency Department (ED) with AVB. We review the various types of AV block dysrhythmias (1st, 2nd, and 3rd degrees) and their underlying etiologies. This discussion also focuses on the presentation, clinical considerations, management and acute treatment of AVB dysrhythmias in the emergent setting.

P wave amplitude and duration may predict immediate recurrence of atrial fibrillation after internal cardioversion

BACKGROUND

Although internal cardioversion (IC) for atrial fibrillation (AF) is effective at restoring sinus rhythm, immediate recurrence (IR) of AF after IC is a major and largely unpredictable clinical problem. The purpose of the study was to determine the role of P wave duration and amplitude in prediction of IR of AF after IC. Forty-five consecutive patients undergoing IC for chronic AF were evaluated.

MATERIAL AND METHODS

After successful IC, 1-minute ECG recording was obtained in all patients. P wave duration and amplitude in Lead II and V1 were measured using computer. Forty patients (88%) had successful IC. Thirteen patients experienced IR of AF within 1 minute of restoring sinus rhythm.

RESULTS AND CONCLUSION

As a result, the incidence of IR of AF after IC was higher in the patients with shorter P wave amplitude (for lead II P<0.01, for V1 P<0.01) and larger P wave duration (for lead II P<0.01, for V1 P<0.05).

Noninvasive recording of His bundle activity with an analog delay device in normal subjects and patients with atrioventricular block

A simplified and clinically applicable method has been developed for real-time noninvasive recording of the electrical activity of the His bundle in the human heart. A surface electrocardiogram (ECG) was obtained from bipolar precordial leads. The electrical signal within the P-QRS segment of the ECG was amplified with a high gain amplifier and delayed with an analog delay device for QRS-triggered signal averaging. The analog delay device consisted of a bucket brigade device (BBD) with an electrical integrated circuit (IC). After filtering with a band width of 50-300 Hz, the delayed signal was processed by a microcomputer system and the signal-to-noise ratio of the signal was improved by the signal averaging technique. Surface His bundle electrocardiograms (SHE) were measured in normal subjects without conduction disorders and in patients with atrio-ventricular (A-V) block. In the same patients, each SHE was nonsimultaneously compared with an invasive His bundle electrogram (HBE) obtained by the intracardiac catheter technique. The results of this comparison confirmed that the noninvasive method of SHE recording has broad clinical applicability and high utility for the screening of patients with latent A-V block before intracardiac catheterization is performed.

Parasympathetic and sympathetic alterations of Mobitz type II heart block

This study examined the effects of changes in parasympathetic and sympathetic tone on the cycle length at which Mobitz type II second degree atrioventricular (AV) block occurred. Four patients who had electrocardiographic evidence of type II AV block and confirmation of block in the His-Purkinje system during electrophysiologic study were evaluated. These patients received intravenous atropine (1.0 to 2.4 mg), propranolol (0.15 mg/kg body weight) or isoproterenol (1 and 2 micrograms/min) alone or in combination. In two of three patients receiving propranolol, the atrial pacing cycle length at which 1:1 His-Purkinje conduction occurred was prolonged relative to control (from 360 to 470 ms and 440 to 590 ms, respectively). In contrast, atropine in the presence of beta-adrenergic blockade shortened the cycle length at which 1:1 His-Purkinje conduction occurred in three of four patients receiving the drug (470 to 390, 630 to 570 and 590 to 560 ms, respectively). Isoproterenol also improved His-Purkinje conduction in the one patient receiving this drug. No agent affected the duration of the HV interval during spontaneous sinus rhythm or right atrial pacing. Thus, drugs that alter autonomic tone influence abnormal His-Purkinje conduction minimally during sinus rhythm but, importantly, may modulate the atrial pacing cycle length at which type II AV block occurs.

Site of conduction delay and electrophysiologic significance of first-degree atrioventricular block in children with heart disease

Associated electrophysiologic abnormalities and site of delay were studied in 20 patients, aged 1.5 to 16.5 years, with congenital heart disease and first-degree atrioventricular (AV) block (PR interval above the 98th percentile for age and heart rate). Eight of the 20 patients with first-degree AV block were studied after 1 or more cardiovascular operations. Refractory periods of the atrium, AV node, His-Purkinje system and ventricle were determined. As a further test for AV nodal integrity, rapid atrial pacing was performed and the cycle at which Wenckebach periodicity occurred was noted. Four groups were identified. Group I included 4 patients (20%) with intraatrial conduction delay (long PA interval). Three patients had depressed sinus nodal function and 1 had depressed AV nodal function. Group II included 7 patients (35%) with AV nodal delay (long AH interval). One patient had sinus nodal depression and 2 had AV nodal depression (prolonged AV nodal refractory period or Wenckebach at a long paced cycle length). Group III included 3 patients (15%) with His-Purkinje delay (long HV interval). Measured functions were normal in all patients. Group IV included 6 patients (30%) with normal or high normal intracardiac intervals with long PR. One patient had sinus nodal dysfunction, 2 patients had long atrial refractory periods, 1 had AV nodal depression; 2 had long refractory period of the His-Purkinje system, and 1 had long ventricular refractory period. Atrial flutter was induced in 1 patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple electrophysiologic manifestations and clinical implications of vagally mediated AV block

Clinical, surface ECG, and intracardiac findings were analyzed in 20 patients with spontaneous conduction disturbances in whom vagally mediated AV block could be induced by carotid sinus pressure during electrophysiologic evaluation. The latter demonstrated that the surface ECG pattern attributed to bradycardia-dependent (phase 4), and paroxysmal block within the His bundle and bundle branches could reflect vagally mediated, bradycardia-associated (rather than bradycardia-dependent), and paroxysmal AV nodal (AH) block. The decision regarding the use of pacemakers was not based on QRS duration or on patterns (or site) of block but on the underlying clinical settings and the correlation of symptoms with maximal ventricular (R-R) pauses. However, more studies are required to extend our findings, especially to other subgroups of patients (or normal individuals) in whom vagally mediated block occurs.

Electrocardiography of arrhythmias: from deductive analysis to laboratory confirmation--twenty-five years of progress

Before the advent of the microelectrode, His bundle recording and direct cardiac pacing, electrocardiographic interpretation of arrhythmias in human beings was based on presumed mechanisms derived by deductive analysis. This indirect approach was forced by the fact that the surface electrocardiogram does not directly record the behavior of the specialized tissue that is the site of origin of most arrhythmias. In the past 25 years it has become possible to record directly from the specialized tissue. The result has been experimental confirmation of several underlying concepts of the electrocardiographic interpretation of arrhythmias and progress evidenced by the conversion of concept to fact.

Bradyarrhythmias: clinical significance and management

Clinicians have long recognized the potentially serious manifestations of extreme bradycardia. However, even marked bradycardia can often be physiologic, and in the presence of impaired ventricular function may offer important compensatory hemodynamic effects. Disorders of the sinoatrial node producing bradycardia include failure of impulse formation, sinoatrial conduction block, concealed sinus-perinodal reentry, carotid sinus hypersensitivity and the constellation of brady- and tachyarrhythmias that compose the "sick sinus syndrome." Bradycardia can also result from intraatrial block, atrioventricular nodal block or infranodal block. In addition, paroxysmal supraventricular tachyarrhythmias may produce concealment into the atrioventricular junction and simultaneous suppression of sinus node rhythmicity, resulting in long pauses. Pseudobradycardias manifesting as slow peripheral pulse rates can result from frequent, nonconducted early atrial premature beats, from ventricular bigeminy or runs of ventricular extrasystoles or from mechanical alternans. Cardiac pacemakers play an important role in the management of patients with severe symptoms attributable to bradyarrhythmias. However, excessive use of pacemakers and the inappropriate selection of physiologically unfavorable pacemaker systems should be avoided. Frequently, patients who are only mildly symptomatic with bradycardia should not receive a cardiac pacemaker because the prognosis is favorable. Patients with the tachy-bradycardia syndrome often require both pharmacologic and pacemaker therapy. In selected patients electrophysiologic testing may be helpful, but the majority of patients are best managed by careful attention to the history, electrocardiogram and ambulatory electrocardiographic recordings.

Electrophysiological characteristics of junctional pacemakers in congenital A-V block and following His bundle cryoablation

The characteristics of the escape mechanism following surgically induced permanent A-V block were investigated and compared with those seen in congenital complete heart block (CHB). Six patients had undergone elective cryothermal ablation of the His bundle for supraventricular arrhythmias unresponsive to pharmacological and pacemaker techniques (group A) and 12 patients had congenital CHB (group B). In the 12 patients in group B the site of block was localized by His bundle electrocardiography to be proximal to the point of recording of the His potential. In 3 patients in group A in whom intracardiac studies were performed it was impossible to record an His potential. There were no significant differences between the control escape rate, junctional recovery time (JRT), and corrected junctional recovery time (cJRT) of the two groups. In group A there were no significant changes in these parameters following the administration of atropine, whereas isoproterenol significantly increased the rate of the subsidiary pacemaker (p less than 0.001) and shortened the JRT (p less than 0.02) and cJRT (p less than 0.02). In group B both atropine (A) and isoproterenol (I) significantly increased escape rate (A, p less than 0.001; I, p less than 0.001) and shortened JRT (A, p less than 0.01; I, p less than 0.001) and cJRT (A, p less than 0.01; I, p less than 0.001). It is concluded that the escape focus in patients with congenital CHB is situated in the A-V node. The escape rhythm following His bundle section is unpredictable and elective permanent pacemaker implantation is indicated.

Wenckebach second-degree A-V block in top-ranking athletes: an old problem revisited

The occurrence of Wenckebach second-degree (Mobitz I) A-V block in apparently normal persons still provides a puzzle for the cardiologist, as the benign nature of this event has been recently questioned. This problem becomes more intriguing when Wenckebach A-V block is encountered in asymptomatic top-ranking athletes, because of medico-legal implications. We report 10 cases of highly-trained athletes, including three with mitral valve prolapse (MVP) features, with a spontaneous or induced Wenckebach second-degree A-V block. Previous ECGs of six subjects, dating from a maximum of 6 years to a minimum of 18 months, were available. Deterioration of A-V conduction has never been documented and all six cases have remained asymptomatic for the whole follow-up period. Athletes have been submitted to a protocol study consisting of ECG recording at rest, during, and after vagal and sympathetic reflex maneuvers, drug administration (isoproterenol and atropine), submaximal and maximal exercise. Nine subjects have been considered to have "normal" responses of the A-V node to provocative tests, since conduction disturbances were improved or normalized by reflex sympathetic stimulations and were completely normalized by autonomic drug administration and exercise. One athlete showed "abnormal" responses to tests. In order to give a conclusive prognostic and medico-legal assessment, we advised him to submit to an invasive electrophysiological investigation. Wenckebach second-degree A-V block in athletes may be a more common finding than so far described, especially when a systematic search is made. In our opinion, this event can still be considered a vagally-induced benign feature of athlete's heart, provided that an immediate improvement of A-V conduction is obtained in response to reflex sympathetic maneuvers, and that a complete normalization after sympathomimetic and vagolytic drug administration and physical exercise is observed. The clinical histories of our athletes and the observed complete disappearance of conduction disturbances after detraining, strongly support this opinion. Wenckebach second-degree A-V block in asymptomatic athletes with MVP features probably does not affect the prognosis if similar favorable responses to the aforesaid tests are observed.

His bundle electrogram in patients with acute myocardial infarction

Thirty-seven patients with acute myocardial infarction complicated by atrioventricular or bundle branch block, or a combination of both, has His bundle electrogram studies performed during their stay in the coronary care unit. The acute mortality of the 14 patients with a complicating bundle branch was 50%. Pump failure was the main cause of death. Three patients in this group had a prolonged H-V interval and one patient had a split blundle of His. The presence or absence of a prolonged H-V interval did not affect mortality in this group of patients. The acute mortality of the 16 patients with an inferior wall myocardial infarction was 6%. The H-V interval was normal in all but one of these patients. The atrioventricular block was caused by a proximal block in all cases. The acute mortality of the seven patients with an anterior wall myocardial infarction was 29%. The H-V interval was prolonged in two of seven patients. Pump failure was the acute cause of the deaths. The presence or absence of a prolonged H-V interval did not affect mortality in this group of patients.

Assessment of atrioventricular conduction in aortic valve disease

To determine the frequency of atrioventricular conduction disturbances in aortic valve disease, 26 consecutive patients (age 54 +/- 2 years) with symptomatic aortic valve disease were studied by His bundle electrocardiography at the time of cardiac catheterisation and were compared with a group of patients who underwent cardiac catheterisation and were found to have coronary artery or mitral valve disease but no aortic valve disease. Patients with aortic valve disease had significantly longer PR, AH, and HV intervals than cardiac patients not having this abnormality. Patients with aortic stenosis had prolonged HV, 52 +/- 6 vs +/- 42 +/- 2 ms (P = 0.06), whereas patients with chronic aortic regurgitation had prolonged PR, 245 +/- 27 vs 163 +/- 5 ms (P less than 0.001), and prolonged AH, 178 +/- 30 vs 102 +/- ms (P less than 0.001). Patients with combined lesions had significant prolongation of PR, AH, and HV intervals. Three patients with acute aortic regurgitation caused by endocarditis had normal atrioventricular conduction. Though the presence of valvular calcification did not significantly alter the pattern of atrioventricular conduction in these patients, those with calcified aortic valves had longer HV (P less than 0.005) than the control group. In addition, ventricular dysfunction or coronary artery disease did not affect the pattern of atrioventricular conduction in these patients. Thus, atrioventricular conduction disturbances are common in symptomatic aortic valve disease. With aortic stenosis the site of delay occurs more frequently below the His deflection, whereas in aortic regurgitation it is more frequent above the His deflection.

Electrophysiologic studies on atrioventricular nodal Wenckebach cycles

Wenckebach cycles with a 4:3 ratio, produced by rapid atrial pacing, were studied in 27 anesthetized denervated dogs using programmed stimulation. A test stimulus (S') could be inserted after any preselected beat of the Wenckebach cycle. An on-line computer measured the atrial (A) to His bundle (H) intervals. In all dogs a progressive increase in atrioventricular (A-V) nodal refractoriness was seen in the effective refractory period for each beat and a rightward shift of the A'-H' relative to the A-A' refractory curves. Atypical Wenckebach cycles could be produced by small changes in the basic cycle length. No evidence for reentry was found from the refractory curves of Wenckebach cycles and by interruption of stimulation after the third stimulus of a 4:3 Wenckebach cycle. Analysis of the A'-H' relative to the H-A' refractory curves did not confirm a positive feedback mechanism. In order to mimic a Wenckebach cycle, a blocked premature beat was inserted during stressed 1:1 conduction. The changes in the refractory curves for successive beats after the premature beat were rate-dependent and similar to those in Wenckebach cycles but smaller in magnitude. In Wenckebach cycles there is a progressive increase in refractoriness, caused by cumulative effect similar to that seen after a blocked beat during stressed 1:1 conduction, until block occurs and the cycle resets.

The inside-out electrocardiographic stress test: a view from the left ventricular cavity

A new method is described for measuring the unipolar left ventricular cavitary electrogram by means of a standard pigtail ventriculography catheter. Experiences with this technique in 30 patients are described with particular reference to changes in the S-T segment of the cavitary electrogram during cardiac stress by atrial pacing. This method allows convenient recording of His bundle potentials from the left ventricular outflow tract in most patients.

Chronic bilateral bundle-branch block. Long-term observations in ambulatory patients

During a period of 28 months, all patients (79) who presented with bilateral bundle-branch block were selected for study from a private practice outpatient population. They were followed prospectively from the date of entry into the study and their charts were reviewed retrospectively. The average age of the participants was 73-3 years and they were observed clinically for a cumulative period of 4237 months (353-08 years). A high incidence of severe heart disease and death was noted among the study group. Twenty-four (30-3%) had a New York Heart Association functional classification of 3 or 4. Eight (10-1%) died. Only one patient died suddenly and he had had a stable electrocardiographic pattern of bilateral bundle-branch block for a period of 118 months (9 years 10 months). Seven patients required permanent pacemakers. In 6 instances death resulted from pump failure; in one it was the result of lung cancer. In none of these 7 individuals did rhythm disturbances contribute to death. In most cases vertigo was not of cardiac origin (88-2%). Eight patients had 11 major surgical procedures with no significant cardiac sequelae. Our observations suggest that elderly patients with chronic bilateral bundle-branch block should be managed conservatively. The prognosis in these patients appears primarily to be related to the degree of myocardial disease rather than to the conduction disorder.

Mechanism of atrioventricular conduction: study on an analogue

A simple analogue of the heart, consisting of neon relaxation oscillators, is presented. The analogue may display several disturbances of the A-V conduction, like normal atrioventricular (A-V) conduction, first-degree heart block, Wenckebach periods, Mobitz II type block, supernormal conduction, complete A-V block, the phenomenon of accrochage in complete A-V block and the absolutely arrhythmic response of the ventricles to a very high atrial rate. The analogue was constructed in the simplest possible way, i.e., using the least possible number of variables. The striking similarities between the properties of relaxation oscillators and cardiac pacemakers on the one hand and between the behavior of the analogue and manifestations of the A-V conduction abnormalities on the other might possibly permit a hypothesis about the mechanism of A-V conduction abnormalities based on the analogue. This mechanism is discussed in detail.

Significance of A-H interval in patients with chronic bundle branch block. Clinical, electrophysiologic and follow-up observations

His bundle electrograms were recorded in 308 adults with chronic bundle branch block. The A-H interval was normal in 249 patients and prolonged in 59. Comparison of patients with normal and prolonged A-H intervals revealed a greater incidence of demonstrable organic heart disease in the latter (P less than 0.01). Dyspnea, cardiomegaly and congestive heart failure were more frequent in patients with A-H prolongation. These patients also had longer P-R intervals and atrioventricular (A-V) nodal effective refractory periods, lower paced rates producing second degree A-V block proximal to the His bundle and a greater frequency of H-V prolongation. All patients were prospectively followed up in a conduction disease clinic with mean follow-up periods (+/- standard error of the mean) of 523 +/- 23 and 588 +/- 47 days in the patients with normal and prolonged A-H intervals, respectively. Seven (3 percent) of the patients with a normal A-H interval had A-V block with probable or definite site of block proximal to the His bundle in three and distal to the His bundle in four. In five of the six patients with a prolonged A-H interval who experienced A-V block (10 percent), the probable or definite site of block was proximal to the His bundle. Mortality (both sudden and nonsudden) was not significantly different in the patients with normal and prolonged A-H intervals. In summary, A-H prolongation was associated with increased incidence of organic heart disease and myocardial dysfunction. The risk of development of A-V nodal block was greater in patients with a prolonged A-H interval but appeared to be of minimal clinical significance.

Progressive improvement of His-Purkinje conduction during recovery from catheter-induced heart block

Complete heart block developed during HBE studies in a patient with left bundle branch block, after inadvertent catheter-induced trauma to the right bundle branch. Normal intraventricular conduction (HV interval) was documented during the initial part of the study, and was demonstrated to be markedly prolonged after the appearance of heart block. Conduction through the right bundle branch improved over a short period of time as manifested by steplike shortenings of the HV interval, until the original conduction velocity was re-established. This case strongly supports the concept that the His-Purkinje system is capable of varying its conduction velocity and further demonstrates that, in patients with bundle branch block, a prolonged HV interval indicates disease of the remaining bundle branch.

Indications for prophylactic preoperative insertion of pacemakers in patients with right bundle branch block and left anterior hemiblock

To determine the need for prophylactic temporary pacing in bifascicular block during surgical and other procedures, a retrospective analysis was carrried out in 38 patients who underwent a total of 74 procedures. The male:female sex ratio was 3.2:1 and mean age was 74 (range 48-96) years. Known organic heart disease was absent in 45 percent of the total group. Patients were divided into four groups on the basis of their preoperative electrocardiograms. Of the 74 procedures, 19 were carried out under general, 22 under spinal and 29 under regional anesthesia; four endoscopic procedures were done without anesthesia. There was only one complication relating to deterioration of AV conduction. It is concluded that asymptomatic patients with right bundle branch block and left anterior hemiblock do not require prophylactic preoperative pacemaker insertion. Though experience is limited, the same may be true of patients with the additional finding of prolongation of PR interval.

Repair of tetralogy of Fallot after catheterization-induced complete heart block

The case of a four-year-old boy with tetralogy of Fallot who developed complete heart block during cardiac catheterization and subsequently underwent surgical repair in the presence of heart block is presented. Return to normal sinus rhythm occurred on the 11th postoperative day, and the manner in which increased atrioventricular conduction appeared was documented with the use of a continuous Holter monitor. Placement of a temporary transvenous pacemaker, systemic heparinization in the preoperative period, and the insertion of a permanent epicardial wire during surgery were performed.

Patterns of atrioventricular conduction in children

In this study, intracardiac electrograms were performed in 20 children--ranging in age from eight months to 18 years and without evidence of conduction disturbances on the scalar electrocardiogram--to determine the normal conduction patterns, response to atrial pacing, and values of refractory periods. Atrial pacing--18 cases--induced a prolongation al AH on increasing heart rates in all; 11 developed Wenckebach block proximal to the bundle of His at the mean pacing rate of 224 per minute +/- 45 (1 S.D.). Refractory periods were shorter than in adults. Study of the pattern of A-V conduction revealed three types of response: (1) the atrium was the limiting structure in 11 cases; (2) the delay occurred in the A-V node only in four cases; and (3) the delay occurred both in the A-V node and His-Purkinje system. This response was observed in one case only.

His bundle electrogram in patients with acute myocardial infarction complicated by atrioventricular or intraventricular conduction disturbances

Seventy-two patients with acute myocardial infarction complicated by atrioventricular or bundle-branch block or a combination of both had His bundle electrogram studies performed during their stay in the coronary care unit. In 19 of the 72 patients a repeat His bundle electrogram was performed before discharge from hospital. These studies demonstrated that 30 of the 32 patients with atrioventricular block and narrow QRS complexes had a block above the origin othe His spike (proximal block). Eleven patients in this group had repeat His bundle electrograms performed before discharge and in 3 patients there was evidence of residual atrioventricular nodal dysfunction. Both the hospital and follow-up mortality in this group was low and there was no evidence to suggest that permanent pacing would benefit these patients. Of the 18 patients with bundle-branch block and a normal PR interval, 9 had prolongation of the HV interval, but there was no difference in mortality in patients with normal or prolonged HV intervals. Twenty-two patients with bundle-branch block also developed atrioventricular block. In 5 of these patients the site of the AV block was proximal and in 14 it was distal, while 3 patients had both proximal and distal block. The hospital mortality in those patients who progressed to second- or third-degree atrioventricular block was considerably higher than in those patients who remained in first-degree atrioventricular block.