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Blood flow velocity in the right coronary artery: Assessment before and after angioplasty
JACC Vol. 24, No. 4
1012
October 1994:1012-7
LOUIS I. HELLER, MD, FACC, KEVIN H. SILVER, MD, BERNARD J. VILLEGAS, MD, FACC, SHARON J. BALCOM, RN, BONNIE H. WEINER, MD, FACC Wotrtwq
@j&vs.
Massuchusetrs
This study ettempted
I) to mess the utility ol rest
flow velocity For the physilore and after right
ty and a loss of distal diastolic prcdomimtnl tbw are characteristlc of physiologically significant s&noses and that lhcse indexes normalize abler successfid curenary artey dilalloa. However, these studies were p~oml~antly performed in lhe left coronary artery. The ulility of monitoring rest velocity variables during angioplasty of the right coronary artery has not been sludied. studied 20 pa&& undergoing angioplasty of #he rtery with use of a Doppler angioplasty guide wire. es were expressed as the mean value + I SD. The rest average peak velocity did not decrease distal tu angi~raphitally slgalficant right corunary artery stenoses (233 f 9.4 cm/s
The response of a stenotic coronary artery to petcutaneous transluminal coronary angioplasty is usually gauged by a
qualitative asswmcnt of the cotonwy angiogtum. However, ciotonaty angiqtaphy is limited in its ability to determine the physiologic significance of a coronary sttmosis (1). Visual estimates ate subjective, resulting in significant intetobservet and intraobservet variability (2-4). Quantitative coronary angiography (5) and tine videodensitometry (6) have been proas more objective methods of angiogtaphic assessment. owever, the diffuse nature of coronary artery disease may limit the utility of measuring petcent diameter stenosis by either method (78). Changes in coronary tone may also affect the angiographic assessment of percent diameter narrowing (9).
FWII the COIUUY Blood Flow Research Laboratory and Division of Cnnfiovarcular Mediiirte, Universityof Massachusetts Medical Center, Worcester. ~~w%s. This work wan supported in part & a grant from Cardiometks. k, Mountain Vii, California. Mm* nx+ed November19.1993; revised manuscript received April 5. 1 : Dr. Louis I. Heller, Diiision of Cardiovascular Medrcm~ thiversity of Masaehusetts Medical Center, 55 Lake Avenue North, Worcester, Massachusetts 01655. 01994 by tk American College of Cardiology
proximal vs. 20.2 f 11.1 cmls d distal veloci(y ratio was 1.4 t 0.9 sigmilcantly decrease aAer angio rence aeon p~ximal an r to detect a was no relatian between p a veloci(y. diameter stenosis and p~xima~/dista~ velocity ratios (r = O.IS, p = 0.55). Diastolic predominant flow was not observed in the ever, a Angie. proximal or distal right coronary artery. erolatin the plasty, diastolic predominairt Row was obse eral and posterior descending coronary arteries. ppler flow velacily indexes are not sting stenoses in the right coronary artery angioplasty. In contra artery proper, diastolic p~ominant posterior descending and poster&era1 coronary arteries. The utility of measuring hyperemic Doppler flow velocity indexes, such as distal coronary flow reserve, for assessing right coronary artery slcnuses mcriis fairer investigation. (J Am Co11 Cardioll994;24:1012-7)
In an attempt to improve these anatomic methods of lesion assessment, functional measures of stenosis severity have been employed. Measurement of coronary artery flow velocity using intracotonary Doppler catheters has been proposed to determine when a physiologically significant obstruction to coronary flow has been removed (10). Recently, a Dop, ‘.er angioplasty guide wire (FloWire, Cardiometrics, Inc) has been developed that allows the measurement of phasic spectral flow velocity in both proximal and distal human arteries (11). Previous investigations using the Doppler guide wire (12,13) have demonstrated that a decrease in distal blood flow velocity and a loss of distal diastolic ptedominam flow are chatacteristic of hemodynamicaliy significant stenoses and that these indexes normalize after successful dilatation. However, these studies were performed predominantly in the left coronary artery. The diagnostic applicability of these left coronary artery variables to the tight coronary artery, which has different phasic blood flow characteristics, has not been evaluated. Unlike the left coronary artery, the right coronary artery has few side branches and therefore rest blood flow velocity may not decrease distal to significant stenoses. In addition, Gregg (14) has shown that phasic flow in the right cororary artery does not occur predominantly during diastole. Accordingly, we 07351a97/94/$7.00
JACC Vol. 24. MO. 4 October 1994:1012-7
RIGHT
CORONARY
ARTERY
NELLER ET AL. BLQ!>D FLOW
1013
. Clinical@haracteristics of Study velocity before and a
Male Age @r) History of myocardial infarction Prior coronary bypass grafting Prior coronary angioplasty
14 (70%) 61.6 t 11.0 10 (50%) 0 7 (35%) 3 (15%)
Diabetes Smoking
8 (40%)
Hypercholesterolemia
ventricle.
Family history of coronary artery disease
13 (65%) 1 I (55%)
Hypertension Calcium channel blocking agents
13 (65%) 20(100%)
Nitrates
17 (85%‘)
Beta-adrenegic
blocking agents
I4 (70%)
Dutapresented are number (a) of patients or mean valtle f SD.
s. Tke records of all patients who underwent a Doppler angioplasty guide wire were rewere included in the study if t successful elective ercutancous t~~~s~~~rni~ial coronary angioplasty of a stenosis the right coronary artery the crux). Twenty patients met t ese se~cctioll criteria and Coronary angioplasty was performed according to the standard clinical protocol at our institution. All patients were pretreated with aspirin, dipyridamole (persantine) and a calcium channel blocking agent. Vascular access was obtained using the Judkins technique. Sufficient intravenous beparin was administered to result in an activated clotting time >300 s before the stenosis was crossed with the 0.018in. (0.046~cm)Doppler angioplasty guide wire. Dilation was performed with an appropriately sized balloon catheter. Dilations were concluded when the residual stenosis was 130% reduction in diameter stenosis by visual assessment. Coronary artery velocity measMrcme ts. All flow measurements were made with a Doppler-tipped angioplasty guide wire. ‘This Doppler guide wire is a 175cm, 0.018-m. flexible, steerable guide wire with a 12-MHz transducer at its tip. The Doppler guide wire has been validated and used in patients during interventional procedures (11). Spectral analysis of the Doppler signal is performed and velocity variables are calculated and displayed. All recordings were made with the angioplasty balloon catheter in the guide catheter. Baseline recordings were made approximately 2 cm proximal and 2 cm distal to the stenosis. Distal measurements were recorded with the sample volume in the distal right coronary artery (as opposed to a posterolateral or posterior descending branch). After successful angioplasty, velocity recordings were repeated proximal and distal to the area dilated. The time-averaged peak velocity and diastolic/systolic velocity ratios (diastolic average peak velocity divided by systolic average peak velocity) were calculated and displayed by the FloMap console. The proximal/distal velocity ratio was then calculated as the quotient of the proximal average peak velocity divided by the distal average peak velocity. Ten minutes after successful angiopjasty, velocity measurements were recorded in the posterior descending coronary artery,
istal right coronary artery (distal to the crux) and in the roximal right coronary artery. In five patients, measurements were also made in the posterolateral coronary artery. These final measurements were made as the guide wire was being he coronary artery after a successful procedure. c analysis. Angiograms were performed with Angiovist contrast medium utilizing a 7-m. (17.78~cm) image intensifier and 30.frame/s filming rate. Angioplasty guide catheters were 8F and injections were made by band. The analysis was performed using the pass Angioplasty Revascularization Investigation (BARI) quautitative cardiac angiographic system developed at Stanford University. The BAR1 system utilizes digital caliper measurements (Digit-Cal, Brown and Sharpe) (E-17). Coronary segment diameters are measured directly from the screen of the XR-35 projector specially equipped with an X -15 hood (Vanguard Instruments Corp.) with a magnification factor of x16. The diameter of the 8F guide catheter was taken as a reference for calibration. The lumen diameter in the adjacent “normal segment” and the minimal lumen diameter in the stenosis were measured. Care was taken to ensure that the measurements were made from exactly the same vessel segments on the pre and post angioplasty films. All measurements were performed by a physician who had no knowledge of the Doppler flow velocity data. Statistical methods. All results were expressed as the mean value 2 1 SD, The differences between the means of the various comparison samples were tested using a Wilcoxon signed rank test. The relation between rest Doppler flow velocity and angiography was assessed by least squares linear regression. An analysis of variance and a subsequent Scheffe’s F test were performed to compare the postangioplasty diastolic/systolic velocity ratios in the d& right coronary artery, the posterior descending coronary artery and the posterolateral coronary artery. A post-hoc power calcu!~rion was performed.
Patient characteristics. The clinical cnaracteristics or’ the study group are shown in Table 1. Twelve of the 20 patients had objective evidence of ischemia documented by exercise
1014
HELLER ET AL. RIGHT CORONARY
JACC Vol. 24, No. 4 October tyc)3:1012-7
ARTERY BLOOQ FLOW
*p < 0.0001
p = N.S.
80
Prc
-
Pi&t
0
% Stenosis -4
re 1. Despite a significant dccrca.sc in percent diamctcr stenosis (% Stcnosia) aficr (Post) successful right cmonxy artery angioplasty, thcrc W;IS no significant chungc in the proximal/distal velocity ratio (P/D), Prc = before angiopiasty.
elcctrwardiographic (ECG) stress testing (4), thallium scintigraphy (7) or rest angina associated with >I mm ST segment depression that resolved with relief of chest pain (I). Of the remaining eight patients, five had postinfarction angina and three had unstable angina without documented ECG changes. No patient had functional tests that were negative for ischemia. Coronary sag pbic measurements. The percent diameter stenosis decreased significantly after angioplasty (Fig. 1). There was a concordant increase in the minimal lumen diameter from 1.0 + 0.3 mm to 2.9 4 0.7 mm after angioplasty (p < 0.0001). Average peak velocity measurements, Rcpresentativc flow velocity tracings are shawn in Figure 2. Before angioplasty, the distal average peak velocity was not significantly decreased
(23.3 t 9.4 proximal vs. 20.2 ‘I- 11.1 cm/s distal, p = 0.20). The proximal/distal velocity ratio was 1.4 + 0.9 before angioplasty and did not decrease significantly after angioplasty (p = 0.58, Fig. 1). A power calculation was performed assuming an expected proximal/distal velocity ratio of 1.7 in all lesions in the study group. The power to detect this difference for an n = 20 and a distal average peak velocity of 20.2 L 11.1 cm/s was 99.4% (z = -2.53). After successful angioplasty, the average peak velocity in the distal right coronary artery did not increase significantly (20.2 t- Il.1 vs. 25.9 ‘c 8.8 cm/s, p = 0.20). Although there was a significant incrcasc in the ~ro~~rn~~~ average peak velocity after angioplasty (23.3 rtr 9.4 vs. 29.7 9 7.6 cm/s, p = 0.02). the magnitude of the change varied considerably (mean + SD 9.0 i: 6.0 cm/s, range - 1.0 to 17.0 cm/s). ~i~sto~ic/systotic velocity tias. The pl~stangi~~p~asty diastoliclsystalic velocity ratios did not change significantly either proximal or distal to the stenosis (Fig. 3). Phasic velocity patterns both proximal and distal to the area dilated were remarkable for prominent systolic components both before and after successful angioplasty. Examples of the postangioplasty phasic velocity profiles in the right coronary artery, posterior descending coronary artery and posterolatcral coronary artery arc shown in Figure 4. There was a significant difference between the diasto~ic/systolic velocity ratios in the distal right coronary artery and those in both the posterior descending and posterolateral coronary io~~~bic data. The proximal/distal velocity ratios were compared with the percent diameter stenoses derived from quantitative angiographic analysis. Least squares linear regression analysis revealed this
Figure 2. Angiograms and Doppler velocity tracings from a patient undergoing right coronary artcry angioplasty. Top IWW, Preangioplasty data. Bottom row, Postangioplasty data. The angiogram before angioplasty revtiled a proximal 78% slcnosis that was associated with a proximal/distal velocity ratio (P/D) of 1.4 and a distal diastolic/systolic velocity ratio (DSVR) of 1.2. After successful angioplasty, the percent diameter stenosis was reduced to 9% as measured by digital calipers: however, the proximal/ distal velocity ratio of 1.3 and the distal diastolicLystolic velocity ratio of 1.1 were essentially unchanged. The proximal and distal average peak velocity did increase after successful angioplasty; however, this trend did not reach statistical significance in our study (see text). APV = average peak velocity.
pe-t stenosis =9.0
P/D = 1.3
DSVR = 1.1
JACC Vol. 244,No. 4 October 1994:101’-7
RIGHT CORONARY
Distal Prc i@M?3.
ThCK
WlS
MMJ pustangioplasty
iltldilkK!llCC
Proximal Post IlChVCCll tllC
ARTERY
%%_bER ET AL. BLOOD FLOW
1015
istal Post
p~C~lllgiOplilSly (Prc)
(Post) diastolic/systolic velocity ratios meitsurcdproximal or distal to the stenosis.
.“~___l_ll___
(DSVR) Proximal RCA
RCA
- PDA
relation to be insignificant both before (r I=0.15, p = 0.3) and after successful augioplasty (r = 0.12, p = 0.7
stu ata. We believe that this is the first clinical study to evaluate phasic blood flow velocity in the right coronary artery tree. We conclude that 1) rest Doppler blood flow indexes are not helpful for evaluating lesions before or after right coronary artery angioplasty, and 2) diastolic predominant flow is characteristic of left ventric;rlar branches (posterior descending and posterolatcral arteries) but is not characteristic of the right coronary artery proper. There was no relation between percent diameter stenosis and proximal/distal velocity ratios in our study. The rest average peak velocity did not decrease distal to angiographitally significant right coronary artery stenoses. The right coronary artery has few branches proximal to a stenosis and, therefore, in accordance with Bernoulli’s theorem, flow proximal to a stenosis may be similar to flow distal to the stenosis. As a result, the proximal/distal velocity ratio was not a useful variable for the functional assessment of right coronary artery stenoses in our patients. Changes in distal average peak velocity measurements were not helpful for assessing right coronary artery stenoses either before or after angioplasty. The distal rest average peak velocity did not significantly increase after successful angioplasty. Although there was a significant increase in the proximal average peak velocity after successful angioplasty, the magnitude of this increase was variable. Accordingly, this variable was of limited utility for assessing stenosis after the intervention. The diastolic/systolic velocity ratios proximal and distal to the stenoses did not change after successful angioplasty in our study. Diastolic predominant flow was not observed in the proximal or distal right coronary artery proper. Although up to 85% of coronary flow in the left coronary artery occurs during
DistalRCAbeyond crux
RCA - PL branch
Figurc4. ‘Pop,During withdrawal of the angioplasty guide wire after a successful procrdure, recordings were made in the proximal right coronary artery (A), distal right coronary artery beyond the crux (B), posterior descending (C) and posterolatcral branches (D). Bottom, Rcprcscntativc tracings recorded after successful angioplasty. Diastolic predominant flow is seen in the posterior descending and postcrolatcral arteries (diastolic/systolic velocity ratio (DSVRJ 2.3 and 2.2, respectively). However, blood flow is equal during systole and diastolc in the proximal and distal right coronary arteries (diastolic/ systolic velocity ratio = 1.0). APV = aver_gc peak velocity; MPV = mcart peak velocity; PDA = posterior dcsccnding artcry; PL = postcrofateral artcry; RCA = right coronary artcry.
diastole, phasic blood flow in the right coronary artcry occurs equally during systole and diastole (14,18,19). This difference may be due to the lower systolic pressures, thinner walls and smaller stresses in the right ventricle (20). Because diastolic predominant flow is not the norm in the right coronary artery proper, restoration of diastolic predominant flow cannot bc used to assess right coronary artery stenoscs after angioplasty. Althougb blood flow in the right coronary artery propel occurred throughout the cardiac cycle, phasic blood flow in the posterior descending and posterolateral coronary arteries was predominantly diastolic. The diastolic predominant flow ob-
1016
HELLER ET AL. RIGHT CORONARY ARTERY BL30D
FLOW
cQ5. After iUl&9hSty, il sigtliticihlltdilkwacc WilS seenbctwcen the diustelic/systulicvclwity ri\ticN (IWR) in the did right coronary artq (RCA) and boththepstcrior Jcswnding(NM) andpstwIi~tCrill(BL) artrries. “p <: 0.01.
sewed in thcic left ventricular branches is similar 1o findings previously rcportcd for fhe left coronary artery. The systolic and diastolic blood flow variations in the left coronary artery h#Jc hen speculated to be due to the effects of the thickwalled left ventricle on intramyocardial pressures, inttdvascular pressures,time-varied resistances and coronary capacitance (21). As the posterior descending and psterolateral Coronaly artcrics leave the atrioventricular (AV) grooveand follow their courseover the left vcntriclc, their phasic blood flow patterns are probably subjcctcd to these same influences. In contrast, blood flow in the right coronary artery proper (within the AV groove) may bc exposed to more uniform time-varied rcsistances throughout the cardiac cycle. In addition. the right coronary artery may be more rz)mpliant and have Iowcr diastolic tlows than tho smaller and more distal post&r descending and posterolatcral branches (22). Relation to other Investigations. Three previous studies (12X$23) have concluded that a reduction in distdl blood How velocity and a loss of distal diastolic pndominant flow are characteristic of hcmodynamically signilicant stcnoscs. However, only 36 of the IfiEl stcnosr‘s included in thcscthree studies were in the right coronary artery. Furthermore, none of the investigators separately iIINIyWd the findings in right coronary artery sbnose~, Donahue et al. (23) did report that velocity proximal and distal to two right coronary artery stcnoses was unchanged despite angiogrdphic and hemodynamic (>30-mm transstenotic pressure gradient) evidcncc of lesion signiiicancc. The remaining 26 right coronary artery lesions in this study were not described. The investigators acknowledged that stenoses proximalto branch points in the proximal right coronary artery may represent u special case in which distal blood tlow v&city does not significantly decrease. Study limitations. Proximal and distal coronary flow rcserve were not recorded in this study. Although rest distal Doppler flow velocitywas not decreasedin our study,it is likely that the preangioplastydistal hypcrcmicresponsewould have been blunted (24). Although results of previous investigations (24) suggest that the coronary flow reserve may not normalize
immediately after coronary angioplasty, the utility of measuring hyperemic blood flow velocity to assessstenosesin the right coronary artery merits further study. Because transstenotic pressure gradients were not measured in our study, a third measure of stenosis severity is not available for comparison. However, coronary angiography remains the historic reference standard for stenosis assessment and the icsions studied were angiographically significant by blinded quantitative analysis. In addition, all patients in our study were referred for angioplasty of lesions that were deemed to bc clinically important and 12 of the patients had documented ohjcctivo cvidencc of ~sc~~c~~~~~~. Phasic Now patterns in the left VcntriCular branches were not recorded bcforc angioplasty. It is thcreforc not known whcthcr successful dilation of stcnoses in the right coronary artcry proper results in rcstWittiOt1 of dhsrolic predomim~lt tlow patterns in thcsc distal branches. Howcvcr, the Dopplrr criteria previously validated in the left coronary artcry were hascd on chnngcs in tlow vclocily patterns proximal and distul to a stenosis: Thcsc criteria could not bc applied to the right coronary artery stcnosesin this study. However, the cffccts of stenoses in the right coronary artery proper on diastolic1 systolic velocity ratios in the posterior descending and posterolateral branches merits further investigation. Because of the rclativcly small sample sjzc studied, it is possible that we failed to dotcct small ditlcrcnccs bctwecn the proximal and distal average peak vclocitics. Although a larger sample size might show a statistically significant decrcasc in the average peak velocity distal to a right coronary stenosis, such a diffcrcncc would probably bc too small to bc clinically useful. Heart rate, left ventricular pressure aud aortic pressure wcrc not controlled in our study. In addition, phasic coronary blood How immcdiatcly after angioplasty may not be represcntative of phasic blood llow in normal coronary artcrics atld their brdnches (23). Noncthcless, these observations have important implications fw conditions in which Doppler guide wires are used to assessstcnoses in the right coronary artery tree. In addition, it would be difficult to recruit patients with normal coronary arteries for a study involving the passing of an angioplasty guide wire into distal branches of the right coronary artery. Clinical significance, Rest Doppler blood flow velocity indexes that have been validated in the left coronary artcry were not useful for assessing stenoscs in the right coronary artery proper before or after angioplasty. In contrast to published data on the left coronary artery (l2), Doppler flow veloci:y did not decrease distal to angiogrdphically significant right coronary artcry stenoses. In addition, diastolic predominant How did not occur in the right coronary artery proper and therefore diastolic/systolic velocity ratios were not useful for lesion assessment. However, diastolic predominant flow was observedin the posterior descendingand posterolateralartcries after successfulangioplasty. Caution is warranted when extrapolating Doppler data from one coronarydistribution to another. The utility of measuring hyperemic Doppler flow velocity indexes, such as distal coronary flow reserve,to assess
t coronary
artery stertoses
for intravascular measurement of coronary artery Ho\vv&city. (‘irculation 1002$5:18YY-‘JI I. 12. Scgal J. Kern MJ, Scott NA, L’t al. Alterations of phasic ccrronq artcrv tj~w velocity in humans during pCrcutanoaus ~orcinary angioplusty. J Am (‘011 Cardiol lYY’~‘t):‘7h-Xh. . .. _ I?. Oliti EO. Kern MJ, Lahwitz AJ. ct al. Analysis of coronary hlocld tlow velocity dynamics in angiographically normal and stenosed artcries befort and after endclumen enlargemcnt~hy nngioplasty. J Am Coil Cardictl lOY~?l:31)X-16.
I. MARCUSM, Skurton DJ. Johnson MR. Collins SM. H;lrristm DG. Kerbcr RE. Visual estimates of pcrccnt diamctcr corcmq stenosis: “A battered gold st;md;&. J Am Coil Cardiol IYXX:I 1:X%-S. 2. Zir LM. Miller SW, Dinsmore RE, Gilbert JP, Hx~hornc JW. Intcrohxqver Vilriilhilily in cammiry angiogrephy.Circulation Y70;.52:627-32. 3. DC ROIICI~‘T/I, Murray JA. Owen W. Variability in the ;m;dysis of alron;lry nngiogrim~s.(‘irculiltiun IY77:SS:314-X. 4. Detre K, Wright E. Murphy ML, ‘I’;lk;tro T. Ohxrvrr qqccmcnt in the CVillllilliOll 0C wroniwy ilflgiogrimls. Circoliitioii lY7S:S!:~~7Y- X0. S. Brown RG. BC~ISOIIE. Frimcr M, Dodge T. Vu;mtit;ttivc ccjrcmnryxtrliog tqihy. c’ir~uliilion lO77:SS:220-37. b. Nichuls AU. Ba%.c AD, tli\n J, R&on DS. WIIWII IW, I’owCr\ ER. C’iiicvitlco-d~tisih,nlulric illlillyhiS0l IllC Cllkl d Coloililry ;lIlgiclplilSly011 coronq stcnotic dimcnsionx A111IIc’art J IOXS:I 15:722-32.
14. Gregg DE. Phasic blood llo~\ and its determinants in ttlc rig/It conmary ilrtcv. Am J Physiol lY37;l lY:SXO-8. IS. Scohlionko DP, Brown BG. Mitten S. ct
the
un;mcathctizcd
dog. An1 J Physiul lYbS;2tlX:224-31.
7. Ellis SC;. Elsctivc Cormliq, ill~gi~lplilSty: tcchniquc illlll cmplic;lIions. lo: Topol EJ. editor. Intavcntionid Cxdiulog. I’hil;~d~lphi;t: SiuItldCrs. 1000: I YY -222,
20. I lt#mim JIE. Trmamur;d myucardial perfusion. Prog C’ardiov:lsc Dis lYX7; 2Y:42Y-04.
X. Arnctt EN. lsnsr JM. Redw~nrdDR. CI al. Coronary artcry narrowing in corcmary IN!ilrtdisease: coinprison of cineailgiograp~iy iIlld~nWr0psy lindina. Ann intern Mcd 1070:01:350-6.
21. Spilim JAE. Brads NPW. Laird JD. Diastolic-systolic coronary How ditl’erencc’sare causedby intramyoc;lrdi;d pump action in 111~;rn~sthctixd dog. Circ Rcs l~JXl;4O:SX4-Y3.
0. Fischcll TA, Derby G. Tsc TM. Stadius ML. Coronary aricry vnsoconstricticin occurs routinely ;tfter percutimcous lransluminid coronary angioplirsty. J Am C’crllCardiol IYXX: 12:1377-481.
22. Chilian WM. Marcus ML. Philsic coronary blood fluw velocity in intnunurnl and epicardial coronq arteric:;. C’irc Rcs IYX2;50:77S-Xl,
IO. O’Ncill WW, WiIlItm JA, B;IICS ER. c! A. Criteria for suc~cs&l corcmq ungiriplustv BS asassstd by alterations in coronary v;lsodilut(~ry roc’rvc. J Am Coil Cardail lYX4$:1382. I I. Doucct~cJW, Carl I’D, PilynC HM, CI al. Valid;nian of ;i Doppler guide wire
2.1.Donahue
TJ. Kern MJ. Aguirrr FV. et al. Assessing 111~hcmodynamic signilicancc of corunary artery stenosch: iinidybi5 of tr;inslesional presbure Ilow rekltionships. J An1 Coil C’ardi!jl lYY3;2?:44Y-58.
14, Wilson RI-. Johnson MR. Marcus ML. L‘I a~. The clfcct of axomuy ;inpioplasly on coronary Ilow rocrvc. (‘irculatioli tYXX:77:X73-SS.
1012
October 1994:1012-7
LOUIS I. HELLER, MD, FACC, KEVIN H. SILVER, MD, BERNARD J. VILLEGAS, MD, FACC, SHARON J. BALCOM, RN, BONNIE H. WEINER, MD, FACC Wotrtwq
@j&vs.
Massuchusetrs
This study ettempted
I) to mess the utility ol rest
flow velocity For the physilore and after right
ty and a loss of distal diastolic prcdomimtnl tbw are characteristlc of physiologically significant s&noses and that lhcse indexes normalize abler successfid curenary artey dilalloa. However, these studies were p~oml~antly performed in lhe left coronary artery. The ulility of monitoring rest velocity variables during angioplasty of the right coronary artery has not been sludied. studied 20 pa&& undergoing angioplasty of #he rtery with use of a Doppler angioplasty guide wire. es were expressed as the mean value + I SD. The rest average peak velocity did not decrease distal tu angi~raphitally slgalficant right corunary artery stenoses (233 f 9.4 cm/s
The response of a stenotic coronary artery to petcutaneous transluminal coronary angioplasty is usually gauged by a
qualitative asswmcnt of the cotonwy angiogtum. However, ciotonaty angiqtaphy is limited in its ability to determine the physiologic significance of a coronary sttmosis (1). Visual estimates ate subjective, resulting in significant intetobservet and intraobservet variability (2-4). Quantitative coronary angiography (5) and tine videodensitometry (6) have been proas more objective methods of angiogtaphic assessment. owever, the diffuse nature of coronary artery disease may limit the utility of measuring petcent diameter stenosis by either method (78). Changes in coronary tone may also affect the angiographic assessment of percent diameter narrowing (9).
FWII the COIUUY Blood Flow Research Laboratory and Division of Cnnfiovarcular Mediiirte, Universityof Massachusetts Medical Center, Worcester. ~~w%s. This work wan supported in part & a grant from Cardiometks. k, Mountain Vii, California. Mm* nx+ed November19.1993; revised manuscript received April 5. 1 : Dr. Louis I. Heller, Diiision of Cardiovascular Medrcm~ thiversity of Masaehusetts Medical Center, 55 Lake Avenue North, Worcester, Massachusetts 01655. 01994 by tk American College of Cardiology
proximal vs. 20.2 f 11.1 cmls d distal veloci(y ratio was 1.4 t 0.9 sigmilcantly decrease aAer angio rence aeon p~ximal an r to detect a was no relatian between p a veloci(y. diameter stenosis and p~xima~/dista~ velocity ratios (r = O.IS, p = 0.55). Diastolic predominant flow was not observed in the ever, a Angie. proximal or distal right coronary artery. erolatin the plasty, diastolic predominairt Row was obse eral and posterior descending coronary arteries. ppler flow velacily indexes are not sting stenoses in the right coronary artery angioplasty. In contra artery proper, diastolic p~ominant posterior descending and poster&era1 coronary arteries. The utility of measuring hyperemic Doppler flow velocity indexes, such as distal coronary flow reserve, for assessing right coronary artery slcnuses mcriis fairer investigation. (J Am Co11 Cardioll994;24:1012-7)
In an attempt to improve these anatomic methods of lesion assessment, functional measures of stenosis severity have been employed. Measurement of coronary artery flow velocity using intracotonary Doppler catheters has been proposed to determine when a physiologically significant obstruction to coronary flow has been removed (10). Recently, a Dop, ‘.er angioplasty guide wire (FloWire, Cardiometrics, Inc) has been developed that allows the measurement of phasic spectral flow velocity in both proximal and distal human arteries (11). Previous investigations using the Doppler guide wire (12,13) have demonstrated that a decrease in distal blood flow velocity and a loss of distal diastolic ptedominam flow are chatacteristic of hemodynamicaliy significant stenoses and that these indexes normalize after successful dilatation. However, these studies were performed predominantly in the left coronary artery. The diagnostic applicability of these left coronary artery variables to the tight coronary artery, which has different phasic blood flow characteristics, has not been evaluated. Unlike the left coronary artery, the right coronary artery has few side branches and therefore rest blood flow velocity may not decrease distal to significant stenoses. In addition, Gregg (14) has shown that phasic flow in the right cororary artery does not occur predominantly during diastole. Accordingly, we 07351a97/94/$7.00
JACC Vol. 24. MO. 4 October 1994:1012-7
RIGHT
CORONARY
ARTERY
NELLER ET AL. BLQ!>D FLOW
1013
. Clinical@haracteristics of Study velocity before and a
Male Age @r) History of myocardial infarction Prior coronary bypass grafting Prior coronary angioplasty
14 (70%) 61.6 t 11.0 10 (50%) 0 7 (35%) 3 (15%)
Diabetes Smoking
8 (40%)
Hypercholesterolemia
ventricle.
Family history of coronary artery disease
13 (65%) 1 I (55%)
Hypertension Calcium channel blocking agents
13 (65%) 20(100%)
Nitrates
17 (85%‘)
Beta-adrenegic
blocking agents
I4 (70%)
Dutapresented are number (a) of patients or mean valtle f SD.
s. Tke records of all patients who underwent a Doppler angioplasty guide wire were rewere included in the study if t successful elective ercutancous t~~~s~~~rni~ial coronary angioplasty of a stenosis the right coronary artery the crux). Twenty patients met t ese se~cctioll criteria and Coronary angioplasty was performed according to the standard clinical protocol at our institution. All patients were pretreated with aspirin, dipyridamole (persantine) and a calcium channel blocking agent. Vascular access was obtained using the Judkins technique. Sufficient intravenous beparin was administered to result in an activated clotting time >300 s before the stenosis was crossed with the 0.018in. (0.046~cm)Doppler angioplasty guide wire. Dilation was performed with an appropriately sized balloon catheter. Dilations were concluded when the residual stenosis was 130% reduction in diameter stenosis by visual assessment. Coronary artery velocity measMrcme ts. All flow measurements were made with a Doppler-tipped angioplasty guide wire. ‘This Doppler guide wire is a 175cm, 0.018-m. flexible, steerable guide wire with a 12-MHz transducer at its tip. The Doppler guide wire has been validated and used in patients during interventional procedures (11). Spectral analysis of the Doppler signal is performed and velocity variables are calculated and displayed. All recordings were made with the angioplasty balloon catheter in the guide catheter. Baseline recordings were made approximately 2 cm proximal and 2 cm distal to the stenosis. Distal measurements were recorded with the sample volume in the distal right coronary artery (as opposed to a posterolateral or posterior descending branch). After successful angioplasty, velocity recordings were repeated proximal and distal to the area dilated. The time-averaged peak velocity and diastolic/systolic velocity ratios (diastolic average peak velocity divided by systolic average peak velocity) were calculated and displayed by the FloMap console. The proximal/distal velocity ratio was then calculated as the quotient of the proximal average peak velocity divided by the distal average peak velocity. Ten minutes after successful angiopjasty, velocity measurements were recorded in the posterior descending coronary artery,
istal right coronary artery (distal to the crux) and in the roximal right coronary artery. In five patients, measurements were also made in the posterolateral coronary artery. These final measurements were made as the guide wire was being he coronary artery after a successful procedure. c analysis. Angiograms were performed with Angiovist contrast medium utilizing a 7-m. (17.78~cm) image intensifier and 30.frame/s filming rate. Angioplasty guide catheters were 8F and injections were made by band. The analysis was performed using the pass Angioplasty Revascularization Investigation (BARI) quautitative cardiac angiographic system developed at Stanford University. The BAR1 system utilizes digital caliper measurements (Digit-Cal, Brown and Sharpe) (E-17). Coronary segment diameters are measured directly from the screen of the XR-35 projector specially equipped with an X -15 hood (Vanguard Instruments Corp.) with a magnification factor of x16. The diameter of the 8F guide catheter was taken as a reference for calibration. The lumen diameter in the adjacent “normal segment” and the minimal lumen diameter in the stenosis were measured. Care was taken to ensure that the measurements were made from exactly the same vessel segments on the pre and post angioplasty films. All measurements were performed by a physician who had no knowledge of the Doppler flow velocity data. Statistical methods. All results were expressed as the mean value 2 1 SD, The differences between the means of the various comparison samples were tested using a Wilcoxon signed rank test. The relation between rest Doppler flow velocity and angiography was assessed by least squares linear regression. An analysis of variance and a subsequent Scheffe’s F test were performed to compare the postangioplasty diastolic/systolic velocity ratios in the d& right coronary artery, the posterior descending coronary artery and the posterolateral coronary artery. A post-hoc power calcu!~rion was performed.
Patient characteristics. The clinical cnaracteristics or’ the study group are shown in Table 1. Twelve of the 20 patients had objective evidence of ischemia documented by exercise
1014
HELLER ET AL. RIGHT CORONARY
JACC Vol. 24, No. 4 October tyc)3:1012-7
ARTERY BLOOQ FLOW
*p < 0.0001
p = N.S.
80
Prc
-
Pi&t
0
% Stenosis -4
re 1. Despite a significant dccrca.sc in percent diamctcr stenosis (% Stcnosia) aficr (Post) successful right cmonxy artery angioplasty, thcrc W;IS no significant chungc in the proximal/distal velocity ratio (P/D), Prc = before angiopiasty.
elcctrwardiographic (ECG) stress testing (4), thallium scintigraphy (7) or rest angina associated with >I mm ST segment depression that resolved with relief of chest pain (I). Of the remaining eight patients, five had postinfarction angina and three had unstable angina without documented ECG changes. No patient had functional tests that were negative for ischemia. Coronary sag pbic measurements. The percent diameter stenosis decreased significantly after angioplasty (Fig. 1). There was a concordant increase in the minimal lumen diameter from 1.0 + 0.3 mm to 2.9 4 0.7 mm after angioplasty (p < 0.0001). Average peak velocity measurements, Rcpresentativc flow velocity tracings are shawn in Figure 2. Before angioplasty, the distal average peak velocity was not significantly decreased
(23.3 t 9.4 proximal vs. 20.2 ‘I- 11.1 cm/s distal, p = 0.20). The proximal/distal velocity ratio was 1.4 + 0.9 before angioplasty and did not decrease significantly after angioplasty (p = 0.58, Fig. 1). A power calculation was performed assuming an expected proximal/distal velocity ratio of 1.7 in all lesions in the study group. The power to detect this difference for an n = 20 and a distal average peak velocity of 20.2 L 11.1 cm/s was 99.4% (z = -2.53). After successful angioplasty, the average peak velocity in the distal right coronary artery did not increase significantly (20.2 t- Il.1 vs. 25.9 ‘c 8.8 cm/s, p = 0.20). Although there was a significant incrcasc in the ~ro~~rn~~~ average peak velocity after angioplasty (23.3 rtr 9.4 vs. 29.7 9 7.6 cm/s, p = 0.02). the magnitude of the change varied considerably (mean + SD 9.0 i: 6.0 cm/s, range - 1.0 to 17.0 cm/s). ~i~sto~ic/systotic velocity tias. The pl~stangi~~p~asty diastoliclsystalic velocity ratios did not change significantly either proximal or distal to the stenosis (Fig. 3). Phasic velocity patterns both proximal and distal to the area dilated were remarkable for prominent systolic components both before and after successful angioplasty. Examples of the postangioplasty phasic velocity profiles in the right coronary artery, posterior descending coronary artery and posterolatcral coronary artery arc shown in Figure 4. There was a significant difference between the diasto~ic/systolic velocity ratios in the distal right coronary artery and those in both the posterior descending and posterolateral coronary io~~~bic data. The proximal/distal velocity ratios were compared with the percent diameter stenoses derived from quantitative angiographic analysis. Least squares linear regression analysis revealed this
Figure 2. Angiograms and Doppler velocity tracings from a patient undergoing right coronary artcry angioplasty. Top IWW, Preangioplasty data. Bottom row, Postangioplasty data. The angiogram before angioplasty revtiled a proximal 78% slcnosis that was associated with a proximal/distal velocity ratio (P/D) of 1.4 and a distal diastolic/systolic velocity ratio (DSVR) of 1.2. After successful angioplasty, the percent diameter stenosis was reduced to 9% as measured by digital calipers: however, the proximal/ distal velocity ratio of 1.3 and the distal diastolicLystolic velocity ratio of 1.1 were essentially unchanged. The proximal and distal average peak velocity did increase after successful angioplasty; however, this trend did not reach statistical significance in our study (see text). APV = average peak velocity.
pe-t stenosis =9.0
P/D = 1.3
DSVR = 1.1
JACC Vol. 244,No. 4 October 1994:101’-7
RIGHT CORONARY
Distal Prc i@M?3.
ThCK
WlS
MMJ pustangioplasty
iltldilkK!llCC
Proximal Post IlChVCCll tllC
ARTERY
%%_bER ET AL. BLOOD FLOW
1015
istal Post
p~C~lllgiOplilSly (Prc)
(Post) diastolic/systolic velocity ratios meitsurcdproximal or distal to the stenosis.
.“~___l_ll___
(DSVR) Proximal RCA
RCA
- PDA
relation to be insignificant both before (r I=0.15, p = 0.3) and after successful augioplasty (r = 0.12, p = 0.7
stu ata. We believe that this is the first clinical study to evaluate phasic blood flow velocity in the right coronary artery tree. We conclude that 1) rest Doppler blood flow indexes are not helpful for evaluating lesions before or after right coronary artery angioplasty, and 2) diastolic predominant flow is characteristic of left ventric;rlar branches (posterior descending and posterolatcral arteries) but is not characteristic of the right coronary artery proper. There was no relation between percent diameter stenosis and proximal/distal velocity ratios in our study. The rest average peak velocity did not decrease distal to angiographitally significant right coronary artery stenoses. The right coronary artery has few branches proximal to a stenosis and, therefore, in accordance with Bernoulli’s theorem, flow proximal to a stenosis may be similar to flow distal to the stenosis. As a result, the proximal/distal velocity ratio was not a useful variable for the functional assessment of right coronary artery stenoses in our patients. Changes in distal average peak velocity measurements were not helpful for assessing right coronary artery stenoses either before or after angioplasty. The distal rest average peak velocity did not significantly increase after successful angioplasty. Although there was a significant increase in the proximal average peak velocity after successful angioplasty, the magnitude of this increase was variable. Accordingly, this variable was of limited utility for assessing stenosis after the intervention. The diastolic/systolic velocity ratios proximal and distal to the stenoses did not change after successful angioplasty in our study. Diastolic predominant flow was not observed in the proximal or distal right coronary artery proper. Although up to 85% of coronary flow in the left coronary artery occurs during
DistalRCAbeyond crux
RCA - PL branch
Figurc4. ‘Pop,During withdrawal of the angioplasty guide wire after a successful procrdure, recordings were made in the proximal right coronary artery (A), distal right coronary artery beyond the crux (B), posterior descending (C) and posterolatcral branches (D). Bottom, Rcprcscntativc tracings recorded after successful angioplasty. Diastolic predominant flow is seen in the posterior descending and postcrolatcral arteries (diastolic/systolic velocity ratio (DSVRJ 2.3 and 2.2, respectively). However, blood flow is equal during systole and diastolc in the proximal and distal right coronary arteries (diastolic/ systolic velocity ratio = 1.0). APV = aver_gc peak velocity; MPV = mcart peak velocity; PDA = posterior dcsccnding artcry; PL = postcrofateral artcry; RCA = right coronary artcry.
diastole, phasic blood flow in the right coronary artcry occurs equally during systole and diastole (14,18,19). This difference may be due to the lower systolic pressures, thinner walls and smaller stresses in the right ventricle (20). Because diastolic predominant flow is not the norm in the right coronary artery proper, restoration of diastolic predominant flow cannot bc used to assess right coronary artery stenoscs after angioplasty. Althougb blood flow in the right coronary artery propel occurred throughout the cardiac cycle, phasic blood flow in the posterior descending and posterolateral coronary arteries was predominantly diastolic. The diastolic predominant flow ob-
1016
HELLER ET AL. RIGHT CORONARY ARTERY BL30D
FLOW
cQ5. After iUl&9hSty, il sigtliticihlltdilkwacc WilS seenbctwcen the diustelic/systulicvclwity ri\ticN (IWR) in the did right coronary artq (RCA) and boththepstcrior Jcswnding(NM) andpstwIi~tCrill(BL) artrries. “p <: 0.01.
sewed in thcic left ventricular branches is similar 1o findings previously rcportcd for fhe left coronary artery. The systolic and diastolic blood flow variations in the left coronary artery h#Jc hen speculated to be due to the effects of the thickwalled left ventricle on intramyocardial pressures, inttdvascular pressures,time-varied resistances and coronary capacitance (21). As the posterior descending and psterolateral Coronaly artcrics leave the atrioventricular (AV) grooveand follow their courseover the left vcntriclc, their phasic blood flow patterns are probably subjcctcd to these same influences. In contrast, blood flow in the right coronary artery proper (within the AV groove) may bc exposed to more uniform time-varied rcsistances throughout the cardiac cycle. In addition. the right coronary artery may be more rz)mpliant and have Iowcr diastolic tlows than tho smaller and more distal post&r descending and posterolatcral branches (22). Relation to other Investigations. Three previous studies (12X$23) have concluded that a reduction in distdl blood How velocity and a loss of distal diastolic pndominant flow are characteristic of hcmodynamically signilicant stcnoscs. However, only 36 of the IfiEl stcnosr‘s included in thcscthree studies were in the right coronary artery. Furthermore, none of the investigators separately iIINIyWd the findings in right coronary artery sbnose~, Donahue et al. (23) did report that velocity proximal and distal to two right coronary artery stcnoses was unchanged despite angiogrdphic and hemodynamic (>30-mm transstenotic pressure gradient) evidcncc of lesion signiiicancc. The remaining 26 right coronary artery lesions in this study were not described. The investigators acknowledged that stenoses proximalto branch points in the proximal right coronary artery may represent u special case in which distal blood tlow v&city does not significantly decrease. Study limitations. Proximal and distal coronary flow rcserve were not recorded in this study. Although rest distal Doppler flow velocitywas not decreasedin our study,it is likely that the preangioplastydistal hypcrcmicresponsewould have been blunted (24). Although results of previous investigations (24) suggest that the coronary flow reserve may not normalize
immediately after coronary angioplasty, the utility of measuring hyperemic blood flow velocity to assessstenosesin the right coronary artery merits further study. Because transstenotic pressure gradients were not measured in our study, a third measure of stenosis severity is not available for comparison. However, coronary angiography remains the historic reference standard for stenosis assessment and the icsions studied were angiographically significant by blinded quantitative analysis. In addition, all patients in our study were referred for angioplasty of lesions that were deemed to bc clinically important and 12 of the patients had documented ohjcctivo cvidencc of ~sc~~c~~~~~~. Phasic Now patterns in the left VcntriCular branches were not recorded bcforc angioplasty. It is thcreforc not known whcthcr successful dilation of stcnoses in the right coronary artcry proper results in rcstWittiOt1 of dhsrolic predomim~lt tlow patterns in thcsc distal branches. Howcvcr, the Dopplrr criteria previously validated in the left coronary artcry were hascd on chnngcs in tlow vclocily patterns proximal and distul to a stenosis: Thcsc criteria could not bc applied to the right coronary artery stcnosesin this study. However, the cffccts of stenoses in the right coronary artery proper on diastolic1 systolic velocity ratios in the posterior descending and posterolateral branches merits further investigation. Because of the rclativcly small sample sjzc studied, it is possible that we failed to dotcct small ditlcrcnccs bctwecn the proximal and distal average peak vclocitics. Although a larger sample size might show a statistically significant decrcasc in the average peak velocity distal to a right coronary stenosis, such a diffcrcncc would probably bc too small to bc clinically useful. Heart rate, left ventricular pressure aud aortic pressure wcrc not controlled in our study. In addition, phasic coronary blood How immcdiatcly after angioplasty may not be represcntative of phasic blood llow in normal coronary artcrics atld their brdnches (23). Noncthcless, these observations have important implications fw conditions in which Doppler guide wires are used to assessstcnoses in the right coronary artery tree. In addition, it would be difficult to recruit patients with normal coronary arteries for a study involving the passing of an angioplasty guide wire into distal branches of the right coronary artery. Clinical significance, Rest Doppler blood flow velocity indexes that have been validated in the left coronary artcry were not useful for assessing stenoscs in the right coronary artery proper before or after angioplasty. In contrast to published data on the left coronary artery (l2), Doppler flow veloci:y did not decrease distal to angiogrdphically significant right coronary artcry stenoses. In addition, diastolic predominant How did not occur in the right coronary artery proper and therefore diastolic/systolic velocity ratios were not useful for lesion assessment. However, diastolic predominant flow was observedin the posterior descendingand posterolateralartcries after successfulangioplasty. Caution is warranted when extrapolating Doppler data from one coronarydistribution to another. The utility of measuring hyperemic Doppler flow velocity indexes, such as distal coronary flow reserve,to assess
t coronary
artery stertoses
for intravascular measurement of coronary artery Ho\vv&city. (‘irculation 1002$5:18YY-‘JI I. 12. Scgal J. Kern MJ, Scott NA, L’t al. Alterations of phasic ccrronq artcrv tj~w velocity in humans during pCrcutanoaus ~orcinary angioplusty. J Am (‘011 Cardiol lYY’~‘t):‘7h-Xh. . .. _ I?. Oliti EO. Kern MJ, Lahwitz AJ. ct al. Analysis of coronary hlocld tlow velocity dynamics in angiographically normal and stenosed artcries befort and after endclumen enlargemcnt~hy nngioplasty. J Am Coil Cardictl lOY~?l:31)X-16.
I. MARCUSM, Skurton DJ. Johnson MR. Collins SM. H;lrristm DG. Kerbcr RE. Visual estimates of pcrccnt diamctcr corcmq stenosis: “A battered gold st;md;&. J Am Coil Cardiol IYXX:I 1:X%-S. 2. Zir LM. Miller SW, Dinsmore RE, Gilbert JP, Hx~hornc JW. Intcrohxqver Vilriilhilily in cammiry angiogrephy.Circulation Y70;.52:627-32. 3. DC ROIICI~‘T/I, Murray JA. Owen W. Variability in the ;m;dysis of alron;lry nngiogrim~s.(‘irculiltiun IY77:SS:314-X. 4. Detre K, Wright E. Murphy ML, ‘I’;lk;tro T. Ohxrvrr qqccmcnt in the CVillllilliOll 0C wroniwy ilflgiogrimls. Circoliitioii lY7S:S!:~~7Y- X0. S. Brown RG. BC~ISOIIE. Frimcr M, Dodge T. Vu;mtit;ttivc ccjrcmnryxtrliog tqihy. c’ir~uliilion lO77:SS:220-37. b. Nichuls AU. Ba%.c AD, tli\n J, R&on DS. WIIWII IW, I’owCr\ ER. C’iiicvitlco-d~tisih,nlulric illlillyhiS0l IllC Cllkl d Coloililry ;lIlgiclplilSly011 coronq stcnotic dimcnsionx A111IIc’art J IOXS:I 15:722-32.
14. Gregg DE. Phasic blood llo~\ and its determinants in ttlc rig/It conmary ilrtcv. Am J Physiol lY37;l lY:SXO-8. IS. Scohlionko DP, Brown BG. Mitten S. ct
the
un;mcathctizcd
dog. An1 J Physiul lYbS;2tlX:224-31.
7. Ellis SC;. Elsctivc Cormliq, ill~gi~lplilSty: tcchniquc illlll cmplic;lIions. lo: Topol EJ. editor. Intavcntionid Cxdiulog. I’hil;~d~lphi;t: SiuItldCrs. 1000: I YY -222,
20. I lt#mim JIE. Trmamur;d myucardial perfusion. Prog C’ardiov:lsc Dis lYX7; 2Y:42Y-04.
X. Arnctt EN. lsnsr JM. Redw~nrdDR. CI al. Coronary artcry narrowing in corcmary IN!ilrtdisease: coinprison of cineailgiograp~iy iIlld~nWr0psy lindina. Ann intern Mcd 1070:01:350-6.
21. Spilim JAE. Brads NPW. Laird JD. Diastolic-systolic coronary How ditl’erencc’sare causedby intramyoc;lrdi;d pump action in 111~;rn~sthctixd dog. Circ Rcs l~JXl;4O:SX4-Y3.
0. Fischcll TA, Derby G. Tsc TM. Stadius ML. Coronary aricry vnsoconstricticin occurs routinely ;tfter percutimcous lransluminid coronary angioplirsty. J Am C’crllCardiol IYXX: 12:1377-481.
22. Chilian WM. Marcus ML. Philsic coronary blood fluw velocity in intnunurnl and epicardial coronq arteric:;. C’irc Rcs IYX2;50:77S-Xl,
IO. O’Ncill WW, WiIlItm JA, B;IICS ER. c! A. Criteria for suc~cs&l corcmq ungiriplustv BS asassstd by alterations in coronary v;lsodilut(~ry roc’rvc. J Am Coil Cardail lYX4$:1382. I I. Doucct~cJW, Carl I’D, PilynC HM, CI al. Valid;nian of ;i Doppler guide wire
2.1.Donahue
TJ. Kern MJ. Aguirrr FV. et al. Assessing 111~hcmodynamic signilicancc of corunary artery stenosch: iinidybi5 of tr;inslesional presbure Ilow rekltionships. J An1 Coil C’ardi!jl lYY3;2?:44Y-58.
14, Wilson RI-. Johnson MR. Marcus ML. L‘I a~. The clfcct of axomuy ;inpioplasly on coronary Ilow rocrvc. (‘irculatioli tYXX:77:X73-SS.