JOURNAL

OF SURGICAL

22,242-263

RESEARCH

(1977)

Comparison of Myocardial for Aortocoronary

Preservation Techniques Bypass Surgery1

ARIE SCHACHNER, M.D. .2 GEORGE SCHIMERT, M.D., THOMAS Z. LAJOS, M.D., ARTHUR B. LEE, JR., M.D., MARIO MONTES, M.D., PETER SCHAEFER, Ph.D., ADRIAN VLADUTIU, M.D., ANAND CHAUDHRY, Ph.D., AND JOHN

H. SIEGEL, M.D.3

The State University of New York at Buffalo, School of Medicine, Pathology, and the Buffalo General Hospital, Buffalo, Submitted

for Publication

Controversy continues over the optimal techniques for the preservation of the myocardium during open heart surgery in clinical practice and in experimental work [9- 121. These divergent opinions reflect difficulties in applying results obtained from different animal models and heart preparations (which rarely mimic the circumstances likely to be present in man) into clinical settings of patients suffering from a progressive valvular or coronary artery disease. In the current study we applied a reproducible multivariable system analysis to the comparison of three methods of myocardial protection used during distal coronary anastomosis: induced ventricular fibrillation (VF), selective intracavitary profound hypothermic arrest (SIPHA), and potassium cardioplegia combined with moderate topical hypothermia (KMTH). The evaluation was based on the assessment of sequential measurements of enzymatic, metabolic, electrocardiographic and cardiodynamic function; ultrastructural integrity; as well as parameters of the physiologic recovery and clinical course. 1 Supported by Grant HL 15676 from the National Heart and Lung Institute. * Dr. Schachner is a Visiting Cardiac Fellow of the Belinson Medical Center, Tel Aviv University, Israel. 3 Address reprint requests to: John H. Siegel, M.D., Dept. of Surgery, Buffalo General Hospital, 100 High St.. Buffalo, NY 14203.

November

Departments of Surgery and New York 14203

23. 1976

These were used as early and complementary indices of myocardial injury during coronary artery surgery. Materials and Methods There were three groups of 10 patients each. Group I included nine male patients and one female patient aged 41 to 67 years (average 55 years) in whom induced ventricular fibrillation4 and moderate total body hypothermia (30°C) was the mode of arrest used for distal coronary anastomosis (Fig. IA). In this group four patients suffered a total of seven previous myocardial infarctions (MI) and another three had systemic hypertension. The average ejection fraction (EF) was 67.7% (range 55-80%). The average fibrillation time was 102 min (range 45-140 min) and the average number of coronary artery bypass grafts (CABG) per patient was 3.9 (range 2-6). Group II consisted of ten male patients aged 46-65 years (average 55 years) in whom selective profound hypothermic arrest (SIPHA) was the method of preservation used during distal coronary anastomosis (Fig. 1B). This method which has been previously described [26] is characterized by a selective homeogeneous profound (I5- 18°C) cooling of the myo4 AC Model 2039 (Metronic).

242 Copyright All rights

0 1977 by Academic Press. Inc. of reproduction in any form reserved.

ISSN 0022-4804

SCHACHNER

ET AL.: MYOCARDIAL

cardial layers with a cold perfusate5 (7- IOOC)using a specially designed double armed perfusion-venting catheter placed into the left ventricle via the apex. Four patients had a total of six previous MI and systemic hypertension was recorded in another three. The average EF was 58% (range 40-75%), the average aortic occlusion time was 82 min (range 38-122 min) and average number of CABG per patient was 3.6 (range 2-5). Group III included ten male patients aged 44 to 65 (average 55 years), five of whom suffered a total of seven previous MI and another two patients had systemic hypertension. In this group, potassium (31 mEq/liter) cardioplegia combined with intermittent topical cooling of the heart (25-27°C) was the technique used to protect the myocardium (Fig. 1C). The cold cardioplegic solution (5-SC) which also contained methylprednisolone sodium succinate 500 mg/liter and 30 ml of 50% glucose was injected into the aortic root through a plastic 16 gauge angio catheter in the totally bypassed beating and empty heart. The initial dose of this solution needed to achieve cardiac arrest ranged between 150-200 ml. At the same time the heart is immersed in cold saline (46°C) for a period of 1-3 min. Intermittent aortic root injection of the cardioplegic solution (roughly 50 ml per each graft) and topical cooling of the heart continues during the performance of the distal coronary anastomoses. The average EF was 63.5% (range 50-75%) and the average aortic cross-clamping time was 64 min (range 28-86 min). The average number of CABG per patient was also 3.6 (range 2-5). Surgical Management

The primary anesthetic agents used were nitrous oxide, morphine and muscle relaxants. The establishment of cardiopulmon5 Plasmalyte 12.5 g/liter.

148 (McGraw

Laboratory)

and Manitol

PRESERVATION

243

TECHNIQUES

ary bypass was carried out in a standard fashion [34]. Reversed isologous saphenous vein grafts taken from the ankle to the knee were utilized, and a continuous suture technique was employed for both proximal and distal anastomosis. Total body perfusion was used only for the distal anastomoses, and where possible the sequential mode of grafting was utilized. Randomization Analysis

and Statistical

Data

The patients were chosen on a random basis depending on the operative schedule. The independent variable was the method of myocardial protection used during distal coronary artery anastomoses. The significance of the difference between the parameters of measurement of the three data groups at each study period was compared by the Student’s t test. The baseline data were not significantly different with regard to age, sex, preoperative clinical and physiological status, or with respect to the number of coronary artery bypass grafts and the duration of cardiac arrest. In each patient the following parameters were evaluated before and sequentially after myocardial preservation and coronary grafting. 1. Clinical assessment. The clinical postcardiopulmonary bypass response was evaluated on the following observations: (a) the incidence of spontaneous vs electrical defibrillation after the completion of the distal coronary anastomoses; (b) the development of postoperative cardiac arrhythmias; (c) the need for postoperative inotropic support; (d) the evolution of a myocardial infarct; (e) prolonged stay in ICU; (f) mortality. 2. Temperature recordings. Patient’s rectal and blood temperatures were continuously measured. The myocardial layer temperatures (epicardium-E, midmyoand subendocardium- S) cardium-M, were recorded every 20-30 min during

244

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

FIG. 1. The three methods used in the comparison of myocardial preservation during Aortocoronary bypass surgery. (A) Induced ventricular fibrillation (VF) combined with moderate total body hypothermia. (B) Selective intracavitary profound hypothermic arrest (SIPHA). (C) Potassium cardioplegia combined with moderate topical cooling of the heart (KMTH).

cardiopulmonary bypass with a special thermistor probe.6 (Figs. 2A, 2B, 2C) 3. Electrocardiographic studies. A twelve lead electrocardiogram was recorded from each patient prior to surgery, immediately after surgery, every 12 hr in the ICU, and once every 48 hr for the remaining days in the hospital. These ECGs were interpreted by the cardiology staff, carefully reviewed by the authors, and reinterpreted by an independent cardiologist whenever a problem arose. 4. Enzymatic and metabolic studies. Plasma samples were obtained for determination of total creatine kinase (CK), creatine kinase isoenzymes (CK-MM, CKMB, CK-BB) and lactate. Samples were obtained prior to surgery and prior to institution of cardiopulmonary bypass and were used as baseline values. Then, simultaneous samples were drawn from the coronary sinus7 and the venous inflow to 6 YSI 524, SE 4184. 7 Redicath 7SF, USCI.

the oxygenator every 20-30 min during total body perfusion. Mixed venous samples were obtained immediately postoperatively, 8 hr, 12 hr, and every 24 hr for the next 48-hr period in the ICU. Total CK was determined by a modification of Rosalki’s method [2]. The CK-isoenzymes were separated electrophoretically on agarose gel in barbital buffer at pH 8.6 and quantified by fluorometic scanning with a Corning 740 system densitometer as described by Roe [24]. Lactate was analyzed from whole perchloric acid extracts or directly from serum by the method of Rosenberg and Rush [25]. 5. Cardiac dynamic studies. The evaluation of cardiovascular dynamics was carried out preoperatively, immediately after surgery, and on successive days in the ICU. Multivariable physiologic data analysis techniques were used as previously described [29, 303. It has been shown that compared to a reference control state (R) of preoperative high risk patients, the entire spectrum of clinical severity

SCHACHNER

ET AL.:

MYOCARLIIAL

PRESERVATION

TECHNIQUES

245

cardiac mixing time (tm) and pulmonary mean dispersive time (td). The cardiac index is decreased and the arteriovenous oxygen difference is markedly elevated reflecting the severity of the decrease in perfusion. The patients actual physiologic state can be easily quantified by determining his specific physiologic distance (in normalized Euclidian units) from each of these states [23, Xi]. The most useful index of all over cardiovascular adequacy is the D/A ratio.

C

Distance to D-State Mean Distance to A-State Mean ’

VENT FIG. 1. (Conrinued)

in various forms of critical illness can be viewed in terms of their similarity to each of four prototype pathophysiologic states (A, B, C, D) which provide a scale for quantification of the patient’s physiologic status at a given moment in his recovery time course. The B and C states represent physiologic patterns of increasing severity characteristic of deteriorating stages in the septic process [29, 301. However, the majority of postcoronary bypass patients fall postoperatively either in the A-state or the Dstate, or range between the two. The Astate which represents normal stress response to surgery, trauma, etc. is characterized by a statistically significant rise in cardiac index (CI), heart rate (HR), and myocardial contractility reflected in shortened cardiac mixing time (t,), pulmonary dispersive time (td) and ejection time (ET) [30]. The parameters of oxygen consumption, arteriovenous oxygen difference (A-V,,) diff and P;O,) or peripheral metabolism (P;CO, or pH:) are generally unchanged. In the D-state (cardiogenic state), there is a fall in cardiac contractility reflected by the lengthening of

This ratio measures the patient’s relative similarity to patients in cardiogenic shock (D-state) compared to his similarity to patients in a normal stress response state (A-state) and this provides a precise index of overall cardiodynamic function. On the basis of sequential cardiodynamic studies using the D/A ratio in coronary surgical patients, three types of recovery trajectories have been identified [23, 27, 291. In the Type I recovery, which is the optimum recovery trajectory, the patient shows a hyperdynamic stress response after surgery (D/A ratio t). The Type II recovery which is the minimal acceptable recovery trajectory is characterized by an initial postsurgical fall into the cardiogenie D-state (D/A ratio 1) with a rapid recovery into a normal stress response within 24 hr (D/A ratio t). In contrast the Type III recovery patients have a prolonged cardiogenic response (D/A ratio J,) with an oscillatory and unstable course of recovery. All of the cardiogenic deaths observed, either early or late, have occurred in this recovery trajectory (Type III) [23, 291. 6. Electron microscopical studies. Core biopsies of the left ventricle were obtained with a Vim-Silverman biopsy needle prior to institution of a cardiopulmonary bypass and 30-60 min after the reperfusion. The fixative agent used was Paraformaldehyde (PAF). All biopsies were

246

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

A

B PO- GROUP I -JM

90 GROUP II - HH

_ _ -CS LACTATE

I

,/ 80

,_*’ ,--

7060.

..__.-_,

,! ,’ r- ._._.

--.._,+

_ ,’

,,-

,/MV

,’ ,jlj

__*-._

LACTATE -4 MV CK-MB

,/,’

,,-._ ._-_-

----cs

LACTATI

70.

\.\ . /’:

//’ : ,’ I

1 ’ I /I I/ I /

80

3

60

;

“‘MV LACTATI

l! / J ,_,’ / ,’ ,‘,, TEMP.

s TIME (min.)

#“@-@--COOLANT M”CK-M~ __I’ TIME (min.)

FIG. 2. Characteristic temperature pattern of the myocardial layers (Epicardium-E, Midmyocardium-M and Subendocardium-S) as correlated to the duration of cardiac arrest and the appearance of CK-MB and lactate levels in the coronary sinus and mixed venous blood. (A) Group I-VF patient. (B) Group IISIPHA patient. (C) Group III-KMTH patient. Note: the low CK-MB levels in group II.

interpreted by two pathologists independently and without having knowledge of the patients group or perfusion status. RESULTS

1. Clinical Course The postoperative clinical course is summarized by Table I. Five out of ten patients (50%) in the SIPHA Group II had spontaneous return of a conducted rhythm on reperfusion after the completion of the coronary anastomosis. Four patients defibrillated spontaneously in the potassium cardioplegia Group III. However, only two patients did so in the ventricular fibrillation Group I, the rest of them requiring one or more electrical defibrillations. The course of three patients in Group I was complicated by cardiac arrhythmias (two experienced multiple ventricular tachyarrhythmias and one developed atrial fibrillation) necessitating prompt anti-arrhythmic treatment and prolonged stay in

the ICU. Only one patient in Group II had an occasional premature ventricular contraction in the first postoperative day. In Group III one patient went into postoperative atria1 fibrillation. This patient stayed five days in ICU and another five in CCU. Another patient from this group showed nodal rhythm in the early postoperative period. Six patients in the VF group I and seven in the KMTH Group III required inotropic support after surgery and in the ICU, compared to only one patient in the SIPHA Group II. Only one patient, from Group III (potassium cardioplegia and moderate topical cooling of the heart), exhibited electrocardiographic changes indicative of an evolving perioperative myocardial infarct. No patients in Group I or Group II developed infarcts. One patient in the ventricular fibrillation Group I died 4 weeks after surgery due to cardiac failure. There were no deaths in Group II or III.

SCHACHNER

ETAL.:

MYOCARDIAL

C W

GROUP III - PA ,CS LACTATE

1

PRESERVATION

247

TECHNIQUES

cardium (the most vulnerable layer to ischemic injury) [5-7, 131 is the coolest in Group II patients. This results from the characteristics of the cooling method (SIPHA) used in this group of patients which induces both intracavitary as well as coronary cooling. It is worthy to note also the strikingly low CK-MB levels in this Group II patient. 3. Electrocardiogram Studies

15

45

75

105 135 TIME (min.)

165

Only one patient (R.S.) from Group III (potassium cardioplegia combined with topical cooling of the heart) had electrocardiographic evidence of an acute inferolateral myocardial injury pattern. No perioperative MI was noticed in the other two groups.

195

FIG. 2. (Conrinued)

4. Enzymatic and Metabolic Studies

Matched coronary sinus (CS) samples had generally higher CK-MB enzyme than Table 2 summarizes the group averages the simultaneously drawn mixed venous for the mean temperature measurements samples, but this difference did not reach statistical significance. of the myocardial layers (EpicardiumThe CK-MB values, which indicate the E, Midmyocardium-M, and Subendocardium-S) during cardiopulmonary by- degree of myocardial cell damage, were pass. The temperatures recorded in Group lowest in the selectively and profoundly II were significantly lower (15 1S’C) than cooled hearts (SIPHA) of Group II patients. those in Group I (30-33”(Z) or Group Table III summarizes the statistical analysis III (25-27°C). Figures 2A, 2B, and 2C (Student’s t test) of the intraoperative illustrate the temporal patterns of the three and postoperative coronary sinus and mixed myocardial layer temperature measure- venous CK-MB and lactate levels. This ments, the duration of cardiac arrest and analysis showed that there were sigthe pattern of appearance of CK-MB and nificantly (P < 0.05) lower CK-MB mean lactate in a typical patient from each values in the coronary sinus blood intragroup. It is evident that the subendo- operatively in Group II (5.97 U/liter) and 2. Temperature Recordings

TABLE

1

POST-OPERATIVECLINICAL DATA” Spontaneous defibrillation Group I Group II Group III

2/10 5110 4110

Cardiac arrhythmias 3110 l/10 2110

Inotropic support 6110 l/10 7110

Evolving MI none none l/l0

Prolonged stay in KU 3110 none I

Mortality l/l0 none none

a Post-operative clinical course in three groups of ten patients each undergoing coronary artery surgery.

248

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

3). The distribution of cases with respect to the mixed venous levels of CK-MB DIFFERENTIAL MYOCARDIAL LAYER TEMPERATURES in the intraoperative and immediate post(“C) (GROUP AVERAGES)~ operative period is shown in Fig. 4. These SubendoMidmyodata show that the method producing the cardial cardial Epicardial lowest myocardial layer temperatures (SIPHA) Group II, also had the lowest Group I 30.0 i 0.5 31.0 2 0.76 33.5 + 0.2 Group II CK-MB release. The method with the 15.0 2 1.0 16.4 2 0.5 18.0 2 0.7 Group III 26.0 2 0.3 25.7 2 0.1 25.1 f 0.63 highest myocardial layer temperatures (VF) Group I, has the highest CK-MB values a Group averages of the differential myocardial layer temperatures in the three study groups during cardio- and the potassium cardioplegia Group III, pulmonary bypass. Note the selectively profound with intermediate myocardial layer tempercooled myocardium in group II patients in compari- atures also had intermediate levels of son to blood and body temperature. CK-MB release. These data suggest a major temperature dependence to myocardial cell Group III (7.64 U/liter) than in the ventric- injury. The lactate levels were moderately eleular fibrillation Group I (17.28 U/liter). There was no significant difference, how- vated in all three groups during cardioever, in the intraoperative period between pulmonary bypass indicating an anerobic the CK-MB values of Group II and III metabolic process (Table 3). The mixed patients either in coronary sinus blood or venous samples had significantly higher mixed venous samples. A significant differ- mean lactate levels in the immediate ence was found in the CK-MB mixed postoperative period (P < 0.05) in Group venous blood in the immediate postoper- III (potassium cardioplegia) patients as ative period. This is seen in the com- compared to the other two groups. It has parison of Group I mean values (85.58 to be stressed however, that the quantitaU/liter) and Group II mean values (7.84 tive magnitude of lactate production was U/liter) P < 0.05 and between Group II far greater in the fibrillating Group I mean values (7.84 U/liter) and Group III reflecting true values during continued mean values (22.32 U/liter), P < 0.005 (Fig. perfusion, in contrast to the cold arrested TABLE 2

CK-MB

90-1

VALUES

GROUP AVERAGE

111111111 @ ‘NTRAoPERAT’VE

80

@,$

IMMEDIATE

POST-OP

MV - MIXED VENOUS CS - CORONARY SINUS

I

II

FIG . 3. Group average for CK-MB release in the intraoperative in the three groups studied

III and immediate postoperative period

SCHACHNER ET AL .: MYOCARDIAL

PRESERVATION

249

TECHNIQUES

GROUPI - 0 GROUPII - 0 170’GROUP 111150i

q

El

IMMED.POST- OP

INTRA- OP

FIG. 4. Distribution of intraoperative and immediate postoperative mixed venous (MV) CK-MB individual patient mean values in the three groups studied. Note that the highest values of CK-MB are confined to the ventricular fibrillation Group I.

(Group II) and potassium cardioplegic (Group III) hearts where the values reflect “wash-out” phenomena after periods of no coronary flow. 5. Postoperative Cardiac Dynamics and Recovery Trajectories All three groups showed an initial depression of cardiac performance post-

operatively, as reflected in lower cardiac indices (CI) and prolonged cardiac mixing times (t,) (Fig. 5). This figure shows that the Group II patients had the greatest increase in cardiac index and smoothest decrease in cardiac mixing time after surgery compared to the Group III or Group I patients. Figures 6A, 6B, and 6C show the serial D/A ratios of all patients projected

TABLE 3 ENZYMATIC AND METABOLIC DATA (GROUP AVERAGE@

Intra-op. CS CK-MB (U/L) Intra-op. MV CK-MB (U/L) Immediate post-op MV CK-MB (U/L) Intra-op. lactate Intra-op. lactate

Group I

Group II

Group III

17.28 ? 12.85

5.91 k 5.41

7.64 2 6.81

0.05 (I-II,

14.79 k 14.1I

5.92 _t 4.70

7.17 F 7.14

NS

85.58 2 100.47

7.84 _t 9.93

22.32 ? 14.71

3.1 ” 1.04

3.2 r 1.27

2.9 t 1.08

NS

2.8 + 1.00

2.3 2 0.82

2.6 k 0.67

0.05 (II-III)

3.6 t 1.63

4.2 2 1.36

0.05 (I-III,

P-Value I-III)

0.05 (I-II) 0.005 (II-III)

CS (JAM)

M.V. (PM)

Immediate post-op MV lactate (PM)

3.1 -t 1.41

II-III)

a Statistical analysis (Student’s t test) of intraoperative and postoperative CS and MV CK-MB and lactate levels. * CS-Coronary Sinus; CK-MB-Myocardial Creatine Phosphokinase; MV-Mixed Venous; NS-Nonsignificant.

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

250

111 P-PREOPERATIVE

.GROW

1.2~DAYS AFTER SURGERY 0 - WEMAJf POST OPERATIVE +-NoTRoPx SUPPORT

”

i

b

i

i

i

i

P-PREOPERATIVE 1.2 -

P

0

1

2

DAYS AFTER SURGERY

0

- ,MMED,NE

+-

INOTROP#

P

0

POSTOPERATIVE SUPPORT 1

I--

FIG. 5. Cardiac index (CI) and cardiac mixing time (rm) in patients from the three groups. Note the more frequent need for inotropic drugs in Groups I and III. GROUP 3.0

GROUP

I P-

II

I’

PREOPERATIVE

O-IMMEDIATE 1.2.3.4

-

POST OPERATIVE

DAYS AFTER SURGERY

* -lNOTROPlC

SUPPORT

2.5

0.5

B 0.0

I-

P

0

1

2

3

4

6

6

i

i

3

4

FIG. 6. Comparison of postoperative recovery trajectories in the three study groups, projected against t 1 SD envelope of the at least acceptable form of recovery for post-aortocoronary bypass patients (Type II trajectory). (A) Ventricular fibrillation, Group I. (B) SIPHA, Group II. (C) Potassium cardioplegia combined with moderate topical cooling of the heart, Group III.

SCHACHNER

ETAL.:

MYOCARDIAL

against the + 1 standard deviation envelope of the Type II physiologic recovery which is the minimum acceptable trajectory of physiologic recovery after aortocoronary bypass [23, 26, 291. There were no Type I recoveries in Group I patients (ventricular fibrillation group) (Fig. 6A). Two patients from Group II (SIPHA) (Fig. 6B) and two patients from Group III (potassium cardioplegia) (Fig. 6C) showed the optimum Type I recovery trajectory (D/A T), a normal stress response where the increase in cardiac flow meets adequately all body demand. The remaining 16 patients from Group II and III and seven of the Group I patients fell within the envelope for Type II recovery, which is the least acceptable type of recovery for coronary surgical patients. In Group I (Fig. 6A), however, three patients showed a Type III recovery, which is a nonacceptable form of physiological adaptation for post surgical coronary patients and one of these Type III patients died four weeks after surgery after a prolonged and difficult clinical course of cardiac decompensation. Of importance is the fact that Group I and Group III patients more frequently required cardiac inotropic agents to support their circula-

x.0-jGROUP I II

P FIG.

0 6.

I (Conrinued)

2

3

4

PRESERVATION

TECHNIQLJES

251

tion in order to achieve an acceptable range of postoperative physiologic adaptation. Significantly, six patients from VF Group 1 (60%) and seven patients from KMTH Group III (70%) needed inotropic support compared to only one patient from the SIPHA Group II ( 10%).

6. Electron Microscopical Studies A total of 500 electron micrographs were carefully reviewed by two electromicroscopic pathologists without knowledge of the patient’s group or perfusion status. In each biopsy, the midmyocardium and subendocardium after coronary anastomosis and reperfusion (30-60 min), were compared to the control precardiopulmonary bypass specimen. A graded scale [l-4] of ultrastructural changes was then applied in the identification and quantification of myocardial injury patterns. This included (a) reversible ultrastructural changes such as interstitial edema, reduction in glycogen granules, dilation of t-tubular system, blurring and/or contraction of Z-lines, depletion of intramitochondrial granules and swelling and/or clumping of mitochondria; (b) irreversible ultrastructural changes such as degeneration of mitochondria and/ or myofibrils. Group I (VF) revealed the most significant ultrastructural changes (Fig. 7A and 7B). All ten patients exhibited some of the reversible changes including marked interstitial edema and depletion of glycogen granules as well as focci of Z-line contraction and mitochondrial clumping and swelling. In seven patients, however, irreversible change such as foccal degeneration of mitochondria and/or myofibrills were clearly documented. Generally the changes were confined to subendocardium and were similar to those found in experimental animals after 60 min of anoxic arrest [S]. Group II (SIPHA) patients showed the myocardium to be remarkably well preserved (Figs. 8A and 88). The ultrastructural changes from normal were minimal, and included mild foccal dilation of the t-tubular system and some reduction

252

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

FIG. 7. Post reperfusion (45 min) electron micrograph of part of left vent ricular subendocardial muscle cell of a 41-year-old patient subjected to ventricular fibrillation and moderate total body hypothermia (Group I) during distal coronary anastomosis. (A) (x21.000). Note the contraction of Z-lines, focal degeneration of myofibrills and mitochondrial (white spots) and the significant reduction of glycogen granules. (B) (~70.000). Note the intra cellular edema separating the mylfibrills and the clumping and swelling of mitochondria PAF fixation, upon embedding.

SCHACHNER

ET AL.: MYOCARDIAL

in glycogen in only three patients. There were no irreversible changes. Group III (KMTH) patients generally showed a well preserved architecture (Figs.

PRESERVATION

TECHNIQUES

253

9A and 9B). One postreperfusion specimen was damaged during the process of fixation and could not be considered (patient 1). Eight out of nine patients in this group

254

JOURNAL OF SURGICAL RESEARCH: VOL. 22. NO. 3, MARCH 1977

FIG. 8. Postreperfusion (45 min) electron micrograph, subendocardial layer of a 50-year-old patient after 76 min of selective intracavitary profound (15-18°C) hypothermic arrest of the heart (SIPHA Group II). Note the normal myocardial ultrastructure. (A) (x21.000). (B) (x70.000). PAF fixation, epon embedding.

showed some foccal reversible changes the most frequent being interstitial edema and swelling (and/or clumping) of mitochondria. A constant finding in the postreperfusion biopsy both in the midmyocardium and in

the subendocardium was that of a pale and swollen nucleus. This finding may represent an osmotic phenomenon, the significance of which is as yet unknown. Only one patient (No. 10) showed some

SCHACHNER

ET AL.: MYOCARDIAL

foccal degeneration of myofibrills and mitochondria. Of interest is that this same patient had also moderately elevated CKMB levels as well as ECG changes indicative of a myocardial injury pattern. DISCUSSION

Intraoperative preservation of the myocardium has recently emerged as a leading

PRESERVATION

TECHNIQUES

255

endeavor in the surgical treatment of cardiac patients. There are many different methods designed to protect the heart during the conduct of open heart surgery [7, 4-12, 15, 16, 19, 351. Many techniques have been advocated for the detection and quantification of myocardial injury. These techniques include measurement of the release of cardiac specific enzymes and other

256

JOURNAL

OF SURGICAL

RESEARCH:

VOL.

22, NO. 3, MARCH

1977

FIG. 9. Postreperfusion (60 min) electron-micrograph, subendocardial layer of a 45-year-old patient after 77 min of potassium cardioplegia combined with moderate topical cooling of the heart. Methylperdnisolone sodium succinate and hypertonic glucose (KMTH Group III) Note the normal myofibrills, slight swelling of mitochondria and swelling and pallor of the nucleus. (A) (x21.000). (B) (x70.000). PAF fixation, epon embedding.

metabolic products [20], the electrical function or perfusion by radionucleotide activity of the myocardium [21], general [20] and the careful assessment of the or regional changes in mechanical func- postoperative clinical course [7, 161.There tion [4, 9, 3 11, imaging of alteration of is no doubt that the application of these

SCHACHNER

ET AL .: MYOCARDIAL

methods has provided a clearer picture of the factors limiting preservation of viable myocardial tissue. It has been recognized, however, that ischemic injury of the myocardium is a complex biological phenomena with physiologic implications. Consequently, individual methods when applied separately, provide only limited information concerning the overall effects of a jeopard-

PRESERVATION

TECHNIQUES

257

ized or damaged heart muscle. In this study we investigated the correlation of ultrastructural changes, the degree of CKMB activity, and the level of anerobic metabolism (lactate production) with the type of physiologic recovery and the clinical need for postoperative inotropic support. The multiparametric evaluation used in

258

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

FIG. 10. Pre- and Postreperfusion (60 min) electron-micrograph, subendocardial layer of a 45-year-old patient after 70 min of anoxic arrest, using selective intracavitary cooling with myocardial layer temperatures kept at 23-26°C. No potassium or steroids used. Note the severe myofibrillar and mitochondrial degeneration with marked intracellular edema. Patient had type II recovery and required no inotropic support. (A) (x70.000) Pre-cardiopulmonary bypass. (B) (x70.000) Post-reperfusion biopsy. PAF fixation, epon embedding.

this study has shown that electrically induced ventricular fibrillation (VF) cornbined with moderate total body hypothermia (Group I> does not offer protection to the ischemic myocardium during

distal coronary anastomosis, even though the coronary

perfusion

pressure

was main-

tained above 80 mm Hg during cardiopulmonary bypass. The assumption based on experimental studies [35] that this

SCHACHNER

ET AL.: MYOCARDIAL

method is safe because the heart remains continually perfused with oxygenated blood has been proved to be misleading. The fibrillating human heart with obstructive atherosclerotic coronary lesions is more vulnerable to a relative reduction of blood flow than is the normal canine heart. Furthermore, reduction in coronary flow (especially in the subendocardium) may also result from increasing left ventricular com-

PRESERVATION

TECHNIQUES

259

pressive forces and/or increasing intramural tensions so that blood flow cannot rise sufficiently to meet the metabolic demands of the fibrillating heart [l, 17, 181. As a consequence, a significant oxygen debt appears to develop in the fibrillating human myocardium causing diversion of cell metabolism to anerobic pathways, evidenced by increased coronary sinus lactate levels. This may result in a profound ATP

260

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

deficit and inefficient energy supply. This may explain why seven out of the ten patients in Group I showed irreversible ultrastructural changes (focal myofibrillar and mitochondrial degeneration) mostly in the subendocardium. The autopsy material from the one VF patient who died four weeks after surgery also revealed extensive foci of subendocardial necrosis. It is important to emphasize that all seven VF patients with myocardial damage also had moderate to high CK-MB and lactate levels in the immediate postoperative period, and six of them needed inotropic drugs to support their hemodynamics. As a result of this prospective study, and from other reported evidences in the literature, we have completely abandoned the use of ventricular fibrillation during open heart surgery. The other two methods, SIPHA and KMTH, had in common the reduction in metabolic requirements of the myocardium although by different mechanisms [l 1, 12, 15, 19, 32, 331. Both methods offer significant technical advantages compared to the VF technique during the performance of distal coronary anastomoses: the field is dry, the heart is still and flaccid and can be retracted easily. The increased facility with which coronary surgery can be carried out during these techniques undoubtedly influences both the speed and the precision of the anastomoses, which in turn may favorably influence long-term graft patency rates. In the evaluation of myocardial preservation, however, there appear to be differences between the two techniques which favor the use of the SIPHA method (Group II). In the present study this method resulted in less myocardial cell injury, as evidenced by significantly (P < 0.005) lower mean CK-MB enzyme levels (7.84 U/liter vs. 22.34 U/liter) and by better preservation and utilization of energy stores for the postoperative stress of myocardial recovery as reflected in significantly (P < 0.05) lower lactate production (4.2 fl vs 3.6 PM). There were

no irreversible ultrastructural changes in the SIPHA (Group II) patients vs one patient in the KMTH (Group III) who showed focal degeneration of myofibrills and mitochordia. Also, in the SIPHA patients the reversible changes were of minimal degree in only three patients, in contrast to the more pronounced changes found in all patients of Group III (potassium arrest combined with moderate topical hypothermia). Of particular interest was the increased amount of interstitial edema and nuclear swelling found in the KMTH Group III patients as compared to the SIPHA group. Myocardial edema, which is known to be an early sign of acute ischemia has been suggested as a potential link in a viscious cycle leading to a postoperative reduction of blood flow and resultant tissue necrosis [ 11, 281. We, like others [9, 14, 161, share the opinion that one of the major determinants of successful myocardial preservation is the level of myocardial layer temperature during cardiac arrest. This view is based on the well known fact that the metabolic requirements of myocardial tissue diminish with decreasing temperatures [ 14- 161. Experimental and clinical data on myocardial oxygen consumption and temperature dependence point out that the greatest benefit of hypothermia occurs within the range of 1%20°C [14, IS]. Our clinical experience is in complete agreement with this finding. Indeed one of our early prestudy patients in whom selective intracavitary profound hypothermic arrest was utilized during CABG, where the myocardial layer temperatures were in the 23-26°C range (the temperature level used in the KMTH patients) showed marked irreversible ultrastructural changes (focal degeneration of mitochondria and myofibrills with marked intercellular and intracellular edema) in the post reperfusion specimen after 72 min of anoxic arrest (Fig. 10). This patient had also high levels of CK-MB as well as EKG changes indicative of perioperative myocardial infarction. These findings are in contrast to

SCHACHNER ET AL.: MYOCARDIAL

those found in the study patients in whom myocardial layer temperature ranged between 1% 18°C. These patients generally had longer anoxic times, but showed extremely well preserved myocardial architecture. It seems that the critical temperature range for myocardial preservation during prolonged anoxic periods (over 60 min) for coronary patients lies at or below 18”C, and that minimal increases in myocardial layer temperature beyond this range have a detrimental effect on the myocardial cell physiology. It would appear that the use of potassium and/or methylprednisolone may extend the safe level of temperature to 25-27”C, based on the studies of the Group III patients. Finally, recognition of the importance of maintainance of viable myocardial mass as determinant of long-term prognosis in patients undergoing open heart procedures has changed the attitudes toward preservation techniques in modern cardiac surgery. This has resulted in attention being focused not only on patient survival after coronary surgery, but also on the well being of the myofibril, as the functional unit of the myocardium, and the integrity of its subcellular compartment. This altered therapeutic approach to preservation may lead in the future to an improved quality of life, as well as to a prolongation of life expectancy for the cardiac surgical patient. SUMMARY

The myocardial properties of three different techniques for cardiac arrest during aortocoronary bypass surgery were analyzed. Ventricular fibrillation and moderate total body hypothermia (30-33°C) (Group I) was found to be an insecure method of preservation. It produced a high incidence of focal irreversible ultrastructural changes (7 of 10 patients), high post-bypass CKMB levels (mean 85.54 U/liter) indicative of myocardial damage, and impaired clinical and physiologic recovery courses. Six out of ten patients needed inotropic support, three had prolonged stay in ICU, and three

PRESERVATION

TECHNIQUES

261

patients showed Type III (unacceptable) recovery trajectories, one of whom died of myocardial decompensation four weeks after surgery. This method, which was the most common one used in our institution, was completely abandoned as a result of these studies. Potassium induced cardioplegia combined with methylprednisolone sodium succinate, hypertonic glucose and intermittent moderate topical cooling (2527°C) of the heart (Group III) offered a generally acceptable form of myocardial protection, as only one patient showed irreversible ultrastructural changes. The mean post-bypass CK-MB level was only moderately elevated (mean 22.32 U/liter), but seven of ten patients needed inotropic support. There were no Type III recovery trajectories and two patients showed an optimal Type I recovery. Only one patient had a prolonged stay in ICU, and another patient exhibited electrocardiographic evidence of a perioperative myocardial injury pattern. Selective intracavitary profound hypothermic arrest (15- 18’C) (SIPHA) offered the best myocardial protection as evidenced by remarkably well preserved ultrastructure and significantly (P < 0.005) lower post-bypass CK-MB levels (mean 7.85 U/L). All SIPHA patients had acceptable physiologic recovery trajectories of the Type I or Type II with minimal need for inotropic support (one patient), and none had a Type III recovery. These data also suggest that the major determinant of a successful myocardial preservation is the level of myocardial layer temperature, being best at the lowest temperature (15- 18”(Z),worst at the highest temperature (30-33°C) and intermediate at 25-27°C. Additional injury may also be induced by ventricular fibrillation which by itself increases myocardial metabolic demands. REFERENCES 1. Baird, R. J., Manktelow, R. T., Shah, P. A., and Ameli, F. M. Intramyocardial pressure: A study of its regional variations and its relationship to intraventricular pressure. J. Thorac. Cnrdiovusc. Surg. 59: 810, 1970.

262

JOURNAL OF SURGICAL RESEARCH: VOL. 22, NO. 3, MARCH 1977

2. Bishop, C., Chu, T. M., and Shihabi, Z. K. Single stable reagent for creatinine kinase assay. Clin. Chem. 12: 299, 1966.

3. Bittar, N., Koke, J. R., Berkoff, H. A., and Kahn, D. R. Histochemical and structural changes in human myocardial cells after cardiopulmonary bypass. Circulation 51: 16, 1975. 4. Braunwald, E. The determinants of myocardial oxygen consumption. Physiologist 12: 65, 1969. 5. Brazier, J., Cooper, N., Buckberg, G. D. Adequacy of subendocardial oxygen delivery: Interaction of determinants of flow, arterial oxygen content, and myocardial oxygen need. Circulation 49: %8, 1974. 6. Buckberg, G. D., Flixler, E. D., Archie, J. P., and Horrman, J. I. E. Experimental subendocardial ischemia in dogs with normal coronary arteries. Circ. Resp. 30: 67, 1972. 7. Buckberg, G. D., Olinger, G. N., Mulder, D. G., and Maloney, J. V. Depressed postoperative cardiac performance. Prevention by adequate myocardial protection during cardiopulmonary bypass. J. Thorac. Cardiovasc. Surg. 70: 974, 1975. 8. Cerra, F. B., Lajos, T. Z., Montes, M., and Siegel, J. H. Structural-functional correlates of reversible myocardial anoxia, J. Surg. Res. 16: 140, 1974. 9. Ebert, P. A., Greenfield, L. J., Austen, W. G., and Morrow, A. G. Experimental comparison of methods for protecting the heart during aortic occlusion. Ann. Surg. 155: 25, 1962. 10. Enright, L. P., Staroscik, R. N., and Reis, R. L. Left ventricular function after occlusion of the ascending aorta: assessments of various methods for protecting the heart during aortic occlusion. Ann. Surg. 155: 25, 1962.

11. Feola, M., Rovetto, M., Soriano, R., Cho, S. Y. and Wiener, L. Glucocorticoid protection of the myocardial cell membrane and the reduction of edema in experimental acute myocardial ischemia. .I. Thorac. Cardiovnsc. Surg. 72: 631, 1976. 12. Gay, W. A., Jr., and Ebert, P. A. Functional metabolic and morphologic effects of potassium induced cardioplegia. Surgery 74: 284, 1973. 13. Ghidoni, J. J., Liotta, D., and Thomas, H. Massive subendocardial damage accompanying prolonged ventricular fibrillation. Amer. J. Pathol. 55: 15, 1969. 14. Greenberg, J. J., Edmund, L. H. Effect of myocardial ischemia at varying temperatures on left ventricular function and tissue oxygen tension. J. Thorac. Cardiovnsc. Surg. 42: 84, 1961. 15. Greenberg, J. J., Edmund, L. H., Brown, R. B. Myocardial metabolism and post arrest function in cold and chemically arrest heart. Surgery 48: 31, 1960. 16. Griepp, R. B., Stinson, E. B., Oyer, P. E., Copeland, J. G., and Shumway, N. E. The superiority of aortic cross-clamping with pro-

found local hypothermia for myocardial protection during aorta-coronary bypass grafting. J. Thorac. Cardiovasc.

Surgery 70: 995, 1975.

17. Hottenrott, C., Maloney, J. V., Jr., and Buckberg, G. Studies of the effects of ventricular fibrillation on the adequacy of regional myocardial flow. III. Mechanisms of ischemia. J. Thorac. and Cardiovasc. Surg. 68: 634, 1974. 18. Hottenrott, C., Maloney, J. V., Jr., and Buckberg, G. Studies of the effects of ventricular fibrillation on the adequacy of regional myocardial flow. I. Electrical vs. spontaneous fibriiSurg. 68: 615, lation. J. Thorac. Cardiovasc. 1974. 19. Legato, M. J., Spiro, D., and Langer, G. A. Ultrastructural alterations produced in mammalian myocardium by variation in perfusate ionic composition. J. Cell. Biol. 37: 1, 1968. 20. Martin, N. D., Zaret, B. L., McGowan, R. L., Wells, H. P., Flamm, M. D. Rubidium-81: A new myocardial scanning agent. Radiology 111: 65, 1974.

21. Muller, J. E., Maroko, P. R., Braunwald E. Evaluation of precordial electrocardiographic mapping as a means of assessing changes in myocardial ischemic injury. Circulation 52: 16, 1975. 22. Oldham, N. H., Jr., Roe, C. R., Young, W. G.,

Jr., and Dixon, S. H. Intraoperative detection of myocardial damage during coronary artery surgery by plasma creatinine-phosphokinase isoenzyme analysis. Surgery 7rl: 917, 1973. 23. Raza, S. T., Vidne, B. A., Farrell, E. J., Lajos, T. Z., Lee, A. B., Schimert, G., and Siegel, J. H. Early and longterm effects of direct myocardial revascularization: A prospective study using multivariable physiologic analysis. Ann. Thorac. Surg. 23(2): 99, 1977.

24. Roe, C. R., Limbird, L. E., Wagner, G. S., and Nerenberg, S. T. Combined isoenzyme analysis in the diagnosis of myocardial injury. Application of electrophoretic methods for the detection and quantification of the CPK-MB isoenzyme. J. Lab. Clin. Med. 80: 577, 1972. 25. Rosenberg, J. C., Rush, B. F. An enzymaticspectrophotomatic determination of pyuric and lactic acid in blood. Clin. Chem. 12: 299, 1%6. 26. Schachner, A., Schimert, G., Lajos, T. Z., Lee, A. B., Jr., and Siegel, J. H. Selective intracavitary and coronary profound hypothermic cardioplegia for myocardial preservation. A new technique. Ann. Thorac. Surg. 23(2): 154, 1977. 27. Schachner, A., Schimert, G., Lajos, T. Z., Lee, A. B., Montes, M., Chaudhry, A., Schaefer, P., Vladutiu, A., and Siegel, J. H. Selective Intracavitary and coronary hypothermic cardioplegia for myocardial preservation: Clinical, Physiologic and ultrastructural evaluation. Arch. Surg. 3(2): 1197, 1976.

SCHACHNER ET AL.: MYOCARDIAL 28. Schwartz, A., Wood, J. M., Allen, J. C., Bornet, E. P., Entman, M. D., Goldstein, M. A., Sordhal, L. A., Szuki, M., Lewis, R. M. Experimental studies: biochemical and morphologic correlates of cardiac ischemia. Amer. J. Cardiol. 32: 46, 1973. 29. Siegel, J. H., Farrell, E. J., Fichthom, J., Lajos, T. Z., Lee, A. B., Schimert, G., and Eberhardt, R. C. The use of multivariable trajectories identifying normal and abnormal time course of recovery after coronary bypass surgery. J. Surg. Res. 18: 341, 1975. 30. Siegel, J. H., Farrell, E., Goldwyn, R. M., and Friedman, H. P. The surgical implication of physiologic patterns in myocardial infarction shock. Surgery 72: 125, 1972. 31. Sonnenblick, E. H., Ross, J., Jr., Covell, J. W., Kaiser, G. A., and Braunwald, E. Velocity

PRESERVATION

TECHNIQUES

263

of contractions as a determinant of myocardial oxygen consumption. Amer. J. Physiol. 209: 919, 1965. 32. Stoney, R. J., Roe, B. B. Ventricular function after induced intermittent ischemia and ventricular fibrillation: Effect of hypothermia. J. Thorac. Cardiovasc.

Surg. 48: 838, 1964.

33. Urschel, H. C., Greenberg, J. J. Differential cardiac hypothermia for elective cardioplegia. Ann. Surg. 152: 845, 1960. 34. Vidne, B. A., Bunnell, I. L., Greene, D. G., Lajos, T. Z., Lee, A. B., Schimert, G. The internal mammary artery coronary bypass graft as the primary method of myocardial revascularization. N. Y. State J. Med. 75: 1211, 1975. 35. Wilson, H. E., Dalton, M. L., and Allison, W. M. Increased fibrillation to avoid anoxia. J. Thorac. Cardiovasc.

Surg. 64: 193, 1972.