Anatomical and Pathophysiological Basics

An atrial septal defect (ASD) is present when, secondary to a structural defect, there is a broad connection between the right and left atria. Atrial septal defect is differentiated from persistent foramen ovale, which is not hemodynamically relevant.

The shunt causes volume overload of the right heart, as the shunt volume is added to the effective cardiac output, which flows to the right atrium from the caval veins. As a result of this volume overload there is dilatation of the right atrium as well as dilatation and hypertrophy of the right ventricle. Both end-diastolic volume and stroke volume of the right ventricle are therefore larger than in the left ventricle. At the same time there is increased perfusion of the lungs, which with midatrial septal defect can be two to three times the cardiac output of the systemic circulation and in extreme cases can rise five- to six-fold.

If there are aberrant pulmonary veins, the size of the left-to-right shunt is determined by the vessel diameter and/or by the size of the drainage area of the pulmonary veins.

Indication

Atrial septal defects can usually be diagnosed by auscultation and by echocardiography. The precise anatomy and morphology of the defects can be determined best with transesophageal echocardiography with contrast administration and cardiac MRI; three-dimensional reconstruction of the findings facilitates the planning of an occlusion. If the diagnosis is unambiguous, cardiac catheterization solely to ascertain the diagnosis is therefore not required.

However, catheterization is indicated if severe pulmonary hypertension (Eisenmenger reaction) or other associated cardiac or vascular defects are suspected. In addition, in older patients and patients with coronary risk factors, coronary angiography should be performed before planned surgery or intervention.

Goals

Demonstration of the location of the defect by direct catheterization

Quantitative determination of the shunt volume and shunt direction

Determination of the pressures in the right ventricle and pulmonary vasculature as well as the pulmonary vascular resistance

Pharmacological provocation (oxygen, nitrates, iloprost, etc.) if required

Evaluate for aberrant pulmonary veins

Evaluate for mitral regurgitation in mitral valve prolapse or in ostium primum defect

Evaluate for additional intracardiac defects

Procedure

Venous and arterial puncture

Pressure measurement in the pulmonary and systemic circulation

Oximetry run in the pulmonary circulation

Arterial oximetry

Catheterization of the defect

Catheterization of aberrant pulmonary veins (if required with pulmonary angiography)

Left ventriculography

Coronary angiography if required

Calculation of pulmonary vascular resistance

– At rest and

– After therapy with inhalation of pure oxygen for 7 to 10 min or (better)

– After pharmacological provocation with inhaled iloprost

Findings on Cardiac Catheterization

Catheterization

With access via the femoral vein the atrial septal defect of the secundum type can be catheterized relatively easily (e.g., with a multipurpose or Swan-Ganz catheter). The level of the catheter crossing from the right to the left atrium can be used to differentiate between ostium secundum, ostium primum and sinus venosus defect. It also needs to be noted whether an ASD II can be crossed at several locations (evidence for a multiperforated septum).

A multipurpose catheter is suitable to engage an aberrant pulmonary vein; with this the superior vena cava and the right atrial wall can be thoroughly and carefully scanned. If necessary the aberrant pulmonary veins can be directly catheterized and also visualized by contrast administration.

However, it is also possible that in large atrial septal defects there only appears to be an aberrant pulmonary vein, as in this case the right-sided pulmonary veins run regularly into the left atrium immediately next to the border of the defect and thus can be easily catheterized when searching for a partial anomalous pulmonary venous connection from the right atrium. This can easily lead to misdiagnoses, which can be avoided by pressure recording during catheter pullback from left atrium to right atrium or by angiographic imaging of the pulmonary vein. Reliable imaging of the pulmonary veins is possible in all cases with cardiac CT and cardiac MRI.

Pressures

With a small atrial septal defect the normal characteristics of the atrial pressure tracings are preserved. With larger defects the v-waves of both atrial pressure tracings become more similar to each other due to the equalization of the diastolic pressure. The higher a-wave in the left atrium is mostly preserved.

Systolic pressure in the right ventricle is often increased. Across the pulmonary valve there is a moderate, flow-induced pressure gradient of 10 to 30 mm Hg as a sign of the functional pulmonary stenosis due to the shunt volume. Pulmonary vascular resistance is calculated to exclude or classify the severity of pulmonary hypertension.

Oximetry

For practical purposes it is usually sufficient to determine the shunt volume as a percentage of the systemic cardiac output. It can be calculated directly from the oxygen saturation values with the following equation:

where:

% O_2PA = oxygen saturation in the pulmonary artery in %

% O_2art = oxygen saturation in the arterial blood in %

% O_2ven = oxygen saturation in the mixed-venous blood in %

It is worth repeating that the sensitivity of the oxygen method is limited and therefore shunt volumes less than 20 % of the cardiac output are not reliably detected. In contrast, the flat course of the oxygen binding curve at higher levels of oxygen saturation results in inaccurate determinations of larger left-to-right shunts, which can be considerably overestimated.

With large left-to-right shunts the oxygen sample from the inferior vena cava should be taken quite caudally, as the pulmonary venous blood can flow across the atrial septal defect into the inferior vena cava as far caudally as the diaphragm. Higher oxygen saturations in the superior vena cava as compared with the inferior vena cava are found in partial anomalous pulmonary venous connection into the superior vena cava.

There is contrast medium flow from the left atrium into the usually enlarged right atrium, with a large left-to-right shunt as far as the inferior vena cava. However, the typically very high cardiac output in the pulmonary circulation leads to a marked dilution of the injected contrast medium, which significantly limits the interpretability of the angiographic images.

Due to the good diagnostic capabilities of modern noninvasive imaging modalities (echocardiography and cardiac MRI), direct angiographic imaging of the defect is required only in exceptional cases.

Interpretation of Findings and Patient Management

The decision whether to occlude the defect (interventionally or surgically) or “watch and wait” with regular follow-up depends on the following factors:

Shunt volume (Q_pulm/Q_syst > 1.5 as indication for occlusion)

The extent of pulmonary hypertension

The patient’sage

The patient’s symptoms

Anatomical and Pathophysiological Basics

Ventricular septal defect (VSD) is the most frequent congenital heart defect in children. In ~25 % of cases the VSD is an isolated defect; in ~30 to 50 % it is combined with other congenital heart defects. VSD also represents ~20 % of congenital defects first diagnosed in adults. Nowadays the initial diagnostic work-up is usually done in infants. In about one-third of cases the defect closes spontaneously during the first years of life.

The most frequent cause of acquired VSD