10

European Versus North American Cardioplegia: Comparison of Bretschneider's and Roe's Cardioplegic Solutions in a Canine Model of Cardiopulmonary Bypass G. J . Wilsoll. R. A. Axfo rd -Gatleq, B. G. Bush , A. D. Romoschin, and D. A. G. Mickle Department of Cardiovascular Surgery. Toronto Genera l Hospital. Toro nto. Ontari o. Canada

Roe's a nd Bretschn eider's crysta lloid ca rdioplegic solutions were compared in a ca nine model of total ca rdiopulmona ry bypass with 4.5 hours of hypothe rmic (27 °e) ischemi c a rrest and 60 m inutes of rcp er fus ion . Bret schneider's solution {Group I. six dogs! preserved tissu e ad enosine triphosp hat e (ATP) ncar contro l levels and maintaine d corona ry efflue nt p I! nea r 7.0 through out the ischemic interva l. w hile Roe' s so lution (Group II. s ix dogs ) allowed progressive acidosis a nd depiction of AlP (P < 0.005 ve rs us con tr ol). Gro up I had s up ra no rmal lcft ventricula r fun ction d uring reperfusion (> 100 % of pre-arrest function ) but Grou p II r ega in ed only 40- 7 5 % of p re- a r rest fun ction. Grou p I had 2 .82 % ± 3.61 % necrosis of hea rt mass a nd Gro up II 9 .33 % ± 8 .2 6 II' < 0 .10) . We conclude that Bretschneider 'w solutio n provi de d be tte r myoca rd ia l p rotection th an lioe's s olu tion . Th e developm en t of aci dos is in the Roe grou p s uggests tha t th e m or e effective buffering of Bre us clmetder:s so lut ion wit h h istid ine is th e prob abl e bas is for its superior ity. Key words

Bufferin g - Can ine mod el - Car d iopleg ia - Card iopulmonary bypass - Myocard ial pres ervati on

Intr od uction Cold crysta lloid ca rdioplegia is widely employed for myoca rd ial protection du ring ca rdiopulmonary bypass ICPBl, but the va rious form ulat ions of crysl alloid cardioplegia in clinica l use dilTer ma rked ly from one another. Preference for a given form ulat ion often va ries regiona lly. For example, Brets chneide r's solulion HTK (5) is bro adly used in Europe but infrequently in Nort h America. with the opposite situation for 1I0e's solution (I ll. These two ca rdioplegics are sim ilar in many resp ects. being calcium-free. .Intracetlular'' sodium form ulations. but dilTe r in sod ium and potassium concentra tion. metab olic su bst rat e content. osmotic agent (glucose versu s ma nnitol + histidine) a nd bu lTerin g capacity (Table l ), These dilTer ences give potential adva ntages or disadvan tages to eac h solution. \Ve have

Thorac . cardiovasc . Surge on 38 (1990) 10-14 © Georg Thieme Verlag Stu ttga rt - New York

Gege nti berste llung der e uropa isc he n mit der nordame rikanisch en Kardioplegie: Verg leich der Brets chneider-Ursun g mit der Roe-Losun g im lI undem odell des ext ra kor pora len Kre islaufs Wir vergJich en Bretschneiderw Kard iop legie u nd lioes Kardtoplcg!c in Versuchen a n Hunden. d ie s ich cxtrakorporaler Zirku lation unter Ab ktihl ung auf27 DC m it 4, 5 Stu nde n Ischem ic und 60 Minuten Hep erfusion u nt erzogen . Wah rend der Ischamie andcrte s ich das myokardi ale ATP n icht viel gegenGber de n pratsch a mlsch en Wert en und d er korc narvendse pi t-wcn bJieb u rn 7 ,0 in Gr uppe I (Bret schn eider's Kard ioplegie. sechs Hunde). wah ren d in Gr u ppe II (Roe's Kardi op legie, sechs Hunde) der AT P-Wert ab na h m IP < 0 ,005 vs . pr aischa mische Werl e) un d der koron a rvenose pi I· Wert s ich au f 6 ,3 redu zierte . w a hrcnd der He perfus ion hatt e Gru pp e I eine su pra no r ma le lIerzfunk tion (> 100 % der pre tscharn tschon We rte), a be r Gru ppe II erre ichte nur 40 -70 % der pr iiis ch ami sch en lIerzfunktion (I' < 0 ,00 01 Gr up pe I vs . Gruppe III. Gruppo I ze igte 2,82 (Yt, ± 3,6 1 % Nekrosen der lIer zm as se und Gruppe II hatte 9 ,33 (Yo ± 8 ,26°;', (I' < 0, 101. Wir sc hlieBe n a us dreson Ergehnisse n , d aB Bret schneide r» Kardi oplegie der Roes Ka rdioplegi e ubc rlcgcn ist.

Table 1 Composition of Cardioplegic Solutions Component (mmol/ l)

Roe's Solution

Bretschneider's Solution

Co " NaCI KO

MgSO. MgO, THAM"

Histidine Histidine-HCI Dextrose Mannitol Tryptophan K-ketoglutarate pH @' 27C

27

30' 3

15 10 8

4

180 15 278

20 2 7.8

I 7.2

• modified from Roe's original formulationof 20 mmol/l KCI •• THAM:I ns (hydroxymethyl) aminomethane.

Recei ved for Publication : May 8. 1989

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Summa r)'

European Versus North American Cardioplegia

Mat erials a nd Methods Experimental Preparation. Twelve healthy. 25 -35 kg. ad ult mongrel dogs were selected for the study, and received hu man e ca re in compliance with the ..Principles of Laboratory Animal Care" formulated by the National Society for Medical Hesea rch a nd the ..Guide for the Care a nd Use of Laborato ry Animals " pre pared by the National Academy of Sciences and publish ed by the National Institutes of Health (NIII Publica tion #80-23. revised 1978). Anes thesia was induced with intrave nous thiopental sodium (Pen tothal, 30 mg/kgt a nd maintained by inh ala tion of 1 : 2 oxygen and nitrous oxide with 0.5%- 1.5 % enflurane (Ethrane) before CPE, a nd during CPH with a bubb le oxygenator mixture of 97% oxygen, 3% ca rbon dioxide and 0.5°;')- 1.5% enflurane . The dogs were prepar ed for CPE afte r the method desc ribed in del Nido ct al. (3) with an extracor porea l circulation temp erature of 27 °Ca nd ischem ic cardiac ar rest achieved a nd maintained by multidose infusions of card ioplegia a t 4 °C. Six dogs received Bretschneider's cardiopleg ic solution a nd the other six received Roe's solution (see Ta ble 1 for composition of solutions). The infusions of both car dloplegic solutions were performed accord ing to the protoco l use d clinically at the Toronto General Hospit al for Roe's cardioplegic solution: a n initial dose of 500- 700 ml at 4 °C was infused over 5 min (approximate ly 70 to 100 mllm inllOO g hea rt), a nd additional doses of25 0 ml were infused at the same rat e at Su-mt nutc intervals . The cardioplegic infusions were performed in this wav to maintain similaritv between the Roe a nd Bretschneider gro up protocols, but in consequence these infusions did not conform exact ly to the reco mmended ad ministrat ion criteria published by Bretschneider's group (na mely, 150 mllminllOO g hea rt at 8 °C for 11 min) (51. Aortic cross-clamp was mainta ined for 4 .5 hour s, followed by 60 minutes of normothermic reper fusion . Anest hesia was main tained du ring reper fusion with intrave nous morphine su lfate (0.5 rug/kg as require d]. After 2-3 minutes of reperfusion, the heart was defibrillated, a nd afte r functional meas ure ments at 15 minutes of reperfusion the dogs received 1 gram of calcium chlor ide. The dogs were euthan ized at the end of the reperfusion period with an overdose of sodium pentobarbital (Euthanyl) a nd potass ium chloride. Functional Assessment. While on total CPB. an intraventr icular balloon was passe d through a left atrio tomy into the left ventricle. The balloon, made of latex an d reinforced with nylon, was compliant to a volume of greater tha n 50 ml. Contro l functional assessme nt was per form ed following initiati on of total CPB but before cross clamp . The balloon was sequentially inflated to 10 , 20. 30, and 40 ml with saline and developed pressure was record ed (peak systolic minus diastolic) with a pr essure transducer. Similar assessme nts were per form ed during reperfusion . Dat a was reported as per centage control developed pressu re (% D. 1'.) to minimize dog-to-dog varia bility in ventricle size. Biochemical Measurements . An in-line piI meter provided consta nt digital read -out of corona ry effluent pl l during CPB. Corona ry effluent sa mples were obtained during cardioplegic infusions an d placed in pre-weighed test tubes conta ining 4 rnl of 0 .6 mol/L perchloric acid. The perchloric acid filtrate was neutr alized to pH 7.0 with 6 mollL KOII. and centrifuged at 4 °C. The pr ecipita te was ass ayed for glycerol a nd lacta te conte nt with a n Abbott V. P. Discrete Analyzer (Abbott Diagnostics, Pasadena . California ). Myoca rdial biopsies from the left ventricular apex were obtai ned immed ia tely before aort ic cross clamp. at the end of the ische mic interval. a nd after 30 and 60 minut es of reperfusion. The biopsies were immediately frozen in liquid nitrogen and later freeze -dried. Once

11

freeze-dr ied, the muscle was dissected to remove blood a nd fibr ous tissue. Tissue adenosine triph ospha te (AT!'), creatine phosphat e (CP), an d lactate wore a na lyzed on a n ABA-! 00 (Abbott) or PerkinElmer (Norwalk, Connectic ut) fluorescence spectrophoto mete r. Morphologic Examination. After euthanization by pentoba rbital overdose and potassiu m chloride injection to arrest the hear t. th e hea rt was excised an d sliced tra nsve rsely from a pex to base in 5 mm sections , which were we ighed a nd then incubat ed in 2,3.5triphenyltetrazolium chloride to delinea te a reas of necrosis. Sta ined hea rt slices were pressed between plexiglass pla tes an d areas of viab le (stain ed) and necrotic (unstained) tissue were tra ced on acetate sheets . Later , the a reas were pla nimetered usi ng an elect ronic digitizer. The fractio n of necrotic to viable myocardium was multiplied to give tho mass ofinfa rcted tissue per slice. The sum of these yielded the tota l mass of infar cted tissue. Results we re recorded as percent age of heart mass infar cted . S tatistical Ana lysis. All measu rem ents between tr ea tment gro ups were compared by the unpa ired Student's t-tost. Meas urements within a treatment group were compa red with the pa ired S tudent's t-test.

Results Biochemic a l Measurem en ts. At the end of the ischemic interval and for the first 30 minutes of reperfusion, tissue lactate conte nt was high er in the Roe tr eatm ent group than in the Bretschn eider group (I' < 0.05 between group s) (Fig. 1). Similar patt erns of CI' depletion during ischemia and supra norma l recover y during re perfusion were obser ved in both groups (Fig. 2). Tissue ATI' rem ain ed near controi levels throughout the ischemic period in the Bret schneider tr eatm ent group , but decr ea sed in the Roe group by the end of ischemia (I' < 0.00 5 versus control, I' < 0.01 betwe en groups) (Fig. 2). Heperfu sion incr eased ATI' in the Roe group, but not to cont roi levels (I' < 0.05 between groups). Corona ry effluent pll (Fig. 3) from Bretschneider-treated hearts rem ain ed near 7.0 throu ghout the ischemic intervai , while the effl uent of the Roe tre atment group becam e progressively more acidic. Efil uent glycer ol and lactate levels (Fig. 4, 5) increased with duration of ischemia in both treatm ent grou ps, but levels in the I/oe tre atment group becam e (and rema ined) significantly higher tha n the Bretschn eider group after 120 min of ischemi a (I' < 0.01 between groups). Fun ctio na l As sessm ent. The Bretschn eider group had supranorma l recover y on reperfu sion (> 100 l Xl pr e-arrest DI') while the Roe group achieved less than 80% of prearrest DI' (Fig. 6). Morphological Assessment. lIeart s protected with Roe's solution had a mean of 9.33% ± 8.26% necros is (mean ± S. D.) and the Bretschneider-treated hearts had a mean of 2.82 % ± 3.61 % (Table II) (I' < 0.10). In every dog, the necrosis occurred in a patchy distribution involving the left and right ventricles, as is typical for ischemic injury to a non-working heart.

Discu ssion Our resu lts show that hearts preser ved with Bretschneider 's cardioplegia had better preservati on of ATI', iess accumu lation of tissue lactates, and superior recovery of function , compared to hearts treate d with Roe's solution. The mean percentage of myocardia l necrosis in the Bretschne ider group was only about one third of that in the Roe group, but becau se of the variation in individual experi-

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compa red these two cardioplegic solutions on th e basis of biochemicai, functional, and morph ologicai indicators of myocardial preservation in dogs treated with multidos e appiication of either cardioplegic during 4.5 hours of ischemic arres t. This mod el of proi onged arrest under moder ate hypoth ermi a was intend ed to pose a n extre me tes t of protective measu res, allowing necrosis to be used as an end point for comparison.

Thorac. cardiovasc. Su rgeofl38 (1990)

G. 1. Wilson et al.

Thom e. ear diovasc. Surgeon 38 (1990) 70 , - --

160

,T

' 40

-

- --

-

-

-

-

-

-

- - - - --

-,

Roe 's

T

60

1

' 20

T

T

T

r /r- -t- -r- t ,

50

r/t--. 1

100 80 60 40

0

~

•

T

Bretschn eider's T t--T !

T T

'

!

150

180

T

, _ _A

10

j

•

o

30

reperfusion

30

270

cont rol

...........

;;

20

Bretschneider 's

ischem ia

i\ .P:::-!~;,// 1

T

30

••

••

20

40

t im e (mi n)

60

90

120

2 10

240

du ration o f ischemi a ( m in)

Fig. 1 l actate content of myocardial biopsiesharvested beforeaortic cross clamp(control),after270 min of cross clamp,andafter 30 min of reperfusion (mg/kg, mean ± standard error, n = 6 dogsper treatment).

Fig.4 Glycerolcontent of coronaryeffluentduring270 min of aortic cross clamp(ml gatheredover30 minper 100gwet weight of myocardium,mean ± standard error, n = 6 dogsper treatment}.

'0, - - - - - - -- - -- - - -- - - - - ---,

0.8

l2 ~

70

60

T

50

i'

!1

40

1 30

,

~

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