Congenital Heart disease - Part 1

on 23.1.11 with 0 comments

Circulatory changes in newborn

During in-utero life, the right atrial pressure is greater than left atrial pressure, since there's less pulmonary blood flow, and greater amount of systemic and placental venous return to right atrium.

Hence, the flap valve of foramen ovale remains patent, allowing blood flow from right to left atrium.

Once the baby takes his/her first breath, the pulmonary vascular resistance decreases, amount of pulmonary blood flow increased by 6 folds. In addition, placental venous return is excluded from the venous return to right atrium, hence left atrial pressure is now greater than right atrial pressure.

This results in obliteration of foramen of ovale.

Ductus arteriosus, which joins the pulmonary artery to the aorta, obliterates within few hours or few days after birth.

Causes of congenital heart disease

1) Maternal disease

Rubella - pulmonary stenosis, PDA
SLE - complete heart block
Diabetes - increased incidence overall

2) Maternal drug usage

Warfarin - pulmonary stenosis, PDA
Fetal alcohol syndrome - ASD, VSD, TOF

3) Chromosomal abnormalities

Down's syndrome - atrioventricular septal defect, VSD

How do they present?

a) Antenatal diagnosis

Fetal echocardiography is now routinely done in UK during 18-20 week of gestation.

Any abnormalities detected will be referred to a pediatric cardiologist for further detail echocardiography.

They'll be scanning mothers with increased risk of having a Down syndrome child, mothers with previous child with congenital heart disease, or mothers with previous h/o of CHD.

Such screening is done so that management plan can be discussed during antenatal period.

b) Heart murmur

Innocent murmurs - detected in 30% of children
More apparent in children during febrile episodes or anemia, due to increased cardiac output.
2 types of innocent murmurs :

i) Ejection murmurs

Due to increased blood flow through ventricles, outflow tracts and great vessels, not due to any structural abnormalities.

ii) Venous hum

Due to increased blood flow through the head and neck veins, characterised by low pitched, rumbling sound heart below the clavicle, intensity increased during inspiration and after exercise.

Hence, easily mistaken as PDA.
Venous hum dissapears after lying down flat, or by compressing jugular vein of same side.

Criteria of innocent murmur

1) Soft, blowing (2nd left ICS) or Short-buzzing (4th left ICS)
2) Ejection murmur
3) No diastolic component
4) S1 and S2 normal, no added sounds
5) No parasternal thrill
6) No radiation
7) Asymptommatic patient

b) Cyanosis

Peripheral cyanosis (bluish discolouration of extremities), must be differentiated from central cyanosis (bluish tongue, oral mucosa, etc), which is due to reduced arterial O2 saturation.

Central cyanosis is only clinically apparent when reduced Hb is >5gm%.
Hence, it is less pronounced in anemic child.

Differential diagnosis for newborn with central cyanosis and respiratory distress (respiratory rate >60 breaths/min) :

Cyanotic heart disease
Respiratory disorders - RDS, pulmonary hypoplasia
Persistent pulmonary hypertension
Infection - sepsis, GBS
In-born metabolic errors - causing acidosis, shock

Causes of cardiac cyanosis :

a) Reduced pulmonary blood flow
b) Abnormal mixing of systemic and pulmonary venous blood

How do you diagnose cyanotic heart disease?

If detailed fetal echocardiography is not immediately available, hyperoxia test can be done.
First, baby is given 100% oxygen for 10 mins.
Later, right radial arterial O2 saturation is determined.
If PaO2 is <15 kPa -> cyanotic heart disease
If PaO2 is >20 kPa -> very unlikely

Immediate airway, breathing and circulatory resuscitation is required.
The cyanosis in early neonatal period is due to closure of ductus arteriosus. (duct-dependent lesion)
Hence, prevention of closure is important in maintaining survival, by giving IV prostaglandin.
Watch out for A/E, eg : apnoea, seizures, hypotension, flushings

c) Heart failure

Causes of heart failure in neonatal period

Left heart obstruction syndrome
Severe coarctation of aorta
Critical aortic valvular stenosis

Causes of heart failure during infancy

Large PDA
Atrioventricular septal defect

What are the symptoms?

Poor feeding
Recurrent chest infections

What are the signs?

Cool peripheries
Failure to thrive
Gallops, heart murmur

During the neonatal period, causes of heart failure is due to presence of a right to left shunt lesion (duct dependent lesion). Hence, less pulmonary blood flow leading to reduced gaseous exchange, hence -> cyanosis.

During infancy, progressive heart failure is usually due to presence of a left to right shunt lesion. Heart failure is due to increased pulmonary blood flow causing pulmonary hypertension.

Symptoms of heart failure increases upto 3 months, since during this period of time, pulmonary vascular resistance is decreasing.
Beyond 3 months, pulmonary vascular resistance increases in response to this left to right shunt lesion and symptoms of heart failure subsides.

In left untreated, it can result in irreversible increased in pulmonary vascular resistance, and around 2nd decade of life, patient develops Eisenmenger's Syndrome.

Usual investigation after congenital heart disease is suspected?

CXR and ECG.
Note that normal CXR and ECG doesn't rule out congenital heart disease.
Both investigations is done for :

Baseline investigation
Assessment of future changes

Time for referral to paediatric cardiologist :

a) Hemodynamic unstability
b) SPO2 < 94%
c) Low volume pulse
d) Presence of heart failure
e) Cyanosis

Acyanotic heart disease

1) Atrial septal defect

80% of ASD is due to secundum ASD
20% of ASD - partial atrioventricular septal defect (PAVSD)

In secundum ASD - the defect is central, involving the foramen of ovale
In PAVSD - the defect is at the AV septum, where there is :

a) Inter-atrial communication at the bottom end of atrial septum and with the AV vales

b) Presence of regurgitant left AV valve (tends to leak)

Clinical features

Asymptommatic (commonest)
Recurrent chest infection/Wheeze
Heart failure
Cardiac arryhthmia

Category: Pediatrics Notes



Post a Comment