the localization of coronary artery stenoses by 12 lead ecg response to graded exercise test:...

The localization of coronary artery stenoses by 12 lead ECG response to graded exercise test: Support for intercoronary steal

Duncan Robertson, M.B., B.S., F.R.C.P.(C), M.R.C.P.(U.K.) William J. Kostuk, M.D., F.R.C.P.(C). Suraj P. Ahuja, M.B., B.S., F.R.C,P.(C)., F.A.C.P. London, Ontario, Canada

There is general agreement tha t the incidence and degree of postexercise ST-segment depression in the electrocardiogram (ECG) correlates directly with the number of significantly diseased coronary arteries. 1 False-negative ECG stress tests may be frequently accounted for by inadequate exercise stress, conveniently measured by the patient's heart rate response, or by minor and hemodynamically insignificant lesions in the coronary arteries. Other possible causes for a false-negative stress test may be (1) failure to use 12 ECG leads after exercise, since the ischemic ST-segment change could occur in leads not recorded, and (2) good collateral flow to the territories supplied by a severely stenosed vessel. Some authors have concluded that there is no correlation between the presence of collaterals and ECG changes, 1 3 ventricular dysfunction, 3.~ or physical work capacity2

The availability of an ECG system which permits the rapid recording of a 12 lead ECG following exercise has permitted us to correlate the localization of coronary artery stenoses and the presence of intercoronary collaterals with the localization of ischemic change on the 12 lead ECG.

The data of all patients who had been subjected to graded exercise testing and cardiac catheterization in our laboratory in the period

From the Cardiac Investigation Unit, University Hospital, London, Ontario, Canada.

Dr. Robertson was supported by a Fellowship Grant from the Ontario Heart Foundation.

Received for publication March 3. 1975,

Reprint requests: Dr. S. P. Ahuja, Cardiac Investigation Unit. Univer- sity Hospital, 339 Windermere Rd., London. Ontario. Canada.

from March, 1973, to December, 1974, were reviewed. Thirty-nine patients were found to have unequivocally abnormal exercise stress tests and abnormal coronary arteriograms. Three patients were excluded from the total group because of coexisting valvular heart disease; however, no patient with coronary ar tery disease alone was excluded.

Method

Graded exercise testing was performed as part of cardiologic evaluation of patients suspected of having ischemic heart disease. The patients were exercised on a Quintron treadmill with elevation of the speed and incline at 3 minute intervals. Exercise was continued until (1) the patient 's pulse rate reached 90 per cent of the predicted maximal heart rate, (2) fatigue, chest pain, or dyspnea necessitated discontinuing the test, or (3) ischemic ST changes or frequent PVC's occurred. A physician was in at tendance at all times and a DC defibrillator and resuscitation equiPment were at hand. A 12 lead ECG was recorded before exercise, immediately after exercise, and at 2, 4, 6, 8, and 10 minutes after exercise. The ECG leads were recorded by a semiautomatic system (Mar- quettel that permitted simultaneous inscription of three leads at a time each of 2.5 seconds' duration. Sets of simultaneous leads were I, II, III, aVL, aVR, aVe, V1 to V3, and V4 to V6.

Continuous oscilloscopic display of Leads V4 to u was observed during exercise, and at the termination of each level of exercise an ECG recording of these leads was made. Before and after exercise the blood pressure was recorded and the heart auscultated. The ECG equipment used

April, 1976, Vol. 91, No. 4, pp. 437-444 Amer ican Heart Journa l 437

Robertson, Kostuk, and Ahuja

Tsble I. G r o u p s 1A to 1D*

Treadmil l exercise stress test

Group

1A

Age Patient (yr.)

F. E.M. 47 W. C. H- 64 D. W. C, 47

G.P. 46 R. A.H. 64 J. J.C. 57

W. V.R. 45 R.T. 48

IB B.E.B. 39 W.H.M. 45

1C J . W . R . 55 G. K.M. 42

I H

X

Heart rate/ min.

90% m a x .

pre- A chiev- Sex dicted ed

M 177 110 M 165 130 M 170 160

M 177 125 M 165 140 M 170 131

M 179 130 M 179 119 M 186 175 M 179 158 M 171 130 M 180 162

M 169 112 M 177 120 M 179 165 M 161 130

X

ST-segment changes

I I I A Va A VL A V~ V, V.,_ V~ V, V~, 1~

X X X X X X X

X

X X

X X X

F.H. 58 X X J .P .B . 47 X X

1D J.L. 45 X X X X E.W. 69 X X X

X X X

X X X

X X X X X X X

X X X X X X X

X X X X )

X X :~

*Group 1, patients with left coronary disease with or without concomitant inferior myocardial infarction. [A, LAD disease: lB. left main coronary art~ disease; 1C, primarily left circumflex coronary artery disease; 1D, major obstruction to left anterior descending and circumflex. In all four groups significant right coronary artery disease m present then previous inferior infarction with akinesis or dyskinesis. ~'R, right coronary artery; LM, left main stem coronary artery; LAD, left anterior descending artery including diagonal branch: CX. left circumflex includ marginal branch. Grading of coronary arteriogram: 0 = normal: t = < 50% stenosis: 2 = > 50% < 90% stenosis: 3 = > 90% < 100% stenosis: 4 = occ SlOn.

:~Pr, prolapsing mitral valve. Grading of ventriculogram: 0 = aormal: 1 = hypokinesis: 2 = akinesis or dyskinesis.

exceeded t h e s t a n d a r d se t by t h e A m e r i c a n H e a r t

Assoc ia t ion C o m m i t t e e on e l e c t r o c a r d i o g r a p h y .

T h e E C G e l ec t rodes were a t t a c h e d be fo re t h e

res t ing t r ac ing was o b t a i n e d and r e m a i n e d in

place t h r o u g h o u t t h e s tudy . W i t h th i s s y s t e m a 12

lead E C G could be o b t a i n e d in 10 seconds . E a c h

t r ac ing was e x a m i n e d w i t h o u t r e f e r ence to t h e

co rona ry a r t e r i o g r a m . T h e leads in w h i c h une-

qu ivoca l S T - s e g m e n t c h a n g e o c c u r r e d w e r e

recorded. Pos i t ive responses were t hose in w h i c h

downs lop ing or h o r i z o n t a l S T - s e g m e n t depres -

sion of g rea t e r t h a n 1 mm. , l a s t i ng for l onge r t h a n

0.08 second, or " i s c h e m i c t y p e " S T - s e g m e n t

e l e v a t i o n occur red .

Card iac c a t h e t e r i z a t i o n was p e r f o r m e d by t h e

p e r c u t a n e o u s S e l d i n g e r t e c h n i q u e f r o m t h e r i g h t

groin. Lef t v e n t r i c u l a r c i n e a n g i o g r a p h y was

ac c ompl i shed in t h e 30 degree r i gh t a n t e r i o r

ob l ique and in t he 45 degree lef t an t er ior o b l i q u e

posi t ions. Se lec t ive c o r o n a r y a r t e r i o g r a p h y was

p e r f o r m e d w i t h J u d k i n ' s p r e f o r m e d ca the te r s .

M u l t i p l e in jec t ions o f t h e r igh t a n d lef t c o r o n a r y

a r te r ies were p e r f o r m e d in the 30 degree r i g h t

a n t e r i o r obl ique, 15 degree r igh t a n t e r i o r ob l ique ,

and 45 degree lef t a n t e r i o r ob l i que posi t ions . In

s o m e c i r c u m s t a n c e s i n j e c t i o n s w e r e m a d e in t h e

a n t e r o p o s t e r i o r p lane . T h e c o r o n a r y a r t e r i o g r a m

and lef t v e n t r i c u l a r c i n e a n g i o g r a m were r eco rded

on 35 m m . c inef i lm a t 60 f r a m e s pe r second.

T h e resul ts of c o r o n a r y a r t e r i o g r a m s and

v e n t r i c u l o g r a p h y were r e v i e w e d by a t l eas t two of

t he a u t h o r s {D. R. a n d S. P. A. or D. R. a n d

W. J: K.). In each case t h e c o r o n a r y a r t e r i o g r a m

was r ev iewed w i t h o u t r e f e r ence to t he exerc ise

s tress test , and a consensus o b t a i n e d as to t he

l oca l i za t ion and s eve r i t y of c o r o n a r y s tenos is as

438 Apr i l , 1976, Vol. 91, No. 4

Exercise ECG and coronary anatomy

Coronary arteriogram ~;

Prey. infarct: ~

1 1 4 1 RT--~LAD Inf. 2 2 4 3 LAD--~RT Inf. 3 0 4 1 RT--*LAD

CX--~RT Ant. 1 0 3 0

1 2 3 2 1 0 3 0 By-

pass to LAD Inf. 3 0 3 0

0 0 3 1 1 2 1 2 1 2 2 0 1 0 0 3

Inf. 4 0 0 3 CX--~RT RT--~CX

Inf. 4 0 1 4 LAD--* RT Inf. 4 0 1 4 LAD-~RT Ant. 4 0 3 3 RT-*LAD Inf. 2 0 3 3

Ventric- ulo-

Collaterals grams

well as the presence and size of col la teral vessels.

The ECG changes were considered concordan t when (1) ischemic ST segment developed in Leads II, III, and aV F af ter exercise in pat ients wi th greater than 90 per cent obst ruct ion of the r ight coronary ar tery or (2) ischemic changes occurred in Leads I, aVL, a n d / o r the chest leads in pa t ien ts with greater than 90 per c e n t obst ruct ion of the divisions of the left coronary a r te ry o r greater than 50 per cent obst ruct ion of its main stem.

Results

The results of the graded exercise stress test, coronary arteriogram, and left vent r icu logram of 32 patients are given in Table I. Groups 1A, 1B, 1C, and 1D ( total 16 pat ients) include pa t ien ts with left coronary a r te ry disease with or wi thou t inferior myocardial infarction. Eight of these pat ients had greater than 50 per cent stenosis of the right coronary a r te ry and of these, six pat ients had greater t han 90 per cent stenosis. All

of the eight pat ients had ECG evidence of previous inferior wall myocardia l infarction, and seven of the eight pat ients showed diaphragmat ic akinesis or dyskinesis on the left ventr iculogram. With one exception (pat ient R. A. H,) the ST- segment changes were confined to Leads I, aV L and V2 through V6. Comparison of Group 1A (primarily left anter ior descending coronary ar tery disease) with Group 1C (primarily left circumflex coronary a r te ry disease) shows no difference in the localization of ST-segment change. The hear t ra te achieved by this group during exercise stress testing was 80 per cent of the predicted maximal. {Mean achieved hea r t rate 139, mean 90 per cent o f the predicted maximal hear t ra te 174.)

Group 2 (Table II) includes only three pat ients who have severe stenosis of bo th the right and left coronary arteries. (Pa t ien t R. G. is included as severe coronary a r te ry stenosis because of a lesion of between 50 and 90 per cent stenosis in the left main coronary a r te ry in addit ion to a similar lesion in the left anter ior descending.) In all three pat ients in Group 2 S T changes were observed in the inferior leads (II, III, and aVe) in addit ion to the precordial leads. Th e hear t ra te achieved by this group during exercise stress test ing was 77 per cent of the 90 per cent predicted maximal. (Mean achieved 133, mean 90 per c e n t - p r e d i c t e d maximal 172.)

Group 3 (Table II) included two pat ients with primarily right coronary ar tery disease. In these patients either the left coronary a r te ry was free of stenoses or only minor lesions {less than 50 per cent) were observed. In b o t h these patients , ST- segment changes were restr icted to Leads II, III , and aV~.

Groups 4A and 4B (Table III) include a to ta l of 11 patients in whom at first sight the ECG ST- segment changes do not appear to be concordant with the coronary a r te ry stenoses. In Group 4A, however, severe stenosis or occlusion is present in one coronary a r te ry (in two cases the left anter ior descending and in two cases the r ight coronary artery). In all four cases the other ma jo r coronary vessel was not severely diseased and supplied large collateral branches to the distal par t of the

s t enosed or occluded coronary ar tery. In Group 4B, more severe grades of stenoses

(between 50 and 90 per cent) are present in the vessels supplying the collaterals. T h e hear t ra te achieved by this group in exercise stress test ing

American Heart Journal 439

Robertson , Kostuk, and Ahuja

] ' ab l e It. G r o u p s 2 and 3*

Age Group Patient (yr.) Sex

2 T .A.S . 58 M A. A.M. 52 M R.G. 51 M

3 D.W. 47 M

Treadmill exercise stress test

Heart rate/ rain.

Pro- Achiev- duced ed

169 90 173 160 174 149 177 150

175 189

ST-segment changes

X X X :~ X X X X X X X X X X )~ X X X

J . R . 32 M X X X

*Group 2, major stenoses of left and right coronary arteries. Group 3, primarily right coronary artery disease. Abbreviations as in Table I.

Tab l e fit. G r o u p s 4A a n d 4B*


Age Group Patient (yr.)

ST-segment changes

I H I I I AVa AVL AVF 171 V2 V~ V~ V~ V

Heart r a ~ / min.

90% m a x .

pre- Achiev- Sex d i c e d ed

M 167 125 F 179 120 M 180 113 M 176 145

F 167 120 M 182 150 M 180 149 M 171 175 M 186 110 M 163 92 M 179 103

4A E.A.L. 61 X X X G.N. 45 X X X J. A.H. 43 X X X X X X X

�9 D . E . 49 X X X X X X X X X

4B V.D. 62 X X X J. T.P. 40 X X X X H. W.R. 44 X X X X R.M. 54 X X X X G. R.L. 35 X X X M.C. 66 X X X X P.J. 45 X X X X X X X X

*Group 4A, primarily single coronary artery disease with insignificant (< 50% stenosis) in vessel supplying collateral channel. Group 4B, severe stenosis (> 90%) in one vessel, moderate stenosis 0< 90%) in vessel supplying collateral channel {patients G. R. L. and R. M. included in tt group because of possibility that the left circumflex was supplying the inferior wall}. Abbreviations as in Table I.

was 73 per c e n t of p r e d i c t e d m a x i m a l ( m e a n

ach ieved 127, m e a n p r e d i c t e d 175).

G r o u p 5 ( T a b l e IV) is a m i s c e l l a n e o u s g r o u p in

wh ich the E C G changes a n d c o r o n a r y a r t e r i o -

graphic f indings were n o n c o n c o r d a n t . I n p a t i e n t s

E. H., K. W. K., a n d H. C. R. c o r o n a r y a r t e r y

s tenoses were e i t h e r less t h a n 50 pe r c e n t or

b e t w e e n 50 a n d 90 per c e n t ' m i l d or m o d e r a t e

o b s t r u c t i o n a n d n o t e x p e c t e d to p r o d u c e S T -

s e g m e n t change . I n a l l t h r e e cases t h e r e was

v e n t r i c u l o g r a p h i c ev idence of m i t r a l v a l v e p r o :

lapse. I n p a t i e n t s E. W. C. and J . A. K. t h e

l oca l i za t ion of S T - s e g m e n t c h a n g e cou ld n o t be

c lear ly r e l a t ed to t h e c o r o n a r y a r t e r y s t enoses

and no co l l a t e r a l vessels were d e m o n s t r a t e d

r ad iog raph i ca l l y to a c c o u n t for n o n c o n c o r d a n t

i schemic changes . P a t i e n t A. V. s h o w e d i schemic

changes in t he in fer ior leads a n d in t h e l a t e r a l

ches t leads w i t h on ly m o d e r a t e d isease of t h e

r igh t c o r o n a r y a r t e r y a n d m i l d d isease of lef t

a n t e r i o r descend ing a n d le f t c i r cumf lex . P a t i e n t

E. F. h a d s igni f icant les ions in b o t h r i g h t a n d le f t

4 4 0 Apr i l , 1976, Vol. 91, No. 4

P r e y .

Infarct.

Inf.

Coronary arteriogram

4 1 3 0 CX--~RT 1 Pr 4 0 3 1 CX--~RT 2 3 2 2 1 1 4 0 0 0 CX & 1

LAD~RT 4 0 1 1 LAD---~RT 0 Pr

Ventric- ago -

Collaterals gram

P r e y .

infarct.

Ant.

Inf.

Inf. Inf. Inf. Ant.


1 1 4 1 R'I'--~LAD 1 1 0 4 1 RT-->LAD 2 3 1 1 1 LAD--~RT 0 4 0 0 0 LAD--> RT 1

4 0 2 1 LAD--~RT 0 4 0 2 0 LAD--~RT 1 3 0 2 1 LAD---~RT 2 1 0 3 3 RT-*LAD 0 Pr 1 3 2 2 RT-->LAD 1 4 0 2 1 LAD-->RT 0 Pr 2 1 4 4 RT--->LAD 2

RT---~CX

Ventri- culo-

Collaterals gram

coronary arteries, wi thout old infarction, and with ECG changes only in the anter ior chest leads. The heart rate response in this pat ient was 74 per cent of predicted max im um compared with a mean of 82 per cent of predicted max imum for all other patients.

Discussion

There is at the present t ime no s tandard method of exercising a pat ient during exercise stress test nor is there any s tandardized ECG lead system.

Of the three methods of exercise stress testing

Exercise ECG and coronary anatomy

m common use, namely the Master two-step test, bicycle ergometry, and graded exercise stress testing on an elevating treadmill, we have chosen the lat ter method for the following reasons. The end point is determined by the pat ient ' s hear t rate response, the exercise being te rmina ted when the patient has achieved 90 per cent or more of his predicted maximal hear t rate, or upon the development of chest pain, fatigue, dyspnea, or o ther subjective symptoms which necessitate discontinuing the procedure. We recognize two impor- tant l imitations of this test, namely, the inability to obtain intraexercise blood pressure recordings and the poor quali ty of the intraexercise ECG as compared with tha t obtained during bicycle ergometry.

The electrode positioning for ECG recording during exercise has not been s tandardized 5 and the investigator has a choice of numerous single- lead or multiple-lead systems. Master and associates 6 found tha t the limb leads more commonly showed ST-segment changes than the chest leads and the major i ty of abnormal changes were in Leads I and II. B r a d y / describing an extensive experience with Master 's two-step test, recorded Leads I, II, V~, V4, and Vs. Sheffield recommended the use of V~, V~, and aVF, 8 or, if a single lead was to be used, the use of V5 or whichever precordial lead had the largest R wave. Most of the ischemic ECG changes are seen in the 2 minute postexercise tracing 9 and in most cases the ECG has returned to normal by 8 minutes.

False-negative test results m a y be due to inadequate exercise stress. Lewis and Wilson '~ performed graded exercise tests and double Master 's step test on the same pat ients and found 81 per cent positive with the graded exercise test and 61 per cent positive in the double Master ' s step test. I t is possible tha t with the use of a limited number of leads or single lead ischemic ST-segment depression may be missed. A negative exercise stress test cannot unequivocal ly rule out even significant coronary ar tery disease. In correlating postexercise ECG's with pathologic grading of coronary ar tery disease, Mat t ingly 2 found tha t in patients with Grade 2/4 coronary artery disease at autopsy, only one out of 17 had shown ischemic depression in exercise testing. Even in those patients graded 4/4, six out of 16 patients did not show ischemic depression in the postexercise ECG. He concluded tha t ST- segment change was present only when severe and diffuse coronary ar tery disease was present.

American Heart Journal 441


Table IV. Group 5*


Heart rate/ min.

90% max.

Age pre- Achier- Patient (yr.) Sex dicted ed

ST-segment changes

I A VR A VL V~ V, H I l l AVF V1 K~

A.V. 56 M 170 132 X X X X X E.H. 58 F 169 129 X X X K.W.K. 54 M 172 145 X X H.C.R. 38 M 184 166 X E.W.C. 53 M 172 150 X X X X J.A.K. 56 M 170 138 X X E.F. 68 M 161 120 X X X X

Y~

X

X

X

*Group 5, miscellaneous group where ECG and coronary arteriographic findings were nonconcordant (involving three patients with prolapsing mitral valv syndrome). Abbreviations as in Table I.

We have attempted to show that with the use of a 12 lead ECG system and with five separate ECG recordings taken after exercise the ischemic ST changes in many cases are concordant with the location and severity of the coronary artery stenoses.

In Groups 1A and 1B (Table I) are patients in whom there is more than 90 per cent stenosis of the left anterior descending coronary artery or patients with between 50 and 90 per cent stenosis of the left main coronary artery. In this group, three patients had more than 50 per cent stenosis of the right coronary artery. In each case this was associated with ECG evidence of an old inferior wall myocardial infarction and a diaphragmatic akinetic or dyskinetic segment on the left ventriculogram. If it can be assumed that such dyskinetic areas represent fibrotic scar tissue which would not be expected to show ischemic change, then the concordance of left anterior descending or left main coronary artery disease with changes in the anterior chest leads is demonstrated. ST- segment changes were equally frequent in Leads V4, Vs, and Vs (seven out of 10 patients in each case).

In Group 1C, severe stenoses (greater than 90 per cent) were present in the circumflex coronary artery and three of the four patients had total occlusion of the right coronary artery with associated ECG change of old inferior wall myocardial infarction and ventriculographic evidence of diaphragmatic akinesis or dyskinesis. If it is again

assumed that such fibrotic scar tissue is incapable of showing ischemic change, then isolated, hemodynamically significant disease of the left circumflex coronary artery produces ischemic ST changes indistinguishable from those of left anterior descending coronary ar tery disease. Changes were equally frequent in Leads V3, V4, and V5 {four of four patients in each case).

A total of four patients showed major stenoses of both the right and left coronary arteries. Three of the patients are included in Group 2 and predictably show changes in Leads II, III, and aV F and in the anterior chest Leads V3 through Vs. The one patient in this group who had suffered an old inferior wall myocardial infarction showed only hypokinesis on the left ventriculogram with no evidence of paradoxical movement. The right coronary artery was not totally occluded, thus patient R. G. likely represented recanalization of a vessel with a hemodynamically significant stenosis causing inferior wall ischemia. Patient E. F. in Group 5 also had severe disease affecting both right and left coronary arteries, without old infarction or aneurysm. This patient showed changes only in the anterior chest leads. The graded exercise stress test of this patient was terminated at the end of Stage I (3 minutes) because of chest pain, 74 per cent of the predicted heart rate having been achieved. It is possible that more severe exercise stress would have revealed ischemic ST-segment changes in Leads II, III, and aV F in this individual. Group 3

442 April, 1976, Vol. 91, No. 4

E x e r c i s e E C G a n d coronary a n a t o m y

Prey.

infarct.


Ventric-

I I I u,o R L M LA D CX Collaterals gram

2 0 1 1 0 1 0 0 1 0 Pr 1 0 i 2 0 Pr 0 0 2 0 0Pr 3 0 2 1 0 3 1 2 2 0 3 1 3 3 RT---)CX 1

includes two patients with occlusions of the right coronary a r te ry without ECG or historical evidence of inferior wall myocardial infarction or dyskinesis on ventriculography. In both these patients ischemic ST changes were observed only in Leads II, III, and aV~.

From the data presented in Groups 1, 2, and 3, it is apparent that patients with hemodynamically significant stenoses of the left coronary artery, the left anterior descending artery, or the left circumflex coronary artery show ischemic ST changes primarily in the chest Leads V2 to V6. 0n ly four of 16 patients showed changes in the limb leads. Patients with exclusive or predomi- nant right coronary artery disease show ischemic ST changes in Leads II, III, and aVF, and patients with hemodynamically significant stenoses of both right and left coronary artery systems show changes in both the inferior limb leads (II, III, and aV F) and in the anterior chest leads.

Levin and associates 1~ found that in radio- graphic assessment of coronary arteriograms hemodynamically moderate stenoses (75 to 89 per cent) were virtually never accompanied by collateral vessels. In the severe coronary artery stenoses (90 to 99 per cent) collateral vessels were frequently visualized~ The presence of communi- cating vessels between the right and left coronary systems is known in neonatal hearts 12 and progressive controlled occlusion of the coronary arteries has led to the development of collateral vessels in the dog heart. 13 Baltaxe 14 and Levin and

associates 15 have described the anatomy o f the collateral circulation as visualized by coronary arteriography. In a coronary artery tree with multiple stenoses and occlusions the dynamics of flow will be complex at rest and even more so during exercise when ischemia occurs. Local hypoxia is a potent coronary vasodilator, and the pressure in the arterial bed distal to a significant stenosis will be further reduced. If the distal part of a diseased coronary artery is supplied with a large collateral flow from the other major coronary artery, and as blood will flow to the area of lowest resistance, it is conceivable tha t ischemia may result in the terri tory of the "don- or" vessels supplying the collateral channels. This possibility was suggested by Rowe TM and the term "coronary steal" applied. Groups 4A and 4B represent 11 patients in whom unequivocal ischemic ST-segment depression occurs in leads which are nonconcordant with the degree and site of coronary artery stenosis. In each of these patients one or more large collateral vessel was demonstrated on coronary arteriography to communicate between the severely diseased vessel and the less severely diseased donor coronary artery. In each instance the degree of stenosis of the donor vessel was not sufficiently great to be expected to give ischemic changes. Group 5 contains seven patients, of whom E. F. has already been discussed. In these patients the ischemic changes occurred with lesser degrees of coronary artery disease than would have been anticipated. Three of these patients demonstrated prolapse of the mitral valve, a condition which is known to be associated with false- positive exercise stress tests. In the three re- maining patients triple-vessel coronary artery disease of mild to moderate severity was present. Collateral vessels were not demonstrated radio- graphically in any patient and the location of ECG change was not concordant with the location of stenoses.

Excluding those three patients in Group 5 with prolapsing mitral valve syndrome, there was lack of concordance between the ECG changes and the severity and location of coronary artery stenoses in four of 36 patients. Twenty-one patients {Groups 1, 2, and 3} showed changes which were predictable with a knowledge of the coronary anatomy. Eleven patients in Groups 4A and 4B showed ischemic changes, either in the area of the donor vessel supplying the collateral channels

American Heart Journal 4 4 3


a lone or in b o t h the a rea of the h e m o d y n a m i c a l l y s ign i f ican t s tenosis a n d the t e r r i t o ry of t he d o n o r

vessels.

Summary

In 39 consecu t ive p a t i e n t s w i th u n e q u i v o c a l l y posi t ive postexercise E C G we have co r r e l a t ed t he loca t ion a n d sever i ty of the c o r o n a r y a r t e r y s tenoses wi th the E C G leads in which i schemic

S T changes occurred. P a t i e n t s wi th m a j o r s tenoses of the r igh t

c o r o n a r y a r te ry , w i th or w i t h o u t disease of t he left co rona ry sys tem, showed i schemic S T

changes in Leads II , I I I , a n d aV F. P a t i e n t s w i t h m a j o r s tenoses of the left c o r o n a r y sy s t em, m a n y of w h o m had suffered old infer ior wa l l i n f a r c t i on ,

showed S T changes in Leads I, aVL, a n d the ches t leads.

A group of 11 p a t i e n t s showed i schemic S T change in leads o the r t h a n those expec ted on the basis of the loca t ion a n d sever i ty of c o r o n a r y a r t e ry s tenoses. In each of these 11 p a t i e n t s large co l la te ra l c h a n n e l s were d o n a t e d by t he vessel in whose t e r r i t o ry the i schemic changes occurred . Th i s f inding lends s u p p o r t co the concep t of

i n t e r c o r o n a r y " s t ea l " d u r i n g exercise in c o r o n a r y a r t e ry disease, a t t he s a m e t ime r e d u c i n g the va lue of the postexercise 12 lead E C G in p red ic t ing the loca t ion a n d sever i ty of c o r o n a r y

a r t e ry stenoses.

REFERENCES 1. Most, A. S., Kemp, H. G., and Gorlin. R.: Postexercise

electrocardiography in patients with arteriographically documented coronary artery disease, Ann. Intern. Med. 71:1043, 1969.

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444 April, 1976, Vol. 91, No. 4

the localization of coronary artery stenoses by 12 lead ecg response to graded exercise test:...

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