Ann Thorac Surg 2003;75:147-151
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
The modified Konno procedure for complex left ventricular outflow tract obstruction
Christopher A. Caldarone, MDa*,
Timothy L. Van Natta, MDa,
Jeffrey R. Frazer, MDb,
Douglas M. Behrendt, MDa
a Division of Cardiothoracic Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
b Department of Pediatrics, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
Accepted for publication June 26, 2002.
* Address reprint requests to Dr Caldarone, Division of Cardiothoracic Surgery, University of Iowa College of Medicine, 200 Hawkins Dr, Suite 1616-A JCP, Iowa City, IA 52242, USA.
e-mail: chris-caldarone{at}uiowa.edu
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Abstract
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BACKGROUND: Complex left ventricular outflow tract (LVOT) obstruction with normal aortic valve function requires aggressive resection in the subaortic region and preservation of the aortic valve. The modified Konno procedure allows generous exposure of the LVOT from the left ventricular apex to the inter leaflet trigones of the aortic valve. Widespread use of this procedure has been limited by concern over injury to the aortic valve, the conduction system, and possibility of residual ventricular septal defect (VSD).
METHODS: Retrospective analysis of pertinent data for all patients undergoing the modified Konno procedure (1994 to 2001) at the University of Iowa were reviewed.
RESULTS: The modified Konno procedure was used in 18 patients (age 1 to 31) for LVOT obstruction associated with diffuse narrowing of the LVOT (n = 7), a discrete fibrous ring (n = 7), or a fibrous ring associated with abnormal mitral attachments (n = 4). Eight patients had previously undergone LVOT resection. There were no perioperative deaths. Estimated LVOT peak gradients by echocardiogram were 70.4 ± 24.2 mm Hg (preoperative) and 19.2 ± 20.4 mm Hg (postoperative) at most recent followup (p < 0.001 vs preop). Aortic insufficiency was moderate in one patient (present preop) and mild or less in all other patients. There were no cases of permanent heart block. Small residual VSDs were present in five patients (28%). Median follow-up is 3.1 years.
CONCLUSIONS: The modified Konno procedure can effectively relieve complex LVOT obstruction and preserve aortic valve function. Extension of this procedure for use in the initial presentation of LVOT may be appropriate in cases at increased risk of recurrent LVOT obstruction.
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Introduction
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In contrast to a simple subaortic membrane, complex left ventricular outflow tract (LVOT) obstruction (including tunnel-like maldevelopment of the LVOT, posterior malalignment of the infundibular septum, diffuse ringlike stenosis, and postresection stenosis) requires aggressive resection to provide unobstructed egress of blood from the left ventricle to the aorta. Left ventricular septoplasty was described by Cooley and Garrett [1] as a technique which allowed full thickness resection of the ventricular septum, patch enlargement of the left ventricular outflow tract up to the aortic valve, and preservation of the aortic valve. A similar, valve sparing septoplasty using an incision through the commissure between the left and right coronary cusps has also been described by Vouhe and colleagues [2]. In contrast to these aortic valve-sparing approaches, the Konno-Rastan procedure involves a similar septal incision with concomitant aortic valve replacement [3, 4]. Preservation of the aortic valve with ventricular septoplasty is commonly referred to as a modified Konno procedure [5–7].
Alternatives to the modified Konno procedure include transaortic myectomy, sacrifice of the aortic valve with a Konno-Rastan procedure, and placement of an apical-aortic valved conduit [2, 8]. Risks associated with the modified Konno procedure include injury to the aortic valve, residual ventricular septal defect, and the potential for complete heart block. The purpose of the present investigation was to evaluate the early efficacy and safety of the modified Konno procedure to relieve complex left ventricular outflow tract obstruction.
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Material and methods
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All patients undergoing modified Konno procedures at the University of Iowa (1994 through 2001) were identified through a surgical database. Pertinent medical records, catheterization, and echocardiographic reports were evaluated. Eighteen patients were identified and constitute the study group. Preoperative characteristics at the time of the modified Konno procedure and initial diagnoses (before development of subaortic obstruction) are listed in Table 1.
Data are presented as means ± standard deviation, or median with ranges as appropriate. Paired data are compared with Student’s t-test. Median follow-up was 3.1 years (range, 0.1 to 6.7 years).
Operative indications
In general, the indication for operative intervention for relief of subaortic obstruction was based on an estimated gradient of more than 30 mm Hg across the LVOT by echocardiogram. New onset or increasing amounts of aortic insufficiency in association with a smaller gradient was also considered an indication for intervention. Catheterization was not used uniformly and was less frequent in the more recent patients. Because all patients had preoperative echocardiograms, peak gradients were used for comparison between patients.
Surgical technique
After initiation of cardiopulmonary bypass and cardioplegic arrest, a transverse aortotomy is created to allow visualization of the aortic valve and LVOT. An oblique incision is created in the right ventricular infundibulum to expose the right ventricular outflow tract (RVOT).
The region of the conduction system is located to the right of a line between the nadir of the right coronary cusp and the septal attachments of the septal leaflet of the tricuspid valve. A ventricular septal incision is created to the left of this line to avoid injury to the conduction system. The septal incision is extended superiorly to level of the aortic valve leaflets allowing visualization of the superior portion of the LVOT. Closure of the aortotomy allows pressurization of the aortic root with cardioplegia and distension of the aortic valve leaflets. This maneuver allows direct visualization of the ventricular surface of the aortic valve leaflets and decreases the risk of injury to the valve leaflets during resection in the subcommissural triangle (Fig 1A).
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Fig 1. Representative intraoperative photographs illustrate some of the anatomic landmarks visualized during the modified Konno procedure. (A) The superior portion of the left ventricular outflow tract (LVOT) is visualized through overlying incisions in the infundibulum and the ventricular septum. The view is toward the patient’s head. At the top of the image, the cusps of the aortic valve are visualized while cardioplegia is administered in the aortic root. A thin jet of cardioplegia is seen due to retraction-related aortic valve insufficiency. Direct visualization of the fibrous trigones allows aggressive subaortic resection in the subcommissural triangle. (B) The inferior end of the LVOT is visualized through the septal incision at the level of the mitral apparatus. The view is toward the left ventricular apex. (RV = right ventricle.)
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The septal incision is carried inferiorly beyond the level of the mitral valve apparatus (Fig 1B). Obstructive muscle, fibrous tissue, accessory mitral valve leaflet tissue or chordae can be resected. Resection of myocardium can also be performed along the leftward side of the septal incision. Leftward resection allows further reduction in LVOT gradient without additional risk of injury to the conduction system. The septal incision is then closed with a patch to further enlarge the LVOT. In the most recent era, the patch was secured with a combination of interrupted and running suture. The infundibular incision can be closed using a patch if the VSD patch has sufficient redundancy to obstruct the right ventricular outflow tract.
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Results
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All patients survived the procedure and are free of reoperation on the LVOT at most recent followup. The median z-score of the aortic annulus was -0.6 (range: -3.4 to 2.0). Preoperative peak systolic gradients across the LVOT were reduced from 70.4 ± 24.2 to 18.6 ± 14.4 mm Hg at hospital discharge and 19.2 ± 20.4 mm Hg at most recent follow-up (p < 0.001 vs preoperative). Figure 2
illustrates the gradient reduction for individual patients. The reduction in gradient for the group is maintained throughout the observation period. One patient (patient 10) had a poor initial reduction in LVOT gradient (aortic annulus z-score: -1.4), whereas two patients (patients 4 and 9) had increasing gradients on most recent echocardiographic examination (gradients: 60 and 56 mm Hg; follow-up: 3.2 and 3.6 years, aortic annulus z-scores: -1.6 and -2.3, respectively). Early postoperative peak LVOT gradients by echocardiogram are illustrated in Figure 3.
In general, early postoperative gradients were higher in patients with small aortic annulus z-scores.
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Fig 2. Estimated peak systolic left ventricular outflow tract gradients (mm Hg) by echocardiogram are plotted for each patient stratified by preoperative, first postoperative, and most recent gradients.
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Fig 3. Estimated peak postoperative systolic left ventricular outflow tract gradients by echocardiogram are plotted against the preoperative z-score of the aortic annulus.
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Concomitant procedures at the time of the modified Konno procedure include aortic valvuloplasty (two patients), mitral valvuloplasty (two patients), and closure of a ventricular septal defect (one patient). The degree of postoperative aortic insufficiency was mild or less in all patients except one. This patient had moderate aortic insufficiency and underwent an aortic valvuloplasty in association with the modified Konno procedure. The amount of aortic insufficiency was unchanged on postoperative echocardiogram.
Four patients (22%) had transient complete heart block in the early postoperative period. These transient episodes occurred early in the series and have not recurred in the last 7 patients. There were no cases of permanent heart block. Permanent left bundle branch block, however, is present in two patients and right bundle branch block is present in ten patients. Trivial residual ventricular septal defects were present in 5 patients (27%) with echocardiographic peak gradients of 70.0 ± 28.5 mm Hg. The incidence of residual ventricular septal defect has also decreased in the latter portion of this series with one residual defect in the last 8 patients, which was too small to allow a gradient to be estimated by echocardiogram.
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Comment
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Transaortic resection of the left ventricular outflow tract is commonly used for initial resection of simple subaortic stenosis (eg, subaortic membrane) using simple excision or enucleation techniques [5]. To further reduce obstruction in the left ventricular outflow tract, a concomitant left ventricular myectomy can be performed, excising a partial thickness strip of the interventricular septum from within the LVOT [9]. Maximal reduction of LVOT obstruction with left ventricular myectomy is limited by the requirement that the resection of the septum remains only partial thickness, thereby avoiding the creation of an iatrogenic ventricular septal defect. Resection of a discrete subaortic stenosis with or without left ventricular myectomy results in satisfactory early reduction in the LVOT gradient in most cases of simple LVOT obstruction [5]. In more complex forms of LVOT obstruction (eg, diffuse stenosis), however, satisfactory reduction of left ventricular gradients is more difficult.
The modified Konno procedure has been reported to effectively reduce complex left ventricular outflow tract gradients through geometric modification of the entire LVOT [1, 6, 10]. By creating a full thickness resection of the left ventricular septum (eg, an iatrogenic VSD), the LVOT diameter is increased by the entire thickness of the interventricular septum. Augmentation of the left ventricular outflow tract is further increased by patching the VSD to allow circumferential expansion of the LVOT, thereby maximally augmenting the diameter of the LVOT (Fig 4).
Furthermore, the extensive exposure of the LVOT allows resection of accessory mitral tissue or chordae, which can contribute to LVOT fibrosis [8]. Thus the procedure can be utilized in a diverse group of patients including those with tunnel-like stenosis occurring after previous resection, stenosis in association with atrioventricular canal, as well as stenosis in association with hypertrophic cardiomyopathy [10].
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Fig 4. Schematic illustration of cross-sectional views of the left and right ventricular outflow tracts before resection for left ventricular outflow tract (LVOT) obstruction. On the left, the LVOT, right ventricular outflow tract (RVOT), and anterior leaflet of the mitral valve (mv) are depicted. In the center, a subaortic myectomy is depicted, which enlarges the LVOT by dimensions equal to the depth (d) and width (w) of the resection. The depth of the resection is less than the thickness of the ventricular septum to avoid creation of an iatrogenic ventricular septal defect. On the right, a modified Konno procedure is depicted. The RVOT is incised and the ventricular septum divided. Augmentation of the LVOT is determined by the full thickness of the septum (s) and the augmented circumference of the septal patch (p). Further resection of myocardium to the left of the septal incision (r) adds additional size to the LVOT.
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Complete removal of all obstruction in the LVOT is important to eliminate turbulence in the subaortic region. Because turbulence has been postulated to promote fibrosis and subsequent restenosis, many authors have suggested that more complete resection should result in lower rates of restenosis [11, 12]. Although this cause and effect relationship is difficult to prove and alternative causes have been proposed [13, 14], clinical series have demonstrated an association between lower postoperative LVOT gradients and lower rates of restenosis [6]. If complete removal of all obstruction (and turbulence) prevents restenosis, then the maximal augmentation of LVOT diameter with the modified Konno procedure will prove to be superior to lesser resections in complex LVOT obstruction, with the stipulation that the procedure does not add significant morbidity.
Another important rationale for maximal reduction in LVOT turbulence relates to the late onset of aortic insufficiency. With long term follow-up, van Son and coworkers [15] reported aortic insufficiency in 39% of patients with simple membranectomy, 28% after myotomy was added, and 7% after myectomy was added, suggesting that more aggressive resection leads to a lower late risk of aortic insufficiency [15]. This data supports the rationale for more aggressive subaortic resection, albeit with the caveat that the data weakly infer a causal relationship between the degree of resection and the late onset of aortic insufficiency.
In the present series, complex stenosis of the LVOT was effectively reduced with the modified Konno procedure while function of the aortic valve was maintained and permanent heart block was avoided. Although small residual VSDs were common in the early portion of the series, they have been reduced by more meticulous attention to the trabeculations in the proximal portions of the interventricular septal incision and do not appear to present a significant hemodynamic lesion. They may, however, represent a potential risk for endocarditis in the future. As noted, however, refinement of surgical technique has eliminated this complication in the latter third of the series. This study examined the combination of interrupted pledgetted mattress sutures in the trabeculated inferior portion of the septal incision with an overlying running suture, which has been an important factor in decreasing the incidence of residual VSD.
Other concerns include the long-term consequences of right bundle branch block. Although this has not resulted in appreciable morbidity within the relatively short followup of the present series, the long-term sequelae of a right bundle branch block are not well described after relief of left ventricular outflow tract obstruction. In adults referred for nuclear exercise testing, the presence of right bundle branch block is an independent predictor of all-cause mortality after controlling for multiple risk factors [16]. Furthermore, persistent changes in left ventricular relaxation and increased ventricular wall and septal thickness are noted years after resection of subaortic stenosis [17]. Thus, these patients will have a bundle branch block in a persistently hypertrophied ventricle with abnormal relaxation properties, which may have long-term prognostic significance.
If the modified Konno procedure can be performed with minimal morbidity in complex forms of LVOT obstruction, does it have a role in simple forms of LVOT obstruction? Recurrent LVOT obstruction is common after resection of simple LVOT obstruction, with reoperation rates of 10%–20% within 10 years after initial resection [6, 11, 15]. At reoperation, the recurrence is often found to be a diffuse fibrotic narrowing of the entire LVOT, supporting the concept that local anatomic factors are responsible for progression of stenosis [15]. Variables predictive of recurrent stenosis include the presence of coarctation and higher early postoperative LVOT gradient [6]. As factors leading to restenosis become better understood, it may be possible to predict which patients with simple stenosis would be better served with a modified Konno procedure at the time of initial resection rather than some less aggressive procedure.
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Conclusion
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Remodeling the left ventricular outflow tract in complex LVOT obstruction with the modified Konno procedure reduces LVOT gradients and preserves aortic valve function with minimal morbidity. If augmentation of LVOT diameter reduces risk of restenosis and late aortic insufficiency, then the use of the modified Konno procedure should result in reduced risk of late reoperation. Although traditionally used for complex LVOT obstruction, the relative safety of the modified Konno procedure supports extension of its application to simple forms of LVOT obstruction in patients at risk for restenosis.
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Abstract
Introduction
