Ann Thorac Surg 2006;82:956-957
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Invited commentary
Anthony Azakie, MD
Pediatric Heart Center, University of California San Francisco, Department of Surgery, University of California Medical Center, 513 Paranassus Ave, San Francisco, CA 94143
(Email: azakiet{at}surgery.ucsf.edu).
Andersen and colleagues [1] report the incidence of complete atrioventricular (AV) conduction block in a selected group of patients who had surgical closure of ventricular septal defect (VSD) at Great Ormond Street during a 26-year period. The results are excellent with an overall incidence of less than 1% for pacemaker insertions after postsurgical AV conduction block. Based on important anatomic and morphologic data, the authors make recommendations to further reduce the risk of injury to the AV conduction axis, supporting the notion that the incidence of the postoperative need for a pacemaker may in fact be less than 0.5%.
The anatomy of the conduction tissue in congenital heart disease is fundamental to surgical practice. Thanks to the many contributions of Anderson and colleagues [1], Becker, Kurosawa, de Leval, and others, many of the morphologic details of the AV conduction axis in congenital heart disease have been defined. Biologic studies of morphologists are a good example of how basic science can impact clinical practice and outcomes. The principles of surgical closure of perimembranous VSD, in general, should include the use of oversized patches, suturing to the right septal surface at least 2 mm away from the rim of the ventricular septum, especially around danger zones, and placement of superficial sutures when transitioning around the posterior inferior rim or crest. Uncomplicated closure of septation defects also requires an understanding of the anatomic variations of special situations including atrial ventricular septal defect (AVSD), double outlet right ventricle (DORV), AV discordance, straddling or overriding AV valves, as well as malaligned VSDs and trabecular, inlet or outlet extensions of perimembranous defects. Surgical AV conduction block necessitating pacemaker insertion should only occur due to undefined anatomic variants or in patients who have a genetic predisposition to AV conduction delay such as in Tbx 5 or Nkx 2.5 mutations. Both Tbx-5 and Nkx 2.5 are important for the development, maturation, and maintenance of the conduction system and haploinssufficiency or heterozygous mutations result in AV conduction block.
The study may demonstrate some biases due to (1) the database search criteria matching VSD closure to pacemaker insertion, (2) the decision not to include septal defect repairs in patients with AVSD, DORV, transposition of the great arteries and VSD, and AV discordant connections, (3) changing practices for insertion of pacemaker for postsurgical heart block for the last 3 decades, and (4) the prevalence of "competing" outcomes (postoperative AV conduction block vs mortality).
Although the study may demonstrate some selection bias, it is an excellent example of current surgical outcomes for VSD closure and development of postoperative heart block. Such outcome data is particularly relevant in the current era of percutaneous transcatheter-based techniques of VSD closure in selected patients. The overall incidence of VSDs in patients with congenital heart disease ranges from 40% to 70%, a subgroup of whom may be considered candidates for device closure by interventional cardiologists. Current percutaneous transcatheter techniques have a 90% success rate for device deployment. There is a 5% to 10% adverse event rate including a 2% to 3% risk of postprocedural complete heart block necessitating pacemaker insertion. Late heart block may also develop after device closure, even as long as 12 to 18 months after device implantation. The report by Andersen and colleagues [1] sets a standard to which interventional approaches should be held, and in the current era isolated VSD closure should have a mortality rate approaching zero, and a risk of complete heart block of less than 1%. Furthermore, current perfusion and myocardial protection strategies (ie, minimal priming volumes, high flow bypass, and mild hypothermia) and the use of modified ultrafiltration can reduce the deleterious effects of cardiopulmonary bypass. Isolated ventricular septal defect closure can be performed with limited skin incisions and partial sternotomy, and the use of intraoperative transesophageal echocardiography may help eliminate any significant residual left-to-right shunt.
As percutaneous techniques and VSD device technology have emerged, they will also be refined and redesigned. The use of different device materials and design of devices that come in numerous sizes and dimensions will reduce the risk of injury to the AV conduction axis, avoid potential distortion of the aortic and tricuspid valves, minimize residual shunts, and increase the likelihood for successful deployment. Ultimately, however, the performance and outcome of percutaneous, transcatheter techniques for VSD closure should be compared with current surgical outcomes.
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References
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- Andersen HØ, de Leval MR, Tsang VT, Elliott MJ, Anderson RH, Cook AC. Is complete heart block after surgical closure of ventricular septum defects still an issue? Ann Thorac Surg 2006;82:948-957.[Abstract/Free Full Text]
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