5

Significance of the Subvalvular Appar atus for Left-Ventricular Dimensions and Systolic Function: Exp erimental Replacement of the Mitr al Valve E. Gams", S. Haql", H. Schad. W. Heimisch, N. Mendler. and F. S ebeninq Dep artment of Cardiac a nd Vascular Surgery, Gennan Heart Cent er Munich. FRG * now at Dep a rtm en t of Card iac Surg ery. University Hosp ital Heidelberg. FRG

To stu dy th e significa nce of the subvalvular appa ratus for leftventricular perform a nce in mitral valve replacement, a new experimental model was developed. In 21 dogs St. J ude pr ostheses were implanted in the mitral position preserving the chordae tendineae and the papillary muscles by plica ting an fixing the mitral leaflets with the pr osthesis on the valvular a nnulus. Flexible steel wir es were slung a round the chordae tendineae of the a nterior a nd the posterior papillary muscle separat ely and passed th rough the left ventricula r wall via ins ulating plastic can nulas. Left-ventricular dimensions and global systolic (unction were measu red dur ing volume loading with blood before a nd after severance of the chordae tendineae by extern al application of electro ca utery to the steel wires . Thus the heart continued beat ing without an y inter fer ence following loss of the subvalvula r apparatus. The extern al left ventricular diameters in the majo r a nd minor axis were determined by sonomicrome try. Left-ventri cular systolic a nd diastolic pressures were mea sured by catheter tip manometers , stroke volume by electromagnetic measurem ents offlcw in the asce nding aorta . When the chordae tendineae had been cut, left-ventricular enddiastolic diam eters in the major axis were increased (+ 2 %), in the minor axis decreased (- 1 %) a t any left-ventricular enddiastolic pr essur e. Systolic short ening of the major axis diamete r was considerab ly reduced (20-27 %) at a ny left-ventricular end diastolic pr essure following severa nce of the chordae tendi neae . Significant increas e of the systolic shorte ning in the minor axis diameter occurred at pr eload levels of3-6 mmHg 05-8 %). while at highe r left-ventricular enddiastolic pressure of7 -8 mmHg no significant changes were pr esent. Pea k systolic left-ventr icular pr essure a nd heart rat e did not change following severa nce of the chordae tend ineae at compara ble pr eload levels, whereas the maximu m rate of rise of left-ventricular pressure (dP/dt mul (- 9 to - 10 %) as well as left-ventricular stroke volume (-7 to - 8 %) decreased significant ly after dest ruc tion of the subvalvular app ar atu s. These results reveal changes of left-ventricular dimensions a nd a n impairment of left-ventricular performance following mitral valve repla cement with excision of the mitral valve leaflets. chordae tendln eae. and papillary muscles. These results suggest that pr eservation ofthe subvalvular a pparatus in mitral valve replacem ent in patients be seriously considered whenever possible. Key words

Mitral valve replace ment - Subvalvula r app a ra tus - Left-ventricular function - Left-ventricula r dimensions - Canine experiments

Bedeutun g des su bva lvularen Iia ltea pparates ftir die linksventr lkula re n Dimensionen und die sys tulische Funktion beim expe rime ntellen ~litralk l appen e rsatz

Urn die Bedeutung des subvalvularen Haltea ppara tes de r Mitralklapp e fur die lins kven trikula re Funktion zu untersu chen . wurde ein neues experimentelles Modell en twickelt. In 21 Hundeversuchen wurden St. Jude-Prothese n in Mitralposition impla ntiert. wobet der sub valvula re Appa rat erhalten blieb und die Kla ppensegel mit der KunststofTprothese am Mitralri ng fixiert wurden. Flexible Stahldrahte wurden urn die Chordae tendineae sowohl des vorderen als a uch des hinteren Pa pillarmuskels geschlungen und mit Hilfe von isolierte n Plastikkan illen durch die Ventrikelwa nd oac h a uBen gestaehen. Durch Elektrokoagulation wu rden die Sehnenfa de n von a uBen d urchtre nn t. so daB das Herz in seinen Kontraktionen nicht ctngeschra nkt war und un behindert weiterschlagen konn te. wahrend der Blutvolumenbelastun g wurden sowohl vor als a uch nac h Durchtren nung der Sehn enfadon Funktionskurven des linken Ventrikel s erstellt. Die auflere n Durchmesser des link en ve ntrtkels wur den mit Hilfe des Ultrascha ll-Laufzeitve rfahre ns in der Langs- und Quer achse bestimml. Die Drucke im linken Ventrikel wurd en mit Katheterspit zenm an omet ern . das linksvent rikulare Schlagvolurnen mit einem elektromagnetis chen Stromu ngsm ess er an der Aorta ascendens gemessen. Nach Durchtrennung der Seh nenfad en nahm bei vergleichba ren linksventrikularen enddiastolischen Drucken der endd iastolische Uingsdurchmesser des linken Vent rikels urn 2% zu. der enddiastolische Querdu rchrnesser dagegen urn 1% ab o Die systolische Verktirz ung im Langsdur chmesser wa r na ch Funktionsverlust des subvalvular en Mitra lklappenapparates bei allen vergleichba re n Vorlaststufen erheblich redu ziert (-27%). Signifikante Ver anderungen der systolischen Verktirz ung wa ren im Querd urchrnesse r nur bel links ventrikularen endd lastolischen Drucken von 3-6 mmHg (Anstiege von 15 bzw. 8%1 vcrhanden . da gegen waren bel hoh eren link sventrikularen endd iastolischen Drucken von 7 -8 mmHg nach Durchtren nun g der Sehnenfad en keine Verand erungen zu erken nen . Ocr systoIische Linksventrikeldru ck und die lIerzfrequenz war en nach Durch trennung der Sehnen fad en nicht vera ndert. wahrend dPI dt max (- 9 % his - 10 %) als a uch das linksventrikula re Schlagvolurnen (- 7% bis -8 %) be l allen vergleichbare n Iinksventrikularen Ftillungsdrucken nach Funktionsverlust des subvalvularen Haltea ppa rat es signifikant abnahme n. Diese Ergebn isse zeigen ve randerungen der linksven trikularen Dimens ionen und eine Beeintrachtigung der systolischen Linksventrikelfunknon. wenn beim Mitralklappeners atz die Kla ppensegel. die Chordae tendineae und die Papillarrnuskeln reseziert werd en. Es erscheint empfehlenswen . beim Mitralkla ppenersa tz am Patient en Teile des suhvalvular en Haltea pparat es - wenn magIich - zu erhal ten.

.. E. Garns was award ed the Ern st-Derra-Prize 1990 for this study Thorac. cardiovasc. Surgeon 39 (1991) 5- 12 © Georg Thieme Verlag Stuttgart -NewYork

Received for Publicat ion : September 7. 1990

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Summa ry

Thome. cardiovasc . Surgeon 39 (J 99 1)

E. Gams, S. Hagl. H. Schad. W Heimisch. N. Mendler. and F. 5e bening

Introduction

Approx ima tely on e million he art valves ha ve been impl a nt ed world wide (33) since in 1960 th e firs t ca rdiac valve repl acem ent was performed in ma n (17, 37). Wher eas during th e ea rly peri od of ca rdiac surgery every four th patient died postoperatively, twenty yea rs lat er th e hos pita l mo rt ality followin g cardiac valve replaceme nt was close to 5% (27). Despite the use of mod ern prosth etic h eart valves with improved flow dyna m ics, refined sur gica l impl antation te chniques , a nd safe myocard ial protectio n metho ds the postoperative long-term results followin g mitral valve replacem en t a re still not sa tisfactory 01, 24). Th e fact th at reconstr uctive surgery of th e m itr a l va lve as oppo sed to mitral valve replacemen t results in much better survival rates an d in fun ctional improvem ent 0 , 6,1 2, 14, 18, 22) m ight be du e to the widely accepte d conven tional surgical technique of resection of both leafl ets and excision of the subvalvula r mi tr a l a ppa ra tus durin g valve replacem ent. In the ea rly sixties Dohlbii ck et a!. (9) as well as Lillehei et a!. (25) pr op osed to pr eser ve th e subvalvular appa ra tus in mitra l valve replacement. The ir posit ive postop er ati ve resul ts were not confirm ed by others (2, 29). The m ethods ava ilable at that time obviously did not allow an investigation isolating the results of the mod ified surgical techn ique . Twent y years la ter th e idea was tak en up ag ai n by Davi d et al. (10) a nd Hetz er et a!. (20). The reasoning behind th e suggest ion not to radi cally resect subvalvula r a ppa ra tu s is based on th e resulting changes in left-ventricular dim ensions (7, 21,2 8, 34, 38). The left-ventricular archi tecture cha nges when th e sub valvular a pparatus is excise d, as ca n be seen from the sch ema tic drawin gs in Fig. 1: in the major axis th e leftventricular enddiastoli c diameter is increased, whereas the minor ax is diam eter is sho rt ene d . Th e qu ad rilateral offo rces resu ltin g fro m the anc h ori ng points of th e subvalvular appa r atu s in th e left-ventricular wall as we ll as in th e mitral valve leaflets, is destroyed whe n the valve leaflets, the chordae tend in eae a nd the papill ary mu scles are resected in mitra l va lve replacem ent (Fig. I , bott om ). Thi s dem onst ra tes that th e su bva lvula r ap para tus is not only a pa ssive element of th e m itra l valve, but also part of th e left ventricle

and makes an essential contribution to left-ventricularfunction . The dia gram illustrates th e task of the subvalvula r appa rat us is to keep the left-ventri cular cha mb er in appropriat e sha pe and size th roughout the ca rdiac cycle: Since enddiastolic length has incr eased a nd syst olic shorten ing decrea se d following des tructio n of th e sub valvular app aratus, th e left ventricle ca n no longer perform with maximum efficiency. Experimental studies were pe rformed during th e past decad es (8, 10 , I S, 29, 31, 32, 36), but they sho wed conflicting resu lts, du e to the fact that the experiments were performed in the isovolurnically beating hea rt pr ep arati on (I S, 32, 36) wh ich is not representative for th e ph ysiologically wo rking heart, the studies we re don e by comparing a se ries of animals with preserved mitral valve apparatus to a series of anim als wit h ex cise d mitral valve (8, 10 , 29) which resu lted in divergent conclusions because of the biological variability in a sm a ll nu mber of an ima ls, - usin g different len gth s of th e cho rdae ten din eae (31) led to insign ifica nt results because it was not possible to con-

Architecture of the left ventricle Subvalvular apparatus intact excised

Fig. 1 Sectionalview of the leftventricle oemonstrating thedimensional changes with the subvalvular apparatusintact (left) andexcised (right) beforeandafter mitral va lve replacement (above).Afterresection ofthesubva lvular apparatus the original polygon offorces is destroyed (below)

trol the fun ction of the subvalvula r a ppa ra tus adeq ua tely from th e out sid e. To avoid th ese methodical a nd techn ical dra wbacks in the experimental set- up we concluded that it is necessary to pr ove th e significa nce of th e modified tech nique of mitral valve replacem en t for th e left-ventricular func tion in the sa me beating heart under com pa ra ble preload and aft erload cond itions . The a im of our study wa s to develo p an experimental model in order to examine the importance of th e ch ordal int egrit y following mitral valve replacem ent. Material and Methods The experiments were performed in 21 anest hetize d dogs of 22 to 31 kg body we ight. Followin g premedication with Combelen. a derivative of phenothiazine (Bayer. Leverkusen . FRG ), anesthesi a was induced by a single intrave nous injection of pentobarbitalsodium (Nembutal, Deutsche Abbott GmbH. Ingelheim. FRG). After intubation and during intravenous infus ion of pancuroniumbromide (Organ on-Teknik a . OberschleiBheim. FRG) the animals we re artificially ventilated by a se rvo ventilator (Siemens-Elema. Stockholm. Swe den). Anes thesia was continued by intravenous infusion of 1.5 mg/ kg/ h of piritramid Ipl pidolcr. Janssen . Dtlsseldorf FRG). No barbiturates were used during the further course of the ex periments. The chest was opened through the 5 th left intercostal s pace . The pericardium w as incised and the edges we re suspended in a way that the contractions of the heart we re not hindered and the s itus of the heart was not cha nged. After i.v. injection of SOOIE/ kg b. w. hepa rin (Heparin-Sodium . B. Braun Melsu ngen . Melsungen . FRG) the heart-lung-machine (Weishaar Electronic. Munchen. FRG) (Didecooxygenator. Mirandola. Italy) was connected by can nulating the femoral artery and the right atrium. During extracorporeal circulation and after cooling to 28 ' C core temperature the ascending aorta w as cross clamped. and 500 ml of 4 °C cold cardiopJegic so lution (Bretschneider soIution-HTK, Kohler Chemie . Alsbachi BergstraBe. FRG) was infused into the asce nding aorta. The left atrium was ope ned and flexible steel wires we re slung around the chordae tendineae of the anterior and the posterior papillary muscles separately. They were lead through the left ven tr icular wa ll to the outside near the atrio-ventricu lar groove via small plastic cannulas . ready to be used for cutting the chordae later on.

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6

Then a St. Jude prosthesis was implanted on the mitral annulus usi ng teflon-felted If-shaped Ethibond sutures. Further function of the native mitral valve w as prevented by plication of the valve leaflets w ith the mitral an nulus. while the whole subvalvular apparatus including the chordae tendineae and the papillary mus cles was preserved in a wa y that the co ntinu ity of the mitral a nnulus . valve leaflets, chordae tendineae and papillary muscle s with the left ventr icular wall was kept intact. Care w as taken that the opening and closing of the valve prosthesis was not impeded . The left atrium was closed and the aorta unclamp ed. The mean ischem ic time w as 47 ± 4 minutes. The heart was defibrillated. During repe rfusio n and rewa rming a cathe ter tip manometer was put into the left ventricle. An elect romagnet ic flow meter (Statham Instr.. Oxnard. California. USA) was put around the asc ending aorta for measurement of the left ve ntricular stroke volume . Heart rate was determi ned from the electrocardiogram. External left-ve nt ricular dimens ions in the major and minor axis were measured by son om icrome try (13. 19). \\'e used circular transdu cers made of lead zirconium titanate (size 0 04 x 5 mml whi ch we re glued on a dacron patch of 2 x 2 cm in size. The patches then were se w n onto the epicardial surface . To dete rmine the major dia meter the transducers w ere fixed on the epicardium close to the aortic root betwee n the pulmonary artery and the left atrium and on the apex of the heart. For measureme nt of the minor diameter the patches were put on the anterior surface of the left ventricle betwee n the left anterior descending co ronary artery and the first diagonal branch and on the posterior wall of the left ventr icle between the first and second marginal branch of the left circumflex coronary artery (Fig. 2),

During volume loading the hemodynamic parameters as well as the left-vent ricular diameters we re record ed continuously. After volume unloading and under norrn ovolemi c co nditio ns th e chordae tendineae of th e a nt erior and the post eri or papillary muscl es wer e severed : the flexible st eel wires which had been passed through the left-ventr icular wall and left loose we re now tight ened fro m the outs ide via the te flon ca nnulae. By passing curre nt th rough th e stee l wires the cho rdae tendineae of each of the a nterior a nd th e posteri or papill a ry m uscles we re cut by elect roca utery while the heart continued beating without any mechanical irritation. Electrical irritation was prevented by the ins ulating teflon . Th e cha nge s Indu ced imm ed iat ely aft er this pr ocedure. i. e. within 30 to 60 seco nds. we re defined as acute cha nges following severance of the cho rdae ten d ineae (see results I) . Sub sequently volum e loading was performed in the same manner as it was done before and again left-ventr icular function curves of the hemod ynamic parameters were recorded. The cha nge s following volum e loading a re describ ed in results II. In order to confirm the complete loss of th e connection left-vent ricula r wall to mitral valve. a t th e end of each exper imen t a gross exa mination of the heart was perform ed . In all exp erim ents the chorda e tendin ea e of the anterior and th e posterior papillary muscle we re show n to be cut com pletely.

Definition ofthe left -ventricular dime ns ions Fig, 2 Drawingof the heart withview into theleftventricular chamber showingthe electrocauterywires (C) aroundthechordae tendineaeoftheanteriorandposterior papilla ry muscleofthe mitral valve andtheultrasound transducers measuring theexternal lett-ventriculardiameterinthe majoraxis(D and D')and inthe minoraxis(d and d'). The 51. Judeprosthesis is inposition

c d

D'

Left-ventricular dimensions were recorded continuously during th e experime nts. Enddiast olic len gth in both axes was defined as the distance of th e ultrasoni c t ran sd uce rs before the rise of left-vent ricula r pressure duri ng eac h ca rdiac cycle. The measure of systo lic sho rten ing of the left ventricle in the major and minor axis diameter was define d as th e reduction of length during the ejection phase of th e systo le. i.e. between th e ope ning and closu re of th e aortic valve.

Statistical ellaluation Ofea ch parameter the mean values and the stand ard error of the mean (SEMI were calculated. The matched pairssigned rank test acco rding to Wilcoxon was a pp lied to compare the results befor e a nd afte r division of th e cho rdae tendi neae a t the sa me pr eload levels. The critica l values for th is test we re ta ken from th e tab les of McComa ck (26). A diITer en ce whe re p < 0.05 was defin ed to be statist ica lly significant.

Experimental protocol Approximately 60 m inu tes post ca rdiopulmonary bypass cont rol values of heart rate. left-ventricula r enddiastolic pressure. left-ventricular systolic pressur e. maximum rate of rise of left-ventri cular pressu re (~ dP/dt m,,) . stroke volume. external left-ventricu lar diameters in the major and minor axis were determined under normovolemi a. Subsequently volume loading was performed by blood transfusion (av e rage 20mVkg b. w.) over a per iod of 10 mi nutes up to pr eload levels of 8mm Hg left-ventricula r enddiastolic pr essure. In a few experime nts high er values of left-ventricular end diastolic pr essure we re reach ed . but rh ythm disturbances like prem ature beats occurred. For this reason these ex periments were excluded from further evaluation.

Results

Acute changes induced by set'erance ofth e chordae tendineae Acute changes are defined as change s occurring immediate ly following the severance of the chordae tendinea e. Th e acute eITects of severance of th e cho rdae tendin eae of th e m itr al valve a re sh own in Fig. 3. Th e X-V plots of the pr essure-length diagram of th e left ventricle are de picted for th e diameters in the major an d minor axis oftbe left ventricle. Th e loop reflects the pr essure-len gth cha nges during one ca rdiac cycle. sta rting from th e left end of the bottom line with ventricular filling. and running counterclockwise

7

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Thorae. eardiovase. Surgeon 39 (1991)

Significance a/the Subva lvular Appara tus

Thome . cardiovasc. Surgeon 39 (1991) left ventriculardiameter

major 72

E. cams. S. Heql. fl. Schad. W Heimisch; N. Mendler. and F. Sebening

78

mm

Table 1 Control valuesimmediatelybeforeand %changesacutelyinduced by severance of the chordae tendineae

minor

55

63

mm

before

2.2 ± 0.5

100

dP/dtma •

LV1'

SV edDmaj edDmin

2100 ± 160 156 ± 6 0.47 ± 0.05 74.4 ± 1.0 59.1 ± 1.6

1 ;

before

f f

after

mH 9

f f

after

(absolute value)

LVedP LVP

before

severance of the chordae tendineoe Fig. 3 Acutelyinducedchangesinthe left-ventricula r pressure (LVP) x length loopsinthemajor(left)and minor(right)axisdiameter beforeandafter severance of the chordae tendineae of themitral valve

with an increase of the left-ventricula r diamete r. At the right end of the bottom line ventricular pressure rises during isovolumic contraction of the left ventricle with a small cha nge in the di am eter len gth . During th e ejection phase the diameter decrease s again and the left-ventricular pressure falls to diast olic levels during relaxation . As far as the major ax is diam eter of th e left ventricle is conce rned (Fig. 3,I eftl, there are two important phenom ena: Immediately, i. e. within seco nds , following the cutti ng man euver , the pr essu re- length curve moves to the right due to the increase of the enddiastolic length of th e left-ventricula r diamete r. At the same time th e systo lic sh orten ing of the major axis diameter, which is represented by the dista nce betwe en the risi ng and the falling slope in th e upp er third of the loop, is dimin ish ed subs tantially. Th ere is little cha nge in the sha pe of the pr essurelength loop of the minor axis diam eter du e to th e decrease of the left-ventricular systolic pressure. However, the minor axis diamet er of the left ventricle is alTected in the opposite direction com pared to the major axis diamete r: There is a sma ll decrease of the en ddiastolic len gth of the minor axis di am et er following severan ce of the cho rdae tendineae, whereas sys tolic shortening in the minor axis - Le. the distance bet ween th e risin g and the falling slope during the ejection phase - does not chan ge after destru ction of th e subva lvula r a ppa ra tu s. Tabl e 1 sum ma rizes th e changes acut ely induced by cutt ing the chordae tendineae. There was n o significan t change in left-ventricular end diastolic pr essure , but leftventricula r systolic pr essure (LVPI (-7 %l. maximum rate of rise of left-ven tri cular pr essur e (dPldtm, ,1(-10 %l. left-ventricular stroke volume (SV) (-10 %1 decr eased , and heart rat e (HRI (+6 %1 increa sed significantly, reflectin g the impaired globa l systolic function of the left ventricle. Th e measurem ent of the diamete rs in the major a nd mino r axis revealed th e acutely induced change of left-ventri cular geome try : Th ere was a sma ll, but significant increase of 1%in the major axis, but a decrease of 1.4 % in the minor axis diameter, demonstrating that the division of th e ch ordae tendineae was followed imm ediately by cha nge s in the sha pe of the left ventricle.

85 ± 2

HR

after

(%change)

(mmHg) (mmHg) {mmHgls) (beats/min)

+5 ± 10 {%) - 7 ± 1 {%)' - 1O ± 2 (%)'

(ml/kg)

- 10 ± 2 (%)' + 1.0 ± 0.3 (%) ' - 1.4 ± 0.3 (%)'

(mm) (mm)

+6 ± 2

(%)'

mean ± SEM (n ~ 13), ' p < 0.05

LVedP LVP

=

dP/dtma•

=

HR

SV edDmaj edDm in

=

= = = =

Left ventricularenddiastolic pressure left ventricular systolic pressure maximum rate of rise of left ventricular pressure heart rate stroke vol ume enddiastolic diameter inthe major axis enddiastoltc diameter inthe minor axis

Changes induced by severance of th e chordae ten dineae during volume loading Effects on left-ventricular dimensions As could be see n in Ta ble I , the acute cha nges of left-ven tricular enddiastolic pressure were inconsistent and not significant immediately following th e division of the cho rdae tendineae (+5 ± 10 %). To reach com pa ra ble pr eload levels befor e an d after division of the subvalvular apparatus, the left-ventricula r enddiastolic pr essure was rai sed bv blood infu sion . Th ese elTects of volume loading on the left-~e ntricu la r diam eters following severa nce of th e chordae tendineae are summarized in Fig. 4 . There was a significa nt increas e of the en dd iastolic diamete r of the major axis of 2- 3 % at a ny preload level of left-ventricula r enddiastolic pressu re from 3- 8 mm Hg, whe n the chordae tendinea e had been cut. Only small bu t significa nt decreases of th e enddiastolic diameter were see n in the minor axis. Th e cha nges in syst olic shortening were mo re prono unced in th e major axis diam eter. At pr eload levels ofl eftventricular enddiastolic pressure of 3- 8 mmHg a corresponding decay of systo lic sho rte ning of 20 -27 % occu rre d . By contras t the syst olic sh ortening of the min or axis dia meter increased significantly in the range 15- 8 %. At left-ventricula r pressures of 7- 8 mm IIg however, there wa s no change of systolic shortening in the minor axis diameter. Effect on globa l left -ventricular performance Global left-ventricula r hem odyn ami cs were det er mined by left-vent ricular systolic pressure, maximum rate of rise of left-ventricular pressure, heart rate and stroke volume, as summa rized in Table 2. Befor e the subvalvula r a ppa ra tus was cut, volume loadi ng by blood tr an sfusions wa s followed by a n in cr ease ofle ft-ventr icular enddiastolic pressure from 3 to 8 m mHg, by an increase of left-ventricula r sys tolic pressu re, of dP/ dtmax• of left-ventricula r stroke volume and by a decr ea se of he a rt rate. After the cho rdae tendineae had been cut , significa nt cha nge s at com parable levels of leftventricula r enddiastolic pressure occurred on ly in dP/ dt m" a nd in left-ventricular stro ke volume, while h eart rate a nd left-ventricular systolic pressure were not altered significa ntly:

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8

Thom e. cardiovasc. Surgeon 39 (1991)

Significance of the Subvalv ular App ara tus (mmHg) 3-4 (I)

Preload level(LVedp) LVP

(mmHg) before (% change) after (mmHgls) before (% change) after (beats/min) before 1%change) after Iml/kg) before 1%change) after

dP/dt",. HR SV

92 ± - 3± 2080± - 9± 153 ± +3 ± 0.47 ± - 7±

LVedP(mmHg) 5-6 (11)

3 2 170 2 7 2 0.04 4

(12) (1 2) (12) 112)"' (12) (12) (9) (9)"'

103± +1± 2480± - 10± 148 ± 0± 0.64± - 8±

3 (12)" 1 (12) 150 (12)" I (12)"' 7 (1 2)" 2 (12) 0.05 (9)" 4 (9)"'

7-8 (111) 114± 3 O±I 2670± 175 -9± 2 149 ± 8 0± 2 0.75± 0.06 - 7± 4

Ill)" Ill) III)" Ill)"" Ill) Ill) (9)" (9)""

9

Table2 Haemodynamic datafrom twelvedogs during volumeloading following mitral valvereplacement with preservationof thechordae tendineae(before)and after severanceof thechordaetendineae(after) at comparable LVedP

mean ± SEM (n);· significant difference (II) vs. (I)and (Ill) vs. (II),·' significant %change ascomparedto "before", p < 0.05 Abbreviations:see Table 1

- myoca rdial protection by the use of cardioplegic solutions has been introd uced (4. 5. 23 . 30. 35): - the surgical techniques have bee n refined - an esth esia had mad e progress and postoperative intensive care has been improved .

systolic shortening +2lJ

•

o

o

~ '-"TT-TT-r

* -8

- 40

+10

+JO

•

•

*

*

.~

o

g

-= = .---::--n:==-c::;:::::J c::p

'E 0 f-

c:::::;::::::J

* -5

*

*

L--...J L--...J L--...J

3- 4

5-6

7-8

LVedP (mmHg)

- IS

L-...J L-...J L--...J

3- 4

5-6

7-8

LVedP (mmHg)

Fig. 4 Changes (%) inleft-ventricularenddiastolic diameterand systolic shortening inthemajorandminor axisfollowing severanceofthechordae tend ineae at different left-ventricular enddiastolic pressures (LVedP) mean ± SEM; • p < 0.05

d P/dtm " was diminish ed by 9-10 % and left-ventricular stroke volume decreased by 7-8 % at any preload level. reflectin g imp airment of left-ventricular systolic function followin g loss of cho rda l int egrit y. Discu ssion

Compa red to th e ea rly period of ca rdiac surgery. hospital mortality following ca rdiac valve replacem ent has been redu ced substantially (27). There are several reasons for the improvem ent of th e resu lts following valve repla cem ent durin g th e past three decades: - ma terials as well as flow dyna mics of the valve prostheses have been improved (3):

Success or failure of cardiac valve surgery can not be measured by the early postope ra tive mort ality a nd peri operative mor bidity. however. it must be judged by the long-term results. Ferruzzi et al. (11)compared the outcome of mitral valve repla cement at the University of Alah am a! USA from 1975 to 1979 and from 1979to 1983 and found no significant difference in the 5-year actuarial survival curves of these two groups of pati ents . In contrast. long-term results following coro nary surgery as well as congenital heart surgery showed significant improvement during the same peri od of time . To explain this dilTeren ce the authors specu lated on insufficient myocardial pro tection and on the fact that pat ient s had come to surgery in an advanced state of the valvular dis ease although the groups did not dilTer in the NYHA-classification. The authors could not explain wh y general progress in cardiac surgery was not reflected in an improvement of the long-term results following mitral valve replacemen t. To measure the funct ional long-term results following ca rdiac valve replacement it is necessary to sub mit patients to exercise tests in the late postoperative course. Kraus et al. 124) exa mined 68 patients following ca rdiac valve replacement and showed that only one third of the patients with aortic valve rep lacement had path ological hemodynami cs during exercise. while 100% of th e pat ients following mitral valve replacement reacted with a rise in pulmonary artery pressure and an inadequate increase of cardiac output during exercise. This mean s that simp le improvement of valvular function does not neces sa rily result in pa thological hemodynamics dur ing exercis e becomin g normal.

The ex perime ntal model Former experimental studies on the significance of the subvalvular appa ratus followin g mitral valve repla cem ent we re performed und er dilTerent methodical conditions. In thirteen canine experiments Lillehei et al. (25) only tried out whe ther it is technically possib le to implant mitral valve proth eses when the chordae tendinea e and parts of the mitral apparatus were preserv ed. The y found it feasible. but did not ma ke an y comparison to control experiments with respect to hemodynamic changes an d left-ventr icula r function.

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end-diastolic diameter

Thorae. ear diovase. Surgeon 39 (1991)

A few yea rs later Rast elli et al. (29) published an experime ntal investigation of left-ventricular function followin g mitral valve repla cem ent with Bjork- Shiley pro stheses in dogs : In five animals th e chordae tendin eae we re excised completely during impl ant ation of th e mitra l valve pr osthesis , in five dogs the posterior mitr al valve leaflet including the chordae tendin ea e we re preserved as proposed by Lillehei et al. (25) and in five additional animals the cho rdae tendineae of the anterior and th e posteri or leaflet were pr eserved. Durin g th e first postoper ati ve days no difference in cardiac output and left atrial pressure was obse rved in the three gro ups . Two mo nth s postoperatively exce rcive tests we re performed and again no difference in the hemod ynamic measurements we re see n. Cohn et al. (8) compa red left-ventricular function of dogs with pr eserved cho rd ae te ndineae to dogs with severed chordae te ndine ae followin g mitr al valve replacement: thirty minutes postoperatively neither stroke work nor the maximum rate of rise of left-ventricular pressure showed any difference in the two groups. In cont rast, David et al. (10) found differe nt effects on left vent ricular funct ion, when they had excise d the mitr al valve complete ly in one series of dogs or resected only the ante rior mitr al valve leaflet with pr eservation of the posterior one includ ing both papill ary muscles in the other se ries of dogs. A few hours post imp lantat ion , ca rdiac output an d ejection frac tion measured by angiogra phic methods we re significantly higher and left-ventricular endd ias tolic pr essure was sign ifican tly lower in the group with preserved subvalvular mitral apparatus. The contra dictory results of th ese experime ntal studies are not only due to differ ent methodic al proce dures. They rather see m to be caused by th e biological variab ility in a small num ber of a nimals. To exclude the interindividual variability of the anima ls and to have contro l on pre load and afte rload conditions Hanse n et al. (15) per formed experiments in th e isovolumi c heart pr eparation . In 1986 they publi sh ed a study on ca nine hearts usin g a latex balloon in the left vent ricle befor e and after division of the chordae tendineae of the mit ral valve while the mitral valve itself was occluded by a disc. They foun d a decrease in left-ventricular peak systolic pressure of 50 % when the chord ae ten dinea e we re divide d. Using the sa me mod el, one year later th e same au thors reported ex periments on the assessment of th e relative contribution of th e ante rior and posterio r papillary mu scle and of the mitral chordae tendineae to left-ventri cular systolic fun ction : When the cho rdae of th e posterior pap illary mu scle we re divided max imum systo lic pressure wa s decrea sed by 16-17 %, while after loss of the ante rior papill ary mu scle function the decrease amounted to 24-27 % in the isovolumi cally beatin g heart. Th ey concluded that preservation of the cho rdae tend ineae of the ante rior papillary mu scle was of grea te r imp ortan ce for globa l left-ventricular systolic funct ion (16). Th e expe rimenta l set up with the isovolumi c heart prep aration , wh ich wa s also used in pigs by Spence et al. (36) with similar result s, involves some technical drawbacks: it ca n be questioned whethe r the intraventricular balloon still allows unrestrained and sufficient left-ventricular contrac tion. It se ems rather unlikely th at th e intraventricular balloon can represent the left-ventricular volume in th e same way and to th e sa me amount whe n the chordae tendin ea e are preserved or whe n they are disconnected. At

E. Game. S. Haql. H. Schad. W Heimisch , N. Mendler, and F. Sebening

higher filling the balloon cannot entw ine itself aro un d the papillary mu scles and th e chordae te ndineae. Consequently, from the dr op of left-ventricular peak systo lic pressu re by 50% a comparable impairment ofleft -ventricular function cannot be derived . The results from the isovolumic heart preparation show a different demand of pr eload for the left vent ricle following loss oft he su bva lvular appa rat us, wh ich ca nnot be met in this expe rimental a pproac h. The fact th at the left ventricle looses its inside stability by disconn ection of the chord ae tend ine ae mig ht the refore be rated too high in thi s experimental model. To investigate the function of the left-ventricular su bvalvular apparatu s S alter et al. (31) use d a peculiar experimental approach : in can ine expe riments St. J ude va ives we re implanted in mitral position . They resected the mitral valve leaflets and the chordae tendinea e and put sutures thro ugh the head of the pa pillary muscles, wh ich we re then kep t in "attached" or "detached" positi on to simulate pr eservation or dest ruction of the sub valvular a pparatus . Under similar enddiastolic pre ssure they foun d no differ ence in left-ventricular stroke wo rk as correlated to the calculated enddiasto lic volume , They concluded that the su bvalvular appa rat us "detached" did not affect left-ven tr icular systolic function unfavoura bly. The disadva ntage of this experime ntal approach was that the cyclic developm ent of ten sion of the papillary mu scles could not be simulated from the outsi de . On the oth er hand deformatio ns of th e left vent ricle could have impaired the mechani sms of ventricular contraction due to an excessive te nsion on the papillary muscles . The stabilizing function of the subvalvular apparatus could have been influenced artificially by exte rnal manipulation . The experimental model we use d allowed to st udy the significance of the subvalvular mitral apparatus in the sa me beating heart. Cho rdae tendineae and papillary mu scles were pr eser ved in mit ral valve imp lantation and left-ventricular funct ion was not hind ered art ificially. Withou t reopening the heart and without any internal reintervention on the mitra l valve, the chordae tendineae we re divided by ext ernal ap plicati on of electroca ute ry and it was possible to investigate left-ventricular function under similar hemod ynamic conditions with and without chordal integrity. Changes in lef t-ventri cular systolic pa rameters Following disconn ection of the chord ae ten din eae, there was a substantial decay of the extent of systolic sho rtening in the major axis diameter which was inversely related to the increase in left-ventricular enddiastolic pressure. In the minor axis diameter, the increased systolic shortening at left-ventricular filling pr essu res of 3- 6 mmH g possibly pa rtially compensate d for the diminution of the contraction am plitude parallel to the major axis. At highe r left-ventricular enddias tolic pr essures , however , the shorteni ng in the minor axis diameter did not differ from the control values . These observations are consistent with these of Salter et al. (31) wh o found no differences in the left-ventricular min or diam eters in the "attached" and "detached" state of the subvalvular appa ratus and, conse quently, also found no changes in stroke work calculated from the minor axis diam et er and the left-ventricular pr essure. As show n in the pressure-lengt h diagram of the minor axis (Fig, 31. the area within the loop - represen tin g a vecto rial compone nt of stroke work - rema ine d unch an ged . Along the majo r axis,

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to

Thom e. cardiovasc. Su rgeon 39 (1991)

Significance ofthe Subooloular Apparatus

Con cl usi o ns Due to th e connec tions between th e subva lvula r a ppa ra tus. th e va lve leaflets . the chordae ten din eae and th e pa pillary mu scles. a nd the left-ventricula r wa ll the mit ral valve is not a plain hea rt va lve. but pa rt of the left ventricular chambe r a nd thus h as to fulfill a sta bilizing fun ction for the left vent ricle. If the subvalvular a ppa ratus is excised in m itra l valve rep lace ment, left-ve ntricula r a rchi tectu re is cha nge d. The dia meter in the major axis a nd sub sequ ently left-ventr icular enddiasto lic size incr ea ses . In add ition systolic sho rt en ing in the major ax is diam eter is diminished a nd stroke volume ca n on ly be kept consta nt by higher preload levels . Tha t mea ns tha t th e sa me left-ventr icula r stro ke wo rk ca n only be achieved by volume loading a nd a t higher wall tension. These find ings sugges t that in mitra l va lve rep lacem ent pr eserv atio n of the subvalvular a ppa ratus is at least of ben efit for pa tients with dilat ed left vent ricles an d imp a ired pr eopera tive ca rdiac fun ction . Refer ences A p pe lba um. A. , S . 7: Kouchouk oe. E. I/. Blackst cue . and J. I\'. Kirk lin : Early Risk of Open lIea rt Surgery for Mitral va lve Dise ase. Am. J. Cardiel. 3i (19i 61201-209 Bjork. V. 0 .. L. Bj ork. and E. Ma ier s. Left -ve n tricu lar fu nction a fte r resectio n of t he pap illary m uscles in pa tien ts w ith tota l mitra l valve re plac eme nt. J. T horac. Ca rdiovasc . Surg. -1-8 f196-1- 1635- 639 3 Bjork. V. 0 .: A New Tilt ing Disc Valve Pro st hesis . Sca nd . J. T hor. Ca rdiovasc . Su rg. 3 (1969) 1-1 0 ~ Br etschneider. I/. .I.: Uber leb en szei t u nd Wiedcrbele bungszeit d es He rzens bei Norma - u nd Hypothermic . Ve rh . Dtsch . Ges. Kreisla ufforschu ng 30 f19641 11- 34 Bretschne ide r. H. J.. G. Hubne r. D. Kno lt.B, l.ohr. II. Ncrdbeck. a ru i P. G. Sp ieckemumn: Myoc ardial resi stan ce a nd tole ra nce to isch em ia : Phys iologica l a nd biochemical basis . J . Cardlovasc. Surg. 16 0 9 i 5 ) 2-1- 1-260 f> Chaffin. J. S .. and It'. .\1. Daggett : Mit ral valv e replacem en t: A n ine year follow -up of r isk s a nd su rviva ls. An n . Tho ra c . Su rg . 27 l19i 91 1

312-3 19 ~

Chi echi. M. A . ~ V. AI. Lees , and R. Thom pso n: Function al a na to my 01 the no rm al m itr a l valve. J. T horacic. Su rg . 32 1195613i8- 39 8 Cohn, L 11. . R. L. Heis, a nd A. G. Morr oio. Left ven tri cul a r function after m it ra l valv e re pla cemen t. J. Thorac. Ca rd iova se. Su rg . 56

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Do h/bac k, 0. , and I/. Schuller: Ope n Correc tion of Mitralln sufflcie ncy . A mod ifica tion of the Sta rr-E dwa rds techni qu e. Acta Chi r. Sca nd . 126 (196 31300- 304 Darid. T E.. II. D. St rauss. E. Me sne r. M. J. Anderse n. I. L sta cDonald. and A J. Bud a: Is it important to prese rve t he ch ord ae te ndineae an d papi lla ry muscles d u ring m itral valve replacem ent? Ca na d .J . Su rg . 24 (198 1) 236 -2 39

Hansen, D. E.. P. D. Cahill. W. M. Deca mo li. D. C. Harrison. G. C Der by. R. S. Mit chell. and D. C. Miller: Valvula r-ve nt ricu la r intera ction: imp orta nce of the mitra l a ppa rat us in ca nine left-ventri cula r systolic perform ance . Circul ati on 73 (198611310 -1320 Hansen. D. E.. P. D. Cahill. G. C. IJerby . and D. C. Miller: Rela tive co nt ributions of t he a nt eri or an d pos terior mitra l chordae te n di nea e to ra nine globalleft vent ricula r systolic function . J. Thora e. Ca rdio vasc . Su rg. 93 (19 8 i l-1- 5- 55 Harken. D. E../I. S. S oroff. W. J. Tay /or, 11. /cLefe mine. S. K. Gupta. and S. l.unzer: Pa rt ia l a nd co mpl ete pros theses in ao rtic ins ufficien cy. J. Tho rac . Cardiova sc. Su rg . -1-0 (196 01i 4-1- - 76 2 lknce. t1.. If . I.. Frye. and F. I/. Ellisjr.: Late hemodynam ic s tud ies a fte r mit ra l va lve s urge ry. J. Thora c. Ca rdiova sc. Surg . 65 119731

35 1- 358

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Heimis ch. w.: Die So no mi kro me t rie in der Horz- und Kreislauffor schu ng: physik alis ch -technlsch e Gr undla ge n u nd Ergebn isse zur Myok a rd -Mech anik u nd Ven t rikel-Ceomet rie. T he sis. Unive rsity of

Munich (19891 Hetzer. R., G. Bouc iouk as . M. Franz. an d II. G. Horst. Mitral val ve replace me nt with preservati on of papill ary muscles an d cho rda e te nd inea e - rev iva l of a seemi ngly for gott en con cep t. Thorac. cardio vasc. Surgeo n 31 0 9831 29 1- 296 21 Ka ra s, s. . a nd R. C. Elkins: Mech anism of Funct ion of the Mitral Valve Lea flets. Chordae Te ndi neac a nd Left-Ven t ricu la r Pap illa ry Muscles in Dogs. Clrc ulat. Hes . 26 l19701689- 696 22 Kay . G. L., J. I/. Kay. P. Zubi ute . T. Yokoy ama. and AI. Mendez: Mitr al va lve re pa ir for m itral reg ur gitation sec ondary to co ron ary a rte ry d isease. Circu la tion 7-1- , Suppl. I (1986188-98 23 Kirs ch, U; G. Rodeu-ald. and P. Kalma r: Ind uced isch em ic a rrest: Clin ica l expe rie nce wi th ca rd iop legia in ope n- hea rt s urgery. J. Th ora c. Cardiovasc. Su rg . 63 (19i 2) 121- 130 2 ~ Kra us, F.. S. Dacia n. and IV. Rudo ip h: Belastu ngsun ter suchungen bpi valvularer Herze rk ran ku ng u nd Herzkla ppenersatz. lIe rz i 20

119821144-1 55 25 Liliehei. C. IV" M . J. Lel'Y . a nd If . C. Bonnabeau: Mitral valv e replacemen l w ith preservati on of pap illa ry mu scles an d cho rda e te ndi neae. J. Th orac. Cardiovas c. Surg. 47 l19641532- 5-1-3 2f> McComack . R. 1.. : Exte nd ed tables of th e Wilcoxon m atch ed pa ir sign ed ra n k st a tistic . J. Am . Sta t. Asso c. 60 (19(5 ) 86-1- -8i 1 2j Mei sner. /I.. N. Mayr . P. S chmidt-Hc belma nn. E. St ruc k. a nd F. Sebeninq: Die Ch ir urgie d er erwor bencn llerzfehle r . Erlangen . Perim ed 198 1 2S Puff. A : Der fun ktionelle Bau der Hcr zka m rne rn . Zwa ng tose Ab ha ndlung aus dem Geb iet d er normal en un d pa t holo gisc hen Ana tornie 8 ). Th ieme . Stuttgart 1960 2'1 Ra s telli. G. C . A G. Tsak iris. R. L. Fry e, an d J. IV. Kirkli n: Exercise to lera nce a nd hem ody namic stud ies aft er re p lace ment of ca n ine m itral valve wi th an d wit hout pr eservation of ch ordae tendi neae. Circu lati on 35 a nd 36. Su pp!. I (196 i 134--1- 1 30 Reid emeis ter , J. C.. G. Heberer. I/. GeM. andJ, P. Thiele: Klin isch e Er gebn isse m it der Ka rd ioplegie d urc h extracellu larcn Na triu m u nd Calciumen tzug und Proca inga be. Lan gen be cks Arc h . Klin . Ch ir .

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Perrazzi. P., D. C. McGifji n. J. H