Ostium Secundum Defect ASD

                        

ASD

Ostium Secundum Defect

Ostium secundum defect, in the region of the fossa ovalis, is the most common form of ASD and is associated with structurally normal atrioventricular (AV) valves. Mitral valve prolapse is rarely an important clinical consideration. Secundum ASDs may be single or multiple (fenestrated atrial septum Large defects may extend

             inferiorly toward the inferior vena cava and ostium of the coronary sinus,

            superiorly toward the superior vena cava, or posteriorly.

Females : males 3:1 in incidence.

Partial anomalous pulmonary venous return, - of the right upper pulmonary vein, may be an associated lesion.

PATHOPHYSIOLOGY.

The degree of left-to-right shunting is dependent on the

            size of the defect,

            relative compliances of the right and left ventricles,

            vascular resistances in the pulmonary and systemic circulations.

In large defects, a considerable shunt of oxygenated blood flows from the left to the right atrium. This blood is added to the usual venous return to the right atrium and is pumped by the right ventricle to the lungs.

In large defects, the ratio of pulmonary to systemic blood flow (Qp:Qs) is usually between 2 and 4:1.

The lack of symptoms in infants with ASDs is due to the structure of the right ventricle in early life - its muscular wall is thick and less compliant, thus reducing the left-to-right shunt.

As the infant becomes older, and pulmonary vascular resistance drops, the right ventricular wall becomes thinner, and the left-to-right shunt across the ASD increases. The large blood flow through the right side of the heart results in enlargement of the right atrium and ventricle and dilatation of the pulmonary artery. The left atrium may be enlarged;

The left ventricle and aorta are normal in size.

the pulmonary arterial pressure is usually normal because of the absence of a high-pressure communication between the pulmonary and systemic circulations.

Pulmonary vascular resistance remains low throughout childhood, - in adulthood - - may result in reversal of the shunt and clinical cyanosis.

CLINICAL MANIFESTATIONS.

child is most often asymptomatic

lesion may be discovered during a physical examination.

In younger children, failure to thrive may be present;

in older children exercise intolerance may be noted. It may go unnoticed by the family until after surgical repair, when the child's growth or activity level increases markedly.

The physical findings of an ASD are

            mild left precordial bulge.

            A right ventricular systolic lift is usually palpable at the left sternal border.

            loud 1st heart sound and sometimes a pulmonic ejection click.

            the 2nd heart sound is characteristically widely split and fixed in its splitting in all phases of respiration. Normally the duration of right ventricular ejection varies with respiration, with inspiration increasing right ventricular volume and delaying the closure of the pulmonary valve. With an ASD, right ventricular diastolic volume is constantly increased and ejection time is prolonged throughout all phases of respiration.

            A systolic ejection murmur is heard; not accompanied by a thrill, is best heard at the left middle and upper sternal border. It is produced by the increased flow across the right ventricular outflow tract into the pulmonary artery, not by low-pressure flow across the ASD.

            A short, rumbling mid-diastolic murmur produced by the increased volume of blood flow across the tricuspid valve is often audible at the lower left sternal border. This finding, which may be subtle and is heard best with the bell of the stethoscope, usually indicates a Qp:Qs of at least 2:1.

LABORATORY DIAGNOSIS.

The chest roentgenogram shows

            enlargement of the right ventricle and atrium depending on the size of the shunt.

            The pulmonary artery is large,

            pulmonary vascularity is increased

            Cardiac enlargement is seen in the lateral view because the right ventricle protrudes anteriorly as its volume increases.

Electrocardiogram –

            volume overload of the right ventricle:

            QRS axis may be normal or there may be right axis deviation,

            minor right ventricular conduction delay (rsR' pattern in the right precordial leads) may be present.

The echocardiogram

            right ventricular volume overload, including increased right ventricular end-diastolic dimension and a flattening and abnormal motion of the ventricular septum.

            The normal septum moves posteriorly during systole and anteriorly during diastole. With right ventricular overload and normal pulmonary vascular resistance, the septal motion is reversed—that is, anterior movement in systole—or the motion may be intermediate so that the septum remains straight.

            The location and size of the atrial defect are readily appreciated by two-dimensional scanning, with a characteristic brightening of the echo image at the edge of the defect (T-artifact).

           

The shunt is confirmed by pulsed and color flow Doppler

cardiac catheterization -- If diagnosis is doubtful, the shunt size cannot be determined reliably from noninvasive tests, or pulmonary vascular disease is suspected, cardiac catheterization confirms the presence of the defect and allows measurement of the shunt ratio and pulmonary pressures.

            The oxygen content of blood from the right atrium will be much higher than that from the superior vena cava.

            This feature may occur with partial anomalous pulmonary venous return to the right atrium, with a ventricular septal defect (VSD) in the presence of tricuspid insufficiency, with AV septal defects associated with left ventricular–to–right atrial shunts, and with aorta–to–right atrial communications (e.g., ruptured sinus of Valsalva aneurysm).

            The pressures in the right side of the heart are usually normal, but small to moderate pressure gradients (<25 mm Hg) may be measured across the right ventricular outflow tract because of functional stenosis related to excessive blood flow.

            The pulmonary vascular resistance is almost always normal.

            The shunt is variable depending on the size of the defect, but it may be of considerable volume (as high as 20 L/min/m2 ).

            Cineangiography, performed with the catheter through the defect and in the right upper pulmonary vein, demonstrates the defect and the location of the right upper pulmonary venous drainage.

Pulmonary angiography demonstrates the defect on the levophase (return of contrast to the left side of the heart after passing through the lungs).

PROGNOSIS AND COMPLICATIONS.

symptoms usually do not appear until the 3rd decade or later.

Pulmonary hypertension, atrial dysrhythmias, tricuspid or mitral insufficiency, and heart failure are late manifestations; these symptoms may first appear during the increased volume load of pregnancy.

Infective endocarditis is extremely rare and antibiotic prophylaxis for isolated secundum ASDs is not recommended.

Postoperative complications, such as late heart failure and atrial fibrillation, are more common in patients who undergo operation after 20 yr of age.

Secundum ASDs may be associated with partial anomalous pulmonary venous return, pulmonary valvular stenosis, VSD, pulmonary arterial branch stenosis, and persistent left superior vena cava, as well as mitral valve prolapse and insufficiency.

Secundum ASDs are associated with the autosomal dominant Holt-Oram syndrome.

TREATMENT.

Surgery is advised for all symptomatic patients and also for asymptomatic patients with a Qp:Qs ratio of at least 2:1.

The timing for elective closure is usually some time after the 1st year and before entry into school.

Closure is carried out at open heart surgery, and the mortality rate is less than 1%.

Repair is preferred during early childhood because the surgical mortality and morbidity are significantly greater in adulthood; the long-term risk of arrhythmia is also greater after ASD repair in adults.

Occlusion devices, implanted transvenously at cardiac catheterization, are in clinical trials.

In patients with small secundum ASDs with minimal left-to-right shunts, the consensus is that closure is not required.

The results after operation in children with large shunts are excellent. Symptoms disappear rapidly, and physical development frequently appears enhanced. The heart size decreases to normal, and the electrocardiogram shows decreased right ventricular forces. Late arrhythmias are less frequent in patients who have had early repair.