Asymmetric Septal Hypertrophy in Patients with Aortic Stenosis: an Adaptive Mechanism Or a Coexistence of Hypertrophic Cardiomyopathy?

View metadata, citation and similar papers at core.ac.uk brought to you by CORE

J AM cou,providedCARDIOl by Elsevier - Publisher783 Connector 1983.1(3)783-9

Asymmetric Septal Hypertrophy in Patients With Aortic Stenosis: An Adaptive Mechanism or a Coexistence of Hypertrophic Cardiomyopathy?

OTTO M. HESS, MD, JAKOB SCHNEIDER, MD, MARCO TURINA, MD, JOHN D. CARROLL, MD, FACC, MARTIN ROTHLIN, MD, HANS P. KRAYENBUEHL, MD

Zurich, Switzerland

Myocardial histologic features andventricular left dy• 1 and 2 (26.5 versus 29.1IJ.; NS), but muscle fiber di• namics were assessed in 24 patients with severe aorticameter of the septum in group 1 was significantlysmaller stenosis, 12 with (group 1) and 12 without (group(24.4 2) IJ.; P < 0.01) than that ofanterolateral the wall in associated asymmetric septalhypertrophy.In 10patients group 2. No morphologic abnormalities typical for hy• from group 1,echocardiographyshowed a septal/pos• pertrophic cardiomyopathy (fiberdisarray)were seen in teriorwall ratio of 1.5; in the other 2, asymmetric septalsamples from the patients in either group. By 18 months hypertrophywas diagnosed by direct inspection at thepostoperatively, septal wall thickness had decreased sig• time of surgery. Septal myectomy in all 12 patientsnificantly in from 2.0 to 1.5 em< (p0.01) and posterior group 1 was completed at the time of aortic valvewall re• thickness from 1.4 to 1.2 cm< (p0.05) in group 1. In group 2, septal wall thickness decreased from 1.5 placement. Septal histologicfeatures were assessedfrom to 1.3 em (NS) and posterior wall thickness from 1.4 to surgical specimens in 10 patients in groupTransseptal 1. 1.2 em (NS) 8 months postoperatively. endomyocardial biopsy specimens ofanterolateral the Asymmetric septalhypertrophyin patients with aor• wall taken during preoperative cardiac catheterization tic stenosis is an adaptive mechanism to the long-stand• were evaluated by light microscopy in 10 patients froming pressure overload, and hence there is no evidence of group 1 and all patients of group 2. coexistenceof idiopathichypertrophiccardiomyopathy Leftventricularend-diastolic and peak systolic pres•and aortic valve disease. Although the degree of valve sure, peak pressure gradient, calculated valve areaobstruction and was similar in both groups,ventricular left angiographic muscle mass did not differ significantlyejection in performance wassignificantlylower in the group groups 1 and 2; ejection fraction (68 versus%; prob• 58 without asymmetric hypertrophy, probably because these ability [p]< 0.01) waslargerand end-diastolic volumepatients had a more advanced stage of myocardial dis• (109 versus 144 ml/m"; difference not significant[NS]) ease. After successful valve replacement, there is a sig• was smaller in group 1 than in group 2. Muscle fibernificant regression of septalhypertrophyin patients with diameter of theanterolateralwall was similar in groups aortic stenosis and asymmetric septalhypertrophy.

Asymmetricseptalhypertrophyhas been found to be theit can alsooccur in patientswith severe aortic stenosis characteristicabnormalityin patientswithhypertrophiccar• (4-8),and it has beensuggestedthat in these patients it is diomyopathy(1-3). It is definedechocardiographicallyby due to acoexistenceof secondaryhypertrophyand hyper• adisproportionalthicknessof theinterventricularseptum as trophiccardiomyopathy.This hypothesiswas based on the comparedwith the leftventricularposteriorwall.However, preoperativeechocardiographicfinding ofasymmetricseptal hypertrophyin patientswith severe aortic stenosis(4,5). In somepatients(5),histologicexaminationof theexcised From the Department of Internal Medicme, Medical Policlinic, Car•septal tissuedemonstratedmorphologicabnormalitiestyp• diology, Institute of Pathology and Surgical Chruc A, University Hospital,ical of hypertrophiccardiomyopathy.In anotherstudy, Zurich, Switzerland. This study was supported by the Swiss NationalThompsonandco-workers(6) found noregressionof myo• Science Foundation, Zurich, Switzerland. Manuscript received July 28, 1982; revised manuscript received October 19, 1982, accepted Octobercardialhypertrophyaftersuccessfulvalvereplacement,and 25, 1982. intraventricularpressuregradientsin four of six patients Address for reprints: Otto M. Hess, MD, Department of Internal Med•suggestedcoexistenceof hypertrophiccardiomyopathyand icine, Medical Policlinic, Division of Cardiology, University Hospital, Raermstrasse 100, 8091 Zurich, SWitzerland. aortic valvedisease.

The purposeof the presentstudy was toexaminethe whom a good qualityechocardiogramwas not obtained, asym• histologic features of themyocardiumand leftventricular metric septal hypertrophy was diagnosed or excluded by left ven• hemodynamicsin 24 patientswith severe aortic stenosis,tricularcineangiographyor by visual and digital inspection of the 12 with and 12 without asymmetric septal hypertrophy,left inventricularoutflow tract during aortic valve replacement, or order todeterminewhetherthelatterconditionis an adaptive by both. M-mode andtwo-dimensionalechocardiographywere repeated mechanism to the long-standing pressure overload or whether 17.6 monthspostoperativelyin group I and 8.1 months postop• it representsa combinationofbothsecondaryhypertrophy eratively in groupQuantitative 2. evaluation of the M-mode echo• andhypertrophiccardiomyopathy. cardiogramsincluded the same variables as during the preoperative examination.However, in two patients from group I and in one patient from group 2, a good qualityechocardiogramwas not Methods obtained. Studypatients.Twenty-fourpatients (7 women and 17 men) Cardiaccatheterization.Informed consent was obtained from with an average age of 51 years (range 25 to 69) were studied.all patients. Premedication consisted of 10chlordiazepoxide mg of Twelve patients (group 1) had severe aortic stenosis with asym•or of 5 mg of diazepam given orally I hour before the procedure. metric septalhypertrophy(mean systolic ventricular-aortic pres•Left ventricular pressure was measured in 24 patients by a Millar sure gradient 74 mm Hg, mean aortic valve areaem", 0.69mean 7F-micromanometerthat had been advanced into the left ventricle aorticregurgitantfraction0.17),and 12 patients (group 2) hadthrough a transseptally introduced 11.5Brockenbrough F guiding severe aortic stenosis butasymmetric no septal hypertrophy (mean catheter (9). The patients then received intravenous heparin in a systolic pressure gradient 67 mm Hg, mean aortic valve areadose 0.74 of 10,000 units. Themicromanometerwas calibrated by ern",mean aorticregurgitantfraction0.18).The 24 patients with superimposing the micromanometer tracing withconventional the severe aortic stenosis were selected from a cohort of 161 patientspressure tracing (9,11). with aortic stenosis with or without aortic regurgitation who under•Monoplane left ventricular cineangiography in the right ante• went cardiaccatheterizationduring the same time interval betweenrior oblique position was performed at midinspiration at a filming October 1977 and January 1982 as did our 24 patients. All patientsrate of 50frames/soQuantitative evaluationend-diastolic of and had M-modeechocardiography,and asymmetric septal hypertro•end-systolic frames for the calculationventricular of left volumes phy was found in only 14 patients. Thus, the incidence of asym•and ejection fraction was carried out according to our standard metric septalhypertrophyin our cohort of 161 patients with aortictechnique(II). Left ventricular muscle mass wascalculatedac• stenosis was9.0%.Two of the 14 patients with asymmetric septalcording to the technique of Rackley et al. (12). hypertrophy were,however,not included in the present study. Left ventricularendomyocardialbiopsy.At the end of the Coronary arteriography was carried out in all 24 patients. catheterization procedure,endomyocardial two biopsies were per• There was a 50% stenosis of the left circumflex coronary arteryformed in 10 of the 12 patients from group I and m all patients in only one patient from group 1; a 50% stenosis of the left anteriorfrom group 2, using a King's College bioptome (9) introduced descending coronary artery was detected in one patient from group into the left ventricle throughBrockenbrough the guiding catheter. 2. Minimal to mild mitralregurgitationwas present in three patients The biopsy specimens were taken fromanterolateral the wall of from group 1(regurgitantfraction ranging from 0.050.14). to All the left ventricle, and other than transient prematureventricular patients had sinus rhythm atpreoperative the evaluation. complexes during most biopsies,complications no occurred in any Echocardiography.M-mode echocardiograms(Organon of the 22 patients. Immediately after the biopsyperformed, was Teknika) were recorded shortly beforepreoperativecardiac cath• the material was fixedglutaraldehyde in and embedded in Epon eterization in theanteroposteriorposition or in the right anterior for quantitative morphometry(9,13,14).The muscle fiber diameter decubitus position according to our standard technique (9). Left and the extent of interstitial fibrosis were determined from semi• ventricularinternaldiameter,shortening of the internal diameter, septal wall thickness andposteriorwall thickness (Fig. I) as well thin sections (1J.L). From several sections of each biopsy specimen, as heart rate weredeterminedin all patients. Two-dimensionalthe muscle fiber diameter wasdeterminedusing a mechanical• echocardiograms(Varian V3(00)were obtained routinely in eachoptical pen (MOP, Kontron GmbH, Zurich). At least 100 measure• patient with M-modeechocardiographyto confirm or exclude ments were performed with this pen. The extent of interstitial asymmetric septalhypertrophyvisually from the two-dimensionalfibrosis was evaluated by usmg the point counting system (13). A echocardiogram.This was done as it is known that a false positivespecial ocular with a grid providing 100 intersection points was diagnosis ofasymmetricseptal hypertrophy can occur with M•used to determine the amount of fibrous tissue; more precisely, modeechocardiography,most commonly as a result of the ultra•the amount ofnonmuscularinterstitial tissue was evaluated by sonic beam passing vertically through the ventricular septum.counting the number of points overlaying interstitial tissue. To Moreover,asymmetricseptal hypertrophy was confirmed at theterm thisnonmuscularinterstitial tissue"interstitialfibrosis"is time of surgery by direct inspection (see later). In two patientssomewhat incorrect, but because fibrous tissue is the largely pre• from each group, the M-mode echocardiogram was not good enoughdominantcomponentof the interstitial space, the"fibrosis" term to provide adequate data and therefore was not includedwas in the used in this context. With this grid, usually 1,000 points were present analysis. The ratio of septal to posterior wall thicknesscounted and the average interstitial fibrosis was calculated in all described by Henry andco-workers(I,10) was used to define patients who underwent biopsy. asymmetry of the leftventricularhypertrophy asseptal-posterior a With use ofthe same technique, the left ventricular muscle fiber wall ratio of 1.3 or greater. In the two patients of each groupdiameter in was determined from septal myocardium obtamed from ASYMMETRIC SEPTAL HYPERTROPHY J AM COLL CARDIOL 785 1983.1(3).783-9

ASYMMETRIC SEPTAL HYPERTROPHY

IVS

AMV LV

Figure1. M-modeechocardiogramin a patientwith aor• tic stenosis andasymmetricseptalhypertrophy(upper PCG panel) and a patient with aortic stenosissymmetric and ECG hypertrophyof the septum and the posterior wall (PW) (lower panel). Theend-diastolic(ed) andend-systolic (aortic valveclosure-As)wallthicknessof theinterven• tricular septum (IVS) and posterior wall (PW) are mea• 7.6.79 1/2 s ec I.K.c!1927 suredjust belowthe mitralvalve. Notethedisproportion- allythickenedinterventricularseptum in the upper panel SYMMETRIC HYPERTROPHY - ~ . ' (septal/posteriorwall ratio 1.50) Theendocardialborder . '''•..' 0·.•"''''' .' .. ~ '. ' -. ~ '., ." of the septum and the posterior wall in the upper panel . .; .....~ ..;'-a e. ' Af ~ : ,," havebeenslightlyretouchedforillustrationpurposes.AMV :. " RV = anteriormitralvalveleaflet;ECG = electrocardiogram. LV = leftventricle;PCG = phonocardiogram;RV = IVS rightventricle 5em[

AMV LV

. , , PCG ~ ECG

3.27.8 0 1/2 s ec D,M.? 19 19

10 of 12 patientswith septalmyectomyduring aortic valve re• pertrophy(septal/posteriorwall ratio 2.0) and of a second patient placement.In 2 ofthese 12patients,myocardialmaterial was not who died ofunsuspected,severe aortic stenosis withasymmetric availablealthoughseptalmyectomywas carriedout. septalhypertrophy(septal/posteriorwall ratio 1.3). These hearts It is obviousthatquantitativeevaluationof endomyocardial were,however,fixed informalineand hence theabsolutevalues biopsyspecimensis limitedbecauseonly small samples of the left of themorphologicdata are notdirectlycomparablewith those ventricularmyocardiumareobtained.In patientswith aortic valve obtainedfrom endomyocardialbiopsies. disease,themorphologicchangesin themyocardiumare more or Aorticvalvereplacement.Severe alterations of the aortic valve less uniformlydistributedoverthe whole leftventricle(15),al• were found in all 24 patients at the timesurgery, of and 5patients though there might be some focalprocessesthat could affect our from group I as well as 4 patients from group 2bicuspid had a quantitativeanalysis.The presentdata of the group I patients valve. All 24 patients showedcalcifications;in 13 of thesepatients, show,however,that the leftventricularmuscle fiberdiameterin the calcificationextendedto the mitral anulus. Aortic valve re• theseptum(intraoperativematerial)and theanterolateralwall (en• placementconsistedof theimplantationof abioprosthesis,ofeither domyocardialbiopsy sample) aresimilar,suggestingthat the mus• theCarpentier-Edwardstype (in eight patients from group I and cle fiberdiametercan bedeterminedwith good accuracy from threepatientsfrom group 2) or theAngell-Shileytype (in four biopsysamples. patientsfrom group I and twopatientsfrom group 2). A me• To illustrate the different morphologic findings in patients with chanicalvalve of theBjork-Shileytype wasimplantedin five hypertrophic cardiomyopathy (16) and patients with aortic valve patientsfrom group 2 and of the St. Jude Medical typeanother in disease (15), we usedquantitativemorphometryto examine at two patientsfrom group 2. postmortem(Fig. 2) the heart of onepatientwho died of unsus• Septal myectomy was carried out by the transaortic approach pectedhypertrophiccardiomyopathywith asymmetricseptalhy- in all J2 patients in group J Intraoperatively,all 12patients 786 J AM Ca LL CARDlOL HESS ET AL 1983.1(3) 783- 9

" r: ...... I ., : ( . ./ ' ~ .';,.... , • , ~ .. /e " ... " i -" . . ...' . . ~ .-~ ...... , " .. . " , , , .' .... ,.... , . :. "' ...... t .", • • - ... ! ' .,. .- •I .,..' ...... '. . ., - .. ", .. J , , .. .. . :.: , ...... ~ . >- .. , ' ." .. '.- . ~ -: • .. - '" . .- : .... " , , . ,.. -" .' ' : ...... -. ,- ...... I , . ~ ..- ..

Figure 2. Histologic section of the interventricular septum at postmort em signifi cantly, larger in group 2 patients without asymmetric examination in a patient with aortic stenosis and asy mmetric septal hy• pertrophy (left) and in a patient with asymmetric septal hypertrophy due septal hypertrophy than in group 1 patients (5.9 versus 5.2 to hypertrophic cardiomyopathy (right) (magnification in both sections 125 cm). Left ventricular systolic shortening of the internal di• X). Moderate muscle fiber hypertrophy with slightly increased interstitial ameter was, however, significantly smaller in group 2 than fibrosis ( == seco ndary myocardial hypertrophy) is evident 10 the patient with aortic stenosis , but severely hypertrophied muscle fibers, fiber disarray ingroup I (34 versus 43%; probability [p] < 0.01). Posterior (whirl formation) and enlarged nuclei are evident in the panent wuh hy• wall thickness was similar in both groups, but both septal pertrophi c cardiom yopathy. Thi s characteristic picture of hypertr ophic wall thickness (2.0 versus 1.5 ern; p < 0.0 I) and septal! cardiomyopathy was not see n In any of the 24 patients with aortic stenosis in our series . posterior wall ratio (1.5 versus 1.1; P < 0.0 I) were sig• nificantlylarger in group I than in group 2. Systolic anterior motion (SAM) of the anterior mitral leaflet was found in showed severe hypertrophy of the interventricular septum with five patients from group I and in none from group 2. In no bulgingintotheleftventricular outfl owtract.There were noserious case did the anterior mitral leaflet reach the interventricular complications in any of the 24 patients operated on. septum, although the typical anterior movement described Statistics, Statisticalcomparisons between thetwogroups were by Henry et al. (10) was noted in these five patients. performed using the Wilcoxon test for two independent groups. In group I. the postoperative evaluation showed a sig• The pre-andpostoperative comparisons were carried out usingthe nificant reduction in septal (2.0 before versus 1.5 ern after Wilcoxon test for paired observations. The mean values ± I operation; p 0.01) and posterior wall thickness (1.4 before standard deviation are given in all tables. < versus 1.2 cm after operation; p < 0.05) as well as a sig• nificant decrease in septal/posterior wall ratio (1.5 before Results versus 1.2 after operation; p < 0.0 I). However, in group Echocardiography (Table 1). Heart rate during routine 2, there were no significant changes in septal or posterior echocardiography did not differsignifi cantly in the twogroups. wall thickness after operation, probably because of the sig• Left ventricular internal diameter was slightly, although not nifi cantly shorter mean postoperative observation time in ASYMMETRIC SEPTAL HYPERTROPHY J AM CaLL CARDIOL 787 19H3 113) 7H39

Table 1. Echocardiographic Finding, Before (pre) and After (post) Operation n HR DD Sh IVS PW IVS/PW Group I Pre 10 73 ± II 5.2 ± 0.7 43 10' 2 0 04 14±0.2, ± 0.21 ± . ± 1 rl.S Post 10 79 ± 17 4.8 ± 0.4r 3712... ± * rI 5 ± 0 4~ 1.2 ± 03...* 1.2 ± 0 3... Group 2 s:, s, Pre to 76 ± 16 5.9 ± 1 3 L34 ± 9 L 1.5 ± 0.4 14 ± 0.2 LI.I ± 02 Post 11 84 ± 19 5.4 ± 1 0 32 ± 10 13 ± 0 1 1.2 ± 0 I 1.1 ± 0.1

* p < 005:t p < 001.given are mean value,:':: I standarddeviauon.D" = lelt ventricularend-dra-tohcinternaldiametertcnu.HR = heart rate(beatvnum.IVS = thickness of the Interventricular septum (em). IVS/PW= -eptal-povtenor wall rauo. po-t~ po-roperauve pre~ preoperative. PW= thrckne-,-,01 the povterun wall (cm) Sh = systohc shortening of the left ventricular mternal diameter(clr)

group2 (8, I months)comparedwithgroupI (17.6months; musclefibers withmoderateinterstitialfibrosis as seen typ• p < 0.005).The leftventricularinternaldiameterdid not ically insecondarymyocardialhypertrophy(15). significantlychangein eithergrouppostoperatively;how• Illustrative cases(Fig.3). Wedeterminedthe left ven• ever,leftventricularsystolicshorteningof the internal di• tricularmusclefiberdiameterof theinterventricularseptum ameterdecreasedsignificantlyin group I from 43% pre• and theposteriorwall in thefollowingtwo patients: one operativelyto 37%postoperatively(p < 0.05),butremained who died ofhypertrophiccardiomyopathyandanotherwho essentiallyunchangedin group2 aftersurgery. died of severe aorticstenosis.Both patientsshowedthe Hemodynamics (Table 2). Left ventricularend-dias• typicalfeaturesof asymmetricseptalhypertrophyat autopsy tolic and peaksystolicpressureas well as heart rate werewith aseptal/posteriorwall ratioof 2.0 and 1.3, respec• similarin the twogroups.Left ventricularend-diastolic tively.FromFigure3, it isevidentthat withhypertrophic volume index wasslightly,althoughnot significantly,el• cardiomyopathythemusclefiberdiameterof the septum is evatedin group2, and leftventricularejectionfraction was significantlylargerthan that of theposteriorwall and is also significantlysmallerin group 2 than in group I (58 versuslargerthan themusclefiberdiameterofthe septum and the 68%; p < 0.01).Left ventricularmuscle mass index was posteriorwall in thepatientwith aorticstenosis.Apparently, similarin both groups (191 versus 194g/rn";differencenot the asymmetryof leftventricularhypertrophyis reflected significant[NS]). also at thecellularlevel inpatientswithhypertrophiccardio• Left ventricular morphology (Table 3). Theaveraged myopathy,whereasasymmetricseptalhypertrophyin pa• muscle fiberdiameteroftheanterolateralwall wassimilar tients with aorticstenosisis notaccompaniedby "abnor• in both groups with aorticstenosis.Moreover,the muscle mally"thick septalmusclefibers. fiberdiameteroftheanterolateralwall and theinterventric• ularseptumdid notdifferin the grouppatients. I However, themusclefiberdiameteroftheanterolateralwall was sig• Discussion nificantlythickerin group 2 than themusclefiberdiameter Echocardiographyhas beensuccessfullyused in the oftheinterventricularseptum in group I (29.1 versus24.4 diagnosisof hypertrophicobstructivecardiomyopathywhen u; p < 0.01).Typicalfeatures ofhypertrophiccardiomy• asymmetrichypertrophyof the interventricularseptum opathy(16), such as fiberdisarrayorseverelyhypertrophied and anarrowoutflowtractand systolicanteriormotion muscle fibers withvacuolesanddegeneratedmitochondria, of the mitralvalve were observed(1-3). However,in were not seen in any patient (Fig. 2). Thecharacteristic most somepatientswithsevereaorticstenosis(4-8)coexisting findings of ourbiopsiesin this group werehypertrophied asymmetricseptalhypertrophywas noted.This coexist-

Table 2. Hemodynamic Data HR LVEDP LVSP EDVI EF LMMI Group I (n = 12) 80 ± II 185 ± 13 217 ± 38 109 ± 50 68 ::':: 7l 191 ::':: 51 Group 2 ... (n = 12) 78 ± 14 175± 8 213 ± 32 144 ± 67 58 ± J 194 ::':: 66 IS

* p < 0.01.given are mean valuesc; I standard devianon. EDVI= left ventricularend-dra-tohcvolume index(ml-nr'),EF ~ lelt ventricular election tracuon('Ir). HR = heart rate (beats/min): LMMI= left ventricular musclerna" mdex(g/m).LVEDP = lett ventricular end-dravtohcpre"ure(rnm Hg) LVSP ~ lett ventricularpea, systolic pressure (mm Hg) 788 J AM COLL CARDIOL HFSS rr ,\ L 1983:1(3) 783- 9

Table3.MorphologicFindings

MFD, n, IF nlF MFD, n, Group 1 (n = 10) 26.5 :t 5.3 120 :t 77 17 7 :t 6 822 :t 356 24.4 :t 4.5 123 ::: 54 Group 2 (n = 12) 29. 1:t 2.3 106 :t 25 18.6 :t 6 975 ::: 87

Givenare mean values± I SO: IF = left ventricular Interstitialfibrosis(o/{). MFD , = leftventricular musclefi berdiameter of the anterolateralwall (p. ). MFD, = left ventricularmuscle fiberdiameterof theinterventricularseptum (p.). n, = number ofmeasurementsperformed, n.,= number ofporntscounted. n,= numberofmeasurement' performed

ence of aortic valve disease and asymmetric septallogic hy• alterations found in severe aortic stenosis are similar pertrophy has been shown as a rare combination of aorticin patients with and without asymmetric septal hypertrophy. valve disease and hypertrophic cardiomyopathy; inThus, one our data document a uniform hypertrophy of the sep• study (5) the excised septal tissue showed the character•tum and anterolateral wall in patients with both aortic ste• istic morphologic abnormalities of hypertrophic cardio•nosis and asymmetric septal hypertrophy; the latter is con• myopathy and another study (6) demonstrated an intrav•sidered tobesecondary to the long-standing pressureoverload entricular pressure gradient late after successfulof valve the left ventricle. The characteristicfindings of hyper• replacement. Therefore, we undertook a retrospectivetrophic study cardiomyopathy were not seen in the asymmetrically using myocardial biopsy samples to determine whetherhypertrophied or septum in patients with aortic stenosis; sim• not asymmetric septal hypertrophy in patients withilarly aortic there was no difference between the muscle fiber di• valve disease truly represents coexistence of hypertrophicameter of the septum and the anterolateral wall. cardiomyopathy and aortic valve disease or is an adaptiveFactorsproducingasymmetricseptalhypertrophy. mechanism to the long-standing pressure overload. The questions now arise of why the septum is more hy• Significance of asymmetricseptalhypertrophyin se• pertrophiedthan the rest of the left ventricle, and why some vere aortic stenosis. Our present data show that thepatients mor• with aortic stenosis do and some do not show asym• phologic features of the interventricular septumand anteriormetric septal hypertrophy. In response to these questions, wall are identical in patients who have both severe aorticone might speculate thatasymmetricseptal hypertrophy is stenosis and asymmetric septal hypertrophy; the morpho-the result of mechanical factors because the left ventricle is smaller in those patients with aortic stenosis who have asym• metric septal hypertrophy than in those without it (Tables I and 2). Therefore, the left ventricle is more like a slit

Figure 3. Muscle fiber diameter of the interventnc ular(lVS) septumand with a straight septum and no curvature. and regional wall posterior wall (PW) at postmortem in a patient with aortic stenosisstress (AS) might be greater in the septum than in the posterior with asymmetric septal hypertrophy (ASH) (solid line)111 a and patient wall. Thus. the increased wall mass in the septum could with asyrnrnetnc septal hypertrophy due to hypertrophic cardiomyopathyrepresent a compensatory mechanism to prevent highly ab• (HOeM) (dotted line ). Note that the fiber thickness of the postenor wall in both patients and the fiber thickness of the111 septumthe patient with normal septal wall stresses. The postoperative echocardi• aorncstenosis are Similar, whereas the fiber thickness of the interventricularograms after removal of the pressure burden show that asym• septum in the patient with cardiomyopathy is sigruficantly shiftedmetry to the of left ventricular hypertrophy'tends to be normalized right to higher fiber diameters. In each patient, multiple measurements of muscle fibers were performed%) (n: mainly by a decrease in septal muscle mass. The patients without asymmetric septal hypertrophy were characterized n 4D I by a slightly reduced left ventricular ejection performance. _ AS WITH ASH which probably reflects a more advanced stage of myo• I 30 - .... HOCM cardial disease due to a longer duration of the pressure overload. This hypothesis of a particularly advanced sec• ondary hypertrophy in these patients is also in agreement 1%1 20 with ourfindingthat musclefibers of the anterolateral wall in group 2 were thicker than the musclefibersof the septum in group I (Fig. 4).Apparently, asymmetric septal hyper• 10 trophy is beneficial for maintaining normal left ventricular ejection performance. Role of septal myectomy. Asymmetric septal hypertro• 10 20 30 40 50 60 phy might have not only a physiologic importance by com• MUS CLE FIBER DIAMETER (II I pensating for the severely increased afterload in patients AsnlMETRIC SEPTAL HYPERTROPHY J AM cou, CARDIOl 789 1983.1(3) 783- 9

AW AW IVS References lASWITH AS HI lAS WITH OU TASH I lAS WITH ASH ) I. Henry WL , Clark CE , Epstein SE. Asymmetric septalypertroph h y 40 (ASH): the unifying link in the IHSS disease spectrum.Circulanon 40 \ - I± ISD 1973;47:827-32. 2. Shah PM. Gramiak R. Adelman AG, Wigle ED. Role ofocar ech• diographyIn diagnostic and hemodynam ic assessment of hypertrophic 30 30 t subaornc stenosis.Circulation1971;44:89-8 1 3. Popp RL, Hamson De. UltrasoundIn the diagnosis andvaluation e of therapy of idiopathic hypertroph ic subaornc stenosisCirculation . 20 :::.. 1969;40:905-1 4. 4. Nanda NC,GramiakR, Shah PM, Stewart S.Deweese JA. Echo• 10 cardiographIn y the diagnosis of idiopathicypertrophic h subaoru c sten• I osis co-existing with aoruc valve disease. Circulanon 1974;50:752• 7. 10 ~ 10 5. Stewan S, NandaNe. DeWeese JA . Simultane ous operative correc• tion of aornc valve stenosis and idiopathic hypertrophic subaornc stenosis Circulanon1975;51,52(suppl 1):1-34-9. n "<10 n=12 n=lO l o 6. ThompsonR, Ahmed M, Pridie R, Yacoub M.ypertrophic H cardio• P L--NS ------' l-

metric septalypertrophy h to prevent left ventricular outflow16 Ferrall'VJ. Morrow AG. RobertsWe. Myocardial ultrastructureIn tract obstruction early after aorticreplacement. valve rdropathic hypertrophic subaortic stenosis Circulation:769- 1972;4572.