- Email: [email protected]
Surface recording of electrical activity from the region of the bundle of His
EXPERIMENTAL STUDIES
Surface Recording of Electrical Activity from the Region of the Bundle of His
NANCY
C. FLOWERS,
MD,
FACCt
R. CHRIS HAND PATRICIA CAREY MARY
C. ORANDER B. MILLER,
0.
MSEE
WALDEN
LEO G. HORAN,
MD,
FACC
Augusta, Georgia
From the Section of Cardiology, Medical Ser-
vice, FHD, Veterans Administration Hospital, and the Department of Medicine, Medical College of Georgia, Augusta, Ga. This study was supported by an award from the Veterans Ad-
ministration,and U. S. Public Health Service &ant HE-l 1667 (National Heart and Lung Institute of the National Institutes of Health, Bethesda, Md.). Manuscript accepted June 27, 1973. t Present address and address for reprints: Nancy C. Flowers, MD, Section of Cardiology, University of Louisville School of Medicine, HealthSciences Center, Louisville, Ky. 40202.
364
March 1974
In 16 dogs, by appropriate filtering and digital averaging on a PDP-9 computer, we were able to enhance the detection of electrical activity of interest in the P-R segment of the electrocardiogram. In instances (1) when such activity in the surface record coincided temporally with the internal recording from the bundle of His area, (2) when, with atrioventricular nodal block, the electrical activity of interest continued to be associated with the internally recorded His bundle deflection and not with atrlal actlvlty, and (3) when, with production of transmission delay between the bundle of His and the ventricle, the surface signal of interest continued to be associated with the internal His bundle deflection, a common signal source was considered likely. In certain instances the surface signal of interest in the P-R segment occurred well after the internally recorded His bundle deflection but about 15 msec before the earliest evidence of ventricular activity. In these instances, when the tests cited were applied and the blip of interest was associated with ventricular activity, the origin of the blip was thought to be in the region of the bundle branches. In the 16 animals studied, one or more pieces of the evidence described were present to localize the origin of the signal. In seven animals, the signal was thought to originate from the bundle of His, In six from the region of the bundle branches and in three from both the bundle of His and bundle branches.
Since Scherlag and co-workers first described the catheter technique for recording His bundle activity in the dog1 and in man,2 there has been a renaissance in extracellular approaches to electrophysiologic-electrocardiographic correlations. Interest in the subject has been intense and reporting logarithmic, especially regarding diagnostic and prognostic information now available in the fractionated P-R segment. During the course of multiple lead, high-speed, high-frequency surface recordings for other purposes, we noted apparent cardiac electrical activity in the P-R segment. The possibility that the activity might arise from the conduction system below the atria1 level but above the ventricular level, and still be accessible through noninvasive means, seemed worthy of exploration. Figure 1 is an example of the type of data that aroused our interest. The top recording-is from a surface site on the chest of a dog slightly anterior to the anterior axillary line in the fifth intercostal space. The middle record is a bipolar intracardiac electrogram recorded from a site near the bundle of His, and the bottom tracing is from the conventional VS nosition. although inverted. A 2:l block at the atrioventricular (ATv) node is- indicated by the failure of the second pacemaker impulse to be conducted below the atria1 level. The His bundle deflection from the intracardiac lead and electrical activity of interest in the P-R segment (referred to as blip1 [Bz] and blip2 [Bz]) are ab-
The American Journal of CARDIOLOGY
Volume 33
SURFACE RECCRDfNG CF HIS BUNDLE ACTtVlTY-FLOWERS
ET AL.
FIGURE1. An amplifiedsurface (S) leaded between 30 and 600 Hz (top), an intracardiac (C) lead recorded from a site near the A-V junction (m) and a surface-recorded conventional but inverted V, lead (bottom) from a dog exposed to a halogenaM hydrocarbon. A = internally recorded atrial activii; B, and 8s = blips of interest in surface P-R segment; H = His bundle activity; P = atrial activity: pi = pacer impulse; R = surface ventricular activity; T = surface-recorded ventricular recovery; V = internally recorded ventricular activity.
right atrium, and an intracardiac recording catheter capable of recording from three bipolar sites-l mm, 1 cm or 1.1 cm apart-was introduced to the region of the bundle of His by the technique described by Scherlag et all An intraarterial luminal catheter was introduced retrograde from the left femoral artery and positioned just distal to the aortic valve near the coronary ostia for delivering medications; an intravenous catheter was positioned in the inferior vena cava for similar purposes. Pacing was instituted from the bipolar pair of recording electrodes that recorded the largest biphasic His bundle deflection, and the chest was mapped in order to find the site of maximal negative and maximal positive potential from the pacemaker impulse. These points were identified on the chest and usually lay to the left and anterior for the maximal positive deflection, and to the right, slightly higher and posterior for the maximal negative deflection. It was hoped that these peak positive and negative points also approximately defined the electrical axis of the bundle of His, which should roughly parallel the axis generated by these electrodes (Fig. 3). The identification of such a site should
sent at the expected point in time, noted by the arrows. This finding suggests that the site of origin of Br and Bs is somewhere below the level of A-V block. The decreased rate of rise and overall amplitude of the His bundle signals from the internal lead can be attributed to the fact that this animal was one of a series in a study on the toxic effects of halogenated hydrocarbons known to have this effect on the His bundle deflection. The 50 beat computerized averages seen in Figure 2 exemplify an effort to amplify the P-R segment in another animal from the same series of toxicologic experiments.
Methods In 16 healthy mongrel dogs-4 anesthetized with morphine sulfate and pentobarbital and 12 with pentobarbital alone-intubation and controlled respiration and normal base-line blood gas values were established. A bipolar pacing catheter was introduced transvenously into the high
I
:. .
FIGURE 2. These 50 beat averages, taken at a sampling rate of 2,OOO/sec, are illustrative of our efforts to amplify the P-R segment in another animal from the same series of toxicologic experiments. At the top left is the surface signal; at the bottom feft, the intracardiac recording from the His bundle area. The top right shows the amplified P-R segment with the surface blip of interest labeled B. The bottom right shows the temporal association of the surface signal of interest above, and the intracardiac recording from the His bundle region below. B = surface blip of interest in P-R segment: H = internally recorded His bundle activity; IC = intracardiac lead; P = surface-recorded atrial activity; R = surface-recorded ventricular activity; S = surface lead: T = surface-recorded ventricular recovery.
:
March 1974
.
_
The American Journal of CARDIOLOGY
.2m
50-U
Volume 33
399
BUBFACE BECOBMNG
OF HIS BUNDLE ACTIVITY-FLOWERS
ET AL.
and the immediate vicinity was searched for an area that gave a repetitive surface deflection at approximately the same time as that of the His spike in the intracardiac electrogram. A similar search was performed on the negative side. The surface signal from the exploring electrode was fed into a Tektronix 26A2 differential amplifier and amplified 100,006 times, filtered between 0.1 and 3,000 Hz initially, and finally with a low-frequency cutoff between 1 and 80 Hz and a high-frequency cutoff of 600 Hz. Time synchronization was achieved by a special triggering network that also served to trigger the PDP-9 computer for averaging. After analog to digital conversion, either single cardiac cycles or 50 or fewer averaged beats were displayed on a storage oscilloscope for analysis and hard copy preparation. The constantly recorded signal on an Ampex FR 1300 tape recorder was available for later analysis, further averaging or preparation in hard copy form of sequential cycles photographed by a Grass oscilloscopic camera (Fig. 6).
Results Figure
7 shows
a recording from the intracardiac and the surface (S) recording below at a pacing rate of 90 beatslmin. The blip of interest in the P-R segment is labeled. The initially prolonged conduction time of 76.6 msec from the low atrium through the A-V node (A-H interval) is ac-
(IC) lead above,
FIGURE 3. Potential map of the chest, obtained in order to find the site of maximal negative and maximal positive deflection from a pacemaker impulse originating from the bipolar pair of recording electrodes that had recorded the largest biphasic His bundle deflection. See text.
help to optimize the chance of correspondence between the most parallel current flow lines of the His bundle and the lead field of an exploring electrode (Fig. 4). An arrangement of electrodes of the bipolar probe type was then designed with an exploring center surrounded by five indifferent points, connected by resistances to give a balanced bipolar configuration (Fig. 5). The site of the exploring electrode was placed at the point of peak positivity,
counted for by the anesthesia induced by morphine and pentobarbital. The base-line conduction time from the bundle of His to the earliest evidence of ventricular activity (H-V interval) was 31.6 msec. In the surface recording, the atria1 to blip (P-B) interval was even longer than the A-H interval since atria1 activity is detected earlier on the surface. From the surface blip of interest in the P-R segment to the earliest onset of ventricular activity (B-R), the time lapse was 20 msec. With pacing, the A-H and P-B intervals increased proportionately, whereas the H-V
FIGURE 4 Wt). Diagram of the lead field search for the surface electrode site that had optimal intersection with the most parallel flow lines from the His bundle and was feast optimal for interfering atrial activity. A = hypothetical atrial activity; E = exploring electrode; H = hypothetical lead axis of His bundle; I = indifferent electrode. FIGURE 5 (right). Bipolar probe type of arrangement connected through balanced resistances. See text.
386
March 1974
of electrodes
The American Journal of CARDIOLOGY
with a central exploring electrode surrounded
Volume 33
by five indifferent
electrodes
SURFACE RECORDlNG OF HIS SUNW
1001:
-
ACTIVITY-FLOWERS
ET AL.
wQ-WSS FIllEn
FIGURE 6. Diagram of mode of amplifying, filtering and displaying surface signal from exploring electrode. A = analog; D = digital; HB = His bundle; K = 1000; PDP-9 = computer. See
text.
and B-R intervals remained fixed. As A-V nodal delay increased with the increased pacing rate, the surface blip of interest emerged as a discrete electrical phenomenon seen in the lower panel. The origin of the surface blip is difficult to ascertain. The shorter duration of the B-R interval compared to that of the H-V interval suggests that the blip might have arisen from one of the bundle branches rather than from the bundle of His. On the other hand, much of the apparent shortening in the B-R interval is due to greater ability of the more distal surface lead to detect the earliest evidence of ventricular activity when compared with the much more local His bundle electrogram with its constricted lead field. Efforts were made to remove the atria1 activity from the region of interest by causing first degree A-V block by administration of propranolol as demonstrated in Figure 8. The bottom pair of records are 50 beat averages of the intracardiac electrogram, and an average of the same 50 beats recorded from a surface lead, identified by the probe technique. The top two records represent the same lead and surface counterpart after administration of 10 mg of propranolol, also a 50 beat average. As the A-H interval spreads, note how BI and B2 fail to move with the atrial activity, but seem to continue to be associated with the intracardiac His bundle deflection and ventricular activity. The timing of Br in the cycle with respect to its relation to ventricular activity and to the internally recorded His bundle activity suggests that the blip probably represents surface evidence of His bundle activity. B2 probably arises from lower down in the conduction system. Figure 9 demonstrates results of an effort to remove ventricular activity from the area of interest by causing conduction delay between the His bundle and the ventricle with administration of procainamide. The top sample is the intracardiac electrogram; the second is the surface counterpart after administration of 750 mg of procainamide. The third record is the intracardiac lead demonstrating H-V prolongation after administration of 1,500 mg of procainamide. Continued association with the surface deflection is seen, with the blip moving neither with atrial nor with ventricular activity but with the His deflection.
The B-R intervals are in each instance 7.5 msec shorter than the intracardiac H-V counterparts. The phenomenon can be accounted for in’ this animal solely by the earlier appearance of ventricular activity as recorded from the surface. The shght difference in appearance of the surface evidence of atria1 activi-
FWURE 7. Simultaneous recording of intracardiac (IC) and surface leads at a pacing rate of 90 beats/min (upper tracing) and 165 beats/min (tower tradng). A = internally recorded atrial activity: AH = atrlat-His interval; B = blip of interest in P-R segment: BR = blip ventricular interval; H = His bundle activity; HV = Hts-ventricular interval: P = atrial activity; PB = atriil-blip interval; R = surface-recorded ventricular activll; S = surface lead: V = internally recorded ventricular activity. See text.
March 1974
The American Journal of CARDIOLOGY
Volume 33
387
SURFACE RECORDlNG OF HIS BUNDLE ACTIVITY-FLOWERS
ET AL.
IC2 PROP
10mg
50-6OOHZ IC 1500mg
BASELINE s
ICl
100 msec
IC
. S
0.02mv
IC
2mv
PACING
S
2 mv
100
: :
FKSURE 8. intracardiac lead and surface electrogram before (hot: tOm pair) and after (top pair) administration of 10 mg of propranol01. A = internally recorded atrial activity; B, and Bz = blips of interest in surface P-R segment; H = His bundle activity; IC = intracardiac lead; ICI = base-line intracardiac lead; I& = intracardiac lead after 10 mg of propranolol; P = surface-recorded atrial activity; PROP = propranolol; R = surface ventricular activity; S, = baseYne surface lead; Sp = surface lead after 10 mg of propranolol: V = internal ventricular activity. See text.
‘_
100
0.02 mv 750H-V
. .
rote
;
47.5 B-R 40
1500 H-V 62 B-R 54.5 FIGURE 9. Intracardiac lead and surface electrogram after administration of procainamide in doses of 1,500 mg (bottom pair) and 750 mg (top palr). A = internally recorded atrial activity; B = blip; BR = blip-ventricular interval; H = His bundle activity; HV = His-ventricular; IC = intracardiac; P = surface-recorded atrial activity; R = surface-recorded ventricular activity: S = surface lead; V = internally recorded ventricular activity. See text.
25
PROCAINAMIDE 750 mg.
.. .
s
’
.F.. **
.L .
r 62.5
.
. :
L
29msec
.024 IC 2mv
s
5
I
H
t
100 msec FIGURE 10. Recording of surface lead and intracardiac electrogram from another dog after administration of procainamkie in doses of 1,500 mg (bottom recording) and 750 mg (top recordlng). B = surface blip of interest; H = His bundle activity; IC = intracardiac lead; R = surface-recorded ventricular activity;,S = surface lead; V = internally recorded ventricular activity. See text.
399
March 1974
The American Journal of CARDIOLOGY
.04mv lmv
FIGURE 11. Demonstration of the possibility of accurate surface measurements of the fractionated P-R interval. The surface recording (top) and the internal recording (bottom) are each averages of the same 50 cardiac cycles. The shorter surface His-ventricular interval is accounted for by the earlier appearance of ventricular activity viewed from the surface. Intervals are in msec. AH = atrial-His interval; H = His bundle activity; HV = His-ventricular interval; PA = high to low right atrial interval; S = surface lead; V = ventricular activity.
Volume 33
SLIRFACE RECORDING OF HIS BUNDLE ACTIVITY-FLOWERS
ty at the two dose levels can be explained by the fact that the low-frequency cutoff at the time of the 750 mg dose of procainamide was 30 Hz, whereas the lowfrequency cutoff at the time of the 1,500 mg dose was 10 Hz. The synchronizing lines were determined by computer with reference to the trigger and should represent true simultaneity. Figure 10, from another animal, again demonstrates the movement of a deflection recorded from the surface lead (S) with the His bundle deflection recorded from the intracardiac lead during progressive and comparable B-R and H-V prolongation with administration of additional amounts of procainamide.
Discussion Verification of suspected His bundle activity in amplified surface P-R segment: There are three ways of attempting to verify the origin of electrical activity recorded in the surface P-R segment. The first is simply temporal association with a carefully verified internal event. The success or believability of this means of verification depends upon an interference-free record and relative lack of activity on either side of the surface recording of alleged His bundle activity and upon an appropriate interval between this deflection and the onset of ventricular activity (Fig. 11). Because the surface evidence of ventricular activity always precedes internal evidence of such activity by 5 to 11 msec, the interval between the suspected surface His bundle activity and surface evidence of ventricular activity is necessarily shorter than that recorded from the internal lead. However,
ET AL.
if the interval is within acceptable ranges, and if the surface signal does not significantly precede the internal His bundle signal, but coincides with it or is only slightly later, there is circumstantial evidence for a common origin of these signals. More supporting evidence is presented if, in addition, atria1 pacing can cause A-V nodal transmission delay and consequent prolongation of the intracardiac A-H interval, and if the alleged His activity on the surface remains associated with the verified His activity from the internal lead. Rather convincing evidence is offered if, further, with pacing at a constant rate, and pharmacologic intervention with agents that remove atria1 activity from the region of the His bundle by introducing A-V nodal delay or remove ventricular activity from His bundle activity by introducing His-ventricular delay, the electrical events of interest in the surface lead continue to associate themselves with the His bundle deflection from the internal lead. It is important to eliminate any possibility of signal leak from amplifier to amplifier since this is a known hazard in multiple lead, simultaneous recording. This possibility was carefully eliminated in our series of experiments by physically removing the internal catheter and verifying the persistence of the surface signal. Implication: As facility is achieved in finding the optimal surface recording site, and as a volume of experience with configuration and timing of internally verified surface signals is accumulated, the examination of the amplified surface P-R segment should become an important addition to the noninvasive approaches of cardiac evaluation.
References 1. Scherlag BJ, Helfant RH, Damato AN: A catheterization technique for His bundle stimulation and recording in the intact dog. J Appl Physiol 25:425-428. 1968
2. Scherlag BJ, Lau SH. Heffant RH, et al: Catheter technique for recording His bundle activity in man. Circulation 39:13-l& 1969
March 1974
The American Journal of CARDIOLOGY
Volume 33
389
Surface Recording of Electrical Activity from the Region of the Bundle of His
NANCY
C. FLOWERS,
MD,
FACCt
R. CHRIS HAND PATRICIA CAREY MARY
C. ORANDER B. MILLER,
0.
MSEE
WALDEN
LEO G. HORAN,
MD,
FACC
Augusta, Georgia
From the Section of Cardiology, Medical Ser-
vice, FHD, Veterans Administration Hospital, and the Department of Medicine, Medical College of Georgia, Augusta, Ga. This study was supported by an award from the Veterans Ad-
ministration,and U. S. Public Health Service &ant HE-l 1667 (National Heart and Lung Institute of the National Institutes of Health, Bethesda, Md.). Manuscript accepted June 27, 1973. t Present address and address for reprints: Nancy C. Flowers, MD, Section of Cardiology, University of Louisville School of Medicine, HealthSciences Center, Louisville, Ky. 40202.
364
March 1974
In 16 dogs, by appropriate filtering and digital averaging on a PDP-9 computer, we were able to enhance the detection of electrical activity of interest in the P-R segment of the electrocardiogram. In instances (1) when such activity in the surface record coincided temporally with the internal recording from the bundle of His area, (2) when, with atrioventricular nodal block, the electrical activity of interest continued to be associated with the internally recorded His bundle deflection and not with atrlal actlvlty, and (3) when, with production of transmission delay between the bundle of His and the ventricle, the surface signal of interest continued to be associated with the internal His bundle deflection, a common signal source was considered likely. In certain instances the surface signal of interest in the P-R segment occurred well after the internally recorded His bundle deflection but about 15 msec before the earliest evidence of ventricular activity. In these instances, when the tests cited were applied and the blip of interest was associated with ventricular activity, the origin of the blip was thought to be in the region of the bundle branches. In the 16 animals studied, one or more pieces of the evidence described were present to localize the origin of the signal. In seven animals, the signal was thought to originate from the bundle of His, In six from the region of the bundle branches and in three from both the bundle of His and bundle branches.
Since Scherlag and co-workers first described the catheter technique for recording His bundle activity in the dog1 and in man,2 there has been a renaissance in extracellular approaches to electrophysiologic-electrocardiographic correlations. Interest in the subject has been intense and reporting logarithmic, especially regarding diagnostic and prognostic information now available in the fractionated P-R segment. During the course of multiple lead, high-speed, high-frequency surface recordings for other purposes, we noted apparent cardiac electrical activity in the P-R segment. The possibility that the activity might arise from the conduction system below the atria1 level but above the ventricular level, and still be accessible through noninvasive means, seemed worthy of exploration. Figure 1 is an example of the type of data that aroused our interest. The top recording-is from a surface site on the chest of a dog slightly anterior to the anterior axillary line in the fifth intercostal space. The middle record is a bipolar intracardiac electrogram recorded from a site near the bundle of His, and the bottom tracing is from the conventional VS nosition. although inverted. A 2:l block at the atrioventricular (ATv) node is- indicated by the failure of the second pacemaker impulse to be conducted below the atria1 level. The His bundle deflection from the intracardiac lead and electrical activity of interest in the P-R segment (referred to as blip1 [Bz] and blip2 [Bz]) are ab-
The American Journal of CARDIOLOGY
Volume 33
SURFACE RECCRDfNG CF HIS BUNDLE ACTtVlTY-FLOWERS
ET AL.
FIGURE1. An amplifiedsurface (S) leaded between 30 and 600 Hz (top), an intracardiac (C) lead recorded from a site near the A-V junction (m) and a surface-recorded conventional but inverted V, lead (bottom) from a dog exposed to a halogenaM hydrocarbon. A = internally recorded atrial activii; B, and 8s = blips of interest in surface P-R segment; H = His bundle activity; P = atrial activity: pi = pacer impulse; R = surface ventricular activity; T = surface-recorded ventricular recovery; V = internally recorded ventricular activity.
right atrium, and an intracardiac recording catheter capable of recording from three bipolar sites-l mm, 1 cm or 1.1 cm apart-was introduced to the region of the bundle of His by the technique described by Scherlag et all An intraarterial luminal catheter was introduced retrograde from the left femoral artery and positioned just distal to the aortic valve near the coronary ostia for delivering medications; an intravenous catheter was positioned in the inferior vena cava for similar purposes. Pacing was instituted from the bipolar pair of recording electrodes that recorded the largest biphasic His bundle deflection, and the chest was mapped in order to find the site of maximal negative and maximal positive potential from the pacemaker impulse. These points were identified on the chest and usually lay to the left and anterior for the maximal positive deflection, and to the right, slightly higher and posterior for the maximal negative deflection. It was hoped that these peak positive and negative points also approximately defined the electrical axis of the bundle of His, which should roughly parallel the axis generated by these electrodes (Fig. 3). The identification of such a site should
sent at the expected point in time, noted by the arrows. This finding suggests that the site of origin of Br and Bs is somewhere below the level of A-V block. The decreased rate of rise and overall amplitude of the His bundle signals from the internal lead can be attributed to the fact that this animal was one of a series in a study on the toxic effects of halogenated hydrocarbons known to have this effect on the His bundle deflection. The 50 beat computerized averages seen in Figure 2 exemplify an effort to amplify the P-R segment in another animal from the same series of toxicologic experiments.
Methods In 16 healthy mongrel dogs-4 anesthetized with morphine sulfate and pentobarbital and 12 with pentobarbital alone-intubation and controlled respiration and normal base-line blood gas values were established. A bipolar pacing catheter was introduced transvenously into the high
I
:. .
FIGURE 2. These 50 beat averages, taken at a sampling rate of 2,OOO/sec, are illustrative of our efforts to amplify the P-R segment in another animal from the same series of toxicologic experiments. At the top left is the surface signal; at the bottom feft, the intracardiac recording from the His bundle area. The top right shows the amplified P-R segment with the surface blip of interest labeled B. The bottom right shows the temporal association of the surface signal of interest above, and the intracardiac recording from the His bundle region below. B = surface blip of interest in P-R segment: H = internally recorded His bundle activity; IC = intracardiac lead; P = surface-recorded atrial activity; R = surface-recorded ventricular activity; S = surface lead: T = surface-recorded ventricular recovery.
:
March 1974
.
_
The American Journal of CARDIOLOGY
.2m
50-U
Volume 33
399
BUBFACE BECOBMNG
OF HIS BUNDLE ACTIVITY-FLOWERS
ET AL.
and the immediate vicinity was searched for an area that gave a repetitive surface deflection at approximately the same time as that of the His spike in the intracardiac electrogram. A similar search was performed on the negative side. The surface signal from the exploring electrode was fed into a Tektronix 26A2 differential amplifier and amplified 100,006 times, filtered between 0.1 and 3,000 Hz initially, and finally with a low-frequency cutoff between 1 and 80 Hz and a high-frequency cutoff of 600 Hz. Time synchronization was achieved by a special triggering network that also served to trigger the PDP-9 computer for averaging. After analog to digital conversion, either single cardiac cycles or 50 or fewer averaged beats were displayed on a storage oscilloscope for analysis and hard copy preparation. The constantly recorded signal on an Ampex FR 1300 tape recorder was available for later analysis, further averaging or preparation in hard copy form of sequential cycles photographed by a Grass oscilloscopic camera (Fig. 6).
Results Figure
7 shows
a recording from the intracardiac and the surface (S) recording below at a pacing rate of 90 beatslmin. The blip of interest in the P-R segment is labeled. The initially prolonged conduction time of 76.6 msec from the low atrium through the A-V node (A-H interval) is ac-
(IC) lead above,
FIGURE 3. Potential map of the chest, obtained in order to find the site of maximal negative and maximal positive deflection from a pacemaker impulse originating from the bipolar pair of recording electrodes that had recorded the largest biphasic His bundle deflection. See text.
help to optimize the chance of correspondence between the most parallel current flow lines of the His bundle and the lead field of an exploring electrode (Fig. 4). An arrangement of electrodes of the bipolar probe type was then designed with an exploring center surrounded by five indifferent points, connected by resistances to give a balanced bipolar configuration (Fig. 5). The site of the exploring electrode was placed at the point of peak positivity,
counted for by the anesthesia induced by morphine and pentobarbital. The base-line conduction time from the bundle of His to the earliest evidence of ventricular activity (H-V interval) was 31.6 msec. In the surface recording, the atria1 to blip (P-B) interval was even longer than the A-H interval since atria1 activity is detected earlier on the surface. From the surface blip of interest in the P-R segment to the earliest onset of ventricular activity (B-R), the time lapse was 20 msec. With pacing, the A-H and P-B intervals increased proportionately, whereas the H-V
FIGURE 4 Wt). Diagram of the lead field search for the surface electrode site that had optimal intersection with the most parallel flow lines from the His bundle and was feast optimal for interfering atrial activity. A = hypothetical atrial activity; E = exploring electrode; H = hypothetical lead axis of His bundle; I = indifferent electrode. FIGURE 5 (right). Bipolar probe type of arrangement connected through balanced resistances. See text.
386
March 1974
of electrodes
The American Journal of CARDIOLOGY
with a central exploring electrode surrounded
Volume 33
by five indifferent
electrodes
SURFACE RECORDlNG OF HIS SUNW
1001:
-
ACTIVITY-FLOWERS
ET AL.
wQ-WSS FIllEn
FIGURE 6. Diagram of mode of amplifying, filtering and displaying surface signal from exploring electrode. A = analog; D = digital; HB = His bundle; K = 1000; PDP-9 = computer. See
text.
and B-R intervals remained fixed. As A-V nodal delay increased with the increased pacing rate, the surface blip of interest emerged as a discrete electrical phenomenon seen in the lower panel. The origin of the surface blip is difficult to ascertain. The shorter duration of the B-R interval compared to that of the H-V interval suggests that the blip might have arisen from one of the bundle branches rather than from the bundle of His. On the other hand, much of the apparent shortening in the B-R interval is due to greater ability of the more distal surface lead to detect the earliest evidence of ventricular activity when compared with the much more local His bundle electrogram with its constricted lead field. Efforts were made to remove the atria1 activity from the region of interest by causing first degree A-V block by administration of propranolol as demonstrated in Figure 8. The bottom pair of records are 50 beat averages of the intracardiac electrogram, and an average of the same 50 beats recorded from a surface lead, identified by the probe technique. The top two records represent the same lead and surface counterpart after administration of 10 mg of propranolol, also a 50 beat average. As the A-H interval spreads, note how BI and B2 fail to move with the atrial activity, but seem to continue to be associated with the intracardiac His bundle deflection and ventricular activity. The timing of Br in the cycle with respect to its relation to ventricular activity and to the internally recorded His bundle activity suggests that the blip probably represents surface evidence of His bundle activity. B2 probably arises from lower down in the conduction system. Figure 9 demonstrates results of an effort to remove ventricular activity from the area of interest by causing conduction delay between the His bundle and the ventricle with administration of procainamide. The top sample is the intracardiac electrogram; the second is the surface counterpart after administration of 750 mg of procainamide. The third record is the intracardiac lead demonstrating H-V prolongation after administration of 1,500 mg of procainamide. Continued association with the surface deflection is seen, with the blip moving neither with atrial nor with ventricular activity but with the His deflection.
The B-R intervals are in each instance 7.5 msec shorter than the intracardiac H-V counterparts. The phenomenon can be accounted for in’ this animal solely by the earlier appearance of ventricular activity as recorded from the surface. The shght difference in appearance of the surface evidence of atria1 activi-
FWURE 7. Simultaneous recording of intracardiac (IC) and surface leads at a pacing rate of 90 beats/min (upper tracing) and 165 beats/min (tower tradng). A = internally recorded atrial activity: AH = atrlat-His interval; B = blip of interest in P-R segment: BR = blip ventricular interval; H = His bundle activity; HV = Hts-ventricular interval: P = atrial activity; PB = atriil-blip interval; R = surface-recorded ventricular activll; S = surface lead: V = internally recorded ventricular activity. See text.
March 1974
The American Journal of CARDIOLOGY
Volume 33
387
SURFACE RECORDlNG OF HIS BUNDLE ACTIVITY-FLOWERS
ET AL.
IC2 PROP
10mg
50-6OOHZ IC 1500mg
BASELINE s
ICl
100 msec
IC
. S
0.02mv
IC
2mv
PACING
S
2 mv
100
: :
FKSURE 8. intracardiac lead and surface electrogram before (hot: tOm pair) and after (top pair) administration of 10 mg of propranol01. A = internally recorded atrial activity; B, and Bz = blips of interest in surface P-R segment; H = His bundle activity; IC = intracardiac lead; ICI = base-line intracardiac lead; I& = intracardiac lead after 10 mg of propranolol; P = surface-recorded atrial activity; PROP = propranolol; R = surface ventricular activity; S, = baseYne surface lead; Sp = surface lead after 10 mg of propranolol: V = internal ventricular activity. See text.
‘_
100
0.02 mv 750H-V
. .
rote
;
47.5 B-R 40
1500 H-V 62 B-R 54.5 FIGURE 9. Intracardiac lead and surface electrogram after administration of procainamide in doses of 1,500 mg (bottom pair) and 750 mg (top palr). A = internally recorded atrial activity; B = blip; BR = blip-ventricular interval; H = His bundle activity; HV = His-ventricular; IC = intracardiac; P = surface-recorded atrial activity; R = surface-recorded ventricular activity: S = surface lead; V = internally recorded ventricular activity. See text.
25
PROCAINAMIDE 750 mg.
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100 msec FIGURE 10. Recording of surface lead and intracardiac electrogram from another dog after administration of procainamkie in doses of 1,500 mg (bottom recording) and 750 mg (top recordlng). B = surface blip of interest; H = His bundle activity; IC = intracardiac lead; R = surface-recorded ventricular activity;,S = surface lead; V = internally recorded ventricular activity. See text.
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FIGURE 11. Demonstration of the possibility of accurate surface measurements of the fractionated P-R interval. The surface recording (top) and the internal recording (bottom) are each averages of the same 50 cardiac cycles. The shorter surface His-ventricular interval is accounted for by the earlier appearance of ventricular activity viewed from the surface. Intervals are in msec. AH = atrial-His interval; H = His bundle activity; HV = His-ventricular interval; PA = high to low right atrial interval; S = surface lead; V = ventricular activity.
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SLIRFACE RECORDING OF HIS BUNDLE ACTIVITY-FLOWERS
ty at the two dose levels can be explained by the fact that the low-frequency cutoff at the time of the 750 mg dose of procainamide was 30 Hz, whereas the lowfrequency cutoff at the time of the 1,500 mg dose was 10 Hz. The synchronizing lines were determined by computer with reference to the trigger and should represent true simultaneity. Figure 10, from another animal, again demonstrates the movement of a deflection recorded from the surface lead (S) with the His bundle deflection recorded from the intracardiac lead during progressive and comparable B-R and H-V prolongation with administration of additional amounts of procainamide.
Discussion Verification of suspected His bundle activity in amplified surface P-R segment: There are three ways of attempting to verify the origin of electrical activity recorded in the surface P-R segment. The first is simply temporal association with a carefully verified internal event. The success or believability of this means of verification depends upon an interference-free record and relative lack of activity on either side of the surface recording of alleged His bundle activity and upon an appropriate interval between this deflection and the onset of ventricular activity (Fig. 11). Because the surface evidence of ventricular activity always precedes internal evidence of such activity by 5 to 11 msec, the interval between the suspected surface His bundle activity and surface evidence of ventricular activity is necessarily shorter than that recorded from the internal lead. However,
ET AL.
if the interval is within acceptable ranges, and if the surface signal does not significantly precede the internal His bundle signal, but coincides with it or is only slightly later, there is circumstantial evidence for a common origin of these signals. More supporting evidence is presented if, in addition, atria1 pacing can cause A-V nodal transmission delay and consequent prolongation of the intracardiac A-H interval, and if the alleged His activity on the surface remains associated with the verified His activity from the internal lead. Rather convincing evidence is offered if, further, with pacing at a constant rate, and pharmacologic intervention with agents that remove atria1 activity from the region of the His bundle by introducing A-V nodal delay or remove ventricular activity from His bundle activity by introducing His-ventricular delay, the electrical events of interest in the surface lead continue to associate themselves with the His bundle deflection from the internal lead. It is important to eliminate any possibility of signal leak from amplifier to amplifier since this is a known hazard in multiple lead, simultaneous recording. This possibility was carefully eliminated in our series of experiments by physically removing the internal catheter and verifying the persistence of the surface signal. Implication: As facility is achieved in finding the optimal surface recording site, and as a volume of experience with configuration and timing of internally verified surface signals is accumulated, the examination of the amplified surface P-R segment should become an important addition to the noninvasive approaches of cardiac evaluation.
References 1. Scherlag BJ, Helfant RH, Damato AN: A catheterization technique for His bundle stimulation and recording in the intact dog. J Appl Physiol 25:425-428. 1968
2. Scherlag BJ, Lau SH. Heffant RH, et al: Catheter technique for recording His bundle activity in man. Circulation 39:13-l& 1969
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