© 2000 American Heart Association, Inc.
Integrative Physiology |
High-Resolution Optical Mapping of the Right Bundle Branch in Connexin40 Knockout Mice Reveals Slow Conduction in the Specialized Conduction System
From the Department of Pharmacology (H.S.T., D.V., J.J., G.E.M.), SUNY Upstate Medical University, Syracuse, NY; the Department of Physiology (A.M.S.), University of Arizona, Tucson, Ariz; and the Department of Neurobiology (D.L.P.), Harvard Medical School, Boston, Mass.
Correspondence to Gregory E. Morley, PhD, Department of Pharmacology, SUNY Upstate Medical University, 766 Irving Ave, Syracuse, NY 13210. E-mail morleyg{at}mail.upstate.edu
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Abstract |
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Abstract—Connexin40 (Cx40) is a major gap junction protein that is expressed in the His-Purkinje system and thought to be a critical determinant of cell-to-cell communication and conduction of electrical impulses. Video maps of the ventricular epicardium and the proximal segment of the right bundle branch (RBB) were obtained using a high-speed CCD camera while simultaneously recording volume-conducted ECGs. In Cx40–/– mice, the PR interval was prolonged (47.4±1.4 in wild-type [WT] [n=6] and 57.5±2.8 in Cx40–/– [n=6]; P<0.01). WT ventricular epicardial activation was characterized by focused breakthroughs that originated first on the right ventricle (RV) and then the left ventricle (LV). In Cx40–/– hearts, the RV breakthrough occurred after the LV breakthrough. Additionally, Cx40–/– mice showed RV breakthrough times that were significantly delayed with respect to QRS complex onset (3.7±0.7 ms in WT [n=6] and 6.5±0.7 ms in Cx40–/– [n=6]; P<0.01), whereas LV breakthrough times did not change. Conduction velocity measurements from optical mapping of the RBB revealed slow conduction in Cx40–/– mice (74.5±3 cm/s in WT [n=7] and 43.7±6 cm/s in Cx40–/– [n=7]; P<0.01). In addition, simultaneous ECG records demonstrated significant delays in Cx40–/– RBB activation time with respect to P time (P-RBB time; 41.6±1.9 ms in WT [n=7] and 55.1±1.3 ms in [n=7]; P<0.01). These data represent the first direct demonstration of conduction defects in the specialized conduction system of Cx40–/– mice and provide new insight into the role of gap junctions in cardiac impulse propagation.
Key Words: optical mapping • specialized conduction system • knockout mice • connexin40
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Introduction |
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Intercellular coupling via gap junction channels is an important determinant of impulse propagation in the heart.1 These channels provide a low resistance pathway that is essential for the coordinated spread of electrical activation, which subsequently triggers the contraction of the heart. Recent studies have indicated that alterations in the expression pattern of cardiac connexin proteins may lead to abnormal electrical coupling and arrhythmias.2 3 4 5 6 Therefore, understanding the role of intercellular communication in impulse propagation is essential.
Three connexins, Cx40, Cx43, and Cx45, are thought to be involved in impulse propagation in the myocardium. Detailed immunolocalization studies have shown that each of these proteins has a unique pattern of expression in the adult heart;6 7 8 however, the functional role of connexin proteins in impulse propagation remains poorly understood. The presence and expression levels of these connexins vary considerably in cardiac tissues with different conduction properties.6 8 9 Cx45 is expressed in the atrioventricular node and proximal portion of the ventricular conduction system.7 Cx43 is expressed in both the atrial and ventricular myocardium.7 10 11 Immunohistochemistry studies in the mouse heart have indicated that Cx40 is expressed mainly in the atrial myocardium and His-Purkinje system.7 12 13 Previous studies have shown that deletion of Cx40 did not affect the expression of the other cardiac connexins or the gross structure of the heart.4 5 On the basis of these studies, it is expected that the targeted deletion of Cx40 will result in conduction deficits in both the atria and specialized conduction system.
The gross structure of the adult mouse specialized conduction system has not been studied in any great detail.14 15 Some histological studies have demonstrated broad similarities between the structure of the specialized conduction system of the mouse and that of larger mammals.14 16 In the mouse, the atrioventricular (AV) bundle has been shown to give rise to a compact right bundle branch (RBB), whereas many left bundle branch (LBB) fibers originate progressively over a wide range. Studies of the canine intraventricular conduction system have shown that the fibers of the RBB and LBB insert into the interventricular septum and the ventricular free walls.16 17 Septal LBB fibers have previously been shown to initiate the first ventricular depolarization (Q wave) in humans and larger mammals, whereas septal RBB insertions contribute to later phases of ventricular activation.16 18 19
The objective of this study was to characterize the electrophysiological consequences of the null mutation of Cx40 (Cx40–/–) on patterns of ventricular activation as well as conduction in the RBB. To achieve these objectives, we have developed an imaging system that is capable of obtaining high-resolution optical maps of electrical excitation in the ventricles and from the proximal segment of the RBB. Our results indicate that deletion of Cx40 does not result in impaired conduction velocity (CV) within the ventricular myocardium. However, in all Cx40–/– mice, epicardial breakthrough activation patterns during sinus rhythm and atrial pacing suggested slowed conduction in the RBB, which was confirmed by direct measurements of CV in the RBB. These data provide a detailed mechanism for the alterations recorded in surface ECGs from Cx40 deficient mice3 4 5 20 and provide important insight into basic mechanisms underlying impulse propagation in the heart.
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Materials and Methods |
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All mapping studies were performed using Langendorff perfused mouse hearts in the absence of any motion reduction techniques on an upright microscope equipped with a cooled CCD camera (Dalsa Inc, CA-D1 128T). The right atrial appendage was paced to study activation patterns in intact left ventricle (LV) and right ventricle (RV) and on the exposed RBB. To confirm the location of the RBB, high-resolution images of acetylcholinesterase (AChE) staining were correlated with the optical mapping results. Ventricular conduction velocities (CVmax and CVmin) were studied by pacing the RV free wall. Ventricular conduction velocities were measured as described previously.21 22 CV in the RBB was determined by linear regression of activation time as a function of distance using the method of least squares.
Stimulus time (S) was defined as the beginning of the
rectangular stimulus artifact obtained from volume-conducted ECGs, and
ventricular activation (Q time) was defined as the first measurable
deflection (above noise) of the QRS complex. LV and RV activation times
were defined as the earliest optical breakthroughs identified on the LV
and RV, respectively. RBB activation was defined as the time at which
the first pixel on the RBB activated in the field of view (see Figure 5
).
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An expanded Materials and Methods section can be found in an online data supplement available at http://www.circresaha.org.
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Results |
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Conscious 6-Lead and Langendorff ECG
Figure 1
shows examples of 6-lead ECG recordings obtained
from a conscious wild-type (WT) and a
Cx40–/– mouse. Although the heart rates of
the 2 animals were similar (WT, 730 bpm;
Cx40–/–, 725 bpm), the PR interval was
clearly prolonged in the Cx40–/– mouse. In
addition, as seen in this example, the QRS complexes recorded from
Cx40–/– mice were more notched than the WT
mice, suggesting an altered ventricular activation sequence. The
Table
summarizes the ECG data obtained from 8 WT and 8
Cx40–/– mice. On average, the PR interval
was significantly prolonged from 35.1±1.5 ms in WT mice to 40.9±1.2
ms in Cx40–/– mice
(P<0.01). Significant differences were also found in
the QRS duration (14.5±0.8 and 16.8±0.7 ms WT and
Cx40–/– mice, respectively;
P<0.04). Moreover, sinus rhythm PR and RR intervals
measured from Langendorff-perfused hearts were similar to the
measurements in conscious mice (RR interval: 178.7±6.3 in WT [n=13]
and 183±8.4 in Cx40–/– [n=13], NS; PR
interval: 34.7±0.9 in WT [n=13] and 44.5±1.4 in
Cx40–/– [n=13];
P<0.001). These data confirm the slower AV conduction
that was reported from anesthetized
Cx40–/–
animals.3 4 5
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Optical Mapping of Purkinje-Activated
Ventricular Myocardium
To determine the mechanisms underlying the surface ECG
alterations, ventricular epicardial activation patterns were recorded
from the anterior surface of both WT and
Cx40–/– mice.
Figure 2 shows color activation maps obtained during sinus
rhythm and right atrial pacing at a cycle of 120 ms. In the left
column, the WT activation pattern is characterized by 2 focused
breakthroughs that originate on the free walls of the right and left
ventricles. The breakthroughs form wavefronts that fully activate the
field of view within 3 ms. In all WT mice during sinus rhythm, the RV
breakthrough either preceded or occurred simultaneously with the LV
breakthrough. These breakthrough sites represent 3D-wave propagation
from Purkinje-muscle junctions (PMJ) originating from the RBB and
LBB.23 Similar
activation patterns were observed in all WT hearts.
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In the right column, the activation patterns recorded from a Cx40–/– mouse appear grossly different. Firstly, the focused LV breakthrough site seen in WT mice was replaced by a more diffuse and patchy activation pattern. In the example shown, the arrows indicate the direction of propagation from multiple breakthrough sites covering a large region of the LV. Secondly, the location of the first breakthrough site on both the LV and RV in Cx40–/– mice was more variable than in WT mice. In this example, the first RV breakthrough in the Cx40–/– heart occurred in the center of the RV free wall, whereas in other cases, the location of the first RV breakthrough site occurred elsewhere on the RV. Finally, in all Cx40–/– mice the breakthrough activation sequence was reversed (ie, the RV breakthrough occurred after the first LV breakthrough). Note that in the example shown, the RV breakthrough during atrial pacing is delayed and is less apparent than during sinus rhythm.
Synchronized Ventricular ECG Recordings
To gain insight into the differences between RV and LV
breakthrough activation patterns, RV and LV activation times were
correlated with the Q time obtained from simultaneous volume-conducted
ECG records.
Figure 3 shows the relation between the Q time and the
optically recorded RV and LV times while pacing the right atria at a
basic cycle length (BCL) of 120 ms.
Figures 3A and 3B show examples of these times and their
relationship for a WT and Cx40–/– mouse,
respectively. Clearly, in the Cx40–/–
mouse, the RV activation time is delayed much more than the LV
activation time relative to onset of the QRS complex.
Figure 3C summarizes all right atrial stimulus (S) to Q time
measurements obtained at the fastest BCL resulting in 1:1 AV capture
(54.6±1.2 in WT [n=6] and 61.5±3.2 in
Cx40–/– [n=6]) and at BCL=120 ms
(47.4±1.4 in WT [n=6] and 57.5±2.8 in
Cx40–/– [n=6]; P<0.01
between genotypes; P<0.02 between cycle lengths). The
increase in the S-Q interval is consistent with the ECG data obtained
in conscious mice (see
Table
).
Figure 3D shows a bar graph summarizing our measurements of
Q to LV time (4.6±0.4 in WT [n=6] and 5.2±0.5 in
Cx40–/– [n=6]; NS) and Q to RV time
(BCL=120: 3.7±0.7 in WT [n=5] and 6.5±0.7 in
Cx40–/– [n=6]; P<0.01)
at a constant BCL of 120 ms. These data indicate that the RV but not LV
time is significantly delayed with respect to the Q time in the
Cx40–/– mice.
Figure 3E illustrates the interval changes between the 2
genotypes. Clearly, in Cx40–/– mice, only
the delayed LV breakthrough is fully accounted for by the late arrival
of the Q wave.
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), RV activation (
), LV
activation (•), and Q (*)
times for both WT (top) and Cx40–/–
(bottom). Whereas the S-Q interval increase accounts for the delayed
arrival of the LV breakthrough (c=a), it does not fully account for the
later arrival of the RV breakthrough (b>a).
P<0.02,
P<0.01.
Ventricular Conduction Measurements
The delayed arrival of the RV breakthrough is likely
attributable to slowed conduction in the RBB; however, to exclude the
possible contribution of conduction defects within the ventricular
myocardium, epicardial conduction patterns and velocities were
determined.
Figure 4 shows activation maps obtained from the RV of a WT
(panel A) and a Cx40–/– (panel B) mouse
while pacing the ventricles directly at a BCL of 120 ms. Pixels were
systematically excluded near the pacing electrode (<1 mm) to remove
any stimulus artifacts and at a distance (>3 mm) to exclude potential
wavefront collisions and 3D-wave
propagation.22
Clearly, the anisotropic conduction pattern in the
Cx40–/– was similar to that of WT.
Figure 4C shows mean CVmax and
CVmin for all WT and
Cx40–/– mice tested. No statistical
differences were found between the 2 genotypes. Similar results were
obtained at a BCL of 90 ms (data not shown). These data indicate that
Cx40 does not significantly contribute to impulse propagation within
the ventricular myocardium, which is in agreement with
multielectrode20 and
immunolocalization studies for
Cx40.7
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RBB Optical Mapping
To determine the contribution of Cx40 in impulse
propagation in the specialized conduction system, high-resolution
optical maps of the proximal segment of the RBB were obtained.
Figure 5A is an image of the right septal wall where the RBB
has been stained with acetylthiocholine iodide, which precipitates in
the presence of AChE activity.
Figure 5B shows a color activation map of the RBB
superimposed on the stained septal preparation. Optical signals
recorded from the right septum are shown in the 2 insets.
Voltage-dependent fluorescence recorded from pixels on the RBB is
expected to originate from both the specialized conduction system and
the underlying ventricular myocardium, giving rise to 2 temporally
distinct action potential upstrokes. Therefore, during antegrade
propagation, the first upstroke should result from a wave of activation
through the RBB, whereas the second should result from the subsequent
activation of the ventricular myocardium. Pixels not on the RBB are
expected to show a single upstroke representing endocardial activation.
The time sequence plots shown in the insets to the right and below
panel B were obtained from pixels falling on the RBB and away from the
RBB, respectively. Clearly, 2 action potential upstrokes are seen in
all of the traces in the right inset, whereas only 1 action potential
upstroke is seen in the bottom inset. In addition, these pixels showed
activation that propagated from base to apex, consistent with antegrade
propagation through the RBB.
Figure 5C shows the pixels that were identified using a
signal-to-noise ratio (SNR) criterion (>4) and the activation
times from these pixels were used to measure RBB conduction velocity.
Gaps in the activation sequence were attributable to uneven staining of
the endocardium. The trace in
Figure 5D shows a volume-conducted ECG obtained during the
optical recording. The color bar above the trace demarcates the
beginning and end of RBB activation. Thus, the RBB optical upstrokes
preceded the QRS complex by 
3 ms and propagated distally toward the
apex, which is again characteristic of RBB activation. These data
represent the first optical recordings obtained from the specialized
conduction system in the right ventricle.
Figure 6 shows a comparison between the activation patterns
recorded from the RBB of a WT (panel A) and a
Cx40–/– (panel B) mouse. These maps depict
the similarities and differences of the RBB activation in the 2 mice.
In both maps, activation begins near the RV base, distal to the septal
leaflet of the tricuspid valve, crosses the septum along the main
septal artery, and extends across the base of the anterior papillary
muscle. In the Cx40–/– example shown, a
smaller segment of the RBB was analyzed because of the early arrival of
the underlying septal activation. Fusion of the RBB and ventricular
action potential upstrokes occurred at distal sites on the bundle,
obscuring RBB upstrokes. This merging of the upstrokes may be
attributable to either delayed RBB activation, resulting from slow
conduction in the RBB, or earlier septal activation. These
possibilities are studied below.
Figure 6C displays the RBB conduction velocity in these 2
hearts. A >50% slowing of CV is apparent in the
Cx40–/– heart. Summary of the RBB
conduction velocity measurements is shown in
Figure 6D. Clearly, the plots show a significant slowing of
CV in the RBB of Cx40–/– mice. No cycle
length dependence could be demonstrated at the cycle lengths tested.
These data indicate that the slower CV contributed to the merging of
RBB and ventricular action potentials upstrokes.
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RBB-Synchronized ECG Recordings
To quantify the extent of RBB delay in relation to
ventricular activation, RBB activation times were compared with Q time.
Figures 7A and 7B illustrate synchronized volume-conducted
ECG recordings from WT and Cx40–/– mice.
Variable QRS morphologies were seen in the dissected RV preparations
from both WT and Cx40–/–.
Figure 7C summarizes S to RBB time and indicates a
prolongation in Cx40–/– mice compared with
WT mice (BCL=120 ms: 41.6±1.9 ms in WT [n=7] and 55.1±1.3 ms in
Cx40–/– [n=7]; BCL=160 ms: 38.7±1.5 ms
in WT [n=7] and 50.6±1.5 ms in Cx40–/–
[n=7]; P<0.001 between genotypes;
P<0.03 between cycle lengths). RBB to Q time measured
in WT (BCL=120 ms: 4.30±0.8 ms; [n=7]) and
Cx40–/– (BCL=120 ms: 1.2±0.5 ms; [n
=7]) mice is shown in
Figures 7D. Cx40–/– mice have a
significantly shorter RBB to Q time (P<0.001). It is
important to note that although the mean RBB to Q time was positive for
Cx40–/– mice, 1 mouse showed RBB
activation that occurred after the onset of the QRS complex.
Figure 7E summarizes the interval changes seen between
genotypes. Clearly, the delayed RBB activation that occurs in
Cx40–/– mice is not fully accounted for by
the late arrival of the Q wave (ie, the S-RBB increase is greater than
the RBB-Q increase). Thus, the additional delay accounting for this
difference must exist proximal to the optically mapped region of the
RBB.
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) times are
shown. Note that the RBB activation time is delayed relative to Q time.
C, Significant S-RBB interval increase in
Cx40–/– compared with WT while pacing at
BCL of 120 ms. D, RBB-Q interval is significantly less than in the
Cx40–/– mice (n=7) compared with WT mice
(n=7). No cycle-dependent differences were detected in RBB-Q intervals
between BCLs of 120 and 160 ms (data not shown). E, Schematic of AV
conduction marking the stimulus (
His-Bundle Branching and LBB Conduction
Time
To better understand the relation of the LBB conduction
time and the Q time, calculations were made using RBB activation maps
to estimate the activation time where branching of the common His
bundle occurs (B time; see online Figure 2; available in an online data
supplement at http://www.circresaha.org). Assuming that the branch
point is 1.5 mm proximal to the optically mapped region of the RBB
(see Lev et al14 for
histological description of branch point), the B time can be
extrapolated from the RBB conduction velocity measurements and the B to
Q time can be determined. Thus, the B to Q time delay provides an
estimate of conduction time in the LBB fibers that give rise to the
start of the QRS complex. From these estimates, B to Q time was not
significantly different between the
Cx40–/– and WT mice (BCL=120 ms: 6.4±0.8
in WT [n=7] and 5±0.5 in Cx40–/–
[n=7]; BCL=160 ms: 6.9±0.7 in WT [n=7] and 5.5±0.7 in
Cx40–/– [n=7]; NS). Therefore, no
detectable conduction defect was found in the LBB using this model.
This finding is in agreement with LV free-wall activation times, which
also indicate nondetectable LBB conduction delays in
Cx40–/–
mice.
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Discussion |
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Impulse propagation in cardiac tissue is the result of many parameters functioning in concert, such as cell excitability,24 intercellular coupling,25 26 27 28 and tissue geometry.29 30 Perturbation of any of these parameters during cardiac disease is associated with slowing of conduction and increased risk of cardiac arrhythmias. Previous reports characterizing the role of intercellular coupling have relied on pharmacological interventions to modulate gap junctional conductance25 26 31 ; hence, those studies have the limitation of nonspecific pharmacological effects. On the other hand, the development of genetic engineering technology has provided a new approach to investigate the role of specific proteins in cardiac disease in the absence of pharmacological interventions.32 33 34 In particular, targeted deletion of connexin proteins offers the potential to investigate the specific roles of these proteins in impulse propagation in the mammalian heart.4 5 35 Because the deletion of Cx40 is not associated with gross cardiac malformations within the myocardium or the His-bundle branches,5 the Cx40–/– mouse provides an elegant model to study the effects of cellular uncoupling on impulse propagation.
ECG Intervals
The ECG data obtained from conscious
Cx40–/– mice confirm the PR and QRS
prolongation that has been previously reported in anesthetized
mice.4 5 In
this study, we focused on the role of Cx40 in the specialized
conduction system and ventricular myocardium. However, Cx40 is also
expressed in the atria. Other studies have reported in some
Cx40–/– mice slower atrial conduction
velocities, prolonged P-wave durations, longer sinus node recovery
times, and atrial
arrhythmias.3 4
Together, these studies provide supporting evidence that Cx40 is an
important determinant of impulse propagation in the atria as well as
the specialized conduction system.
Ventricular Activation in the Absence of
Cx40
The null mutation of Cx40 resulted in obvious
differences in both RV and LV activation patterns and times. Unlike WT
mice, the LV of Cx40–/– mice showed
multiple breakthrough sites on the anterior surface. In addition, the
first breakthrough on the RV varied more in location than that of the
LV and showed significant delays with respect to the first LV
breakthrough. Because of the broader distribution of left compared with
RBB fibers in
mice,14 conduction
failures resulting from cellular uncoupling in the absence of Cx40 is
expected to manifest as islands of epicardial activations surrounded by
areas of quiescence. This patchy failure of conduction may occur at
branching Purkinje fiber sites or at PMJs, where source-sink mismatches
exist because of a change in the geometry in the propagating
pathway.29
Effects on the safety factor for propagation attributable to a reduction in intercellular coupling and abrupt changes in tissue geometry have been studied in patterned cell cultures.27 29 36 In the whole heart, the best-known example of current-to-load mismatch is that of the PMJ.37 38 At PMJs, depolarizing current (source) originating from a small Purkinje fiber has to provide enough excitatory current for a large ventricular mass of tissue (sink). Studies conducted on this subject have shown that successful propagation is indeed challenged by this transition.36 38
Indeed, in larger mammals, which show a larger spatial distribution of LBB fiber insertions, a patchy and diffuse epicardial activation pattern is seen in the LV but not the RV.17 39 In our experiments, large delays in the RV breakthrough times resulted in significant changes in the sequence of RV epicardial activation attributable to a sweeping wave of activation from the LV. Hence, we cannot exclude the possibility that patchy patterns of conduction block also exist in the RV of the mouse heart. On the other hand, from our data, these isolated, local propagation failures do not provide a satisfactory mechanism for the overall delayed activation of the RV in Cx40–/– mice.
Conduction Slowing in the RBB of
Cx40–/– Mice
Using newly developed high-resolution imaging
techniques, RBB activation was quantitatively measured to determine the
source of RV activation delays. Qualitatively, the activation pattern
of the RBB in the Cx40–/– mice was similar
to that seen in the WT. In both cases, activation began near the septal
leaflet of the tricuspid valve and continued distally to the base of
the anterior papillary muscle. However, quantitative measurements of
RBB conduction velocities showed a significant slowing in
Cx40–/– mice. Therefore, the lack of Cx40
in the RBB resulted in significant conduction slowing, which
additionally resulted in delayed RV free-wall activation.
During optical mapping, it was noticed that RV septal activation occurred before the complete activation of the RBB in the Cx40–/– mice. Moreover, simultaneous ECGs indicated that the RBB in the Cx40–/– mice activated later with respect to the start of the QRS complex. Because the LBB is presumed to activate the septum and cause the first deflection of the QRS complex, both the Q-time and RV septal activation represent surrogate markers of LBB activation.16 18 Thus, both the optical and ECG measurements suggest that the RBB is more affected than the LBB via these surrogate markers. With improved technology and strides in optical mapping techniques, future left septal mapping studies in Cx40–/– mice may directly demonstrate the role of Cx40 in the LBB.
Role of Connexin45
The presence of Cx45 in the His-Purkinje system cannot
be forgotten.7 In
Cx40–/– mice, the existence of successful
conduction through the RBB and LBB provides reason to implicate Cx45 as
the remaining intercellular coupler in these tissues. Moreover, the
lack of a detectable delay in the LV conduction system in
Cx40–/– mice leads to speculation that
Cx45 is maintaining near normal conduction through this safer pathway.
It is also important to note that because the RBB is anatomically
thinner and action potential durations are longer than those in the
LBB,16 40 41
it is expected that a lower safety factor for antegrade conduction
exists through the right
pathway.36 42
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Acknowledgments |
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This work was supported by Program Project Grant PO1 HL 39707 from the National Heart, Lung and Blood Institute. We would like to thank Dr Mario Delmar for his contribution during the initial phase of this study. We would also like to thank Matthew Brunson and Robert Morton for providing excellent technical support.
Received August 29, 2000; revision received September 19, 2000; accepted September 19, 2000.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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1. Kleber AG, Fast VG, Rohr S. Continuous and discontinuous propagation. In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology: From Cell to Bedside. Philadelphia, Pa: WB Saunders Co; 2000:205–213.
2. van der Velden HM, van Kempen MJ, Wijffels MC, van Zijverden M, Groenewegen WA, Allessie MA, Jongsma HJ. Altered pattern of connexin40 distribution in persistent atrial fibrillation in the goat. J Cardiovasc Electrophysiol. 1998;9:596–607.[Medline] [Order article via Infotrieve]
3.
Hagendorff
A, Schumacher B, Kirchhoff S, Luderitz B, Willecke K. Conduction
disturbances and increased atrial vulnerability in connexin40-deficient
mice analyzed by transesophageal stimulation.
Circulation. 1999;99:1508–1515.
4. Kirchhoff S, Nelles E, Hagendorff A, Kruger O, Traub O, Willecke K. Reduced cardiac conduction velocity and predisposition to arrhythmias in connexin40-deficient mice. Curr Biol. 1998;8:299–302.[Medline] [Order article via Infotrieve]
5. Simon AM, Goodenough DA, Paul DL. Mice lacking connexin40 have cardiac conduction abnormalities characteristic of atrioventricular block and bundle branch block. Curr Biol. 1998;8:295–298.[Medline] [Order article via Infotrieve]
6.
Bastide
B, Neyses L, Ganten D, Paul M, Willecke K, Traub O. Gap junction
protein connexin40 is preferentially expressed in vascular endothelium
and conductive bundles of rat myocardium and is increased under
hypertensive conditions. Circ Res. 1993;73:1138–1149.
7.
Coppen
SR, Severs NJ, Gourdie RG. Connexin45 (
6)
expression delineates an extended conduction system in the embryonic
and mature rodent heart. Dev Genet. 1999;24:82–90.[Medline]
[Order article via Infotrieve]
8. Davis LM, Rodefeld ME, Green K, Beyer EC, Saffitz JE. Gap junction protein phenotypes of the human heart and conduction system. J Cardiovasc Electrophysiol. 1995;6:813–822.[Medline] [Order article via Infotrieve]
9.
de Wit
C, Roos F. Impaired conduction of vasodilation along arterioles in
connexin40-deficient mice. Circ Res. 2000;86:649–655.
10.
Delorme
B, Dahl E, Jarry-Guichard T, Briand JP, Willecke K, Gros D,
Theveniau-Ruissy M. Expression pattern of connexin gene products at the
early developmental stages of the mouse cardiovascular system.
Circ Res. 1997;81:423–437.
11.
van
Kempen MJ, Fromaget C, Gros D, Moorman AF, Lamers WH. Spatial
distribution of connexin43, the major cardiac gap junction protein, in
the developing and adult rat heart. Circ Res. 1991;68:1638–1651.
12. Gros DB, Jongsma HJ. Connexins in mammalian heart function. Bioessays. 1996;18:719–730.[Medline] [Order article via Infotrieve]
13. Gourdie RG, Severs NJ, Green CR, Rothery S, Germroth P, Thompson RP. The spatial distribution and relative abundance of gap-junctional connexin40 and connexin43 correlate to functional properties of components of the cardiac atrioventricular conduction system. J Cell Sci. 1993;105:985–991.[Abstract]
14. Lev M, Thaemert JC. The conduction system of the mouse heart. Acta Anat (Basel). 1973;85:342–352.[Medline] [Order article via Infotrieve]
15.
Moorman
AF, de Jong F, Denyn MM, Lamers WH. Development of the cardiac
conduction system. Circ Res. 1998;82:629–644.
16.
Myerburg
RJ, Nilsson K, Gelband H. Physiology of canine intraventricular
conduction and endocardial excitation. Circ Res. 1972;30:217–243.
17.
Myerburg
RJ, Stewart JW, Hoffman BF. Electrophysiological properties of the
canine peripheral A-V conducting system. Circ Res. 1970;26:361–378.
18. Dunn MI, Lipman BS. Lipmann-Massie Clinical Electrophysiology. Chicago, Ill: Year Book; 1989.
19.
Durrer
D. Total excitation of the isolated human heart.
Circulation. 1970;41:899–912.
20. Verheule S, van Batenburg CC, Coenjaerts FJ, Kirchhoff S, Willecke K, Jongsma HJ. Cardiac conduction abnormalities in mice lacking the gap junction protein connexin40. J Cardiovasc Electrophysiol. 1999;10:1380–1389.[Medline] [Order article via Infotrieve]
21. Bayly PV, KenKnight BH, Rogers JM, Hillsley RE, Ideker RE, Smith WM. Estimation of conduction velocity vector fields from epicardial mapping data. IEEE Trans Biomed Eng. 1998;45:563–571.[Medline] [Order article via Infotrieve]
22. Morley GE, Vaidya D, Samie FH, Lo CW, Delmar M, Jalife J. Characterization of conduction in the ventricles of normal and heterozygous connexin43 knockout mice using optical mapping. J Cardiovasc Electrophysiol. 1999;10:1361–1375.[Medline] [Order article via Infotrieve]
23.
Berenfeld
O, Jalife J. Purkinje-muscle reentry as a mechanism of polymorphic
ventricular arrhythmias in a 3-dimensional model of the ventricles.
Circ Res. 1998;82:1063–1077.
24. Cranefield PF. The Conduction of the Cardiac Impulse. New York, NY: Futura; 1975.
25.
Jalife
J, Sicouri S, Delmar M, Michaels DC. Electrical uncoupling and impulse
propagation in isolated sheep Purkinje fibers. Am J
Physiol. 1989;257:H179–H189.
26.
Rohr
S, Kucera JP, Kleber AG. Slow conduction in cardiac tissue, I: effects
of a reduction of excitability versus a reduction of electrical
coupling on microconduction. Circ Res. 1998;83:781–794.
27.
Kucera
JP, Kleber AG, Rohr S. Slow conduction in cardiac tissue, II: effects
of branching tissue geometry. Circ Res. 1998;83:795–805.
28. Cole WC, Picone JB, Sperelakis N. Gap junction uncoupling and discontinuous propagation in the heart: a comparison of experimental data with computer simulations. Biophys J. 1988;53:809–818.[Medline] [Order article via Infotrieve]
29.
Rohr
S, Kucera JP, Fast VG, Kleber AG. Paradoxical improvement of impulse
conduction in cardiac tissue by partial cellular uncoupling.
Science. 1997;275:841–844.
30. Berenfeld O, Pertsov AM. Dynamics of intramural scroll waves in three-dimensional continuous myocardium with rotational anisotropy. J Theor Biol. 1999;199:383–394.[Medline] [Order article via Infotrieve]
31.
Valiunas
V, Bukauskas FF, Weingart R. Conductances and selective permeability of
connexin43 gap junction channels examined in neonatal rat heart cells.
Circ Res. 1997;80:708–719.
32.
Lee P,
Morley G, Huang Q, Fischer A, Seiler S, Horner JW, Factor S, Vaidya D,
Jalife J, Fishman GI. Conditional lineage ablation to model human
diseases. Proc Natl Acad Sci
U S A. 1998;95:11371–11376.
33.
James
JF, Hewett TE, Robbins J. Cardiac physiology in transgenic mice.
Circ Res. 1998;82:407–415.
34. Jalife J, Morley GE, Vaidya D. Connexins and impulse propagation in the mouse heart. J Cardiovasc Electrophysiol. 1999;10:1649–1663.[Medline] [Order article via Infotrieve]
35.
Reaume
AG, de Sousa PA, Kulkarni S, Langille BL, Zhu D, Davies TC, Juneja SC,
Kidder GM, Rossant J. Cardiac malformation in neonatal mice
lacking connexin43. Science. 1995;267:1831–1834.
36. Fast VG, Kleber AG. Block of impulse propagation at an abrupt tissue expansion: evaluation of the critical strand diameter in 2- and 3-dimensional computer models. Cardiovasc Res. 1995;30:449–459.[Medline] [Order article via Infotrieve]
37.
Mendez
C, Mueller WJ, Urguiaga X. Propagation of impulses across the Purkinje
fiber-muscle junctions in the dog heart. Circ Res. 1970;26:135–150.
38.
Sasyniuk
BI, Mendez C. A mechanism for reentry in canine ventricular tissue.
Circ Res. 1971;28:3–15.
39. Kawasuji M, Iwa T. Spread of the epicardial excitation in right bundle branch block pattern. Jpn Circ J. 1978;42:1041–1056.[Medline] [Order article via Infotrieve]
40.
Myerburg
RJ. The gating mechanism in the distal atrioventricular conducting
system. Circulation. 1971;43:955–960.
41.
Myerburg
RJ, Gelband H, Hoffman BF. Functional characteristics of the gating
mechanism in the canine A-V conducting system. Circ
Res. 1971;28:136–147.
42. Fast VG, Kleber AG. Cardiac tissue geometry as a determinant of unidirectional conduction block: assessment of microscopic excitation spread by optical mapping in patterned cell cultures and in a computer model. Cardiovasc Res. 1995;29:697–707.[Medline] [Order article via Infotrieve]
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|
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|
|
|
|
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