comparison between metabolic changes in local venous and coronary sinus blood after acute...

Comparison Between Metabolic Changes in Local

Venous and Coronary Sinus Blood After

Acute Experimental Coronary Arterial Occlusion

PATRICIA OWEN, BSc

MICHAEL THOMAS, MD, MRCP

VAL YOUNG, MB, MC, Path

and LIONEL OPIE, MD, MRCP

London, England

From the Medical Research Council, Car- diovascular Unit, The Royal Postgraduate Medical School, London W. 12. England. Manuscript received March 24, 1969, ac- cepted October 24, 1969.

Address for reprints: Patricia Owen, BSc, Medical Research Council, Cardiovascular Research Unit, Royal Postgraduate Med- ical School, Ducane Road, London W. 12. England.

A technique for the study of local metabolic changes in coronary venous blood draining from a small area of ischemic myocardium is described. Overt left ventricular failure, ventricular arrhythmias and possible secondary effects on local metabolic changes were avoided. Metabolic changes in local coronary venous blood and in coronary sinus blood were compared. Gross changes detected by local coronary venous sampling were not observed in coronary sinus blood samples. The possible relevance of this observation to clinical studies was noted.

The small ischemic lesion usually involved less than 10 percent of the heart volume and was characterized by acute ST segment elevation in the epicardial electrocardiogram and by positive changes in values for local coronary venous blood lactate, pyruvate, lactate/ pyruvate ratio, glucose, potassium and phosphate. Free fatty acids and beta hydroxybutyrate and acetoacetate levels were also studied. The technique and its results are compared with other methods of study of the metabolism of ischemic heart tissue.

Ventricular failure and ventricular arrhythmias after acute myocardial

infarction in man may often fail to respond to treatment, notwith-

standing recent therapeutic advances. A fuller understanding of the

problems involved at the level of cell and tissue pathophysiology is

required. Direct analysis of the metabolic events in the myocardial

infarct is not possible in patients, and further experimental work in

animals is indicated. Metabolic changes in experimental myocardial ischemia have been

assessed by two major analytic approaches. First, tissue metabolic

changes have been analyzed.l-lo Such studies have yielded much valu-

able information that could not have been obtained by other means,

although repeated tissue biopsies raise the question of possible effects

of tissue trauma. Second, previous workers have used measurements of arterio-coronary sinus differences after the acute reduction of blood flow to a large part of the left ventricle.s*ll~l” However, the size of the left ventricular lesion, ventricular failure’” and overall reduction in

coronary flow may complicate the interpretation of metabolic data. Another problem in interpreting some of these studies is that. coronary sinus blood represents mixed venous blood from both ischemic and nonischemic areas of tissue.

Therefore, it was desirable to design an experimental model of myocardial infarction involving only a small volume of heart muscle and with only minimal impairment of overall ventricular function. In

562 The American Journal of CARDIOLOGY

METABOLISM OF ISCHEMIC HEART TISSUE

particular, the technique described here allowed the

local sampling of blood directly from the site of the

ischemic tissue. Metabolic changes in local venous and

coronary sinus blood were systematically compared, since the validity of coronary sinus blood samples in

representing local metabolic cvcnts is crucial to many

experimental and clinical studies. Local coronary ven-

ous samples showed metabolic changes that could not

be detected in coronary sinus blood.

Methods

Production of Myocardial lschemia

Seventeen greyhound dogs weighing between 60 and 70 lb., were anesthetized by intravenously administered t.hiopental and maintained unconscious by inter- mittent intravenous injections of pentobarbital. Under radiologic control, a no. 7 or no. 8 Goodale-Lubin catheter (U. S. Catheter and Instrument Corp., Glens Falls, N. Y.1 was inserted high in the coronary sinus by way of a jugular vein. l5 A large bore plastic can- nula was inserted into a femoral artery. The heart was exposed through a left thoracotomy, respiration being maintained by a Harvard type respiration pump and an endotracheal tube.

The parietal pericardium overlying the anterolat- era1 aspect of the heart was removed. An anterolateral branch of the left interventricular descending coronary artery (Fig. 1) was selected, and with limited dissection a silk ligature was placed loosely around it. Usually there were two venae commitantes, one of which was catheterized by a PE60 polyethylene tube (Intramedic, Clay Adams, New York) with use of a Seldinger method. The catheter lumen was kept patent by frequent gentle flushing with a dilute hep- arin-saline solution (about 1 unit/ml).

Electrocardiographic m-onitoring using limb leads together with an epicardial lead was continuously undertaken before and after local coronary artery ligation.

Control blood samples were not taken until at least 30 minutes after preliminary placing of the catheters. Serial blood samples were taken from the femoral artery, local coronary vein and coronary sinus. The arterial ligature was then tied and further blood samples were taken until the end of the experimental period (usually 2 to 3 hoursl, when the animal was killed with intravenously administered potassium chloride or pentobarbital.

Post,mortem nrteriograms and venograms were performed to record (1) the area of myocardium sup- plied by the ligated artery; (2) the location of the tip of the coronary venous catheter and the anatomy of the venous drainage of the ischemic zone; and (3) the position of the tip of the coronary sinus catheter. This latter was also confirmed by direct palpation of the coronary sinus.

Arteriograms were obtained by catheterizing the occluded local coronary artery after potassium arrest

VOLUME 25, MAY 1970

Figure 1. Diagram representing the coronary arterial anatomy of a dog, showing the site of local venous sampling (point X) and typical site of local arterial occlusion (point Y) in a small anterolateral ischemic lesion involving approxi- mately 5 percent of the heart volume. Point Z represents the site of great coronary vein sampling used in some of the experiments.

of the heart. Hypaque@ (65 percent ) was injected under radiologic control until the local arterial trcr was outlined. A film was taken after which Hypaque was washed away hy injecting a saline solution through the catheter. A local vcnogram was then similarly obtained with the venous catheter in the position utilized for metabolic studies. Metal markers were placed to indicate the site of arterial occlusion.

The heart was excised at the end of the experiment and the area served by the ligated artery was delinc- ated by observation of the surface arterial anatomy of the ventricle and study of the arteriographic findings. The volume of this “ischemic” area was excised and estimated by water displacement and comparison with the displacement value of the whole heart.

Hemodynamic Measurements

In preliminary studies, the hemodynnmic effects of ligation of a small anterolatcrnl branch of the interventricular artery were txamincd. In two studies left ventricular and left atria1 pressures were measured with the use of catheters and Statham P23Gb strain gauges. Aortic velocity was rccordcd by means of a Mills catheter tip electromagnetic velocity probe.]” On two occasions a cuff type flowmeter (Statham) was placed on the main interventricular artery. Ligature of the anterolaternl branch of the intervrn- tricular coronary artcry protluccd no increase in left atria1 pressure and no fall in left ventricular systolic pressure. No major change in aortic flow velocity followed. Similarly ligature of the small antcrolaternl artery had no major effect on overall interventricular arterial hlood flow meter.

On one occasion

as measured by a cuff tyl’e flow-

a 2 mm cuff type flowmeter was

OWEN ET AL.

TABLE I

Details of Experimental Data

Heart* lschemic Lactate/ Free Dog Weight Volume Volume Pyruvate Potas- Fatty 8-hydroxy- Aceto-

no. (lb) Sex (ml) (%I Lactate Pyruvate Ratio Glucose sium Phosphate Acids butyrate acetate

1 80 M 400 8 + + + + + + - - -

2 65 M 310 6 + + + + + + - + - 3 62 M 300 12 + - + 7+ - + - - - 4 66 M 230 2 + - + + ND + - - - 5 64 M 240 6 + + + + + - - - 6 70 M 296 8 + 1 + + + + - - -

7 70 M 350 4 + - + + + + - - + 8 60 F 293 12 + - + + + + - - -

9 62 M 340 3 + + + + + + ND - - 10 75 M 283 10 + - + + + + ND -

11 58 M 257 4 + - + ND + + - N’D ND 12 59 M 306 4 + - + ND + -I- ND ND ND 13 60 M 344 7 + + + ND + + ND - -

14 74 M 425 12 ND ND ND ND + + ND ND ND 15 60 M 280 3 + + + + + + ND - - 16 70 M 400 4 ND ND ND ND + + ND ND ND 17 57 M 2% 3 ND ND ND ND + + ND ND ND

* Specific gravity of heart = 1.5. ND = not done.

placed proximal to the ligature site on the anterolateral branch of the descending coronary artery before tightening the ligature. Flow was shown to fall abruptly to zero levels after tying.

Biochemical Estimations

Pyruvate, acetoacetate, lactate and (Shydroxy- butyrate : About 6 ml of blood was ejected into 6 ml of ice-cold perchloric acid (0.7 M) in a weighed cen- trifuge tube. The tube was immediately shaken, re- weighed and the precipitate centrifuged down at 4C. The supernatant fluid was removed and frozen before enzymatic measurements were made of levels of pyruvate and acetoacetate (within 24 hours) and lactate and 6-hydroxybutyrate (within 6 days). Pyruvate and acetoacetate were successively measured in the same cuvette by modifications of the methods of Gloster and Harris?? and Williamson et al.la Lactate was measured by a modification of the method of Horn and Bn_u-# and 6-hydroxybutyrate by the method of Williamson et all8 Added internal standards for pyruvate and lactate and 6-hydroxybutyrate gave recovery rates of 95 to 100 percent.

Plasma free fatty acids: Five milliliters of blood was taken for extraction. Free fatty acids were measured by the microtitration method of DolezO as modi- fied by Chlouverakis.2l

Plasma potassium and inorganic phosphate : About 4 ml of blood was taken, and the plasma was immediately separated before storage in the frozen state. Both potassium and inorganic phosphate levels were determined on the AutoAnalyser, potassium by flame photometry (Technicon Methodology Manual,

method N-20b) and phosphate by a modification of the method of Fiske and Subbarow (Technicon manual, method N 26). Use of frequent interposition of standards and a laboratory serum pool of known value guarded against instrumental errors.

Plasma glucose : Plasma glucose was measured manually in duplicate by a glucose-oxidase method.2”

Results After the control values were taken at about 10

minute intervals before ligation of the local artery, serial blood samples were taken from the femoral artery, local coronary vein and coronary sinus from the time of ligation for a period ranging from 30 to 150 minutes. Chemical estimates of the substances and metabolites enumerated in the methods section showed that the pattern of metabolic change was comparable in 12 of the 18 dogs. In 1 dog in which there were no positive changes a dual arterial blood supply to the test zone was demonstrated by postmortem arteriograms. In view of the consistency of the results, presentation of data has been focused on individual experiments illustrated in Figures 2 to 6. Table I gives details of all animal experiments together with itemized metabolic changes. In the table, positive change after arterial ligation represents an increased venoarterial difference of the following values for each substance: blood lactate (local coronary venous-arterial level) range, 0.4 to 1.7 mM = 36 to 420 percent of arterial level ; blood

554 The Americen Journel of CARDIOLOGY


Figure. 2. Experiment 4. Lactate, pyruvate and Iactate/pyruvate ratios in arterial, local venous and coronary sinus blood before and after local anterolateral coronary artery occlusion. Coronary sinus blood samples more than 60 minutes after coronary artery occlusion were taken from a polyethylene catheter passed through the coronary sinus catheter to the great coronary vein (see Fig. 1).

Llgatlan 3

l-

i_ -1

TIME in Muten

pyruvate increase, 0.01 to 0.04 mM = 22 to 50 percent of arterial level. Lactate/pyruvate ratio increased between 50 and 450 percent of the control value. Plasma glucose : local coronary venous concentration fell by 10 to 40 mg = 18 to 40 percent of the arterial level. Plasma potassium: local coronary venous concentration exceeded arterial level by 0.3 to 1.2 mEq/liter = 7 to 33 percent of the arterial level. Plasma phosphate: local coronary venous concentration exceeded arterial level by 0.4 to 2.9 mM = 15 to 80 percent of the arterial level. Positive change in IShydroxybutyrate and acetoacetate indicates 0.03 mM difference or greater (local coronary venous- arterial level).

Lactate and pyruvate (Fig. 2): Measurements of the venous blood lactate/pyruvate ratio are generally

Figure 3. Experiment 16. Plasma potassium concentrations in arterial, local venous and coronary sinus blood before and after local anterolateral coronary artery occlusion.

held to be useful in the assessment of tissue anaerobic metabolism.23-25 Figure 2 shows the changes of blood lactate and pyruvate values observed in a typical experiment. In general the resting lactate/ pyruvate ratios in the local vein and the coronary sinus were of the order of 10 to 1 or less.

After ligation, the lactate concentration in the local venous blood increased by more than 100 percent. Therefore, lactate uptake by the heart after ligation changed into marked and continued lactate discharge by the ischemic zone. In most cases, the venous lactate level slowly decreased during the suc- ceeding 90 to 120 minutes but still remained higher than the arterial value.

In the control period there was usually a small level of pyruvate uptake by the heart. After arterial liga-

VOLUMIE 25, MAY 1970 555

OWEN ET AL.

z ::I1 Figure 4. Experiment 16. Plasma phosphate concentrations in arterial,

-30 -20 -10 0 IO 20 30 40 SO a0 70 w 90 100 110 local venous and coronary sinus blood

TIME Ill dnutrr

tion, the local venous concentration of pyruvate

tended to increase and in some experiments exceeded

the arterial level. Therefore, the greatly increased

lactate/pyruvate ratios after ligation of the artery

are largely related to an increased concentration of lactate in the local coronary venous blood.

Plasma potassium (Fig. 3) : In the normal rest-

ing situation,’ the arterial, local coronary vein and

coronary sinus potassium values were similar. After

local coronary arterial ligation, the concentration of

potassium in the local venous blood rose rapidly to

exceed the arterial (and coronary sinus) values by

a mean value of 0.4 k 0.1 mEq/liter (SEM 16 values).

The values remained of this order for 3 to 15 minutes

and then tended to fall towards the base line at 20

to 30 minutes. However, thereafter there was again

a tendency for local venous potassium loss to in-

crease slightly toward the end of the experimental

period. In Figure 3, the fall in local venous con-

centration of potassium at. 20 to 30 minutes was

pronounced, as was the subsequent increase in po-

tassium concentration. In all these experiments, po-

tassium loss was not detected in coronary sinus blood

samples. Plasma inorganic phosphate (Fig. 4): During

the resting period, the arterial local venous and coro-

sol ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ 1 -so -so -40 -30 0 x) 40 so 00 loo Ix) 140

TIME k mblut*s

Figure 5. Plasma glucose concentrations in arterial and local venous blood before and after local anterolateral coronary artery occlusion in experiment 5.

before and after local anterolateral coronary artery occlusion.

nary sinus inorganic phosphate values were similar,

that is there was neither uptake by nor discharge from

the heart. After arterial occlusion, the concentration of

phosphate in the local vein rose by an average of 1

millinormal (mN1, and usually fell within 15 min-

utes to a value of about 0.5 mN in excess of the

arterial value. Subsequent venous values were usually

between 0 and 0.5 mN above the corresponding ar-

terial value.

Plasma glucose (Fig. 5) : In the resting period,

the arteriovenous plasma glucose differences for both

the local vein and the coronary sinus were small, usu-

ally less than 10 mg/lOO ml. The arterial-local ve-

nous difference became much wider after local coro-

nary artery occlusion and remained wide throughout

the experimental period. Thus, the arterial-local venous

difference usually increased by 3 to 4 times after

arterial ligation.

Plasma free fatty acids (Fig. 6) and blood ketones : Throughout the whole experiment there was

little change in arteriovenous difference of free fatty

acids or of ketones. Values in local venous and coro-

nary sinus blood were similar throughout. Figure 6 il-

lustrates an experiment in which a local artery was

< 1000-

=I

I l.igatkm Lipatbll z LigWon

i 710 - 1 1 1

l . ..a-..

z 500 -

.‘. ,,.. . .._ l

ti

‘. a-.._*, . .._ .,.’

.__........_. l ..-.-..

w IS0 - 4:’

I 0-

x

0. ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ 1 -60 -40 -20 0 20 40 60 60 loo Ix) 140 It0 I80

TIM I” mkutis

Figure 6. Experiment 6. Plasma free fatty acid concentrations in arterial local venous and coronary sinus blood before and after local anterolateral artery occlusion. Two subsequent ligations of similar anterolateral branches lying on either side of the local artery failed to change plasma concentrations of free fatty acids in the local vein or coronary sinus blood.

566 The American Journel of CARDIOLOGY


occluded and blood samples taken from a local venous

catheter. Subsequently adjacent arteries were occluded,

also without change in the values for local venous or

coronary sinus blood.

Local venous changes versus coronary sinus changes : It was a striking finding that major meta-

bolic changes observed in the local coronary venous

blood were not associated with similar changes in

the coronary sinus blood. The tip of the coronary sinus

catheter was usually at least 4 cm from the coronary

sinus orifice. On five occasions blood samples were

drawn from the junction of the coronary sinus and

the great coronary vein. On two occasions blood was

taken from the great coronary vein where it was visi-

ble through the anterior thoracotomy (Fig. 1)) the

tip of the catheter being 8 to 10 cm from the orifice of the coronary sinus. On one occasion (Fig. 2)

samples were obtained from a polyethylene catheter

passed through the coronary sinus catheter to the

great cardiac vein. In these experiments insignificant

metabolic changes were found in the coronary sinus

blood during the period when major metabolic changes

were found in local coronary venous blood. Electrocardiographic changes: An elevation of

t,he S-T segment was evident on the epicardial electro-

cardiogram immediately after arterial occlusion. No

arrhythmias were observed.

Discussion

Previous Observations on the Metabolic Sequelae of Coronary Arterial Occlusion

Grayzel et a1.l found a rapid loss of glycogen and accumulation of lactate in the zone of the ligated

artery. Measurement.s of arterio-coronary sinus differ-

ences of lactate showed uptake of lactate by the

heart but lactate discharge after ligation.2J1 Him-

with et a1.2 suggested that uptake of glucose by the

ischemic area could allow production of lactate by

the ischemic zone. Early loss of potassium into the

coronary venous blood was shown by Dennis and

M00re.12 More recently, refined biochemical techniques have

shown both a breakdown of high energy phosphate

compounds in the ischemic zone within minutes after

ligationlO and release of catecholamines.26 The initial

loss of glycogen has been related to activation of

the enzyme phosphorylase. The cellular mechanisms

involved may be initiated by release of catecholamines from the ischemic tissue.%

Appraisal of Present Preparation

To follow the evolution of metabolic changes after coronary arterial ligation, sequential sampling is ad-

vantageous. Analysis of repetitive heart biopsy ma-

terial reveals serial changes in the intrncelluh~r con-

tent of enzymes and metal~olitc~.ln Tisslit trauma

may be minimized if biopsy specimthtls :W small.

Repetitive venous sampling gives rom1~lcn~cntnry in-

formation concerning the rate at which nlctabolitcs and ions enter and leave the ischemic zone. Tissue

values of potassium decrease very little in t.hc first hour after arterial occlusion,” whereas changes in vcn-

ous concentration of potassium (Fig. 3) arc found

much sooner.12*“‘.“’ Venous sampling also avoids pos-

sible tissue trauma after biopsy.

In most previous studies blood was sxmplccl from the coronary sinus or a major venous branch after onset of ischemia.11.1:‘,14.27 9 ,. uch methods suffer from

a double defect. First, lesions affecting a substantial

part of the left ventricle may cause left ventricular

failure with secondary changes superimposed on the

primary metabolic changes in the ischttmic tissue.

During progressive reduction of blood flow in the left main coronary artery in dogs, coronary sinus

lactate levels begin to exceed the arterial levels, simul-

taneously with a rise in left atria1 prcssurc.Zx ,S;rcond,

occlusion of a major coronary artery in dogs is fre-

quently followed by ventricular arrhythmia, which

may influcncc myocardial mctaholism”!‘--:~:~ and limit the time available for studies during sinus rhythm.

The principle of detecting metabolic changes in

the local venous blood leaving an area of cxpcri- mental ischemin has already been referred to by

previous workers. “We However, no systematic com-

parison has been made of the changes in local \‘cnous and coronary sinus blood, nor have 1 he merits of

local venous sampling been specifically assessed.

The particular advantages of th,e prcpamtion described are: (1) The coronary venous catheterization

technique allows repeated sampling of blood from

small veins within the ischemic area. (2 I Thr animals consistently survive in good condition without lethal

arrhythmias or circulatory failure. (3) The amount!

of tissue rendered ischemic is small (mean less than

10 percent of heart volume), and arterial occlusion

produces no major changes in left ventricular func-

tion. Disadvantages are ( 1) Thoracotomy is necessary.

(2) Variation of arterial and venous anatomy some-

times prohibits successful local venous catheterization. (3) The technique of catheterization is not easy. (4) The small size of the venous catheter nccessi-

tates the use of a dilute hcparin solution. t.5) The local venous catheter, although advanced so that, the tip lies in a venule thought to be about 0.5 t,o 1.0 mm in internal diameter, cannot be regarded as sampling entirely representative effluent blood from the ischcl- mic zone. Venous anastomoses, shown by vrnograms,

sometimes form a plexus allowing some sampling of

VOLUME 25, MAY 1970 567

OWEN ET AL.

blood from nonischemic zones. It may be possible to draw blood alongside the catheter in the direction opposite to normal venous flow. (6) It is not known whether sampling influences the degree to which tissue metabolic changes are reflected in local venous blood. (7) The local venous catheter may limit the normal flow of venous blood, although control experiments performed without a local venous catheter indicated that such limitation had not occurred.

Greyhounds were used as the standard experimental animal because the anatomy of the coronary vascu- lature made local venous catheterization less difficult than in mongrels. The use of greyhounds has the disadvantages that they have large hearts3* with thick ventricular walls and also polycythemia (mean hemoglobin 17 g/100 ml in present series).

Blood Flow to Local lschemic Zone

Interpretation of the observed metabolic changes must include consideration of ‘the changes in local blood flow. Ligature of the major artery supplying the local zone results in a precipitous fall to zero of blood flow from that source, as confirmed by use of a small electromagnetic flowmeter of the cuff type. Perfusion of the ischemic area is, therefore, limited to blood flow from collateral sources. Postmortem arteriography suggested that with one exception there were no obvious arterial anastomoses in the ischemic zone. Measurements by other workerss6*ge of collateral blood flow to larger infarcts by clearance of la3Xenon or by a thermocouple have given values of about 30 to 40 percent of the control flow at 30 to 60 minutes after coronary arterial occlusion. However, when the infarction is small, collateral flow may be greater.“’

A valid measurement of blood flow in the ischemic zone would be difficult. to obtain although highly desirable in converting arteriovenous differences to absolute uptake and discharge of metabolites. Flow- meter techniques cannot be used. Measurements of radioisotope tracer washout are open to criticism because of the small size of the ischemic lesion. Flow estimations might be based on the Fick principle, using arteriovenous differences of potassium, for example, and by making serial determinations of the rate of loss of tissue potassium in the ischemic zone. However, even after 1 hour the decrease in tissue potassium is not large enough to be accurately measured.5 Also, collateral blood flow may not be homo- geneous, thus complicating interpretation.

Metabolic Patterns Observed After Arterial Ligation

The alterations in arteriovenous metabolic patterns were increased arteriovenous differences of glucose ; release of lactate, potassium and inorganic phosphate; a decreased arteriovenous difference of py-

ruvate ; and usually no change in arteriovenous differences of free fatty acids and ketone bodies.

Before assessing the significance of arteriovenous difference of various metabolites in terms of tissue metabolism, the influence of blood flow reduction re- quires clarification. Decreased blood flow to an area with normal oxidative metabolism may lead to a corresponding lowering of the venous oxygen satura- tion for the same oxygen uptake (Fick principle). Similarly, the arteriovenous difference of glucose may change merely as a consequence of an increased extraction from the blood but with the same absolute uptake. Normally glucose arteriovenous difference is very small (7.5 mg/lOO ml in the present experiments). However, 30 minutes after ligation the mean arteriovenous difference was 27 mg/lOO ml. Such a difference would be compatible with an unchanged absolute uptake of glucose if blood flow fell to about 28 percent of the control value. If blood flow were reduced even further, say to 10 percent of the control rate, then the observed arteriovenous difference could represent the combined effect of both blood flow reduction and decreased absolute uptake of glucose by the ischemic tissue. Conversely, if blood flow after ligation were greater, for example 50 percent of the control rate, then an increased absolute uptake of glucose by the ischemic tissue would be probable.

Arteriovenous diflerences of free fatty acids, p- hydroxybutyrate and acetoacetate were usually unchanged. Thus, absolute uptake of these substances by the ischemic tissue was reduced by the same fac- tor by which the blood flow was decreased. The unchanged arteriovenous uptake of free fatty acids and ketones contrasts with the increased arteriovenous difference of glucose and is compatible with a shift from lipid to carbohydrate metabolism in the ischemic zone.38

The peak discharge 04 lactate in.to the local vein was about 1.0 mM/liter and occurred between 8 and 42 minutes after ligation. Lactate discharged could be derived either from tissue glycogen or from circulating glucose. Wollenberger and KrausesO have stressed the role of glycogen breakdown in the early ischemic situation, but utilization of circulating glucose for lactate production must be considered since stores of glycogen are limited. In our experiments, the mean arteriovenous glucose difference at the time of maximal lactate discharge was about 20 mg/lOO ml or 1.1 mM/liter, which would produce a lactate concentration of 2.2 mM/liter if all the glucose uptake were converted to lactate. A comparison of this expected lactate value with the observed peak discharge of 1.0 mM/liter suggests that at the most only about half of the glucose uptake could be ac- counted for by lactate production. If the glucose up-

568 The American Journal of CARDIOLOGY

take is greater than expected from the observed

lactate discharge, the possibility of aerobic respiration

is raised. In this connection, Jennings and Wartman4”

have suggested that in the early stages experimental

myocardial infarction may consist of a mixture of

dead, living and injured cells.

In the case of pyruvate, mean arteriovenous differ-

ence after ligation decreased, and local venous values

sometimes exceeded arterial levels, thus suggesting

increased intracellular pyruvate concentration of py-

ruvate. An. outstanding feature of the m,etabolic changes

in the blood draining the ischemic area was the increased K+ concentration. This finding was virtually

constant. The loss of K+ previously observed in

tissue and coronary sinus studies after experimental

arterial ligation”*6 has been the subject of much

speculation as to its possible causal role in cardiac

arrhythmias after acute myocardial infarction in

man. However, cardiac arrhythmias in our prepara-

t,ion were strikingly absent.4g

Another constant finding was the increase in inorganic phosphate in the 1oca.l venous blood. The

pattern of increase of local venous inorganic phosphate levels after arterial occlusion differed from

that of potassium, being initially very much greater

(two to five times in the first 20 minutes after ligation)

but at a later stage the difference was obviously less.

These data are given greater emphasis because esti-

mations of phosphate and potassium levels were made

from the same blood samples, thereby normalizing

them with respect to blood flow.

Compounds containing high energy phosphate

bonds, such as adenosine triphosphate and phospho-

creatine, break down within minutes of the production

of experimental myocardial infarction.lO Increased

levels of venous inorganic phosphate are presumably

secondary to increased levels of intracellular free

inorganic phosphate, derived from breakdown of

phosphorylated compounds. Therefore, the loss of in-

organic phosphate from acutely ischemic heart mus-

cle may need to be considered an additional index

of metabolic damage. Arteriovenous values of free fatty acids were not


much altered after ligation. Uptake of free fatty

acids by ischemic heart tissue is known to occur.4z

However, once taken up free fatty acids are not

utilized to produce energy except by aerobic systems.

In ischemic heart tissue, there is increased incorpor-

ation of labeled free fatty acid into tissue triglyc-

eride.4” Thus, as suggested by Scheurr and Brach-

feld,42 such a sequence of events may be the basis of

the observed histologic increase of sudanophilic lipid material in or around’ the infarct area.“”

Changes in the Local Vein with Negative Changes in the Coronary Sinus

Various studies of metabolic changes detected in

coronary sinus blood in patients with coronary heart

disease, both at, rest and on exercise, have been de-

scribed.444s Herman et a1.47 have advanced the in-

terpretation of coronary sinus metabolic changes by

selective sampling of venous blood draining from

various major cardiac areas. Good correlation was

found between localized coronary arterial disease, as

shown by coronary arteriography, and regional differ-

ences in lactate discharge. An extension of this prin-

ciple is seen in our results. Even in the presence of

marked metabolic changes in the local coronary vein,

no changes were found in samples obtained high in

the great coronary vein near where the latter starts

to accompany the anterior descending coronary ar-

tery (Fig. 1 and 2). The clinical implications of our

findings are that negative metabolic changes in blood

samples obtained by presently available methods

from the coronary venous system of patients with

ischemic heart disease in no way exclude gross local

venous metabolic changes.

Acknowledgments

We wish to thank Professor .J. P. Shillingford and Professor I. D. P. Wootton for their encouragement and support, We are indebted to Miss Susan Bailey, Mr. Peter Burgess, Miss *Jean Powell and also Mr.

J. Robson and Mr. M. Cussen of the Department of Experimental Surgery, the Royal Postgraduate Medical School, London, for technical assistance. We also thank Dr. K. R. L. Mansford for advice.

References

Grayzel DM, Tennant R, Stringer SW, et al: Observa- tions on coronary occlusion. III. Chemical and histologic changes. Proc Sot Exp Biol bled 31837-838. 1933 Himwich HE, Goldfarb W, Nahum LH: Changes of the carbohydrate metabolism of the heart following coronary occlusion. Amer J Physiol 109:403-408, 1934 Tennrnt R, Grayzel DM, Sutherland FA, et al: Studies on experimental coronary occlusion. Chemical and an- atomical changes in the myocardium after coronary ligation. Amer Heart J 12:168-173, 1936

Hastings AB, Blumgart HL, Lowry OH, et al: Chemical changes in the heart following experimental temporary coronary occlusion. Trans Ass Amer Physicians 54:237-243, 1939 Jennings RB, Grout JR, Smetters GW: Studies on the localization of potassium in early myocardial ischemic injury. Arch Path (Chicago) 63:58&592, 1957 Cummings JR: Electmlyte changes in heart tissue and coronary arterial and venous plasma following coronary occlusion. Circ Res 8:86%870, 1960

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OWEN ET AL.

7.

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570 The American Journal of CARDIOLOQY

comparison between metabolic changes in local venous and coronary sinus blood after acute...

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