Chronic coronary artery constriction leads to moderate myocyte loss and left ventricular dysfunction and failure in rats

(1)

Chronic coronary artery constriction leads to

moderate myocyte loss and left ventricular

dysfunction and failure in rats.

P Anversa, … , P Li, J M Capasso

J Clin Invest. 1992;89(2):618-629. https://doi.org/10.1172/JCI115628.

Coronary artery narrowing, ranging from 19% to 61%, was induced in rats and ventricular performance, myocardial damage, and myocyte hypertrophy were examined 1 mo later. Animals were separated into two groups, exhibiting ventricular dysfunction and failure, respectively. Dysfunction consisted of a 2.4-fold increase in left ventricular end diastolic pressure (LVEDP), 15% decrease in left ventricular peak systolic pressure (LVPSP), 24% reduction in developed pressure (DP), and a 16% depression in-dP/dt. Failure was defined on the basis of a 4.7-fold elevation in LVEDP, and a 26%, 47%, 45%, and 41% decrease in LVPSP, DP, +dP/dt, and -dP/dt. Moreover, in this group, right ventricular end diastolic and systolic pressures increased 5.5- and 1.2-fold. Left and right ventricular weights expanded 23% and 51% with dysfunction and 30% and 56% with failure. Left ventricular hypertrophy was characterized by ventricular dilation and wall thinning which were more severe in the failing animals. Foci of damage were found in both groups but tissue injury was more prominent in the endomyocardium and in failing rats. Finally, myocyte loss in the ventricle was 10% and 20% with dysfunction and failure whereas the corresponding enlargements of the unaffected myocytes were 34% and 53%. Thus, coronary narrowing led to abnormalities in cardiac dynamics with an increase in diastolic wall stress and extensive ventricular remodeling in spite of a moderate loss […]

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(2)

Chronic

Coronary

Artery Constriction Leads

to

Moderate Myocyte

Loss and Left Ventricular Dysfunction and Failure

in

Rats

Piero Anversa, Xun Zhang, Peng Li, and Joseph M. Capasso

DepartmentofMedicine, New York Medical College, Valhalla,New York 10595

Abstract

Coronary artery narrowing, ranging from 19% to 61%, was in-duced inrats and ventricular performance, myocardial damage, andmyocyte hypertrophy were examined1 molater.Animals were separated into two groups, exhibiting ventricular dysfunc-tion and failure, respectively. Dysfuncdysfunc-tion consisted of a 2.4-fold increase in left ventricular end diastolic pressure (LVEDP), 15% decrease in left ventricular peak systolic pres-sure(LVPSP),24%reduction in developed pressure (DP), and a16%depression in-dP/dt.Failure wasdefinedonthebasis of a4.7-foldelevationin LVEDP, anda26%, 47%, 45%, and 41% decrease inLVPSP, DP, +dP/dt, and -dP/dt.Moreover, in this group,rightventricular enddiastolic and systolic pressures increased 5.5- and 1.2-fold. Left and right ventricular weights expanded 23% and 51% withdysfunctionand 30% and 56% with

failure. Left ventricular hypertrophywas characterizedby ven-triculardilationand wallthinning whichweremore severe in thefailinganimals. Foci of damagewerefound in both groups buttissueinjurywas moreprominent in theendomyocardium

and infailingrats. Finally, myocyte loss in the ventricle was 10% and 20% with dysfunction and failure whereas the

corre-spondingenlargements of the unaffectedmyocytes were 34% and 53%.Thus, coronarynarrowingledtoabnormalities in

car-diacdynamicswithanincrease in diastolic wallstressand

ex-tensive ventricular remodelingin spite ofamoderate loss of myocytes and compensatory reactivehypertrophyof the viable cells.(J. Clin.Invest.1992.89:618-629.) Keywords: left and right ventriculardynamics*

myocardial damage.

myocyte

hy-pertrophy* ventricularremodeling* wallstress

Introduction

In a large number ofpatients affected by chronic coronary arterydisease,themagnitude of constriction oftheepicardial

coronaryarteries by atherosclerosisdoesnotcorrespondtothe

severity oftheclinical manifestationsof

myocardial

dysfunc-tion and failure(1-7). Similar degrees ofcoronarystenosis de-tected

angiographically

have been foundtobeassociatedwith

variablehemodynamic abnormalities,raisingquestionson the

significanceofthesefixedobstructionsof the coronary treein

theprediction ofthe short- and long-term outcomes of isch-emic heartdiseaseclinically (7). This apparent inconsistency

Addressreprint requests to Dr. Anversa, Department of Medicine, Vosburgh Pavillion-Room 303, New York Medical College, Val-halla,NY10595.

Receivedfor publication10 June 1991 and in revisedform 26 Au-gust 1991.

becomesevengreater whenanatomicalfindings are taken into account(7-12). Histologic examination of hearts of patients who diedofcongestive ischemic heart disease reveals that only smallquantities ofviablemyocardium have been replaced by scarredtissue(9, 12),suggestingthat the overall extent ofdam-ageintheventricularwall may not reflect a loss of myocytes which would be considered critical for the induction of irrevers-iblecardiac failureanddeath. Studies in humans(13, 14) and

animals(15, 16) have demonstrated thatocclusion ofa major coronary artery,resultinginacutetransmuralmyocardial in-farction, leads to overtcardiacfailure when the destruction in muscle massaffects40-50%ofthe myocyte population of the leftventricle. Moreover, ventriculardecompensation persists duringthehealingprocess(17-19)andlong thereafter (20, 21).

Importantly, adirect relationshipexists between healed infarct

size and ventricularperformanceinanimals(18)and humans (22, 23),further emphasizing potential differences inthe

gene-sisof cardiac failure produced by occlusiveandnonocclusive

coronary stenosis. However, this suspected discrepancy has never been documented and, on the assumption that such a phenomenonisreal, thereisnoknowledge on themechanisms responsible for the development of congestive heart failure with coronarynarrowing. Thus, a relevant question to be ad-dressed is whetherpartial reductionsin luminaldiameter ofa major epicardial coronary artery result in animpairment of ventricular functionwhen<40-50% ofmyocytes are lost or is

this quantity required to generate severe ventricular

decom-pensation, mimickingtheconditionof

myocardial

infarction-induced cardiac failure.Inaddition, it is still unknown whether comparable losses ofmyocytes in a segmental fashion,

i.e.,

myocardial infarction,or inascattered manner across thewall, i.e., ischemic cardiomyopathy,evokeidenticalhypertrophic

re-actionsontheremaining unaffectedcells.Finally, myocytoly-tic necrosismay

persist

withtime in the presenceofa fixed nonocclusivelesionofamajorcoronary artery andthisprocess may

affect

ventricularremodeling (24, 25)and the recoveryof

structure and function chronically.

Therefore,

coronary

narrowingwasproducedinratsand thefunctionaland

anatom-icalvariablescontrollingventricular wallstresswereevaluated

1 mo aftersurgery. Furthermore,themagnitudes ofmyocyte lossand reactive cellular hypertrophyweremeasured morpho-metrically. The1-mointervalwaschosenbecauseof

Perfusion pressurewasadjustedtothemeanarterial pressure measured invivo. The left ventricular chamberwasfilled with fixative andkeptat a pressure equal to the in vivo measured end-diastolic pressure throughout the fixation procedure (24). After perfusionwith pH 7.2 phosphatebufferfor 3 min, the coronary vasculaturewasperfusedfor 15 min with a solution containing2%paraformaldehydeand 2.5%

glutaraldehyde (15). Subsequently, the heart was excised and the weightsoftheleft ventricleincluding the septum and theright ventricle

wererecorded. Itshould be noted that in 2 of the 19 coronary

con-strictedratsperfusionfixationwas notadequate. Therefore, quantita-tive morphologywasrestrictedto17experimentalrats.

Degreeofcoronary artery narrowing. The initial 2-3-mm segment

oftheleft coronary artery wasdissected freetolocalize the level of

coronaryconstriction.The vesselwasthencuttransverselytoexpose the lumen ofthe coronary artery attheregion oftheligature. The luminal diameter of the vessel adjacenttothenarrowedsiteand in the constrictedportionweremeasured withadissecting microscope having

anincorporatedocularreticle.Maximal and minimalinternal

diame-tersin each of thesetwolocationsweredeterminedatx20,and the

geometricmeanvaluewascalculated(24, 25).Thedegree of

constric-tionwasevaluatedbycomparingthe vesseldiameter above the stenosis with the diameter at the level of the stenosis. This approach was pre-ferredtocomparisonsbetweenexperimentalandsham-operated

con-trol rats, in ordertominimize thevariabilityin the coronary

vascula-tureamonganimals.

Ventricular dimension. The major intracavitary axis of the left ven-tricle from apex to base was measured by sectioning the elliptical chamberparalleltothelongitudinaldiameter. Subsequently, each left ventriclewasserial-sectioned into 2-mm-thickrings perpendicular

tothelongitudinalaxistoobtainsix equally spaced parallel planes from thebasetothe apex in which the average wall thickness of the free wall and chamberluminal diameterweremeasured.Eightmeasurementsof the leftventricular free wall in each sectionwere collected and their values averaged. The minimal and maximal diameters of the

ventricu-larchamberateachof the sixsampled levelsweredetermined and their geometricmean wascomputed(27). The longandtransversediameters

wereemployedtocalculatechambervolume (27). Rightventricular

wallthickness near the base, in the portion containing the coronary artery, was also measured by averaging 10 determinations in each heart. Moreover, the measurements of wall thickness, chamber radius, andventricular end diastolic pressure in the left ventricle were used to compute diastolic transmural wall stress (28) at each of the six sites examined from base to apex. Systolic transmural wall stress was also calculated in a similar manner (24, 28).

Tissue sampling. In all 27 animals, the two middle slices of the left ventricle, nearly halfway between the apex and the base, were cut in thinner sections in order to obtain three to four slices, -1 mm in thickness, which were subsequently postfixed in osmium, dehydrated inacetone, and flat embedded in araldite. Sections 1-2 jim thick were cutwith a glass knife, 38 mm long (model 2078 Histoknife Maker, LKBInstruments, Gaithersburg, MD), and a rotary microtome (HM 350, Microm, Carl Zeiss, Inc., Thornwood, NY). These sections, which contained the entire thickness of the wall, were stained with toluidine bluefor quantitative measurements. 15 consecutive fields, each from theendomyocardium and epimyocardium in each animal, were exam-ined at a calibrated magnification ofx400with a reticle containing 42 sampling points (105844, Wild Heerbrugg Instruments, Inc., Farming-dale, NY). This reticle defined an uncompressed tissue area of 62,500

JAm2,whichwasemployedtodetermine the numberof lesions

repre-sented by foci of damage per unit area of myocardium. Moreover, the fraction of points lying over these foci was measured to compute the volume fraction of lesions in the myocardium and the average cross-sectional area of the lesion profiles. Sarcomere length was measured in the midregion of the wall at Xl,000 by averaging groups of 10 sarcomeres each. 10 such determinations were collected in each left ventricle.

Sites in these slices with myofibers oriented in the longitudinal or transverse direction were cut free with a razor blade from the thick embedded sections. Approximately 25-30 blocks collected from each animal were then reembedded in small flat molds (29).

Myocyte size and number. Ten randomly chosen tissue blocks from eachleft ventricle were sectioned at a thickness of 0.75Mmandstained with toluidine blue. Morphometric sampling at a magnification of

X1,000 consisted of counting the number of myocyte nuclear profiles, N(n), in a measured area, A, of tissue sections in which cardiac muscle fibers were cut transversely. A square tissue area of 9,950 Mm2 was delineated in the microscopic field by the 42 sampling points ocular reticle. A total of 20-26 such fields were evaluated in the endomyocar-dial and epimyocardial regions of each ventricle of each animal to determine the number of nuclear profiles per unit area of myocardium, N(n)A, and the volume fraction of myocytes, V(m)v, in the myocar-dium of the inner and outer layers of the wall.

Nuclear length, D(n), was determined in the endomyocardial and epimyocardial regions of each left ventricle from 50 measurements each made atX1,250 inlongitudinally oriented myocytes viewed with amicroscope having an ocular micrometer accurate to 0.5 Mm. Ten blocks with myofibers sectioned parallel to their length were cut, sec-tions at - 2 Mmin thickness collected and stained, and 10

measure-ments of nuclear length were recorded from each tissue section, 5 each foreach region of the wall.

From the estimation of N(n)A and D(n), the number of myocyte nuclei per unit volume of myocardium,N(n)v,wascomputed using the equation(15,29):

=

_N(n)AIN(n)v

₍₁₎

Myocyte cell volume per nucleus in the inner and outer layers ofthe wallof each left ventricle, V(m)",wasobtainedfrom the volume frac-tionof myocytes, V(m)v, divided by thenumberof myocyte nuclei per unit volumeofmyocardium:

(2)

Thetotalnumberof myocyte nuclei in eachventricle,N(n)T,was

thenderived fromtheproductof the numberperunitvolume,

N(n)v,

(4)

and the total ventricular volume of viable myocardium, VT, previously

measuredfrom thelarge sectionsof theventricle.

N(n)T=_N(n)vX _VT ₍₃₎

In this case,N(n)vwas evaluated byaveragingthe valuesobtained in the inner and outerlayersofthe wallineachventricle.Asimilar approach was used when regional morphometricvalues of volume fraction of tissuecomponents, numericaldensity ofnuclei, nuclear

length,and cellvolumeper nucleuswere expressedasindicatorsofthe

entirewall. Thetheoreticalaspects andpractical applications ofthe

morphometric procedurebriefly summarizedabovehaverecentlybeen

describedin detail(30).

Samplingsize. The magnitudeofsampling utilized in this investi-gationwas selected onthe basisof previous workperformed inour

laboratoryand theprincipleof Poissonstatistics (30).Thelattercan be

usedas a reasonableguideline formorphometricdatacollection since it providesa moreconservative estimateofnecessary counts than more

specificformulationsderived for pointcounts andprofilecounts(20).

By assuming thatbiological variability among animals inagiven experi-mentalgroupis 10%, countingerrorsin each animal should also be limitedby the sameorderof magnitude forthe leastfrequentstructure

(20).In the presentstudy,the areaofmyocardiumsampledyieldan

averageof 168, 173,and341 nuclearprofilecountsforthe endomyo-cardium, epimyocardium andwallofeach coronaryconstricted left ventricle, respectively.Correspondingsamplingerrorsforthese values

were7.7%, 7.6%, and 5.4%. Counts incontrol animals were 172, 180,

and 352 which yielded samplingerrors per animal of 7.6%, 7.4%, and5.3%.

Data collectionandanalysis.Alltissuesamples were coded and the

codewas broken attheendoftheexperiment.Results arepresentedas

mean±SDcomputedfromthe average measurementsobtainedfrom eachrat. Statisticalsignificance forcomparisonbetween two

measure-mentswithin the wallofeachventriclewasdeterminedusingthepaired Student'st test.Statisticalsignificanceinmultiple comparisonsamong

independentgroupsofdata, inwhichanalysis ofvarianceandtheFtest

indicatedthepresenceof significantdifferences,wasdetermined bythe

Scheffemethod(31).ValuesofP<0.05wereconsideredtobe

signifi-cant. Because measurements presentedwere notobtained in all ani-mals,n values for each parameter measured are listed in the text or the

legendof each figure.

Results

Thesurgical procedureemployedfortheimpositionofa

non-occlusive stenosis of the leftcoronary arterynearitsorigin

re-sulted inreductions in luminal diameterrangingfrom 19%to

61%.Physiologicalmeasurementsof cardiacdynamics demon-stratedthatcoronary arterynarrowingaffected heart function in avariable fashion andthis impairmentwas notcorrelated withthe degree ofconstriction. This phenomenon has

previ-ously beendescribed45 min(24)and 5 d(25) aftercoronary

stenosis. Becauseof thedifferencesinventricularperformance, the 19animals withvesselnarrowingweresubdivided intotwo

groupsof8 and 11 rats,respectively. The firstgroupincluded animals in whichleft ventricular developedpressure was .75

mm Hg, +dP/dt was 2 9,000 mm Hg/s and -dP/dt was 2 8,000 mm Hg/s. Moreover, noalterations in right

ventricu-larperformance were noted. The second groupincluded rats

withvaluesof left ventricular developedpressure,+dP/dtand -dP/dt belowthose stated above. Attimes, abnormalities in right ventricularfunctionwere alsopresent. The degreeof coro-nary constriction in the first and second group of rats was

46±12% (n = 8) and 43±18% (n = _{11), respectively. These}

changes indiameter correspondedto a69±15% and 64±19% reduction in luminal cross-sectional area. On thebasis of the

TableI.Effects ofCoronaryArtery Constriction onArterial Blood

PressureandHeart Rate

Narrowed animals Sham-operated

animals GroupI Group 2 (n=9) (n=8) (n=11)

Bodyweight (g) 381±22 395±18 410±21*

Arterialblood pressure(mm Hg)

Systolic 119±7 100±7* 87±12**

Diastolic 86± 10 66±8* 65±10*

Mean 97±8 77+7* 72±11*

Heart rate(bpm) 355±47 314±43 351±51

Results areshownasmean±SD.*Value thatisstatistically signifi-cantly different fromthecorrespondingvaluein control animals,P

<0.05.*_Value_that_is_{statistically}_{significantly different from}_the correspondingvalue in group 1animals,P<0.05.

hemodynamic profile(see below), itwasconcluded that these rats exhibited left ventricular dysfunction (group 1) and left ventricular failure (group 2).

Global cardiac performance. Table I shows that body weight was similarin controls and in the first group ofrats with coronary constriction,whereas an 8%increasewas measured in the second groupof experimental animals. Moreover,

sys-tolic, diassys-tolic, and mean arterial pressures were decreased 16%, 23%, and 21% in thefirstgroup and 27%, 24%, and 26% inthe second groupofratswithcoronarystenosis.However, heart rate was notdifferentin control and coronary narrowed rats.

Fig. 1 illustratesthatalterationsinleft ventricular minimal diastolic pressure

(LVMDP),'

end-diastolic pressure(LVEDP), peaksystolic pressure(LVPSP), anddevelopedpressure

(DP)

occurredas aresult of coronary stenosis.Inthe first group of rats LVEDPincreased 2.4-fold (P<0.02),andLVPSP andDP decreased 15%(P<0.002)and 24%(P<0.0001). However,in the second group,LVMDPand LVEDPaugmented9.7-fold(P <0.001)and 4.7-fold(P<_0.0001), whereas LVPSP and DP diminished 26%(P < _0.0001)and47%(P <_0.0001). More-over, incomparisonwith the first group of coronary stenosed rats, animalsin the second group showed valuesofLVMDP and LVEDPwhichwere5.7-fold(P<0.001)and 1.9-fold(P <0.001)greater, and values ofLVPSP and DP whichwere13% (P<0.03)and 31%(P<0.0001)lower.

Fig. 2demonstrates that in thefirstgroupof coronary ar-tery narrowedrats+dP/dt remainedessentiallyconstantwhile

-dP/dt decreased 16% (P<0.03). However, the reduction in

-dP/dtwas notsufficienttoaffect the +dP/dt to-dP/dt ratio. Inthe second groupofstenosed rats+dP/dtand-dP/dt were reducedby 45% (P<0.0001) and 41% (P < 0.0001) and these

changesmaintained the +dP/dt to -dP/dt ratio substantially

constant.On the other hand, when the two experimental ani-mal groups were compared, the second group had values of +dP/dt and -dP/dtwhichwere38% (P<0.0001)and 29% (P

<0.001)lower thanthose in thefirst group. Moreover, an11%

1. Abbreviationsused in thispaper:DP, developed pressure; LVEDP,

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100

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Figure 1.Effectsof chronic

coronaryarterynarrowing

onleft ventricularpressures

inanimals withleft

ventricu-lardysfunction(LV-D)and

leftventricular failure

(LV-F). Results arepresentedas mean±SD. *Value

signifi-cantly different fromthe

correspondingresultin

con-trolanimals(C). 'Value sig-nificantly different from the

correspondingresultin

ani-malswithleft ventricular

dysfunction.(C,n =9;LV-D,

n=8;LV-F,n= 11.)

(P<0.02) reduction in +dP/dtto-dP/dt ratiowasalso noted. Although right ventricular functionwaspreserved in the first groupofrats, in the secondgroupof animals right ventricular end-diastolicpressure(control, 1.12±1.19;group1,1.99±1.15;

group2,6.16±2.21 mmHg) and peak systolicpressure

(con-trol, 27.57±1.89; group 1, 29.76±2.39; group2, 32.81±3.20 mm Hg) increased 5.5-fold (P < 0.0001) and 1.2-fold (P

<0.001), respectively.

Insummary,chroniccoronaryarteryconstriction resulted inanimpairment of myocardial performance ranging from left ventricular dysfunction (group 1) to left ventricular failure (group 2).

Gross cardiac characteristics. Coronary constriction re-sulted in an increase in weight of the left (control, 805+83;

group 1,987±94; group2, 1,050±90 mg) and right (control,

234± 16;group 1,354±57;group2, 364±55mmHg) ventricles and these augmentations in myocardialmass were similar in animals withleft ventricular dysfunction and failure. Left and right ventricular weights expanded 23% (P<0.002) and51 %(P

<0.0001) ingroup 1 rats, and 30% (P< 0.001) and 56% (P <0.0001) ingroup 2 rats. These changes provokeda29% (P <0.0001) and 36% (P <0.0001)greaterheart weight in ani-mals withcardiac dysfunction and failure, respectively (con-trol, 1,039±100;group 1, 1,341±102;group2, 1,414± 101 mm

Hg). Because of the small variations in body weightamongthe experimental and control animal groups (Table I), the in-creasesinheart weight and left and right ventricular weight-to-body weight ratios aftercoronarystenosisweresimilartothose found withrespect toweight changes alone (Datanotshown).

Insummary,chroniccoronaryarterynarrowing ledto bi-ventricular hypertrophy. Myocardial hypertrophy, however, wassignificantlygreaterin theright than in the left ventricle.

Ventricular size and shape. Figs. 3 and 4 illustrate the

changesinwallthickness (Fig. 3) and chamber diameter (Fig. 4) aftercoronaryarteryconstrictionateach of the six levels of the left ventricle from basetoapex.In comparison with con-trols, group 1 andgroup2 ratsshowedsimilar alterations in

these anatomical parameters. Wall thickness in group 1

de-creased,respectively 19% (P<0.01), 19% (P<0.01), 16% (NS), 11%(NS), 14% (NS), and 32% (P<0.001),atlevels 1,2, 3,4, 5, and 6. Corresponding changes in group 2 were -18% (P

<0.01), -18% (P<0.01), -17% (NS), -16% (NS), -20% (P <0.01), and -35% (P<0.0001).Average right ventricular wall thicknesswasincreased 46% (P<0.004) and 30% (P<0.04), in

group 1 andgroup2animals(controls, 0.80±0.10mm;group

1 1.17+0.22mm;group2, 1.04±0.23 mm).

Incontrast tothe thinning ofthe wall, ventricular chamber diameter (Fig. 4) increasedas aresult ofcoronaryartery con-striction.Inanimals with ventricular dysfunction, cavitary

di-ameterexpanded 17%(NS),24%(P<0.004), 21% (P<0.01),

13% (NS), 3% (NS), and-18%(NS) from baseto_apex.Inthe

presenceof ventricular failure, the augmentations in chamber diameter were 22% (P < 0.01), 32% (P< 0.0001), 32% (P <0.0002),23%(P<0.002), 11%(NS), and -2% (NS).

More-over, the longitudinal axis of the ventricular cavity was 11.95±0.79 mmincontrols, 15.56±0.39mmingroup 1, and 15.86±0.48 mmingroup2. Thus, this anatomicalparameter

increased 30% (P<0.0001) and 33% (P<0.0001) in animals

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Figure2. Effects of chroniccoronaryarterynarrowingonleft

ven-tricularrateofpressurerise(+dP/dt)anddecay (-dP/dt), and their

ratio. Resultsarepresentedasmean±SD.*Valuesignificantly

differ-entfromthecorrespondingresultincontrolanimals(C).'Value sig-nificantly different from the correspondingresultinanimals with left

ventricular dysfunction. (C,n=9; LV-D,n=8; LV-F,n= 11.)

with ventricular dysfunction and failure, respectively. These

changesresulted in marked increasesincavitary volume, 63% (P<0.004)ingroup 1 and 93%(P<_0.0001)ingroup2 (con-trols,346±99

,gl;

group1,567±151 Al;group2,667±126

,l).

It

should be pointed out that the shape of the heart was also affected bycoronarynarrowing, since the ratios oftransverse

cavitary diameters and longitudinal axis, decreased 13% (P

<0.03),22%(P<0.01),and 37%(P<0.001)in the last three

levels towards theapexinanimals withdysfunction,and 18%

(P <0.01) and 26%(P<_0.005)inthetwoapical ringswith

failure(datanotshown). Inaddition,the ratios of wall

thick-ness-to-chamber radius decreased from base to apex in both groups ofexperimental animals. Finally, average sarcomere

lengthwas2.01±0.03

_,m

incontrols, 2.06±0.04

,gm

in animals withleftventriculardysfunction,and 2.15±0.04

_gm

in animals withleftventricular failure.

In summary,chronic coronary artery constriction led to an increase inventricularchambervolume,adecrease inleft

ven-tricular wall thickness anda change in shape of the heart

to-wards a moreelliptical configuration.

Wall stress. The measurementsofwallthickness,chamber diameter, and ventricular pressures have been employed to compute the distribution ofsystolic anddiastolicwall stress from the endocardium to the epicardium in each of the six layers examined(Fig. 5).Whereasdiastolic wall stress increased

significantly throughoutthe wall and from basetoapex after coronaryconstriction,anopposite phenomenonwasobserved in terms ofsystolic wall stress. The greater depressions in

ven-tricularpumpperformancewereassociated withthelarger in-creases in diastolic wallstresswhereassystolicwallstress de-creased.

Insummary,chroniccoronary arterynarrowing produced

anelevationindiastolicwallstressandadecrease insystolic

wall stress which were proportional to the degree of impair-ment inventricular dynamics.

Myocardial damage. Consistent with previous observations

(24, 25),light microscopicexamination of the left ventricular

myocardium showed that multiple foci of acute and chronic

tissue and myocyteinjurywerepresent in coronary stenosed rats. Acutelesions consistedof isolated myocytes with focal or

extensive loss ofcytoplasmic structures and appearance of largecytoplasmicvacuoles. Chronic damage was characterized byfocallossof myocytes and consequent reparative processes indifferentphasesofhealing. The morphometric analysis of myocardial injury associated with coronary constriction did

not

distinguish

amongthesedifferent forms of tissue and

myo-cytedamage. They wereconsideredpartof the same process,

simplyinvariousstagesofevolution, and consequently

com-binedinthisquantitative evaluation.

Fig.6 demonstrates that the volume percent of damage in the myocardium increased markedly as a result of coronary

narrowing. In comparisonwith sham-operated controls, this structural parameterincreased 13-fold(P<0.005), 12-fold (P

< 0.001), and 12-fold (P< 0.001) in the endomyocardium,

epimyocardium,andacrossthe wall of animalswith left

ven-triculardysfunction.Inthe presenceof left ventricular failure, theseincreaseswere22-fold (P<0.0001), 19-fold(P<0.0001),

and20-fold (P<0.0001), respectively. Moreover, animalsin

thisgroup had valuesof volumefraction oftissue injury which

were 72% (P < 0.02), 57% (P<0.03), and 64% (P < 0.002) higher than those measured in the inner and outer layers of the ventricle and in the wallofratswith ventricular dysfunction only.

Fig.7shows thatthesize of the lesion profiles in the myo-cardiumwas approximately two- to threefold greater in ani-mals with coronary constriction than in controls. Although thesesites wereconsistently larger in animals with ventricular failure than in those with myocardial dysfunction, only the

49%difference found intheendomyocardiumwasstatistically

significant(P<0.01). Moreover, the number of lesion profiles per square millimeter of tissue increased 6.9-fold(P<0.001),

5.8-fold (P<0.0001),and6.3-fold (P<0.0001),inthe

endo-myocardium, epiendo-myocardium, and as an average across the Us

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1 2 3 4 5 6 1 2 3 4 5 6

Base Apex Base Apex

Figure3.Effectsofchronic coronary artery narrowing on left ventricular wall thickness from the basal to the apical region. (A) Controls; (B) left ventriculardysfunction;(C)left ventricular failure. Results are presented as mean±SD. *Value significantly different from the corresponding result in control animals (C).'Valuesignificantly different from the corresponding result in animals with left ventricular dysfunction. (C, n = 9; LV-D, n=8; LV-F, n= 11.)

wall in rat with ventricular dysfunction (Fig. 8). Corresponding increases in ventricular failure were 7.9-fold (P<0.0001), 7.7-fold (P<0.0001), and7.8-fold(P<0.0001).

Insummary, the magnitude of chronic myocardial damage induced bycoronary artery constriction was greater in the pres-enceof ventricular failurethanmyocardial dysfunction.

Number ofmyocyte nuclei in the ventricle. The primary measurementsthat were used for the derivationofthe numeri-caldensityof myocyte nuclei per unit volumeof myocardium

consisted in the determinationofthe numberofmyocyte

nu-cleiperunitareaofnondamagedtissueand in theevaluationof

average nuclear length. These parameters wereobtainedin the

endomyocardium and epimyocardium of each ventricle and thencombinedto compute anaverage value in the wall (data not shown). The product ofthese average values combined with the aggregate volume of viable myocardium in the ventri-clesyieldedthe total numberof myocyte nuclei in the ventri-cles(15, 16, 21, 32). The resultsobtainedin control and coro-naryconstricted rats are shown in Fig. 9.

Incomparison with sham-operated control animals, coro-nary narrowed rats showing ventricular dysfunction exhibited

a 10%(P<0.04) loss in the total number of myocyte nuclei of theleft ventricularwall.Agreater loss in myocyte nucleiwas found with ventricular failure (Fig.9). With respect to control value, a 20% (P < 0.0001) reduction in nuclei was demon-strated in this group. Moreover, this parameterwas 12% (P

<0.02)lower inanimals with cardiac failurethan in those with

myocardial dysfunction.It should be noted that these decreases in the total number of myocytenucleiin the ventricle corre-spondtoidenticalchanges in myocyte number if the propor-tion between mononucleated andbinucleatedcells in the

myo-cardium remainsessentiallyconstant(32).

In summary, chronic coronary artery constrictionled to myocyte loss which was greater with ventricular failurethan

withmyocardial dysfunction.

Myocyte cell volume. Fig. 10 shows the measurements of

myocyte cell volume per nucleusobtainedin theleft ventricle

of control and coronary narrowed rats.Thiscellular parameter was notstatisticallydifferent in the endocardial andepicardial

layersofthe wall insham-operated controls, and theregional increases with ventricular dysfunctiondid notaffect this

char-acteristic. Myocyte cell volume per nucleusin thisgroup

in-1-

_I

B

4 5 6 1 2

Apex Base

K

3 4 5 6

Apex

Figure4.Effectsof chroniccoronaryarterynarrowingonleftventricular chamber diameterfrom the basaltotheapical region. (A) Controls; (B)

left ventriculardysfunction; (C)left ventricularfailure. Resultsarepresentedasmean±SD. *Valuesignificantlydifferent from thecorresponding

result in controlanimals(C). 'Value significantlydifferent from thecorrespondingresult in animals with left ventriculardysfunction. (C,n

=9; LV-D,_n=8;LV-F,_n= 11.)

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900 800 700 600 500 400 300 200 100

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450 400 350 300 250-200 150 100 _

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Figure 5. Effects of chroniccoronaryarterynarrowingonleft ventricular diastolicandsystolicwallstress,fromthebasal to theapical regionof the ventricle andfrom the endocardiumtotheepicardium.Theincreases in diastolic wall stress withdysfunctionandfailureareallsignificant and the valuesinthefailinggroupareallhigherthan thoseinthedysfunctiongroup.The decreases insystolicwall stress withnarrowingare

significant onlyinthe inneronethird of the wall of bothexperimentalanimalgroups and the reduction with failure isgreaterthan with dys-function. (C,n=9;LV-D,n=8; LV-F,n= 11.)

creased 39%(P<0.0001)intheendomyocardium and 29% (P <0.0001)intheepimyocardium resultinginanaverage34%(P <_{0.0001) increase in the wall. Corresponding enlargements}in myocyte cell volume per nucleus with failure were 71% (P <0.0001), 37% (P<0.0001), and 53% (P<0.0001). This dis-proportionate expansion in volume of endomyocardial

myo-cytesresulted inadifferenceinsize between endocardial and epicardialmyocytes. Infailinganimals, endocardialmyocytes

were 16%(P< 0.001) larger than epicardialmyocytes.

More-over, the hypertrophic response of endocardial myocytes in failing ventricleswas24%(P<0.001)greaterthanthat ofendo-cardial myocytes in ventricles with myocardial dysfunction. Finally, average myocytecell volumepernucleus in the wall was 14%(P<0.01)larger in animals with failure than in those with ventricular dysfunction.

In summary, chroniccoronary artery constriction led to

myocyte cellular hypertrophy which wasgreater in the

pres-enceofventricularfailure than myocardial dysfunction. Correlation analysis. Table II illustrates the results of

re-gressionanalysis correlating various functional and anatomical

parameterswithrespect tothereduction in cross-sectionalarea

of the coronaryarterylumen.Thistypeofstatistical evaluation

wasperformed separately in animals with left ventricular

dys-function (group 1), left ventricular failure (group 2), and in the entire experimental animal population (group 1 + group2).

Measurements of ventricular performance, including LVEDP, LVPSP, +dP/dt, and -dP/dt, didnotcorrelatewith the

magni-tude of coronary artery narrowing. Similarly, the typical

aspects of ventricularremodeling, represented bychamber di-ameter, wallthickness, myocytecell volumepernucleus,and

totalnumber ofmyocyte nuclei,werenot correlatedwiththe

degreeofcoronaryarterystenosis.

Discussion

The findings of the current study demonstrate that chronic

constriction of the left main coronary artery ofone month

duration was associated with alterations in cardiac perfor-manceconsistingof left ventricular dysfunction and failure.

Thesetwoabnormal hemodynamicstateswerefound in

combi-nations with extensiveventricularremodelingcharacterizedby chamber enlargementandthinningofthe wall. These

anatomi-cal variationsinconjunctionwith thedepressedfunction

pro-vokedamarked elevationindiastolicventricularstress.

More-over,discreteareasofmyocardialinjurycharacterizedbysites

ofacute myocytolytic necrosis and multiplefoci of

replace-ment fibrosis in various phases ofhealing were found. The

magnitude of myocyte losswas modest, accountingfor 10% and 20% of the total myocytepopulation in thepresence of

ventriculardysfunction and failure, respectively.The myocyte

cellular hypertrophicresponseexceeded the extent ofcells

be-ing lost since the correspondbe-ing increasesin myocyte cell

vol-umepernucleuswere34% and 53%.Therefore,afixed lesion

ofamajor epicardialartery ledtosevereimpairmentofleft side

pump dynamics in spite ofreactive growth mechanisms in

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left ventricular failure with elevated

filling

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car-diac output andaminimal

capacity

to

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preload

and afterload stresses has been encountered

(17). However,

with

relativelysmall

infarcts,

comprisingupto35% of the left

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nodetectable

impairment

of cardiac function has been found

(17,

21).

A similar discrepancy between the impact of coronary narrowingand occlusiononventricular function has been

dem-a

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Figure6.Effects of chroniccoronary artery narrowing on the volume percentof myocardialdamagein the left ventricular wall. Results are presented as mean±SD.*Valuesignificantlydifferent from the

corre-spondingresultincontrolanimals (C).'Valuesignificantlydifferent

fromthecorrespondingresult in animals with left ventricular dys-function.(C,n=8;LV-D, n=7;LV-F, n= 10.)

myocytes which resultedin anincrease in muscle mass of the affected ventricle.

Myocyte lossand ventricular performance. Datain this in-vestigation indicate that obstructions ofthe left coronary artery nearitsorigin, generating a 45% average reduction in vessel luminal diameter, were accompanied by either a 10% loss of cellsand ventriculardysfunction,ora20% cell loss and ventric-ularfailure. Thus, important differences exist between the

ef-fectsof chronic coronarynarrowingand thoseof total coronary

occlusiononcardiac hemodynamics. Alterations in ventricular

isoo

A

1600 A

1400

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1000 _

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Figure 7. Effects of chroniccoronaryarterynarrowingonthe size of

thelesion profiles in the left ventricular wall. Resultsarepresented

asmean±SD. *Value significantly different from the corresponding result in control animals (C).'Valuesignificantly different from the corresponding result in animals with left ventricular dysfunction.(C,

n=8; LV-D,n=7; LV-F,n= 10.)

rA

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Figure 8. Effects of chroniccoronaryarterynarrowingonthenumber

oflesionprofilesintheleft ventricular wall. Resultsarepresentedas

mean±SD. *Valuesignificantlydifferent fromthecorresponding

re-sultincontrolanimals(C).'Valuesignificantlydifferentfromthe correspondingresult in animals withleftventriculardysfunction.(C,

n=8; LV-D,n=7; LV-F,n= 10.)

onstrated acutely after the reduction in caliberofthe vessel lumen.Whereas with complete obstruction ofamajor epicar-dial artery and myocardial infarction, large destructions in

musclemass arerequiredtoimpair myocardial contractile per-formance (15, 16),coronary stenosis and relatively moderate

myocardial damage are accompanied by an immediate (24) andpersistent (25) depressioninleftsidepumpdynamics. On thebasisofthese observations,thepossibilitymaybeadvanced thatasuddenchangeincoronaryarterydiametermayresultin scatteredlossofmyocytesandprofound impairmentin

ventric-Figure 9. Effects of chroniccoronaryarterynarrowingonthe total

number ofmyocytenuclei inthe left ventricle.Resultsarepresented

asmean±SD. *Value significantly differentfrom the corresponding

result in control animals (C).'Value significantlydifferent fromthe corresponding result in animals with left ventriculardysfunction.(C,

n=9; LV-D,_n=7; LV-F,_n= 10.)

ularperformance (24, 33)whichmayreverseifthe

abnormal-ityinthe vesselwallresolves(33). On the other hand,afixed

lesion of thecoronary artery,modestinnature, mayprovoke

chronicand diffuse myocyte death(25)whichmayconstitutea

formofmyocardial damage capableofcontinuously offsetting

thereservecompensatorymechanismsof theinjured ventricle, leadingtoirreversible myocardial dysfunctionandovert

con-gestiveheart failure. Caution should be exercised in the transla-tion of theseexperimental studies to thehuman population affectedby atherosclerosisofthecoronaryarteries.

Atheroscle-rosis isadiseasestatethatprogressesover anumberofyears,

although acutehemorrhagewithintheatheroscleroticplaque

maygeneratesudden constrictionsinvessel luminal diameter. Finally,itshouldberecognizedthatthe evaluationof

myo-cytecell loss basedonthe changesinthe number of myocyte

nuclei in the ventricle maybeinfluenced byachangeinthe

proportion of mononucleated cells to multinucleated cells.

However,the number of nucleipermyocyte has been foundto

be essentially unchanged in left ventricular dysfunction and

failure(27, 32).Onthe otherhand,itcannotbeexcludedthat the calculated percentlossof myocytesfollowingcoronary ar-tery stenosis mayhavebeenpartially affectedbysucha

phe-nomenon.

Characteristics ofmyocyte loss and ventricular size. The quantitativeestimates of themagnitudeof myocyte loss asso-ciated withcoronaryarterynarrowingdiscussed above donot

provide informationonthedistributionofthisphenomenon

on theventricle. However, themorphometric analysisofthe

volumepercentage,number,andsizeoflesion fociinthe tissue demonstrated that damage to the myocardium involved the entire ventricular wall butwas moresevereinthe endomyocar-dium. Moreover, the magnitude ofthis formof damagewas

greater in animals with left ventricular failure than in those

withcardiac dysfunction. Importantly, myocytolytic necrosis

with acute loss of discrete groups ofcells was present one

monthafterthe surgical imposition ofcoronarystenosis.

Fi-nally, these pathological structural changes were found in combination with a marked increase in ventricular cavitary volume.

A

Epimyocardium 6o

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soB Endomyocardium

25

20 F

15 F 10 F

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25 F 20 F

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Figure 10. Effects of chroniccoronaryarterynarrowingonmyocyte

size in the leftventricle. Resultsarepresentedasmean±SD.*Value

significantly different from the corresponding resultincontrol ani-mals(C). 'Valuesignificantly different from the corresponding result inanimals withleft ventriculardysfunction. (C,n=9; LV-D,n=7; LV-F,n= 10.)

Thepossibility that ongoing isolated myocytolytic necrosis playsacentral role in the genesis of chamber enlargement is supported here by theextentof ventricular dilatationobserved followingcoronaryconstriction.In contrast,asingle episode of extensivemyocytenecrosisinasegmental fashion (15,21) does

notprovokeanexpansion in cavitary volume unless regional damageinvolves< 35% of the entire ventricularwall,early (16)

and late(19-21) afterthe ischemicevent. Moreover, similar

observations havebeen made inhumans (34-36). Then, the question is whether focal myocardial damage is sufficientto

explainthechangesinventricularcavitary volumeorwhether

additional mechanisms haveto beconsideredto account for the augmentation in ventricular size.

Cellloss, discrete in nature, canaffect ventricular dimen-sionsin two ways: acutely and chronically. Theacute conse-quencesreflect the necrotic phase in whichdyingmyocytes are

overstretched in diastole and noncontracting in systole, leading

todiastolic and systolic wallthinning.On theotherhand, the

chroniceffects include thereparativeprocessesassociated with healing andscarformation. Onthis basis, the increase in dia-stoliccavitarydiameter should be identicaltothe decrease in

wallthicknessproduced by thefractionof damage inthe wall.

Although this calculation exaggerates this phenomenon

be-causeitassumesthattissue injury doesnotcontributetowall thickness andmyocytesdonothypertrophy laterally, augmen-tationsin chamber diameterof3% and6% hadtobeexpected with dysfunctionandfailure.However,cavitary diameter, half-way between the base and the apex,increased respectively by 23% and 32%.Moreover,consistentwith previous results (24) only smallvariationsinsarcomerelength occurred in this

ani-mal model inspite ofanincrease in end-diastolicpressure. In this regard,adecrease in thepassive extensibilityofsarcomeres

has been observed in chronic left ventricular dilation (37), es-tablished cardiac hypertrophy (38), andacute left ventricular failure (39) in different modelsystems.Thus, thinning of the

wall andlengthening ofsarcomeresin myocytes can account

only in partforthe magnitudesofventriculardilation

mea-sured hereonemonthaftercoronarynarrowing.

The mechanism responsible for ventricular wall and chamberremodeling after nonocclusive constrictionsofmajor coronaryarteriesisatpresentunknown. However, the possibil-itymayberaised that architecturalrearrangementofmyocytes

with side-to-side slippage ofmuscle cells mayhavecontributed

totheexpansionincavitaryvolume(24). Side-to-side slippage

ofmyocyteswithinthewall(16)wouldgenerate areductionin themural numberof cells,wallthinningand chamber

enlarge-mentin the transverse direction. The lateral slidingof myo-cytesfromtheendocardialtotheepicardial surface ofthe

ven-tricular wallcanalso beanticipatedtoresultinanincrease in thelongitudinalaxisofthe heartproportionaltotheextentof

cellslippage. Thus, the decrease in the number of cells in the

transverse orientation leadsto anincrease in the number of cells in the longitudinalaxis. The majoraxis of the ventricle will thenincreaseby afactor involvingnumberofcells, average

celldiameter'Andtheangle oforientationof muscle cells with

respect tothelongitudinaldiameter of the heart.

Theobservations hereof increases in the longitudinal and

transverse diameters with thinning ofthe wall in spite ofa

cellularhypertrophicresponse suggestthatacute andchronic mechanisms have both beenoperative duringthe one month intervalstudied.Theexpansionin cavitary volumemaybethe criticaldeterminantinalteringthecapacity ofthe heartto re-store normalcardiacperformance. Shouldthemechanism of

cellmovementbeeffective in the presenceofcoronary

narrow-ing,acuteandchronicmyocytolytic necrosis wouldhave to be

regardedas animportant,butsecondaryeventdictated bythe

mechanicalconsequencesgenerated by the interaction ofwall

remodeling and ventricularpressure (24, 25). Moreover, the overallexpansioninventricularcavitaryvolumecreates a

me-chanicaldisadvantagetothe myocytesin thewallbyincreasing

diastolicmural stress whenfewercells are presenttohandlethe load. Asa result ofthese anatomical and functional

adapta-tions, ahypertrophicreaction ofmyocytesis elicitedand the

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Table II.Correlation Analysis betweenCoronaryArtery Constriction andPhysiologic andAnatomic Parameters

Group % Area LVEDP LVPSP +dP/dt -dP/dt CD WT CS CN

I(n= 8)

I;=

0.510 0.180 -0.440 -0.490 -0.150 0.370 0.450 0.120

P

= _0.190 _0.660 _0.280 _0.210 _0.720 _0.630 _0.310 _0.780

2(n= II)

Ir

=

-0.030

-0.230 -0.080 -0.220 0.350 -0.240 -0.040 -0.030

P= 0.920 0.510 0.810 0.520 0.330 0.500 0.920 0.940

Ir= 0.004 -0.041 0.025 -0.054 0.058 0.066 -0.046 0.136

1 +2(n= 19) _p=

_0.990

0.860 0.910 0.820 0.810 0.800 0.850 0.610

Linear regression analysis comparingtherelation betweenthedegree of coronary artery constriction,as apercentage of the total luminal cross-sectionalarea andvariousparametersof cardiac functionand structure.Abbreviations: +dP/dt,peakrateofleft ventricular pressure rise; -dP/dt, peakrateof left ventricularpressuredecay;CD, left ventricularchamberdiameter;WT, left ventricularwallthickness; CS, myocyte cell sizepernucleus,CN,totalnumberof myocyte nuclei;r,correlationcoefficient;P,Pvalue.

natureof the mechanicalstimuluswilldetermineaprevailing

increasein cell lengthwith additionalchamberdilation.Data consistent with this sequence of events have been obtained

afteracute(16)andchronic (21) myocardial infarction. Myocytehypertrophy and wall stress. Findingsinthis

inves-tigationindicate that myocytehypertrophyoccurredas aresult

ofcoronary artery narrowing and the magnitude ofcellular enlargement was greater inanimalswith leftventricular failure, 53%,than inratswith myocardial

dysfunction,

34%.Inspite of

these cellular growth mechanisms, which not only compen-sated but exceeded the amountofmuscle masslostby focal

myocyte cell death,diastolicwallstress wasmarkedly elevated. Since myocardial hypertrophy was 23% and 30% in thetwo

groups ofanimalswhereasintracavitaryvolumeincreased63%

and93%, theventricular mass-to-chamber volume ratio de-creased 25% and 33%withdysfunctionandfailure.

Itis the current view that myocytegrowthinhypertrophyis

proportionaltothe amountofstressimposedontheheart(40,

41). Increasingpressure load on the adult heartinduces

con-centric ventricular hypertrophy in which wall thickness

in-creaseswithoutchamberenlargement(40). Thisphenomenon

is accomplished by lateral expansion of myocytes with no change in the numberofcells acrossthe wall or in average myocyte length (42). According to the law of Laplace, the greater myocytediameterwouldproduceaproportional thick-ening ofthewall that shouldoffsetthe

higher

peak

systolic

wall stressresulting fromtheelevationin pressure(40, 41).In

con-trast, an

increasing

volume loadinduces enlargement ofthe

ventricular chamber without a relative increase in its wall

thickness, that

is,

compensated eccentric

hypertrophy (42).

Chamberdilatation is

accompanied

bya

proportional

increase

in wallthicknesssothattheratio of wallthickness-to-chamber

radius remains constant (42). At the cellularlevel, chamber enlargement appears to be brought about through lengthening of myocytes withonly slight variationsin myocytecross

sec-tionalareaand no change in sarcomere length (42).

Lengthen-ing of myocytes would have the effect of counteracting the greaterend-diastolic wall stress (40, 41) by contributing to the enlargement in chamber volume and the decrease indiastolic filling pressure. However, when the relationship between chambersize and wall thickness is notmaintained,

decompen-satedeccentric hypertrophy develops(43),asappearsto bethe

case in chronic coronary artery constriction in which wall

thickness-to-chambersradiusratio decreased from basetoapex

inallanimals. Consistent with previous observations (24, 25), diastolic overload may represent the prevailing mechanical

stimulus implicated in the acute (24), subacute (25), and chronic growth responses of the myocardium. This chronic

effect has been documented here 1 mo after surgery.

Although the analysis of the functional and anatomical characteristics ofthe left ventricle after coronary artery narrow-ingallowed the identification of the overload responsible for the hypertrophic adaptation of the unaffected myocardium, moredifficult is the understanding ofthe hypertrophic reaction ofthe right ventricle in the presence of normal and abnormal right side function. Rightventricularhypertrophy was accom-paniedbyanincrease in average wall thickness which was

com-parabletothe expansion in right ventricular weight in animals with preservedrightventricular dynamics but significantly less in ratswith impaired right ventricular performance. Such a phenomenon implies an increase in right ventricular chamber volume (42) in the latter group which, incombinationwith the altered function, suggests that a diastolic Laplace overloadwas

operative on the right ventricle as well.

Temporaleffects ofcoronary arterynarrowing.Theresults

inthe current studysignificantlyextendpreviousobservations obtained in ourlaboratory in this animal model(24,25). Al-though myocardial damage andimpairmentin cardiac func-tionwerepreviouslydocumented, questions remainedwhether hypertrophy of the unaffectedcells was capable ofrestoring cardiac pump performance and whether myocyte damage per-sistedovertimecreatingachronicongoingprocess.Findingsin this investigation clearly indicate that myocyte hypertrophy does not normalize myocardialdysfunction,and that cell loss continuesto occur at onemonthafter coronary artery

narrow-ing.Importantly, themagnitude of myocyte losswasmodest but sufficienttoengendersevereventricular dilation and

con-tribute to the maintenance of depressedcontractility. Finally, theinteraction between theabnormalityinmyocardial

struc-tureandimpaired ventricular dynamicswasfound to ensue a sustained elevation in ventricular loading.

Inconclusion,afixed reduction in luminal diameter of the left main coronary artery leads to chronic and diffuse myocyte loss with extensive ventricular remodeling, decompensated ec-centric hypertrophy, and severe deterioration in ventricular pumpperformancewhich may progress into overt congestive heartfailure and death, mimicking the cardiomyopathic heart in humans.

Acknowledgments

(13)

Thiswork was supported by National Institutes of Health grants

HL-38132, HL-39902, and HL-40561 and a grant-in-aid from the

AmericanHeartAssociation,New YorkStateAffiliate,Inc.

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narrowing at necropsy insuddencoronarydeath: analysis of 31 patients and

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