(Circulation. 2001;103:1212.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
Intracoronary Doppler– and Quantitative Coronary Angiography–Derived Predictors of Major Adverse Cardiac Events After Stent Implantation
From the Cardiology Department, University of Essen, Essen, Germany (M.H., D.B., R.E.); Ospedale di Circolo, Varese, Italy (E.V.); Academic Medical Center, Amsterdam, Netherlands (J.J.P.); Universitair Ziekenhuis, Antwerpen, Belgium (C.V.); and Kardiologische Universitätsklinik, Allgemeines Krankenhaus, Wien, Austria (P.P.).
Correspondence to Michael Haude, MD, Cardiology Department, University of Essen, Hufelandstraße 55, 45122 Essen, Germany.
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionReferences |
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Background—Distal coronary flow velocity reserve (CVR) is significantly improved after a successful balloon angioplasty (PTCA). Furthermore, a postinterventional CVR >2.5 and a percent diameter stenosis (%DS)
35% are predictive for a low incidence of major adverse cardiac
events (MACE) at 6 months of 16%. Similar results are lacking for
coronary stenting.
Methods and Results—In
150 patients, baseline and hyperemic coronary flow velocities were
recorded with a Doppler guidewire distal to the target lesion and in an
unobstructed reference artery before and after PTCA, after stenting,
and at 6 months. Distal CVR and relative CVR
(CVRrel) were calculated. Logistic regression
and receiver operating characteristic analyses were applied to
determine prognostic cutoff values of CVR,
CVRrel, %DS, and minimal lumen diameter
separately and in combination to predict MACE at 6 months. After
stenting, CVR (2.96±0.87 versus 2.40±0.7;
P=0.001),
CVRrel (1.02±0.24 versus 0.81±0.24;
P=0.001), and minimal lumen
diameter (2.98±0.56 versus 2.11±0.74 mm;
P=0.001) were significantly
higher than after PTCA. Thirty-three patients developed MACE. A
postinterventional CVRrel>0.88 was the best
single predictor of MACE, with an incidence of 6.8%, whereas the
combination of a CVRrel>0.88 and a %DS
11.2% predicted an incidence of MACE of
1.5%.
Conclusions—Measurement of CVRrel and %DS after stent implantation are best suitable to predict MACE at 6 months.
Key Words: stents • blood flow • restenosis • angioplasty • prognosis
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Recently, Doppler flow wires became available to measure coronary blood flow velocity reserve (CVR) during human cardiac catheterization and to calculate CVR as a physiological measure of stenosis severity.1 2 Using this device, the Doppler Endpoint Balloon Angioplasty Trial Europe (DEBATE) documented a significant increase in CVR distal to the target lesion to 2.5 after a successful balloon angioplasty (PTCA).3 Clinically even more relevant, a subgroup of patients with a postprocedural CVR of >2.5 and a residual diameter stenosis (%DS) of
35% presented an incidence of
major adverse cardiac events (MACE) of only 16% at 6 months.
Nevertheless, the DEBATE trial left some unanswered questions. Is this
CVR value of 2.5 the best that can be achieved postinterventionally in
the presence of residual stenosis, because it is common after PTCA? If
residual stenosis can be minimized and distal CVR optimized, do these
patients present MACE less frequently? Stents minimize residual stenosis and create a rounder arterial conduit with a smoothened surface.4 5 Thereby, improved local blood flow conditions can be expected.6 7 8 9 10
The purpose of this observational trial was to identify the short-term and long-term impact of the stent on absolute and relative CVR and on patients’ clinical outcome by coronary blood flow velocity measurements.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Patients
Table 1
summarizes baseline characteristics of 150
patients with elective stent implantation who were enrolled in the
study. They had to be symptomatic and/or to present objective ischemia
in a stress test. Lesion length was limited to 15 mm to allow coverage
with a single stent. All patients gave informed consent for the initial
procedure, including stent placement and blood flow velocity
measurements, and for a 6-month invasive control.
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Subacute myocardial infarction (MI), chronic total occlusion of the target lesion, 3-vessel disease, or contraindications against stenting were exclusion criteria.
Interventional Procedure, Including Flow
Velocity Measurements
Premedication included acetylsalicylic acid 100 to
300 mg/d. Before intervention, 5000 to 10 000 IU heparin IV was
administered, but no glycoprotein IIb/IIIa inhibitors. Coronary
angiography was performed according to local practice. After the
diagnostic part, a 6F or 8F guiding catheter was inserted, and a
0.014-in Doppler guidewire (Flo Wire, Endosonics) was passed through
the target lesion with the tip positioned >2 cm distal to the
stenosis. Then distal blood flow velocity recordings were obtained
under basal and during hyperemic conditions induced by intracoronary
injection of 12 µg adenosine to the right or 18 µg to the left
coronary artery. During flow velocity measurements, the guiding
catheter should be withdrawn from the ostium to provide maximum flow.
Good-quality recordings were necessary to continue with the study. PTCA
was performed according to local practice with a balloon-to-artery
ratio of 
1 to 1. In 72 patients (48%), the Flo Wire was used as the
interventional guidewire, and in the remaining patients, an additional
"working" wire was positioned. Control angiography was performed in
2 planes identical to the preinterventional coronary angiography. At
least 5 minutes after the final balloon deflation and 3 minutes after
the preceding contrast injection, blood flow velocity measurements were
repeated at baseline and during hyperemia. Then stents were implanted
according to local practice, with the same balloon size as for PTCA,
with an implantation pressure of 12 atm. Stents were dilated in 68
patients (45%) with pressures 14 atm. When control coronary
angiography documented a good angiographic result, blood flow velocity
measurements at baseline and during hyperemia were repeated. Finally,
wires were withdrawn from the target artery, and the Doppler guidewire
was positioned in the mid part of an unobstructed reference vessel
(left anterior descending artery in 62 patients [41%], left
circumflex artery [LCx] in 64 [43%], and right coronary artery in
24 [16%]) to perform blood flow velocity recordings at baseline and
during hyperemia.
Follow-Up Procedures
After 5.9±0.4 months, all patients underwent
reevaluation of their clinical status, a stress test, and repeat
cardiac catheterization. Coronary angiography was performed in
identical views as during the initial procedure. Blood flow velocity
recordings were repeated at baseline and during hyperemia distal to the
previously treated vessel site and in the nonstenotic reference artery.
Angiographic restenosis was defined as a >50% DS at the previously
treated vessel site.
Definition of MACE
Death, MI, and restenosis requiring target lesion
revascularization (TLR) were selected as MACE. Q-wave MI was defined as
any postprocedural increase of creatinine phosphokinase (CPK) to >3
times the local threshold value with 8% CPK-MB fraction and the
development of new Q waves, whereas non–Q-wave MI was based solely on
enzyme increase. TLR was intended when symptomatic patients with or
without pathological stress test presented a >50% DS independent of
the results of the blood flow velocity recordings.
Coronary Blood Flow Velocity
Measurements
Doppler flow velocity spectra were recorded
continuously on videotape with the FloMap or FloMod system
(Endosonics), which automatically detect maximum blood flow velocity
and calculate absolute CVR as the ratio of average peak velocity (APV)
during maximum hyperemia divided by baseline
APV.11 In addition, relative
CVR (CVRrel) was calculated as the ratio of
absolute CVR distal to the target lesion divided by absolute CVR in the
unobstructed reference
artery.12 13 14
Blood flow velocity recordings and coronary angiograms were analyzed
offline in a core laboratory at the University of
Essen.
Quantitative Coronary
Angiography
After intracoronary injection of 0.2 mg nitroglycerin
or 1 to 3 mg isosorbide dinitrate, coronary angiograms for quantitative
analysis were performed before and after PTCA, after stenting, and at 6
months. We used the edge-detection system developed by Reiber et al
(CMS, Medis).15 The mean
variation for this system in determining the absolute diameter is
0.13 mm. For calibration, the non–contrast-filled guiding catheter
was used. From 2 orthogonal views, minimal lumen diameter (MLD),
interpolated reference diameter, and %DS were calculated as a
mean.
Statistical Analysis
Continuous variables are expressed as mean±SD.
Differences within these variables were evaluated by ANOVA and paired
or unpaired Student’s t test
when appropriate. Qualitative variables were analyzed by
2 or Fisher’s exact test.
According to the statistical approach in the DEBATE trial, both univariate and multivariate logistic regression analyses were performed to study the diagnostic value of quantitative coronary angiography (QCA) and Doppler parameters to predict MACE at 6 months. No additional clinical variables were introduced into the model, because the specific aim of the study was to identify Doppler and QCA indices predictive of MACE after stenting. Each observed value of the significant predictive variables was considered a possible "prognostic threshold." Sensitivity and specificity were calculated at each threshold. Receiver operating characteristic (ROC) curves were constructed, and the areas under the ROC curve are reported with 95% confidence limits.16
Finally, the "best" threshold of a significant
predictive variable was defined as the cutoff point where sensitivity
equals specificity.17 On the
basis of this threshold, the patient population was divided into 2
categories. The frequency of events in both categories was determined,
and differences were evaluated by 2
analysis with the report of relative risks. Two-sided probability
values are reported for all appropriate tests, with statistical
significance taken at the 0.05 probability
level.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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In all 150 patients, sequential Doppler recordings and coronary angiograms were of sufficient quality to perform quantitative analysis. No patient was lost to clinical and angiographic follow-up.
Major Adverse Cardiac Events
Thirty-three patients developed MACE. No patient died.
Five patients (3%) developed non–Q-wave MIs (maximum CPK rise of
418±108 IU/L and CPK-MB rise of 55±12 IU/L) 1 to 5 days after the
intervention. In these patients, residual %DS was significantly larger
(27±11% versus 12±13%,
P=0.001) and
CVRrel significantly lower (0.79±0.18 versus
1.03±0.25, P=0.001). All
patients with non–Q-wave MI were treated medically. Angiographic
restenosis requiring TLR was documented in 28 patients
(19%).
Doppler Flow Velocity Measurements
Figure 1 illustrates a representative case
example.
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There was no significant shift (=15%) in baseline APV
distal to the target lesion and in the reference artery during
measurements
(Figure 2). In contrast, a stepwise significant increase in
hyperemic distal APV was measured after PTCA and stenting, which
decreased nonsignificantly at follow-up because of 28 patients with
restenosis
(Figure 2). Distal CVR increased significantly after PTCA and
again after stenting and thereby reached the level of the
reference CVR with no significant change at follow-up
(Figure 2). CVRrel also increased
significantly after PTCA and stenting but decreased nonsignificantly at
follow-up because of 28 patients with restenosis
(Figure 3). CVRrel at follow-up in
patients without restenosis was similar to that after stenting
(1.02±0.24 versus 1.05±0.22;
P=0.224). Reference CVRs during
the initial procedure and at follow-up were not significantly different
(2.94±0.74 versus 3.09±0.78;
P=0.167).
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In 18 (12%) of 150 patients, CVR in the unobstructed
coronary artery was 2.0, reflecting microvascular disease. After
stenting, CVRrel was 1.01±0.16 in these
patients versus 1.02±0.23 in the remaining patients. Furthermore, the
MACE rate was similar, occurring in 4 (22.2%) of 18 patients versus 29
(21.9%) of 132 patients.
No physiologically relevant changes in blood pressure (systolic blood pressure 135±25 mm Hg before PTCA, 133±23 mm Hg after PTCA, 131±26 mm Hg after stent implantation, and 137±26 mm Hg at follow-up) or heart rate (71±12 bpm before PTCA, 70±13 bpm after PTCA, 68±11 bpm after stent implantation, 72±13 bpm at follow-up) were noted.
Quantitative Coronary Angiography
Initial lesion length was 10.22±2.98 mm. MLD increased
from 0.92±0.51 to 2.11±0.74 mm after PTCA
(P=0.001) and to 2.98±0.56 mm
after stent implantation
(P=0.001 versus after PTCA),
whereas %DS decreased from 68±7% to 36±16% after PTCA
(P=0.001) and to 13±14% after
stent implantation (P=0.001
versus after PTCA). After 5.9±0.4 months, MLDs (2.17±0.70 mm;
P=0.001) were smaller and %DS
(33±17%; P=0.001) larger.
Angiographic restenosis was documented in 28 patients
(19%).
Doppler- and QCA-Derived Predictive Values
for MACE
Table 2 summarizes Doppler and QCA parameters as
independent risk factors for MACE. A postinterventional DS of >11.2%
was a better predictor than an MLD of 2.77 mm. The difference of ROC
areas was 11.7% (95% CI 1.4% to 22.1%;
P=0.026). A
CVRrel of 0.88 after stenting was a better
functional predictor of MACE than a distal CVR of 2.86. The
difference of ROC areas was 13.2% (95% CI 3.3% to 23.1%;
P=0.009). Distal CVR and
CVRrel after stent implantation were
significantly lower and %DS significantly higher in patients with
MACE, whereas postinterventional MLD was not statistically different in
patients with or without MACE
(Table 3).
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Subgroup Analysis
Best results on MACE were obtained in patients
with a postinterventional CVRrel of >0.88 who
presented an incidence of 6.8%
(Figure 4a). If morphometric and functional cutoff criteria
are combined, patients with a poststent
CVRrel>0.88 and a residual DS of 11.2%
presented a MACE rate of only 1.5%
(Figure 4b). Patients not fulfilling the morphometric cutoff
criteria had a 2.84- to 3.13-fold higher relative risk for MACE
(Figure 5), whereas patients who did not fulfill the
functional cutoff criteria presented a 3.26- to 7.78-fold higher
relative risk. Patients who did not fulfill the combined morphometric
and functional criteria presented a 4.18- to 26.54-fold higher relative
risk for MACE.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Our study documents that distal CVR and CVRrel are significantly improved after successful stent implantation compared with PTCA alone, apart from the well-known enlargement of luminal dimensions. This supports previous reports using intracoronary Doppler or densitometric evaluations of CVR.6 7 8 9 18
Furthermore, intracoronary Doppler– and QCA-derived parameters could be identified that were predictive for MACE at 6 months. A %DS was the best single independent morphometric parameter derived from QCA to predict MACE with a cutoff value of 11.2%, which was substantially lower than the value of 35% after PTCA in the DEBATE trial.3 CVRrel was found to be the overall best independent parameter and clearly topped distal CVR as a functional parameter to predict MACE. Because CVRrel was not calculated in the DEBATE trial, only distal CVR values after PTCA can be compared. These were almost identical, documenting that underdilatation in our study is unlikely.
One advantage of CVRrel over CVR is
the unequivocal normal value of 1, whereas there is an ongoing debate
concerning the cutoff value for a normal CVR, which is reported to
range between 1.8 and
3.0.19 20 21
Especially in the presence of additional microvascular
disease,22 23 24
CVR after a successful stent implantation with minimization of the
residual stenosis can remain low. This particular aspect may be
neglected if CVRrel is applied. Patients with a
postinterventional CVRrel of >0.88 showed an
incidence of MACE of 6.5% at 6 months, which improved to 1.5% if
these patients were additionally screened for a postinterventional DS
of 11.2%. By use of these new cutoff criteria, a more favorable
outcome can be predicted after stenting compared with the results of
the DEBATE trial for PTCA.
Because TLR was the main contributor to MACE, the combined Doppler- and QCA-derived parameters may also predict the extent of the restenosis process. Stents inhibit elastic recoil and thereby create a larger postinterventional lumen than PTCA, which better compensates for vessel shrinkage and neointima proliferation causing restenosis. Nevertheless, it is surprising that flow parameters, especially CVRrel, predict restenosis and TLR better than any morphometric QCA parameter. An immediate and almost complete recovery of the microvascular response may predict a less aggressive neointimal response.
More recently, intracoronary pressure measurements25 after PTCA and stent implantation with the calculation of fractional flow reserve presented results similar to those documented here.26 This is not surprising, because a previous report showed a close correlation between CVRrel and fractional flow reserve, which was not documented for distal CVR.
Limitations of the Present Study
To answer the above-listed questions, Doppler flow
velocity and QCA measurements were performed in carefully selected
patients scheduled for stent implantation. Most patients had
single-vessel coronary artery disease to allow Doppler measurements in
a nonobstructed reference vessel. The study results cannot
automatically be transferred to patients with lesions in the right
coronary artery, although no data are available to support different
results on CVR or CVRrel compared with the left
anterior descending or left circumflex artery.
Furthermore, CVRrel cannot be calculated in patients with 3-vessel coronary artery disease.
Patients with MIs were excluded because microvascular recovery of the infarcted vascular bed after restoration of the supplying epicardial vessel by stent implantation is unpredictable.21 Translesion pressure measurements with calculation of fractional flow reserve seem to be superior in this setting.
We accepted only predefined changes in blood pressure, heart rate, and baseline APV throughout the individual measurement sequence to avoid side effects on derived blood flow parameters.27 In particular, a significant shift of baseline APV has a substantial impact on CVR and CVRrel.28 To compensate for such a shift, our group recently reported an algorithm to calculate a corrected baseline APV before calculating CVR and CVRrel.29
Because investigators were not blinded to the Doppler flow velocity and QCA results at follow-up, the incidence of TLR could be driven by these measurements. Nevertheless, the indication for TLR was predefined on the basis of the patient’s angina status and/or the objective documentation of ischemia during a stress test.
We applied the same statistical approach to define cutoff values as was chosen in the DEBATE trial, which is more objective than predefined sensitivity or specificity values.
This study should evaluate the predictive value of Doppler- and QCA-derived parameters alone, instead of combining them with other demographic or procedural parameters predictive of restenosis. It can be speculated that any reasonable combination of well-known risk factors for restenosis together with the derived Doppler and QCA parameters could provide different results.
Furthermore, it is questionable whether stent-like post-PTCA results with a residual stenosis <11.2% provide a beneficial long-term outcome similar to that for stented patients presented here. The aspect of provisional stenting based on Doppler-derived flow velocity parameters is covered in part by 2 large prospective multicenter randomized trials (DEBATE 2 and DESTINI), which are completed and await publication.
Clinical Implications
Study results document that patients with stent
implantation can be stratified for their long-term prognosis on the
basis of Doppler- and QCA-derived parameters measured immediately after
intervention. Because the improvement of CVR and
CVRrel after stenting is driven by lumen
enlargement and by the immediate recovery of microvascular capacity,
operators should first try to minimize DS to 11.2% and to gain an
MLD of >2.77 mm controlled by QCA, which sometimes requires stent
dilatation with higher pressure or larger balloons. Nevertheless, the
subsequent individual impact on Doppler parameters remains
unpredictable. In our patients, 45% fulfilled the optimal criteria to
prevent MACE without additional stent
dilatation.
Received July 27, 2000; revision received November 6, 2000; accepted November 6, 2000.
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