Symposium on Electophysiologic Correlates of Clinical Arrhythmias. 3. Contribution of His bundle recordings to the understanding of clinical arrhythmias

Electrocardiogram: his bundle potentials can be recorded noninvasively beat by beat on surface electrocardiogram

Background

The micro waveform of His bundle potential can’t be recorded beat-to-beat on surface electrocardiogram yet. We have found that the micro-wavelets before QRS complex may be related to atrioventricular conduction system potentials. This study is to explore the possibility of His bundle potential can be noninvasively recorded on surface electrocardiogram.

Methods

We randomized 65 patients undergoing radiofrequency catheter ablation of paroxysmal superventricular tachycardia (exclude overt Wolff-Parkinson-White syndrome) to receive “conventional electrocardiogram” and “new electrocardiogram” before the procedure. His bundle electrogram was collected during the procedure. Comparative analysis of PA_s (PA interval recorded on surface electrocardiogram), AH_s (AH interval recorded on surface electrocardiogram) and HV_s (HV interval recorded on surface electrocardiogram) interval recorded on surface “new electrocardiogram” and PA, AH, HV interval recorded on His bundle electrogram was investigated.

Results

There was no difference (P > 0.05) between groups in HV_s interval (49.63 ± 6.19 ms) and HV interval (49.35 ± 6.49 ms). Results of correlational analysis found that HV_S interval was significantly positively associated with HV interval (r = 0.929; P < 0.01).

Conclusions

His bundle potentials can be noninvasively recorded on surface electrocardiogram. Noninvasive His bundle potential tracing might represent a new method for locating the site of atrioventricular block and identifying the origin of a wide QRS complex.

New micro waveforms firstly recorded on electrocardiogram in human

In our study, not only the P-QRS-T waves but also the micro-wavelets before QRS complex (in P wave and PR segment) and after QRS complex (ST segment and upstroke of T wave) were first to be identified on surface electrocardiogram in human by the "new electrocardiogram" machine (model PHS-A10) according to conventional 12-lead electrocardiogram connection methods. By comparison to the conventional electrocardiogram in 100 cases of healthy individuals and several patients with arrhythmias, we have found that the wavelets before P wave theoretically reflected electrical activity of sinus node and the micro-wavelets before QRS complex may be related to atrioventricular conduction system (atrioventricular node, His bundle and bundle branch) potentials. Noninvasive atrioventricular node and His bundle potential tracing will contribute to differentiation of the origin of wide QRS and the location of the atrioventricular block. We also have found that the wavelets after QRS complex may be associated with phase 2 and 3 repolarization of ventricular action potential, which will further reveal ventricular repolarization changes.

Assessment of atrioventricular nodal physiology in the mouse

Transgenic mice are increasingly being utilized for understanding cardiac electrophysiologic abnormalities. However, little is known about the normal atrioventricular nodal and infraHisian physiology in the mouse because of the prior inability to record a His-bundle deflection. We present the first comprehensive examination of the murine atrioventricular nodal and His-Purkinje systems employing His-bundle recordings. Normal, healthy, male C57BL/6J mice (n = 48) underwent an in vivo electrophysiology study using a 2 F octapolar electrode catheter. Effective refractory periods were determined during premature atrial and ventricular stimulation. The PR interval measured 44 +/- 6 ms with a mean sinus cycle length of 185 +/- 42 ms. Baseline AH intervals were 36 +/- 5 ms and HV intervals were 10 +/- 2 ms. At a pacing cycle length of 140 ms the atrioventricular nodal effective refractory period (AVNERP) and atrial effective refractory period (AERP) were 86 +/- 19 ms and 57 +/- 17 ms, respectively. The mean AV Wenckebach and 2:1 paced cycle length were 103 +/- 14 ms and 84 +/- 13 ms, respectively. Premature atrial stimulation curves were asymptotic without discontinuity. A subset of nine mice was studied after administration of isoproterenol. The sinus cycle length, AVNERP and AERP decreased significantly from baseline measurements. This method establishes a practical and feasible technique to record in vivo His-bundle electrograms in the mouse to assess atrioventricular nodal and infraHisian physiology. Use of this model will allow for the examination of abnormalities of atrioventricular nodal and infraHisian conduction in transgenic murine models.

The electrophysiologic characteristics of the transplanted human heart

The electrophysiologic characteristics of the denervated human heart were assessed in 14 cardiac transplant recipients. Conduction intervals and refractory periods were measured at pacing cycle lengths of 500 msec and 400 msec. The faster pacing rate caused lengthening of the AH interval (83 +/- 23 msec to 116 +/- 41 msec, p less than 0.01) and shortening of the QT (338 +/- 27 msec to 313 +/- 22 msec, p less than 0.001) and JT (249 +/- 21 msec to 229 +/- 19 msec, p less than 0.001) intervals. There was no change in the SA, HV, or QRS durations. Wenckebach periodicity occurred at a longer cycle length in the retrograde than in the anterograde direction (409 +/- 96 msec vs 318 +/- 46 msec, p less than 0.01) and anterograde conduction was better than retrograde conduction in 13 of the 14 patients (93%). Increasing pacing cycle length resulted in shortening of the atrial effective (203 +/- 28 msec to 190 +/- 25 msec, p less than 0.001), ventricular effective (224 +/- 18 msec to 211 +/- 17 msec, p less than 0.01), and AV nodal functional (367 +/- 38 msec to 357 +/- 36 msec, NS) refractory periods. The AV nodal effective refractory period lengthened (294 +/- 31 msec to 314 +/- 52 msec, p less than 0.05). There was a close correlation between AV Wenckebach cycle length and the functional refractory period of the AV node (r = 0.853, p less than 0.001). These results are qualitatively and quantitatively similar to those reported in the innervated heart. The autonomic nervous system appears to have little influence on the resting electrophysiologic characteristics of the atrioventricular conduction system in the innervated heart.

Electrophysiological abnormalities in the transplanted human heart

Fourteen relatively long term survivors of cardiac transplantation underwent systematic electrophysiological evaluation and ambulatory electrocardiographic monitoring. Six patients had prolonged conduction intervals during sinus rhythm. Sinus node function could be assessed in all donor atria and in 10 recipient atria. Sinus node recovery times were prolonged in four of the donor atria and in six recipient atria. In the donor atria abnormalities of sinus node automaticity were invariably associated with abnormalities of sinoatrial conduction. Four patients showed functional duality of atrioventricular nodal conduction during programmed extrastimulation, but no patient developed re-entrant arrhythmia. During ambulatory electrocardiographic monitoring no pronounced tachyarrhythmias were recorded. Three patients showed abnormalities of sinus node impulse formation. All three patients had abnormal sinus node recovery times during their electrophysiological study. Long term survivors of cardiac transplantation have a high incidence of electrophysiological abnormalities. Abnormalities of donor sinus node function are probably of clinical significance. The clinical significance of abnormalities detected within the atrioventricular conduction system of the denervated heart remains to be elucidated.

Acute electrophysiological effects of flecainide acetate on cardiac conduction and refractoriness in man

The electrophysiological effects of flecainide acetate (2 mg/kg as an intravenous infusion over five minutes) were assessed in 47 patients undergoing electrophysiological study. Seven patients had normal electrophysiology, 16 had a direct accessory atrioventricular pathway, 12 had dual atrioventricular nodal (AH) pathways, five had paroxysmal ventricular tachycardia, six had conduction system disease, and one patient had a left atrial tachycardia. No significant change occurred in sinus cycle length. The PA interval, AH interval, and HV interval were all significantly prolonged. The QRS complex duration increased significantly. The QT interval showed slight prolongation due entirely to the increase in QRS duration. Refractoriness of the atrial and ventricular myocardium was slightly prolonged, but was significant only at ventricular level. No significant change occurred in refractoriness of the normal atrioventricular node. Pronounced prolongation of retrograde "fast" AH pathway refractoriness was observed in those patients with dual AH pathways. Anterograde and retrograde accessory pathway refractoriness were both greatly increased. These electrophysiological properties strongly suggest that flecainide will be useful in the management of a wide variety of cardiac arrhythmias. It should be administered, however, with caution to patients with pre-existing conduction system disease. Because repolarization is not delayed flecainide is unlikely to induce ventricular arrhythmias related to prolongation of the QT interval.

A comparison of clinical electrophysiologic studies in different institutions

Although electrophysiologic studies have been used to evaluate tachycardia and AV conduction for over 10 years, there are no data comparing measurements obtained on the same patient studied in two institutions. We compared the records of 27 patients who underwent electrophysiologic studies at two different institutions and one patient studied twice in the same institution by two different investigators. We sought to determine if basic intervals, observed tachycardia, and diagnoses were comparable. We found no significant difference between the reported sinus cycle length, atrial-His interval, and His-ventricular interval when the patients were evaluated as a group. However, there were important measurement differences between the two studies in individual patients. The cycle length of induced tachycardias having similar QRS morphology and AV relation was also similar for the group, but individual patients again demonstrated important differences between the two studies. The diagnosis of the tachycardia varied in four patients. This report suggests that intracardiac recordings and the diagnosis of observed tachycardias are comparable among institutions studying the same patient when the group results are compared. However, individual patients demonstrate important measurement differences between the two institutions.

Swallowing-dependent atrial tachyarrhythmias. Their mechanism

We describe here the case of one patient who exhibited several types of atrial tachyarrhythmias induced by swallowing. There was no evidence of other cardiac or gastroesophagic abnormalities. The electrophysiologic study demonstrated a second degree A-V block due to block within the atria. Our findings suggest that the mechanism operative may be an intra-atrial micro-reentry induced by an increased vagovagal reflex triggered by the normal esophageal peristalsis.

The syndrome of normal electrocardiograms, accessory pathways and paroxysmal tachycardias

Tachycardias may be associated with the pre-excitation syndrome, a short PR interval or a prolonged QT interval. This report describes seven patients whose electrocardiograms (ECGs) did not reveal any of the above-named conditions. All of the patients presented with syncopal episodes, and the history of palpitations was elicited in five of the patients. His bundle electrogram studies in all of the patients showed an essentially unchanged AH interval with atrial pacing rates up to 180 beats/min. This can only be explained by a total bypass of the AV node. Two of the patients were also paced from the ventricle, and an unchanged pacing stimulus to A wave interval was observed. This signifies in these patients a functioning bypass pathway in the retrograde direction as well. Thus it would appear that pre-excitation cannot by eliminated as a diagnostic possibility even if the ECG is normal.

Ventricular activity during atrial fibrillation. Studies with His bundle electrography

His bundle electrograms were recorded in 12 patients with atrial fibrillation. In all cases but one, the dominant rhythm was atrial fibrillation. In 1 case the dominant rhythm was fascicular tachycardia due probably to digitalis overdosage. However ventricular, fascicular and junctional beats could be often recognized on His bundle tracings, even when QRS configuration was similar to supraventricular conducted beats due to atrial fibrillation. In the patients in whom sinus rhythm occurred, the H-V interval was unchanged. Although it is admitted that during atrial fibrillation the zone of concealment of A-V conduction is in the A-V nodal area, concealed penetration of atrial impulses in the fascicular system may be encountered in patients not treated with digitalis.

Recurrent tachycardias due to an accessory pathway

A 48 year old female presented with a long history of palpitations and syncopal episodes. His bundle electrogram studies were performed in order to evaluate the conduction system. The electrocardiogram (ECG) revealed normal PR and QRS intervals, while the unpaced His electrogram was normal. With atrial pacing rates of 110 to 180 beats/min, the AH and HV intervals remained essentially unchanged. This signifies that there was an accessory conduction pathway which bypassed the AV node. Thus, pre-excitation can not be eliminated as a diagnostic possibility even if the ECG is normal.

Pharmacologic therapy of ventricular arrhythmias

To treat patients with ventricular arrhythmias properly, one must characterize the arrhythmia, define the underlying heart disease and look for and treat reversible causes. When arrhythmias are suitable for pharmacologic suppression, it is necessary to predefine therapeutic goals, then carefully document that the drug accomplishes these goals. Knowledge of a drug's metabolism, excretion, active metabolites and plasma protein binding is often required for full understanding of its clinical effect. Pharmacokinetic principles require that antiarrhythmic drugs be given on a rigid schedule and that plasma drug levels be frequently determined. Use of compartment models and the principle of superposition can enable one to achieve and maintain therapeutic drug concentrations while avoiding toxic side effects. The drugs commonly used to treat arrhythmias, lidocaine, propranolol, procainamide, diphenylhydantoin and quinidine, as well as some newer agents, have specific pharmacokinetics and toxic effects that must be understood.

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.

Left ventricular approach for recording His bundle potential in man

The electrical potentials of the His bundle (HB) were recorded from the left ventricular endocardial surface in 28 patients ranging from 16 to 63 years of age. In 14 of the patients the left bundle branch (LB) potentials were also obtained. Placement of a bipolar electrode catheter tip toward the interventricular septum, right at and also 1 to 2 cm below the aortic valve, resulted in stable recordings of both potentials in successive cardiac cycles even at performing atrial or HB pacing from the right heart. The following intervals were measured in milliseconds (msec): P-A, A-H, H, H-V, LB, and LB-V. The average values in 12 patients (average age 26 plus or minus 7 years and average heart rate 90 plus or minus 16 beats per minute) with normal A-V conduction were as follows: P-A 28 plus or minus 7, A-H 76 plus or minus 16, H 19 plus or minus 3 and H-V 45 plus or minus 6 msec. The average values for LB and LB-V in 10 of these 12 patients were 15 plus or minus 3 and 25 plus or minus 3 msec respectively. Validation of the His bundle electrogram (HBE) from the left ventricular endocardial surface was based on simultaneous recordings of the intracardiac electrograms from both left and right sides of the heart in 18 patients. The individual average values for the intervals obtained from both sides of the heart in these patients were statistically not different, except that the H potential was slightly longer in duration fr m the left heart (P equals 0.05). Among these, 16 showed simultaneous onset of the H potentials, and the LB-V and RB-V conduction times from comparable points were almost the same. Indications for the left sided electro-physiologic studies include the following situations: (a) inability to record H from the right of the heart; (b) giant right atrium; and (c) possibly during atrial fibrillation.

Direct and reflex cardiac bradydysrhythmias from small vagal nerve stiumaltions

Alterations in cardiac pacemaker location, its rate of discharge, and A-V conduction patterns were induced in anesthetized adult dogs by electrical stimulation of the thoracic vagi and their small cardiac branches before and after cervical vagotomy. Electrical activity from small, contiguous bipolar silver electrodes was amplified and recorded by an optical oscillograph. The electrodes were located over the SA node, the three internodal pathways, the left atrium, and ventricular epicardium. A hoffman-type plaque electrode was placed over the A-V node to record a His bundle electrogram simultaneously with a Lead II electrocardiogram. Electrical stimulation of the intact left recurrent laryngeal nerve and its cardiac branches before and after vagotomy induced both direct and reflex effects on SA nodal cycle length. Efferent dromotropic effects on the A-V node varied from first- to third-degree heart block during stimulation of individual left recurrent cardiac branches. Stimulation of the right recurrent cardiac nerve induced atrial bradycardia with heart block above the His bundle. Stimulation of individual right vagal branches near the heart induced bradycardia, cardiac asystole, shifts in atrial pacemaker location, or activation of His pacemakers. Establishment of the His rhythm probably indicates selective inhibition of supraventricular but not of the His bundle. Asystole and His rhythms induced during stimulation of the more caudal branches of the right cardiac vagal nerves were generally reflexly mediated and were abolished by cervical vagotomy.

Intracardiac electrography in children and young adults

The interpretation of IE recorded in children has been hampered by a lack of agreement regarding normal values. We recorded IE in 158 children and young adults (ages, three days to 33 years) to define the various conduction intervals in normal and disease states. The HBP was recorded in 156 subjects. In 85 subjects with normal conduction indicated by surface ECG, including 19 subjects with normal hearts, there were no statistically significant age-related differences in internodal, A-V nodal, or His-Purkinje conduction intervals. Therapeutic levels of digitalis did not alter the conduction intervals. In 11 subjects with first degree A-V block and in five subjects with congenital complete A-V block, the site of block as determined by IE could not be predicted from the surface ECG. No abnormalities in conduction intervals were found in 18 subjects with right bundle branch block (surgically induced in 17 cases). Intracardiac electrography with recording of the HBP was found to be a safe, informative technique for electrophysiologic investigations in children and young adults.

Catheter-induced intra-Hisian and intrafascicular block during recording of His bundle electrograms

Mechanical injury of the atrioventricular (A-V) node, His bundle, and right bundle branch is a potential complication of His bundle recording. In the presence of left bundle branch block, catheter-induced injury of the right bundle branch may cause prolongation of A-V conduction time or even complete A-V block. Two cases are reported in which catheter-induced transient high grade Mobitz II A-V block, acute reversible prolongation of infranodal conduction time with probable intra-Hisian conduction delay, and persistent (6 hours duration) complete A-V block occurred in patients with left bundle branch block. The observations made indicate that A-V conduction times and the appearance of "split His" potentials may be influenced by the recording catheter itself, and suggest that the operators be prepared to institute immediate right ventricular pacing when His bundle recordings are obtained in patients with left bundle branch block.

Conduction intervals and conduction velocity in the human cardiac conduction system. Studies during open-heart surgery

Specialized fiber electrograms were recorded in 64 patients during open-heart surgery. Intervals were measured from the proximal His bundle, distal His bundle, and right and left bundle branches to the earliest QRS deflection in the limb lead ECG (pH-Q, dH-Q, RB-Q, and LB-Q interval, respectively). There was an increase of pH-Q intervals with increasing age such that at age 3 months the normal range of pH-Q interval was 13-27 msec, while at 14 years of age it was 32-54 msec. For patients 15 years of age and older, the normal range of pH-Q interval was 35-54 msec, similar to that reported by several investigators using catheter technic and suggesting that most His bundle electrograms recorded by catheter technic in fact record from the proximal His bundle. The dH-Q interval varied from 18 to 35 msec, the RB-Q interval from 18 to 30 msec, and the LB-Q interval from 20 to 39 msec. These normal ranges of RB-Q and LB-Q intervals are greater than previously reported. Overlaps existed between the normal range of pH-O and dH-Q or LB-Q intervals, dH-Q and RB-Q or LB-Q intervals and, at least in children, the pH-Q and RB-Q intervals. Thus the timing of a specialized fiber electrogram does not necessarily reflect its anatomic location. AV nodal electrograms were not recorded although the recording sites included the known anatomic location of the AV node. Conduction velocity in the His bundle was determined and averaged 1.5 m/sec (range 1.3-1.7 m/sec).

The His bundle electrogram

The His bundle electrogram is discussed with respect to its rationale, methods for its recording and evaluation, findings with its use in the various forms of heart block and arrhythmias, its clinical value, and its limitations.