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2. Anatomy of the ventricular septum The anatomy and location of VSD's not infrequently causes confusion among adult cardiologists due to the inaccurate use of terminology. The most common defects are perimembranous VSDs, which are located underneath the aortic valve in the left ventricular outflow tract, with an opening on the right ventricular side incorporating the membranous septum, which is located in mid-superior portion of the septum closely related to the tricuspid valve and crux of the heart. These defects, also termed “infracristal VSDs”, account for about 80% of all VSDs and can extend into the inlet or outlet portions of the ventricular septum. Closely related to these defects are the classical inlet-type VSDs which account for about 5-8% of all congenital VSDs. These defects are located more posterior underneath the tricuspid valve and in their classical form are completely surrounded by muscular septal tissue. However, in practice the perimembranous and the inlet-type VSD are often confluent and difficult to distinguish. A rare form of VSDs (5-7%) are those located superior directly underneath the pulmonary valve (subpulmonary) within the conus/infundibular ventricular septum in the outlet portion of the right ventricle. These defects, unless very large, are not related to the tricuspid valve and are associated with fibrous continuity of the aortic and pulmonary valve. They have been termed supracristal or doubly-committed VSDs and have an increased risk of developing progressive aortic insufficiency. Muscular VSDs account for 5-20% of all congenital VSDs. Most commonly these defects are located within the apex or mid-muscular septum, whereas anterior or postero-inferior location as well as a multifenestrated ventricular septum (“Swiss cheese” VSDs) is rare. 3. Ventricular septal defects in the adult population VSD's are rare in the adult population without congenital heart disease. Most frequently the adult cardiologist encounters this entity after myocardial infarction. Less commonly the adult cardiologist will encounter these abnormalities as a result of cardiac trauma or iatrogenic, for example after surgical replacement of the aortic valve. These patients are frequently high-risk candidates for surgical closure and the presence of a hemodynamically significant VSD should be considered a relative indication for VSD device closure. The incidence of post myocardial infarction ventricular septal rupture remains as high as 0.2%. Ventricular septal rupture (VSR) is usually observed within 1 week of the initial myocardial infarction (MI) and still carries a poor prognosis. Without surgical or percutaneous VSD closure the mortality exceeds 90% and even with surgical intervention the reported early mortality ranges between 19% and 46%. Cardiogenic shock and inferior myocardial infarcts are poor prognostic factors and the clinical course of post-infarction VSDs is characterized by sudden hemodynamic deterioration even in patients who appear clinically stable, which does not allow much room for conservative management. The outcome of transcatheter closure of post-infarct VSDs has been less favorable than reported results of congenital muscular VSDs. In 2003 Holzer, et al reported a 30-day mortality of 28% in 18 patients in whom transcatheter closure with the Amplatzer post-infarct muscular VSD device was attempted. Szkutnik and colleagues reported a series of 7 patients in whom device closure using the Amplatzer septal occluder (ASO) as well as the Amplatzer muscular VSD device was attempted with one death. However, the procedures were performed in acutely surviving patients between 2 and 10 weeks after the initial myocardial infarct. Complicating factors of transcatheter device closure have been identified as the frequently moribund status of these patients as well as VSD enlargement due to ongoing necrosis of surrounding tissues. This contributes to the residual VSDs which were observed in up to 80% of patients. Another group of patients encountered by the adult cardiologist are patients with a small hemodynamically insignificant VSDs and a secondary history of endocarditis. Device closure in these patients should be considered elective after adequate treatment of endocarditis. 4. Patient selection 4.a. General indications for VSD closure A non-restrictive VSD with pulmonary hypertension in the absence of irreversible pulmonary vascular disease is an absolute indication for closure of the defect. Closure is also recommended in asymptomatic older children and adults with a restrictive VSD but a hemodynamically significant left-to-right shunt (usually Qp: Qs > 1.5: 1), to prevent long-term complications such as pulmonary hypertension, arrhythmias, aortic regurgitation, double chambered right ventricle or endocarditis. A very sensitive tool to evaluate significant left-to-right shunts is transthoracic echocardiography, demonstrating volume loading of left atrium (LA) and/or left ventricle (LV). Further indications for VSD closure are the presence of VSD-related complications, such as subacute bacterial endocarditis (SBE) or the development of aortic regurgitation as a result of aortic cusp prolapse into the VSD. 4.b. Surgical closure versus percutaneous device closure Large non-restrictive ventricular septal defects in either perimembranous or muscular location in small infants will remain the domain of cardiac surgical intervention for some time. A recent study by Holzer and colleagues, reporting the results of device closure of muscular VSDs in 75 patients suggests an increased risks of complications and an increased risk of residual shunts in infants of lower weight at the time of the procedure. However, in older children and adults the results of percutaneous VSD device closure have significantly improved, especially since the introduction of the Amplatzer VSD devices, and this procedure should therefore be considered a suitable alternative to surgical intervention. This is specifically true for muscular VSDs, where the overall mortality and frequency of residual VSDs after surgical VSD closure remains higher than for perimembranous VSDs. These VSDs are frequently hidden within the coarse right ventricular trabeculations, thereby difficult to localize through the standard surgical approach via the right atrium. The recent results of percutaneous closure of perimembranous VSDs using the Amplatzer membranous VSD device have also been encouraging, with closure rates of up to 92% within 1 week of the procedure without any major device related complications. This procedure could therefore be offered as an equivalent alternative to surgical intervention in larger patients. 4.c. Percutaneous approach or perventricular approach Several authors have reported intraoperative device closure of muscular VSD's. However, many of the reports advocated the use of cardiopulmonary bypass to place the device under direct vision. Recently, Bacha and colleagues reported on the “perventricular” approach to close VSDs in the operating room under transesophageal echocardiography (TEE) guidance without cardiopulmonary bypass, using the Amplatzer mVSD device with excellent results. This type of approach is favorable in smaller patients where the size of delivery sheath may be associated with rhythm disturbances and hemodynamic compromise. In addition, patients with concomitant cardiac anomalies requiring surgical correction would benefit from this approach. 5. Pre-procedure evaluation All patients require careful assessment to plan and prepare a successful percutaneous intervention. The indications for VSD device closure need to be reviewed and the patient's pertinent history forms a crucial part of the pre-procedure assessment. Chest X-Ray and electrocardiogram form an important part of the routine assessment. The EKG needs to be analyzed for evidence of ventricular hypertrophy, pre-existing AV block or bundle branch block as well as presence of arrhythmias. The CXR needs to be reviewed for the presence of cardiomegaly, abnormal pulmonary vascular pattern suggestive of pulmonary hypertension or other pulmonary abnormalities. Laboratory investigations, such as renal function, complete blood count or blood grouping can usually be postponed until the day of catheterization but may need to be performed earlier if there is a suggestion of coexisting renal abnormalities. The most important component of the pre-procedure assessment is transthoracic echocardiography. Echocardiographic evidence of a reduced doppler gradient across the VSD (non-restrictive) in the absence of right ventricular outflow tract obstruction, or evidence of LV volume overload, as suggested by an increased LVEDD above the normal reference range, need to be carefully documented. The size, number and locations of all VSD's need to be analyzed. Also, the relationship to cardiac valves and chordal attachments of AV valves needs to be documented. All standard views should be utilized to adequately document the morphology of the VSD(s), with parasternal short-axis view, long axis view and apical 4-chamber view being the most important to evaluate the precise location of the VSD. The parasternal long axis view demonstrates perimembranous VSD's as well as anterior mid-muscular VSDs. The short axis view at the level of the aortic valves facilitates differentiation between perimembranous VSDs (7-12 o'clock) and subpulmonary VSDs (1-2 o'clock). Short axis view at the level near the tip of the mitral valve demonstrates anterior defects between 12-1 o'clock, mid-muscular defects between 9-12 o'clock and inlet defects between 7-9 o'clock. The 4-chamber view at the level of the atrioventricular valves can be utilized to demonstrate apical VSDs, mid-muscular VSDs, inlet-type VSDs as well as perimembranous VSDs. In addition, the 5-chamber view demonstrates high anterior subaortic perimembranous VSDs. For subaortic defects, the margin to the aortic valve needs to be carefully evaluated. A distance of less than 4-5 mm would favour the use of the Amplatzer membranous VSD device, whereas a distance of less the 2 mm would be considered unsuitable for any form of device closure. Supracristal defects are unsuitable for VSD device closure. It is important to document pre-existing valvar regurgitation or Doppler gradients across aortic, pulmonary or AV valves for comparison with post closure echocardiograms. 6. The Amplatzer VSD devices 6.a. General description The group of Amplatzer VSD devices (AGA Medical Corporation, Golden Valley, MN) are made of nitinol wire. Nitinol is an alloy of nickel and titanium. The devices are self-expandable consisting of two flat disks that are linked via a central connecting waist, the diameter of which determines the size of the device. Polyester fabric is incorporated into each disk as well as the waist to enhance thrombosis. 6.b. The muscular VSD device The Amplatzer muscular VSD device has two disks that exceeds the diameter of the connecting waist by 8-mm. The connecting waist itself has a length of 7 mm. The device is available in sizes from 4-18 mm, requiring delivery sheaths size between 6-9 Fr. 6.c. The post-infarct VSD device The Amplatzer post-infarct muscular VSD device is similar in design to the muscular device with two differences: the length of the waist is 10-mm to accommodate the thick septum in adult patients and the disks are 10-mm larger than the connecting waist. The device is available in sizes ranging from 16-24 mm, requiring delivery sheaths size between 9-12 Fr. 6.d. The membranous VSD device The Amplatzer membranous VSD occluder is the most recent addition to the family of Amplatzer VSD devices. The two disks are unequal with the aortic end of the asymmetrical left ventricular disk exceeding the connecting waist (length 1.5 mm) by only 0.5 mm to avoid impingement on the aortic valve, whereas the apical end is 5.5 mm larger than the waist. The apical end of the left ventricular disk contains a platinum marker. The right ventricular disk in contrast symmetrically exceeds the diameter of the connecting waist by 2-mm. The device is available in sizes from 4-18 mm, requiring delivery sheaths size between 7-9 Fr. 6.e. The delivery systems
6.e.i. General The delivery system for muscular and post infarct VSD is identical to that for the Amplatzer septal occluder. It consists of a long Mullins type sheath with its dilator; cable; loader and a pin vise. 6.e.ii. The membranous VSD device The delivery system for the membranous VSD device is similar to that for the ASD with an additional catheter (Pusher) to facilitate correct deployment of the device. The pusher has a metal capsule used to align the flat portion of the screw of the membranous VSD device. This is important for correct orientation of the LV disk. The delivery sheath is braided and has a very tight curve to facilitate positioning in the LV apex. 7. Procedure-protocol and technique 7.a. General technique
7.a.i. Preparation 7.b. Technical and anatomical considerations
The techniques described below have been reported in great detail by Hijazi and colleagues as well as Thanopoulos and colleagues. All procedures should routinely be performed under general anaesthesia for patient comfort during TEE monitoring and to avoid patient movements during crucial parts of the device delivery process. An initial complete assessment is performed to re-evaluate and reconfirm the anatomic details previously obtained by transthoracic echocardiography. Multiple views should be applied to exactly evaluate the VSD size, such as transgastric, frontal 4-chamber and basal short-axis-view. Meticulous attention should be spent evaluating valvar regurgitation and stenosis. Patients should receive appropriate antibiotic prophylaxis for the procedure (Cefazolin 20 mg/kg up to 1 g). 7.a.ii. Vascular access and hemodynamic evaluation Femoral artery and vein are accessed routinely for all VSDs. In addition, the right internal jugular vein is accessed if the VSD is located in mid, posterior or apical septum. Heparin is administered at 100 IU/kg and the activated clotting time (ACT) is maintained above 200 seconds throughout the procedure. A routine right and left heart catheterization is then performed to specifically evaluate the degree of left-to-right shunt as well as pulmonary vascular resistance. Evidence of a fixed pulmonary vascular resistance above 7 Wood Units should be considered a contraindication for VSD closure. 7.a.iii. Angiography and device size Initial angiography is usually performed within the left ventricle in single-plane or biplane projection. The frontal camera is positioned 60 degree left anterior oblique (LAO) and 20-30 degree cranial angulation for VSDs in the perimembranous or anterior muscular region and slightly less LAO (35-45 degree) for other muscular VSDs. The device is chosen to be 1-2 mm larger than the largest size of VSD, as determined by TEE and angiography. Some operators may want to utilize balloon sizing to determine the appropriate device size. In our opinion this is usually not necessary due to the stiffness of the muscular ventricular septum. For post infarct VSD's, we recommend the use of a device 50% larger than the measured diameter of the VSD due to ongoing necrosis of the tissue surrounding the VSD. This should reduce the incidence of residual shunts or device embolization. 7.a.iv. Crossing the VSD and arteriovenous loop-muscular VSD The most common approach is to cross the VSD from the left ventricle. In our experience the Judkins right coronary catheter is most suitable to cross the VSD. We usually use a soft-tipped angled glide wire to cross the VSD and position the wire and Judkins right coronary catheter into a branch pulmonary artery. The wire is then exchanged to a soft J-tipped exchange length 0.035” wire which is positioned into either branch pulmonary artery. This wire is then snared using an Amplatz Gooseneck snare (Microvena Corporation) and exteriorised via the right internal jugular vein (for VSDs in mid, posterior or apical septum) or femoral vein (for all other VSD locations). The created arteriovenous loop functions as a stable rail to advance the delivery sheath. Formation of a veno-venous loop using a transseptal puncture is less suitable for device delivery due to sheath angulation and potential damage of the mitral valve apparatus. Some larger mid-muscular or apical VSDs can be successfully crossed from the right ventricular approach, thereby placing an exchange length guidewire into the left ventricular apex. However, care should be taken to enter the appropriate communication, which can be difficult to locate within the right ventricular trabeculations. 7.a.v. Positioning of the delivery sheath A crucial part of the procedure is the placement of the delivery sheath. The sheath is usually advanced over the guide wire from the jugular or femoral venous approach, which avoids placing a larger size sheath in the femoral artery. A retrograde approach via the femoral artery is reserved for cases where placement of the delivery sheath from a right sided approach proves difficult. Difficulties can be encountered in the right ventricular apex due to steep angulation of the delivery sheath (muscular VSDs) and when crossing the VSD itself. Care has to be taken to overcome resistance by using only gentle forward-and backward movements. It is at this part during the procedure when the tension of the arteriovenous loop (maintained on both ends) as well as the impingement of the delivery sheath on the ventricular septum can cause rhythm disturbances, bradycardia and temporary drop in blood pressure. The delivery sheath should be advanced until it reaches a safe position within the ascending aorta. The dilator is then slowly withdrawn and in cases where kinking of the delivery sheath during device advancement appear more likely, an additional 0.018” glide wire can be kept inside the delivery sheath. The approach at this stage then varies according to VSD location. For VSDs approached from the internal jugular vein the sheath is left positioned in the ascending aorta whereas for VSDs approached from the femoral vein the sheath is positioned within the LV apex or kept in the ascending aorta (for anterior muscular VSDs). 7.a.vi. Advancement of the device The next stage of the procedure is the advancement of the device. The 0.035” J-tipped wire is being removed and the tip of the delivery system is kept in the ascending aorta or left ventricle. The device is attached to the delivery cable and pulled into the loader either under saline or blood seal. We prefer blood as this accelerates the clotting of the device itself. If a glide wire is being used for additional stability and to prevent kinking of the delivery sheath it has to be introduced next to the device through the loader and the Tuohy Borst connector at the end of the loader. The loader is then being flushed with blood or saline and placed inside the delivery sheath and the device slowly advanced. Advancing may require a significant force and care should be taken not to bend the delivery cable. Once the device has been advanced to the tip of the delivery sheath the glide wire, if being used, should be removed. 7.a.vii. Device deployment If the delivery sheath has been placed in the ascending aorta it is slowly pulled back until it reaches LV mid-cavity. The left ventricular disk is then slowly deployed taking care not to impinge on the mitral valve apparatus. TEE guidance is of paramount importance during this stage of the procedure. In cases of high muscular VSDs where the delivery sheath is positioned in the ascending aorta, a portion of the left ventricular disk can be deployed distal to the aortic valve. This should reduce the risk of the delivery system “falling back” into the right ventricle when pulling back across the aortic valve. Once the aortic valve has been crossed the LV disk is deployed completely by retracting the sheath in mid-cavity position. The whole assembly consisting of delivery sheath, cable and device is then pulled back against the ventricular septum under TEE guidance until an adequate position has been achieved, and then the waist is deployed under mild tension and continuous TEE guidance. Once adequate position is confirmed via angiography (via a Pigtail catheter advanced from the arterial side) and TEE, the right ventricular disk is being deployed. Once a good position has been confirmed by TEE and angiography, without impingement on neighbouring structures and valves, the device can be released using counter-clockwise rotation with the pin wise. Further confirmation of device position by TEE should be obtained after the device has been released. 7.a.viii. Crossing the VSD, arteriovenous loop, device delivery-membranous VSD Deployment of a membranous VSD device requires some considerations. Fig. 2 demonstrates the various steps of closure in a patient with a large size perimembranous VSD. The most important steps in the protocol are:
7.b.i. VSD size and location 7.c. Follow-upIn a recent study by Holzer and colleagues a larger VSD size has not been found to be associated with an increased risk of complications. 38% of muscular VSDs have been found to occur in overlapping regions of the ventricular septum, whereas isolated VSDs located anterior have been described in 13%, apical in 14%, mid-muscular in 33% and posterior in only 2% of patients, who underwent VSD device closure. From our own experience we encountered greater difficulties in closing posterior and some anterior muscular VSDs when compared to VSDs located in apical and mid-muscular position. These defects are frequently difficult to cross. The advancement of a wire into the main pulmonary artery in posterior defects is often hindered by the overlying tricuspid valve and positioning of the delivery sheath is more often complicated by kinking than in mid-muscular position. Some larger mid-muscular VSDs can be successfully crossed from a right-ventricular approach, thereby allowing positioning an exchange length guide wire within the LV and thereby avoiding the need of an arteriovenous wire loop formation. 7.b.ii. Swiss cheese/multiple VSDs Multiple muscular VSDs are associated with increased surgical morbidity and mortality. Although a larger number of VSDs has not been found to be associated with an increased risk for the occurrence of procedure or device related complications, they have been found to be associated with significantly increased fluoroscopy and procedure times. The main limitation in closing Swiss-cheese type VSDs is the length of the procedure and the amount of contrast used. Not infrequently however, patient can be treated successfully in multiple sessions. 7.b.iii. Crossing prosthetic valves Retrograde catheterization of the left ventricle through a prosthetic aortic valve has to be carefully considered and performed avoiding any “brute force”. Some reports have described catheter entrapment with fatal outcome due to severe acute aortic regurgitation. Recently we reported the successful closure of iatrogenic ventricular septal defects in two patients with a prosthetic St. Jude and Medtronic aortic valves. Using a careful approach avoided significant complications in both patients, and documented that device closure in patients with a prosthetic aortic valve is feasible. Following the procedure patients should usually be observed for 24 hours as an inpatient. During this time investigations should include a CXR for device position, echocardiography to assess for residual VSDs, right ventricular pressures and left ventricular dimensions and EKG to document any arrhythmias or conduction anomalies. Patients should receive two further doses of antibiotics and a 24-hour Holter recording should be commenced directly following the procedure. All patients should receive low dose aspirin or an equivalent anti-platelet drug for 6 months following the procedure. Prophylaxis for bacterial endocarditis should be continued for at least 6 months following the procedure and can subsequently be discontinued once complete closure has been documented. Follow-up visits should be scheduled at 6-months and subsequently in 1-2 yearly intervals. Each follow-up visit should include clinical and echocardiographic assessment as well as an EKG. A chest X-ray should be repeated every 1-2 years. The degree of a residual shunt should be assessed by echocardiography by measuring the width of the color jet as it exits through the ventricular septum. The shunt should be classified as trivial for a width < 1 mm, small for a width between 1 and 2 mm, moderate for a width between 2 and 4 mm and large for a width > 4 mm as suggested by Boutin and colleagues for assessment of residual shunting after ASD device closure. 7.d. Complications For muscular VSD's, procedure related complications occurred as frequently as 37%, however, only 6.7% of patients encountered unresolved complications, such as RBBB or stroke. 2 patients (2.7%) died as a direct result of the procedure. For perimembranous VSD's, device related complications included trivial aortic insufficiency, progression of trivial tricuspid regurgitation and temporary ventricular arrhythmias during sheath manipulation without hemodynamic compromise occurred in much less frequency. Post infarct VSD's continue to carry a grave prognosis, even with percutaneous VSD device closure. Although Holzer and colleagues recently reported the procedure to be successful in 16 of 18 patients, the 30-day mortality was as high as 28%. These results compare favorably with other reports of surgical as well as transcatheter closure of post-infarction VSDs. Cardiac arrhythmias are common and require the presence of an experienced cardiac anesthetist during these procedures. Most cases of air and clot embolization can be avoided using meticulous techniques of catheter and wire exchange, as well as keeping the ACT above 200 seconds. Device embolization should be a rare event in experienced centers. However, the potential for device embolization does require surgical “in-house” back-up for these procedures as well as equipment and technical skills of the interventionalist to attempt percutaneous retrieval of the device. Another potential complication not listed includes hemolysis, which is related to the presence of a residual shunt. The incidence can be reduced by pre-soaking the device with the patients own blood prior to heparinization. Echocardiography is extremely important to identify device or procedure related valvar regurgitation as well as pericardial effusion and a final assessment should be completed prior to discharge from the hospital. 7.e. Residual shunts The reported closure rates using the Amplatzer muscular and membranous VSD devices have been excellent. Arora and colleagues reported a 0% frequency of residual shunts in 90 patients after device closure of VSD's using the Amplatzer muscular VSD device (follow-up: 1-48 months). In the largest US trial, Holzer and colleagues documented closure rates of 34/72 (47.2%) at 24 hours post procedure, increasing to 32/46 (69.6%) at 6-month and 24/26 (92.3%) at 12 months. Bass, et al reported excellent closure rates when using the membranous VSD device to close perimembranous VSD's in 25 patients. In 92% complete occlusion was documented within 15 minutes of device deployment by transesophageal echocardiography as well as angiography. Two patients had a tiny residual shunt at 15 minutes and 24 hours following the procedure. Unfortunately, results of transcatheter device closure of post-infarct VSD's are less favourable. Immediate results demonstrated no residual shunt in 2/15 patients, a trivial residual shunt in 4/15 patients, and a small residual shunt in 9/15 patients. At subsequent outpatient follow up the VSD was reported as closed in 2/10 patients, 6/10 patients had a trivial or small residual shunt and 2/10 patients had a moderate residual shunt. These residual shunts are predominantly related to enlargement of the VSD due to ongoing necrosis after myocardial infarction. 8. Summary In conclusion, the most recent studies suggest that the family of Amplatzer VSD devices can be safely used to close muscular as well as perimembranous VSD's. The mortality as well as the incidence of permanent morbidity is low and closure rates are excellent. Appropriate patient and device selection is of paramount importance to the success of the procedure and should include anatomical and morphological details of the VSDs. However, operator experience forms the basis for a successful procedure. Device closure of VSD's should therefore be considered as an important alternative to the standard surgical approach to close ventricular septal defects in the pediatric and adult populations. (Table and figures are not provided.) |
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