Cardiothoracic & Oesophageal Surgery by Mike Poullis

Atrial Septal defects

Formation of the atrial septum occurs with the occurrence of two components. The septum primum grows from the cranial portion of the primitive atrium and fuses with the endocardial cushions. The second portion or the septum secundum grows from the posterosuperior aspect of the atrium to the right of the primum septum. The septum secundum covers the defect in the inferior aspect of the septum primum known as the ostium primum.The septum secundum does not fuse with the endocardial cushions. The superior portion of the primum septum then degenerates and when covered by the s.secundum forms the foramen ovale. Types of ASD according to Edwards- Secundum type-level of the fossa ovalis Sinus venosus type-associated with anomalous return of right upper pulmonary vein Ostium primum ASD posterior to fossa ovalis Raghib type-absent coronary sinus with Left SVC connection to left atrium. Multiple coalescent defects-essentially forming common atrium
Incidence	10 percent CHD, 3:2 male:female
Age at Presentation	Variable according to type. May be asymptomatic into adulthood.
Clinical	Murmur on preschool physical exam. Cyanosis in the Raghib type. Adult with ASD and Rheumatic mitral valve disease=Lutenbacher syndrome. Auscultation shows wide fixed splitting of the P2 sound with pulmonary flow murmur.
Pulmonary Vasculature	Normal to increased
Radiologic Findings	Secundum type ASD Prominent central PA's Peripheral pruning of vessels with pulmonary hypertension Prominent RV outflow tract may encroach on the retrosternal space Left atrium NOT enlarged because the LA can decompress into RA via the defect. Angiography-presence of mixing at the atrial level is inferred when an indistinct left atrial border is observed on the levophase of a right ventricular injection.
Associations	Holt Oram syndrome Autosomal Dominant Upper extremity bony ray anomalies
Complications	Eisenmenger's Syndrome
Other associated Congenital Heart Defects	Left SVC to coronary sinus-10 percent PAPVR to RA or SVC with sinus venosus type Mitral valve prolapse-30 percent
Treatment	Surgical closure

Embryology

The atrial septum develops from a combination of the septum primum and septum secundum. The primum septum grows from the superior roof of the atrium towards the endocardial cushions (atrioventricular valves) from the fourth week of embryonic life. There is a gap or ostium primum between the inferior margin of the primum septum and the endocardial cushions. Before fusion of the primum septum with the endocardial cushions, a second opening, the ostium secundum, appears in the primum septum. Between week 5 and 6 of cardiogenesis, the septum secundum develops with 2 limbs, the inferior of which fuses with the lowest portion of the atrial septum joining with the endocardial cushions. There is an opening in the septum secundum called the foramen ovale, which lies immediately to the right of the septum primum and may result in a right to left communication between the atria. After birth, the two septa fuse in the region of the foramen ovale, however in 25-30% of normal hearts there is incomplete fusion of the flap of the septum primum and secundum with a patent foramen ovale with the potential for a right to left shunt and paradoxical embolism.

Genetics: Holt-Oram syndrome is associated with autosomal dominant inherited ASDs with absent or hypoplastic radii, and ECG findings of 1st degree AV block and RBBB. There is 100% penetrance with this disorder and approximately 40% of cases represent new mutations.

Patent Foramen Ovale

Introduction

Background: Patent foramen ovale is an anatomical interatrial communication with potential for right-to-left shunt. Foramen ovale has been known since the time of Galen. In 1564, Leonardi Botali, an Italian surgeon, was the first to describe the presence of foramen ovale at birth. However, the function of foramen ovale in utero was not known at that time. In 1877, Cohnheim described paradoxical embolism in relation to patent foramen ovale.

Pathophysiology: Patent foramen ovale is a flaplike opening between the atrial septa primum and secundum at the location of the fossa ovalis that persists after age 1 year. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting. Once the pulmonary circulation is established after birth, left atrial pressure increases, allowing functional closure of the foramen ovale. This is followed by anatomical closure of the septum primum and septum secundum by the age of 1 year.

The Mayo Clinic autopsy study revealed that the size of a patent foramen ovale increases from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life, as the valve of fossa ovalis stretches with age.

With increasing evidence that patent foramen ovale is the culprit in paradoxical embolic events, the relative importance of the anomaly is being reevaluated. James Lock, MD, has postulated that patent foramen ovale anatomy results in a cul-de-sac between the septa primum and secundum, predisposing individuals to hemostasis and clot formation. Any conditions that increase right atrial pressure more than left atrial pressure can induce paradoxical flow and may result in an embolic event.

This reasoning has greatly altered the previous conception of patent foramen ovale and is changing current management of the condition.

Frequency:

In the US: Patent foramen ovale is detected in 10-15% of the population by contrast transthoracic echocardiography. Autopsy studies show 27% prevalence of probe-patent foramen ovale. This difference is probably due to the ability to directly visualize patent foramen ovale on autopsy study, while contrast echocardiography relies on detection of secondary physiologic phenomena.

Clinical

History: Most patients with isolated patent foramen ovale are asymptomatic. Patients may have a history of stroke or transient ischemic event of undefined etiology.

Physical: No abnormal cardiac clinical findings are associated with isolated patent foramen ovale.

Workup

Lab Studies:

No specific lab tests are necessary to diagnose patent foramen ovale.

Imaging Studies:

Echocardiography

In some instances, patent foramen ovale is detectable with color flow Doppler imaging. A small "flame" of color signal may be seen in the middle region of the atrial septum.

Contrast echocardiography usually is required to detect small patent foramen ovale. After obtaining optimal visualization of the atrial septum on transthoracic or transesophageal echocardiography, a bolus of agitated saline is injected into an antecubital vein. Subsequently, microbubbles appear in the right atrium. The study is positive for patent foramen ovale if the microbubbles appear in the left atrium within 3 cardiac cycles of their appearance in the right atrium. Valsalva maneuver increases right atrial pressure and facilitates right-to-left shunting.

Transesophageal contrast echocardiography provides superior visualization of the atrial septum and therefore is preferred to transthoracic contrast echocardiography for detecting patent foramen ovale. When clinically indicated, transesophageal contrast echocardiography is strongly recommended for patients whose findings on transthoracic echocardiography are negative.

Other Tests:

No specific electrocardiographic findings are noted in patent foramen ovale.

Treatment

Medical Care: Most patients with a patent foramen ovale as an isolated finding receive no special treatment. No consensus exists on treatment of patent foramen ovale in patients with transient ischemic attack or stroke.

When patent foramen ovale is associated with an otherwise unexplained neurologic event, traditional treatment has been antiplatelet (ie, aspirin) therapy alone in low-risk patients or combined with warfarin in high-risk individuals to prevent cryptogenic stroke. With administration of warfarin, the international normalized ratio (INR) is maintained at 2-3. Consultation with a neurologist is mandatory to direct this treatment.

The recurrence rate of stroke or transient ischemic attack has been reported to be as high as 3.4-3.9% per year.

In patients with atrial septal aneurysm and patent foramen ovale, the risk of first recurrent stroke within 2 years has been reported to be as high as 9%, while the rate of subsequent stroke or transient ischemic attack recurrence within 2 years increases to 22%.

Surgical Care: Surgical closure of patent foramen ovale with double continuous suture has resulted in elimination of residual shunt across the patent foramen ovale.

Surgical therapy: Although relatively simple, surgical therapy is invasive, costly, and painful, and is associated with all the usual risks of cardiac surgery.

Catheter-based treatment

Closure of patent foramen ovale during cardiac catheterization is an emerging therapeutic option for patent foramen ovale.

Strict guidelines dictate patient selection for catheter-based intervention; the criteria include recurrent cryptogenic stroke due to presumed paradoxical embolism through patent foramen ovale and failure of conventional drug therapy. The procedure requires a hospital stay of 24-48 hours and prophylactic aspirin or warfarin for 6 months following the procedure. After more than 5 years of follow-up observation, the results are promising.

Follow up

In/Out Patient Meds:

Aspirin or warfarin is required for 6 months following closure of patent foramen ovale during cardiac catheterization.

Complications:

Complications of catheter-based closure of patent foramen ovale, such as embolism of device, device entrapment within the Chiari network, frame fracture, vessel damage, or perforation of atrial wall, may require further surgery.

Other possible complications include air embolism during device delivery, thrombus formation around the device, and infective endocarditis.

Miscellaneous

Medical/Legal Pitfalls:

Patent foramen ovale often is considered in the differential diagnosis of cryptogenic stroke. At present, no consensus guidelines exist for the treatment of patent foramen ovale. The following issues remain unsettled:

Treatment of asymptomatic patients with patent foramen ovale

Duration of medical therapy after stroke or transient ischemic event

Optimal time to close patent foramen ovale

In the setting of patent foramen ovale, risk of stroke recurrence is not trivial. Risk associated with long-term anticoagulation is also not trivial. Surgical closure reduces the risk of stroke recurrence from patent foramen ovale and reduces the need for anticoagulation. Catheter-based techniques are an emerging option for closing patent foramen ovale.

Special Concerns:

Misconceptions: Clinicians must know what a patent foramen ovale is and what it is not.

The defect in patent foramen ovale is not a result of missing tissue; therefore, very specific hemodynamics must be present (ie, right atrial pressure exceeding left atrial pressure) for shunting to occur.

Patent foramen ovale is not associated with an increased risk of endocarditis. Antibiotic prophylaxis is not indicated.