Cardiovascular Journal of Africa: Vol 28 No 3 (May/June 2017)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 3, May/June 2017

AFRICA

Discussion

During embryogenesis, the sinus venosus consists of the right

and left horns. Each receives blood from the common cardinal,

vitelline and umbilical veins. During gestation, the left horn,

after obliteration of the above veins, evolves into the coronary

sinus and oblique vein of the left atrium, while the right becomes

incorporated into the right atrium. The right common cardinal

vein and the proximal part of the right anterior cardinal vein

build the right superior vena cava. The left anterior cardinal

vein changes into the internal jugular vein. The presence of the

left anterior cardinal vein and obliteration of the left common

cardinal vein leads to the formation of the left superior vena

cava, which drains into the right atrium through the coronary

sinus.

12,13

The presence of a PLSVC has a significant influence on the

anatomy of the heart and venous system. Although our autopsy

study revealed enlargement of the heart chambers, the largest

change concerned the CS. We compared the dimensions of

the CS and selected heart structures from this case with mean

dimensions obtained by measuring nearly 200 structurally

normal hearts (23% female; mean age 46.7 ± 19.1 years) without

PLSVC in our previous studies.

14,15

The diameter of the CS

described in this case report (17.17 mm) was the largest of all

observed autopsy specimens, almost twice the average of all

previous measurements (mean 9.2 ± 2.7 mm). The existence of a

common left pulmonary vein trunk may also have been the result

of the PLSVC, which limited the free space in the area where the

left inferior pulmonary vein should be.

The PLSVC drains about 20% of the whole venous return,

and therefore significantly enhanced venous return via the CS

forces an increase in its dimensions. Moreover, an increased

blood volume flowing into the CS leads to the atrophy of

the Vieussens, Thebesian and other heart vein valves. The

enlargement of the CS is also often mentioned by other authors

as the most characteristic change in the anatomy of the heart.

Furthermore, our observed changes were related to the size

of the valves; the mitral valve area was substantially reduced

(2.6 cm

; mean value 4.2 ± 1.8 cm

), which may have been an

outcome of the pressure exerted by an enlarged CS on the left

atrium and mitral ring. The tricuspid valve area (5.3 cm

) did

not differ significantly compared to the average value of 4.8

± 1.6 cm

. Venous return via the right superior vena cava was

reduced, due to blood draining from the left arm, neck and

head via the PLSVC. These haemodynamic effects explain the

reduced dimensions of the right superior vena cava; AP = 17.3

mm and ML = 16.5 mm (mean 20.1 ± 3.6 mm and 18.3 ± 3.4

mm, respectively). Also the weight of the heart (613 g) showed an

increase in comparison with the average value of 432.7 ± 112.8

g, with no cause of heart enlargement other than the PLSVC.

General and specific haemodynamic effects from the presence

of the PLSVC vary between cases and depend largely on the

coexistence of other heart abnormalities. The presence of a

PLSVC influences mainly the blood flow in the atria and cardiac

venous system. Patients with PLSVC are mainly asymptomatic

or minimally symptomatic.

The most common variant of this anomaly is as follows;

the PLSVC drains into the right atrium with a right superior

vena cava present, which usually does not cause significant

haemodynamic changes and clinical consequences. However, if

the PLSVC drains into the left atrium, right-to-left cardiac shunt

with desaturation and cyanosis as a consequence, is observed.

The latter case often needs surgical intervention.

1,18

Other complications resulting from the existence of PLSVC

include difficulty in pulmonary artery catheterisation,

cerebral abscess,

arrhythmia and thromboembolic events

or difficulties in left-sided right heart and cardiac venous

system catheterisation.

Enlarged CS (exerting pressure on the

atrioventricular node) or absence of the right superior vena cava

are common causes of cardiac rhythm disorders. The presence

of a huge CS due to a persistent PLSVC can alter cardiac

haemodynamics by significant reduction of the left atrium size

and impediment of its outflow via the mitral valve, as presented

in this case.

A PLSVC often coexists with other congenital heart defects,

therefore early detection of this anomaly may be very important

for the future outcome of the patient.

Isolated PLSVC without

a superior vena cava is very rare (0.1% of the population).

22,23

the majority of known cases, the CS is unroofed, which causes

a right-to-left shunt of blood.

In 10 to 20% of patients, the

PLSVC drains into the left atrium, which may be associated with

more dangerous haemodynamic complications. It is also worth

mentioning that the incidence of defects in foetuses is higher than

in the general population. This is due to the double mechanism:

anatomical anomalies may cause spontaneous miscarriage, as

well as the existence of PLSVC along with other heart defects

may lead to premature death.

Although diagnosis is not very complicated, the anomaly

often remains unnoticed, especially when it is clinically inaudible.

PLSVC is very often discovered accidentally during invasive

cardiac procedures, mostly during routine left-sided right-heart

catheterisation, surgical procedures or insertion of a venous

central line.

21,24

The presence of PLSVC can result in left-

sided heart obstruction, which can cause a decrease in heart

compliance and as a result, lower stroke volume.

On chest X-ray, PLSVC can be seen as a widened shadow of

the aorta with a visible venous half-moon shadow from the left

side of the aortic arch to the middle of the left clavicle. Basic

diagnostic methods include transoesophageal and transthoracic

echocardiography. Other commonly used methods comprise

conventional contrast venography, computed tomography and

magnetic resonance venography.

Prenatal diagnosis is based on

echocardiography and mostly reveals an enlargement of the CS.

Conclusions

We present a case in which the PLSVC significantly affected

anatomical relationships and dimensions of the heart. The

PLSVC draining into the CS led to its enlargement and to

atrophy of the Vieussens and Thebesian valves. The huge CS

could have altered cardiac haemodynamics with a significant

reduction in the size of the left atrium and impediment of its

outflow via the mitral valve. Also the drainage of the pulmonary

vein into the left atrium may have been affected due to the

presence of the PLSVC.

References

Zhong YL, Long X-M, Jiang L-Y, He B-F, Lin H, Luo P,

et al

. Surgical

treatment of dextroversion, isolated persistent left superior vena cava

draining into the left atrium.

J Card Surg

2015;

(10): 767–770.