Discussion
Although the diagnostic procedures, surgical techniques, and results are standardized for patients with isolated ventricular septal defects, diagnosis is less secure, surgical techniques are more varied, and published incidence of perioperative mortality, ventricular dysfunction, and complete heart block are higher in those with multiple defects, including the Swiss-cheese septum,. Major associated cardiac lesions add to the complexity of repair.1-72
Analysis of the STS Congenital Heart Surgery Database analysis over a period of 4 years revealed that, when defects are multiple, it takes longer to close them. When compared with the more common isolated perimembranous defects, the rate of heart block is three times higher with multiple defects. The rate of unplanned reoperation is over four times higher even with isolated muscular septal defects, and almost twice as high with multiple septal defects. Before discharge from the hospital, the mortality rate is over twice as high with muscular septal defects, and over three times as high with multiple septal defects.29-32 As already discussed, however, it did not prove possible to analyse the outcomes in terms of the outcomes for the anatomical combinations of multiple defects as suggested in our reviews. This is something that might be achieved in the future, since the anatomical differences are striking, and certainly impact on the optimal therapeutic approach.
The key to closure of multiple defects is accurate identification, edge detection, and proper cavitary entry. Guidance for closure have been described by multiple investigators using three dimensional color-coded echocardiography, echocardiographic en-face reconstruction of the right ventricular septal surface, contrast enhanced and multidetector computed tomography, fast gradient magnetic resonance cardiac imaging, angiocardiography, and perventricular wire placement, or by cardioscopy.1-9,14,22-28,71
Taken together, these investigations collectively provide comprehensive assessment of anatomical information to obtain an accurate preoperative diagnosis, yet it remains difficult to ascertain whether all defects are recognised, particularly when one large defect is non-restrictive.1-28,59,64,71 Our review revealed several instances of diagnosis of additional defects intraoperatively, postoperatively, or at necropsy.1,7,13
The optimal surgical repair involves complete closure of the multiple defects. Ideally the moderator band and septomarginal trabeculation should remain intact, without a need for ventriculotomy, without compromising the size of the ventricular cavities, without producing ventricular dysfunction, surgical complete heart block, aortic and tricuspid regurgitation, and without compromising the coronary arterial flow. That this ideal has yet to be achieved is evident from the numerous surgical and interventional techniques described, along with short-term follow-up studies that report an undesirable incidence of perioperative mortality and morbidity.1-72 Residual defects, and postoperative myocardial dysfunction, are still the Achille’s heel of poor surgical results. They are related mainly to the uncertainty of location of the defects, and the difficulty in obtaining complete closure without right and/or left ventriculotomy.1-17,19-27,29-32,41,43,46-53,59,61,65
With the evolving knowledge of the complex variable anatomy, individualized surgical techniques have been described to suit the different anatomical variants. Some approaches, furthermore, are suitable for several variants. All surgeons acknowledge, nonetheless, that these defects, when multiple, are difficult to close, particularly in small infants presenting with congestive cardiac failure.1-17,19-27,29-32,41,43,46-53,59,61,65
It may be hard to recognize the boundaries of defects because the moderator band and multiple trabeculations hide apical defects, while Swiss-cheese defects may remain misdiagnosed.1-72Visualization and closure of most muscular defects is usually possible via a right atriotomy. Exposure of apical defects from the right side, however, has been plagued by poor visualization, and the uncertainties of identifying the true margins of the defects when approaching through the coarse trabeculations of right ventricular apex.1-72 These problems are then still further exacerbated in the setting of the Swiss-cheese septum. It is because of the limited exposure, and difficulties in exploring Swiss-cheese defects, that banding of the pulmonary trunk is still being performed in premature infants with low body weight to protect the pulmonary vascular bed and to relieve symptoms of congestive heart failure to delay definitive repair.14-17,30-32
As we have discussed, such banding can also have its place in treatment of individuals with other combinations of multiple defects. Presently, banding as an initial palliative procedure is being performed in select institutions under specific circumstances. These include the proximity of margins of the defect to the atrioventricular conduction axis, which predisposes to atrioventricular block in small infants when constraints exist in terms of space for placing a permanent pacemaker. Other indications include multiple apical defects, particularly the Swiss-cheese septum, selected patients with large trabeculations traversing the defects that could interfere with complete closure, co-existing perimembranous and muscular inlet defects, an associations with coarctation in infants aged less than 2 months, association with lesions such as twisted atrioventricular connections and those selected individuals deemed generally to be at high-risk.13,14,16,17,30-32,37 The staged approach, furthermore, is known to promote spontaneous closure of some of the smaller defects. Against these potential advantages must be weighed the deleterious effects of biventricular muscular and fibrous hypertrophy and long-lasting hypoxia leading to arrhythmic events, increased mortality, and chronic heart failure.22-24,30,32,41,42,48
Since the pulmonary vascular bed is both pressure and volume overloaded, there is difficulty in determining the optimal tightness of the band. Hence the need for frequent reoperations for adjustment. The added complexity of the second stage includes pericardial adhesions, need for pulmonary arterioplasty, damage to the potential neoaortic valve and right ventricular hypertrophy, further contributing to difficult exposure of septal defects.16,17,29-32 To address these concerns, Corno and associates introduced the telemetrically adjustable FloWatch pulmonary artery band (FloWatch-PAB®). Use of this approach not only eliminates the requirement of reoperation to adjust the band, but also allows for precise and progressive tightening over days or weeks.16,17 The non-circular shape of FloWatch, furthermore, maintains the pliability of pulmonary arterial wall and avoids pulmonary arterioplasty.
The approach through the left ventricle still retains its advocates. Thus, when using this technique, Aaron and Hanna demonstrated that exposure and repair of apical defects was much easier.11 It is particularly appropriate for those cases with a solitary defect seemingly having multiple channels when assessed from the right ventricle. Its use has been advocated by multiple surgeons producing small series with excellent short- and long-term results. Recently, a limited apical left ventriculotomy approach has been introduced.2,57,61,65 Debate continues, nonetheless, with regard to its potential risks. The exposure gained can also be disappointing at times. Because of all these considerations, some argue that the risks, in the long-term, are unacceptable, since they include apical dyskinesia, aneurysm formation, left ventricular dysfunction, ventricular arrhythmia, and the need for cardiac transplantation.2,30-32,57-61,65,66 The mechanisms identified that result in left ventricular dysfunction and aneurysm formation have included damage to epicardial coronary arteries, the myocardium, and the left ventricular conduction system.11,58,60,61 It is also the case that the precise anatomic location and orientation of the ventriculotomy has great impact on the results. Waldhausen and DiBernardo, for example, demonstrated that a longitudinal left ventriculotomy causes less disruption to coronary vasculature, less injury to papillary muscles, better preservation of ventricular function, and smaller areas of ischemia when compared to transverse lesions.2,58
The advocates of an apical right ventriculotomy have demonstrated the safety and effectiveness of this approach for large solitary apical defects with multiple overlying trabeculations, and for apical and anterior defects.12-15 The technical features include a limited right ventricular incision that is close to left anterior interventricular coronary artery without endangering the vessel. As described by Tsang and associates, a ventriculotomy in this area allows entry to the space between the papillary muscles and the septum.15
All surgeons acknowledge that the Swiss-cheese septum is particularly difficult to close, particularly when encountered in neonates and premature infants with low body weight presenting with congestive cardiac failure.1-72 The true Swiss-cheese septum emdodies all the morphologic features of so-called “non-compaction”. Repair of the non-compacted septum essentially involves ventricular septation, either with an oversized patch, or by right ventricular apical exclusion. Outcomes of such procedures may be complicated by abnormal ventricular function requiring cardiac transplantation. In many circumstances, initial placement of an adjustable pulmonary arterial band remains a safer and desirable option.14,16,17,30-32 The techniques of “over-sized pericardial patch”, “composite patch”, “double patch sandwiching the septum”, “felt sandwich patch” have all been described, with or without transection of moderator band/septal trabeculations without left ventriculotomy.1-8,79 The majority of patients required prolonged diuretics, angiotensin converting enzyme inhibitors, thereby suggesting impairment of left ventricular function in the postoperative period. The non-compacted septum can be notoriously difficult to identify before the initial repair. Once obvious defects have been closed, additional defects can be unmasked, and may require additional intervention.1-8 If a large patch is used to cover the entire septum, it is desirable to address multiple points of fixation to avoid the development of aneurysmal new septum.4,5 Although the use of oversized pericardial patches yielded good results, residual defects are frequently reported, along with reduced right ventricular size, and late complications including cardiac cirrhosis, late opening of the oval fossa, and atrial tachyarrhythmias.68
It follows that there are wide variations in practice between centers in the approach to interventions for multiple muscular septal defects. Many surgeons prefer to repair mid muscular septal defects in the operating room using traditional techniques.7-14,38,72 Recently, transcatheter device closure and hybrid techniques for closure of multiple muscular septal defects have reported encouraging early outcomes. Percutaneous device closure in infants below 5 kg poses a variety of challenges because of low body weight and poor venous access.22-25,28,52-55 The stiff delivery catheters and sheath can splint open the tricuspid valve, mitral valve, and/or aortic valve, leading to arrhythmias, heart block and hemodynamic decompensation. In these clinical situations, a perventricular hybrid approach is a feasible “off pump” therapeutic option with acceptable mortality and morbidity.23-25,51-55,69
Recommendations were suggested in 2011 by the American Heart Association for device closure of multiple muscular septal defects. Infants weighing more than 5 kg, and children and adolescents with hemodynamically significant shunts were placed in Class IIA. In Class IIB were placed neonates, and infants weighing less than 5 kg with hemodynamically significant lesions and associated cardiac defects requiring cardiopulmonary bypass, albeit for initial hybrid perventricular closure off bypass, followed by surgical repair of the remaining defects. Neonates, infants and children with hemodynamically significant inlet multiple septal defects with inadequate space between the defect and the atrioventricular or arterial valves were not recommended for closure.28 When considering these recommendations, it is those multiple defects located in the mid, apical, inferior, or anterior parts of the apical septum that are most amenable to closure in transcatheter fashion.19-28,52-55 In recent years, with the introduction of the Amplatzer muscular and perimembranous occluders, the hybrid perventricular technique has been used for selected individuals with perimembranous and outlet defects to avoid surgical intervention, or to simplify operative repair.67,73-78 In the multicentric trial on device closure carried out in the United States of America, almost three-quarters of individuals had only a single device inserted. In nearly one-fifth, however, it was necessary to use two devices, while three devices were needed in just over one-twentieth.28 Other investigators have also reported successful closure with multiple devices.28,52-55 The exclusion criteria of device closure include weight less than 3 kg, distances of less than 4 mm between the defects and valvar leaflets, pulmonary vascular resistance greater than 7 indexed Wood units, sepsis, more than trivial aortic or tricuspid regurgitation, obvious aortic valve prolapse, diameters greater than 10mm, preoperative arrhythmias, and contraindications to antiplatelet agents.19-28 Patients with multiple ventricular septal defects with associated defects or undergoing hybrid procedures, represent a set of very particular clinical situations. A collaborative approach using transcatheter/hybrid device closure followed by surgical repair is emerging when preoperative evaluation is suggestive of relatively inaccessible location of the septal defect which may necessitate an incision in the systemic ventricle and those with complex associated lesions.28-32,45,61,78 The advantages of percutaneous closure include avoidance of transection of trabeculations, avoidance of ventricular incisions and immediate confirmation of adequate closure. As already discussed, however, multiple adverse events have been reported in four series of intraoperative closure.28,60,67-70
Pooling the available data for interventional closure of multiple defects reveals an incidence of such adverse events of between 2.8% and 45%. The reported complications are many and varied. They include arrhythmias, cardiac arrest, device embolization, residual shunting, cardiac perforation, and even procedure-related death.19-28,60,66-70 When compared with surgery, in which complete heart block appears early postoperatively, complete heart block is unpredictable after device closure, and is a late problem. Direct compression, inflammatory reaction, and formation of scarring in the conduction tissues have all been variously incriminated as the causative mechanism of complete heart block.19-28,66-70,73,80