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(Circulation. 1997;95:2044-2052.)
© 1997 American Heart Association, Inc.
Articles |
From the Cardiovascular Institute, El Camino Hospital, Mountain View, CA (G.W.S., F.G.S.G.); Case Western Reserve University, Cleveland, Ohio (J.M.H., H.S.); Herz Zentrum, Bad Krozingen, Germany (A.F.); Klinikum Innenstadt, University of Munich, Germany (H.M.); and St Vincent's Hospital, Indianapolis, Ind (T.J.L.).
| Abstract |
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Methods and Results After angiographically guided PTCA of 104 lesions in 102 patients, IVUS was performed, and if atheromatous remodeling was present, PTCA was repeated with larger balloons sized halfway between the lumen and external elastic membrane. Plaque occupied a mean of 51±15% of the angiographically "normal" reference segments. Further balloon upsizing by 0.25 to 1.25 mm was therefore performed in 76 lesions (73%), increasing the nominal balloon-to-artery ratio from 1.12±0.15 after standard PTCA to 1.30±0.17 after IVUS-guided PTCA (P<.0001). As a result, the angiographic minimal luminal diameter further increased from 1.95±0.49 to 2.21±0.47 mm, the % diameter stenosis fell from 28±15% to 18±14%, and the IVUS lumen area rose from 3.16±1.04 to 4.52±1.14 mm2 (all P<.0001). The incidence of angiographic dissection was not increased after IVUS-guided balloon upsizing (37% versus 40%, P=.67), and major complications occurred in only 2 patients (1.9%).
Conclusions The demonstration by IVUS of atheromatous remodeling permits the safe use of balloons traditionally considered oversized, resulting in significantly improved luminal dimensions without increased rates of dissection or ischemic complications.
Key Words: angioplasty remodeling ultrasonics imaging coronary disease
| Introduction |
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Pathological studies13 14 15 have demonstrated that as atherosclerotic plaque accumulates, arterial remodeling with compensatory vessel enlargement develops to preserve the lumen. This homeostatic process has become known as the "Glagov phenomenon." Such atheromatous accumulation with vessel expansion has been shown to be ubiquitous in otherwise angiographically normal-appearing reference segments adjacent to more obvious coronary stenoses.13 14 15 As a consequence, the degree of atherosclerosis is significantly underestimated by coronary arteriography. The extent of atherosclerosis in both the lesion and reference segments can be accurately measured on-line with IVUS imaging.16 17 18 We hypothesized that the presence of angiographically unsuspected atheromatous accumulation with vessel expansion in the region of the PTCA target lesion and adjacent reference segments would safely accommodate balloons traditionally considered oversized and result in improved procedural results of balloon dilatation.
| Methods |
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Overview
Standard PTCA was performed with visual angiographic guidance
alone until an "optimal" result was obtained. IVUS was then
performed, and if evidence of significant plaque burden with larger
vessel dimensions than expected by angiography was present in the
region of the target lesion and adjacent reference segments, PTCA was
repeated with larger balloons regardless of the initial angiographic
result, followed by final angiographic and IVUS assessment. QCA and
IVUS analyses were performed by an independent core
laboratory.
Patients
Patients of any age undergoing elective PTCA of one or more
native coronary artery stenoses (de novo or
restenotic) were considered for enrollment. Exclusion criteria
included myocardial infarction within 4 days of the procedure,
unprotected left main disease, nonsurgical candidates, lesion
angulation >60°, and angiographic evidence of heavy lesion
calcification. Lesions with mild to moderate calcification were not
excluded. This study was approved by the institutional review board of
each participating institution. Informed consent was obtained from
all patients.
Study Protocol
Biplane angiography was performed in two orthogonal views that
displayed the most severe aspect of the lesion and minimized vessel
overlap. Intracoronary nitroglycerin was
administered before all angiographic runs. PTCA was initially performed
by standard techniques with angiographic guidance alone. No methods or
rules were prespecified for the performance of standard PTCA.
Specifically, to simulate real-world practice, no guidelines were given
for balloon sizing strategy or number and timing of inflations.
Typically, balloons were sized approximately to the mean of the
proximal and distal reference segments. However, oversized and/or
prolonged balloon inflations were permitted as necessary. Noncompliant
or semicompliant balloons were typically used. The operator was to
persist until an optimal result was obtained, that is, the point at
which the procedure would normally be terminated. Neither on-line QCA
nor IVUS was used during this phase. Alternative nonballoon
technologies, such as atherectomy or stenting, were allowed only for
treatment of true impending or actual coronary occlusion and
were not permitted for optimization of an otherwise borderline
result.
After optimal standard PTCA with angiographic guidance alone, IVUS was
performed with a 3.5F diagnostic catheter (Visions F/X,
Endosonics Corp). In this design, 32 concentrically arranged elements
at the tip of the catheter each operate in send and receive mode as a
synthetic aperture array to digitally reconstruct a tomographic
ultrasound image free of nonuniform rotational distortion. Gain, gray
scale, and persistence are calibrated on-line in each patient.
Ring-down artifact (appearing as annular or specular brightness at the
catheter edge, produced by energy that leaks from the send to the
receive circuitry) is electronically subtracted in the radiofrequency
region before the image is reconstructed. As a result, a true IVUS
image is created with a blanking diameter of
1.4 mm. Because
IVUS was performed only after PTCA, accurate luminal measurements were
not limited by the physical size of the catheter or ring-down.
A slow pullback was performed manually beginning distal to the distal reference segment and ending proximal to the proximal reference segment. Minimal and maximal lumen and vessel diameters were then measured on-line in both the proximal and distal reference segments. Reference measures were taken at proximal and distal sites adjacent to the lesion that correlated with the angiographically normal-appearing reference segments. Vessel size was measured at the medial-adventitial interface (approximating the external elastic membrane). From these measures, the mean lumen and vessel diameters at each reference site were determined.
Method for IVUS-Defined Balloon Selection
We hypothesized that the presence of glagovian remodeling with
vessel expansion at the lesion site and adjacent reference segments
should allow the safe use of a balloon sized halfway between the mean
lumen diameter (typically the normal reference measure for balloon
sizing) and the true vessel diameter (approximated by the external
elastic membrane). Measures were taken from both the proximal and
distal reference segments. The following equation was then used to
determine the size of an upsized balloon with the measures from the
limiting reference segment (either the proximal or distal reference
site that would return the smaller value): balloon size=(mean lumen
diameter+mean vessel diameter)/2.
In addition, the mean vessel diameter along the length of the lesion
had to be greater than this value. The method of IVUS-guided balloon
upsizing is demonstrated in Fig 1
. Repeat PTCA was then
performed with the upsized balloon regardless of the initial
angiographic result, with the time and pressure of inflation again
determined by the angiographic response to dilatation. Quarter-sized
balloons were used routinely for accurate sizing. If the formula
returned an irregular value, the closest-size balloon was chosen. If
the value returned by the formula was equal to or less than the balloon
size already used, no further PTCA was performed.
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Quantitative Coronary Analysis
QCA was performed before PTCA, after standard PTCA, and after
IVUS-guided upsized PTCA with commercial analysis packages
(Artrek, ImageComm and CAAS II, Pie Medical) at an independent core
laboratory. Because two orthogonal views with minimal vessel overlap
and foreshortening were infrequently present, the single most
severe view (before PTCA) was analyzed. A 15- to 20-mm segment
surrounding the stenosis was analyzed, with the guiding
catheter used for scaling. The reference segment was defined as the
region neighboring the stenosis, which was used for the IVUS
reference dimension calculation by the investigator at the time of
PTCA. If the lesion was immediately proximal to a bifurcation, the
proximal reference segment was used; in cases of true ostial disease,
the distal reference segment was used. The mean reference diameter, the
length of the stenosis, and the lesion MLD were recorded.
The lesion was graded according to the modified AHA/ACC classification
before intervention.19 After both routine and IVUS-guided
PTCA, the presence of dissection in the lesion was graded according to
the NHLBI classification.20 Flow in the study vessel was
graded according to the TIMI classification.21 During both
standard and upsized balloon inflation, the mean diameter of the
balloon during the highest-pressure inflation was determined with the
same QCA software.
Quantitative IVUS Analysis
IVUS images were reviewed off-line at the core laboratory.
Selected tomograms were digitized and analyzed with
semiautomated boundary detection software (Technology Solutions Group,
Ltd).22 Images were selected from the reference segment
used by the investigator for measurements during PTCA, the narrowest
portion of the stenosis after routine PTCA, and when
applicable, after IVUS-guided upsized balloon inflation. The luminal
boundary and the medial-adventitial interface were defined. The
analysis package then calculated the minimum, maximum, and mean
diameters for the lumen and the total vessel, the areas of the lumen,
total vessel, and plaque, and the thickness of the plaque. The percent
plaque area was defined as the percentage of the total vessel area
occupied by plaque. An eccentricity index was calculated for the lumen
and total vessel defined as the maximal diameter divided by the minimal
diameter. Eccentricity index for plaque was defined as the maximal
plaque thickness divided by the minimal thickness. Of note, for both
QCA and IVUS, the true physiological MLD was
determined along the length of the lesion before and after balloon
upsizing; by definition, therefore, the exact axial position of the
tomograms analyzed at the site of the MLD before and after
upsizing frequently varied.
Subjective measures of plaque morphology, dissection, and calcification were also assigned after review of the entire video sequence. Morphology in the reference and lesion segments was determined according to the classification of Hodgson et al23 : normal, intimal thickening, soft plaque, fibrous plaque, mixed plaque, and calcified plaque. The maximal measured arc of calcium in the lesion and reference segments was recorded. Dissections were graded according to the classification of Hoyne et al24 : (A) partial tear, (B) tear through plaque, (C) tear(s) with separated edges extending behind plaque, (D) extensive >180° dissection behind the plaque, (E1) concentric plaque without dissection, and (E2) eccentric plaque without dissection.
Definitions
PTCA success was defined as a <50% residual stenosis
by QCA with no major procedural or in-hospital complications (death,
bypass surgery, or Q-wave myocardial infarction).
Statistical Analysis
Categorical variables were compared by
2 analysis or Fisher's exact test.
Continuous variables are presented as mean±SD and were
compared by a two-tailed Student's t test, either paired or
unpaired as appropriate. Cumulative percentile plots were generated for
comparative MLDs and %DS as determined by QCA and IVUS in patients in
whom IVUS-guided balloon upsizing was performed.
Multivariate analysis was performed with
standard software (Statistica 5.0, StatSoft). Procedural, angiographic,
and IVUS variables with a P<.20 by
univariate analysis were entered into a forward,
stepwise multiple linear regression analysis to determine their
independent relationship to the angiographic final lesion %DS. The
independent variables entered included (all from QCA unless
otherwise indicated) %DS before PTCA, reference size, lesion length,
final balloon size, final balloon-to-artery ratio, highest inflation
pressure, number of inflations, degree of balloon upsizing, IVUS lesion
morphology, IVUS calcium arc (degrees), ACC/AHA type, and whether or
not balloon upsizing was performed.
| Results |
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Standard PTCA
The details of the PTCA procedure and results appear in
Table 2
. By QCA, standard PTCA resulted in a reduction in %DS from
71.9±16.3% to 26.8±15.0% and an increase in MLD from 0.75±0.46 to
1.96±0.50 mm (both P<.0001). There was no
significant change in reference vessel size.
IVUS Measures After Standard PTCA (Table
2)
Significant atheromatous remodeling with vessel
expansion was present in the angiographically normal-appearing
limiting reference adjacent to the target lesion. Plaque occupied
51.3±15.4% of the reference segment, with mean plaque thickness of
0.64±0.30 mm. After standard PTCA, the percent plaque area at the
lesion site was 75.8±8.7% of the reference segment.
IVUS-Guided Balloon Upsizing
On the basis of the true vessel size and the extent of plaque
burden in the limiting reference segment, additional PTCA with upsized
balloons was performed in 76 lesions (73%). As seen in Fig 2
, the degree of upsizing (nominal balloon size) ranged
from 0.25 to 1.25 mm, with a median increase in balloon size of
0.50 mm. The nominal balloon-to-artery ratio was therefore
increased from 1.12±0.15 to 1.30±0.17 (P<.0001). The
QCA-measured balloon-to-artery ratio increased from 1.00±0.12 to
1.12±0.13 (P<.0001).
|
As seen in Table 3
and Fig 3
, significant
improvements in MLD and %DS, measured by both QCA and IVUS, were
achieved in lesions in which IVUS-guided balloon upsizing was
performed. A case example is shown in Fig 4
. Considering
the effect of selective balloon upsizing on the entire population, IVUS
guidance resulted in a significant increase in MLD with a corresponding
reduction in %DS compared with standard PTCA (Fig 5
).
By multiple regression analysis, the variable most strongly
predictive of the final %DS was the measured balloon-to-artery ratio
(Table 4
). By the 50% DS criterion, PTCA was successful
in 95.1% of lesions after standard optimal PTCA versus 99.0% after
IVUS-guided upsized PTCA (P=.049).
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Coronary Dissections and Clinical Complications
By QCA, there was no significant increase in the occurrence of any
dissection (37.3% versus 40.2%, P=.67) or type B or
greater dissections (16.7% versus 22.5%, P=.29) after
IVUS-guided upsized PTCA compared with standard PTCA, respectively (Fig 6
). Severe dissections (angiographic types D and E) were
rare and not increased by IVUS-guided balloon upsizing (4.9% versus
4.9%, P=1.0). By IVUS (Fig 6
), although a trend was
present toward an increased rate of mild to moderate dissections
(types A and B) after IVUS-guided balloon upsizing compared with
routine PTCA (42.1% versus 30.8%, respectively, P=.08),
there was no difference in the rate of severe (types C and D)
dissections (14.8% versus 11.7%, P=.54) with the two
strategies.
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Major in-hospital complications developed in 2 patients (1.9%), both of whom had IVUS-guided upsizing. A 77-year-old woman presenting with a subtotal bifurcation lesion of the distal right coronary artery with TIMI grade 2 flow underwent PTCA, which resulted in a 35% residual stenosis and a type A dissection after both standard PTCA and IVUS-guided balloon upsizing. Out-of-laboratory closure of the posterior descending artery developed, necessitating bypass surgery. A 72-year-old woman presenting with an acute myocardial infarction was treated with tissue plasminogen activator. Angiography 4 days later showed a totally occluded mid left anterior descending artery. PTCA restored patency, with a 22% residual stenosis. A type B dissection was present after both standard PTCA and IVUS-guided upsizing. Out-of-laboratory closure developed, which was successfully treated with a stent. There were no patient deaths. Of note, no patient with an angiographic or IVUS type C or greater dissection developed a major ischemic complication.
| Discussion |
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Unfortunately, previous attempts to improve on the results of PTCA by sizing the balloon significantly larger than the nearest normal reference segment lumen have resulted in unacceptably high rates of major dissection and ischemic complications. Roubin et al11 randomized 336 patients undergoing PTCA to receive balloons either smaller or larger than the reference vessel lumen. The measured balloon-to-artery ratios were 1.13±0.14 in the large balloon size arm versus 0.93±0.12 in the small balloon arm. No difference in the acute %DS was found (28% versus 31%, respectively, P=NS), nor was there a significant difference in the angiographic dissection rate (13% versus 9%). Dissections in the larger-balloon group tended to be more severe, however, resulting in trends toward a higher incidence of myocardial infarction (8% versus 3%, P=.056) and bypass surgery (8% versus 4%, P=.15). The authors concluded that "In general, a balloon:artery ratio close to unity is appropriate," and "... the intention to reduce restenosis by oversizing balloons will result in increased complications... ."11
These results were supported by a retrospective study by Nichols et al12 examining the outcomes of 120 patients who had undergone PTCA. With the ratio of the package nominal balloon size (unmeasured) to the measured reference arterial size (by cinevideodensitometry), oversized balloons with a ratio of >1.3 resulted in a higher incidence of dissections than did the use of smaller balloons (37% versus 4%), some of which (not specified) resulted in compromised flow. As a result of these severe dissections, there was no difference in the %DS after oversized balloons versus those not oversized.
In the present study, the selective use of oversized balloons with IVUS guidance resulted in a significant decrease in the mean angiographic %DS in the entire population (from 27% to 19%), with a corresponding increase in MLD. The mean 19% stenosis achieved after IVUS-guided PTCA is the lowest stenosis ever reported from any PTCA series using QCA techniques for lesion assessment. IVUS confirmed a marked increase in mean lumen area (from 3.31 to 4.34 mm2). Furthermore, the oversized balloon strategy as applied did not result in an increase in severe dissections or ischemic complications. Major adverse events occurred in only 2 patients (1.9%), both with mild dissection.
The differences between the improved results of PTCA in the present report versus the adverse outcomes of the aforementioned studies in which oversized balloons were used cannot be attributed to the use of smaller balloons in the upsized group in the present trial. Allowing for differences in technique, the measured upsized balloon-to-artery ratio of 1.12±0.15 in this study (which did not result in an increased dissection or complication rate) is similar to the measured 1.13±0.14 balloon-to-artery ratio in the large-balloon group in the Emory study, which was associated with a high risk of ischemic complications.11
Furthermore, the possibility that the relative improvement in
lumen dimensions after upsized balloon inflation was due to inadequate
dilatation having been performed in the visually guided standard PTCA
arm of the present study may also be eliminated. In this regard,
the distinction is made between the expected nominal versus the actual
measured balloon diameters and balloon-to-artery ratios. The standard
mean balloon inflation pressure of 7.3±2.3 atm before IVUS-guided
upsizing (Table 2
) is above the level at which the balloons used in
this study would have been expected to achieve nominal diameter (5 to 6
atm). That the QCA-measured balloon diameter of 2.68±0.43 mm was
below the expected nominal diameter of 3.02±0.36 mm does not
imply that inadequate dilatation was performed; rather, this reflects
either the effects of vessel constraint, asymmetric balloon expansion
in fibrocalcific lesions, or a possible systemic undermeasuring error
by the QCA technique. This point is evidenced by the fact that the
2.68±0.43-mm QCA-measured balloon diameter was matched appropriately
for the mean measured vessel diameter of 2.67±0.48 mm, resulting
in a balloon-to-artery ratio of 1.01±0.13, the standard currently
recommended for routine PTCA.11 12 Most significantly,
although some variability may have been introduced by our asking only
that the operators achieve an optimal angiographic result before IVUS,
the mean 27% stenosis achieved before IVUS guidance in the
present study compares favorably to the 30% to 35% post-PTCA mean
stenoses reported in other large PTCA series,3 4 5 6 7
indicating that adequate PTCA was performed before balloon
upsizing.
The improved results of PTCA with balloons traditionally considered oversized in the present protocol are most likely due to the strategy of IVUS-guided selective oversized balloon inflations. We found that, on average, plaque occupied 51.3±15.4% of the angiographically normal reference segments, virtually identical to the 50.7±12.7% reference segment plaque burden reported by Mintz et al.16 The presence of such glagovian remodeling with vessel expansion permitted the safe use of balloons sized halfway between the lumen and external elastic membrane. It should be noted that although the balloons thus used were oversized by traditional angiographic standards (mean nominal balloon-to-artery ratio of 1.30), the true balloon-to-artery ratio, measuring arterial size out to the external elastic membrane by IVUS, was only 0.81±0.12 and did not vary significantly between the patients in whom balloon upsizing was and was not performed (0.82±0.13 versus 0.78±0.13, respectively, P=.11).
The fundamental role of IVUS guidance in the selection of the ultimate
"oversized" balloon diameter must be emphasized. The degree of
plaque burden at the lesion site and in the adjacent reference segments
was found to be tremendously variable, ranging from 0.30 to
2.26 mm in thickness. As a result, the increment in balloon
upsizing above the standard balloon diameter visually chosen varied
widely, ranging from 0.25 to 1.25 mm (Fig 2
). Furthermore, on the
basis of IVUS demonstrating that a maximally sized balloon had already
been used, no further upsizing was performed in 27% of lesions. In
contrast, in the angiographically guided trials in which the use
of balloons visually sized greater than the reference segment resulted
in increased major dissections and/or complications,11 12
oversized balloons were applied indiscriminately, that is, to all
vessels. Although not proven by this study, the application of balloons
sized larger than the true vessel size (external elastic membrane)
would be expected to result in major arterial disruption.
Because the degree of plaque burden and the true vessel size can be
determined only with IVUS, IVUS is required for the accurate selection
of properly sized oversized balloons if an aggressive balloon sizing
strategy is to be safely carried out.
Study Limitations
The study population consisted mostly of ACC/AHA type B1 and B2
lesions. The results of this study cannot necessarily be extended to
more complex type C lesions, especially extremely angulated and heavily
calcified stenoses (although the degree of lesion calcification
and plaque morphology was not a determinant of luminal gain after
IVUS-guided upsizing). Second, the method used in the present
protocol involved oversizing halfway between the lumen and external
elastic membrane. It is unknown whether a greater degree of upsizing
would be safely tolerated and result in further improved acute results.
Third, the study protocol used the patient as his or her own control,
using sequential balloon inflations from standard sizing to IVUS-guided
balloon upsizing. The safety and efficacy of imaging with IVUS before
dilatation to directly guide the selection of upsized balloons were not
tested.
Fourth, because angiography was not performed at 24 hours after the procedure, the effects of delayed elastic recoil were not assessed. Hanet et al,25 however, demonstrated that at 24 hours, the MLD in lesions after PTCA performed with oversized balloons (measured balloon-to-artery ratio >1) actually increases, whereas no change occurs after PTCA with standard-sized balloons. Thus, the absolute luminal gains of the oversized balloon sizing strategy reported in the present study may in fact be underestimated. Fifth, balloon upsizing was not performed in the 27% of patients in whom IVUS demonstrated minimal atheromatous remodeling and in whom a balloon already sized at least halfway between the lumen and external elastic membrane had initially been used. Although our hypothesis holds that further balloon upsizing in these patients would be unsafe and result in major arterial disruption, this was not directly proven. To do so would have required use of markedly oversized balloons by IVUS criteria, which was not felt to be ethical and which most likely was the cause of the high dissection and complication rates in prior studies in which large balloons were applied indiscriminately.11 12 Sixth, the present study used two-dimensional IVUS imaging with a deliberate, slow pullback technique. With additional refinement and validation, automated, quantitative three-dimensional reconstruction of both lumen and vessel boundaries has the potential to further simplify IVUS guidance of interventional procedures.26
Finally, although no direct conclusions can be drawn about reduced restenosis rates from the improved acute procedural results of PTCA obtained by the IVUS strategy described here, it should be noted that the magnitude of luminal gain after IVUS-guided PTCA compared with standard dilatation in the present study is similar to that achieved after stenting compared with PTCA in the STRESS and BENESTENT trials.6 7 Because previous studies have shown that the late loss index after percutaneous intervention is determined primarily by the acute results achieved (among other biological and lesion-specific factors) and is either device independent3 6 7 27 or actually less after PTCA compared with other techniques,28 the greater MLDs and reduced %DS achieved by IVUS-guided balloon sizing should translate into improved long-term outcomes. As a corollary, the improved results with IVUS-guided PTCA may translate into fewer patients requiring more expensive technologies, such as stenting.29 Randomized trials will be required to definitely prove this hypothesis, however, and to examine the relative cost efficacy of a routine IVUS strategy in patients undergoing PTCA.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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| Footnotes |
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| Appendix 1 |
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El Camino Hospital, Mountain View, Calif: Gregg W. Stone, MD; Fred G. St Goar, MD; Nancy Richardson.
St Vincent's Hospital, Indianapolis, Ind: Thomas J. Linnemeier, MD; Don A. Rothbaum, MD; Ronald J. Landin, MD; Michael W. Ball, MD; Zachary I. Hodes, MD, PhD; Daniel L. Lipps, MD; Robert V. Riddell, MD; Gregory B. Elsner, MD; Susan A. Gowan, RN; Janice L. Coverdale, RN.
Herz Zentrum, Bad Krozingen, Germany: Axel Frey, MD, PhD; Christian Muller, MD; Joachim Buttner, MD; Nicholas Jander, MD; Valerio Bassignana, MD; Hans-Peter Bestehorn, MD; Jens Petersen, MD; Evelyn Langer, MTA.
Klinikum Innenstadt, University of Munich, Germany: Harald Mudra, MD; Volker Klauss, MD; Frank Werner, MD; Evelyn Reger, MD.
Core Angiographic and Ultrasound Laboratory, Case Western Reserve University: John McB. Hodgson, MD; James Berry, MS; Helen Sheehan, RN; Donna Smith, BS.
Received July 16, 1996; revision received November 19, 1996; accepted November 25, 1996.
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