(Circulation. 2000;102:2959.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
Immediate Changes of Collateral Function After Successful Recanalization of Chronic Total Coronary Occlusions
From the Clinic for Internal Medicine III, Friedrich-Schiller-University Jena, Jena, Germany.
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Abstract |
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Background—Coronary collaterals are essential to maintain myocardial function in chronic total coronary occlusions (TCOs). The aim of the present study was to assess the collateral circulation in TCOs before coronary angioplasty and to determine the recruitable collateral perfusion after recanalization by use of intracoronary Doppler flow velocimetry.
Methods and Results—In 21 patients with TCOs (duration >4 weeks), Doppler recordings of basal collateral flow were obtained before the first balloon inflation. Angioplasty was performed with stent implantation in all lesions. At the end of the procedure, recruitable collateral flow was measured during a repeat balloon inflation. The collateral flow index (CFI) was calculated from the velocity integral during the occlusion/velocity integral of antegrade flow. In 17 of 21 patients, angiography was repeated after 24 hours, and CFI was reassessed. Average peak velocity of collateral flow was 10.9±5.6 cm/s with a predominantly systolic flow (diastolic/systolic velocity ratio <0.5) compared with antegrade flow (diastolic/systolic velocity ratio >1.5). After recanalization, the average peak velocity of recruitable collateral flow dropped by >50% to 4.7±2.5 cm/s. CFI fell from 0.48±0.25 to 0.21±0.16 (P<0.001). There was no further change of CFI during the following 24 hours. CFI was higher in patients with preserved regional ventricular function than in those with akinetic myocardium (0.57±0.23 versus 0.38±0.12, P<0.05).
Conclusions—Collateral circulation in TCO provided 50% of antegrade coronary flow. A considerable fraction of collateral flow was immediately lost after recanalization, indicating that TCO may not remain protected from future ischemic events by a well-developed collateral function.
Key Words: occlusion • collateral circulation • angioplasty • ultrasonics
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Introduction |
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Collaterals can maintain viability or provide a minimum nutritional supply for the myocardium distal to occluded coronary arteries.1 2 3 In patients with chronic total coronary occlusions (TCOs), collaterals are regularly visible and are a prerequisite indicating revascularization. Coronary angioplasty (PTCA) of TCOs carries a high incidence of recurrence because of the high rate of reocclusion,4 5 and the persistence of collaterals after PTCA may influence the risk of reocclusion and of ischemic events.6 7 8
Collateral circulation in humans was until recently assessed by contrast angiography,9 by determining the coronary wedge pressure during balloon occlusion,10 or indirectly by radionuclide studies.11 The availability of miniaturized sensors to monitor coronary flow and pressure in humans enabled a more direct approach in the assessment of the coronary collateral circulation. Many studies were carried out during PTCA of nonocclusive coronary lesions as a model of ischemia.7 12 13 14 Some studies on the function of collaterals included patients with TCOs, but no distinction was made between nonocclusive and occlusive lesions.15 16 17 18 19 20
Because the recurrence of TCOs after PTCA often leads to clinical symptoms, including myocardial infarction,4 5 21 22 23 we assumed that the collateral function in TCO would change after reopening of the artery. The present study should assess these changes during the first 24 hours after recanalization by use of Doppler flow velocimetry.
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Methods |
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Patients
The study group consisted of 21 consecutive patients with a successful PTCA of a TCO. The TCO was defined as follows: (1) duration of the occlusion >4 weeks, as determined from a previous angiogram, the date of a prior infarction, or the onset of symptoms, and (2) Thrombolysis in Myocardial Infarction (TIMI)24 grade 0 coronary flow. Indications for the recanalizations were (1) evidence of ischemia (exercise bicycle test or scintigraphy) related to the occlusion, (2) viable myocardium detected by PET using fluorodeoxyglucose in an akinetic segment, (3) spontaneously visible collaterals, and (4) written informed consent. The median duration of the occlusion was 2.7 months (range 1 to 87 months).
Angioplasty Procedure
The femoral approach and 7F guiding catheters were
used. All patients received a bolus of 10 000 IU heparin, and they
were on aspirin (100 mg) and clopidogrel (75 mg) for 4 weeks. All
patients were on oral nitrate or molsidomine, which was continued
during the day of the procedure. An over-the-wire exchange catheter
(Transit, Cordis) was used in all cases. When the lesion was crossed by
a 0.014-in guidewire, the exchange catheter was passed through the
occlusion. When this was not possible in 5 lesions, a low-profile
over-the-wire balloon catheter (Bandit, Scimed) was used instead. No
patient was included if a predilatation was required to cross the
lesion for the following measurements. After positioning of the
catheter tip distal to the occlusion, the guidewire was exchanged for
the Doppler wire, and the Doppler recording was
performed. The PTCA was continued with a support wire, and a balloon
was selected according to the operator’s estimation of the vessel
size. In small vessels of 
3.0-mm diameter (8 patients), the
dilatation was optimized by intracoronary ultrasound as
described previously.25 All
TCOs received stents, with multiple stents in 33% of the
lesions.
Protocol of Intracoronary Doppler
Velocimetry
The baseline measurements of collateral flow were
performed before the first balloon inflation. The distal
coronary bed was visualized by injecting contrast media through
the exchange catheter to identify major branches and to assist
positioning of the Doppler wire (FloWire, Endosonics Corp) distal
to the occlusion. Nitroglycerin (0.1 mg) was injected
through the catheter before the Doppler wire was inserted. The wire
position was documented on cine film. A potential problem of the basal
collateral flow recording could be an unaccounted contribution
of antegrade flow along the exchange catheter within the occlusive
lesion. This could be ruled out in all patients by lack of contrast
passage during proximal contrast injection into the recanalized artery
while the exchange catheter was in place. The continuously recorded
Doppler signal of collateral flow did not change during this
injection.
After the stent implantation was completed, 0.1 mg nitroglycerin was again applied, and the Doppler wire was reintroduced to the previously documented position to record the antegrade coronary flow. The final balloon was reinflated within the stent, and the recruitable collateral flow was recorded. Specific care was taken to keep the wire at an identical position relative to vessel side branches, which was ascertained by fluoroscopy of the wire tip on 2 orthogonal planes. In all cases, the recording was repeated 3 times with the Doppler wire moved within a range of 10 mm to obtain the recording with the maximum flow velocity integral to be used for quantification.
A repeat angiography after 20 to 24 hours was performed in 17 of the 21 patients. None of the patients had an early reocclusion. A Doppler wire was advanced through the stented lesion. The antegrade flow at a position identical to the one of the prior examination was recorded. Subsequently, a balloon catheter of the identical size of the one used on the previous day was inflated within the stent, and the recruitable collateral flow distal to the occlusion was recorded as described above.
Analysis of Intracoronary Flow
Velocity
The Doppler guidewire was connected to a console
(FloMap, Endosonics Corp). Coronary flow velocity signals were
recorded on Super VHS tape. In case of correct detection of the
systolic and diastolic phase of the signal and the
outline of the velocity signal, the automated measurement algorithm of
the console was used. When this algorithm failed because of artifacts,
the measurements were performed manually. The manual tracing was
performed in a blinded fashion by 1 investigator who averaged the
velocity signals of 3 cardiac cycles. The comparison of automated and
manual measurements in 10 patients showed a difference for the
quantitative values of the same recordings of <3%. All
collateral flow signals were measured manually to eliminate the wall
motion artifacts from the automated algorithm
(Figure 1
). For manual measurements, printouts of the
Doppler flow were scanned into a PC and measured with the use of
SigmaScan Pro (SPSS Inc).
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The following parameters were obtained: the velocity integral during systole and diastole, the total velocity integral (TVI), the duration of systole and diastole, the average peak systolic and diastolic velocities (ASV and ADV, respectively), and the relative duration of collateral flow/cardiac cycle. Depending on the relative position of the Doppler wire to the collateral inflow, the detected flow could be antegrade, retrograde, or bidirectional; therefore, the absolute values were used for further computation. The calculations of average peak velocity (APV), ASV, ADV, and the diastolic to systolic velocity ratio (DSVR) were performed with a standard worksheet program. A collateral flow index (CFI)14 was calculated as the ratio of TVI before reopening of the occluded artery and TVI of the antegrade flow after PTCA at the same location. The recruitable CFI was obtained at the end of the recanalization procedure and after 24 hours during reocclusion with a balloon catheter.
Angiographic Assessment of Collateral
Flow
The collaterals to the occluded coronary
artery were assessed by contrast injection of the donor artery and were
graded according to the classification of Rentrop et
al.9 As an inclusion
criterion, preinterventional collateral flow was of grade 2 (partial
epicardial filling of the occluded artery) or 3 (complete epicardial
filling of the occluded artery). The anatomic pathway of the
collaterals was categorized as epicardial, as intramyocardial, and as
undefinable.18 This
assessment was repeated at the end of the PTCA procedure and on the
next day. The grading was performed independently by 2 experienced
investigators, and in case of discordance, consensus was obtained with
a third investigator.
Statistical Analysis
Data are given as the mean±SD. Changes of
parameters between baseline and subsequent measurements
were evaluated by a paired t
test. A Student unpaired t
test, or a 
2 test when appropriate, was
used to analyze differences between patient groups. A
probability level of P<0.05
was considered significant. The calculations were performed on a PC
with use of the statistical software program Statistica for Windows
(Version 5, StatSoft Inc).
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Results |
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Clinical and Angiographic Characteristics
Characteristics of patients are shown in (Table 1
). Fifteen patients had a history of
myocardial infarction. Akinesia in the area supplied by the occluded
artery was observed in 10 patients, and no or only moderate hypokinesia
was observed in 11 patients. The collaterals were of angiographic grade
2 in 24% and grade 3 in 76% of the patients. An epicardial collateral
pathway was found in 33% of the patients.
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Specific Features of Collateral Flow in
TCOs
A retrograde collateral flow signal was found in 7
patients, and both retrograde and antegrade flows were found in 8
patients. The collateral flow profile showed 2 basic patterns: (1) a
predominantly systolic flow with only minor or no
diastolic flow in 11 patients and (2) a biphasic
systolic and diastolic flow with marked
diastolic contribution in 10 patients. Examples are shown
in
Figure 1
. Mean arterial pressure at the
beginning of the procedure was 102±20 mm Hg; it dropped to
94±21 mm Hg after intracoronary
nitroglycerin administration.
Changes of Collateral Flow After
Recanalization
The recruitable collateral flow was recorded 48±17
minutes after the baseline recording. An example is shown in
Figure 2. The APV dropped from 10.9±5.6 to 4.7±2.5 cm/s
(P<0.001). The
systolic flow contribution was higher in basal and recruitable
collaterals of the right compared with the left coronary artery
(Table 2). There were also qualitative changes of the flow
pattern. In 11 patients with a predominantly systolic flow, the
diastolic flow contribution was further reduced. In 5 of 10
patients with a biphasic collateral flow, it changed to a predominantly
systolic flow. Only in 5 patients did the pattern remain
similar to that during baseline but with a reduced relative
diastolic contribution. In 17 patients with a repeat
measurement after 23.7±11.7 hours, the collateral flow showed no
further significant changes
(Figure 3).
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Antegrade Coronary Flow After
Recanalization
The flow pattern in both left and right
coronary arteries was predominantly diastolic with
a higher DSVR compared with the collateral flow signal
(Figure 4). ASV was higher in the right coronary
artery compared with the left coronary artery
(Table 2). The parameters of antegrade flow did
not change significantly within 24
hours.
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CFI Before and After
Recanalization
CFI was 0.48±0.25 before the
recanalization, and 81% of the patients had a CFI
>0.30. After PTCA, CFI dropped to 0.21±0.16
(P<0.001), with no further
change within 24 hours (CFI 0.19±0.15,
Figure 5). One patient had a basal CFI >1 recorded in
the distal circumflex artery with an epicardial collateral; the CFI
dropped after PTCA but remained the highest among all individuals.
There was only 1 patient with an increase of CFI on day 1, but the
recording was affected by tachyarrhythmia of
170 bpm. After recanalization, only 20% of the
patients retained a CFI >0.30. During the balloon reocclusion of 3
minutes, no increase in recruitable collateral flow over time could be
detected. No collaterals were visible by angiography after PTCA and
after 24 hours.
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Factors With Possible Influence on Collateral
Flow in TCO
Patients with a prior myocardial infarction did not
show any difference in basal or recruitable collateral flow. Likewise,
none of the following parameters had an influence on
collateral flow: history of hypertension, diabetes mellitus, sex,
duration of occlusion 
3 months or >3 months, left
ventricular ejection fraction 0.48 or >0.48, or
intramyocardial or epicardial collateral pathway.
The influence of regional ventricular function
was assessed by comparing patients with akinesia or severe hypokinesia
(n=10) with those with moderate or no regional dysfunction (n=11). The
basal CFI was higher with normal regional function (0.57±0.23 versus
0.38±0.12, P<0.05), and a
similar difference was observed for recruitable CFI (0.31±0.19 versus
0.14±0.07, P<0.05)
(Figure 6).
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Discussion |
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Collateral Function in TCOs
The collateral circulation can be assessed by recording pressure and flow distal to an occluded artery. Pijls and colleagues7 26 calculated a pressure-derived CFI, and a similar index was derived from Doppler velocimetry.14 The Doppler-derived CFI in the present study of TCO of 0.48 before recanalization was in the range observed in nonocclusive lesions with spontaneously visible collaterals.13 14 20
The collateral flow was predominantly systolic, whereas the antegrade coronary flow after recanalization was predominantly diastolic.15 18 The variability of collateral pathways18 and the intrinsic difference of physiological coronary flow in the right and left coronary artery with different intramyocardial pressure exerted on the collateral vessels may explain the patterns of collateral flow. The systolic predominance of collateral flow was ascribed to the pumping of blood from compressed intramyocardial collaterals to the epicardial vessels.18 27
Changes in Collateral Function After
Recanalization
After recanalization, the
recruitable CFI during reocclusion dropped below 50% of its baseline
value. There were also qualitative changes of collateral flow with a
reduction of the diastolic flow contribution (see
Figure 2). The duration of basal collateral flow of 87% of
the cardiac cycle dropped to 60%. A long flow duration was considered
to be an indicator of sufficient
collateralization.19 The
reduced flow duration of recruitable collaterals indicated a reduced
collateral function
(Table 2).
Collateral flow is determined by the resistance of the collateral vessel and of the vascular bed distal to the occlusion. The underlying mechanism of an immediate change in collateral function could be an increase of collateral and/or peripheral resistance. The improved perfusion by antegrade flow may induce these hemodynamic changes, which were not immediately reversed during balloon reocclusion. It is possible that the collateral function would gradually improve during persistent reocclusion. There is anecdotal evidence that collaterals in TCO remain instantaneously recruitable even several years after successful revascularization.28 29 In a small study of 8 patients with TCOs, 25% suffered from myocardial infarction during follow-up with no reappearance of collaterals.30 Recent trials of stenting in TCO report infarction rates up to 6% during a follow-up period of 6 months.21 22 23 Thus, not all TCOs remain protected from ischemic events by a well-developed collateral circulation after PTCA. This is supported by our direct observation of immediate changes of collateral flow after PTCA.
Possible Determinants of Collateral
Flow
The major determinant for CFI appeared to be the extent
of regional dysfunction distal to the occluded artery, whereas CFI was
independent of a history of hypertension, diabetes mellitus, prior
myocardial infarction, global left ventricular function, or
duration of the occlusion. CFI was higher in lesions that supplied a
myocardial area with normal or moderate regional dysfunction compared
with an akinetic myocardial area. This difference was also evident
after PTCA, indicating that collateral supply for normokinetic
myocardium remained superior to that for akinetic
myocardium
(Figure 5).
In 81% of our patients, the CFI was higher than the level considered to protect from ischemia during PTCA.7 10 12 13 However, this level of CFI does not protect from exercise ischemia and can lead to regional myocardial dysfunction even in the absence of infarction.11 Most of the patients with TCOs had a history of infarction despite a high CFI, which indicates that the collaterals were not yet fully developed at the time of infarction. Similar observations of a large proportion of prior myocardial infarction in patients with well-developed collaterals were made in previous studies.13 20
Study Limitations
With Doppler flow velocimetry, 2 sets of data are
comparable only at identical sites of measurement and with constant
vessel diameters. These prerequisites were addressed by exact
positioning of the Doppler wire under fluoroscopic control and by
applying vasodilators. Still, a change of the distal coronary
diameter before recanalization compared with the
diameter during balloon occlusion cannot be ruled out. The value of CFI
may be affected by a flow-mediated increase in vessel diameter after
recanalization. Because of a larger vessel cross
section or an increase in the perfused vascular bed (ie, a reduced
peripheral resistance), the antegrade flow velocity would
be lower but represent a higher flow than the collateral flow,
and the CFI would be overestimated.
The difference in basal and recruitable collateral flow could be due to difficulties in obtaining high-quality signals during reocclusion. Aside from careful and repeated sampling, the qualitative changes of the systolic and diastolic phase of the collateral flow signal at baseline and during reocclusion and the similarity of the recordings immediately and 24 hours after recanalization indicate that the observed changes in collateral flow were genuine.
Conclusions
The physiological role of
collaterals in TCO is to preserve ventricular function.
This is supported by our observation of a high collateral flow in the
presence of a preserved regional function. The immediate loss of a
large fraction of collateral flow after
recanalization indicates that TCOs do not
necessarily remain protected from future ischemic events by
recruitable collaterals. Therefore, one should limit the attempt to
recanalize a well-collateralized occluded coronary artery to
those patients with clinical signs and symptoms of ischemia.
Further studies with long-term follow-up in a larger patient group are
needed to establish whether the recruitable collateral function would
determine the risk of future ischemic events after
recanalization.
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Footnotes |
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Reprint requests to Gerald S. Werner, MD, Klinik für Innere Medizin III, Friedrich-Schiller-Universität, Erlanger Allee 101, D-07740 Jena, Germany.
Received May 9, 2000; revision received July 31, 2000; accepted August 3, 2000.
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G. S. Werner, B. M. Richartz, S. Heinke, M. Ferrari, and H. R. Figulla Impaired acute collateral recruitment as a possible mechanism for increased cardiac adverse events in patients with diabetes mellitus Eur. Heart J., June 2, 2003; 24(12): 1134 - 1142. [Abstract] [Full Text] [PDF]
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G. S. Werner, M. Ferrari, S. Heinke, F. Kuethe, R. Surber, B. M. Richartz, and H. R. Figulla Angiographic Assessment of Collateral Connections in Comparison With Invasively Determined Collateral Function in Chronic Coronary Occlusions Circulation, April 22, 2003; 107(15): 1972 - 1977. [Abstract] [Full Text] [PDF]
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Z. R. Yousef, S. R. Redwood, C. A. Bucknall, A. N. Sulke, and M. S. Marber Late intervention after anterior myocardial infarction: effects on left ventricular size, function, quality of life, and exercise tolerance: Results of the Open Artery Trial (TOAT Study) J. Am. Coll. Cardiol., September 4, 2002; 40(5): 869 - 876. [Abstract] [Full Text] [PDF]
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G. S. Werner and H. R. Figulla Direct Assessment of Coronary Steal and Associated Changes of Collateral Hemodynamics in Chronic Total Coronary Occlusions Circulation, July 23, 2002; 106(4): 435 - 440. [Abstract] [Full Text] [PDF]
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G. S. Werner, C. Seiler, T. Pohl, K. Wustmann, D. Hutter, P.-A. Nicolet, S. Windecker, F. R. Eberli, and B. Meier Promotion of Collateral Growth by Granulocyte-Macrophage Colony-Stimulating Factor in Patients With Coronary Artery Disease * Response Circulation, May 14, 2002; 105 (19): e175 - e175. [Full Text] [PDF]
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G. S. Werner, M. Ferrari, S. Betge, O. Gastmann, B. M. Richartz, and H. R. Figulla Collateral Function in Chronic Total Coronary Occlusions Is Related to Regional Myocardial Function and Duration of Occlusion Circulation, December 4, 2001; 104(23): 2784 - 2790. [Abstract] [Full Text] [PDF]
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S. K. Chugh, G. S. Werner, B. M. Richartz, O. Gastmann, M. Ferrari, and H. R. Figulla Collateral Flow Index to Assess Myocardial Viability: Chugh's Hypothesis Revisited Response Circulation, September 25, 2001; 104 (13): e74 - e74. [Full Text] [PDF]
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