effect of coronary collaterals on left ventricular function at rest and during stress

Effect of coronary cotlaterals on left ventricular

function at rest and during stress

Franz Schwarz, M.D. Willem ‘Flameng, M.D. Roland Ensslen, M.D. Michael Sesto, M.D. Jochen Thormann, M.D. Bad Nauheim, West Germany

During recent years there still exists controversy concerning the effectiveness of coronary collateral vessels in man as a compensatory mechanism for the loss of blood flow consequent to coronary obstruction.‘-” In the dog heart rudimentary collateral vessels enlarge during gradual occlusion of a major coronary artery and perfuse the myocardium distal to complete occlusion to such an extent that only little or no myocardial damage results in this area provided the luminal narrowing was slow enough.12aZ3 Pathologic and ang-iographic studies in man have also shown that severe coronary obstructions are not regularly associated with transmural myocardial infarction or scars if an adequate compensating collateral circulation exists.“-“, 24-29 Large differences in size and extent of collaterals can be shown by angiog- raphy and comparison of preoperative angio- grams and intraoperative flow measurements indicate that radiographic appearance of coronary collateral circulation is related to the flow capacity of these vesse1s.30. 31 Furthermore, normal flow in the area distal to complete coronary occlusion could be measured by radioisotope studies in several patients in whom cinearteriog- raphy revealed an adequate retrograde filling of the occluded artery.“2-34 Therefore the angiographic evaluation seems to be a reliable method to estimate collateral flow. The purpose of this study was to investigate the adequacy of coronary collaterals in the presence of complete coro-

From the Ken&h&‘-Klinik, Bad Nauheim, West Germany.

Received for publication Jan. 11, 1977.

Accepted for publication Mar. 4, 1977.

Reprint requests:-F. Schwarz, M.D., Kerckhoff-Klinik, Beneke-Straw, D 6350 Bad Nauheim, West Germany.

nary occlusion by measuring total and regional left ventricular contractile function at rest and during stress. Clinical data were reviewed to compare coronary morphology and subjective complaints.

Methods

A consecutive series of 169 patients having significant coronary artery disease (more than 75 per cent luminal obstruction of at least one major coronary artery) was studied. From this series all patients with complete occlusion of the proximal part of at least one of the three major coronary arteries were selected (87 patients). Additional coronary stenoses of less than 75 per cent luminal narrowing were present in a few patients and were not considered. Patients with atria1 fibrillation, with valvular heart disease, with severe disease of the main stem of the left coronary artery, and patients with technically poor angiographies were excluded from the study.

Cardiac catheterization was performed without premeditation in the fasting state. A biplane cineventriculogram (30 degree right anterior oblique position, 50 ml. Renografin, 36 frames per second using 35 mm. films and six inch image intensifiers) was followed by coronary arteriography in the right and left anterior oblique posi- tions using the Judkins technique.“5 A pacing test was performed in a subgroup of 12 of 87 patients with complete occlusion of the descending branch of the left coronary artery. Six of these patients showed good collaterals and six showed poor collaterals (as defined below) to the occluded vessel. For this purpose a bipolar pacing electrode was placed into the apex of the right ventricle (via

570 May, 1978, Vol. 95, No. 5 0002-8703f 78/0595-057O$QO.80/0 0 1978 The C. V. Mosby Co

Coronary collaterals and LV function

Fig. 1 A and B. A, Well collateralized occlusion of the anterior descending branch of the left coronary artery. Left coronary injection, RAO projection, early filling phase; complete occlusion of the anterior descending branch (arrow) with retrograde filling over a large collateral vessel (arrowhead) originating from the patent marginal branch. B, Late filling phase; uninterrupted filling of the distal segment and septal branches are seen.

femoral vein). Thirty minutes after the last coronary arteriogram, right ventricular pacing was started at a rate of 110 b.p.m. and was gradually increased under left ventricular pressure registra- tion to a rate of 180 b.p.m. This rate was kept constant for one minute. After stopping of pacing, ventriculography was immediately repeated. If pain occurred during this procedure nitroglycerin was given after ventriculography and pain was relieved in all cases where it was observed.

The coronary occlusions of the anterior descending branch (LAD), the circumflex branch (LC), of the left coronary artery and the right coronary artery (RC) as well as the collateral circulation were analyzed from the cineangio- grams and were tabulated.

Radiographic criteria for the presence of collateral vessels were (a) retrograde filling of a major vessel after injection of contrast medium into another vessel, or (b) filling of the distal segment of a proximal occluded major vessel after injection into the proximal stump of the same artery. Collateralization was termed “good” if the distal segment of the occluded artery and its branches was visualized without interruption and if the average caliber of the distal segment measured greater than 1.0 mm. after correction for the angiographic magnification. When the distal segment was interrupted and/or the average

caliber was only 1.0 mm. or less collateral circulation was considered “poor.” Each case was evaluated including measurement of the distal segment by two observers. In cases which showed two or three vessel occlusions good collateralization was accepted if each vessel fulfilled the criteria for good collaterals. This classification of collaterals resembles that used by several investigators,g, lo. a4 but differs from that used by others.“. j(’ Examples of well-collateralized occlusions are shown in Figs. 1 and 2.

Quantitative biplane ventriculography was performed using the area-length method.“6, 87 For calculation of segmental wall motion and LV volumes, ectopic and postectopic cycles were eliminated. The ventriculograms of 17 normal patients without heart disease (average age 44.3 + 3.5 years) served as controls. Biplane ejection fraction was derived from the ratio of angiographic stroke volume to end-diastolic volume times 100 per cent. Segmental wall motion was quantitatively analyzed according to the technique of Herman and Gorlin.“” End-diastolic and end-systolic silhouettes were outlined from the 30 degree right anterior oblique projection. The long axis (L) was drawn from the midaortic root to the apex and three equally spaced perpendiculars were constructed, creating six hemiaxis from the long axis to the endocardial surface. These axis

American Heart Journal 571

S&war2 et al.

Fig. 2. Well collateralized occlusion of the circumflex branch of the left coronary artery. The occluded circumflex branch (arrow) shows complete retrograde filling from diagonal branches (arrowhead). In this case not a single large collateral vessel was found but an extensive collateral network was discovered instead. In addition, atria1 collaterals to the right coronary artery are opacified.

Fig. 3. End-diastolic and end-systolic silhouettes are depicted with the system of hemiaxes.

were drawn for each silhouette (Fig. 3). The percentage shortening was calculated as diastolic minus systolic axis divided by diastolic axis times 100 per cent.

Clinical data of patients with comparable numbers and localizations of coronary artery occlusions but different stages of collateralization

572

were reviewed from 87 investigated patients to get two groups with comparable severity of coronary artery disease: twenty patients had good and 27 had poor collaterals. The history of angina pectoris and dyspnea was graded according to the NYHA. Any history of previous myocardial infarction was noted based on clinical, electro- graphic, and enzymatic data. A treadmill exercise test was performed according to Kasser and BrucP with continuous ECG monitoring. The ST-segment changes after submaximal exercise were measured and averaged over at least 10 beats.

Results

Well-collateralized occlusions were found in 35 patients, poorly or not collateralized occlusions were found in 52 patients.

Table I presents the average values of biplane ejection fraction at rest and the distribution into seven subgroups with various combinations of complete coronary occlusions separated by the degree of collateralization. Well-collateralized LAD occlusions were found less frequently (nine patients) than poorly-collateralized LAD ocelu- sions (22 patients). Well-collateralized RC occlusions (11 patients) were found with equal frequency compared to poorly collateralized RC

May, 1978, Vol. 95, No. 5


occlusions (10 patients). Isolated LC, and two and three vessel occlusions were rarely found (Table I). The ejection fraction was significantly higher in well-collateralized LAD occlusion and RC occlusion as compared to poorly-collateralized occlusions of the same subgroup (p < 0.001). Comparison with the average of normal individ- uals shows no significant difference (p > 0.05) of ejection fraction in patients with well-collateralized occlusion of LAD and occlusion of RC. In contrast, poorly-collateralized occlusions of LAD, RC, LAD + RC, and RC + LC showed significantly depressed ejection fractions (all p < 0.001). All other subgroups were too small for statistical comparisons.

The analysis of segmental wall motion is shown in Table II. In poorly-collateralized LAD occlusion anterior wall motion (R, to R,, L) was significantly lower than in well-collateralized LAD occlusion (p < 0.05, respectively, < 0.01, p < 0.001). The same was found in RC occlusion for inferior wall motion (R, to R,). Comparison of normally contracting ventricles to well-collateralized occlusions reveals slight hypokinesia of R, and L in well-Collateralized’LAD occlusion and normal motion in well-collateralized RC occlusion (p > 0.05). Severely reduced wall motion was found in poorly-collateralized occlusions of the same areas (p < 0.01, respectively, p < 0.001).

Table III presents mean values of anterior wall motion at rest and after pacing. Pacing drasti- cally reduced wall motion in well-collateralized LAD occlusions if sets of paired observations are compared (p < 0.05, respectively, < 0.01). Poor- ly-collateralized occlusions, however, showed severely depressed wall motion at rest and remained unchanged after stress (p > 0.05).

Table IV summarizes clinical data of two patient groups with comparable numbers and localizations of coronary occlusions separated by the presence or absence of good collaterals. Patients with good collaterals to the occluded vessels have more severe angina (p < 0.001) and more severe ST-segment changes during exercise (p < 0.01) than patients with poor collaterals. Patients with poor collaterals have more severe dyspnea (p < 0.01) and more histories of previous infarctions if compared to patients with good collaterals (p < 0.001).

Discussion

A well-developed collateral circulation sup- plying the distal segment of a completely

Table I. Ejection fraction at rest in patients with coronary artery occlusions and different stages of collateralization

LAD 9 Ix: 4 RC 11 LAD+RC 4 LAD + 3

LC RC +LC 3 LAD+ 1

RC+ LC Normal 17

59.6 t 2.3? 22 41.4 f 1.4*** p c 0.001 66.5 f 3.7 4 51.0 r 4.0 - 67.6 + 2.lt 10 51.0 f 2.6*** p < 0.001 69.0 -c 3.3 4 29.0 + 1.4 - 47.7 f 2.1 6 34.7 r 3.4’” -

57.7 + 3.7 5 45.0 + 2.6*** - 42.0 1 33.0

65.2 k 1.9 coronary

arteries

Abbreviations: LAD = anterior descending branch of the left coronary artery; LC = circumflex branch of the left coronary artery; RC = right coronary artery; Pat. No. = number of patients. *** = p < 0.001 or t = p> 0.05 denotes sign&ant differences if compared to the ejection fraction of patients with normal coronky arteries. Mean values f S.E.M.

occluded coronary artery preserves myocardial function partially. Preservation of myocardial function at rest was demonstrated by a normal ejection fraction, a nearly normal regional wall motion, and a low incidence of past myocardial infarctions. During stress the limited capacity of good collaterals was detected by a drastic fall of segmental wall motion after pacing and severe ST-segment changes during treadmill exercise.

From dog experiments it is known that during gradual occlusion of a major coronary artery, collaterals enlarge rather rapidly by an active growth process.**. 43 The degree to which collaterals can protect the myocardium depends on the time available for their development.‘3, I4 The higher the speed of the occlusion, the lower the chance for collaterals to compensate for it.*“. 45 Quantification of the protective effect of collaterals on myocardial function during life requires comparison of patients with equal degree of coronary artery disease but with and without collaterals. Since the severity of coronary stenoses is difficult to measure angiographically we investigated only patients with complete coronary artery occlusions. In addition, we believe that the effect of coronary collateral circulation can be evaluated in complete coronary artery occlusion


Schwarz et al.

Table II. Segmental wall motion at rest in patients with coronary artery occlusion and different stages of collateralization

Shortening of hemiaxes

R, R, R3 R, Ri R,; L

LAD Occlu- sion

Good 47.4 f 3.at 33.0 t 2.3* 36.1 + 2.3 46.3 +- 5.9 39.8 5 3.7 20.8 f 4.0 12.7 f 1.9** collaterals Poor 26.4 f 4.3** 11.9 k 3.1*** 9.8 f 3.3*** 28.5 -c 5.8 36.4 k 2.9 26.8 rf- 1.7 8.3 f l.O*** collaterals

P values

RC Occlu- sion

to.01 < 0.001 to.001 n.s. U.S. ns. to.05 Good 55.7 f 4.1 47.0 f 4.8 45.7 f 3.9 35.9 f 3.6 30.3 F 3.6 21.9 5 2.8 20.6 f 1.3 collaterals Poor 43.9 f 5.9 36.2 2 5.4 40.1 -c 5.3 10.7 i 4.8*** 5.9 + 3.0*** 13.1 rt 2.9** 16.4 + 1.6 collaterals

P values Normal coronary

arteries

n.s. n.s. n.s. to.001 to.001 co.05 n.s. 52.6 k 5.7 47.0 f 4.1 42.1 2 2.5 34.0 +- 3.2 32.3 f 3.1 27.0 -1- 2.8 19.4 k 3.4

Abbreviations: LAD = anterior deacendiig branch of the left coronary artery; RC = right coronary artery. *= p < 0.05; **= p < 0.01; ***= p < 0.001 denotes sig&icant differences between the groups with occluded vessels and patients with normal coronary arteries. tMean values k S.E.M.

Table III. Anterior wall motion at rest and after pacing in patients with LAD occlusion and different stages of collateralization

I Shortening of hem&es (sa)

RI

Rest 56.2 zt 3.9-f Pacing 25.8 f 6.5 P values cro.01

tMean values r S.E.M.

Good collaterals

& R,

36.0 + 2.5 32.0 +- 4.1 15.7 2 3.5 10.3 -c 6.1

(0.01 <0.05

L

9.8 f 2.6 5.8 t 1.1

n.s.

Poor collaterals

RI R, & L

26.7 + 9.1 10.0 -+ 4.0 4.0 k 2.7 6.2 + 0.7 20.2 f 5.0 9.5 zk 3.6 3.0 2 2.4 5.8 k 1.4

ns. n.s. n.s. ns.

only, since any additional flow through coronary stenoses may contribute to preservation of myocardial function. In the dog heart it could be demonstrated that maximal cohateral flow to the perfusion beyond a stenosis is not achieved before the vessel is completely occ1uded.*o

Patients with well-collateralized occlusions showed higher ejection fractions, better regional wall motion, and a smaller percentage of previous myocardial infarctions in contrast to patients with poor collaterals. The latter patients had severely depressed myocardial function. Their dysfunction is caused by severe loss of wall motion in the area previously supplied by the occluded artery. The loss of wall motion associated with a high incidence of previous infarctions suggests that asynergy in these patients is a result of myocardial fibrosis. This is confirmed by

results of Starr and associates41 who found in 35 of 36 patients with severe left ventricular segmental contraction abnormalities significant myocardial fibrosis in the corresponding left ventricular wall at ‘autopsy.

Our results are in agreement with the findings of others; Levin’O reported normal contractility at rest in 43 per cent, hypokinesia in 52 per cent, and akinesia in 5 per cent of 86 completely occluded adequately collateralized arteries, while occlusions with inadequate collaterals showed normal contractility inonly 11 per cent, hypokinesia in 16 per cent, and akinesia in 73 per cent. Gensini and da Co&as described five patients with completely obstructed arteries and collaterals with normal resting electrocardiograms, while all patients without collaterals had abnormal electrocardiograms. There is considerable disagreement

574 May, 1978, Vol. 95, No. 5


between our results and those .of Helfant and colleagues,” Lavine and co-workers” and Carol1 and associates.6 These studies investigated patients with stenoses greater than 75 per cent. Helfant and colleagues* and Lavine and co-work- er.9 subdivided collaterals into present or absent. Carol1 and associates6 differentiated four collateral classes (“no,” “poor,” “fair,” “good”). The groups with collaterals showed an equaP 6 or increased5 number of abnormal ventriculograms as compared to the group without collaterals. The conclusion was that collaterals do not protect from the development of ventricular asynergy. This disagreement is probably due to the different patient populations studied (stenoses of more than 75 per cenF 5. 6 or complete occlusion in our study) and to the different gradations used for collaterals.

Our clinical data revealed a high incidence of severe angina and marked ST-segment changes during exercise in patients with good collateralization. In addition, pacing stress induced a marked reduction of wall motion indicative of acute myocardial ischemia in these patients. These findings are in accordance with the experi- ence of others who reported no protective effect of coronary collaterals against acute myocardial ischemia as measured by treadmiI1 stress test.4 This implies that the area perfused by good collaterals mainly consisting of viable myocardium becomes ischemic, since collaterals are not able to increase their flow capacity proportional to the increased oxygen demands.

Summary

The influence of coronary collateral vessels on resting left ventricular function was investigated in 87 consecutive patients with complete coronary artery occlusion of at least one of the three major coronary vessels. The morphology of coronary and collateral circulation was evaluated by coronary arteriography. Left ventricular function was assessed by biplane ejection fraction and segmental wall motion was evaluated by hemiaxes shortening. Collaterals to occluded arteries were graded as good or poor, according to the caliber of the distal vessel segment. Patients were divided into those with good collaterals (n = %5), and those with poor or absent collaterals (n = 53, furthermore, these two groups were subdivided according to the location of coronary artery occlusion. Collateralized single vessel

Table IV. Clinical data of patients with equal numbers and localizations of coronary artery occlusions and different stages of collateralization

I Good Poor colluterals collaterals I P values

Angina1 pain 3.4 -+ 0.2t 1.3 + 0.3 to.001 (NYHA Class)

Exercise test (ST- 0.30 _’ 0.04 0.13 f 0.03 to.01 changes in mV.)

Dyspnea (NYHA Class)

0.6 f 0.2 1.9 +- 0.3 CO.01

History of previous infarction

20% 89% <O.ool

fMean values f S.E.M.

occlusions were found more frequently than collateralized multiple vessel occlusions. Ejection fraction and segmental wall motion was significantly better in well collateralized occlusions than in poorly collateralized occlusions of LAD or RC and was normal or depressed only slightly if compared to 17 patients without heart disease. In contrast, total and regional myocardial function was severely depressed in poorly ‘collateralized LAD or RC occlusion. Ventriculography after rapid ventricular pacing was performed in 12 of 87 patients with well collateralized or poorly collateralized LAD occlusion to evaluate to what extent coronary collaterals protect anterior wall motion during increased oxygen demand. Pacing induced a drastic fall of anterior wall motion in well collateralized segments whereas no change was found in poorly collateralized segments. Reviewing clinical data of two patient groups with comparable numbers and locations of occlusions revealed in the well collateralized group more severe angina (p < 0.001) and ST-segment changes during exercise (p < 0.01) than in the poorly collateralized group. The latter showed more severe dyspnoe (p < 0.01) and more histories of previous infarctions (p < 0.001). We conclude that well-developed collateral vessels to a complete occluded artery prevent severe asynergy at rest but not during stress.

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Schwarz et al.

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effect of coronary collaterals on left ventricular function at rest and during stress

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