Transcript ATRIAL SEPTAL DEFECT

FOETAL CIRCULATION
CIRCULATION AFTER BIRTH
EMBRYOLOGY
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Embryologically, the septum primum separates the two atria first, moving
inferiorly toward the endocardial cushions. The ventricular septum forms by
moving upward from the ventricles to the endocardial cushions at the same
time. If the atrial septum does not make it all the way, the residual defect in
the septum primum (ostium primum) results in the primum ASD.
If the septum primum makes it all the way, a hole or holes (fenestrations)
form in the middle of the septum (forming the ostium secundum). A second
septum then moves down the right side of the first and normally covers the
ostium secundum hole. If it does not cover the hole, a secundum ASD is
present.
The septum secundum normally completely covers the right side of the
atrial septum except for an ovale hole in it (the foramen ovale). If the septae
do not fuse, a patent path from the RA to the LA persists (the patent
foramen ovale PFO).
The most common form of ASD (80% of cases) is persistence of the ostium
secundum in the mid septum; less commonly, the ostium primum (which is
low in the septum) persists
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NORMAL PRESSURES
ATRIAL WAVES
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a= atrial contraction
c= contraction of ventricle and closure of tricuspid valve
x=x descent
v=venous filling
y= y descent due to opening of tricuspid valve
SWAN GANZ CATHETER
RIGHT HEART PRESSURES
Haemodynamic Parameters
Essentials of Diagnosis
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•Often asymptomatic and discovered on routine physical examination.
•RV lift; S2 widely split and fixed.
•Grade IIII/VI systolic ejection murmur at pulmonary area.
•ECG shows RV conduction delay;
•radiograph shows dilated pulmonary arteries and increased vascularity;
echocardiography/Doppler diagnostic.
•A PFO is present in 25% of the population but can lead to paradoxical
emboli and cerebrovascular events. Suspicion should be highest in patients
who had cryptogenic stroke before age 55.
•In all cases, normally oxygenated blood from the higher-pressure LA
passes into the RA, increasing RV output and pulmonary blood flow. In
children, the degree of shunting across these defects may be quite large
(3:1 or so). As the RV diastolic pressure rises from the chronic volume
overload, the RA pressure may rise and the degree of left-to-right shunting
may decrease. Eventually, the shunt may even be right-to-left and cyanosis
appears
ASD
CHAMBER PRESSURES
• Simultaneous left and right atrial and differential pressure across an
atrial septal defect. The pressure difference across the defect is
greatest before the v wave. The right atrial pressure tracing is
inverted because it is recorded by a differential manometer
SYMPTOMS AND SIGNS
• Patients with small or moderate ASDs and with a PFO are
asymptomatic unless a complication occurs.
• With large shunts, exertional dyspnoea or cardiac failure may
develop, most commonly in the fourth decade of life or later.
• Prominent RV and PA pulsations are readily visible and palpable.
• A moderately loud systolic ejection murmur can be heard in the
second and third interspaces parasternally as a result of increased
PA flow.
• S2 is widely split and does not vary with breathing due to the fact
that the left-to-right shunt decreases as the RA pressure increases
with inspiration
EISENMENGER COMPLEX
The pulmonary pressures are
modestly elevated in most patients
with an ASD due to the high pulmonary
blood flow, but severe pulmonary
hypertension (Eisenmenger's complex)
is actually rare, occurring in only about
15% of the patients (see illustration).
Eventual RV failure may occur, and
most shunts should be corrected
unless they are quite small (< 1.5:1
right-to-left shunt). In adults, a large
right-to-left shunt may have begun to
reverse, so the absolute size at the
time the patient is studied may
underestimate what it was some years
ago. In addition,
in most patients the LV compliance
normally declines more over time than
the RV, and the natural history of small
atrial septal shunts is to increase as
the patient ages (unless RV failure
ensues).
ECG IN ASD
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Right axis deviation or RVH may be present depending on the size of the RV volume overload
(see ECG); (see ECG). Incomplete or complete right bundle branch block is present in nearly all
cases of ASD, and superior axis deviation is noted in the AV canal defect, where complete heart
block is often seen as well. With sinus venosus defects, the P axis is leftward of +15 due to
abnormal atrial activation with loss of the upper RA tissue from around the sinus node
XRAY IN ASD
• The chest radiograph shows large pulmonary arteries, increased
pulmonary vascularity, an enlarged RA and RV, and a small aortic
knob with all pre-tricuspid cardiac left-to-right shunts.
DIAGNOSTIC STUDIES
• Echocardiography demonstrates evidence of RA and RV volume
overload. The atrial defect is usually observed, though sinus
venosus defects may be elusive.
• Many patients with a PFO also have a redundant atrial septum
(atrial septal aneurysm) that promotes right-to-left shunting.
Echocardiography with agitated saline bubble contrast can
demonstrate a right-to-left shunt and both pulsed and colour flow
Doppler flow studies can demonstrate shunting in either direction
(see Video). A TEE is helpful when transthoracic echocardiography
quality is not optimal, and it improves the sensitivity for small shunts
and provides a better assessment of PFO anatomy. Radionuclide
flow studies quantify left-to-right shunting by observing the bolus of
contrast within the lung fields and demonstrating early recirculation.
Both CT and MRI can also elucidate the atrial septal anatomy as
well, and allow for observation of associated lesions. Cardiac
catheterization is often helpful, especially if there are associated
anomalous pulmonary veins. The size and location of the shunt can
be determined and the pulmonary pressure and pulmonary vascular
resistance (PVR) measured (see ECG). Cardiac catheterization is
required if percutaneous closure is to be contemplated
Prognosis & Treatment
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Patients with small atrial shunts may live a normal life span. Large shunts
usually cause disability by age 40 years. Because left-to-right shunts tend to
increase with age-related changes in LV compliance, most clinicians believe
that closure of all shunts over 1.5:1 should be accomplished.
Increased PVR and hypertension secondary to pulmonary vascular disease
rarely occur in childhood or young adult life in secundum defects but are
more common in primum defects. Significant pulmonary hypertension rarely
develops in older patients. After age 40 years, cardiac arrhythmias
(especially atrial fibrillation) and heart failure may occur due to the chronic
right heart volume overload.
Paradoxical systemic arterial embolization becomes more of a concern as
RV compliance is lost and the left-to-right shunt begins to reverse.
PFOs are not associated with significant shunting, and therefore the
patients are asymptomatic and the heart size is normal. However, PFOs are
responsible for most paradoxical emboli and are one of the most frequent
causes of cryptogenic strokes in patients under age 55 years. That is likely
because there is often right-to-left or bidirectional shunting, and the IVC
blood is directed toward the foramen ovale by the eustachian valve.
Intervention
• Small ASDs do not require intervention. The easiest way to decide if
a shunt is small is by echocardiography. If the shunt is not creating
an RV volume overload, then one can assume the shunt needs no
further evaluation.
• For larger deficits (those with an RV volume overload), surgery can
be done at very low risk.
• Surgery involves anything from simple stitching of the foramen
closed to patching of the hole with Dacron or a pericardial patch.
Anomalous pulmonary venous connections are baffled to the LA
through the sinus venosus defect when such anomalous veins are
present.
• For ostium secundum ASDs, percutaneous closure by use of a
variety of devices is now preferred over surgery. The percutaneous
closure devices often resemble double umbrellas that lock the
septum between the Dacron umbrellas when opened
PFO
• Patients with a PFO may have symptoms related to stroke or
transient ischemic attack (especially if the age is under 55) or have
hypoxemia (especially upon standing so called platypnea
orthodeoxia).
• There are data that suggest that migraine headaches may be more
common in patients with a PFO, suggesting some unknown
substance normally metabolized in the lung is entering the systemic
circulation through the PFO.
• For patients with cryptogenic stroke or transient ischemic attack, it
is uncertain whether closure of the PFO, either by open surgical or
percutaneous techniques, has any advantage over anticoagulation
with either warfarin or aspirin. Although there are no data yet
suggesting that PFO closure is better than medical therapy, ongoing
randomized trials should help settle this issue.