Surgery in muscular subaortic stenosis

Progress

Cardiovascular

in

Diseases

1’01,. Xl, NO. 2

Surgery

SEPTEMHER,

in Muscular

Subaortic

196s

Stenosis

I

T IS NO1V some 11 years since brock first ckxribed muscular subaortic stenosis.‘.2 In the intervening years a great deal has been learned about the electr~)cardiographic, ;-0.1~.1;.“,,3~-t t. 1:1clinical,‘-‘i genetic, 3,i~,~,Y,12.1:.1I.“,.:.v-,,.-I-I-I~; /i I; -, ~lenlodyl~an~ic,l-‘,!‘-~t t,lli.-Ll.it~l;‘i . ;.:1,1;.1!1,~1,2i.:~‘..,, , ,,I, t-t: ,,,,, il.,.;.‘,. radiologic ‘I.12 t~~,l;.‘lo.“i.Ri,~0,44.60.ib.i!~ aspects ph;trlllitcodyllamIliCI”““G”; and pathologic’-:,. m’ of this condition, Although there is 110~7 general agreement about many aspects of this intriguing entity there is a lack of agreement as to what it should be called. Functional aortic stenosis,+ idiopathic hypertrophic subaortic stenosis (HISS),” obstructive cardiomyopathy,’ hypertrophic obstructive cardiomyoaortic stenosis,‘l asymmetrical hyperpathy ( HOCM ) ,41 diffuse subvalvular trophy of the heart,;* muscular subaortic stenosis’;,17 have all been suggested. There is also disagreement as to how it should be approached surgically.7,“‘-‘“” Even in these unsettled areas there is increasing clarification. The names most commonly used are hypertrophic or mnscular subaortic stenosis and hyperfrophic obstructive cardiomyopathy. We have personally found it convenient to use the term subaortic stenosis when considering the various types of obstruction to left ventricular outflow and obstructive cardiomyopathy in considering the various types of cardiomyopathy. The surgical approach is basically either that of dividing the obstructing muscle (“dividers”) or that of resecting the muscle (“resectors”). This review, although basically surgical in orientation, attempts to draw together information concerning the nature of the condition in order that the results of the surgical efforts may be placed in perspective and more completely understood. The obstruction to the left ventricular outflow is caused by systolic apposition of the asymmetrically hypertrophied ventricular septum and the anterior leaflet of the mitral valve. In early systole there is no obstruction to ventricular outflow and rapid ejection of blood into the aorta occurs at this time,10*,1~12accounting Iirriversity of Toronto, and From the Departments of Medicine and Surgery, vascular Unit and CardiovascukW Surgical Division, Toronto General Hospital. 7’his stud!! was supported in part bc/ the Ontario Heart Foundation.

the Cat&o-

for the sharp upstroke to the arterial pulse. As systole progresses, the apposition of the ventricular septum and anterior mitral leaflet results in obstruction to ventricular outflow, the development of the characteristic intraventriculal pressure gradient and a late-onset systolic ejection murmur that is maximal at, or just medial to, the cardiac apex. As might be expected with the anterior mitral leaflet forming one side of the obstruction, mitral regurgitation is commonly associated with this type of outflow tract obstruction, and this added lesion contributes to the apical systolic murmur. Decreased distensibility or compliance of the left vmtricle!‘~‘7 (due to the ventricular hypertrophy ) results in left ventricular end-diastolic pressure elevation and the presence of a left atria1 gallop sound that at times is palpable and associated with a double apex lmlt.f2.‘; Paradoxical splitting of the second heart sound reflects prolonged left \~entricular ejection resulting from the outflow obstruction, The majority of patients have mild subvalvular obstruction to right ventricular outflow that can at times be recognized by a separate systolic ejection murmur in the pulmonary area.17 Occasionally the right sided obstruction to outflow is hemodynamically significant. Right ventricular hypertrophy and septal encroachment on this cavity cause decreased right ventricular compliance that results in right ventricular end-diastolic pressure elevation and prominent A waves in the right atrium and jugular venous puls~‘.‘~ The inspiratory rise in the A wave in the IW~OUS pulse reflects the inability of the nondistensible right \rentricle to accept an increased venous return without a rise in pressure. The total clinical and hemodynamic picture. therefore, reflects biventricular inflow and outflow tract obstruction, the left-sided lesion being decidedly predominant. As with other varieties of obstruction to left ventricular outflow ( supravalvular, valvular and fibrous subvalvular aortic stenosis ) , angina pectoris, syncope and dyspnea on exertion are the cardinal symptoms. In contradistinction to these fixed varieties of obstruction to left ventricular outflow, the severity of symptoms in muscular subaortic stenosis may Kuy spontaneously with that variable nature of the obstruction itself. Not only does the obstruction to \rcntricular outflow vary spontaneously, but various pharmacologic agents alter the severity of the stenosis in a specific manner. Thus, drugs having a positkc inotropic effect ( digitalis glycosides,‘” isol)rOtereiiol.‘~‘~~“.~“.~~ ) and agents causing peripheral vasodilation ( amyl nitrite”‘,Y1-Y i.7i’ nitroglycerine’ ’ ) increase the severity of obstruction. Conversely, pharmacologic agents causing peripheral vasoconstriction ( methoxamine,“. angiotensill,“‘.;” norepinephrine, “‘.“‘~“, neosynephrine;’ ) reduce or abolish the obstruction and the beta adrencrgic block ing agent propranolol prevents intensification of the obstruction caused by isopr0teren01.7”,77 The mechanism of these drug actions is still somewhat controversial but increased obstruction is believed to result from positive inotropism, decreased aortic pressure, decreased ventricular volume ;md tachycardia. Conversely, negative inotropism, increased aortic pressure or \.entricular volume, and bradycardia result in amelioration of the outflow tract obstruction. The fact that the obstruction is intemified in the postextrasystolk lw;~t’L \vhich

S~W:ERI-

IN

3fUSCULAR

SUBAORTIC

STENOSIS

AORTA

LEFT ATRIUM

L.V.O.T.

L.V.I.T.

LL

L.V.

APEX

Fig. I-Diagram of the left heart &unhers viewed from the left side of the body. is that area of the left ventricle below The left ventricular outflow tract (L.v.o.T.) the aortic valve whose lateral boundaries are the ventricular septum (anteromedially~ and. the anterior leaflet of the mitral valve (posterolaterally). The left ventricular inflow tract (L.V.I.T.) is that area of the left ventricle helow the mitral valve. One may further divide the left ventricular cavity into a third area, the left ventriculal apex (L.V. apex). The terms inflow and outflow refer to the direction of blood flow relative to the left ventricle. (From Wigle et al.. Can. hled. Assoc. J. 95:793, 1966. With the permission of the editors).

is associateclwith a larger than normal end-diastolic volume, but with a lowel than normal aortic pressure, suggests that the lower aortic pressure plus postextrasystolic potentiation of contraction , are responsible for the intensifktion of obstruction in this circumstance. A significant percentage of patients with muscular subaortic stenosismanifest abnormal Q waves in the electrocardiogram in various limb leads and in thcx left lateral precordial leads. Tall right precordial R waves may accompau)these abnormalities. These unusual electrocardiographic findings, which ma!. suggest myocardial infarction, have been attributed to ventricular septal hyl,ertrophy,~“. I ,.,,c-i3 the bizarre nature of the myocardial fiber hypertrophy in the septum,“‘Ei or possibly to premature acti\,ation of the subendocardium of the left ventricle.104J”5 The preceding account of some features of muscular subaortic stenosis is reviewed in order that the results of the various surgical procedures may b<> appreciated. Prior to reviewing the results of the different surgical techniques in this condition, two further problems that hear upon the advisability of surgery deseraremention. These are: I ) the nature of intraventricular pressure differences in man, and 2) the relation of the mitral insufficiency to the outflon, tract

obstruction.

1. lrztruoentricular

Pressure Diferenws

in Alarm

An intraventricular pressure difference denotes that the left ventricular SYStolic pressure in one portion of the ventricle esceeds the systolic pressure in another

portion

of this chamber.

Prior

to considering

the nature

of these prc‘s-

sure differences, it is well to define 3 anatomic areas of the left ventricle, i.e.., the left ventricular inflow tract, the left ventricular outflow tract, and the apex of the left ventricle. These anatomic areas are defined in Fig. 1. Characteristic;~lly,

an jntraventricular

pressure

difference

has been associnted

\\‘11.1.’

I* !\I

I>!,:,

\lJ~:l,\l-\,\.

111(:1~1.0\\~

LEFT

AORTA

LEFT VENTRICLE

Fig. %(Left) Because the obstructiou to left ventricular Olltflow (arroiv) in muscular subaortic stenosis is caused bv svstolic apposition of the ventricular septum and anterior leaflet of the mitral valve,. th; intraventricular pressure distal to the stenosis (and proximal to the aortic valve) is low (+), whereas all ventricular pressures proximal to the stenosis including the one jnst inside the nlitral \~11vc (the inflow tract pressure) are elevated (+ + i. (Right) When an intraventricular pressure difference is recorded due to catheter entrapment from cavitv obliteration, the elevated ventricular pressure is recorded only in the area of entrapment (+ +). The intraventricular systolic pressure in all other areas of the left ventricular cavity, including that in the’ inflow tract just inside the mitral valve, is low (+) and equal to aortic systolic pressure. The three areas of the left ventricle represented by the + signs in each of these diagrams are, from above downward, the outflow tract just below the aortic valve (subaortic region), the inflow tract just inside the mitral valve. and the left ventricular apex. (From Wigle et al., (:u. hled. ASSOC. J. 95:793, 1966. \Vith the permission of the c&t(q). with subaortic stenosis ( muscular or fibrous ) , in which all \~c~ntricular prcssurcs proximal to the outflow tract obstruction, including that just inside the mitral valve ( initial inflow tract pressure”‘~‘“’ ) are elevated above the systolic pressure in the outflow tract distal to the stenosis’!‘-“” (Fig. 2, left.) Figs. 3 and 3

demonstrate in patients with muscular subaortic stenosis that the inflow tract pressure as well as all ventricular pressures proximal to the outflow obstruction are elevated above the aortic systolic pressure (which is equal to the outflo\\r systolic pressure distal to the stenosis( Fig. 2, left). Several authors have drawn attention to the fact that an elevated ventricular systolic pressure may also be recorded by a cardiac catheter that has become entrapped or imbedded in left ventricular myocardium.““‘.” This is most like11 to occur when the apex of the left ventricle empties unusually rapidly, the myocardium in the evacuated portion of the ventricle entrapping the catheter.‘““-‘” The same phenomenon may occur when a catheter is advanced against the left ventricular wall. Recent studies have demonstrated that, in the presence of an intraventricular pressure difference due to catheter entrapment in myocardium, the left ventricular systolic pressure just inside the mitral valve (initial inflow tract pre.wure) is not elevated but is precisely equal to the outflow tract and aortic systolic pressures as well as to all truly intracavity

INITIAL

L.V.I.T.

PRESSURE,

I

TERMINAL

L.V.I.T.

PRESSURE

VENTRICLE

alnl”M

o

E.C.G. /

Fig. D-Left heart pressure recordings from a case of muscular subuortic stenosis. Aortic pressure recording is continuous. An end-bole transseptal catheter’i4,‘;‘i records left atria1 pressure at the left. When the cathetcl- enters the left ventricle via thra mitral valve (center) the initial left ventricular inflow tract (L.V.I.T.) pressure is found to be high, exceeding am-tic svstolic pressure: the latter equals the systolic pressure in the left ventricular outflov tract distal to the obstruction. Similarly as the transseptal catheter is drawn back into left atrium from the left ventricle (right). the terminal left ventricular inflow tract (L.\‘.I.T.) pressure is high. With the use of this techniquc~ in which it is considered impossible for the catheter to become entrapped in myocardium when recording the initial left ventricular inflow tract pressllrtx, the elevated ventricular pressure provides evidence of the presence of outflow tract obstruction. Note that the ventriclJar pressIll-e declines at, or before. the dierotic notch in the aortic pressure pulse (see test). (From \Viglfl et al.. C:;lllad. \led. Ass. J. 05:193. 1966. \\‘itll the permissiol~ of the rditors). prc5surr*s.“‘-’ ” [ Figs. 2, right, and 5. ) Not only is the left \-entricular inBo\\ tract prvssurc low in the pr~wncc of an intrav~,ntricular pressure differcnccx

ducx to cathctcr entrnpimnt in myocardium from cavity obliteration, but thr> &vated ventricular pressure frequently declines aftcar the dicrotic notch in aortic pressure (Fig. 5, right 1. Blood cannot 1~’ withdrawn in systole from thr proximal em1of the cathctcsr recording the cl
Assessment of the relationship between left ventricular ejection time and the intra~entricular pressure difference also serves to differentiate the pressure difference that results from muscular subaortic stenosis from that due to catheter entrapment in myocardium. I lJ Thus, in muscular subaortic stenosis there is a direct relationship between the magnitude of the pwssure gradient and the degree of prolongation of the ejection time, as one would c>spect with obstruction to Ieft ventricular outflow. This direct relationship exists at rest and following pharmacological or surgical alteration of the degree of obstruction. In contradistinction, there is an inverse relationship between the ejection time and the magnitude of the intra\~entricular pressure difference when the latter results from catheter entrapment in the myocardium.“”

2. Mitrul Regurgitation in Muscular Subaot-tic Stenosis The

occurrence

of mitral

regurgitation

has been

recognized

as an integral

SUR(:ERl’

IN

1\IUSCULAR

SUBAORTIC

STENOSIS

TRANSSEPTAL CATHETER IN L.V. INFlOW TRACT

mm. Hg. --160--

TRANSSEPTAL CATHETER ENTRAPPED IN L.V. APEX r

P

P

Fig. 5-Tla1 tsseptal catheter 1x)sitions (hottom) with corresponding intrncardiac prcwwe recordings (top) in a patient with left \w~triculx cavitv obliteration (demonstrated cille:li~gioSrapllicallv). \\:ith the truwseptal catheter ill the left ventricular (L.\ .) ilrflom tract, just inside’the mitral valve, (left panel) there is no left ventriculnraortic, s]Lstolic pressure differelw~ i.e. the L.1’. inflo\v tract preswre is not elevated. \V~IC~II the transseptnl catheter was nclva~~ced to the left ventricul;u apex n (right lx~wl i left ventricular pressure exceeded xwtic lxesswe (aud declined following the dicrotic itckh in aortic prrss~wei. The cleated apical L.1’. systolic pressure is the rcslllt of cnvit\r ol~literation with collaequellt c~athrtw cwtrapmellt ill rn~wc;wdiunI.

Rcbcrtntly \vr have completed a study on tht. nature of nlitral regurgitation in 11muscular sllbaortic stenosis using a dye dilution technique.’ ly In these studies 2 CC’. of indocyanine green \\we injected into the left \w~tricle prorinxd to the obstruction during constant \vithdrawal of blood from the left atrium. This twhniquc has permitted an assessment of the dtgrec of nlitral regurgitation in this condition without ;I catheter being across the mitral \xl\~ and in the ahsc~ncc~ of estrasystoles. In :37 d!,e dilution studies in X3 patients in whom ;m i,itr~lv~~ntri~ulur pressure gradient was recorded, there \~xs in\xrinhly SOIIIC

!I0 CONTROL

ANGIOTENSIN mm.Hg.

--160-

LEFT JENTRICLE

LEFT ATRIUM

i

REGURGITANT FLOW ( LEFT ATRIUM 1 \

n

REGURGITANT FLOW (LEFT ATRIUM 1

2 cc INTO

INDOCYANINE LEFT VENTRICLE

GREEN (t)

Fig. 6-hIitra1 insufficiency secondary to papillary muscle dysfunction in a patient with a post-myocardial infarction left ventricular aneurysm. Top, simultaneous left atria1 and ventricular pressures before (left) and during (right) angiotensin infusion. The indicator dilution curves (bottom) were inscribed (from right to left) followinfi left ventricular injection of green dye by constant withdrawal of blood from the left atrium (regurgitant ffow, smooth line) and by an oximeter placed on the right eal (forward flow, wavy line), before (left) and during (right) angiotensin infusion. Comparison of the regurgitant flow curves in control conditions (left) and during angiotensin infusion (right) revealed a marked increase in the amount of regurgitant flow during angiotensin infusion, signifying an increase in the degree of mitral insufficiency. (From Wigle et al., Can. Med. Assoc. J. 97299. 1967. With the permissiorr nf the editors.) degree of mitral insufficiency present. The severity of the mitral lesion was graded as trivial in 9, mild in 11, moderate in 11 and severe in 6, of these studies. In 15 patients the dye dilution studies were repeated during amelioration or abolition of the outflow tract obstruction by the infusion of angiotensin. Prior to discussing these results it is well to indicate that in the common forms of mitral insufficiency (not associated with outflow tract obstruction) the infusion of a vasoconstricting agent, such angiotensin, results in an increased severity of the mitral leakllGslls,llo (Fig. 6). Dye dilution studies of the mitral

ANGIOTENSIN O.Ol8luqJKg

CONTROL

bin.

mm.Hg LEFT VENTRICLE A0 RTA

ECG CARDIAC OUTPUT MEAN GRADIENT EJECTION TIME ,,.. ~, .~., I

L.U

L./MIN./M2 mm.Hg ~~.,

(SEC.)

2.16 36 .42 /

___-___-

2.92 7 .32

I :

2 ml. INDOCYANINE GREEN DYE IN-I-0 LEFT VENTRICLE ( 9) Fig. ‘7-Mitral insufficiency in a patient with surgically proved muscular subaortic stenosis. Top, simultaneous left ventricular and aortic pressures before (left) and during (right) angiotensin infusion. Bottom, indicator dilution curves inscribed (from right to left) following left ventricular injection of green dye by constant withdrawal of blood from the left atrium (regurgitant flow, smooth line) and by an oximeter placed on the right ear (forward flow, wavy line) before (left) and during (right) angiotensin infusion. In control conditions (bottom, left), in the presence of severe outflow tract obstruction, a significant degree of mitral insufficiency is indicated bv the large amount of early-appearing dye in the left atrium (regurgitant flow) and bv the distortion of the downstroke of the forward flow curve. During angiotensin infusion the left ventricular-aortic systolic pressure gradient was reduced from 58 to n ( mm. Hg (top, right) and the mitral insufficiency was virtually abolished (bottom. right), as indicated by the small amount of early-appearing dye in the left atrium (regurgitant flow) and by the absence of any distortion of the downstroke of the forward flow curve. (From Wigle et al., C:ar~. Med. Assoc. J. 97299, 1967. With thfr permission of the editors). insufficiency in muscular subnortic stenosis during angiotensin infusion revealed that in 11 of 15 patients the mitral regurgitation was reduced, or abolished, \&en the obstruction to outflow was reduced or abolished ( Fig. 7). This would

indicate to us that in these patients the rrritral regurgitation \vtr.s sc~mdar!. to the outflow tract obstruction. In 4 of the 15 patients, however, the tlcbgrec of mitral insufficiency was unchanged during angiotensin abolition of the: outflow tract obstruction. In these 4 patients the mitral regurgitation appeared to be independent of the outflow tract obstruction. One of these patients has of the subsequently been demonstrated to have an additional abnormality mitral valve. It is the current practice in this laboratory to carry out these dye dilution studies before and during angiotensin infusion in all patients being considered for surgery. If the mitral regurgitation is abolished at the time of abolition of the outflow tract obstruction by angiotensin. then we would expect the surgical abolition of the obstruction to result also in abolition of the mitral insufficiency. Conversely, if the pharmacologic abolition of the obstruction to outflow has no effect on the mitral regurgitation. then an additional abnormality of the mitral val\~ should b’r suspected, and if surgery is to he undertaken, the mitral valve mechanism should be examined.’ I7 Cineangiographic studies in patients with muscular subaortic stenosis have demonstrated early rapid ejection of blood into the aorta followed by late onset of mitral insufficiency that occurs principally following the visualization of the outflow tract obstruction. The mitral insulficiency appeared to account in large measure for the small end-diastolic volume that is characteristic of the condition. I Ii Pmu~rs OF S~HGICAL PHOCEDURES IN MUSCULAR SUBAORTIC STENOSIS

This section considers the indications, techniques, results and complications of surgery in muscular subnortic stenosis from this hospital and a review of the results of surgery carried out in a number of other centers. At least seven different operative techniques have been described to alleviate the outflow tract obstruction in this condition.‘.“‘-‘“” The relatively simple technique of ventriculomyotomy using an aortic approach has been utilized extensively by 1Clorrow,“‘,“‘,“” BentalI,““~“L Sousa,“” and Bigelow,'X~"~l" and their associates. As experience was gained, some of these authors added minor Arariations, such as lengthening the incision of the muscle mass towards the apex,!” excising small amounts of muscle from the edges,!” creating a trough with a double incision’“” or changing the exact point of the incision, depending upon the anatomy. Because the basic goal of this procedure has been the interruption of the circumferentially oriented deep constrictor muscles of the left ventricle, these authors could be classified as “Dividers.” Dissatisfaction with the visualization afforded by this irortic approach, cornbined with a desire to remove 2~s much of the obstructing musculature as feasible, has led to the evolution of a group that might be called “Resectors.” Kirklin and associates”.!” md subsequently Barrett-Boyes and associates!“’ have used a combined aortic and left ventricular approach to excise muscle from the hypertrophied septum. It would appear that with increasing c]inic;rl experience, the degree of resection has become more extensive. Julian >I&

SVIKXRY

IN

3Il~SClJLAR

SUBAOBTIC

STENOSIS

93

associates described a different approach through a “fish-mouth” incision in the apex of the left ventricle:; Dobell and Scott’” and Lillehei and associates” hn\,ch utilized resection by a left atria1 approach, the latter authors suggesting that associated mitral insufficiency could thus be managed at the same time. Ha&en-and later Cooley and associates!” advocated a right ventriculotomy to rcbsect the hypertrophied septal muscle from the right side. The resulting thinned septum alle\Gted the left ventricular outflow obstruction and conduction disturbancz were avoided. Other approaches have &O been des~ril,~~l.~!‘.!‘l,!‘;

Fifty-five patients with muscular subaortic stenosis have been studied hemodynamically in the past 10 years at the Toronto General Hospital. In 5 additional patients this lesion has been diagnosed o11 clinical grounds alone. From this experience a total of 20 patients ha\re undergone the ventriculomyototny ol)(,r;\ti()*l.“.‘-‘.!” These patients were selected for surgery mainly on the basis of tllc, se\.erity of their symptoms of angina, dyspnea or syncope (or presyncop(* ) ou exertion. Congestive heart failure has beeu a rare occurrence in our exp~~rience. Two E-year-old boys were operated upon in the absence of severtsyinptolnatology. One of these had been demonstrated to have severe obstruction at rest and the second boy had a brother drop dead suddenly at the sang age. 111 S of the 20 patients the condition was familial. Two patients were opc.ratcd upon following the development of gastrointestinal symptoms while on propranolol. A411patients had the clinical mtl hemod~mamic features charactcristic of the condition. Prcoperatively, the prclssurc gradient varied from $5to 1.50 mm IIg (average 61 mn~. Hg) while the left \~entricular end-diastolic prc’ssurc \aricd from 9-36 nun. Hg. ( nveragc 21 nnn. Hg). The pressurr gradients across the right \~rntricular outfloiv \micd from O-19 mm Hg in 16 patichnts. In only one patient was the obstruction to the right ventricular outflo\v considered to be hemodynamically significant ( 44 nun. -Hg) All patients \vere operated upon using cardiopulmonary byllass. Body and corollar)- perfusion temperatures were kept above :32”C to a\roid \.entricular fibrillation, as the lesion M’;~s inore adequately ;~ssesscd with a beating heart. Left coronary artcry perfuskm was continuous. Hight coronary artery perfusion ~1s intermittmt to permit adquute visualization of thr outflow tract during thcb incision. If the aortic root \vas small, botlk perfusion cannulae at times had to bc rctlllo\-c>d to allo\\, proper csposurc. A right-angled retractor was usc4 to rc+rac,t the left and right coronary cusps of the mrtic \7llvc~ anteriorl) ill order to \~isualizc~ the vcsntricular outflow tract ( Fig. S ) . The cmlarged septunl was easily seen anteriorly and to thcl patient’s right through the aortototll)- incision. -4 bar of nmsck extending from the enlarged septum into the anterior frets wall of the left ventricle wx \-isualized directly below t!lc aortic v;ll\~. In most casts this bar had an easily palpablc~ upper and 1owc.r margin and its origin from the scptuur could 1~ assessed. This origin lay in linv \vith the cmmmissurt lwtwcen the left al1t1 right coronary cusps of the

\\-l(:l.l’.

‘I’l~I\rHI.I.:,

\l)l,.l.\i

\x.

I~I(:I~‘I.o\\

Fig. 8-A. This operative diagranl demonstrates the n~uscle bar arising frolll th(’ septum just under the nortic valve cusps. B. 13~ palpation, the origin of the bar from the septum appeared to lie slightlv to the right of the commissurc between the right and left coronary cusps. Illcision- bv direct visiotk is made in this area. C. Finger pressure is utilized to deepen the incision until the superficial, rubbery muscle fibers (From l3igelow et al.. 1. Thorac. Cardiov. “g iv?,” forming a U-shaped depressioll. Sl~rg. 52:514, 1966. With the permission of the rditors).

aortic valve, or slightly to the right under thr apex of the right coronary cusp ( Fig. 9). The incision into the bar was made at its junction with the septum (Fig. 9). At this point, the bar was narrow, thick, and easily defined, A gritty sensation was often sensed as the scalpel created an incision about 0.5 to 1 cm. deep extending from the base of the aortic valve cusps to the lower margin of the bar, a distance that varied from 2 to 5 cm. The index finger then deepened the incision and using alternate scalpel division and digital pressure, the incision was completed. Usually, a sensation of the muscle “giving way” was encountered and the cut edges retracted, “opening up” the outflow tract. Rc-

kKtiOn of thcl cut cdgcs of the incision iu s!~tolc \ws c*sscntial to the success of the operation. If this retraction did uot occur, further dqwning or extension of the incision was carried out, or mow rarely a second incision was niadc. A number of complications ha\-e arisen from this approach to the surgery of muscular subaortic stenosis. \‘wtricular septul defects have resulted from the \-cntriculomyotomy incision. This complication has not been encountered in this Feries in spite of the close approximation of the right \a~tricular outflow tract. Aortic insufficiency, secondary to cstension of the incision into the origin in 3 patients, but has of the right coronary cusp of the aortic val\~e, occurred not hecn reported in other series, This particular complication indicates that it WIS at times considered necessary to cxtcmtl the incision right up to the aortic vnl\,e cusps in order to completel>~ divide the obstructing muscle. In 2 of tllcscl patients the torn aortic val\~c cusp was rwog~~izecl imrncdiatcly and dealt

Preop. mmtig 100

LEFT VENTRICULAR OUTFLOW GRADIENTS

60-

40-

20-

O-

Fig. lo-This graph demonstrates the relief of the llreol>erative left ventricular gradients by the velltricdomyotomv operation. Postoperative studies were made 1 to 3-I months (average 11) after oper:itioli. Drug stimulation was carried out with amyl nitrite inhalation, isoproterenol infusion, or acute digitalizatioll. (From Kgelow et al., 1. Thorac. and Cardiov. Surg. n‘2:513. 1966. With the permission of the editors). with by direct suture. In the third patient, the aortjc \xl\-c L\YIS replaced 3 months after the initial operation because of the presence of moderately severe aortic insufficiency. All 3 patients arc now well. Complete heart block resulting from the \~entricnlomyotonl~ incision occurred in :3 patients. 111 2 the 1110~4 WAS temporary and lasted less than one week. The third patient died of ;L low output syndrome 21 hours postoperatively. In this series, right \xmtricular outflow obstruction of surgical significance was encountered in only one patient. The initial ~cntriculoln~otorn~ operation resulted in conrplrte abolition of the obstruction to left \-cntricular outflo\v; ho\xxa\-er, the pressure gradient across the right \w~triculnr outflo\v tract renlained at 34 mm. Hg. As the patient had inadequate relief of s)-mptoms, ;L scw~nd operation utilizing Harken’s right-sided approxh” and cxtensivc resection of septal musclr nw thcrefow carried out. Of the 20 patients operated upon. there wcrc :3 hospital deaths. Of the 17 survivors, 13 have returned to this center for postoperative clinical evaluation. Two patients, who have been followed elsewhere, haye not bechn rccntheterized but have lxw~ described as having significant relief of symptoms and one patient has been lost to follow-up. One patient died 24 hours postoperatively of ;i low cardiac output syndrome. A second patient also This patient also had complete heart block (. see above). died 24 hours postoperatively of uncontrolled sul~r;~v~~~ltricular arrhythmias. The third patient died at the time of surgery possibly tl~w to poor left coronary artery perfusion. The ~cntriculomyotomy incision was demonstrated at postmortem to be adequate in all 3 patients. Of the 14 patients returning for clinical i~ssc5snwnt, 10 \vc’rc’ classified as

SUlK.k;RT

IN

XIC-SCULAR

SUBAORTIC

STENOSIS

9;

PR8 -0) APRIL

‘)s

POlT-oP MARGIl

W8

Fig. ll-Preoperative (top) ad postoperative (lmttom) simultaneous left ventricdu and aortic pressure recordings at rest (left). following ~umvl nitrite ii~halatioil (ceutey) and following intravenous iujection of isol~roterenol (isuprel) (right) in a 1%year-old bov \vho did not have sigdcaut obstruction at rest. hut who had one syncopal epkocie on exertion and whose Ixother dropped dead at the same age. Postoperatively, pharmacologic stimulation Failed to produce e\ridel ICC‘ of outflow tract &struction whereas iclenticxl stimulation lxeoperntivelv l~duc~~cl ;L significant pressure gradient x~oss the left ~~entricular olitfl0w tract. having cscelknt results in that they were asymptornatic at full nornlal activity. Two were classed as having a good result ( marked improvement in symptoms ) and one had iI fair result (marked fatigue continued postoperatively, although angina and clyspnea were relirved ) . One patient had ;I poor result associated with a persisting postcarcliotomy syndrome. Thirteen patients consented to late hemodynmnic reassessment one to 34 months after operation.!” At left heart catheterization, 10 of these 13 patients had no gradient across the left ventricular outflow tract at rest ( Fig. 10). Drug stimulation with anlyl nitrite inhalation, isoproterenol infusion or acute digitali-

mm.l49. 160-

PIE-OP

MAY

k5

-no

POST-OP

MARCH

166

MO.-

Fig. 12-Preoperative (left) and postoperative (right) simultaneous Ieft ve!ltricular and aortic pressure recordings from ;I patient with musclar subnortic stenosis. Postoperatively there is no pressure gradient ;lcross the left ventricular outflow tract at rest or in the postextrasvstolic heat. zation failed to produce a gradient in 7 of these patients (Fig. 11). In 2 no drug stimulation was carried out; however, there was no gradient in the postextrasystolic beat in each (Fig, 12). Only one of the 10 patients who had complete abolition of the gradient postoperatively developed such a gradient following isoproterenol infusion, amyl nitrite inhalation or in the post extrasystolic brat. Each of these provocative maneuvers produced a gradient of 40 mm. Hg in this patient. Three patients of the 1:3 who were catheterized had a resting gradient of 5-10 mm. Hg postoperatively, and in these, drug stimulation resulted in a gradient of no more than 20 mm. Hg (Fig. 10). Left ventricular end-diastolic pressure decreased by 5 mm. Hg or more in 7 of the 12 patients in whom it was elevated preoperatively. In 2 of the remaining 5 patients without a significant fall in left ventricular end-diastolic pressure there was significant mitral insufficiency postoperatively due to ruptured chordae tendinne. Left ventricular cineangiography has demonstrated little change in ventricular volumes but the site of the incision in the left ventricular outflow tract may be recognized in both the left and right anterior oblique views (Fig. 13). As would be expected in patients in whom obstruction to left \-cntricular outflow has been relieved, the reduction or abolition of the pressure gradient across the left ventricular outflow tract \vas invariably accompanied by a reduction in left ventricular ejection time.‘lz Nine of the 13 patients who underwent hemodynamic assessment postoperatively were studied by dye dilution technique for evidence of mitral insufficiency. Of 8 patients having complete abolition of the outflow obstruction, 4 had no mitral insufficiency, 2 had a trivial mitral leak, one had mosderatc and another severe mitral insufficiency postoperatively. The mitral insufficiency in the latter 2 cases was the result of torn chordae tendinae of the anterior mitral leaflet. The patient with severe postoperative mitral regurgitation required a mitral annuloplasty one year following the ventriculomyotomy procedure. In

Fig. 13-Postoperative left anterior obliqne left ve~ltricular cineangiogrnm demonstrating visualization of the ~~e~ltriclllomyotom\~ incision (;~rrow) ill the left ventricnlar OLdlfW tract.

one patient in whom the outflon tract obstruction \V;LSreduced but not abolwas also reduced. ished, the mitral insufficiency Postoperative left and,/or right anterior obliclue left ventricular cineaugiogrants were carried out in all 11 patients. In 6 patients in whom the outflow tract obstruction was completely relieved, thrw \\XS no mitral insufficiency. Three patients had trivial mitral insufficiency postoperatively. Two of these had postoperative outflow tract gradients of S-10 mm. Hg at rest; the third patient had no outflow tract gradient postoperati\.cl>-. One patient had moderate mitral insufficiency postoperatively associated with multiple ventricular extrasystolcs. The remaining patient had serve mitral insufficiency postoperatively due to ruptured chordae tendinae of the anterior mitral leaflet. Both the dye dilution and cineangiographic studies indicatcx reduction or abolition of the mitral insufficiency postoperati\.ely when thew is A reduction or abolition of the olltflow tract obstruction.

There have lwcw :3 lak dc9ths. 21 to 5 jaws following surger!‘. =111 3 of thwc patients were deinonstrated l~en~odynami~~ill~ to ha\-c no outflon- tracat 01~ struction postoperativelp and 2 of thcwi ww ~onsidcred to ha\-e clinically awllent results. The mode of these deaths dewr\xx mention. One Dyear-old male died when he fell ofI’ the roof of a three-storlhousc~. :3 ycbars postoperati\.rly. This paticwt had rc+urncd to fllll ~lnpl&-n~c~llt hut had IXYW noted to haw vwtricwlar preinaturci lwats I”)stopC’r;lti\.c,l!.. T\~Y) years prior to dent11 an cpisodc of \~~ntricular tach)-cardia had IXYW si~c~~~ssfull~~ trcatcd \rith procaine aniidc. The patkilt consistentl\~ -. wglectcd to takcl this nwdication subsequently and it \vould appear possible. indeed liliel! . that this fall 1~~1s precipitated by a \witriculx arrhythmia. The sc~~xid pticwt I\-ith an cx~-llent result died 5 years I”)stopc‘r;\ti\.cl!. during induction of auc~stlwsia for a ~holecystecton~y in a small hospital. This \vws ;L tragic oc’wrrcwcc ill that this cnrpnter had ~NXW al+ to return to work full time postoprrati\.c~l!. ant1 Ilad related one incident wlwr~ licl had \valkcd for :t lnilc through sno\f’ up to his laws without synq~toms. The third late death wcwrrcd ill thtl ptirut who required mitral nnnuloplast)for niitral insufficienc!~ due to ruptured chordae tendinae one ywr following the \-entriculom~otom~ operation. This patient continued to be symptomatic postoperativcl y and had lwcw unal~k to return to work. Shortly before death, on his o\vn accord. 11~ doubkd his close of digoxin. He was admitted \vith digitalis intoxication, hnd a cwdiac arrest, was resuscitated, and died one week Inter of confluent l&tcral l~r~~~cho~~~~c~umonia. All :3 of these hearts from the ptknts who died :3 to 5 !wrs postoprmtiv~l~

101

ha\x~ beeu awilablc for post~nortem exuninatioll. Figs. 1-L and 13 demonstrator thus tlratnatic sprexling apart of the cut edges of th(b \~r~rtriculom!~ot~~ll~~ incision ii1 2 of these hearts.

1. “Dil;itlea.” Keccntly, thy extcnsi\,c and ~~211tlocumented surgical expricwc(~ with musdu subaortic* stenosis at the ,National Heart Institute has been rc.portt.tl ly hlorrow ct al.““’ Twenty-fi\,e of 126 patients with this condition ha\:(~ bwn operated upon. All \vvre synptotnatic :nd had preoIwrati\v~ outflow 102 n~m. Hg). Twenty-one tract gradients at rest of 36-17.3 mm Hg (awragc paticwts had elevated end-diastolic pressures, the awragr being 19 mm. Hg. Outflow trot grdicnts \-arying from 11 Four patients had right \w~tricular to 60 111111. Hq A degree of mitral insufficicwcy \vas cltwonstrated at angir)gr:~l)lt!. in I4 of the 19 patients. TIK~ opcwtivc technique \ws similar to that describtd previously from this cyqlt~r.‘” In the first 5 ptieuts 3 ventriculoni~ otoniy incision without muscle rcscct ion V.U carried out from an aortic upprodl. In the ren~ining 20 ptirnts, the cqwration has consisted ot 2 paxllel incisions, 1 cm. apart, through the vnard superficial muscle layers. Thcsc~ incisions were deepened 1)~ docwdiun~ digital Inxwure and the ridge of n~~cle bc+wxw~ then incisions was resected. At tiltlcs the initial incisions :u~cl the resection vwc‘ carried out from an apical stab v,-ouncl. Retraction of the margins of the rewctd channel was notd to o(‘c11r during systole at the end of the procedure.

after operation had unrelieved right \rentricular outflow tract ol)structiou and artrial fibrillation. The other death occurred 8 months after operation. Th(b cause of this patient’s death was uncertain but she had developed cardiac failure complicated by hemiparesis 2 months prior to death. Heart block. necessitating a permanent cardiac pacemaker, occurred in 2 patients and 01~ patient developed a small ventricular septal defect. Of the 2‘3 sun+vors, 21 had been followed from I to 8 years. Fifteen of thesca patients were completely asymptomatic while 4 continued to have minor symptomatology, primarily angina pectoris. 0~ patient experienced recurrent supraventricular arrhythmias and clyspnea and a second patient br~camc~ psychotic after being asymptomatic for 2 years. All 21 patients have been studied by postoperative heart catheterization. There was no pressure gradient across the left ventricular outflow tract at rest in 19 patients and small gradients of 8 and 11 mm. Hg in the remaining 2 patients. In 7 of 13 patients who had no resting outflow tract gradient postoperatively, the Valsalva maneuver rcsulted in gradients of from 10 to 50 mm. Hg. Infusion of isoproterenol postoperatively produced a gradient of from 21-52 mm. Hg in -5 of 9 patients who had no gradient at rest. Thus, the Valsal~~l maneuver failed to provoke :I infusion gradient post-operatively in 6 of I3 patients, \\Thile isoproterenol failed to provoke a gradient post operatively in d of 9 patients. Four of S patients with mitral insufficiency preoperatively had no mitral insufficiency 01I postoperative angiographic studies. Bentall and his associates have also utilized the transaortic approach with division of the muscular bar in line with the commissure between the left and right coronary cusp of the aortic valve.“* With time, they have tended to extend the length of the incision towards the ventricular apes and resect minimal portions of muscle. Sixteen symptomatic patients were operated upon, with 12 long-term sur\i\.ors. Deaths were clue to induced heart block in two, (one of whom also had a perforation of the ventricular septum), an aortotomy tear in the third, and \,entricular fibrillation in the fourth patient. Three months to six and a half years l’ostoI)““tiVC’ly, 3 patients were asymptomtic, 7 were improved, and 2 were unchanged sylnptomatically. In an earier report.“” 7 of these long-term survivors had been recatheterized. In 5 the gradient was reduced and in 2 it \vas increased. Isoprotcrenol infusion failed to increase the postoperative pressure gradient in 2 patients. Six of the 7 patients had a lower left ventricular end-diastolic pressure postoperatively. In 3 patients, significant preoperative mitral insufficiency had been reduced or abolished. II. “Resectors.” Kirklin and associates!“: have operated upon 16 patients with muscular subaortic stenosis. In 13 patients, resection of muscle from the hypertrophiecl ventricular septum was carried out by a combined aortic ancl left ventriculotomy approach:’ In one patient the muscular resection was carried out by the aortic approach alone. In a second patient, muscular resection was carried out from the right side of the septum. This patient developed complete, heart block and died on the first postoperative day. A third patient underwent a transaortic ventriculomyotomy and died 2 weeks postoperatively. These authors have abandoned these last three procedures, preferring the enhanced

visualization permitted by the combined nortic, and left \-entriculotomy approach. All 16 patients were symptomatic and had preoperative left \.entricular outflow pressure gradients of 30 to 140 mm. Hg. hlitral insufficiency was demonstrated on angiography in 4 and an additional ~3patients were noted to have mitral insufficiency at operation. III a followup, 4 to 38 months after operation. all but one of the 14 survivors were greatly improvc~d. One patient had COIItinwtl mild disability due to angina pectoris and paroxysmal atria1 fibrillation. In 4 postoperative cardiac catheterizations there was no gradient across the left ventricular outflow tract in 2; a gradient of 30 and 30 mm. Hg was rrcordcd in thusother 2 patients. \Vith isoproterenol stimulation, the 2 patients \vith no left \.tWricular outflow tract obstruction at rest, &\-eloped swl~ ;I grxlient, while in the other 2 the gradient increased. Left ventriculograins sholred little challgc compared with prc‘operati\.c> studies c~xcept for ;I left \wtricwlar ane~irysm in one patient. Cooley et al.” have operated upon 26 patients who preoperatively llad systolic pressure gradients across the left \:entriculur outflow tract ranging from 19 to 130 tmn. Hg (average 76 mm. Hg). Initially, .‘3patients underwent transaortic, \.entriculomyotomy, one with cautery excision of muscle. All 3 patients sur\ i\,erl surgery. A combined aortic and left ventricular approach \vith left septcctomy DXS used in 13 patients. In this group there were 2 deaths, ow fronr ventricular fibrillation and one from congesti\re heart failure. As experiC’Il(‘(‘ \vas gained the rescctional techniques \\-ere c~xtended. In 7 patients, scptal muscle resection was carried out through a right ~~~ntriculot0n-r~~as descrilwd by Harken.” Two deaths occurred irr this group, one from \-entricular fibrillation and one from congestive heart failure. The wmaining 3 patients ~mclcrwent both left and right ventricular septectomies, one at a single operation and 2 patients at separate operations. One of these,patients died follo\ving the second operation of complete heart block. Non-fatal complications included complete heart block, a left I-entricular anwr\wn. dela\~~tl stc~rnalunion and postoperative hemorrhage. All but 011~ of the 21 long-term survivors \wrc said to lw improvc,d clinically. Sis patients had hemodynamic reassessment, 5 to 11 months postoperati\~ely. After left septcctomy, 3 patients showed a reduction in the left \w~tricular outflow tract gradient and one showed no change. Following the right septectomy operation. one patient had no gradient postoperatiwly and OIIP patient had a reduction in the outflow tract gradient. The left ventricular cw-diastolic pressure was reduced postoperatively in 3 of these 6 patients. A dc+ailecl postoperati\rc study o11 12 pnticnts has been documented b? lkwratt-Boycs and associates.‘“’Six had the transaortic approach with muscle rcwction that became march extensive as experience was gained. The last 6 patients had muscle resection through the combined aortic-left ventricular approach described by Kirklin and Ellis.” .-Ill patients were symptomatic. Outflow tract pressure gradients ranged from ,54to 1.34nun. Hg. In 6 the left \w~triclllar end-diastolic pressure was elevated. One Ixltient was considered to Ira\~s significant mitral insufficiency. There mwe no operative deaths. On(~

patient with inadecluatcl relief of the outflo\v tract obstruction ( tl&w~ined at the time of operation ), ultimately died 4% months Iatw. Thercs \VCW no instances of heart block. One patient developed a smnll \witricular ;uwIqwn and OII(’ a small ventricular septal defect. Ail the surviving 11 patients exhibited \ arying degrees of symptomatic improvement, one to 32 months postoperati\,ely. Three patients who had ;I poor clinical result were sho\vn to ha\,e residual Ixxwure gradients of front 68 to 79 mm. Hg. Of the remaining 8 patients who wew considerably improved postoperatively, one had no pressure gradient across the left ventricular outflow tract while seven had gradients ranging from 3 to 2.3 JJJJJI. Hg. Isoproterenol infusion failed to provoke a gradient in the patient that had no gradient at rest, but resulted in outflow tract gradients ranging from 28 to 100 mg. in 5 patients. The left ventricular end-diastolic pressure fell to, or remained, normal in 10 patients and was increased in one patient. Mitral insufficiency, which was present in one patient vreoperatively was abolished by the muscle resecting procc~dure. The authors felt that the ~nusck resection through this combined approach had resulted in a more complctc~ abolition of the outflow tract obstruction. Lillehei et al.“” have reported their operative results in h: patients lvith muscular subaortic stenosis. Three early patients in their series underwent septal muscle resections through the combined aortic and left I-rntriculotomy approach. Two of these patients died 6 and 56 months after operation. 2&i third patient developed a left ventricular aneurysm which was resected 5 years after the initial operation. This patient had no residual left \rentricular outflow tract obstruction alid has made a complete recovery. These authors subsecluently began using the transatrial approach described by Dobell and Scott.“’ IJl this procedure a left atriotomy WLS done, the anterior cusp of the mitral valvc~ was detached, and the septal muscle was resected. In .5 patients operated upon by this technique, thcrc was OJW c&y hospital death due to a disrupted llritral suture line. h sec:md patient in whom a prosthetic mitral ~il\xa \vas irrscrlcd, died 3 months after the opwxtion. Of the 13 remaining patients. ow had the anterior leaflet of the mitral val\~ advanced because of mitral insufFicicJlc)-. These :3 surviving patients continued to bc well. One was rwathetcrized :3 weeks postoperatively and showed a reduction in the left \w~tricular outflow, tract gradient from 55 JJIJJI. Hg preoperatively to 30 mm. IIg postoperutivcly. In a second patient, the gradient \vas reduced from 100 mm. Hg preoperati\,cl) to 15 mm. Hg, 11 months postopelati\.cl~.. IhCXVlOA~I The results of surgery in muscular subaortic stenosis indicate that- the outflow tract obstructim can be abolished, that the left ventricular end-diastolic pressure may be reduced, and mitral insufficiency may he reduced or abolished. The majority of patients note significant clinical improvement. The most encouraging postoperative results thus far reco’rded in the literature ;Lre those in which the surgical technique has involved ~,entriculomyotomy with or without additional resection of muscle. The resection of muscle in addition to the

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muscle-splitting myotomy incision, does not appear to offer any advantage in so far a~ postoperative hemodynamics are concerned. The postoperati\:c results of gross muscle resecting procedures (without ventriculomyotomy ) as currently reported in the literature are not as encouraging. Why then, is the muscle-splitting incision alone apparently as successful as any surgical procedurc yet devised for musclar subaortic stenosis? Initially, it was suggested that a myotomy incisir)n in the left ventricular outflow tract might lessen the subaortic stenosis by producing a left bundle branch block.’ Evidence has been provided, ho\ve\,er, that complete abolition of the outflow obstruction may occur in the alxencc of the production of an? x’entricular conduction defect.!‘: It should be stated that the ventriculomyotomy incision. usuallv does product fairly specific electrocardiographic chnng~s ~~Osto~~eTutively~‘:‘~“.!‘” Thus, when the incision is made in line with the comrnissllre between the left and right coronary cusps of the aortic valve, left axis deviation is produced postoperatively, presumably from cutting the anterior divisions of the left bundle branch. When the incision is made more mediaIll. ( under the right coronary cusp) complete left bundle branch block may 1~ produced. Of additional interest is the fact that the myotomy incision ~SO abolishes the abnormal Q waves when present preoperatively, providing e\itlencc~ that activation of the hvpertrophied septum is rcsponsiblc for these unusual electrocardiographic abnormnhties in this condition.“” In one patient who unclenvent the \rentriculomyotonr~ operation elsewhere, the postoperati\x~ t,lectrocar~liogr3111 demonstrated both the loss of the dmornd Q waves MK~ the tlcvelopment of left axis tleviation, yet the stenosis was unaffected by this surgcsry. This observation, together \vith the obsc~r\xtion that the stenosis nla>’ 1~ rcxlieved without production of any \-entricular conduction defect, \v~dd indicate that postoperative alteration of \.entricular actiKttion md conduction bears no relation to the success of this form of surgcrv. 1lorrow and Rrockenbrough compared the \-el;triculolnyoto*ll!. operation for Itmscular suhaortic stenosis to the Fredct-Hamstrdt operation for hypertrophic pyloric: stenosis and to the He&r opcratiolt for cardiospasm.‘” In both of these latter operations the principle of the procedure is to cut across the long axis of the circumfereiitially arranged hyp(~rtropliic muscle. In So doing. the c*ut edges of the severed muscle spread apart on contraction. This analog\. of tlrth \~entriculomyotomy operation to these two procedures is particularly apl~ropriate. The deep bulbospiral muscle encircles the base of the left ventrick whilr, the deep sinospiral muscle c~ncirclcs the base of both the left and right vcl~tricles.“” ‘The base of the ventricular septum largely consists of thescl Thus, cutting perpendicul~~rlg, cir~lmlferenti~~lly arranged ~nuscle bundles. XI-ass their long axis in the \~clrtriculomyc,tonly incision, the cut edges of these muscle 1)undles spread apart in systole. This spreading of the cut edges “opens up” thca outflow tract in systole. whereas prc’oprrati~~tly the contraction of thcsc, muscles closes down the outflow tract in s>,stole. ln the technique of this type of surgery, stress is laid upon: 1) cutting across the Lvhole midth of the obstructing band of muscle: and 2) cutting the obstructing muscle to sufficient

depth. Only 11~achieving both these prrrecpisitc~s to swcess will the cut rdg~~s

106

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‘I‘1~I~lHI.~:.

AI)KI.XI

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sllred I\lplt sufficicntlv . in svstolc to rclic\,e the obstruction. ()f p;rrticular not(, . is the fwt that the incision in our patients has been lirnitt>d to the OutHow, tract and need not extend down to the apes of the left \.cntricle. Postmortem examination in the :3 patients in the series from this center vvllo died :3 to .3 yews folIowing the ventriculomyotollly operation and who vverc shown to ha\.{ 110 obstruction postoperatively, demonstrated the dramatic manner in vvhich the cut edges of the incision spread apart. It would seem possible that the v7~rinble success achieved by means of operations based on resection of muscle may be related to whether or not the area of muscle causing the obstruction is removed. in muscular subaortic stenosis, there is gross overgrowth of cardiac muscle particularly in the septum and adjacent anterior left ventricular wall. The resection of large amounts of this abnormal septal musculature may have little effect on the outflow tract obstruction if that part of muscle overgrowth causing the obstruction is left untouched, or is incompletely resected. A number of studies have now demonstrated that relief of the outflow tract obstruction by ventriculomyotomy or muscle resection may also result in lessening or abolition of the mitral insufficiency. Since the anterior leaflet of the mitral valve has not been touched by these surgical procedures, yet forms one side of the obstruction, relief of both the obstruction and the mitral insufficiency in some cases suggests that the septal musculature is the primary fault in this condition. If septal encroachment on the outflow tract causes the obstruction, by impinging on the anterior mitral leaflet which becomes stretched over the muscular prominence, then prevention of septal encroachment by a muscle-splitting incision could reasonably be expected to abolish both the stenosis and the mitral leak. Bjork et al., however, have reported cases in which the obstruction appeared to be related to an abnormally attached anterior mitral leaflet.“‘l The exact reason for the left ventricular end-diastolic pressure reduction is less clear but is probably related to the relief of both the outflow tract obstruction and the mitral insufficiency. Whether the various surgical procedures could result in increased ventricular distensibility or compliance postoperatively is unknown. The postoperative relief of syncopal episodes and angina pectoris is probably related to the relief of outflow tract obstruction, whereas the relief of dyspnen could result from a lessening or abolition of the mitral insufficiency and a reduction in left ventricular end-diastolic and left atria1 pressures. Prior to the introduction of propranolol we advised surgery in patients with muscular subaortic stenosiswhen they had significant symptomatology. A number of patients with large pressure gradients without symptoms were followed conservatively, with restricted activities. At the present time, patients with significant symptomatology, as well as those with severe obstruction but without symptoms, are being given a trial on propranolol therapy. We have thus far administered propranolol to 14 patients with muscular subaortic stenosis. In 2 the drug had to be discontinued because of gastrointestinal side effects. Twelve patients are currently receiving long-term propranolol therapy and we have been encouraged by the symptomatic relief some achieved when the dose

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of the drug is sufficient to cause slight bradycardia. The range of dose has been from 80 to 240 mgm. per day in divided dosage. Several of these patients have had incomplete relief of symptoms and are now being considered for surgery. It would be our present impression that the symptomatic relief achieved by adequate propranolol therapy has been somewhat less than that achieved by the most successful surgical procedures. At present, the decision as to whether surgery is advisable in muscular subaortic stenosis is based on the severity of the symptoms, the severity of the outflow tract obstruction, the response to propranolol therapy, and whether or not the mitral insufficiency appears secondary to the outflow tract obstruction. Patients in whom angiotensin infusion abolishes both the outflow tract obstruction and the mitral insufficiency are currently considered better candidates for surgery than those patients in whom angiotensin infusion abolishes the outflow tract obstruction but fails to effect the degree of mitral insufhciency. Three patients in the latter category are presently on long-term propranolol therapy until we understand more compIetely the significance of mitral insufficiency that is not related to the outflow tract obstruction in this condition. If such patients require surgery in the future, at the time of operation the mitral valve mechanism would be carefully examined in addition to carrying out the ventriculomyotomy incision. It should be stressed that although the ventriculomyotomy operation can relieve the outflow tract obstruction and the mitral insufficiency in muscular subaortic stenosis, as well as lower left ventricular end-diastolic pressure, it does not affect the primary overgrowth of muscle in these hearts. That the latter remains an important feature postoperatively in some of these patients is perhaps attested to by 2 of the 3 late deaths in our own surgical experience with these patients. ACKNOWLEDGEMENTS The authors wish to express their appreciation to Drs. l’ves Marquis and Pierre Auger who aided in the postoperative hemodynamic studies, to Dr. Malcolm Silver, Department of Pathology, University of Toronto, for preparing Fig. 5, and to Miss Dorothy Goodwin for secretarial assistance and Misses Jean McKeekan, B.Sc. and Neives Gonzalez for technical assistanrc*.

REFERENCES 1. Brock, R. C.: Functional obstruction of the left ventricle. Guy Hosp. Rep. 106:221, 1957. 2. Brock, R. C.: Functional obstruction of the left ventricle. Guy Hosp. Rep. 108:126, 1959. 3. Bercu, B. A., Diettert, G. A., Danforth, W. H., Pund, E. E., Jr., Shlvin, R. C., and Belliveau, R. R.: Pseudo-aortic stenosis produced by ventricular hypertrophy. Amer. J. Med. 25:814, 1958. 4. Morrow, A. G., and Braunwald, E.: Functional aortic stenosis: A malformation

characterized by resistance to the left ventricular outflow without anatomic ohstruction. Circulation 20: 181, 1959. 5. Brachfeld, N., and Gorlin, R.: Subaortic stenosis: A revised concept of the disease. hledicine 38:415, 1959. 6. Brent, L. B., Aburano, A., Fisher, D. L., Moran, 1‘. J., Myers, J. D., and Taylor, W. J.: Familial muscular subaortic stenosis: An unrecognized form of “idiopathic heart disease” with clinic and autopsy observations. Circulation 21: 167, 1960. 7. Goodwin, J. F., Hollman, A., Cleland,

10s P., and Teare, I).: Obstructive cardiomyopathy simulating aortic stenosis. Brit. Heart J. 22:403, 1960. 8. Neufeld, H. N., Ongley, P. A., and Edwards, J. E.: Combined congenital subaortic stenosis and infundibular pulmonary stenosis. Brit. Heart J. 22:686, 1960. 9. Braunwald, E., Morrow, A. G., Cornell, W. P., Aygen, M. M., and Hilbish, T. F.: Idiopathic hypertrophic subaortic stenosis. Amer. J. Med. 29:924, 1960. 10. Livesay, W. R., Wagner, E. L., and .4rmbrust, C. A., Jr.; Functional subaortic stenosis due to cardiomyopathy of unknown origin. Amer. Heart J. 60:955, 1960. 11. Brachfeld, N., and Gorlin, R.: Functional subaortic stenosis. Ann. Intern. Rled. 54:1, 1961. 12. Pare, J. A. P., Fraser. R. G., Pirozynski, W. J., Shank, J. A., and Stubbington, D. : Hereditary cardiovascuIar dysplasia. Amer. J. hled. 31:37, 1961. 13. Menges, H., Jr., Brandenburg, R. O., and Brown, A. L., Jr.: The clinical, hentodynamic, and pathologic diagnosis of muscular subvalvular aortic stenosis. Circulation 24:1126, 1961. 14. Boiteau, G. ht., and Allenstein, B. J.: Hypertrophic subaortic stenosis: Clinical and hemodynamic studies with special reference to pulse contour measurement. Amer. J. Cardiol. 8:614, 1961. 15. Stampbach, V. O., Wyler, F., Rents&, M., and Schiipbach, P.: Diagnostische und hamodynamische Probleme bei der Aortenstenose. Cardiologia 38: 112, 1961. 16. Daoud, G., Gallaher, M. E., and Kaplan, S.: Muscular subaortic stenosis. Amer. J. Cardiol. 73860, 1961. 17. Wiglc, E. D., Heimbecker, R. O., and Gunton, R. W.: Idiopathic ventricular septal hypertrophy causing muscular suhaortic stenosis. Circulation 26:325, 1962. 18. Calvin, J. L., Perloff, J. Ii., Conrad, P. W., and Hufnagel, C. A.: Idiopathic hypertrophic subaortic stenosis. Amer. Heart J. 63:477, 196”. 19. Stampbach, V. O., and Senn, A.: Die idiopathische hypertrophische subaortens&nose. Schweiz. Med. Wschr. 92: 125, 1962. 20. Serratto, M., and Benvenuto, R.: Chnical physiologic and anatomic observations in 3 cases of idiopathic hypertrophic subaortic stenosis. Panminerva Med. 4:229, W.

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1962. 21. Hansen, I’. I;., Davidsen, H. (i., airtl Fabricius, J. : Subvalvular aortic stenosis of muscular type. Acta bled. Stand. 171:743, 1962. 22. Joly, F.: Le diagnostic cles stenoscs idiopathiques de la chambre de chasse clu ventricule gauche. Coeur Med. Intern. 1: 447, 1962. 23. Siang, S. C., Gum, L. H., and Chong, T. P.: Aortic subvalvular stenosis from myocxrdial hypertrophy. Singapore Med. J. 3: 138, 1962. 24. Wood, R. S., Taylor, W. J., Wheat, >I. W., Jr., and Schiebler, G. L.: Muscular suhaortic stenosis in childhood: Report of occurrence in three siblings. Pediatrics 30: 749, 196”. 2,s. Bevcgard, S., Jonsson, B., and Karlof, I.: Low snbvalvular aortic and pulmonic stenosis caused by asymmetrical hypertrophy and derangement of muscle bundles of the ventricular wall. Acta Med. &and. 172:269, 1962. 26. Volta, S. D., and Sossai, R. 1~. M.: Le stenosi subaortiche (stenosi aortica sottovalvolare e stenosi infundiholare ) Atti Sot. Ital. Cardiol. 22:133, 1962. 27. Fishleder, B. L., Bermudez, F., and Friedland, Ch.: Estenosis subaortica dinamica: Su diagnostic0 clinic0 y por metados graficos rsternos. Arch. de1 Institute de Cardiologia de hlesico 32:430, 1962. 28. Kariv, I., and Solomon, M.: Familial cardiomyopathy. Proc. Tel. Hashomer Hosp. I: 53, 1962. 29. Sonlie, I-‘., Joly, I’., and Carlotti, J.: Les stenoses idiopathiques de la chemhre de chassc clu ventriculc gauche. Acta Cardio. 17:335, 1967. 30. <:rossc-Brockhoff, F., and Loogen, F.: Infundihulnr pulmonary stenosis in chronic left ventricular cardiopathy. Deutsche bled. Wschr. 87:525, 1962. 31. McIntosh, H. D., Sealy, W. C., Whalen, R. E., Cohen, A. I., and Sumner, R. G.: Obstruction to outflow tract of left ventricle. Arch. Intern. Med. 110:84, 1962. 32. Menges, H., Jr.: Muscular suhvalvular aortic stenosis. Amer. Heart J. 64:137, 1962. 3.3. Nordanstrom, B., and Ovenfors, C. 0.: Low subvalvular aortic and pulmonic stenosis with hypertrophy and abnormal arrangement of the muscle l~undles of the

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