Embryology Gestational Week 4 Gestational Week 4-6 Gestational Week 4 Gestational Week 4-6 A thin, crescent shaped wedge of tissue of (septum primum) grows towards and fuses with endocardial cushions. The remaining opening is called the ostuim primum. The remaining opening is called the ostuim primum. As the septum primum is growing down, the endocardial cushions fuse and the ostium primum is eventually obliterated.
Embryology The interatrial septum forms during the first and second months of fetal development. fetal developmentfetal development Stage I is the formation of the septum primum. septum primum septum primum The septum primum walls off a crescent-shaped portion of the hole between the right and left atria. Foramen primum (also called the ostium primum) stays open oramen primumostium primumoramen primumostium primum The remaining part of the opening between the right and left atria is closed by the septum secundum. septum secundumseptum secundum The 2 tissue layers overlap like a flap, allowing blood flow to continue during fetal life. Changes in circulation at birth, closes the flap permanently. birth
Anatomy and Physiology Extends from cavo- atrial junction with superior and inferior vena cavae Ends near the atrio- ventricular canal near the tricuspid valve
Ostium Secundum Most common type of ASD Center of the septum between the right and left atrium Variant of this type of ASD is called a Patent Foramen Ovale (PFO) which is very small.
Ostium Primum Next most common type Located in the lower portion of the atrial septum. Will often have a mitral valve defect associated with it called a mitral valve cleft. A mitral valve cleft is a slit-like or elongated hole usually involves the anterior leaflet of the mitral valve.
Sinus Venosus Least common type of ASD Located in the upper portion of the atrial septum. Association with an abnormal pulmonary vein connection Four pulmonary veins, two from the right lung and two from the left lung, normally return red blood to the left atrium. Usually with a sinus venosus ASD, a pulmonary vein from the right lung will be abnormally connected to the right atrium instead of the left atrium. This is called an anomalous pulmonary vein. ..\asd-veno.jpg..\asd-veno.jpg
Foramen Ovale Remnant of fetal circulation Behaves like flap valve Opens during increased intra- thoracic pressure
Incidence and Prevalence one of the most common congenital heart defects seen in pediatric cardiology 7-10% of all patients with congenital heart disease Twice as frequent in females than males
Shunt Determination Normally… Pulmonary Blood Flow = Systemic Blood Flow Shunt Suspected If…Shunt Suspected If… Pulmonary Artery Saturation >80% (?Left-Right) Unexplained Arterial Saturation less than 93% (Right to Left) may also see in Pulmonary Edema, Pulmonary Disease, over sedation and cardiogenic shock Types of Shunts Systemic Circulation to Pulmonary Circulation Left to right Pulmonary Circulation to Systemic Circulation Right to Left
Principles of the Oxymetric Method Blood Sampling from various chambers to determine Oxygen Saturation Left to Right Shunt is present when a significant increase in blood oxygen saturation is found between 2 right sided vessels or chambers
Oximetric Method “Shunt Run” is performed if a difference of 8% or more is noted in blood sampling between chambers Blood samples taken from all right sided locations: IVC, SVC, Right Atrium, Right Ventricle and Pulmonary Artery In case of Inter-atrial shunt multiple samples should be collected from the High, middle and low right atrium
Saturation Run Obtain Samples from… –IVC: High and Low –SVC: High and Low –Right Atrium: High, Middle and Low –Right Ventricle: Inflow and Outflow tracts, mid-cavity –Pulmonary Artery: Main, Left or Right Localizing Right to Left Shunts one should also obtain…. –Pulmonary Vein –Left Atrium –Left Ventricle –Distal Aorta
Fick Equation to Calculate Oxygen Content Assumes in steady state that… that rate of substance entering (C in x Qflow) is equal to the rateof substance leaving (C out x Qflow) + the rate at which indicator, V, is added. (C out x Qflow) + the rate at which indicator, V, is added. Flow= Oxygen consumption/Arterial- Venous oxygen content difference Flow= Oxygen consumption/Arterial- Venous oxygen content difference Where oxygen content is determined by automated methods oxygen consumption is assumed based on patient’s age, gender and body surface area when not directly measured
Shunt Quantification Pulmonary Blood Flow Oxygen consumption _________________________________________ Difference in oxygen content across pulmonary bed (PvO2-PaO2) Systemic Blood Flow Oxygen Consumption _________________________________________ Difference in oxygen content across systemic bed (SaO2- MvO2) Effective Blood Flow: Fraction of Mixed Venous blood received by the lungs without contamination from shunt Oxygen Consumption __________________(PvO2-MvO2)
Flamm Formula Average Oxygen Content in Chambers proximal to the Shunt Method to calculate Mixed Venous Oxygen content Need to factor in Contribution from IVC and SVC which is not equal Flamm Equation: 3xSVC Oxygen Content + IVC Oxygen Content ______________________________________4
In the Absence of Shunt PBF=SBF=EBF
How Significant is the Shunt? Flow Ratio PBF/SBF 2.0 or more = Large Left to Right Shunt 1.0 or less= Net Right to left Shunt No need to measure Oxygen consumption Since this number will cancel out of the equation
Indicator Dilution Method More Sensitive for smaller shunts Cannot localize the level of left to right shunt Left to Right : Dye (indocyanine green) is injected into pulmonary artery and a sample is taken from the systemic artery Right to Left: dye injected just proximal to the presumed shunt and blood sample is taken from systemic artery
Interpretation of Indicator Dilution Method
Eisenmenger Syndrome defect in the septum between the atria increased flow through the lungs after birth. eventually result in pulmonary hypertension. The first indication of this may be a reduction in heart size –flow overload is converted to a pressure overload ( to which the heart responds with hypertrophy, rather than dilatation ). Reduction in heart-size, pressure overloadpressure overload As the left-to-right shunt is converted by reversal of flow across the septum to right-to-left shunt, the patient becomes cyanotic from mixing of un-oxygenated blood. Cyanosis is thus a late feature of Atrial Septal defect. If cyanosis is present from birth, ASD will be complicated by one or more contributions: –Pulmonary Stenosis. –Patent Ductus, usually causes a very large pulmonary artery and enlargement of the aorta. –Common Atrium, allowing complete mixing of oxygenated and unoxygenated blood. –Truncus arteriosus, complete mixing at aortic level.
Pregnancy and ASD Well tolerated after closure Increased risk of paradoxical emboli peri and post partum Contraindicated in Eisenmenger Syndrome –Maternal mortality 50% –Fetal Mortality 60%
TTE and ASD Transthoracic echocardiogram four chamber view to evaluate atrial septal defect. Note presence of inter-atrial communication between left and right atrium.
Indications for Intervention Asymptomatic Children –Right Heart dilation –ASD> 5mm –No signs of Spontaneous Closure Older Patients –Hemodynamically insignificant ASD with Qp/Qs<1.5 if concern for stroke Pulmonary Hypertension –PA pressures> 2/3 systemic arterial resistance –Pulmonary artery reactivity with vasodilator challenge –Reversible changes on lung biopsy Net L->R Shunt of 1.5:1
Treatment Options 1976, King et al published the first attempt to close an ASD with a double umbrella device Size of the sheath was 23 Fr Primary Method of to date for closure is surgical Recent advances in interventional closure techniques
Trans-catheter Closure Technique Implantation of one or more devices via catheter method Eliminates need for cardio-pulmonary bypass No need to stop the heart with cardioplegic agents
Patient Selection Strict Food and Drug Administration guidelines Efficacy measured using data from strict follow up Follow-up at regular intervals- 3, 6, and 12 months the year following the initial procedure Any adverse events require follow up for 5-7 years
Patient Selection Defects smaller than 20-25mm in diameter Should not have defects in the very upper or lower portions of the septum Ostium Primum or Sinus Venosus, not good candidates because defect usually involves heart valves or abnormal venous drainage from the lungs Only benefit Ostium Secundum defects No lower age limit, but must weigh more than 8-10 kg
Trans-catheter Approach Device is advance through an introducer sheath One- Half of the device is deployed on left side of atrial septum, the second half is deployed on the right side A “sandwich” is formed over the defect 6-8 weeks, device as a frame work for scar tissue to form In children the new tissue formation with continue to grow
TTE post Intervention Transesophageal echocardiogram showing Amplatzer device placed across the defect forming a “sandwich” over the atrial septal defect
TTE after intervention Transthoracic echocardiogram four chamber view one day after Amplatzer device placement
Complete resolution of shunt Transthoracic echocardiogram one day after Amplatzer device placed with highlighted area that shows no further shunting of blood across atrial septum.
Tissue formation over Helex device in canine model In vivo tissue response demonstrating flat profile, conformance to the septum, and nonthrombogenic Occluder material; top photo shows left atrial view; bottom photo shows right atrial side view.
Amplitizer Atrial Septal Defect Occluder AGA Medical, Golden Valley Mn FDA approved for Secundum lesions Nitinol mesh frame work and left/right atrial disks Filled with poly-fabric to promote thrombosus Cost $11K, Surgery$ 21K
Helex atrial septal defect device. W.L. Gore & Associates July 1999 Nitinol, nickel/titanium alloy Wire frame in shape of coil with Gore-Tex 9 Fr introducer sheath Cost: $6000
Helex Septal Occluder Delivery System components
Helex Septal Occluder Device components
Outcomes Amplatzer study 100 children and adults –Mean age 13.3 –93 patients successful implantation –Occlusion rate at 3 months total occlusion –Improve RV and LV function and decreased LA volumes Percutaneous Closure and Functional Capacity –32 adults mean age 43 yo –Qp/Qs 2.0+ –6 months-improved O2 uptake with exercise as compared pre-closure status
Comparison to Surgery Study of children and young adults Median age 9.8 y 442 underwent Amplatzer placement 154 underwent surgery Success rate 100% surgery, 96 % Amplatzer Complication 7% Amplatzer, 24 % surgery
Complication of Percutaneous Intervention Early –Device Embolization –A. Fib, SVT –Heart Block –Pericardial Effusion –Groin Hematoma –Device Fractures –Cardiac Perforation Device Erosion Sudden Death
Participation in sports th Bethesda Conference on Eligibility Recommendations for Competitive Athletes with Cardiovascular Abnormalities… Small defect no Pulmonary HTN partcipate in all sports Large Defect, normal PA pressures all competative sports Moderate to large ASD and Pulmonary HTN sever- no competative sports ASD and mild Pulmonary HTN Low intensisty sports
Follow Up 3-6 months post intervention –May participate in sports if no Pulm HTN, Heart Block, or Myocardial Dysfunction –Exercise evaluation if these conditions exist –American Heart Association, no endocarditis prophylaxis post corrrection of ASD unless patient has MR or MV malformation
Follow Up Aspirin and Plavix 6 months post percutaneous closure