Our study demonstrated that TTE may be employed for the assessment of VSD, selection of patients for device closure, and guidance of perventricular device placement in infants. Because of relatively clear definition of VSD anatomy in infants, subcostal views are practically useful in guiding the procedure of perventricular device placement.
TEE is of course the best choice for all kinds of patients in the situation of perventricular device placement because of the clear view of cardiac structures, which markedly improves assessment of device position, proximity to valve structures and residual flow. It is reported to be safe and feasible to perform transthoracic device closure of VSDs without cardiopulmonary bypass [16–19]. TTE is usually used as a tool of preparation by screening the candidates for perventricular device placement, regarding the resolution and image quality, TTE is inferior to TEE, but TTE examination in infants under general anesthesia usually have approving images, and TTE subcostal views is easy to manipulate and more welcoming by surgeons, and may be used as a guiding tool in infants with perimembranous VSD, and no patients in TTE group need to place transesophageal probe additionally because of imaging problem. Because relative deficiency of medical resource and unbalanced development in developing countries such as China, we believe that TTE-guidance may act as an alternative choice in this circumstance. When device placement is likely to be difficult, TEE-guidance is indicated, and we would also emphasize that TTE-guided VSD closure could only be carried out carefully by experienced hands.
Although morphologic variants of perimembranous VSD are common, we choose this “suitable” type of perimembranous VSD for device closure guided by TTE alone, as we know this type of VSD was more easily to apply device implantation. Here we would emphasize our inclusion criteria of VSD closure, a size of about 3 to 8 mm of perimembranous VSD may be good candidate for device closure; and an aortic rim of at least 2 mm is considered safe. In our experiences, deficiency of the aortic rim is a risk factor for unsuccessful closure and a significant predictor for residual leakage , A sufficient aortic rim is crucial for safe and stable positioning of the device and for prevention of impingement of the aortic valves. When aortic regurgitation does occur, we recommend using an asymmetrical device or transferring to open surgery, if new-onset mild above aortic regurgitation and residual shunting exist after the device placement, open surgery is the best choice and necessary. When pulmonary hypertension occurs with a large VSD, the ventricular septum may impinge towards left ventricle, thus affecting the parallel line of ventricular septum to the front wall of aorta, in such case may be confused as malaligned VSD. And we had encountered one event of dropout of occluder in TTE group and open surgery confirmed a malaligned defect in the perimembranous area. Careful echocardiographic evaluation is needed to exclude the malaligned VSD [20–22] because this special type of VSD is not amenable to minimally perventricular device occlusion, and must be treated with open surgery.
Compared with TEE, TTE has several disadvantages in guiding device closure of a VSD. First, because the surgical field is at the lower sternum, it is somewhat inconvenient for the ultrasonic specialist to hold the probe in a fixed position. Fortunately, by tilting the probe, it is easy to clearly show most of the main structures of the right and left inflow/outflow tracts. Secondly, the problem of contamination must be emphasized because of subcostal windows adjacent to the surgical field, therefore, we used a sterile sheath to cover the probe, and probe was placed subcostally at least 5 cm away from the surgical field. When TEE is used in infants, we have some concern about gastroesophageal injury and respiratory compression . Using TTE guidance sometimes can eliminate such complications, and it is quite satisfactory to apply echo guidance with TTE in infants even less than 5 Kg.
Some technical considerations of perventricular VSD device closure should also be addressed. First, passing the guide-wire and the delivery sheath across the defect is a crucial step for successful closure. The echo reflection of the guide-wire and delivery sheath is easy to find. When passing the delivery sheath along the guide-wire, caution should be exercised in examining the tip of the delivery sheath going through the defect, at this moment right red blood may arise from the other end of the delivery sheath, this observation can also help to identify the tip of delivery sheath into the left ventricle. The surgeons and ultrasonic specialists should always be cautious not to damage cardiac structures such as the aortic or mitral valves during the procedure. Second, TEE used in the early stages of the study provided a lot of experiences, and in later stages of the study TEE probe had problem, we applied only TTE to guide VSD closure in the TTE group. Our results show that the TTE group had a reduced procedure time compared with the TEE group. Because TTE subcostal views are reliable in detection and evaluation of VSD in infants, we hope that performing the VSD closure under TTE guidance could reduce procedure time and also provide increased patient comfort.
The study is limited by the biases inherent in a retrospective registry. In addition, the decision as to which VSD closure would be most appropriate in each case was made at the discretion of the ultrasonic specialist, the surgeon, and the patient’s parents. The study was conducted in only one institution, and the sample of study was not large. A longer follow-up period is also needed to evaluate the results.