SURGICAL ANATOMY OF CONDUCTION SYSTEM IN NORMAL AND CHD AND APPLIED IMPORTANCE WITH RELATION TO VARIOUS CARDIAC SURGERIES

1. Presented by- dr.Kiran.G
Moderater – dr.RV Kumar

3. 1. The sinoatrial (SA) node is a spindle-shaped structure composed
of a fibrous tissue matrix with closely packed cells. It is 10-20 mm
long, 2-3 mm wide, and thick, tending to narrow caudally toward
the inferior vena cava (IVC). The SA node is located less than 1
mm from the epicardial surface, laterally in the right atrial sulcus
terminalis at the junction of the anteromedial aspect of the
superior vena cava (SVC) and the right atrium (RA).
2. The artery supplying the sinus node branches from the right
coronary artery in 55-60% of hearts or the left circumflex artery in
40-45% of hearts. The artery approaches the node from a
clockwise or counterclockwise direction around the SVC–RA
junction.[3]
3. The SA node is densely innervated with postganglionic
adrenergic and cholinergic nerve terminals. Neurotransmitters
modulate the SA node discharge rate by stimulation of beta-
adrenergic and muscarinic receptors. Both beta1 and beta2
adrenoceptors subtypes are present in the SA node. The human
SA node contains a more than 3-fold greater density of beta-
adrenergic and muscarinic cholinergic receptors than the adjacent
atrial tissue.[4]

4.  Anatomic evidence suggests the presence of 3
intra-atrial pathways: (1) anterior internodal
pathway, (2) middle internodal tract, and (3)
posterior internodal tract.
 The anterior internodal pathway begins at the
anterior margin of the SA node and curves
anteriorly around the SVC to enter the anterior
interatrial band, called the Bachmann. This band
continues to the left atrium (LA), with the anterior
internodal pathway entering the superior margin
of the AV node. The Bachmann bundle is a large
muscle bundle that appears to conduct the cardiac
impulse preferentially from the RA to the LA.

5.  The middle internodal tract begins at the superior
and posterior margins of the sinus node, travels
behind the SVC to the crest of the interatrial
septum, and descends in the interatrial septum to
the superior margin of the AV node.
 The posterior internodal tract starts at the posterior
margin of the sinus node and travels posteriorly
around the SVC and along the crista terminalis to
the eustachian ridge and then into the interatrial
septum above the coronary sinus, where it joins
the posterior portion of the AV node. These groups
of internodal tissue are best referred to as
internodal atrial myocardium, not tracts, as they
do not appear to be histologically discrete
specialized tracts

7.  The compact portion of the atrioventricular
(AV) node is a superficial structure located just
beneath the RA endocardium, anterior to the
ostium of the coronary sinus, and directly
above the insertion of the septal leaflet of the
tricuspid valve. It is at the apex of a triangle
formed by the tricuspid annulus and the
tendon of Todaro, which originates in the
central fibrous body and passes posteriorly
through the atrial septum to continue with the
eustachian valve

9.  In 85-90% of human hearts, the arterial supply
to the AV node is a branch from the right
coronary artery that originates at the posterior
intersection of the AV and interventricular
grooves (crux). In the remaining 10-15% of the
hearts, a branch of the left circumflex coronary
artery provides the AV nodal artery.
 Fibers in the lower part of the AV node may
exhibit automatic impulse formation.
 The main function of the AV node is
modulation of the atrial impulse transmission
to the ventricles to coordinate atrial and
ventricular contractions.

10.  The bundle of His is a structure that connects with the distal
part of the compact AV node, perforates the central fibrous
body, and continues through the annulus fibrosus, where it
is called the nonbranching portion as it penetrates the
membranous septum.
 Connective tissue of the central fibrous body and
membranous septum encloses the penetrating portion of the
AV bundle, which may send out extensions into the central
fibrous body. Proximal cells of the penetrating portion are
heterogeneous and resemble those of the compact AV node;
distal cells are similar to cells in the proximal bundle
branches.
 Branches from the anterior and posterior descending
coronary arteries supply the upper muscular
interventricular septum with blood, which makes the
conduction system at this site more impervious to the
ischemic damage, unless the ischemia is extensive

12.  The bundle branches originate at the superior margin
of the muscular interventricular septum, immediately
below the membranous septum, with the cells of the
left bundle branch cascading downward as a
continuous sheet onto the septum beneath the
noncoronary aortic cusp. The right bundle branch
continues intramyocardially as an unbranched
extension of the AV bundle down the right side of the
interventricular septum to the apex of the right
ventricle and base of the anterior papillary muscle. The
anatomy of the left bundle branch system may be
variable and may not conform to a constant bifascicular
division. However, for clinical purposes and
electrocardiography (ECG), the concept of a
trifascicular system remains useful

14.  The terminal Purkinje fibers connect with the
ends of the bundle branches to form
interweaving networks on the endocardial
surface of both ventricles, which transmit the
cardiac impulse almost simultaneously to the
entire right and left ventricular endocardium.
Purkinje fibers tend to be less concentrated at
the base of the ventricle and the papillary
muscle tips. They penetrate only the inner third
of the endocardium. Purkinje fibers appear to
be more resistant to ischemia than ordinary
myocardial fibers.

17. Myocardial cells have several different electrophysiologic
properties:
1. Automaticity - refers to the ability to spontaneously
generate an electrical impulse.
2. Excitability - means that the cardiac cells have the
ability to respond to an electrical impulse.
3. Conductivity - allows for transmission of the electrical
impulse to another cardiac cell.
4. Contractility - refers to the ability to contract after an
electrical impulse is received.
5. Rhythmicity - is the cell's ability to send electrical
impulses in a regularly and evenly paced manner.,
and
 Refractoriness - refers to the cell's inability to respond
to another electrical impulse

18. Myocardial cells contain actin and myosin
filaments and contracts by means of the sliding
filament mechanism. Myocardial cells are
joined by gap junctions, due to which electrical
impulses can spread to all cells in the mass.

22. SA node Represented on the ECG as P wave
AV node conduction is represented on the ECG as the PR
Interval
The Bundle Branch and purkinje fibre depolarisation constitutes
ventricular depolarisation Represented on the ECG as the QRS
Atrial repolarisation occurs within the QRS & therefore is masked
Ventricular repolarisation is represented on the ECG as a T wave

24. 1. RBBB( rt vent vol overload)
2. Prolonged PR interval (atrial enlargement
leading to increassed internodal conduction
distance)
3. Crochetage (M shaped) in inferior ECG leads
4. ostium primum a - left axis deviation.
ostium secundum - right axis deviation.

26.  The relationship of the defect to the ostium of
the coronary sinus, membranous portion of the
AV septum, and commissural area between the
septal and anterior tricuspid leaflets is studied
because these features serve as guides to the
location of the AV node and penetrating
portion of the bundle of His
 To avoid damaging the AV node,the sutures
must not be placed too far from the edge
anteriorly.

28.  Because coronary sinus ASDs are close to the
AV node, stitches must be placed near the edge
of the defect superiorly in tissue that may not
be strong. For these reasons, patch closure is
generally advisable.

29. 1. When the right superior pulmonary veins
enter more cephalad in the SVC (more than
about 2 cm above the cavoatrial junction)
2. when the SVC is small (as in the presence
of bilateral SVCs)
To avoid sinus node dysfunction with incisions
across the cavoatrial junction

30. sinus venosus malformation with right upper and middle lobe pulmonary veins
entering superior vena cava (SVC). A, Right upper and middle pulmonary veins entering
SVC. Right atrial appendage is amputated. B, High SVC or innominate vein is
cannulated. Dashed line indicates the transecting incision in SVC

31. C, Cephalad end of transected SVC is anastomosed to amputated right atrial appendage. For
mobilization, azygos vein is divided. D, Small incision is made in right atrial wall. Lateral edge of
SVC orifice is sutured to lower rim of subcaval atrial septal defect (ASD), or the pathway is
completed with a pericardial or polytetrafluoroethylene patch. Cardiac end of transected SVC is
closed. E, Right pulmonary vein blood now flows (arrows) across the roofed ASD into left atrium

32. 1. Closure of ASDs in children has been shown to
improve AV conduction, decrease AV nodal
refractory periods, and improve sinus node
function in most patients early
postoperatively
2. Presumably this improvement results from
reduction in RV and right atrial volume after
ablation of the left-to-right shunt at the atrial
level.

33.  In patients over about age 40, almost half of
those not in atrial fibrillation preoperatively
develop it late postoperatively. This tendency
to atrial fibrillation or flutter late
postoperatively may be less when venous
cannulation is directly into the venae
cavae rather than through the right
atrial appendage

34.  prevalence of changed heart rhythms
after repair is similar in patients with
fossa ovalis ASDs and those with sinus
venosus malformation
 sick sinus syndrome or junctional
rhythm late postoperatively are seen in
patients where incision is made across the
cavoatrial junction for SV type ASD

36. 1. Truex described the location of the specialized
conduction tissue in hearts with VSD.
2. In a more detailed study, Lev expanded on
this topic
3. Kirklin and DuShane developed a surgical
technique that avoided producing heart block
during VSD repair

38.  the AV node and penetrating portion of the bundle
of His are in their normal position in hearts with
perimembranous VSDs.
 As the bundle penetrates the fibrous right trigone
of the central fibrous body at the base of the
noncoronary cusp of the aortic valve, it lies along
the posteroinferior border of perimembranous and
inlet-type VSDs. As the bundle continues along the
inferior border of the VSD (at times slightly to the
left or right of the free edge),the left bundle branch
fascicles emerge from the branching portion. Only
the right bundle branch remains when the bundle
reaches the level of the muscle of Lancisi.

39.  The perimembranous VSD is intimately
associated with the bundle of His which in a d-
loop heart passes through the tricuspid
annulus at the posterior and inferior corner of
the VSD.
 The bundle soon branches into the right
and left bundle branch

40. Repair of perimembranous ventricular septal defect (VSD) from right atrium,
continuous suture technique.
Right atriotomy is parallel to atrioventricular groove from right atrial appendage toward
inferior vena cava. Stay sutures are placed to expose tricuspid orifice. Superior edge of
VSD is not visible because of overlying anterior leaflet of tricuspid valve.
Atrioventricular node lies within triangle of Koch,with bundle of His penetrating to
ventricular septum at posterior angle of VSD, where it is particularly vulnerable to injury

41. Bundle of His crosses beneath septal leaflet of tricuspid valve. Stitches must not penetrate
tricuspid anulus or into atrial myocardium, to preserve integrity of conduction system

42. Via rt ventriclotomy At a point 5 to 7 mm below inferior margin of VSD, suture line is tran
septal leaflet onto ventricular septum. Stitching continues along inferior rim of VSD,
with stitches placed 5 to 7 mm below rim until reaching muscle of Lancisi. An alternative
technique uses interrupted pledgeted mattress sutures for very thin portions of the
septal leaflet and posteroinferior edge of defect (conduction system) to facilitate secure
suture placement while avoiding conduction system. Remainder of suture line employs
a continuous suture technique.

43.  for Perimembranous Ventricular Septal Defect the RV approach
may be used for repair of perimembranous VSDs and results in
low hospital mortality even in patients with high Rp.
 The RV approach has the advantage that the nadir of the
noncoronary cusp of the aortic valve, which is the area of the right
trigone and bundle of His, can be accurately visualized, which
may be helpful in choosing the suture technique that will
minimize prevalence of heart block
The RV approach has the disadvantages of
(1) leaving a scar in the RV,
(2) being associated with a higher prevalence of complete RBBB
than with an atrial approach,
and (3) possibly resulting in more ventricular arrhythmias late
postoperatively.
.

44.  The right atrial approach may be used almost
exclusively, a practice begun in about 1960 at
the Mayo Clinic. An accurate repair can be
obtained through a right atrial approach in
nearly all cases. Associated infundibular
pulmonary stenosis can be excised. An RV scar
is avoided, and occurrence of RBBB is lower
than with the transventricular approach.H11
With the right atrial approach, however,
techniques must be accurate to avoid damaging
the tricuspid valve , leaflets or chordae

45.  Since the right atrium must connect with the left ventricle
(i.e. atrioventricular discordance), it is not surprising that
the conduction system is abnormal. Pioneering work in this
area was undertaken by Anderson and colleagues.
 In corrected transposition (C-TGA), the functional
atrioventricular node arises anteriorly and superiorly and is
usually lodged between the annulus of the mitral valve .
 This functional AV node is therefore superior to the usual
location of the AV node which may be present as an
accessory node.

46.  Often there is a posterior atrioventricular node in its usual
position within the triangle of Koch, but it is usually
disconnected from the remainder of the conduction tissue.
 The conduction system in C-TGA is more tenuous than that
of normal hearts. Fibrosis of the junction between the
atrioventricular node and the atrioventricular bundle has
been seen in older patients
 Artrial switch operation- Post operative arrhythmia less
compared to Mustard and Senning operation.

48.  Categorised – Left or right – based on morphological
operative single ventricle
 Single right ventricle- no conduction disturbances.
 Single left ventricle- AV node is hypoplastic
- Prolonged PR interval culminating
in complete heart block

49.  Complete absence
of communication
between the right
atrium and right
ventricle
 About 3 % of
congenital heart
disease

50.  SA node is normal.
 Posterior small AV node originates in close relation
to Tendon of Todaro.
 Occasionally, the branching bundle may
be in close proximity to the posteroinferior rim of the
foramen and the right bundle-branch may lie
subendocardially in the rim of the defect.

51.  It is important, therefore, to appreciate
that the atrioventricular node is in close relation to the
tendon of Todaro, which is a readily identifiable
landmark during surgical exposure.
Closure of the foramen should usually be
accomplished safely provided that
deep sutures are not placed in the posteroinferior
quadrant.

52.  Usual type of arrythmias with Atrial surgery are SVT
of which AF, Atrial flutter and junctional rhythms
are most common.
 In large ostium primum type defect because of
posteriorly displaced AV node , it is frequently
associated with prolonged AV conduction.
 Small osteum secundum defect causes no problem
during repair.

53.  Hypothermia, ischemic arrest , direct injury to
conduction system, haematoma, injury to SA nodal
artery , oedema , forign body reaction to suture
material all are responsible for arrhythmias
 The most common conduction disturbance that
occurs after ventricular surgery is RBB block .
 RBBB can be due to direct injury to main RBB or
right ventriculotomy ( in fallots tetrology surgery )
by disrupting the right ventricular subendocardial
purkinje network

54. Clockwise from anterolateral commissure are the aortic cusps, conduction system,
Atrioventricular septum, coronary sinus, and circumflex coronary artery,
which are at risk when bites are taken too deeply
Mitral valve

55. Aortic valve and conduction system

56. Care must be taken while removing
calcium from the region of the
membranous septum and right trigone,
Beneath the noncoronary cusp–
right coronary cusp commissuret and
rigorous avoidance of suture penetration
of the membranous septum near
its junction with the muscular septum

57. Tricuspid valve and conduction system

58. THANK YOU