EDITORIAL

"DOES THE LEFT HAND KNOW. . ."

Roxane McKay*, MD, FRCS, FRCSC, FACC Department of Cardiology and Cardiovascular Surgery Hamad Medical Corporation, Doha, Qatar

   Ventricular septal defect is the most common congenital heart malformation. As an isolated lesion, it accounts for 20%-30% of patients with congenital heart disease1 and, more sensitive detection using color flow Doppler imaging has recently estimated an incidence as great as 5.6-5.7 per 1,000 live births2. Of that number, at least 80% will close spontaneously, usually during the first year of life.
Traditionally, most patients who have come to surgery for isolated ventricular septal defect have done so for intractable heart failure, failure to thrive, recurrent pulmonary infections, or pulmonary hypertension. This also is usually during the first year of life, with the average age in one reported series being 2.9 months, 8.6 months, 11.4 month, and 14.6 months for these situations, respectively3. At an older age, indications for closure have been a pulmonary-to-systemic flow ration in excess of 1.5:1 or the onset of aortic regurgitation, although the suboptimal clinical course of some adults in whom the defect was considered too small for surgery4, taken into consideration with the low morbidity and mortality of operation, has more recently supported closure of all ventricular septal defects, regardless of size5.
   In this issue of Heart Views, Dr. Assad Al-Hroob and colleagues report their initial experience with transcatheter closure of ventricular septal defects using the Amplatzer asymmetric ventricular septal defect occluder. This series of twelve patients, nine of whom had perimembranous defects, compares extremely favorably, both in its size and in the quality of results, to others recently published6,7. It is noteworthy that complete closure was obtained in all of the perimembranous lesions with no serious complications or prolonge convalescence. While most of these patients, on hemodynamic criteria, would have been borderline candidates for surgical intervention, nearly all had some reduction in left ventricular end diastolic volume, providing further evidence that closure of even small defects may be beneficial in the longer term. These probably are the type of ventricular septal defect-covered with fibrous tissue-which often require the technically more complicated manoeuvre of tricuspid valvar detachment for surgical access. Device closure of ventricular septal defects, at this point in time, would thus seem to compliment surgical practice in addressing an older group of patients with smaller interventricular communications.
   As clinical work evolves, advances in one aspect of a speciality, often unmask deficiencies in another, and percutaneous transcatheter interventions appear to be no exception. Following the work of Soto8, ventricular septal defects which extended the tricuspid valve and hence abutted upon the membranous septum, were designated "perimembranous" and described as they would be seen by the surgeon working in the right ventricle. Morphologically, the essence of a perimembranous ventricular septal defect is an area of fibrous continuity between leaflets of the tricuspid and aortic valves. Such defects were further categorized according to the part of the ventricular septum into which they extended, again on the right side of the heart, as perimembranous "central", "inlet", or "outlet" defects9. This nomenclature was useful because it conveyed information regarding the position of the specialized conduction tissue, the atrioventricular valves, and the medial papillary muscle complex, all of which are important in relation to a patch sutured on the right side of the ventricular septum. But what may be more important for interventional device closure, as emphasized in this report, is the morphology of the left side of the heart. It is well known that the left and right sides of the ventricular septum in congenitally malformed hearts do not necessarily correspond with each other. 
   The distance of the upper margin of the ventricular septal defect from the aortic valve is one consideration. Depending upon whether a perimembranous ventricular septal defect is also "juxtaaortic", there may or may not be sufficient tissue to attach an occluder device without entrapment or distortion of the valvar leaflet(Figure).

Photographs of the left side of the ventricular septum showing two hearts which both have a perimembranous ventricular septal defect. In the heart on the left (A), the defect reaches the aortic valve and there is no margin of fibrous tissue for attachment of an occluder device. The defect shown on the right (B), in contrast, is separated from the aortic valve by tissue which would permit device closure.
Drawn from illustrations in Smith A and McKay R, A Practical Atlas of Congenital Heart Disease, Springer-Verlag, Heidelberg, 2003.

(Figure). Moreover, this rim of tissue on which the occluder is positioned may or may not have the potential to develop subaortic obstruction, because the device also has depth on the left ventricular side of the septum. A third consideration is the width of the left ventricular outflow tract. When this is long and narrow, such as the so-called "goose-neck" deformity in atrioventricular septal defect, the heart may be altogether unsuitable for device implantation, as the authors found in this experience. What is now needed is a new terminology, that will describe a ventricular septal defect in relation of the left ventricular side of the septum and subaortic area, stressing these morphological features.
   A second issue which emerges from the comparison of this series with that reported by Thanopoulos7 is how accurately present technology is able to measure the size of a ventricular septal defect. Despite, with one exception, having a left-to-right shunt of less than 2.0:1, the ventricular septal defects closed by Al-Hroob and colleagues all would be considered fairly large by surgical standards. They ranged from 6.3 to 13 millimeters in diameter on transesophageal echocardiography, and they were closed with large devices (6 to14 millimeters). In contrast, apparently smaller defects (2.5 to 8 millimeters in diameter) had larger shunts (Qp:Qs 1.5 to 2.4) in the Thanopoulos series and were equally successfully closed with smaller devices (4 to 8 millimeters). While the precise size of a ventricular septal defect has not been critical for surgical management, where the patch is fashioned after actually seeing the hole, it does become important when the operator must select an expensive, preformed occluder based on echocardiographic measurements.
It is only through complete and accurate characterization of the patients and procedures that long-term follow-up will be able to answer questionsregardingthromboemboliccomplications, endocarditis, device-patient mismatch, and cardiac growth following device closure of ventricular septal defects.

References

1. Mitchell SC, Korones SB, Berendes HW. Congenital heart disease in 56,109 births. Circulation 1971;43:323-32.

2. Meberg A, Otterstad JE, Froland G, Sorland S, Nitter- Hauge S. Increasing incidence of ventricular septal defects caused by improved detection rate. Acta Paediatr 1994;83:653-7.

3. Barratt-Boyes BG, Neutze JM, Clarkson PM, Shardey GC, Brandt PWT. Repair of ventricular septal defect in the first two years of life using profound hypothermia- circulatory arrest techniques. Ann Surg 1976;184:376- 90.

4. Otterstad JE, Erikssen J, Michelsen S, Nitter-Haug S. Long-term follow-up in isolated ventricular septal defect considered to small to warrant operation. J Intern Med 1990;4:305-9.

5. Backer CL, Winters RC, Zales VR, Takami H, Muster AJ, Benson DW Jr, Mavroudis C. Restrictive ventricular septal defect: how small is too small to close? Ann Thorac Surg 1993;56:1014-8.

6. Arora R, Trehan V, Kumar A, Kalra GS, Nigam M. Transcatheter closure of congenital ventricular septal defects: experience with various devices. J Interv Cardiol 200316:83-91.

7. Thanopoulos BD, Tsaousis GS, Karanasios E, Eleftherakis NG, Paphitis C. Transcatheter closure of perimembranous ventricular septal defects with the Amplatzer asymmetric ventricular septal defect occluder: preliminary experience in children. Heart 2003;89:918- 22.

8. Soto B, Ceballos R, Kirklin JW. Ventricular septal defects: a surgical viewpoint. J Am Coll Cardiol 1989;14:1291-7.

9. Anderson RH. The anatomy of ventricular septal defects and their conduction tissues. In: Stark J, deLeval M (eds.). Surgery for Congenital Heart Defects, Second Edition. W.B. Saunders Company, Philadelphia, 1994, pp115-38.