Discrete Subaortic Stenosis: Assessing Adequacy of Myectomy by Transesophageal Echocardiography

Discrete Subaortic Stenosis: Assessing Adequacy of Myectomy by Transesophageal Echocardiography Erkan Kuralay, M.D., Ertugrul Ozal, M.D., Hakan Bingol, M.D., Faruk Cingoz, M.D., and Harun Tatar, M.D. Cardiovascular Surgery Department, Gulhane Military Medical Academy, Ankara, Turkey ABSTRACT Background; Membranectomy and myectomy are standard therapy for discrete subaortic stenosis (DS) and are associated with l o w rates of endocarditis, recurrence, and aortic insufficiency. Extensive myectomy increases risk of complications such as conduction tissue damage and iatrogenic ventricular septal defect (VSD). Materials and Methods: Fortyfive adult patients with DS underwent operations in Gulhane Military Medical Academy. Exertional dyspnea was the principal symptom in 29 (64.496) patients. Transesophageal echocardiography (TEE) was performed routinely in all patients t o assess t h e length and depth of needed myectomy during the perioperative period. Aortic insufficiency (All was also noted preoperatively in 31 (68.9%) and a history of aortic valve endocarditis was present in 4 (8.9%) patients. Results: Myectomy was performed according t o TEE measurements. A n average of 10 mm in width, 10 mm in depth, and 2.3 mm in length of septal tissue was resected. The mean left ventricle-aorta peak systolic gradient decreased from 70.2 f 9.7 t o 17.2 2 2.7 mmHg (p < 0.001). Aortic valve repair was performed in 8 (7.8%) patients and aortic valve replacement in 11 (24.4%) patients a t the initial operation. Iatrogenic VSD did not occur in any of the patients. Average postoperative left ventricular outflow tract diameter was 21 rt 1.5 mm. Temporary complete heart block occurred in three patients. There was an early residual gradient (36 f 8 mmHg) resulting from temporary hypercontraction t h a t decreased (18 2 5 mmHg) in t h e first postoperative day. Conclusions: Myectomy under perioperative TEE measurement is safe and effective in the treatment of DS. TEE-guided myectomy reduces complications such as complete heart block and iatrogenic VSD. (J Card Surg 1999; 14:348-353) Subvalvular aortic stenosis accounts for 8% to

30% of patients with congenital left ventricle outflow tract (LVOT) obstruction. Occasionally, it is secondary to a circumferential fibromuscular tunnel, but more commonly results from a discrete membrane immediately below the aortic valve.

Address for correspondence: Erkan Kuralay, M.D., Gulhane Lojmanlari Pamir Apt. No. 15, Etlik, Ankara, Turkey 0601 0. Fax: (90)312-435-47-32; e-mail: [email protected]

Discrete membranous subaortic stenosis has been shown to be amenable to operative treatment, resulting in normalization of left ventricle pressure in most patients.14 Discrete subaortic stenosis (DS) has been classified as either a thin, fibrous membrane (Type I) or a thicker fibromuscular band (Type Although the underlying congenital anatomic substrate leading to the development of DS has been well described,6 the natural history of progressive obstruction is unpredictable.6-9 Aortic insufficiency (All is the most common

J CARD SURG 1999;i4:348-353

acquired lesion of the aortic valve in DS and is believed to result from trauma to the valve cusps by an abnormal jet flow pattern caused by the lesion.l0 The Al can progress postoperatively despite relief of the LVOT stenosis of DS,I1 but worsening of the Al in DS can be slowed or stopped with adequate operative resection of DS.l0 The aortic valve remains a potential site for development of endocarditis in DS as a result of valve thickening from the jet flow pattern. The incidence is up to 13%.12As for Al, successful relief of LVOT obstruction is believed to reduce the risk of endocarditis in DS.IO Recurrence of subaortic stenosis and new subaortic membrane development have been reported even 27 years after operative r e ~ e c t i 0 n . Some l~ groups advocate concomitant selective myectomy to achieve full relief of the LVOT stenosis, 10,14,15 whereas others have reported that myectomy adds little to reducing the risk of recurrence of DS.l1 The goal of our study was to evaluate effectiveness of transesophageal echocardiography (TEE)-guided myectomy for reducing postoperative complications such as complete heart block and iatrogenic ventricular septal defects (VSDs) in DS pathology.

KURALAY, ET AL. DISCRETE SUBAORTE STENOSIS

TABLE 1 Associated Cardiac Defects FibroFibrous muscular Number Membrane Band of DS* DSt Patients Bicuspid aortic valve Aorta coarctation Atrial septal defect Patent ductus arteriosus lnfundibular pulmonary stenosis Ventricular septal defect

Forty-five adult patients with DS underwent operations between 1990 and 1998 at Gulhane Military Medical Academy Department of Cardiovascular Surgery. Average age was 22 2 3 years (range 18-36 years); there were four female patients. Cardiac catheterization, including both right and left heart and transthoracic echocardiography (TTE) were performed in all patients, and TEE examinations were performed routinely after 1990. A monoplane TEE probe (Hewlett Packard 21 362 A) was used until 1993; since then an Omniplane TEE probe (Hewlett Packard 21367 A) has been used. There were 32 DS patients with thin, fibrous membrane and 13 DS patients with thicker, fibromuscular band. Associated cardiac defects are shown in Table 1 . Three patients with aortic coarctation and one patient with patent ductus arteriosus (PDA) first underwent primary operation to repair these defects two months before cardiac operations. Principal symptoms were exertional dyspnea (64.4%) and palpitation (55.5%).Histories of fatigue, chest pain, syncope, dizziness, and bacterial endocarditis were also obtained (Table 2). Average left ventricle-

40

3

1

4

8.9

2 2 1

1 1 1

3 3 2

6.7 6.7 4.4

1

-

1

2.2

1

-

1

2.2

*Total of 32 patients. +Total of 13 patients. ' DS = discrete subaortic stenosis.

~~~~

TABLE 2 Clinical Finding of Patients With Discrete Subaortic Stenosis (DS)

FINDING

MATERIALS AND METHODS

349

FibroFibrous muscular Number Membrane Band of DS* DSt Patients 96

Exertional dyspnea Palpitation Fatigue Chest Pain Dizziness Syncope Endocarditis Asymptomatic

21 14 10 9 5 3 3 6

8 11 7 2 2 3 1 1

29 25 17 11 7 6 4 7

64.4 55.5 37.8 24.4 15.5 13.3 8.9 15.5

*Total of 32 patients. +Totalof 13 patients.

aortic (LV-Ao) peak systolic gradient was 70.2 2 9.7 mmHg (range 33-85 mmHg). Indications for surgical treatment were peak systolic gradient > 40 mmHg, evidence of new or progressive Al, and coexisting cardiac malformations requiring surgical intervention. New evidence of Al also had a crucial role as an indication for surgical treatment. Surgery was done without regard for LV-Ao gradient when new Al was noted. Most of the patients with DS had abnormalities of the aortic valve; in a few cases it was congenital, whereas in the majority of case it was acquired. Bicuspid aortic valve was found in four (8.9%) patients, three of whom were stenotic. Al was the most common acquired

350

KURAIAY, ET AL. DISCRETE SUBAORTIC STENOSIS

valve abnormality and was found in 31 (68.9%) patients. We used the ratio of proximal jet diameter/ LVOT diameter for grading Al (ratio < 25% grade I, 25% to 46% grade II, 46% to 64% grade Ill, and > 64% grade IV).16 According to this classification, 6 were grade I, 18 were grade II, 5 were grade Ill, and 2 were grade IV. Grading of Al may be a problem in patients with DS because the discrete membrane is close to the base of the aortic cusps. Regurgitant blood flow from the aortic valve in diastole abuts the discrete membrane and creates additional turbulent flow. Measurement of the proximal jet diameter becomes difficult (overestimates), so the ratio of grading becomes an approximation. A similar problem is also encountered when the penetration of regurgitant flow (underestimate) is measured.17 The discrete membrane can slow the regurgitant jet velocity, and this penetration of reverse flow into the left ventricle is diminished. This handicaps grading of Al in the preoperative period, therefore the aortic valve should be carefully inspected during the operation. TEE examinations were done both in the perioperative and postoperative period. Perioperative echocardiographic examination just before cardiopulmonary bypass has a crucial role for estimating necessary length and depth of myectomy and for grading Al. Transesophageal measurements were done on mid esophageal view at 150" to 160" in which both the discrete membrane and the hypertrophic parts of the interventricular septum can be easily identified. Length and depth of hypertropic interventricular septum were measured and all data were reported to the surgeon. TEE measurements were also repeated in the same position before termination from bypass. Outflow tract diameter was also measured. Echocardiographic follow-up was performed yearly for an average of 6.7 t 0.82 years (1-8.4 years). Surgical technique

Cardiopulmonary bypass with moderate hypothermia (29" to 31") was used consistently. Topical hypothermia was added for myocardial protection during the aortic period. St. Thomas II crystaloid cardioplegia was infused initially from the aortic root, and additional infusion was given every 20 minutes into the coronary ostia. Aorto-

J CARD SURG 1999;14:348-353

tomy was transversed close to the sinus ridge and extended into the noncoronary sinus. The subvalvular area was visualized by retracting the aortic leaflets. Membranous obstruction was identified as a thin, crescent-shaped fibrous membrane extending across the anterior portion of the outflow tract beneath the aortic annulus and attaching a t each border to the anterior mitral leaflet. Occasionally, there was circumferential obstruction continuing across the anterior mitral leaflet. Commonly, the membrane was contiguous with the base of the right and left cusps of aortic valve. Detaching the membrane from the ventricular septum by blunt dissection toward each end of the crescent was performed in thin, fibrous membrane type lesions. Dissection was made by blade in thicker fibromuscular band type lesions. All abnormal fibrous suspensions between the mitral valve and the aortic annulus were excised. Left ventricular myectomy was then performed by scalpel. A stay suture was attached to the hypertrophied interventricular septum to improve surgical exposure. The first ventricular myotomy incision began 2-3 mm right of the midpoint of the right coronary cusp. The second incision was placed 10 mm to the left of and parallel to the first incision; the third incision was transverse and connected to the previous two incisions. The width of myectomy was 10 m m in all cases. Depth and length of myectomy were done according to perioperative transesophageal measurements. We resected septa1 tissue 10 mm in width and on average 10 '-t 1.2 m m in depth and 2.3 t 1.1 mm in length. Our goal was to increase the outflow tract size to over 18 mm in patients with a narrow outflow tract. When the outflow tract was greater than 18 mm, myectomy was performed only to remove hypertrophied interventricular septum. Great care was taken to avoid injury to conduction tissue between the right and noncoronary cusps and the anterior leaflet of the mitral valve in which the membrane occasionally was adherent. Incisions were initiated 5-10 mm below the aortic annulus, because the ventricular septum was frequently thin in this basal area and could not create outflow obstruction; also, iatrogenic VSD could be avoided. The aortic valve was inspected carefully, repaired, and replaced. Statistical analysis was performed with SPSS software version 7.0 (SPSS, Chicago, 111, USA). Clinical data are expressed as the means plus or

KURALAY, ET AL. DISCRETE SUBAORTIC STENOSIS

J CARD SURG 1999;14:348-353

minus the standard deviation. Differences were analyzed with an independent t-test. The differences were considered to significant for values of p < 0.05. RESULTS

All patients were weaned successfully from cardiopulmonary bypass; there was no hospital mortality. Six patients required low-dose inotropic agents. Average aortic clamp time was 31 ? 8 minutes and average cardiopulmonary bypass time was 41 t 5 minutes. The aortic valve was stenotic in three patients with bicuspid aortic valve. Aortic commissurotomy (AC) was done in one of these patients. Aortic valve replacement (AVR) was done in the other two patients who had bicuspid aortic valve. Aortic cusp resuspansion was done in eight patients. AVR was also performed in 11 patients because of extensive fibrosis and destruction of cusps. Four of these patients had a history of infectious endocarditis. Aortic valve insufficiency was found in 21 patients by postoperative TEE examinations. There were 9 grade I and 12 grade II Als in the early postoperative period. Al increased in two patients in whom aortic valve resuspansion was done; AVR was done in the second postoperative year for these patients. We have not found any increase of Al in the other patients during the follow-up period. Endocarditis did not develop in any patient after operation. Complete heart block developed in three patients. All of them resolved within the first postoperative week. Left bundle branch block occurred in 23 (51.I YO)patients; iatrogenic VSD did not occur. LV-Ao peak systolic gradient was measured in all cases just after weaning from cardiopulmonary bypass. Average LV-Ao peak systolic gradient was 36 t 8 mmHg in these measurements. LVAo gradient was measured 5, 10, and 24 hours after operation. Average LV-Ao gradient was 28 ? 4 mmHg at 5 hours, 24 ? 6 mmHg at 10 hours, and 18 5 5 mmHg at 24 hours. Average LV-Ao peak systolic gradient was 17.2 t 2.7 mmHg at discharge period examinations. Thus the LV-Ao peak systolic gradient decreased from 70.2 t 9.7 to 17.2 5 2.7 mmHg (p < 0.001). Beta-blockers were administrated in 27 (60%) patients. Average LVOT diameter was 21 t 1.5 mm (range 18.3-24.2 mm). There were two female pa-

351

tients with left ventricular outflow < I9 m m (18.3 and 18.5 mm). These patients had small body surface area so they did not have residual outflow tract stenosis. All patients experienced follow-up echocardiographic examinations every year; there was no sudden death within the follow-up period. New onset LVOT obstruction was found in one case 4 years postoperatively. The LV-Ao peak systolic gradient was 31 mmHg. AVR had been done in the first operation; calcium channel blockers had been administrated and the patient's functional capacity remained in Class ll. Operation was not advised t o this patient. DISCUSSION Discrete subvalvular stenosis may often result in a severe form of left ventricular obstruction, and LV-Ao gradient of > 50 mmHg has been noted in 88%'* of patients. Knowledge of the pathogenesis of this lesion has proven elusive, but a number of theories have been proposed to explain its occurrence. The explanations attribute DS to congenital,lg inflammatory,20 genetic,21 and acquired22causes. Another important feature of DS is its progressive nature. Although there is no evidence that DS is present at birth, it usually becomes evident during the first decade of life. This observation has led to the suggestion that fixed subvalvular stenosis is an acquired lesion whose hemodynamic severity can progress with time23.24; but embryogenetic factors may influence the development of DS. The presence of an intrinsically long and narrowed LVOT may cause alterations in blood flow patterns within the heart during early embryogenesis, leading to the accumulation of cells near the crest of the ventricular septum.24These cells may later differentiate into the fibromuscular tissue that narrows the subaortic region. Another theory about the progressive nature of DS is explained by the Rodbard phenomenon.25 Rodbard reproduced abnormal flow in an animal model; in accordance with Bernoulli's principle of energy conservation, progressively stenotic lesions were produced. Although clear knowledge of the precise pathogenesis is limited, several aspects of the disease are more clearly defined; thus there is an established association with Al and endocarditis, and there is a substantial recurrence rate after surgical excision. The results of surgical treatment of DS in adults has been reported, but a number of these studies

352

J CARD SURG 1999;14:348-353

KURAMY, ET AL. DISCRETE SUBAORTIC STENOSIS

are limited.26 DS may have a serious course in adult patients. LV-Ao peak systolic gradient is higher than in children and septal hypertrophy is prominent in adults. Al is frequent; endocarditis is common and the aortic cusps are more distorted than in childhood. AVR and valve repair are usually required in most patients. We performed 8 aortic cusp repairs (1 7.8%) and 1 1 AVRs (24.4%) in our group of adult patients. Septa1 hypertrophy was found in all patients and myectomy was required. The depth and length of myectomy should not be done as in hypertrophied cardiomyopathy. Development of iatrogenic VSDs ~~,~~ have been reported in a few s t ~ d i e s . Development of conduction system damage such as complete heart block can easily occur during the overzealous myectomy. The width of the myectomy was 10 mm in all cases. Depth and length of the myectomy should be done according to TEE measurements. We had resected septal tissue in an average of 10 m m in width, 10 2 1.2mm in depth, and 2.3 2 1.1 mm in length. Preoperatively, Al is common in these patients.1° Al may progress postoperatively, despite relief of the LVOT stenosis.ll But usually worsening of the At in DS can be slowed or stopped with adequate resection of DS and added myecOur data support those last conclutomy.2#10,14 sions. Al was found in 21 patients in the postoperative period. Al was increased in only two patients who underwent additional valvular surgical correction at their initial operation.

CONCLUSIONS The aortic valve remains a potential site for development of endocarditis in DS even after surgery, with a reported incidence rate of up to 13%.12 The predisposing factors are a high LVOT gradient and Al. We have not found endocarditis in our follow-up period. Recurrent LVOT obstruction after resection is well documented and reoperation is required at a rate of 6% to 30%.10s27-30 This high rate is attributed to inadequate resection at the first operation, but a component of dynamic obstruction is also responsible.22Ashraff” and Cain27reported that myectomy did not decrease recurrences requiring reoperation. Reoperation rate was > 15% in these studies. Rayburn and coworkers used extensive myectomy in DS and reported a reoperation rate of 4.3%. Only one case of mild LVOT ob-

struction (31 mmHg) occurred after initial operation, which we attributed to controlled myectomy under TEE guidelines. Membranectomy and myectomy in adult patients with DS is a safe and effective treatment of this pathology. Our results show a decrease in postoperative LV-Ao gradient and a low rate of recurrent postoperative LVOT obstruction without progression of Al or development of endocarditis. Although a residual gradient may be present at the end of the operation, reduction of the LVOT gradient can be expected in most patients within 24 hours. During the repair of DS, the surgeon should be confident that myectomy was properly and completely p e r f ~ r m e d .Perioperative ~~ TEE to access the depth and length of myectomy not only reduces complications such as heart block and iatrogenic VSD but also provides effective minimal myectomy for reducing the postoperative residual gradient.

REFERENCES 1. Frommelt MA, Snider R, Bove EL, et al: Echocardiographic assessment of subvalvular aortic stenosis before and after operation. J Am Coll Cardiol 1992;19:1018-1023. 2. Hazekamp MG, Frank M, Hardjowijono R, et al: Surgery for membranous subaortic stenosis: Long term follow-up. Eur J Cardiothorac Surg 1993;7: 356-359. 3. Lupinetti FM, Pridijian AK, Callow LB, et al: Optimum treatment of discrete subaortic stenosis. Ann Thorac Surg 1992;54:467-471. 4. Jaumin P, Rubay J, Lintermans J, et al: Surgical treatment of subvalvular aortic stenosis: Long term results. J Cardiovasc Surg 1990;31:31-35. 5. Kelly DT, Wulfsberg E, Rowe RD: Discrete subaortic stenosis. Circulation 1972;46:309-322. 6. Kleinert S, Geva T: Echocardiographic morphometry and geometry of the left ventricular outflow tract in fixed subaortic stenosis. J Am Coil Cardiol 1 993;22: 1501-1 508. 7. Silverman NH, Gerlis LM, Ho SY, et al: Fibrous obstruction within the left ventricular outflow tract associated with ventricular septal defect: A pathologic study. J Am Coll Cardiol 1995;25:475-481. 8. Sommerville J: Fixed subaortic stenosis: A frequently misunderstood lesion. Int J Cardioi 1985; 8: 145-148. 9. Gewilling M, Daenen W, Dumoulin M, et al: Rheologic genesis of discrete subvalvular aortic stenosis: A Doppler echocardiographic study. J Am Coil Cardiol 1992;19:818-824.

J CARD SURG 1999;14:348-353

10. Wright GB, Keane JF, Nadas AS, et al: Fixed subaortic stenosis in young: Medical and surgical course in 83 patients. Am J Cardiol 1983;52:830-

835. 11. Ashraf H, Cotroneo MD, Dhar N: Long-term results

after excision of fixed subaortic stenosis. J Thorac Cardiovasc Surg 1985;90:864-871. 12. Kaltz NM, Buckley MJ, Liberthson RR: Discrete membranous subaortic stenosis. Report of 31 patients, review of the literature and delineation of management. Circulation 1977;56:1034-I038. 13. Maron BJ, Graham MD, Poliac LC, et al: Recurrence of a discrete sub aortic membrane 27 years after operative resection. Am J Cardiol 1995;76:

104-105. 14. Hardesty RL, Griffith BP, Mathews RA: Discrete subvalvular stenosis. An evaluation of operative therapy. J Thorac Cardiovasc Surg 1984;118:79-

83. 15. McKay R, Ross DN: Technique for the relief of discrete subaortic stenosis. J Thorac Cardiovasc Surg

1982;84:917-920. 16. Perry GJ, Helmcke F, Nanda NC, et al: Evaluation of aortic insufficiency by Doppler color flow mapping. J Am Coll Cardiol 1987;9:952-959. 17. Ciobanu M, Abbasi AS, Allen M, et al: Pulsed Doppler echocardiography in diagnosis and estimation of severity of aortic insufficiency. Am J Cardiol 1982;49:339-343. 18. Newfeld EA, Muster AJ, Paul MH, et al: Discrete subvalvular aortic stenosis in childhood. Am J Cardiol 1976;38:53-61. 19. Schorstein KA: Lecture on the fate of the bulbis cordis in human heart. Lancet 1924;2:1267-1272. 20. Cheevers N. Observations on the disease of the orifice and valves of the aorta. Guys Hosp Rep

1978;1842:387-442.

KURALAY, ET AL. DISCRETE SUBAORTIC STENOSIS

353

21. Pyle RL, Patterson DF, Chacko S: Genetics and pathology of discrete subaortic stenosis in the Newfoundland dog. Am Heart J 1976;3:324-334. 22. Somerville J, Stone S, Ross D: Fate of patients with fixed subaortic stenosis after surgical removal. Br Heart J 1980;43:629-647. 23. Borow KM, Glagov S: Discrete subvalvular aortic stenosis: Is the presence of upstream complex blood flow disturbance an important pathogenic factor? J Am Coll Cardiol 1992;19:825-827. 24. Rosenquist GC, Clark EB, McAllister HA, et al: Increased mitral-aortic separation in discrete subaortic stenosis. Circulation 1979;60:70-74. 25. Rodbard S: Physical factors in the progression of stenotic vascular lesions. Circulation 1958;17:41041 7. 26. Sung CS, Price EC, Cooley DA: Discrete subaortic stenosis in adults. Am J Cardiol 1978;42:283-290. 27. Cain T, Campbell D, Patton B, et al: Operation for the discrete subvalvular aortic stenosis. J Thorac Cardiovasc Surg 1984;87:366-370. 28. Douville EC, Sade RM, Crawford FA Jr, et al: Subvalvar aortic stenosis: Timing of operation. Ann Thorac Surg 1990;50:29-34. 29. Jacops JP, Palatianos GM, Cintron JR, et al: Transaortic resection of the subaortic membrane: Treatment for subvalvular aortic stenosis. Chest 1994;106:46-51. 30. Brown J, Stevents L, Lynch L, et al: Surgery for discrete subvalvular aortic stenosis: Actuarial survival, hemodynamic results and acquired aortic regurgitation. Ann Thorac Surg 1985;40:151-155. 31. Ziskind Z, Goor DA, Peleg E, et al: The perioperative fate of residual gradients after repair of discrete subaortic stenosis and time-related blood levels of catecholamines. J Thorac Cardiovasc Surg 1988;96:423-426.