Bundle Recordings Research Articles

Electrophysiologic effects of mexiletine in children.

The effects of intravenous administration of mexiletine on the refractory periods of the atrium and atrioventricular (AV) node were studied using His bundle recordings and the extrastimulus technique with atrial pacing. The drug was administered to 10 children with heart disease in an intravenous bolus dose of 3 mg/Kg, injected over a 5-min period, followed by an infusion of 1 mg/Kg/hr of mexiletine, achieving a mean therapeutic plasma concentration of 0.762 +/- 0.270 microgram/ml. The AH and HV intervals, the resting sinus cycle length, and the functional and effective refractory periods of the atrium and AV node were measured before and 5 min after initiation of the mexiletine infusion. The sinus cycle length was reduced significantly. However, neither the refractory periods nor the AH and HV intervals changed in a significant manner. Except for the heart rate, these results are similar to those reported in adults without conduction disturbances. In adults, mexiletine did not affect the sinus cycle length. However, in children, it consistently increased the heart rate. The lack of side effects in children is in contrast to adults, who usually suffer from gastrointestinal and neurologic symptoms upon receiving comparable doses parenterally.

Electrophysiologic changes after tiapamil in coronary and noncoronary patients.

26 patients who had undergone right heart catheterization were enrolled in the study. The average age was 51.7 +/- 15 years. Half the patients showed coronary artery disease at selective coronary angiography. His bundle recordings and atrial pacing were performed before and 10 min after 1 or 1.5 mg/kg i.v. tiapamil. In addition, arterial blood pressure was recorded. P-R interval increased from a mean value of 153 +/- 36 to 168 +/- 49 ms (p less than 0.05) due to an increase in the A-H time from 88 +/- 19 to 97 +/- 23 ms (p less than 0.05). Arterial blood pressure and heart rate decreased significantly. These changes were more pronounced in patients with coronary artery disease. In the groups with the higher dosage, the differences from the control values were greater than in the patient groups receiving 1.0 mg/kg. Sinus node recovery time tended to increase in all groups but the differences did not reach significance. Patients with the 'sick sinus syndrome' were not studied.

Electrophysiologic evaluation of encainide with use of monophasic action potential recording

The electrophysiologic effects of encainide in the intact dog heart were evaluated with the use of monophasic action potential and His bundle recordings. Eight mongrel dogs were given 2.7 mg/kg body weight of encainide in two intravenous infusions. Plasma concentration, blood pressure, surface electrocardiogram, atrial and His bundle electrograms, right atrial and ventricular monophasic action potentials and the right atrial and ventricular effective and functional refractory periods were recorded before and 15 to 45 minutes after each infusion. Basic cycle length and A-H, H-V, QRS and Q-T C intervals were significantly prolonged after administration of the drug. The refractory periods and the monophasic action potential durations were significantly increased in both the atrium and the ventricle although the increases were more pronounced in the atrium. It is concluded that encainide is a class I antiarrhythmic agent with properties very similar to those of quinidine.

A study of dromotropic effects of intracoronary arterial injections of various contrast materials in anesthetized dogs.

In two groups of open-chest, pentobarbital-anesthetized dogs, cardiac dromotropic effects of contrast materials were studied, using His bundle recordings. Retrograde injections (3 and 6 ml) in the left anterior descending coronary artery were done with iodinated compounds (ioxaglate solution, iopamidol, diatrizoate solution) and iso-osmolar glucose solutions as controls. Administration of 6 ml of contrast material and glucose solution resulted in a significant prolongation of StH interval with no change in HV; on QRS the increase was significant but more slight and more brief. In group 1 (n = 8) the maximum effect (6 ml) on atrioventricular conduction was significantly greater with diatrizoate solution than with iso-osmolar glucose solution and with ioxaglate solution: + 25.1 ± 2.8%, + 15.0 ± 3.6%, + 10.7 ± 1.8%, respectively. On QRS interval, the maximum increase was significant after ioxaglate (+ 8.7 ± 3.1%) and after diatrizoate (+ 13.5 ± 5.0%). There were no significant differences among the effects of these different solutions. In group 2 (n = 8), at 6 ml, ioxaglate, iopamidol, and their iso-osmolar glucose solution exerted similar and significant dromotropic effects: on StH, + 4.6 ± 0.8%, + 4.4 ± 1.2%, + 5.6 ± 1.0%, respectively; on QRS, + 6.7 ± 2.7%, + 5.9 ± 2.1%, + 5.7 ± 2.2%, respectively. The importance of the osmolarity factor on intracardiac conduction is emphasized by comparison of the osmolality of diatrizoate (1700 mOsm/kg), which is higher than those of ioxaglate (580 mOsm/kg) and iopamidol (740 mOsm/kg). Direct toxicity of the molecule possibly also plays a role, since the effects of diatrizoate were significantly greater on atrioventricular conduction than those of isoosmotic glucose solution.

Advances in the diagnosis and treatment of tachydysrhythmias in children

Major advances have recently been made in the identification and management of tachydysrhythmias in children. These include diagnostic improvements in both noninvasive techniques (24-hour ambulatory ECG monitoring and transtelephonic ECG transmission) and invasive techniques (His bundle recordings and intracardiac stimulation studies). In consort, there also have been new developments in tachyarrhythmia therapy. For example, propranolol has been popularized for treating tachycardias in children; the dosage range has been modified and higher doses are now used with safety, when necessary. Further, the calcium channel blocking agent, verapamil, has become accepted in Europe and South America as an effective drug for acute and chronic treatment of supraventricular tachycardia (SVT) in children and is scheduled for widespread use in the United States. The most exciting development in invasive treatment has been the use of surgical techniques and pacemakers for management of certain patients with severe or persistent forms of tachydysrhythmias.

Evidence for adenosine mediation of atrioventricular block in the ischemic canine myocardium.

Adenosine levels in oxygen-deprived myocardium can rise to 10- 100 microM concentrations known to cause atrioventricular (AV) conduction delay and block. We reported that the AV conduction delay and block caused by hypoxia is markedly attenuated by 10 microM aminophylline, and adenosine competitive antagonist. THe purpose of the present study was to investigate adenosine's role in ischemic AV conduction disturbances. Dogs were anesthetized and instrumented for His bundle and surface electrogram recordings. The total AV conduction time was subdivided in to atrial-His bundle (AH) and His bundle-ventricle intervals. The atrioventricular node artery (AVNA) was cannulated for selective injection of drugs in the AV node region. Adenosine (10 to 100 microgram), as a 2-ml bolus injection, rapidly produced a dose-dependent, transient increase in the AH interval; a 1,000-microgram dose caused second degree AV block. The duration of the increase in AH interval was also dose-dependent. Dipyridamole, and inhibitor of nucleoside transport, potentiated the negative dromotropic effects of adenosine, whereas aminophylline attenuated them. In some dogs, after cannulation of the AVNA, first and second degree AV block occurred spontaneously or were induced by rapid atrial pacing. Injection of the aminophylline (5 mg/kg, i.e.) or theophylline (100-1,000 microgram) into the AVNA rapidly reversed the AV blocks. Upon washout of the drugs the AV blocks recurred. We conclude that endogenously released adenosine may account for a major fraction of the AV conduction delay and block associated with impaired blood supply to the AV node, and the theophylline and aminophylline reverse the AV conduction defect by antagonizing the effects of adenosine.

Cardiac electrophysiologic effects of quinidine and propranolol isomers in anesthetized dogs: concentration-response relationships.

Electrophysiological properties of quinidine and the two isomers of propranolol were compared in pentobarbital-anesthetized dogs using His bundle recordings and programmed stimulation in order to differentiate the effects resulting from beta-blockade from those related to nonspecific membrane-stabilizing effects. Quinidine in the plasma concentration range of 2.7-20 microM/liter resulted in concentration-dependent increases in atrionodal and His-Purkinje system conduction times and in the atrial effective refractory period. Quinidine did not produce any significant concentration-dependent change in atrioventricular (AV) nodal and ventricular refractory periods, sinus node automaticity, or QTc interval duration. Propranolol isomers in concentration range of 0.03-0.85 microM/liter produced a concentration-dependent increase in atrionodal conduction time but exerted no significant effect on His-Purkinje conduction time, QTc duration, or ventricular refractory period. Both isomers increased the atrial effective refractory period, but with slopes of concentration-response regression lines which were significantly different from those of quinidine. Only l-propranolol produced concentration-dependent increases in AV nodal refractory period, Wenckebach cycle length, and sinus node recovery time. These results suggest that the electrophysiological effects of propranolol isomers are related to beta-blockade and are significantly different from those resulting from the membrane-stabilizing effect of quinidine.

Noninvasive recording of the His bundle electrogram: value of supplementary verapamil.

We obtained noninvasive recordings of the His bundle electrogram using the Marquette high resolution MAC unit in 65 patients and 5 normal subjects. Overlap of atrial activity prevented identification of a His potential in 25 subjects, in 23 of whom the PR interval was equal to or less than 160 ms. After intravenous verapamil (10 mg) the AH interval was lengthened, with an increase in the PR interval of 10-60 (mean 20) ms. A characteristic His bundle electrogram was recorded in 48 of the 70; in 8 there was persistent atrial activity and in 4 electrical interference could have obscured a His potential. In 10 patients the absence of a His complex despite a clear "window" of at least 70 ms between the end of atrial activity and the onset of ventricular depolarization suggested that its vector was outside the plane of the electrode arrangement, or that there was a prolonged H-V interval; the latter has been confirmed in 2 patients. Intracardiac His bundle recordings in 25 subjects who had characteristic surface electrical activity of the His bundle disclosed good correlation between invasive and noninvasive measurements of the H-V interval. This noninvasive technique using portable equipment, which permits serial evaluation of the His bundle electrogram, may facilitate prospective studies in patients with conduction disease.

Noninvasive recording of the His-Purkinje system electrical activity by a digital system design

The atrioventricular conduction pathways which are composed of the atrioventricular node and the His-Purkinje system (HPS) form a specialized conduction system in the heart that participates in the control of the ventricular conduction. His bundle recordings require cardiac catheterization in the diagnosis of abnormalities within the HPS. These recordings have limitations that include discomfort, a slight morbidity risk, and limited recording area within the heart. This report outlines a non-invasive technique that utilizes high gain, wide band filtering and coherent signals averaging to extract the electrical activity of the HPS at the body surface. We have designed a portable instrument which enables: (i) a high gain, very low noise, optically isolated differential amplifier; (ii) an online digital QRS detector based on the principle of contour limiting which detects the desired QRS complexes and generates a very accurate trigger for the coherent signal averaging; (iii) a digital memory averager. This instrument can be used as an automatic clinical tool or as a data acquisition and preprocessing system for high frequency ECG and many other low level electrophysiological signals.

Radiotherapy as a Cause of Complete Atrioventricular Block in Hodgkin's Disease

A 20-year-old man contracted Hodgkin's disease and was treated with mantle radiotherapy. Heart block developed 11 years later. Electrocardiograms revealed predominant atrioventricular (AV) block and occasional AV conduction. Intracardiac electrograms demonstrated that the site of AV block was above the level of the His bundle. A permanent transvenous pacemaker was implanted. Seven months later the patient died of complications from cryptococcal meningitis. Pathological study of the heart revealed marked arteriosclerosis with fibrosis of the epicardium, myocardium, and endocardium. Examination of the conduction system revealed extensive arteriolosclerosis of the sinoatrial node and its approaches. In addition, there was marked fibrosis of the approaches to the AV node, the AV bundle, and both bundle branches. There was no evidence of Hodgkin's disease. This case documents the rare occurrence of AV block due to tissue destruction by radiotherapy. There was a good correlation between block proximal to the His bundle recording site and fibrosis of the approaches to the AV node.

Noninvasive his bundle recording. Experience from three years of clinical trials

Noninvasive his bundle recording. Experience from three years of clinical trials

Current Controversies in Cardiovascular Disease

Current Controversies in Cardiovascular Diseaseis written for the practicing internist and cardiologist. The textbook concisely summarizes the current debates by prominent adult and pediatric cardiologists and cardiovascular surgeons regarding the diagnosis and the treatment of patients with coronary artery disease, hypertension, floppy mitral valve syndrome, pulmonary emboli, and selected aspects of congenital heart disease, including the treatment of patent ductus arteriosus and palliative vs corrective surgery. Each chapter presents the opposing viewpoints and experience of two authorities on a single issue. The emphasis is on arguments for and against procedures such as coronary arteriography, radionucleotide angiography, ST-segment mapping, echocardiography, His bundle recordings, hemodynamic monitoring, pericardiocentesis, pulmonary arteriography, and coronary artery bypass surgery. The quality of the chapters, however, does vary. Lack of properly randomized investigations on controversial issues permits expression of opinion as found in the debates on exercise and anticoagulation in patients with coronary artery disease. Authoritative summaries

His bundle electrogram recording using a multipolar electrode catheter via the arm veins

In eighteen patients with atrioventricular conduction disturbance, His bundle electrograms were studied via the arm vein. A 6F Berkovits-Castellanos USCI hexapolar electrode catheter was introduced into the right atrium and looped across the tricuspid valve in a "golf club" shape. The main aim was to leave the two distal electrodes in contact with the atrial endocardium to perform atrial pacing, while displaying the other four electrodes along the superior angle of the tricuspid valve for proximal and distal His bundle recordings. His bundle electrograms were successfully obtained in all cases. The arm approach provides an alternate route whenever the femoral approach is not feasible. Moreover, the use of an hexapolar electrode catheter provides some practical advantages: 1) it enables atrial pacing to be performed, as well as proximal and distal His bundle recording to be obtained, by using the same multipolar electrode catheter; and 2) it allows long-term monitoring of His bundle potentials, in view of the stability of His bundle recordings. Finally, the arm approach could be the method of choice for the study of His bundle electrograms during leg supine exercise in selected patients.

Simultaneous anterograde fast-slow atrioventricular nodal pathway conduction after procainamide

Three patients with paroxysmal supraventricular tachycardia underwent electrophysiologic studies that included His bundle recordings, incremental atrial and ventricular pacing and extrastimulation before and after intravenous infusion of 500 mg of procainamide. In all three patients the tachycardia was induced during atrial pacing or premature atrial stimulation, or both. Two of the three patients had discontinuous atrioventricular (A-V) nodal curves with induction of a slow-fast tachycardia during failure in anterograde fast pathway conduction and one patient had a smooth A-V nodal curve with induction of a slow-fast tachycardia at critical A-H interval delays. After procainamide: (1) in all three patients atrial pacing induced A-V nodal Wenckebach periodicity (cycle length 300 to 400 ms) resulting in simultaneous anterograde fast and slow pathway conduction (one atrial beat resulting in two QRS complexes) and retrograde fast pathway conduction initiating an echo response or a slow-fast tachycardia, or both; (2) in all three patients there was enhanced conduction and shortening of refractoriness of the anterograde fast pathway and depressed conduction and lengthening of refractoriness of the retrograde fast pathway; and (3) in two patients there was inability to sustain tachycardia because of selective block within the retrograde fast pathway. In conclusion: (1) procainamide altered conduction and refractoriness of the anterograde fast and slow pathways so that simultaneous conduction could occur during atrial pacing, resulting in a double ventricular response and a slow-fast echo or tachycardia, or both; and (2) the differential effects of procainamide on anterograde fast and retrograde fast pathways suggests two functional A-V nodal fast pathways, one for anterograde and the other for retrograde conduction.

Effects of mild hyperkalemia on conduction velocity and effective refractory period in various parts of the dog heart in situ.

Effects of mild hyperkalemia on conduction velocity, effective refractory periods (ERPs) and sinus rate were studied on 16 anesthetized dogs, using endocavitary His bundle recordings, the extrastimulus method and standard electrocardiogram. Six dogs were placed under acetylcholine infusion (300 micrograms/kg/min) (ACh group), 10 received atropine sulfate 0.2 mg/kg intravenously (atropine group). Intraventricular conduction time, ventricular ERP and QRS duration of the EKG were studied on 7 other open-chested dogs (ventricular group). During a 60 min potassium chloride infusion (0.025 mmol/kg/min, 30 min, then 0.05 mmol/kg/min, 30 min), following observations were made: - In the ACh group, AV node conduction time (A-H interval) decreased by 20% and AV node ERP by 17%, whereas, in the atropine group, the former parameter was not affected and atrial ERP increased by 29%. - At the same time, sinus rate increased in the ACh group and was unaffected in the atropine group. - Conduction times in atrial contractile tissue (S-A interval), His-Purkinje system (H-V interval) and ventricular contractile tissue, like ventricular ERP, exhibited no variation or very slight, occasionally biphasic variations under both conditions. These results can be accounted for by an "anticholinergic" effect of mild hyperkalemia which is discussed.

Clinical evaluation of an improved high resolution ECG cart for recording the His bundle electrogram non-invasively.

The Marquette high resolution MCA-1 ECG cart can record the His bundle electrogram non-invasively at the bedside. The second generation MAC-1 has several unique features and technical advances which may now make the technique clinically applicable. In addition to amplification and signal averaging, an adjustable input filtration system excludes beats which are unacceptably "noisy" compared to a 4 beat template. Thus, extremely "clean" signals are presented for processing by the average allowing resolution of very low amplitude signals. Clear unequivocal His bundle recordings were obtainable in 25 of 55 patients (45%). A correlation coefficient of +.97 was obtained between invasive and non-invasive HV intervals. The 55% failure rate was attributed to prolonged atrial activity in 31%, short PR in 9%, and technically unsatisfactory recordings with excessive or overwhelming noise which did not allow appreciable signal resolution in 15%.

In Vivo Changes in Canine Ventricular Cardiac Conduction during Halothane Anesthesia

Changes in the ventricular conduction system associated with halothane anesthesia were investigated by direct methods of His bundle recording, pacing, and premature stimulation in a canine model. In eight animals a change from 1.5% to 2.4% halothane concentrations was associated with significant prolongation of epicardial activation times by an average of 2.4 and 2.9 msec during atrial and His bundle paced rhythms, respectively. Ventricular functional refractory periods decreased significantly by an average of 7.3 msec, the effective refractory period of the ventricular conduction system did not system did not change, and epicardial conduction delays at the effective refractory period decreased. In six other animals the addition of 1.5% halothane to basal thipental anesthesia was not associated with prolongation of epicardial activation times or decreased ventricular functional refractory periods. However, the effective refractory period of the ventricular conduction system significantly decreased by an average of 9.1 msec, and epicardial conduction delays at the effective refractory period significantly increased by an average of 9.6 msec. A change in halothane concentrations from 1.5% to 2.4% is associated with depression of ventricular conduction and shortened duration of refractory periods in the ventricular conduction system in vivo in a manner consistent with the reported actions of halothane on Purkinje fibers in vitro.

Possible risks of general anesthesia in patients with intraventricular conduction disturbances.

In order to assess the risk of complete AV block in patients with intraventricular conduction disturbances who undergo general anesthesia, 20 patients with various conduction defects (7 LBBB, 1 RBBB and 1st degree AV block, 1 incomplete RBBB, 9 RBBB + LAH and 2 RBBB + LPH) were studied by means of His bundle recording and corrected sinus node recovery time (CSNRT) before and after the subministration of thiopental (0.2 g I.V.), succinylcholine (1 mg/kg I.V.), Fluothane (1%) and Ethrane (1.6%). Nineteen patients displayed signs of dizziness or syncope; both the sinus rate and the CSNRT, did not undergo significant variations. A slight and not significant variation of intranodal conduction during sinus rhythm was observed after Fluothane administration (AH was prolonged by 8%). A less evident negative dromotropic action of thiopental and Ethrane was only revealed by atrial pacing. No significant variations were demonstrated in His-ventricular conduction after administration of the various drugs. The maximum average increase (1.5%) of the H-V interval was observed after administration of succinylcholine. Acute AV block distal to the His bundle appeared in three patients after succinylcholine administration.

Pacing-induced alternate Wenckebach periods: incidence and clinical significance.

Alternate Wenckebach periods have been defined as episodes of 2:1 atrioventricular (AV) block in which conducted P waves exhibit progressive PR prolongation until two or three successively blocked P waves. Ocurrence of this phenomenon during atrial pacing has been established. Thirty-six patients were studied and right atrial pacing was achieved at increasing rates up to 350 beats/min in order to induce alternate Wenckebach periods. His bundle recordings were obtained in every patient. The patients were subdivided into three groups according to the AV nodal conduction time (AH interval): normal AH (75-130 ms) was present in 17 patients, short AH (70 ms) in 13 patients and prolonged AH (130 ms) in eight patients. Alternate Wenckebach periods were observed in 29 patients (80.5%). In every patient alternate Wenckebach periods occurred at the AV node level. Atrial pacing failed to induce alternate Wenckebach periods in seven patients, six of whom belonged to the short AH group. In four patients 3:1 block never appeared because of block at the atrial level. Two patients presented 2:1 and 3:1 infrahissian block without significant AH prolongation. The remaining patient developed atrial fibrillation. Alternate Wenckebach periods were observed in six of nine patients after intravenous atropine. This study suggests: 1. pacing-induced alternate Wenckebach periods at the AV node level are a physiologic phenomenon; and 2. total or partial bypass (or accelerated AV conduction) atrial refractoriness or vulnerability or block at a lower level may prevent its occurrence.

Electrophysiologic studies in patients with ventricular inversion and "corrected transposition".

We evaluated the intracardiac conduction intervals using His bundle recordings in 40 patients with ventricular inversion and 1-transposition of the great arteries. Twenty-nine subjects had 1:1 atrioventricular (AV) conduction. In 15 of those with normal PR intervals and QRS durations, the conduction intervals were not different from those of subjects with normal hearts. In the 14 patients with first-degree AV block, the block was located between the sinus node and AV node in four, between the low right atrium and bundle of His in seven, and below the common bundle of His in four. In 11 subjects with complete AV block, the stie of block was above the site of the His potential in four, below in two and within the His bundle in one. In four patients we could not record a His potential and thus could not localize the site of block. Complete block below the His recording site was associated with syncope in one patient and sudden death in another. His bundle recording is a safe technique for studying the conduction system in children with ventricular inversion and 1-transposition of the great arteries.