DR RAKESH KUMARMCH CTVS,AIIMS,NEW DELHI

• TGA like tetralogy and DORV is an anomaly of conotruncal development.

• Two basic theories that attempt to explain the development of conotruncal anomalies.

• Conotruncus which will ultimately form the aorta and pulmonary artery formed as a single tube.

• A process of spiral septation divides the conotruncus into the two great vessels which should wrap around each other.

• If the septum does not ‘spiral’ in the usual fashion at all, the great vessels will be parallel to each other and there will be transposition of the great arteries.

Usually the aortic, tricuspid and mitral valves are in fibrous continuity, united by the fibrous skeleton of the heart.

Only the pulmonary valve is separate, being lifted superiorly from the other three valves by the subpulmonary conus (infundibulum)

• Van Praagh suggested that there is no subpulmonary conus and the aorta comes to lie anterior to the pulmonary artery.

• There is a fibrous continuity between the pulmonary and mitral valves rather than the usual continuity between the aortic and mitral valves.

• Only the aortic valve is separate from the other three valves.

NORMAL HEART TGA HEART

• RIGHT VENTRICLE• LEFT VENTRICLE• VENTRICULAR WALL THICKNESS, CAVITY

SHAPE & FUNCTION• ATRIA• CONDUCTION SYSTEM• GREAT ARTERIES• CORONARY ARTERIES• PULMONARY VASCULAR DISEASE• CO-EXISTING CARDIAC ANOMALIES

Normally positioned, hypertrophied, and large in TGA.

In about 90% of cases: ◦Subaortic conus is seen, ◦Aorta is rightward and anterior and

ascends parallel to the posterior and leftward pulmonary trunk.

INFUNDIBULAR SEPTUM JOINING NORMALLY WITH THE VENTRICULAR SEPTUM BETWEEN THE LIMBS OF THE TSM

HYPERTROPHIED RV

Less wedging of the pulmonary trunk between the mitral and tricuspid valves in TGA than of the aorta in normal hearts.

Larger area of contiguity exists between the mitral and tricuspid valves than normally.

These atrioventricular (AV) valves may be at virtually the same level, and the AV septum and membranous interventricular septum are then smaller than usual or (rarely) absent.

The right fibrous trigone is abnormally shaped and attenuated.

• Infrequently contains a conus typically pulmonary mitral fibrous continuity exists, comparable with aortic mitral continuity in the normal heart.

MITRAL VALVE

PULMONARYVALVE

In about 8% of hearts with TGA, and most often in those with a VSD, a subpulmonary conus is present in the LV.

The subpulmonary conus is frequently stenotic.

RV wall is considerably thicker than normal at birth and increases in thickness with age.

LV wall is of normal thickness at birth. Wall thickness remains static, however,

leading to less-than-normal thickness within a few weeks of birth and a relatively thin wall by age 2 to 4 months.

LV cavity is the usual ellipsoid in shape at birth but soon becomes banana shaped.

RV function is usually normal in TGA in the perinatal period.

Thereafter, when the ventricular septum is intact, RV end-diastolic volume is increased and RV ejection fraction decreased.

Depressed RV function results from relative myocardial hypoxia or the geometry of the chamber & unlikely by increased afterload or decreased preload.

Are normally formed in TGA. Right atrial size is usually larger than

normal, particularly when the ventricular septum is intact.

• AV node and bundle of His lie in a normal position.

• The left bundle branch originates more

distally from the bundle of His than usual and arises as a single cord rather than a sheath.

Damage to the bifurcation of the bundle at VSD closure is more likely to produce complete heart block than in the normally structured heart.

• The aorta is most often directed anterior or slightly to the right.

• In 13% to 30% of patients with TGA, aortic and pulmonary commissures are not precisely aligned because of malalignment of either the aortic or mitral valve.

• Recognition of commissural malalignment is important in planning the coronary transfer as well as preventing neoaortic valve regurgitation.

Usually arise from the aortic sinuses that face the pulmonary trunk, regardless of the inter-relationships of the great arteries.

Thus, the noncoronary sinus is usually the anterior one.

• A more universally applicable scheme is the Leiden convention – proposed by the anatomists Gittenberger-DeGroot

and Sauer who were working in Leiden, Holland.

• According to Leiden convention Using the perspective of an individual

looking from the aorta to the pulmonary artery:

sinus 1 – adjacent to the pulmonary artery on the right-handside of the observer

sinus 2 – adjacent to the pulmonary artery on the left handside of the observer

sinus 1 Usually gives rise to the anterior descending and circumflex coronary arteries.

sinus 2 usually gives rise to the right coronary artery.

This can be abbreviated as (1AD,CX; 2R)

Originally described by Yacoub and Radley-Smith in 1978.

Usually the arteries all arise from a single ostium in the center of the sinus.

Alternatively, they may arise from a double barreled ostium consisting of two ostia immediately adjacent to each other and constituting essentially a single ostium.

Now that repair of simple TGA is usually performed in the first few weeks of life, and repair of TGA with VSD is usually performed in the first few months of life, pulmonary vascular disease has almost disappeared.

About 75% of neonates presenting with TGA have no important coexisting cardiac anomaly other than a patent foramen ovale or an atrial septal defect.

About 25% to 40% have a large or small VSD.

Only about 5% have associated LVOTO.

Same types of VSD occur with TGA as occur in hearts with a primary VSD.

Conoventricular defects of the several different varieties are most common.

In some hearts with conoventricular VSDs, the infundibular septum is malaligned and fails to insert within the Y of the TSM.

The septum may be displaced leftward, resulting in a variable degree of LVOTO and or rightward, tending to result in RV (subaortic) obstruction.

• Development of LVOTO, which produces subpulmonary obstruction, is part of the natural history of many patients with TGA.

• The obstruction may be dynamic or anatomic.

• LVOTO occurs in an important way at birth or within a few days in only 0.7% of patients with TGA and intact ventricular septum.

Obstruction is present in about 20% of patients born with TGA and VSD.

LVOTO may become apparent or develop after birth in other patients, thus reaching an overall prevalence of 30% to 35%.

RV SIDE LV SIDEMALALIGNED INFUNDIBULUM DEVIATED TOWARDS LV

TSM

RV

VSD

PV

MALALIGNED INFUNDIBULAR SEPTUM MERGING WITH LV WALL VSD

AORTICVALVE

PRV>PLV

LEFT WARD BULGING OF IVS

DYNAMIC OBSTRUCTIO

N

Particularly likely to occur if the aorta lies anterior and more to the left than usual, with increased wedging of the subpulmonary area.

• Important structural anomalies of the mitral valve are present in 20% to 30% of hearts with TGA, mostly in combination with a VSD,

• But the majority are not functionally important.

• The most important from a surgical standpoint are those of mitral valve overriding or straddling, in which the mitral valve leaflet is frequently cleft.

Coexisting aortic obstruction can be discrete (coarctation or less often, interrupted aortic arch) or caused by distal arch hypoplasia.

Rarely, it occurs when the ventricular septum is essentially intact, but it occurs in 7% to 10% of patients with TGA and VSD.

In the normal heart the systemic and pulmonary circulations are in series, in transposition they function as two separate and parallel circuits.

After birth, the oxygenated pulmonary venous blood does not reach the systemic circuit, and the systemic venous return does not circulate to the lungs.

This results in severe systemic arterial desaturation.

Absence of any communication between the pulmonary and systemic circulations is incompatible with life.

• Depends upon:– pulmonary vascular resistance, – Inter-atrial communication.

• When inter-atrial communication is non-restrictive &

• The presence of a ventricular septal defect can have a variable influence on the circulation.

• This in part depends on the:– size of the defect, – the presence of interatrial mixing, and – the pulmonary vascular resistance

• A large interventricular communication may lead to unrestricted flow to the lungs may result in symptomatic heart failure.

PREVALENCE: Common form of congenital heart disease,

occurring in 1 : 2100 to 1 : 4500 births

Accounts for 7-8% of all congenital heart disease.

2 : 1Male predominance increases to 3.3 : 1 when

the ventricular septum is essentially intact

• When patients with all varieties of TGA are considered:

– 55% survive 1 month, – 15% survive 6 months, and – only 10% survive 1 year

• Survival without treatment is different among subsets.

• It is particularly poor in untreated patients with TGA and essentially intact ventricular septum:

– 80% at 1 week – 17% at 2 months and – 4% at 1 year

• In patients with TGA and VSD, early survival is higher:

– 91% at 1 month, – 43% at 5 months, and – 32% at 1 year

The combination of large VSD and aortic obstruction (coarctation, interrupted aortic arch) is particularly lethal: all patients die within a few months of birth with severe heart failure.

In patients with TGA, VSD, and LVOTO, early survival is still better, reaching ◦ 70% at 1 year and ◦ 29% at 5 years,

This is because in many patients LVOTO is only moderate initially.

Poor survival in patients with TGA and essentially intact ventricular septum is related primarily to hypoxia.

Intercurrent pulmonary infections may develop and are particularly lethal because they reduce Qep and lead rapidly to increasing hypoxia, acidemia, and death.

• Death in this group may also result from cerebro-vascular events, usually caused by:– the polycythemia and – increased blood viscosity (both secondary to

severe cyanosis) particularly in association with

dehydration.• Nonfatal cerebrovascular events occur in

about 6% of patients treated by BAS and include cerebral abscess.

Patients with TGA and VSD usually die with heart failure.

Hypoxia is the primary cause of morbidity and mortality in patients with TGA, VSD and LVOTO.