FOCUS: Atrial Septal Defects — Structural Heart Disease in Adults

Department of Pediatrics, Division of Pediatric Cardiology, The University of Texas-Houston Medical School/Children’s Memorial Hermann Hospital, Houston, Texas E-mail: p.syamasundar.rao@uth.tmc.edu

_________________________________

J INVASIVE CARDIOL 2009;21:A6–A10
There are three major types of atrial septal defects (ASDs) and these include ostium secundum, ostium primum and sinus venosus defects. ASDs constitute 8–13% of all congenital heart defects. In the ostium secundum ASD, there is a pathological deficiency of septal tissue in the region of the fossa ovalis, and these defects may be small or large. In the majority of instances, these are single defects, though occasionally, multiple defects and fenestrated defects may also be present. Because of left-to-right shunting across the defect, the right atrium and right ventricle are dilated and somewhat hypertrophied. Similarly, the main and branch pulmonary arteries are also enlarged. Pulmonary vascular obstructive changes are not usually seen until adulthood. While most children and adolescents are largely asymptomatic, adult subjects tend to be symptomatic, presenting with exertional dyspnea, decreased exercise tolerance or palpitations. Because of atrial dilatation, they may have episodes of supraventricular tachycardia, atrial fibrillation or flutter; also, tricuspid valve regurgitation, pulmonary hypertension or right heart failure may be present. Ostium primum ASDs are within the family of endocardial cushion defects and almost always feature a cleft in the mitral valve causing mitral regurgitation. Apart from the defect being close (adjacent) to the atrioventricular valve, the mitral cleft (regurgitation) needs to be addressed. With current technology, surgical therapy is the only available option. Sinus venosus defects have an associated partial anomalous pulmonary venous connection either to the superior vena cava or the right atrium. Surgical diversion (baffle) of the anomalous vein into the left atrium is necessary at the time of surgical repair of the defect and is not amenable to transcatheter closure. A patent foramen ovale (PFO) may be present in 25–30% of the normal population and does not require treatment unless associated with presumed paradoxical embolism, platypnea-orthodeoxia syndrome, migraine, decompression illness and severe hypoxemia secondary to right-to-left shunting (though PFO) in patients with right ventricular infarction or elevated pulmonary artery pressures due to pulmonary embolism, pulmonary parenchymal disease or other causes. Considerations related to the closure of PFOs are entirely different from those for the closure of ostium secundum ASDs. This issue of the Journal primarily focuses on ostium secundum ASDs in adult subjects, although one paper reporting complications associated with PFO closure is included. Following the description of surgical closure of an ASD in the early 1950s, it rapidly became the standard treatment for atrial defects. Surgical closure of an ostium secundum ASD is safe and effective, with negligible mortality, however, the morbidity associated with sternotomy/thoracotomy, cardiopulmonary bypass, postoperative complications and residual surgical scarring cannot be avoided. Presumably for these and other reasons, several groups of cardiologists embarked upon the development of transcatheter methods to close ASDs. The studies by King, Rashkind and their associates in the 1970s demonstrated the feasibility of transcatheter ASD closure with King and Mill’s device and the hooked Rashkind device, respectively. Subsequently, a number of other ASD occlusion devices were designed and investigated. The devices were initially tested in animal models, followed later by clinical trials in human subjects. These devices include: King and Mill’s device (1976); the hooked Rashkind device (1977); the double-disk Rashkind device (1983); the clamshell occluder (1990); the first-, second- and third-generation buttoned devices (1990); the ASDOS (ASD occlusion system) (1991); the modified Rashkind patent ductus arteriosus umbrella device (1994); the inverted buttoned device (1997); the Das^™ Angel Wings occluder device (1998; Microvena Corp., White Bear Lake, Minnesota); the Amplatzer Septal Occluder (1998; AGA Medical Corp., Golden Valley, Minnesota); the CardioSEAL^® and STARFlex^® devices (1998; NMT Medical, Inc., Boston, Massachusetts); the fourth-generation buttoned device (2000); the Gore Helex^® Septal Occluder (2000; W.L. Gore, Flagstaff, Arizona); the COD (centering-on-demand) buttoned device (2001); and the transcatheter patch (2002). Other devices, including the Nitocclud PFO (pfm AG, Köln, Germany); the BioSTAR^® bioabsorbable septal repair implant (NMT Medical); the Occlutech (Occlutech, Helsingborg, Sweden); the Solysafe device (Swissimplant, Solothurn, Switzerland); and the Heart R Septal Occluder (manufactured in China), are more recent entries. A number of other devices are currently in FDA-approved (under Investigational Device Exemption) clinical trials in the U.S. and in local IRB-approved clinical trials in other countries. At present, only two devices, namely, the Amplatzer septal occluder and the Gore Helex septal occluder are approved by the FDA for general clinical use to close ASDs. The Amplatzer septal occluder is the most commonly used ASD closure device worldwide. Because of its more recent approval, the experience with the Helex device is limited. In this issue of the Journal, Al-Hindi and associates (Rush University Medical Center, Chicago, Illinois) and I (University of Texas-Houston) present articles that discuss issues regarding closure of ostium secundum ASDs in adults. Although there is some overlap, my review article discusses transcatheter closure of ASDs in adults, while Al-Hindi and colleagues focus on the elderly population. Based on extensive review of the literature, I have concluded that adults with untreated ASDs tend to have decreased event-free survival rates when compared to the normal population, and that surgical closure of ASDs is safe and effective with high event-free survival rates. Furthermore, the closure of ASDs prevents functional deterioration, improves cardiac function and increases functional capacity, and the earlier the closure is undertaken, the better the long-term prognosis. My review article concludes, therefore, that adults with hemodynamically significant ASDs, irrespective of symptoms, should undergo ASD closure. A comparison of surgical closure with device closure revealed similar effectiveness, but device closure appears to confer less morbidity. Of the many devices that have been designed and tested, only two are approved by the FDA for clinical use. I have described the method of implantation of the Amplatzer septal occluder in some detail, followed by addressing issues related to the management of complex forms of ASDs. In addition to discussing the indications for ASD closure, available devices, comparison with surgery, procedural details, anticipated benefits from transcatheter closure, and complications associated with ASD closure, Al-Hindi et al address an important clinical challenge, namely, the reduced diastolic elasticity of the left ventricle, which is particularly seen in the elderly, and causes restrictive filling of the left ventricle. The authors note that ASDs provide a decompressive effect, preventing high left ventricular end-diastolic pressure. When the ASD is closed, the pop-off mechanism no longer exists. The patients may develop pulmonary edema and may require prolonged mechanical ventilation and inotropic support. If the baseline left atrial pressure is higher than 15 mmHg, they recommend temporary balloon occlusion of the defect for 10–15 minutes and remeasuring the left atrial pressure (or pulmonary artery wedge pressure). If the pressure increases by more than 5 mmHg, the authors suggest not closing the defect at that sitting and treating the patient with afterload-reducing agents and diuretics for 1–2 weeks. Balloon occlusion left atrial pressures are remeasured and if the pressure does not increase by more that 5 mmHg, device occlusion of the ASD may be undertaken. If the pressure continues to be high, a fenestrated device may be used. Bijulal et al, from Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, India, describe thrombotic complication in a 22-year-old patient during attempted closure of a large ASD. They used a 12 Fr sheath for device delivery. Because of prolapse of the device, five different unsuccessful attempts were made to implant the device. In the transesophageal echocardiography (TEE) prior to considering use of a larger device to oversize the defect, they noted a 15 mm x 10 mm thrombus at the superior vena cava-right atrial junction. Due to a concern for thrombus dislodgement and embolization, they immediately sent the patient for surgical repair. The authors appear to have anticoagulated the patient adequately. They discuss the reasons for the peculiar location of the thrombus as well as the causes of thrombus formation, but were unable to come up with a valid explanation. In the final paper in this section, Schoen et al report two patients (ages 31 and 25 years) who underwent PFO closure using the Intrasept PFO closure system (Cardia, Inc., Eagan, Minnesota) for the prevention of recurrence of paradoxical embolism. On routine follow-up TEE 1 and 3 months later, respectively, the patients were found to have an aorta-to-right atrial fistula due to perforation of the aorta with the struts of the device. The findings were confirmed by magnetic resonance imaging and subsequently at surgery. The struts were surgically removed and the defect closed with a felt or pericardial patch. Both patients recovered rapidly and were discharged at 6 and 7 days, respectively, after surgery, in good condition. The authors estimate an incidence of 0.05% of this complication with this device at their center. They suggest that this potential complication should be considered in the decision-making process for device closure of PFOs. The focus on ASDs in this issue includes a great deal of information on percutaneous closure of ASDs in adults that I hope is useful for the reader. The reported complications emphasize the need for continued diligence by the interventionalist in order to improve the chances of successful outcomes.