Rõ ràng, tuy nhiên, bất cứ điều gì các nhóm, nhịp tâm thất phải không được gây phương hại đến hiệu suất tâm thất trái. Phải đặt máy tạo nhịp tâm thất đỉnh có thể có hoặc không có thể được tối ưu, tùy thuộc vào giải phẫu tim bẩm sinh hiện tại và liên quan đến vật liệu cấy ghép | Problems with right ventricular apical pacing 21 It is clear however that whatever the group right ventricular pacing must not be detrimental to left ventricular performance. Right ventricular apical pacing may or may not be optimal depending on existing congenital heart anatomy and associated implanted prosthetic materials which may alter normal contractility. For instance patients following repaired ventricular or endocardial septal defects may have calcified patch material and fibrotic tissue extending along the septum which can effectively preclude any lead attachment in that area. In addition the prosthetic material may hinder normal septal contractility. In such patients the apical region may be a more effective implant site 53 . Alternative sites such as right ventricular outflow pacing particularly in the septum may prove to be more effective 54 . However it cannot always be determined where the lead actually lies in the outflow tract. The same principles apply for ICD leads although the actual positioning is not as critical if ventricular pacing is avoided. The detrimental effects of ventricular pacing should also be considered when programming the implanted device. In patients with sick sinus syndrome it may be possible to use only atrial pacing. If a ventricular lead has also been implanted the atrioventricular delay should be extended to create minimal ventricular pacing. A number of algorithms are available from most pacing companies to search for atrioventricular conduction and thus minimize ventricular pacing. One new algorithm uses a new dual chamber pacing mode which is essentially AAI R . Failure to conduct to the ventricle is immediately recognized and the pacemaker automatically switches mode to dual chamber pacing AAIsafeR Symphony DR 2250 ELA Medical Cedex France and EnRhythm P1501DR Medtronic Inc. Minneapolis MN USA . This mode of pacing is useful in patients with prolonged or varying PR intervals where it may be difficult to stretch the .
