(Circulation. 1998;98:2133-2140.)
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Cardiology, Academic Medical Center, Amsterdam, Netherlands.
Correspondence to Jan J. Piek, MD, Department of Cardiology, B2-108, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, PO Box 22700, 1100 DE Amsterdam, Netherlands. E-mail j.j.piek{at}amc.uva.nl
| Abstract |
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Methods and ResultsA total of 54 patients with 1-vessel disease
and normal left ventricular function were studied after
balloon angioplasty (n=34) or stent implantation (n=20). Distal
coronary blood flow velocity reserve (CFR) was defined as the
ratio of adenosine-induced hyperemic versus baseline
blood flow velocity with a 0.014-in Doppler guidewire. The relative
CFR was defined as the ratio of the distal CFR and the reference CFR
measured in the normal adjacent coronary artery.
Hemodynamic and angiographic measurements were
performed before and directly after balloon angioplasty or stent
implantation and at 6-month follow-up. CFR after PTCA
2.5 was defined
as an impaired CFR. Immediately after PTCA, CFR improved toward the
range of the reference artery CFR. In both the balloon-treated and the
stent-treated groups, initial high CFR values decreased and impaired
CFR values increased at follow-up toward the values of the reference
CFR in patients without restenosis. Impaired CFR after balloon
angioplasty (33%) or stent implantation (58%) in patients without
restenosis was related to an increased baseline flow velocity
that normalized at follow-up. Patients with an increase of CFR after
stenting were characterized by an unaltered baseline flow velocity and
an increased adenosine-induced hyperemic flow
velocity.
ConclusionsAn impaired CFR (
2.5) is a frequent finding after
balloon angioplasty or stent implantation as a result of a high
baseline flow velocity. Normalization of impaired CFR at follow-up in
patients without restenosis was associated with a decline of
the baseline flow velocity after both balloon angioplasty and stent
implantation, supporting the contention that this phenomenon relates to
a slow recovery of autoregulation of the microvascular bed.
Key Words: angioplasty stents blood flow
| Introduction |
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2.5) immediately after balloon angioplasty was associated
with a high incidence of recurrent angina, need for
revascularization procedures, and a high
restenosis rate.6 The hypothesis that
impaired coronary flow reserve after balloon angioplasty is due
to residual lumen obstruction was supported by studies showing a
normalization of impaired coronary flow reserve after optimal
vascular lumen enlargement by stent
implantation.7 8 However, other studies
demonstrated a spontaneous improvement of impaired coronary
flow reserve after balloon angioplasty without adjunctive
coronary intervention due to remodeling of the epicardial
lesion9 and/or a slow recovery of autoregulation
of the microvascular tone.10 11 Consequently,
controversy exists regarding the mechanisms involved in the effect of
coronary angioplasty on the distal coronary flow
reserve. In view of its clinical relevance, we studied the immediate
and long-term effects of PTCA on the distal coronary flow
velocity reserve (CFR) balloon angioplasty with coronary stent
implantation. | Methods |
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Cardiac Catheterization
Therapy with all antianginal medication was continued until
cardiac catheterization. Cardiac
catheterization was performed in all patients by the
percutaneous femoral approach. All patients received
heparin 5000 IU IV as a bolus at the beginning of the
catheterization. Additional heparin was administered if
the procedure lasted >90 minutes.
Quantitative Coronary Angiography
Off-line analysis of the angiographic severity of the
coronary narrowing was performed by use of an automated contour
detection algorithm (QCA-CMS version 3.32,
MEDIS).12 The outer diameter of the fluid-filled
guiding catheter, centered, was used as a scaling device to obtain
absolute arterial dimensions. Two orthogonal
projections of the coronary artery lesion during the
end-diastolic phase were used to assess biplane
analysis of the minimal lumen diameter (MLD) and the percent
diameter stenosis of the coronary narrowing.
Angiographic restenosis was defined as a diameter
stenosis >50% at follow-up assessed by quantitative
coronary angiography (QCA).
Coronary Blood Flow Velocity Analysis
All coronary blood flow velocity measurements with the
Doppler angioplasty guidewire (FloWire, EndoSonics) were performed
as previously described.13 After on-line
assessment of the baseline average peak velocity (APV),
hyperemia was induced by administration of an
intracoronary bolus of adenosine (12 µg in the right
coronary artery; 18 µg in the left coronary artery).
CFR was defined as the ratio of the adenosine-induced
hyperemic/baseline APV. The reference CFR was determined in an
adjacent angiographically normal coronary artery. The relative
CFR (rCFR) was defined as the ratio of the distal/reference CFR. An
impaired CFR after PTCA was defined as a CFR
2.5.6
Study Protocol
Nitroglycerin (0.1 mg IC) was administered every
30 minutes throughout the procedure. A Doppler guidewire was
inserted across the coronary narrowing before the first balloon
inflation to obtain optimal and stable baseline and
adenosine-induced hyperemic coronary blood flow
velocity signals. The balloon catheter was advanced over the
Doppler guidewire at the site of the coronary narrowing.
Consecutive balloon inflations of 1 to 2 minutes' duration were
performed until an angiographically satisfactory result was achieved
after a waiting time of 10 minutes. A successful balloon angioplasty
was defined as a diameter stenosis <50% by visual assessment.
Coronary stents (Palmaz-Schatz, Johnson & Johnson) were
implanted under guidance by intravascular ultrasound imaging for
optimal deployment against the vascular wall. Angiography was performed
after successful balloon angioplasty or stent implantation and at
follow-up in the same directions as before balloon angioplasty.
Baseline and adenosine-induced hyperemic
coronary blood flow velocity measurements were performed at the
same location distal to the dilated segment and in an angiographically
normal reference coronary artery as well.
Statistical Analysis
Continuous data are presented as mean±SD.
2 analysis was used to detect a
difference in categorical patient characteristics. A 2-tailed paired
t test (or Wilcoxon test for
nonparametric data) was used to identify variation within
subjects. A 2-tailed unpaired t test (or Mann-Whitney test
for nonparametric data) was used to assess differences in
continuous variables. Forward stepwise linear regression
analysis was used to assess the independent explanatory
variables for the alterations of the absolute and relative CFRs at
follow-up in both the balloon-treated and stent-treated patients.
Potential explanatory variables having an association after
univariate analysis (P<0.1) were
included. A value of P<0.05 was considered statistically
significant.
| Results |
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QCA Data in Patients Without Restenosis at
Follow-Up
Standard balloon angioplasty and high-pressure stent implantation
(14±3 bar) resulted in a direct improvement of the angiographic
variables (Table 2
). Follow-up in the stent-treated patient group
revealed a reduction of the arterial dimensions. However,
all angiographic luminal dimensions were larger at follow-up in the
stent-treated group than in the balloon-treated group (Table 2
).
Blood Flow Velocity Data in Patients Without Restenosis
The reference CFR of the normal coronary artery after PTCA
was 3.3±0.4 in the balloon-treated patients and 3.2±0.7 in the
stent-treated patients and did not change at follow-up in either of the
patient groups (3.2±0.6 and 3.0±0.4, respectively).
CFR and rCFR increased after standard balloon angioplasty (Table 2
).
Stent implantation resulted in a significant increase in
adenosine-induced hyperemic blood flow velocity but did
not yield an increase in CFR and rCFR as a result of a nonsignificant
increase in baseline blood flow velocity (Table 2
).
When the pooled data before balloon angioplasty and at follow-up were
used, the overall linear relationship between CFR and rCFR in the both
patient groups, including patients with restenosis, was strong
(r=0.93, Figure 1
). An
absolute CFR cutoff value of 2.5 was in accordance with a relative CFR
cutoff value of 0.80 (Figure 1
).
|
Normalization of the CFR and rCFR at Follow-Up in Patients
Without Restenosis
Balloon-treated patients demonstrated similar CFR and rCFR at
follow-up, as measured directly after balloon angioplasty (Table 2
).
However, a correlation between the CFR of the dilated vessel and the
CFR of the normal reference vessel was absent after balloon angioplasty
(Figure 2A
). This correlation improved at
follow-up (r=0.63, Figure 2B
) as a result of alterations of
the CFR of the dilated vessel. When all patient characteristics,
angiographic and hemodynamic variables, and their
changes at follow-up were used, stepwise regression analysis
revealed the CFR after balloon angioplasty (r=-0.74,
P<0.0001; Figure 3
) and the
alterations of the reference CFR at follow-up (r=0.39,
P=0.07) to be the only independent explanatory variables
for the alterations of the CFR at follow-up
(y=2.1-0.70xCFR after balloon
angioplasty+0.67xalterations of the reference CFR at follow-up,
r2=0.79, P<0.0001). The rCFR
immediately after balloon angioplasty was the sole independent
variable for the alterations of the rCFR at follow-up
(r=-0.82, P<0.0001; Figure 3
). The CFR after
stent implantation was lower than the reference CFR (3.2±0.7), whereas
it was in the range of the reference CFR at follow-up. The relationship
between CFR and reference CFR was moderate after stent placement
(Figure 2C
) and slightly improved at follow-up (Figure 2D
). After
stepwise regression analysis, alterations of the CFR during
follow-up were explained by the CFR immediately after stent
implantation (r=-0.93, P<0.0001; Figure 3
). The
rCFR after stent implantation was the only explanatory variable for
the alterations of the rCFR during follow-up after stepwise regression
analysis. The regression lines of the CFR and rCFR were similar
in stent-treated and balloon-treated patient groups (Figure 3
).
|
|
Impaired CFR After Balloon Angioplasty
Of all 54 patients, 23 (43%) demonstrated impaired CFR (
2.5)
immediately after balloon angioplasty; of these 23 patients, 14 did not
receive adjunct stent implantation. Five of these 14 patients of the
balloon-treated group developed angiographic restenosis at late
follow-up. The 9 patients without restenosis at follow-up
demonstrated a nonsignificant increase of CFR (P=0.07) and a
significant increase of rCFR during follow-up (P<0.05;
Table 3
). Baseline APV after balloon
angioplasty in the balloon-treated patient group was higher in patients
with impaired CFR than in patients without impaired CFR after balloon
angioplasty (Figure 4
, Table 3
). There
were no other angiographic or hemodynamic differences
(Table 3
) between the two groups.
|
|
In the stent-treated group, 8 of 19 patients demonstrated impaired CFR after balloon angioplasty. After stent implantation, impaired CFR and rCFR improved toward values within the range of the reference coronary artery (from 2.0±0.2 to 2.7±0.9 and from 0.68±0.19 to 0.89±0.21, respectively; both P=0.07). These alterations were related to a nonsignificant increase of the hyperemic blood flow velocity (45±14 to 54±23 cm/s; P=0.18), whereas the baseline blood flow velocity remained unchanged after stent implantation (23±7 to 23±14 cm/s).
Impaired CFR After Stent Implantation
Immediately after stent implantation, 11 patients demonstrated an
impaired CFR (2.0±0.3; Table 4
, Figure 3A
). None of these patients developed restenosis at follow-up.
Impaired CFR after stent implantation improved at follow-up toward
values documented in patients without impaired CFR after stent
implantation (Table 4
). Impaired CFR was related to a transient
increase of the baseline APV after stent implantation compared with
patients without impaired CFR (Figure 4
, Table 4
). In patients with
impaired CFR after stent implantation, the angiographic variables
and adenosine-induced hyperemic APV were similar to
those values in patients without impaired CFR and remained similar at
follow-up (Figure 4
, Table 4
).
|
Impaired rCFR After PTCA
The rCFR cutoff value was determined to be 2.5/3.1=0.80 (Figure 1
). Patients with an impaired rCFR (
0.80) after PTCA demonstrated
results similar to those of patients with impaired CFR (
2.5) after
PTCA; ie, a transient increase of the baseline blood flow velocity
compared with those patients without impaired rCFR (>0.80) in the
balloon-treated patient group (26±20 cm/s, n=9, versus 14±4 cm/s,
n=18; P<0.05) and in the stent-treated patient group
(33±18 cm/s, n=10, versus 18±9 cm/s, n=9; P<0.05).
| Discussion |
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Immediate Effect on CFR After Balloon Angioplasty or Stent
Implantation
In this study, the average CFR improved immediately after balloon
angioplasty to a value that was within the range of the CFR of the
normal reference coronary artery. This improvement after
balloon angioplasty is in accordance with the findings of several other
studies evaluating myocardial or coronary flow reserve using
digital subtraction angiography,14
PET,15 or distal blood flow velocity
measurements.3 6
Impaired CFR After PTCA
In the balloon-treated patients as well as in the stent-treated
patient group, an impaired CFR was related to a higher baseline blood
flow velocity, whereas the adenosine-induced hyperemic
response was similar to that of patients without impaired CFR. These
findings are in accordance with other studies that demonstrated an
impaired coronary flow reserve immediately after balloon
angioplasty, compared with normal values of the control group, due to
an increased baseline coronary blood
flow.10 16 Several mechanisms have been
postulated for the observed increase in baseline flow velocity after
PTCA, such as (1) failure of the peripheral
arterial vascular bed to vasoconstrict appropriately on the
sudden increase in distal coronary pressure produced by
coronary angioplasty, (2) epicardial vasoconstriction at the
site of the Doppler guidewire tip mediated by a myogenic response
and/or neural mechanisms,17 18 or (3) the
influence of drug therapy.19 20 However, all
patients were treated with nitroglycerin during the
procedure, and there was no difference in drug therapy (nitrates,
calcium antagonists, ß-blockers, or ACE
inhibitors) between patients with and without impaired CFR
after PTCA. Finally, baseline blood flow velocity can still be elevated
by the hyperemic response after balloon occlusion. The
hyperemic effect of balloon occlusion should be minimal after
the 10 minutes that we used as the time period between the balloon
occlusion and the blood flow velocity measurements. Nevertheless, the
precise mechanism responsible for the elevated baseline blood flow
velocity immediately after PTCA remains unelucidated and requires
further investigation.
The similar adenosine-induced hyperemic response in
patients with impaired CFR, as in patients without impaired CFR after
balloon angioplasty or stent implantation (Tables 3
and 4
), eliminates
several potential mechanisms affecting the CFR immediately after PTCA,
ie, residual lumen obstruction, diffuse coronary artery disease
undetectable by angiography, differences in drug therapy, platelet
activation, microembolization of platelet aggregates, and release
of platelet-mediated vasomotor products that occur after
angioplasty-induced medial injury.21
A residual epicardial stenosis may be responsible for an impaired CFR after balloon angioplasty due to a reduction in adenosine-induced hyperemic blood flow velocity. This is illustrated in patients with impaired CFR after balloon angioplasty in the stent-treated patient group. High-pressure stent implantation resulted in augmentation of the angiographic lumen in conjunction with an immediate increase of the absolute and relative CFRs. This improvement in CFR was achieved by an increase of the adenosine-induced hyperemic response after stent implantation while the baseline flow velocity remained unchanged. This phenomenon was also reported by other studies, suggesting an important role of residual lumen obstruction for impaired CFR after balloon angioplasty.7 8 Nevertheless, the mean CFR for the whole patient group remained unchanged after stent implantation as a result of a variable response in CFR, ie, 9 of 19 patients showed an increase and 10 patients showed a decrease.
Long-Term Effect of Balloon Angioplasty and Stent
Implantation
Several studies reported a delayed recovery of impaired
coronary flow reserve at follow-up toward the higher reference
values of control subjects.9 11 22 Improvement of
the impaired myocardial or coronary flow reserve was considered
to be related to a temporarily increased baseline value or a
temporarily impaired hyperemic blood flow immediately after
angioplasty22 or potentially related to an
improvement of the stenosis geometry at
follow-up.9 Our results described a long-term
response after balloon angioplasty similar to that found after stent
implantation (Figure 3
). This indicates that the long-term adaptation
of the CFR toward normal reference values is not due to epicardial
remodeling at the site of the lesion. In this respect, our findings are
not in agreement with the findings of Zijlstra et
al,9 who reported that an increase of CFR was
associated with an improvement in arterial luminal
dimensions. Furthermore, patients with impaired CFR after PTCA
demonstrated a decrease of the high baseline blood flow velocity at
follow-up toward the baseline values of patients without impaired CFR
(Figure 4
). These findings emphasize the important role of the slow
recovery of autoregulation in explaining the transiently impaired
CFR immediately after PTCA.
Relative CFR
The present study shows the long-term effect of PTCA on the
distal CFR, revealing "normalization" toward values of the
reference coronary artery in patients without
restenosis. At present, the literature regarding the effect
of PTCA on CFR is restricted to the analysis of the dilated
coronary artery. Nevertheless, CFR measurements are subject to
a high interpatient variability that is related to a variety of
physiological23 24 and
pathophysiological
conditions.25 26 27 The absolute CFR
2.5 as a
definition of impaired CFR after PTCA is based on data obtained in a
selected patient population. A CFR >2.5 after successful PTCA is in
accordance with a rCFR >0.80 (Figure 1
). This value is in agreement
with a study by Kern et al28 yielding rCFR of
>0.81 after stent implantation in all patients, including a subset
with impaired CFR of the reference vessel. The use of rCFR may be
important in those patients with an impaired CFR related to the
aforementioned (patho-)physiological
conditions.8 29 The present study suggests
that a CFR of 2.0, used as a cutoff value for diagnostic
purposes in several studies, is in accordance with an rCFR of 0.60
(Figure 1
). Nevertheless, the role of the rCFR for
diagnostic and therapeutic purposes is at present the
subject of study in multicenter trials.
Limitations of the Study
Intracoronary blood flow velocity assessment is a
sensitive technique for the detection of alterations in
coronary blood flow, but this method is also prone to technical
failures, and accurate measurements depend on the time, skill, and
experience of the cardiologist.
The site of the repeated blood flow velocity measurements was determined by angiography, although this method for making repeated measurements may have been a contributing factor in the variations noted. Moreover, these single-center results were obtained in a uniform selected group of patients, which limits extrapolation to other patient categories or other institutions.
The reference CFR was measured only immediately after PTCA and at late follow-up to calculate the relative CFR. The reference CFR was not measured before PTCA, although recent studies indicate that this limitation is not a major drawback of the present study.9 30
In the present study, the role of remodeling in the normalization
process of the CFR was limited, on the basis of long-term normalization
effects in patients treated with balloon angioplasty similar to those
treated with stent implantation (Figure 4
). However, complete
evaluation of remodeling cannot be judged without intravascular
ultrasound, which was not performed in the present
study.31
Furthermore, this study was not designed to evaluate the time period of improvement of the distal CFR after PTCA. Several studies implied a normalization of the average coronary vasodilatory reserve within 3 months.22 32
Clinical Implications
Patients with impaired CFR after balloon angioplasty may benefit
from additional stent implantation instead of omitting adjunct
intervention; ie, better long-term angiographic and
hemodynamic results and less restenosis at
follow-up. For this reason, assessment of the CFR and/or CFR directly
after angiographically satisfactory balloon angioplasty can be a
cost-effective tool for decision making regarding adjunctive stenting.
However, the limited number of patients studied precludes conclusions
regarding the selection of patients with impaired CFR after balloon
angioplasty who may benefit from additional stent implantation. This
clinically relevant issue is currently being evaluated in multicenter
studies involving larger cohorts of patients (DEBATE 2 and
DESTINI study).
| Acknowledgments |
|---|
Received January 14, 1998; revision received June 25, 1998; accepted July 11, 1998.
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2.5)
values after PTCA increased at follow-up toward the values of the
reference CFR in patients without restenosis. A transiently
impaired CFR after PTCA was a frequent finding and was a result of a
high baseline flow velocity after PTCA that normalized at follow-up,
supporting the contention that this phenomenon relates to a slow
recovery of the microvascular autoregulation.This article has been cited by other articles:
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