adenosine diphosphate induced platelet aggregation in myocardial infarction and ischemic heart...

Atherosclerosis, 17 (1973) 107-120 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

107

ADENOSINE DIPHOSPHATE INDUCED PLATELET AGGREGATION IN MYOCARDIAL INFARCTION AND ISCHEMIC HEART DISEASE

F. DREYFUSS AND J. ZAHAVI

University Department of Medicine B, Tel Aviv University Medical School, and Ichilov Municipal Government Hospital, Tel Aviv (Israel)

(Received May 24th, 1972)

SUMMARY

Adenosine diphosphate (ADP) induced platelet aggregation has been studied by a nephelometric method in 66 men with myocardial infarction (MI). Most of them were followed for several months and some for up to 2 years. They were compared to 20 normal controls.

With ADP 5.9 y/ml, curves of normal controls were monophasic with pronounced disaggregation. Day to day variations appeared occasionally in the rate of aggregation.

Within the first 3 days of the MI, in 80 % of the patients, the curves were monophasic or biphasic pathological showing greater extent of aggregation and lack of or minimal disaggregation. This abnormal pattern was noted in most patients for several months and in some for up to 2 years. Three peaks in abnormal aggregation and disaggregation after the acute MI were found: during the 4th-6th day, the IOth-16th day and the day of discharge from hospital. This latter observation represents most probably a psychological stress phenomenon. Consequently platelets of MI patients are more responsive to added ADP. The abnormal pattern was more pronounced in patients with recurrent Ml, severe congestive heart failure or pulmonary embolism. Yet neither diabetes nor hypertension had apparently any similar effect. No correlation was found between the age of normals or patients and any one of the calculated parameters. The increased responsiveness of platelets to ADP in MI patients indicates disturbed hemostasis in these patients. It might also play a role in the pathogenesis of atherosclerosis.

Key words: Atherosclerosis - Ischemic (coronary) heart disease - Myocardial infarction - PlateIet aggregation

108 F. DREYFUSS, J. ZAHAVI

INTRODUCTION

Platelet aggregation (PA) studied in vitro by the responsiveness of titrated platelet rich plasma to adenosine diphosphate (ADP) or examined microscopically, has been found to be abnormal in myocardial infarction (MI)1*2”*3, but with much overlap with controlst. Others have not confirmed the former observation&s. We have recently described an abnormal pattern of ADP induced PA in MI with little overlap with normal controlss. Regarding increased PA as a potential indicator and presumable component of a thrombogenic state, it seemed important to observe PA behaviour in MI patients for a time period extending beyond the acute phase.

PATIENTS

Sixty six male patients, 34-91 years of age (mean 60.9) were studied at various time intervals after the acute MI (Table 1). In 47 patients, PA tests were done in the first 6-72 hours: 14 out of the 47 were retested once every 24 days during the first month. Six patients out of the 47 were studied for l-24 months; in them, PA tests were carried out once every month for the first 3 months, thereafter, once in 3 months. In addition to the above 47, another 10 patients were tested 6 months and an addition- al 9 for 12 months after an episode of MI.

The clinical diagnosis of MI was confirmed by electrocardiographic evidence, increased serum glutamic oxaloacetic transaminase and, in two cases by autopsy. The patients received opiates, antibiotics, digitalis and oral diuretics when indicated, but no anticoagulants or antiaggregating drugs such as aspirin, clofibrate or dipyri- damol. Patients were compared with 20 healthy men aged 34-65 years (mean 48.9), 11 of whom were age matched with 11 MI patients. In most of the patients and the normal controls, serum uric acid and plasma fibrinogen were determined concomitantly with the PA.

TABLE 1

ADENOSINE DIPHOSPHATE INDUCED PLATELET AGGREGATION TESTS IN MYOCARDIAL INFARCTION (MI) PATIENTS AT VARIOUS TIME INTERVALS AFTER THE MI

Total Recurrent Hyper- MI tensive

vascular disease

No. of MI Patients 66 11 4

No. of tests with ADP 5.9 y/ml 182

No. of tests with ADP 0.59 y/ml 160

Diabetes After infarction mellitus

6-72 3-28 I-6 6-12 13-24 hours days months months months

23 47 14 17 13 6

47 80 30 16 9

44 67 28 15 6

ADENOSINE DIPHOSPHATE INDUCED PLATELET AGGREGATION 109

MATERIAL AND METHODS

The fragiligraph model D2 was used *. PA was studied by a nephelometric methods. The tests were run for 60 minutes in fasting titrated platelet rich plasma (PRP) at a constant platelet concentration of 250,000 per mms with buffered ADP (in tris-HCl, 0.01 M, pH 7.4) both at a concentration of 5.9 y/ml (13.8 x lo-sM) and 0.59 y/ml (1.38 x lo-s&I). Seven parameters were computed from the recorded curves namely :

(1) SA =

(2) PR = (3) TInax =

(4) D msx =

(5) &lax = (6) ~960 =

(7) z =

spontaneous aggregation : (a) extent in ‘A,

(b) rate = extent in %

time needed to reach maximum extent in min ’ primary rise in optical density (O.D.) in % (extent of B in Fig. 1). time needed to reach maximum aggregation in minutes (from A to C in Fig. 1). duration of maximum aggregation in minutes (from C to D in Fig. 1). extent of maximum aggregation in % (extent of C in Fig. 1). extent of aggregation at 60 minutes. aggregation time in seconds.

The extent was calculated from the formula:

O.D. of (PRP 1.6 ml + 0.1 ml BSS) - O.D. of (PRP 1.6 ml + 0.1 ml ADP) O.D. of (PRP 1.6 ml + 0.1 ml BSS) - O.D. of (PPP 1.6 ml + 0.1 ml BSS)

(in which BSS = buffered saline solution), and t from:

z = - [dt/dln (T- Too)],

where T is the light transmission at time t and Tco the light transmission at t -+ co.

RESULTS

Normal curves When ADP, 5.9 y/ml, was added to titrated PRP of normals, the recorded

curves were monophasic with three distinct regions (Fig. 1): a primary rise (PR) in optical density; aggregation of blood platelets; pronounced disaggregation of platelets to mean level of 48.7 % of Emax (S.D. = 14.32) (Table 2A). Spontaneous aggregation (SA) was recorded only in a few controls in whom its extent did not exceed 8 %. At an ADP concentration of 0.59 y/ml, PR appeared in all normals but PA was minimal and was recorded only in 12 out of 20; the curves were all monophasic normal (Table 2B).

* Elron Electronic Industries Ltd. Haifa, Israel.

TAB

LE

2A

AD

EN

OSI

NE

D

IPH

OSP

HA

TE

IN

DU

CE

D

PLA

TE

LET

A

GG

RE

GA

TIO

N

IN

NO

RM

AL

CO

NT

RO

LS

AN

D

MY

OC

AR

DL~

L IN

FA

RC

~ON

(M

I)

PAT

IEN

TS

WIT

HIN

T

HE

F

IRST

6-

72

HO

UR

S

AF

TE

R

TH

E

MI

= 0

Nor

mal

con

trol

s M

Ipat

ient

s

No.

of p

atie

nts

AD

P 5.

9 yJ

ml

S.D

. N

o. o

fpat

ient

s A

DP

5.9

yJm

l S.

D.

P

PR

20

-7.3

5 f

5.37

47

-1

.39

f 2.

38

< 0.

001

T max

20

4.

15

. f

1.48

47

7.

41

f 2.

87

< 0.

001

&X

X

20

2.42

f

1.38

47

14

.69

f 10

.91

< 0.

001

E *a

x 20

61

.03

i 11

.4

47

75.2

f

9.09

<

0.00

1 Ea

o 20

29

.72

f 14

.32

47

64.1

f

13.2

<

0.00

1

PR =

prim

ary

rise

in o

ptic

al d

ensi

ty

in %

; T

mlL

x = t

ime

need

ed

to r

each

max

imum

ag

greg

atio

n in

min

utes

; D

ma,

=

dura

tion

of

max

imum

ag

greg

atio

n in

min

utes

; E

max

=

exte

nt

of m

axim

um

aggr

egat

ion

in

‘%; E

GO

=

exte

nt

of a

ggre

gatio

n at

60

min

utes

in

‘A

. Pl

atel

et

conc

entra

tion

250,

000/

mm

3.

TAB

LE

2B

AD

EN

OSI

NE

D

IPH

OSP

HA

TE

IN

DU

CE

D

PLA

TE

LET

A

GG

RE

GA

TIO

N

IN

NO

RM

AL

CO

NT

RO

LS

AN

D

MY

OC

AR

DIA

L IN

FA

RC

TIO

N

(MI)

PA

TIE

NT

S W

ITH

IN

TH

E

FIR

ST

6-72

H

OU

RS

A

FT

ER

T

HE

M

I

Nor

mal

con

trol

s M

Ipat

ient

s

No.

of

AD

P S.

D.

subg

roup

A

subg

roup

B

patie

nts

0.59

y/m

l -

No.

of

AD

P S.

D.

P N

o. o

f A

DP

S.D

. P

patie

nts

0.59

y/m

l pa

tient

s 0.

59 y

/ml

P

PR

20

-3.1

2 f

2.79

28

1.

11

+ 2.

06

0.00

4 15

0.

036

* 0.

009

< 0.

001

F!

T max

12

1.

67

f 0.

75

28

2.49

f

1.34

0.

028

15

9.45

f

5.45

<

0.00

1 “c

(I’W

“8

D

max

12

1.

63

& 1

.13

28

3.23

+

1.68

0.

003

15

24.6

6 &

14.

46

< 0.

001

.Q

E nl

BX

12

13

.52

& 5

.82

28

18.5

5 +C

5.69

0.

008

15

57.4

8 f

16.3

4 <

0.00

1 g

J-G

o 12

4.

09

+ 3.

47

28

7.17

f

6.65

0.

073

15

53.3

6 i

18.0

1 <

0.00

1 (W

9 f;

Lege

nd

as i

n Ta

ble

2A.


Fig. 1. Curves of 1.6 ml platelet rich plasma of (A) normal control (monophasic normal) and (B, C) 2 patients with acute myocardial infarction. B: monophasic pathological; C: curve with biphasic tendency. Distance from number to number 120 set, direction up indicates fall in optical density. At A, ADP 5.9 y/ml was added. Platelet concentration 250,OOO/mms.

Curves of MIpatients (jirst 6-72 hours) In most MI patients the pattern was abnormal. Spontaneous aggregation

appeared in 95% of the patients with a mean extent of 14% and a mean rate of 4.3 %/min.; it was more pronounced than in normals. In 12 patients it resulted in a PA curve (Fig. 2) with a mean extent of 30.2% and a mean rate of 7.2 %/min. When ADP 5.9 y/ml was added, the curves were of two types: (a) monophasic pathological (exponential-like shape) in 37 out of 47 patients (Fig. 1). The primary rise in optical density was absent in 30 of these patients and minimal in 7. Tmax was longer whilst D,,, and Emax were significantly greater than in normals; the final disaggregation (Eso) was absent or minimal (Fig. IB) (Table 2A). (b) Biphasic pathological curves or curves with a biphasic tendency (Fig. 1C). These curves appeared in 2 patients, in whom the final disaggregation was also minimal. As to the remaining 8 patients, in 6 the curves were monophasic with rate and extent of aggregation at the upper limit of normal but with no PR in O.D. - pointing to a pathological trend; only in 2 out of the 47, were the curves monophasic normal.


Fig. 2. Spontaneous aggregation of 1.6 ml platelet rich plasma of an acute myocardial infarction patient. Distance from number to number 120 sec. Direction up indicates fall in optical density. Platelet concentration 250,OOOjmms.

PA curves at an ADP concentration of 0.59 y/ml were recorded only in 43 out of the244 patients studied. The curves could be divided into two subgroups (Table 2B): subgroup A - monophasic (16 patients) and curves with biphasic tendency (12 patients) with rate and extent approaching the range of normal but significantly different in all parameters except EGO and Tmax (Table 2B). Subgroup B - monophasic pathological (3 patients) and biphasic pathological without disaggregation (12patients), altogether 35 y0 of the patients; the curves were similar to the PA curves obtained with ADP 5.9 y/ml and significantly abnormal (Table 2B).

MI patients (3-28 days) In 14 MI patients with ADP 5.9 y/ml, there was increasing abnormality in the

curves during the 4th-6th day; it was noted in parameters Dmax, Emax and Es0 (Fig. 3); however, only the variations in D mitx and EGO showed statistical significance (P = 0.05 - Wilcoxon matched pair tests - non parametric). Thereafter during the lOth-16th days there was a second period of increased abnormality, though significant only for Dmax (Fig. 3). On the days following the 17th, there was no change in the curves, except on the day of discharge from the hospital when there was a clear increase in Lax (P = 0.002) and EP,O (P = 0.004). Furthermore, in 4 patients whose PA curves had been normal or at the upper limit of normal in the first 3 days of the acute event, on the following days (4th-6th day) all became definitely abnormal in all parameters. This might point to a plasma factor appearing during the acute MI and causing abnormal PA curves. At any rate, during the entire course of hospitalization, the curves were abnormal in 12 out of the 14 patients with significant changes compared to normals except in PR. The PR was absent only in the first 6 days, thereafter it was within the normal range. Spontaneous aggregation was observed during the entire course of hospitalization in most patients, the highest values being obtained during the first 6 days.

Of the 14 patients studied, one died after 18 days; in 11 the PA curves remained abnormal when the patients were discharged from hospital, yet 2 who suffered from a non-penetrating MI, had had abnormal curves on admission, but when discharged after 18 days, the PA curves were at the upper limit of normal.

CXTLAV OF AGGIICGAT~W A7 60 m.wrEs I

5 ,

.

5 (D Q ro .a 24

Fig. 3. Follow-up study of three parameters (ILax, Emax, EBO) of aggregation curves of 14 myocardial infarction patients compared with 20 normal controls. The rectangles represent standard deviation. Platelet concentration 250,000/mm3.

114 F. DREYFUSS, .I. ZAHAVI

The two periods of increasing abnormality were noted also in parameter z (aggregation time) (Fig. 4). The more pathological the curves, the greater was r; the extent of aggregation at z was also greater, and the aggregates coarser. Briefly, by computing z we express both the rate and extent of aggregation at a fixed point of the exponential curve.

With ADP 0.59 y/ml, in subgroup B (6 patients) the two periods of increased abnormality in the curves, i.e. during the 4th-6th, and lOth-16th day, were noted just the same as with ADP 5.9 y/ml (P < 0.001). As for subgroup A (7 patients) the curves were within the normal range for PR, Emax, &O and significantly different in D,,,.

MZpatients -follow-up studies Patients studied up to 2 years after the MI at different time intervals showed

abnormal curves with ADP 5.9 y/ml (Table 3), most of them exhibiting a tendency to biphasic shape. This was noted in 13 out of 17 patients studied for l-6 months, in 12 out of 13 studied from 6-12 months and in 5 out of 6 patients studied from 13-24 months. Only in the remaining 6 out of the 36 MI patients, were the curves at the upper limit of normal.

In general, in the more acutely ill patients with pulmonary embolism or severe congestive heart failure, the abnormality in the curves was more pronounced compared to other MI patients. In patients running a moderate to mild course, no direct relationship was observed between changes in abnormality of the curves and the fluctuations in the clinical course. In 2 patients with cardiogenic shock, PA was decreased reaching subnormal levels during the collapse; yet the curves became abnormal after 24 hours, a behaviour similar to the one observed by O’Brien et al. on the day of major surgery and the one following it’.

Recurrent myocardial infarction and PA The abnormality of PA curves was more pronounced in patients with recurrent

MI compared to those who had their first infarct. It persisted in most of these patients

s rp 9 i0 2i ib DGS

Fig. 4. Follow-up study of aggregation time of exponential curves of 14 myocardial infarction patients. Note the increasing abnormality of the curves during the lOth-16th day and on the day of discharge from hospital. Platelet concentration 25O,OOO/mm3.

TABL

E 3A

%

FO

LLO

W-U

P ST

UD

Y O

F A

DEN

OSI

NE

DlP

HO

SPH

ATE

IN

DU

CED

PL

ATE

LET

AG

GR

EGA

TIO

N

IN

MYO

CA

RD

IAL

INFA

RC

TIO

N

PATI

ENTS

8

AD

P 5.

9 y]

ml

2 u l-

6 m

onth

s 13

pat

ient

s 7-

12

mon

ths

12 p

atie

nts

13-2

4 m

onth

s 5

patie

nts

g g m

ean

S.D

. P

mea

n S.

D.

P m

ean

S.D

. P

%

$ PR

2.

83

2.53

<

0.00

1 2.

17

2.55

<

0.00

1 2.

42

2.73

0.

016

Fd

T m

ax

6.34

2.

18

0.01

9 5.

35

1.10

0.

007

6.04

2.

79

0.00

3 2

DIl

la*

22.1

3 16

.34

< 0.

001

15.6

8 11

.09

< 0.

001

31.8

6 16

.47

< 0.

001

El%

U

78.1

3 9.

85

< 0.

001

74.9

6 7.

98

< 0.

001

69.9

5 7.

27

0.03

5 z

EGO

68

.77

13.8

6 <

0.00

1 63

.65

8.89

<

0.00

1 66

.45

9.45

<

0.00

1 G

u F

Lege

nd a

s in

Tab

le 2

A.

z P TA

BLE

3B

3 * FO

LLO

W-U

P ST

UD

Y O

F A

DEN

OSI

NE

DIP

HO

SPH

ATE

IN

DU

CED

PL

ATE

LET

AG

GR

EGA

TIO

N

IN

MYO

CA

RD

IAL

INFA

RC

TIO

N

PATI

ENTS

8 !z

AD

P 0.

59 y

/ml

$ I-

6 m

onth

s 17

patie

nts

t!

subg

roup

A

12

pat

ient

s su

bgro

up

B 5

pat

ient

s 8

mea

n S.

D.

P m

ean

S.D

. P

PR

3.42

2.

93

NS

1.74

2.

63

0.11

5 (N

S)

TlU

,X

1.7

1.27

N

S 6.

36

1.23

<

0.00

1 D

IUX

3.

86

1.81

<

0.00

1 22

.93

17.0

8 <

0.00

1 E

UW

LX

14.4

9 7.

98

NS

62.4

1 17

.65

< 0.

001

Eso

4.92

5.

6 N

S 57

.6

18.5

1 <

0.00

1

Lege

nd a

s in

Tab

le 2

A.

TABL

E 3C

FOLL

OW

-UP

STU

DY

OF

AD

ENO

SIN

E D

IPH

OSP

HA

TE

IND

UC

ED

PLA

TELE

T A

GG

REG

ATI

ON

IN

M

YOC

AR

DIA

L IN

FAR

CTl

ON

PA

TBN

TS

AD

P 0.

59 y

/ml

7-12

mon

ths

II p

atie

nts

13-2

4 m

onth

s 6

patie

nts

subg

roup

A 7

pat

ient

s su

bgro

up B

4 p

atie

nts

subg

roup

B 2

pat

ient

s

mea

n S.

D.

P m

ean

S.D

. P

mea

n S.

D.

P

PR

3.24

3.

11

NS

2.79

22

.79

NS

0 0

< 0.

001

T m

lLx

2.14

0.

82

NS

5.6

0.47

0.

001

6 3.

6 <

0.00

1 D

msx

4.

25

1.82

<

0.00

1 20

.3

18.3

0.

01

24.5

18

.2

< 0.

001

EIl

l,X

11.0

6 5.

07

0.18

4 49

.07

8.99

0.

001

47.4

5 24

.7

< 0.

001

(NW

E

so

7.34

2.

68

0.02

5 36

16

.3

0.00

1 40

.9

18.8

1 <

0.00

1

Lege

nd a

s in

Tab

le 2

A.


for many months. Curves were usually monophasic pathological with ADP 5.9 y/ml and biphasic pathological with ADP 0.59 y/ml. The clinical course was also more severe in these patients.

Diabetes and hypertension No direct relationship was observed between diabetes mellitus and/or hyper-

tensive vascular disease and the abnormality of the curves as long as the clinical course was not complicated by severe congestive heart failure and/or pulmonary embolism.

Serum uric acid, plasma,fibrinogen and PA, and ESR No direct relationship was observed between the levels of serum uric acid,

plasma fibrinogen and the fluctuations in the abnormality of the curves. The mean serum uric acid level was 4.94 mg %; it was above 5.5 mg % in 12 out of 47 patients. The mean plasma fibrinogen was 367 mg%, it exceeded 400 mg% in 6 out of 14 patients. Only in 2 patients was plasma fibrinogen elevated and were PA curves distinctly abnormal at the same time. The ESR was elevated as usual in the first 6 days; in those patients in whom it was particularly high, the curves were more abnormal. On the other hand, during the 2nd period of increased PA abnormality (IOth-16th day) ESR was usually only slightly elevated.

DISCUSSION

Previous studies of PA have shown that the outcome of PA tests depends on various factors such as platelet concentration, temperature, concentration of aggregat- ing agent, divalent cation concentration (calcium and magnesium), and rate of stirringsb+le. Furthermore, day to day differences have been noted in normal indivi- dualsilJ2. Finally samples from the same patients under mental stress, prior to surgical operation, or after exercise show marked changes when tested immediately and one hour after blood withdrawal is. To minimize these factors, we have standard- ized our method using always the same conditions with regard to fixed platelet concentration (250,000 per mms) and ADP concentration. In addition, we have analysed mathematically and statistically several parameters of aggregation and disaggregation curves and have shown the following: (a) very good correlation exists between Tmax, E m&x, Eao and between D,,, and Eso, both in normals and patients. (b) Day to day variations in the PA of normals were sometimes noted in the extent of maximum aggregation, Emax not exceeding 8%. The same change appeared when the same sample was tested repeatedly on the same day, up to 5 hours. Yet variations in the other parameters (TmaX, ESO, Dmax), were minimal. (c) When using parameters PR, Dmax and Eao as an index of normality of the curves, only 3 out of the 47 MI patients showed overlap with normal controls. (d) No correlation was found between each one of the parameters and the age of normal subjects or patients.

We consequently believe that our method is reliable, semiquantitative and repro-


ducible. It certainly measures the response of platelets to added ADP. It has been stated14 that the apparently irreversible aggregation is an artifact of the in vitro test system. We do not entirely agree with this interpretation for the following reasons: using the above standardization, we have found significant disaggregation of platelets in normal controls by repeated tests at various times after blood withdrawal, whilst in patients disaggregation was minimal or absent; platelet aggregates in normals were fine and easily separable, whereas in most patients they were large, coarse and unseparable; after improvement of the clinical condition, some patients who previous- ly had shown minimal disaggregation, now exhibited significant disaggregation; with very high concentrations of ADP, 59 y/ml and above, disaggregation did not appear in normal controls. Consequently we would rather consider ADP induced PA as a model of in vim behaviour.

MI patients differed from normals during the first 3 days in several parameters: they presented clear cut spontaneous aggregation (SA) with rate and extent significantly greater than in normals. This was not the result of plasma stirring, low temperature, low citrate concentration, high platelet count or various other causes as cited by Haanen and Holdrinetab since it was noted with fresh plasma at 37°C with a citrate concentration of 3.8 ‘A, and platelet count of 250,000 per mm3 at a constant stirring rate. Our results do not confirm the observation of O’Brien et al. who found the same extent of SA in normals and abnormals l; this is probably due to a difference in methods. In addition, PA of MI patients differed from the one of normals in the following respects: lack or minimal primary rise in O.D., most probably the result of platelet contractionls; time needed to reach maximum aggregation and maximal extent (TmsX and E,,d greater than in controls though with some overlap; duration of maximum aggregation (Dmax) and final disaggregation, significantly greater and with minimum overlap with controls. Our results are in accordance with those obtained by O’Brien, Breddin and Ardlie i,saJ, but they are more specific and quantitative and in contrast to those who did not find such difference&s.

Aggregation time z expressing accurately by one figure both the rate and extent of the PA, facilitates comparison of one curve with another. This parameter is constant and well defined. However, we were unable to express normal curves by -c since they are a combination of three exponentials. We also could not confirm the results of Holdrinet et al. of logarithmic scatter of both the aggregation and disaggregation curves of normalsi6.

The increasing abnormality in the PA curves on the 4th-6th day and on the lOth-16th respectively represents an important aspect of disturbed hemostasisr’. It might be due to plasma factors released from the damaged myocardium or vessel walls such as plasma catecholaminesls or to the platelets’ membrane being more responsive to ADP. The first phase of increased PA (4th-6th day) might occasionally be due to pericarditis of MI. We have shown such increased PA in acute benign pericarditisl5. As for the increased PA on the IOth-16th day, this might be one of the contributory causes of thromboembolic complications during that periodis. Our results during this period parallel those of Emmons and Mitchell who observed in-


creased PA on the 10th day after surgical operations20. The increased PA and the significant spontaneous aggregation in MI are most probably the result of plasma factors such as catecholamines, beta lipoproteins and fatty acids which were found increased in MIisg21*22. All these substances are able to induce and enhance PAs,sp 23-25. The possible role however, of other unknown plasma factors or increased responsiveness of platelets to ADP cannot be ruled out.

Abnormal platelet aggregation does not occur only in MI. We have found increased PA in thromboembolic diseases, cerebrovascular accidents (CVA) and acute infectionsae. Yet in infections the curves returned to normal some time after their subsidence. In CVA and thromboembolic diseases the pattern of PA was different and the changes were less pronounced than in MI. Other authors found increased PA and platelet adhesiveness in ischemic heart disease, peripheral vascular disease, acute infections, venous thrombosis, pulmonary embolism, after oral contraceptives and after surgical operations2@-32. The PA test used by us may serve as a useful guide in the assessment of drugs which inhibit PA. It might also be of help in differentiating chest pains arising from coronary insufficiency or due to other causes from the one due to MI.

The abnormal pattern of ADP induced PA in ischemic heart disease patients, present for many months and even years after the MI, and more pronounced in patients with recurrent MI, points to disturbed hemostasis in these patients. It might explain to some extent their increased tendency to thrombosis and represent a contributory factor in the pathogenesis of atherosclerosisl4Js.

ACKNOWLEDGEMENTS

We acknowledge gratefully the financial support of this work by grants given by Mr. Morris Nelkin of Houston, Texas, and Mr. Raphael Wormser of Bnei Brak, Israel. We also thank Dr. M. Brown, Statistician, Computor Unit of Tel Aviv Univer- sity, for his help.

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