Myocardial Tissue pCO 2 and Calcium Content during Ventricular Fibrillation and Reperfusion Periods

Minoru KOBAYASHI, Hiroyuki ORITA, Takao SHIMANUKI. Manabu FUKASAWA, Takao WATANABE, Michio KONO, Hiromasa ABE, Setsuo KURAOKA

and Masahiko WASmO

ABSTRACT: Forty-one patients who underwent cardiac surgery under conditions of systemic hypothermia and intermittent cold crystalloid potas- sium cardioplegia were studied, in order to elucidate the effects of ventricular fibrillation and reperfusion on the myocardium, by using the intramyocardial pCO 2 and temperature sensor. All patients were assigned to 2 groups, namely; group A (21 cases), in which the time between the aorta declamping and defibrillation was under 10 minutes, and group B (20 cases) in which the time was over 10 minutes. In both groups A and B, myocardial pCO 2 increased at the rate of 3.58 • 1.70 and 2.16 + 0.62 mmHg/min (p(0.05) after aorta declamping, respectively and the myocardial pCO 2 decreased at the rate of 5.59 ___ 0.60 and 4.18 • 0.76 mmHg/min (p<0.05) after defibrillation, respectively. In group A, the myocardial calcium content, pre-CPB (cardio pulmonary bypass) was 10.98 • 1.62 nmol/mg/dry weight and at the time of aorta declamping it was 15.90 • 1.81 nmol/mg/dry weight (p<0.05). In group B, the myocardial calcium content, pre-CPB, was 14.62 • 2.15 nmol/mg/dry weight and at the time of aorta declamping it was 18.23 • 4.36 nmol/mg/dry weight (p<0.05). At both three and six hours after the operation, the left ventricular work index per "minute (LVWI) in group A showed better cardiac pump function than that in group B. We therefore conclude that when reperfusion is encountered, acidosis can be minimized by prompt defibrillation.

KEY WORDS: myocardial tissue pCO2, calcium content, ventricular fibril- lation

INTRODUCTION

In order to find an ideal technique of myocardial protection, one must well under- stand the histophysiological events (ventricu- lar fibrillation (Vf) and reperfusion injury)

The Second Department of Surgery, Yamagata Uni- �9 versity School of Medicine, Yamagata, Japan

Reprint requests to: Minoru Kobayashi, MD, The Second Department of Surgery, Yamagata University School of Medicine, Zao-Iida, Yamagata City, Yama- gata 990-23, Japan

that may be encountered during cardiac operations. Relationships between these two events have been clarified to some extent by basic animal studies, however, only a few clinical studies on Vf during extracorporeal circulation, or on reperfusion injury and its influences can be found in the literature. It was due to this fact that the authors recently clinically investigated the variances in myo- cardial tissue pCO 2 and the calcium content, both before the application of extracor- poreal circulation and after aorta declamp- ing. The cardiac functions during the early

JAPANESE JOURNAL OF SURGERY, VOL. 18, No. 5 pp. 494-501, 1988

Volume 18 Number 5 Tissue pCO 2 and Ca content after declamping 495

postsurgical stage were also investigated, using a temperature-correctable pCO 2 mea- suring device.

MATERIALS AND METHODS

The possible changes in myocardial tissue pCO 2 during Vfwere explored in two groups of subjects, namely; group A, in which the time period between aorta declamping and defibrillation was 10 minutes or less a n d , group B in which the time period was more than 10 minutes. As shown in Table 1, group A consisted of 21 adult patients and group B consisted of 20 adult patients. T h e mean age of the subjects was 50.4 ----_ 2.3 years in group A and 54.0 + 2.3 years in group B. The patients ' valve diseases are also listed in Table 1.

Cold crystalloid cardioplegic solution (G.K. fluid: 5 per cent glucose 1000 ml, K 20 mEq, 8.4 per cent N a H C O 3 20 ml, osmotic pressure 320-330 m O s m / L , pH 8.0-8.1 at 4~ was infused via the left coronary ostium in the patients with aortic valvular disease and via the aortic base in the other patients. The volume of infused cardioplegic solution was 1138 _ 68.3 ml for group A and 1370 • 105.2 ml for group B.

Determination of myocardial pCO 2 A temperature-correctable P H pCO 2 mea-

suring device (KR-500, :Kurare, combined with an NEC compute r PC 800 mark-II), an ISFET (ion sensitive field effective transistor) and a pCO 2 tempera ture sensor (CO-1035, Kurare) were employed in this measurement . The sensor was fitted in accordance with the technique of Orita. 1

Determination of calcium "content in the atrial muscles This measu remen t was carried out accord-

ing to the technique o f Fukasawa; 2,3 namely, the atrial muscles were sampled at the time of intubation into the superior vena cava and within 10.5 • 4.2 minutes after the aorta declamping, 80-300 mg of wet tissue be ing sampled each time. After washing off the blood or solvent f rom the sampled atrial muscle, its wet weight was then determined and, a f t e rd ry ing it for 24 hours at 100~ its dry weight was measured. Next, after heat ing the muscle tissue at 150~ with 0.5-1.0 ml of condensed nitric acid, protein was removed from the sample l and dissolved in organic solvents, using 10 mM Lantan and 50 mM HCL. The Calcium content was determined with a H I T A C H I 170-70 Zemann t ameless atomic absorption meter at 423 nm and was

Table 1. Clinical Presentation of Patients

Group A (n=21) Group B (n-----20)

Time between aorta declamping and defibrillation 10 min. below 10 rain. above

IHD--ACBG 3 5

Valve Disease AVRTMVR 1 4 AVR 4 5 MVR 9 2 OMC 3 2 AVR+OMC+TAP 1 MVR+TAP 2

Mean age (years) 50.4---+2.3 54.0--+2.3

(mean + SEM) Abbreviations: IHD--ACBG, ischemic heart disease--aortic coronary bypass graft; AVR, aortic valve replacement; MVR, mitral valve replacement; OMC, open mitral commissurotomy; TAP, tricuspid annuloplasty

496 Kobayashi et al. Jpn. J. Surg. September 1988

expressed in terms of nmo l /mg /we t tissue and n m o l / m g / d r y tissue.

CPK-MB, serum myoglobin and L VWI was determined The above parameters were investigated. Statistical analysis of the obtained data was

done using the mean • SEM technique, the Student's t-test and paired t-test.

(p<0.05) (Fig. 1). The mean myocardial temperature at defibrilla- tion The temperature was 30.8 -4- 0.68~ in

group A and 29.6 -4- 1.6~ in group B, showing no significant difference (Fig. 1).

Serum lactate Serum lactate increased cumulatively 2 to

RESULTS

The mean time period between aorta declamp- ing and defibrillation The mean timelength was 5.38 • 0.32

minutes in group A and 21.4 • 0.47 minutes in group B. Thus, a significant difference was noted between the two groups (p<0.005).

The mean myocardial temperature at aorta declamping The temperature was 21.5 • 1.0~ in

group A and 18.0 -4-1.40~ in group B, thus showing a significant inter group difference

32

30

23 z

'N

o ~ 2o

17

p<0.05 f - -

}

t

INs!

I I I i I

Aorta Declamping Defibrillation

mean • SEM

Fig. 1. Myocardial temperature. �9 Group A (n=21) �9 Group B (n=20)

I

60 = I

40

mg/dl 70 " �9 (n=12) (n=5)

I

1" T mean _+ SD ur

Pre-' Total' Belfore 2 5 10 3; minutes OPE Bypass Ao. Dec . | Declamp|_j

5rain 5rain LAfter Ao

(Ventrieular Fibrillation)

Fig. 2. S-Lactate during initial period of reflow.

10

{

p<0.05

t t

0 I A B

mean -+ SEM

Fig. 3. Reduction in myocardial Pco2 (mmHg/min) during 10 minutes after defibrillation.

Serum myoglobin and CPK-MB The 5-minute mean of the myoglobin level

30 minutes after aorta declamping. The values after aorta declamping at 2 min and 10 min were 52.4 • 5.8 mg/dl and 53.4 • 8.3 mg/dl respectively (Fig. 2).

pCO 2 reduction during the 10 minutes immedi- ately after defibrillation pCO, dropped by 5.59 • 0.6 mmHg/min

in group A and 4.18 • 0.76 mmHg/min in group B. Thus, group A showed a signifi- cantly sharp reduction in pCO 2 (p<0.05) (Fig. 3).

Ca* content in the atrial muscles In 20 patients from group A, the mean Ca*

content in the wet tissue was 2.46 • 0.40 before CPB and 3.64 • 0.76 nmol/mg after aorta declamping. In the same patients, the mean Ca* content in the dry tissue was 10.98 • 1.62 before CPB and 15.90 • 1.81 nmol/mg after declamping (p<0.05). In 17 patients from group B, the mean Ca content in the wet tissue was 3.10 • 0.52 before CPB and 3.64 _+ 0.81 nmol/mg after declamping. The same content in the dry tissue was 14.62 • 2.15 before CPB and 18.23 • 4.36 nmol/mg after declamping (p<0.05). Fig. 4 shows the ratio of change (A per cent) in this parameter.

A~ 200

.~ 150

o a)

100

50

0

p<0.005 [ i < 0 ~

t---p < O. 05--J Lp<O.05

mean • SEM

Fig. 4. Change of calcium in atrial muscles. A O

w e t t i s s u e c a c o n t e n t (n=5) B �9

A A d r y t i s s u e c a c o n t e n t (n=5) B �9

IU/L 120

9O

60

30

05

Volume 18 Tissue pCO 2 and Ca content after declamping 497 Number 5

i i i P 0 A B A B

Aorta Declamp After Operation 5 rain. 3 hrs.

mean ! SEM Fig. 5. CPK-MB.

550

50C

45C

z

"~ 400

350

300 p<0,05

I r i i 0 A B A B

Aorta Declamp After Operation 5 rain. 3 hrs.

mean - SEM

Fig. 6. Myoglobin.

498 Kobayashi et al. sJPn. J. Surg. tember 1988

kg. m/m2/min p<O.05

8

A

[p<0.05.

A B

Fig. 7.

3hrs 6hrs

[--- After Operation mean • SEM

LVWI (left v e n t r i c u l a r work index) .

after aorta declamping was 493.9 _+ 32.9 in group A and 497.6 _ 48.4 ng /ml in group B, thus showing no significant difference be- tween the two groups. The 3-hour mean after the operation was 346.4 • 36.3 in group A and 474.2 ----- 74.6 ng /ml in group B, showing a significantly h ighe r value in group B (p<0.05).

T h e CPK-MB leve l d e t e r m i n e d five minutes after aorta declamping was 29.8 --+ 4.4 in group A and 34.5 __+ 9.5 IU/L in group B. The same level at 3 hours after the operation was 59.4 _+ 6.8 in group A and 93.5 • 18.8 I U /L in group B. Thus, a significant difference was seen (p~0.05) indicating the influence of global ischemia in group B (Figs. 5 and 6).

LVW/ We investigated to what extent the time

period between aorta declamping and Vf might adversely ,affect the postoperative car- diac function. Three hours after the opera- tion, the left ventficular work index was 6.00 __ 1.15 in g r o u p A a n d 4.61 __+ 1 .08 k g ' m / m 2 / m i n in group B. Six hours after operation, the same index was 6.76 _+ 1.52 in group A and 4.55 __+ 1.38 kg �9 m /m2 /min in group B (p<0.05) (Fig. 7).

DISCUSSION

Until now, a variety of studies have been

carried out for the purpose of effecting myocardial protection during open heart surgery, by means of suppressing myocardial energy demands and decreasing myocardial acidosis with the use of various techniques. 4-s Furthermore, some medical institutions have been applying cold blood cardioplegia using oxygen-added blood, which is a more effec- tive technique since it can reduce the nega- tive oxygen balance to a minimum during anaerobic metabolism in an ischemic state. Although these techniques have been effec- tively used, the mechanism of the onset of Vf and reperfusion injury after declamping has not been sufficiently analyzed. To explore the possible changes in ischemic cardiac muscles during hemostasis, Jennings et al. 9 carried out a study on dogs in which myo- cardial infarction was artificially induced. Many other researchers, 1~ in order to prevent these events, have studied the effect of cardioplegia using cardioplegic solution in combination with core cooling and topical cooling techniques. Amano, 13 for example, repor ted an electron-microscopic finding that" ischemic changes became quite mild and no abnorma l deposit o f Ca n in the mitochondria was seen when the muscles were kept at about 20~ using a cardioplegic solution. In our previous animal study on myocardial pCO 2, the elevation in myocar- dial tissue pCO 2 could be suppressed to about 1.0 mmHg/min , while it became more marked when the temperature of the cardiac muscles increased. Therefore, if the myocar- dial temperature is kept below 20~ bio- chemical dysfunctions of cardiac muscles will be reduced less rapidly and the time of global ischemia may be prolonged without causing major problems. Regarding the myo- cardial protection during aorta clamping, a variety of studies have been made concern- ing the composition 15,~6 and injecting method of cardioplegic so lu t ionY -2~ Reperfusion after global myocardial ischemia occurs in the following way; an abnormal inflow and out-flow of electrolytes become induced by the broken membraneous hemostasis under

Volume 18 Number 5 Tissue pCO 2 and Ca content after declamping 499

the i schemic condi t ions , ~2,2~ af ter which lactate increase, 1 resulting in a reperfusion acidosis and rapid accumulat ion of pCO 2 in the myocard ia l t issues?, 14,23,~4 A m o n g these events, the relationship of reperfusion injury to Ca ~ has begun to receive atten- tion3 ~-27 When anaerobic metabolism is pro- moted by anoxia or ischemia, there occurs an accumulation of lactic acid and other organic acids, leading to p H reduction and, subsequently, acidosis. Hearse et a138 re- ported that perfusion and oxygen supply resulted in the breaking up o f an obstacle occurring in the cardiac muscles. This intra- cellular Ca ~ overloading induces activation of proteases and ATPase as well as the release of lysosome enzymes, thus leading to an over consumption and depletion of ATP a n d i r r evers ib le d i so rde r s in the mito- chondria3 9 Aziz et al? ~ repor ted that the mitochondrial and total myocardial Ca ~ in heart- implanted rats expressed abnormal in- fluxes during the postreperfusion time (0-4 hours) , fo l lowing the p e a k level at ten minutes, and then gradually decreased. Sig- nificant increases in total myocardial Ca ~ were seen ten minutes and two hours fol- lowing reperfusion. In the same study, no Ca ~ elevation was noted when the heart was kept in a 4 to 6~ physiological saline solution during the 24 hour ischemic period. Fukasawa 2,3 invest igated extracel lular Ca ~ ions, and their findings indicate that the p h e n o m e n o n of calcium paradox, as report- ed by Z immerman and Hul sman in 1965, 25 can be evaluated on the basis o f myocardial Ca ~ kinetics without examining the changes in intracellular Ca ~ ions. The patients of this study also revealed a tendency similar to the one repor ted by Fukasawa, but the Ca ~ content in the atrial muscles o f our patients showed significant elevation after aorta de- c lamping. Fu r the rmore , an exper imen ta l modeP revealed the Ca ~ content as be ing elevated after ischemia, when determined 10 minutes after reperfusion (a 39 per cent increase in the left ventricular muscles and a 50 p e r cen t i n c r e a s e in the left a t r ia l

muscles). Such excessive inflow of Ca # is r e p o r t e d to occur m o r e marked ly w h e n acidosis occurs. 9,31 Acidosis was noted in these studies after a rapid increase in tissue pCO 2 during Vf seen after reperfusion. Simi- lar findings have also been repor ted by Khuri and Sudo3 ~-24 Moreover, there is a report which indicates that progression of acidosis during Vf was found with a myocar- dial p H sensor. The incidence of calcium paradox is repor ted 22 to decrease at low temperatures 31 or when an alkaline perfusate is used? 2 Investigations have suggested a n u m b e r of interventions that could poten- tially reduce injury with reflow. These in- clude; avoiding ventricular fibrillation and left ventricular distention, decreasing ionic calcium and increas ing secondary b lood cardioplegia, which all need to be consider- ed. Khuri et a l . y Orita 1 and Fukasawa 2 emphasize the benefits of smooth defibrilla- tion within 10 to 15 minutes after reperfu- sion.

W h e n we e x a m i n e d card iac func t ion (LVWI) d u r i n g the ear ly p o s t o p e r a t i v e period, we found that it was better preserved in those cases who received Vf after 10 minutes or longer. Digeness et al? 3 say that an elevated Ca ~ is not consistent with re- covery in cardiac function. In our previous clinical and animal studies, TM the myocardial pCO~ showed rapid elevation after reperfu- sion, sometimes reaching a level of 200 m m H g or more. We think that this finding may reflect a physiological time lag in con- version from anaerobic metabolism to aerob- ic metabolism. This assumption seems to explain the results that such an elevation did not fatally affect the myocardial reversibility. O f course, as is well known, progression of reperfusion acidosis caused by the excessive inflow of Ca ~ and the abnormal accumula- tion of myocardial pCO2, is not favorable to cardiac muscles.

(Received for publication on Apr. 20, 1987)

500 Kobayashi et al. Jpn. J. Surg. September 1988

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