Atrial Septial Defect

8/10/2019 Atrial Septial Defect

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FOETAL CIRCULATION


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CIRCULATION AFTER BIRTH


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EMBRYOLOGY

Embryologically, the septum primum separates the two atria first, movinginferiorly toward the endocardial cushions. The ventricular septum forms bymoving upward from the ventricles to the endocardial cushions at the sametime. If the atrial septum does not make it all the way, the residual defect inthe 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 secondseptum then moves down the right side of the first and normally covers theostium secundum hole. If it does not cover the hole, a secundum ASD ispresent.

The septum secundum normally completely covers the right side of theatrial septum except for an ovale hole in it (the foramen ovale). If the septaedo 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 islow in the septum) persists

.


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NORMAL PRESSURES


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ATRIAL WAVES

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


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SWAN GANZ CATHETER


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RIGHT HEART PRESSURES


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Haemodynamic Parameters


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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

Essentials of Diagnosis


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ASD


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CHAMBER PRESSURES

Simultaneous left and right atrial and differential pressure across anatrial septal defect. The pressure difference across the defect isgreatest before the vwave. The right atrial pressure tracing isinverted because it is recorded by a differential manometer


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SYMPTOMS AND SIGNS

Patients with small or moderate ASDs and with a PFO areasymptomatic unless a complication occurs.

With large shunts, exertional dyspnoea or cardiac failure maydevelop, 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 thesecond and third interspaces parasternally as a result of increasedPA flow.

S2 is widely split and does not vary with breathing due to the factthat the left-to-right shunt decreases as the RA pressure increaseswith inspiration


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EISENMENGER COMPLEXThe pulmonary pressures aremodestly elevated in most patientswith an ASD due to the highpulmonary blood flow, but severepulmonary hypertension(Eisenmenger's complex) is actuallyrare, occurring in only about 15% ofthe patients (see illustration).

Eventual RV failure may occur, and

most shunts should be correctedunless they are quite small (< 1.5:1right-to-left shunt). In adults, a largeright-to-left shunt may have begun toreverse, so the absolute size at thetime the patient is studied mayunderestimate what it was some yearsago. In addition,

in most patients the LV compliancenormally declines more over time thanthe RV, and the natural history of smallatrial septal shunts is to increase asthe patient ages (unless RV failureensues).

ECG IN ASD


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ECG IN ASD

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 allcases of ASD, and superior axis deviation is noted in the AV canal defect, where complete heartblock is often seen as well. With sinus venosus defects, the P axis is leftward of +15 due toabnormal atrial activation with loss of the upper RA tissue from around the sinus node


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XRAY IN ASD

The chest radiograph shows large pulmonary arteries, increasedpulmonary vascularity, an enlarged RA and RV, and a small aortic

knob with all pre-tricuspid cardiac left-to-right shunts.


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DIAGNOSTIC STUDIES

Echocardiography demonstrates evidence of RA and RV volumeoverload. The atrial defect is usually observed, though sinusvenosus 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 candemonstrate a right-to-left shunt and both pulsed and colour flowDoppler flow studies can demonstrate shunting in either direction

(see Video). A TEE is helpful when transthoracic echocardiographyquality is not optimal, and it improves the sensitivity for small shuntsand provides a better assessment of PFO anatomy. Radionuclideflow studies quantify left-to-right shunting by observing the bolus ofcontrast within the lung fields and demonstrating early recirculation.Both CT and MRI can also elucidate the atrial septal anatomy aswell, and allow for observation of associated lesions. Cardiaccatheterization is often helpful, especially if there are associatedanomalous pulmonary veins. The size and location of the shunt canbe determined and the pulmonary pressure and pulmonary vascularresistance (PVR) measured (see ECG). Cardiac catheterization isrequired if percutaneous closure is to be contemplated


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Prognosis & Treatment

Patients with small atrial shunts may live a normal life span. Large shuntsusually cause disability by age 40 years. Because left-to-right shunts tend toincrease with age-related changes in LV compliance, most clinicians believethat 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 aremore common in primum defects. Significant pulmonary hypertension rarelydevelops in older patients. After age 40 years, cardiac arrhythmias(especially atrial fibrillation) and heart failure may occur due to the chronicright heart volume overload.

Paradoxical systemic arterial embolization becomes more of a concern asRV compliance is lost and the left-to-right shunt begins to reverse.

PFOs are not associated with significant shunting, and therefore thepatients are asymptomatic and the heart size is normal. However, PFOs areresponsible for most paradoxical emboli and are one of the most frequentcauses of cryptogenic strokes in patients under age 55 years. That is likelybecause there is often right-to-left or bidirectional shunting, and the IVCblood is directed toward the foramen ovale by the eustachian valve.


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Intervention

Small ASDs do not require intervention. The easiest way to decide ifa shunt is small is by echocardiography. If the shunt is not creatingan RV volume overload, then one can assume the shunt needs nofurther evaluation.

For larger deficits (those with an RV volume overload), surgery canbe done at very low risk.

Surgery involves anything from simple stitching of the foramenclosed to patching of the hole with Dacron or a pericardial patch.

Anomalous pulmonary venous connections are baffled to the LAthrough the sinus venosus defect when such anomalous veins arepresent.

For ostium secundum ASDs, percutaneous closure by use of a

variety of devices is now preferred over surgery. The percutaneousclosure devices often resemble double umbrellas that lock theseptum between the Dacron umbrellas when opened


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PFO

Patients with a PFO may have symptoms related to stroke ortransient ischemic attack (especially if the age is under 55) or havehypoxemia (especially upon standing so called platypneaorthodeoxia).

There are data that suggest that migraine headaches may be morecommon in patients with a PFO, suggesting some unknown

substance normally metabolized in the lung is entering the systemiccirculation through the PFO.

For patients with cryptogenic stroke or transient ischemic attack, itis uncertain whether closure of the PFO, either by open surgical orpercutaneous techniques, has any advantage over anticoagulationwith either warfarin or aspirin. Although there are no data yet

suggesting that PFO closure is better than medical therapy, ongoingrandomized trials should help settle this issue.


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Atrial Septial Defect

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