Natural History of Left Anterior Descending Coronary Artery Obstruction: Significance of Location of Stenoses in Medically Treated Patients

Transcription

1 Clin. Crdiol. 8, (1985) 0 Clinicl Crdiology Publishing Co., Inc. Originl Contributions Nturl History of Left Anterior Descending Coronry Artery Obstruction: Significnce of Loction of Stenoses in Mediclly Treted Ptients J. K. SAMAHA, M.D., M. J. CONNOR, Ph.D, R. TRIBBLE, M.S., F. w. KROETZ, M.D., J. M. SULLIVAN, M.D., K. B. RAMANATHAN, M.D., D. M. MIRVIS, M.D. Crdic Lbortories, Bptist Memoril Hospitl, Division of Crdiovsculr Diseses, University of Tennessee Center for Helth Sciences, nd Medicl Service, Veterns Administrtion Medicl Center, Memphis, Tennessee, USA Summry: We exmined the prognostic significnce of n obstmctive lesion in the proximl left nterior descending (LAD) coronry rtery. Five-yer or longer followup dt were exmined from 311 ptients with > 70 % obstruction of the LAD treted without surgery. Mortlity ws compred in subsets with lesions proximl to nd distl to the first septl perforting rtery. Survivl curves were worse in ptients with proximl thn with distl LAD disese (p <0.05); lesion loction remined significnt determinnt of survivl when ejection frction, ge, nd sex were controlled using Cox regression model. However, when ptient subsets were exmined, survivl with proximl LAD disese ws worse thn with distl obstruction only in the presence of n ssocited right coronry rtery lesion nd n ejection frction of less thn 40% (p<o.ol). Ptients with proximl LAD plus right coronry lesions hd 5-yer mortlity rte (34.08*8.9%) tht ws not significntly (p > 0.05) different from tht of group of 66 ptients with >50% nrrowing of the Address for reprints: Dvid M, Minis, M.D. 956 Court Avenue Room F208 Memphis, TN USA Received: September 17, 1984 Accepted with revision: Februry 28, 1985 left min coronry rtery (24.02*4.3%). Thus, proximl LAD disese is more significnt thn is distl lesion only in the presence of right coronry obstruction. This twovessel combintion results in mortlity rte s high s tht ssocited with left min coronry rtery obstruction. Key words: coronry rtery disese, coronry rteriogrphy, left min coronry rtery disese Introduction The nturl history of ptients with coronry rtery disese is lrgely determined by the extent of vsculr obstruction nd by the resulting functionl consequences. Thus, three-vessel disese hs higher mortlity rte thn hs two-vessel disese, nd ptients with double-vessel obstruction hve higher mortlity rte thn do those with single lesions (Hms et l., 1980; Mock et l., 1982). Similrly, ptients with impired ventriculr function hve worse survivl experience thn do those with similr coronry pthontomy but with norml crdic bility (Hmmermeister et l., 1979; Hrris et l., 1980; Mock et l., 1982). Certin specific lesions my, however, hve specil significnce beyond tht nticipted by these fctors. One such lesion is obstruction in the proximl portion of the left nterior descending (LAD) coronry rtery. This bnormlity hs been ssocited with higher mortlity rte thn with distl disese both in chronic coronry disese (Brooks et l., 1982; Cliff et l., 1983) nd fter cute myocrdil infrction (Tylor et l., 1980). Becuse of the importnce of these findings, we hve reviewed our

2 416 Clin. Crdiol. Vol. 8, August 1985 experience, with emphsis on the different effects of proximl nd distl nterior descending lesion in the bsence nd, prticulrly, in the presence of other obstructive lesions. Methods Ptient Popultion The Crdic Disese Registry of the Bptist Memoril Hospitl ws initited in 1972, s method for centrl storge of dt on ll ptients undergoing crdic ctheteriztion. Informtion coded includes clinicl, lbortory, ngiogrphic, nd hemodynmic vribles. A detiled follow-up procedure is incorported into the system. A computer-generted form is miled to ech ptient nnully on the nniversry of the ctheteriztion dte. The follow-up questionnire is miled to the referring physicin or directly to the ptient. Two weeks fter the initil miling, second form is sent to ptients who hve not responded. If no response to this is received, the ptient s physicin is directly contcted to obtin the requisite informtion. Dt sought includes survivl nd clinicl sttus. This report is bsed upon ptients ctheterized between Jnury 1972 nd Mrch 1977, in whom follow-up informtion ws vilble for t lest 5 yers or who died during the follow-up period. All cuses of deth were included. Complete follow-up informtion ws vilble on 3230 ptients. Two specific ptient groups were evluted. First, ll ptients with significnt ( > 70%) stenosis of the left nterior descending coronry rtery with or without lesions in other coronry obstruction were selected. Those with mjor lesions (> 50%) of the left min coronry rtery were excluded from this first group. Second, subjects with lesion obstructing t lest 50% of the luminl dimeter of the left min coronry rtery were studied. All ptients were mnged by their referring physicins. None of the ptients included in this study underwent coronry rtery surgery. This decision ws mde entirely by the ptient s physicin or physicins, who directed ptient cre throughout the follow-up period. Ctheteriztion Protocol Crdic ctheteriztion ws performed using stndrd techniques with filming in multiple views. The coronry ntomy ws divided into 27 segments, nd the degree of stenosis grded for ech. Lesions in the LAD were coded s proximl if locted proximl to the first septl perforting rtery nd distl if beyond tht brnch. If both proximl nd distl lesions were present, the proximl obstruction ws given priority nd the ptient ws included in the proximl subset. Ejection frction ws computed by routine ngiogrphic formule. Methods did not chnge during the study period. Sttisticl Methods Five-yer mortlity rtes nd corresponding stndrd errors were clculted bsed on cturil life tbles. Differences in survivl rtes mong groups were tested using nonprmetric rnk sttistic (Lee-Desu), which is symptoticlly distributed s Chi-squre (Hull nd Nie, 1981). This procedure compres one entire survivl curve to nother, rther thn survivl t ny specific time point. Thus, sttisticl problems creted by smll ptient smples t the end of follow-up periods re reduced. The reltionships between mortlity nd ge, sex, nd lesion loction were simultneously ssessed using Cox s proportionl hzrd model. This is nlogous to multiple regression pplied to censored dt. A step-wise pproch (vrible inclusion lph = 0.10 nd vrible removl lph = 0.15) identified significnt vribles ffecting survivorship (Lee, 1980). Results Five-yer or longer follow-up dt were vilble on 3 11 ptients with significnt ( > 70 %) obstruction in the left nterior descending coronry rtery who did not undergo surgicl revsculriztion. Descriptive informtion bout these ptients nd the number nd loctions of other coronry rteril lesions is presented in Tble I. In 110 subjects, the LAD lesion ws in the proximl vessel (Group I); of these, 50 hd no other lesion (Group IA), 44 hd two-vessel disese (Groups IB nd IC), nd 16 hd three-vessel disese (Group ID). Of the 201 subjects with distl LAD obstruction (Group 11), 67 hd single- (Group IIC), 86 hd double- (Groups IIB nd IIC), nd 48 hd triple-vessel (Group IID) disese. Age nd sex distributions were not different in the vrious groups nd subgroups listed. Ejection frction ws, in contrst, significntly lower in ptients with proximl (Group I) thn with distl (Group 11) LAD disese. Comprison of subgroups demonstrted tht ejection frction ws significntly lower in those with single-vessel disese of the proximl LAD (Group IA) nd in those with right coronry plus proximl LAD disese (Group IB) thn in corresponding subsets with distl LAD obstruction (Groups IIA, IIB). The position of the LAD obstruction did not significntly relte to ejection frction in subjects with LAD plus circumflex or with three-vessel disese. Mortlity rtes for ech group nd subgroup re listed in Tble II. Vlues tbulted include 5-yer mortlity percentges for ech ptient set nd the Chi-squre nd ssocited p vlue compring the overll survivl curves of ptients with proximl to those with distl LAD lesions. Exmples of the curves re presented in Figures 1-4. Overll Group Comprisons Ptients with proximl LAD disese (Group I) hd significntly worse (p =0.016) survivl experience thn

3 ~ ~ J. K. Smh et l.: Proximl vs. distl LAD lesions 417 TABLE I Description of ptient groups qnd subgroups Group I IA IB IC ID 11 IIA IIB IIC IID Lesion Proximl LAD LAD only + RCA +LCX +RCA+LCX Distl LAD LAD only + RCA + LCX + RCA + LCX Sex Ejection fxction N Age (yrfse) (% mle) (% fse) f f f f f f f f lf f f 20.8" f20.8" 48.5 f 22.7' 51.2f f k f * f f21.4 ' Vlues for proximl LAD grouplsubgbroup significntly (p ~0.05) less thn for corresponding distl LAD group/subgroup. Abbreviurions: LAD = left nterior descending rtery; RCA = right coronry rtery; LCX = left circumflex fiery; N = number of subjects in grouplsubgroup. TABLE I1 5-Yer mortlity rtes (%) for ptient groups nd subgroups 5-Yer mortlity rtes" Survivl curve comprisonb Group/Subgroup Proximl LAD Distl LAD X P Totl Subgroups LAD only + RCA + LCX + RCA + LCX 24.02f4.3% 16.55f3.1% f 5.O 7.32 f f f f f f f (I Five-yer mortlity rtes (% f 1 SE); The Chi-squre vlue compring survivl curves with proximl nd distl LAD disese nd the ssocited p vlue defining the significnce of the difference between the two curves, Abbrevitions: LAD = left nterior descending; LCX = left circumflex; RCA = right coronry; X = Chi-squre; p = probbility. did those with distl disese (Group 11). Five-yer mortlity rtes for these two groups were 24.02f4.3% nd 16.55*3.1%. As noted bove, the nonprmetric rnk sttistic comprison of the overll surivl curves ws relied upon to reduce the effects of smll numbers of ptients surviving to the ends of the follow-up period. The survivl curves for these two groups were significntly different nd re plotted Figure 1. Becuse ejection frction ws lower in Group I thn in Group I1 nd becuse lower ejection frction is known to reduce survivl (Hmmermeister et l., 1979; Hms et l., 1980; Mock et l., 1982), survivl comprisons between the two groups were djusted for differences in ejection frction. This ws ccomplished in two wys. First, ptients in ech grouphbgroup were divided into two subsets, one with ejection frctions of 40% or greter nd nother with vlues less thn 40%. Within ech group, survivl curves for the two subgroups were significntly different (p <0.01), with poorer survivl in the subset with lower ejection frction (Tble III). When ptients with proximl LAD disese with ejection frctions of less thn 40% were compred to those with distl lesions nd low ejection frctions, those with proximl disese continued to hve higher mortlity However, when groups with ejection frctions of 40% or greter were compred, survivl with proximl nd distl lesions ws equivlent. Second, differences in ejection frction were controlled by using Cox regression model. Vribles included in the Egression nlysis included ge, sex, ejection frction, nd loction of LAD lesion (proximl or distl). Results re listed in Tble IV. Age, ejection frction, nd lesion loction were ll significnt predictors of mortlity. Thus, lthough lesion loction nd ejection frction were relted to ech other, both fctors independently determined outcome.

4 418 Clin. Crdiol. Vol. 8, August 1985 TABLE III 5-Yer mortlity rtes (%) for ptient subgroups subdivided by ejection frction 5-Yer mortlity rtes (%)" Survivl curve comprisonsb Grouphubgroup Proximl (N) Distl (N) X P All LAD (I nd II) EF>40% 9.0k3.0 (65) 10.0f3.0 (143) EF<40% 61.5f9.0 (31) 49.2f4.2 (30) LAD only (IA nd IIA) EF>40% 4.2f4.1 (29) O.OfO.0 (48) EF<40% 41.3f14.6 (14) 50.0f25.0 (4) LAD + RCA (IB nd IIB) EF>40% 17.0f4.0 (21) 16.0f6.0 (55) EF<40%.0f0.0 (9) 20.0f12.6 (10) Five-yer mortlity rtes (% f 1 SE); the Chi-squre vlues compring overll survivl curve nd the ssocited p-vlue defining the significnce of the difference in the curves with proximl nd distl LAD disese. Abbrevitions: LAD = left nterior descending; RCA = right coronxy xtery; EF = ejection frction; X = Chi-squre; p = probbility; N = number of ptients in ech group, in prentheses. TABLE IV Cox regression nlysis of fctors predicting outcome Vrible Age Sex Ejection frctiop LAD lesion loction Coefficient in ptient subgroups Single-vessel LAD + RCA All cses LAD disese disese Fctor not significnt FIG. 1 Survivl curves for Group I [ll ptients with proximl LAD lesion, plad (-)I nd for Group I1 [ll ptients with distl LAD, dlad (- - -)I. The number of ptients surviving t 20-month intervls re listed for ech group. Verticl brs t the 60-month point represent stndd emrs of the 5-yer mortlity mtes of the two groups. As listed in Tble II, the two survivl curves were significntly different.

5 J. K. Smh et l.: Proximl vs. distl LAD lesions I c n B 2o FIG. 2 Survivl curves for ptient subgroups with two-vessel coronry rtery disese. (A) Curves for subgroups with proximl LAD (plad) plus right coronry rtery (RCA) obstruction (Group IB) (-) nd with distl LAD (dlad) nd RCA obstructions (Group IIB) (- - -). (B) Curves for subgroups with plad nd left circumflex (LCX) disese (Group IC) (-) nd with dlad nd LCX obstruction (Group UC) (- - -). Conventions re s in Figure 1, The two curves in (A) re sttisticlly different wheres those in (B) re not (Tble n). Single-Vessel Disese An LAD lesion ws the only significnt obstruction in 117 ptients. In 50, the lesion ws proximl (Group IA) nd in 67 it ws distl (Group IIA).Although the 5-yer mortlity rte ws lower in ptients with distl (7.32f3.6%) thn with proximl (12.97f5.0%) disese, the survivl curves were not significntly different (p=o. 16). Two-Vessel Disese Two-vessel disese ws present in 130 ptients. Of these, 44 hd proximl LAD disese; the second lesion ws in the right coronry rtery in 33 (Group IB) nd in the left circumflex vessel in 11 (Group IC). Distl LAD disese ws detected in 86 ptients; of these, 68 hd right coronry (Group IIJ3) nd 18 hd left circumflex obstruction (Group IIC) (Tble I). As indicted in Tble 11, ptients with proximl LAD plus right coronry disese hd significntly higher mortlity rte (34.08&8.9%) thn did those with distl LAD nd right coronry lesions (15.98&5.4%). "he survivl curves for these two subgroups (IB nd IIB) re shown in Figure 2, nd re significntly different (p=0.017). As discussed bove, the effects of differences in ejection frction between those with proximl nd distl LAD disese nd right coronry lesions were studied (Tble III). In ptients with ejection frctions less thn 40%, distl disese ws ssocited with better survivl thn with prox U I O'f I I 1 I I FIG. 3 Survivl curves for the two subsets of ptients with three-vessel coronry rtery disese, one with proximl LAD [plad, Group ID (-)I with one with distl LAD [dlad, Group IID (- - -)] lesions. The two curves re not sttisticlly different.

6 420 Clin. Crdiol. Vol. 8, August T 1 I FIG. 4 Survivl curves compring the experience of the group of ptients with left min coronry rtery disese (LM) to tht of subgroup IB with proximl LAD (plad) nd right coronry rtery (RCA) disese (-) nd to tht of subgroup IC with plad nd left circumflex (LCX) obstruction (- - -). 0 iml lesions (p=0.05). However, if ejection frction ws greter thn 40%, survivl in both subgroups with right coronry lesions ws similr. Cox regression nlysis ws lso used to compre the effects of LAD lesion loction nd ejection frction (Tble IV). Both lesion loction nd ejection frction were independent determinnts of outcome. In contrst, in cses in which the second lesion ws in the left circumflex rtery, survivl ws similr with proximl (Group IC) nd with distl (Group IIC) LAD lesions. Both 5-yer mortlity rtes (Tble 11) nd survivl curves (Figure 2B) were not different (Tble 11). Three-Vessel Disese Lesions in ll three mjor vessel systems were present in 64 cses. The LAD lesion ws proximl in 16 (Group ID) nd distl in 48 (Group IID) ptients. Five-yer mortlity rtes (Tble 11) nd survivl curves (Figure 3) for the two subgroups were not significntly different. Left Min Coronry Arteril Obstruction An dditionl 66 ptients hd greter thn 50% obstruction in the left min coronry rtery. Five-yer mortlity rte in this group ws 34.49k6.7%. Overll survivl experience in this subset ws thn for the entire group of ptients with proximl LAD disese. When subgroups of ptients with proximl LAD lesions were compred to the left min disese group, the results demonstrted tht, first, survivl in ptients with proximl LAD lesions lone ws significntly better thn for those with left min disese. Second, in the presence of either right or circumflex obstruction or both, survivl ws not different to tht of the left min lesion group (Fig. 4). Discussion Numerous reports hve suggested tht isolted disese of the left nterior descending coronry rtery hs more severe implictions thn does obstruction of ny other single vessel. In six studies compiled by Abedin nd Dck (1977), the mortlity rte of ptients with LAD disese ws 4.1 % per yer; with obstructions in either the right or circumflex vessel, the rte ws 2.4% per yer. Lesions in the LAD hve lso been reported in 85% of ptients with single-vessel disese suffering crdic rrest (Griffith et l., 1977) nd in 78% of those with recent onset of unstble ngin (Victor et l., 1981). In 127 cses of sudden deth reported by Jnushkevichius er l. (1977), n LAD lesion ws demonstrted in 93 %. Presence of lesion in the LAD proximl to the origin of the first septl perforting rtery hs lso been shown to hve greter significnce thn more distl lesions in the vessel. First, higher mortlity rtes hve been reported with proximl thn with distl lesions. Cliff er l. (1983) reported five times higher 5-yer mortlity rte with proximl thn with distl lesions. In group of 106 ptients studied fter cute infrction, 21 % of 48 with proximl LAD lesion died; only 2 of 58 without this ob-

7 J. K. Smh et l.: Proximl vs. distl LAD lesions 42 1 struction succumbed (Tylor et l., 1980). Eight-yer mortlity rtes, reported by Griffith et l. (1977), in ptients previously experiencing sudden crdic deth were 52 % if proximl LAD lesion ws observed, 22% if distl LAD lesion ws present, nd 0% if neither ws demonstrted. Of 112 ptients considered cndidtes for coronry rtery bypss surgery but not undergoing opertion, 33 of 42 ptients with proximl LAD disese died; of the other 70, only 18 died (Johnson nd Kyser, 1973). Finlly, Schuster et l. (1 98 1) reported 6 1 % incidence of thrombotic occlusion of the proximl LAD in ptients suffering ftl cute myocrdil infrction. Thus, this lesion my hve clinicl import nlogous to left min rteril disese (Rhimtool, 1984). Secondly, other studies hve described different functionl consequences of proximl nd distl lesions. Ejection frction is lower nd number of bnormlly contrcting segments is higher with the proximl lesion (Brooks et l., 1982; Tylor et l., 1980). Kumpuris et l. (1980) documented bnorml systolic left ventriculr function in the bsence of prior infrction only in ptients with proximl LAD lesion; in subjects with prior infrction, dysfunction ws more severe with proximl thn with distl LAD disese. In tht study, the position of n isolted right coronry rtery lesion ws not determintive. Abnorml septl motion ws reported by Gordon nd Kerber (1977) to occur in 50% of those with proximl but in only 30% with distl disese. Dt presented here extend these prior observtions. First, survivl ws lower in ptients with proximl (Group I) thn with distl (Group II) LAD disese (Tble II). This finding is consistent with reports cited bove (Brooks et l., 1982; Cliff et l., 1983; Gordon nd Kerber, 1977; Johnson nd Kyser, 1983; Kumpuris et l., 1980; Rhimtool, 1984; Schuster et l., 1981; Tylor et l., 1980). A reson usully offered for this is the lrger myocrdil region t risk of ischemi from chronic ischemi or from single occlusive event with the proximl lesion (Gordon nd Kerber, 1977; Hutter, 1980; Kumpuris et l., 1980; Rhimtool, 1984). This is consistent with the finding of lower ejection frction with proximl obstruction in our dt (Tble I) s in prior reports (Brooks et l., 1982; Tylor et l., 1980). Schuster et l. (1981), however, demonstrted tht infrct size t postmortem exmintion ws only slightly lrger with proximl thn with distl LAD disese. Other fctors tht my ffect survivl with the proximl lesion include involvement of the proximl intrventriculr conduction system, nd greter propensity for ventriculr dysrhythmis (Jnushkevichius et l., 1977; Schulze et l., 1977). In the present study, however, this incresed mortlity ws confined to ptients in certin ngiogrphiclly defined subgroups. As shown in Tbles I1 nd 111, survivl ws less fvorble only in ptients with n ssocited right coronry rtery lesion with reduced ejection frction. These dt re lso consistent with prior reports. Jnushkevichius et l. (1977) reported higher incidence of LAD nd right coronry rtery lesions in ptients with sudden deth thn of other two-vessel combintions. In contrst, Webster et l. (1974) found no significnt difference in outcome in ptients with ny of the possible double-vessel disese pirs. However, in ptients with single-vessel disese, with n ssocited circumflex rtery lesion, or with three-vessel disese, loction of the LAD obstruction ws not determinnt of survivl. This result is diffennt thn those of Cliff ef l. (1983), Brooks et l. (1982), Tylor et l. (1980), nd Giffth et l. (1977), but is in ccord with the report by.webster et l. (1974). This ltter investigtion found similr 6-yer mortlity rtes in ptients with isolted proximl nd isolted distl LAD disese. Resons for these differences re not pprent. A possible mechnism for the specil significnce of proximl LAD lesion when combined with right coronry rtery obstruction my be suggested. Levin (1974), s well s others, described the collterl pthwys tht cn provide blood flow to tissues distl to coronry obstruction. Collterl vessels to n obstructed right coronry rtery originted from the LAD in 39 of 1 12 cses. Of these, 28 utilized septl brnches. With coexistnt proximl LAD lesion, these collterls would be inopertive but would frequently be functionl with distl LAD lesions. Similrly, with LAD occlusion, 49 of 99 collterl pthwys originted from the right coronry rtery. Of these, 15 included connection from conus brnch of the right coronry to the very proximl LAD. In the presence of proximl LAD lesion, these collterls might not form or would be of little functionl vlue in supplying the nteroseptl left ventricle. Thus, in both cses, proximl LAD lesion restricts collterl inflow to the territory t risk. A second comprison demonstrting the significnce of proximl LAD lesion involves study of the group with left min coronry rtery disese. Ptients with proximl LAD disese plus either right nd or circumflex rtery obstruction hd survivl experience s bd s did ptients with left min disese. In contrst, those with distl LAD disese fired significntly better thn did those with left min obstruction. These dt re thus consistent with the concept of left min equivlency (Cliff et l., 1984; Hutter, 1980) of multiple proximl vessel obstructions. Certin limittions of this effort must be cknowledged. First, the ptients were studied in retrospective mnner without investigtor involvement in mngement decisions (i.e., the choice of medicl rther thn surgicl therpy). Indeed, the resons for the choice were generlly unvilble. Second, ptients were subdivided in this s well s in most other studies by single ngiogrpbic description (i.e., lesion of more thn 50% or 70% luminl dimeter). Differences, if ny, in subsets with 70, 90, or % obstructions would be missed. In this nd other cses, such subselection would result in too few subjects per cell for meningful study.

8 422 Clin. Crdiol. Vol. 8, August 1985 References Abedin Z, Dck S: Isolted left nterior descending coronry rtery disese: Choice of therpy. Am J Crdiol 40, 654 (1977) Brooks N. Cttell M, Jennings K, Blcon R, Honey M, Lyton C: Isolted disese of left nterior descending coronry rtery. Angiogrphic nd clinicl study of 21 8 ptients. Br Hert J 47, 71 (1982) Cliff RM, Tombechi Y, Lee KL, Phillips H, Pryor DB, Hre11 FE, Hms PJ, Peter RH, Behr VS, Kong Y, Rosti RA: Outcome in one-vessel coronry rtery disese. Circultion 67, 283 (1983) Cliff RM, Conley MJ, Behr VS, Hrrell FE, Lee KL, Pryor DB, McKinnis RA, Rosti RA: Left min equivlent coronry rtery disese: Its clinicl presenttion nd prognostic significnce with nonsurgicl therpy. Am J Crdiol 53, 1484 (1984) Gordon MJ, Kehr RE: Interventriculr septl motion in ptients with proximl nd distl left nterior descending coronry rtery lesions. Circultion 55, 338 (1977) Griffith LSC, Plti EV, Angel1 CS, Grunwld L: Coronry rteriogrphic nd electwnliogrphic correltes of sudden crdic deth. Acr Med Scnd (suppl.) 615, 43 (1977) Hmmermeister KE, DeRouen TA, Dodge HT: Vribles predictive of survivl in ptients with coronry disese. Circultion 59, 421 (1979) Hms PJ, Lee KL, Hrrell FE, Behr VS, Rosti RA: Outcome in mediclly treted coronry rtery disese. Circultion 62, 718 (1980) Hull CH, Nie NH: SPSS Updres 7-9. McGrw-Hill, New York (1981) Hutter AM: Is there left min equivlent? Circultion 62, 207 (1980) Jnushkevichius ZI, Bloohz JN, Stliorityte El, Bubiniene AV, Milshuskiene MA, Grbusks VJ, Mzheik AA, Ryzhkovile MV, Kmruskiene DB, Rgishis JR: Sudden out-of-hospitl coronry deth nd chronic lesions of coronry rteries nd myocrdium. Act Med Scnd (suppl.) 615, 33 (1977) Johnson WD, Kyser KL: An expnded indiction for coronry surgery. Ann Thorc Surg 16, 1 (1973) Kumpuris AG, Quinones MA, Knon D, Miller RR: Isolted stenosis of left nterior descending or right coronry rtery: Reltion between site of stenosis nd ventriculr dysfunction nd therpeutic implictions. Am J Crdiol 46, 13 (1980) Lee, ET: Sttisticl Methods for Survivl Dt Anlysis. Lifetime Lerning Publictions, Belmont, CA (1980) Levin DC: Pthwys nd functionl significnce of the coronry collterl circultin. Circultion 50, 83 1 (1974) Mock MB, Ringqvist I, Fisher LD, Dvis KB, Chitmn BR, Kouchoukos NT, Kiser GC, Aldermn E, Ryn TJ, Russel RO, Mullin S, Fry D, Killip T, nd prticipnts in the Coronry Artery Surgery Study: Surivl of mediclly treted ptients in the Coronry Artery Surgery Study (CASS) registry. Circultion 66, 562 (1982) Rhimtool SH: Left min equivlence is still n unproved hypothesis but proximl left nterior descending coronry rtery disese is high-risk lesion. AmJ Crdiol 53, 1719 (1984) Schulze RA, Humphries JO, Griffith LSC, Ducci H, Achuff S, Bird MG, Mellits ED, Pitt B: Left ventriculr nd coronry ngiogrphic ntomy. Reltionship to ventriculr imtbility in the lte hospitl phse of cute myocrdil infrction. Circultion 55, 839 (1977) Schuster EH, Griffith LS, Bulkley BH: Prepondernce of cute proximl left nterior descending coronry rteril lesions in ftl myocrdil infmion: A clinic0 pthologic study. Am J Crdiol 47, 1189 (1981) Tylor GJ, Humphries JO, Mellits ED, Pitt B, Schulze RA, Griffith LSC, Achuff ST: Predictors of clinicl course, Coronry ntomy nd left ventriculr function fter recovery from cute myocrdil infrction. Circultion 62, 960 (1980) Victor MF, Likoff MJ, Mintz GS, Likoff W: Unstble ngin pectoris of new onset: A prospective clinicl nd rteriorgrphic study of 75 ptients. Am J Crdiol47, 228 (1981) Webster JS, Moberg C, Rincon G: Nturl history of severe proximl coronry rtery disese s documented by coronry cinengiogrphy. Am J Crdiol 33, 195 (1974)