Asymmetric distribution of left ventricular asynergy in coronary artery disease and its relation to coronary stenoses

AsymmetricDistributionof left Ventricular Asynergyin CoronaryArtery Diseaseand Its Relationto CoronaryStenoses DAVID W. KOHL, MD, EDWARD W. BOUGH, MD, KENNETH S. KORR, MD, WILLIAM E. BODEN, MD, and ELAN J. GANDSMAN, PhD

In 100 patients with coronary artery disease (CAD), the prevalence and severity of asynergy was determined for 9 left ventricular (LV) segments by both radlonuclkte and contrast angiography. The anterior, septal and lateral LV walls had significantly more prevalent and more severe asynergy in the medial segments than in the basal segments. In contrast, the inferior LV wall exhibited equally severe asynergy in both the medial and basal segments. In general, asynergy was most severe in the apical, medial septal, medial inferior and basal inferior LV segments. Thii asymmetric distribution of LV asynergy could not be explained by the distribution of occlusions or stgnfficant stenoses in the arterial tree, which were relatively uniformly distributed among the left anterior descending (32 % ), teft circumflex

M

(29%) and right (26%) coronary arteries. It is postulated instead that the asymmetric distribution of LV asynergy results from asymmetry of the coronary arterial tree supplying the feft ventricle and that the prevalence of asynergy in an LV segment is directly related to its vascular distance from the coronary ostia. Unlike the relatively direct supply of the left anterior descending and circumflex arteries to the basal segments of the anterior, septal and lateral LV walls, the arterial supply to the basal inferior wall begins only after the right or dominant circumflex artery has traversed the length of the atrtoventricular groove, significantly Increasing tts susceptibility to the pressure attenuation and occlusive jeopardy of more proximal stenoses. (Am J Cardiol 1967;59:543-546)

vocardial damage in coronarv arterv disease (CAD] is usually segmental and not diffuse. The apex is frequently identified as the most common site of localized asynergyQ and aneurysm formation,3p4 but the segmental prevalence of asynergy in other myocardial segments has not been established for a large population of living persons with CAD. Studies have focused on the degree of agreement between noninvasive measures of segmental asynergy,5v6 on the prognostic value of an assessment of coronary anatomy and global left ventricular (LV) function,7-10 or on the limitations of the surface electrocardiogram in predicting and localizing LV asynergy.ll-I5 We undertook a population study to determine if distal myocardial asynergy

was significantly more common than basal asynergy, and if so, whether this was true for all walls of the heart. We defined the prevalence of asynergy in the basal and medial segments of each major LV wall as well as the apex in 100 patients with arteriographically defined CAD.

I

Methods Patients: The study population comprised 100 selected patients (81 men, 19 women] with at least lvessel CAD and asynergy of at least 1 LV segment determined by coronary arteriography and radionuelide ventriculography. To ensure that all wall motion abnormalities were ischemic in origin, patients were excluded for valvular heart disease other than mild mitral regurgitation. Patients were 35 to 78 years old (mean 52). Radionuclide angiography: Radionuclide ventriculograms were recorded in the anterior and 30” caudally angulated left anterior oblique projections. Ejection fraction images were generated by a modification of the method of Maddox et a1.16J7 The left ventricle

From the Department of Medicine, The Miriam Hospital and Brown University, Providence, Rhode Island. Manuscript received December 6,1986; revised manuscript received October 7,1986, accepted October 8,1986. Address for reprints: Edward W. Bough, MD, Cardiovascular Institute, 2660 Grant Road, Mountain View, California 94040. 543

544

ASYMMETRIC

DISTRIBUTION

OF LEFT VENTRICULAR

ASYNERGY

was separatedinto 9 segments(Fig. 1):basaland medial segmentsfor the anterior,inferior, septaland lateral walls, as well as an apical segment.An experienced observerunaware of the catheterizationfindings reviewed thesestudies and graded LV segmentalwall motion on an ordinal, nonparametricscale:1 = normal segmentalwall motion, 2 = hypokinesia,and 3 = akinesia or dyskinesia. Catheterization: All patients underwent coronary arteriography.Ninety-five patientsunderwent singleplane and 23 biplane ventriculography. Data on all coronary arterial segmentswere recorded using the standard Coronary Artery Surgery Study (CASS)format.l8 Stenoseswere consideredsignificant if at least 50% in the left main segmentand at least 70% in the other coronary segments. Contrast ventriculograms were assessedfor segmentalasynergyusing the same format as for radionuclide ventriculograms. Data analysis: The distribution of wall motion scores for paired basal and medial segmentswere comparedby chi-squareanalysis.The 9 LV segments were then ranked for overall severity of asynergyvia a wall motion index, calculated for each segment by summing the wall motion scores(1 through 3) and dividing by the number of patients analyzed. For radionuclide ventriculography, 100 examples of eachsegmentwere available for analysis.For contrast ventriculography95 anterior, inferior and apical segmentswere drawn from single-plane ventriculograms:the 23patientswho underwent biplane studies provided septal and lateral segmentsas well. Becausethe radionuclide and contrastventriculogramswere reviewed and gradedindependently,data from both are presented.Since biplane yentriculogramswere not routinely performed, the radionuclide studies provide much more complete data regarding

ANT @ANTERIOR @ANTERIOR

LAO (BASAL) 0vlEDIAL)

@ APICAL

(BASAL 1

@ SEPTAL (MEDIAL) @ APICAL

@ INFERIOR

(MEDIAL)

@ INFERIOR

(BASAL)

FIGURE 1. Left ventricular anterior (ANT) and left radlonucllde and contrast

@ SEPTAL

@ LATERAL @ LATERAL

(MEDIAL) (BASAL)

segments Identlfled and scored for the anterior oblique (LAO) projectlons from ventrlculography. MV = mitral valve.

the septal and lateral walls. Inclusion of contrastdata allowed for review of the level of agreementbetween 2 separatemeasuresof wall motion for the bulk of the study population.

Results The distribution of wall motion scoresfrom radionuclide ventriculographyis listed in Table I. The number of patientsexhibiting eachlevel of wall motion for the paired basal and medial segmentsare tabulated. Chi-squareanalysisallowed statistical comparison of paired basal and medial segmentsfor both the prevalence and severity of myocardial asynergy.Asynergy was significantly more severein the medial segment than in the basalsegmentof the anterior (p
Discussion If the coronary circulation is conceptualized as a symmetric cascadefrom the baseof a conical left ventricle toward the apex, it is logical to assumethat the

March

TABLE I

Left Ventricular

I,1987

JOURNAL

OF CARDIOLOGY

Volume

inferior

Septal

545

Lateral

Basal

Medial

Apical

Basal

Medial

Basal

Medial

Basal

Medial

88 11

56 35

36 24

32 32

30 32

48 31

48 19

73 18

52 30

9

40

36

38

21

33

9

1 p
59

Asynergy Dlstrlbution (Radlonuclide)

Anterior

Normal Hypokinetic Akinetic/ dyskinetic

THE AMERICAN

NS

18

p = 0.06

p
Septal

Lateral

NS = not significant.

TABLE II

Left Ventricular

Asynergy Dlstrlbutlon (Anglography)

Anterior

Normal Hypokinetic Aklneticl dyskinetic

Inferior

Basal

Medial

Apical

Basal

Medlal

Basal

86 7

54 32

44 16

45 26

40 34

16 8

9

35

24

0 p
21

Medial 9 3

1 p = 0.00:’

NS

Sasal

Medial

20 3

13 10

0

0 p <0.05

NS = not significant.

apical segmentwould be most susceptibleto infarction and asynergy,with preservation of more basal seg ments-another way of stating that “the heart dies from the apex up.” The coronary circulation, however, is not symmetric with respectto the left ventricle. In a right dominant systemthe right coronaryartery must traversethe entire atrioventricular groove before giving off any branchesthat might supply even the mostbasal aspect of the inferior wall. The situation is similar, if less marked, in a left dominant system.In addition, the LV apex is usually supplied by the left anterior descending artery, as the right coronary and circumflex arteries rarely extend this far distally. In our study, the inferior wall was significantly more likely to display asynergy than the other LV walls, being as frequently involved as the apex. The basal and medial inferior segmentswere unique in displaying an equal distribution of asynergy.We postulate that increased vascular distance along the courseof the coronaryarterial tree beforereceiving its vascularsupply accountsfor the increasedjeopardy of the inferior wall in general, and its basal segmentin particular. Our coronary arterial data reveal a fairly even distribution of critical diseasebetweenthe 3 coronary arteries,findings consistentwith previous large angiographicstudies.lge20 In our study, the right coronary artery was actually the leastdiseasedand the left anterior descending artery the most diseased.Since the increasedprevalenceof inferobasalasynergydoes not result from an increased prevalence of right or circumflex coronary artery lesions, we postulate insteadthat this increasedinferobasal asynergyresults from the long courseof either the right or dominant circumflex artery beforesupplying the most basalportion of the inferior wall, an anatomic feature that in-

TABLE Ill

Lefl Ventricular

Segment Rank by Wall Motlon Index

Radionuclide Medial Apical Sasal Medial Basal Medial Medial Sasal Sasal

inferior

2.08 2.04 2.04 1.85 1.73 1.86 1.53 1.36 1.13

inferior septal septal lateral anterior lateral anterlor

1 = normal

Angiography

wall motion:

2 = hypokinesia;

Medial Apical Medial Basal Medial Medial Basal Basal Basal

septal inferlor inferior anterior lateral septal lateral anterlor

2.09 1.91 1.80 1.80 1.53 1.43 1.35 1.13 1.07

3 = akinesla/dysklnesia.

creasessusceptibility to the pressureattenuation and occlusive jeopardy of more proximal stenoses. Our findings are in substantial agreement with those of Savageet a1,15who studied 24 well circumscribed infarcts at autopsy with longitudinal section and planimetry of the infarcted area. Their findings and ours are consistentwith the conclusion that left anterior descendingartery infarcts exhibit asynergyin the distal anterior, septaland apical segments,whereas right coronary and circumflex infarcts show relatively more asynergyin the basal inferior wall. The increasedjeopardy of the basal inferior segmentis in distinct contrastto the basal anterior segment,where studies of both mild wall motion abnormalities21and large anteriorinfarcts with aneurysmformationz2indicate that normal function is almost always preserved. It may be that basal anterior asynergyoccurs almost solely in the presenceof left main occlusion,a condition that frequently precipitates sudden death from arrhythmias and does not permit precise delineation of the infarct zone by pathologic examination or ventriculographic techniques.

ASYMMETRIC

546

TABLE IV

DISTRIBUTION

OF LEFT VENTRICULAR

ASYNERGY

Summary of Coronary Artery Anatomy by CASS’ Segments 1

Coronary

(<70% Stenosis. Anterograde)

Afiery Right (CASS l-4) (n = 365) Ante&r descending (CASS 11-17) (n = 567) Circumflex (CASS 11, 16-22,

2 (<70% Stenosls, Collateralized)

3 (270%

190

(52%) 350

(2820%) (7:)

311

55

40 (11%)

(26%) (3:)

(68%)

3+4

(occluded)

(15%) 147

(62%) 27)

stenosis)

4

32

(6%)

179 (32%)

106

24

132

(24%)

(5%)

(29%)

(n = 457) ‘Coronary

Artery

Surgery

Study.

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