Improved Procedural Results of Coronary Angioplasty With Intravascular Ultrasound–Guided Balloon Sizing
The CLOUT Pilot Trial
Background Indiscriminate use of balloons larger than the angiographic reference segment lumen results in high rates of ischemic complications after percutaneous transluminal coronary angioplasty (PTCA). We hypothesized that angiographically unsuspected atheromatous remodeling with vessel expansion (the Glagov phenomenon) at and adjacent to PTCA target lesions would safely accommodate oversized balloons in selected patients undergoing PTCA with intravascular ultrasound (IVUS) guidance.
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.
Since its initial description by Andreas Grüntzig in 1978,1 2 PTCA has been performed by selection of a balloon with a nominal diameter approximating that of the normal-appearing reference segment adjacent to the lesion. By QCA, the typical post-PTCA result is a mean residual stenosis of 30% to 35%, with subsequent restenosis rates of 30% to 50%.3 4 5 6 7 Numerous studies have clearly established that a major determinant of the rate of restenosis is the %DS or MLD achieved after intervention,3 5 6 7 8 9 10 the so-called “bigger is better” doctrine. Unfortunately, attempts to improve on the procedural results of PTCA by use of balloons larger than the angiographic reference lumen diameter have resulted in unacceptably high rates of major arterial dissection, myocardial infarction, and emergent bypass surgery.11 12 The basic technique of PTCA has therefore remained unchanged since its inception nearly 20 years ago. As a result, there has been a move away from PTCA toward more complex and expensive technologies, such as coronary stenting, that reduce restenosis by achieving a larger initial lumen.6 7
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.
In this study, IVUS was used to guide the selection of balloons traditionally considered oversized on the basis of the degree of plaque burden and vessel expansion in the target lesion and adjacent reference segments. The aim was to determine whether the use of such oversized balloons would result in improved lumen enlargement without major dissections and complications.
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 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.
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.
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.
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).
Categorical variables were compared by χ2 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.
Demographic and Baseline Characteristics
PTCA of 104 lesions was performed in 102 patients. The clinical and angiographic features of the patient population appear in Tables 1⇓ and 2⇓. Twenty-four lesions (23%) had previously been dilated, and 4 lesions (4%) were totally occluded before PTCA. By IVUS, plaque morphology was soft in 29% of patients, fibrotic in 1%, calcific in 26%, and mixed in 44%.
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).
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.
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.
Several studies with high rates of angiographic follow-up3 5 6 7 8 9 10 11 12 have demonstrated a strong relationship between the adequacy of the lumen achieved after PTCA and the subsequent restenosis rate when defined as a binary measure (%DS >50%). Thus, the procedural goal of PTCA should be to safely achieve as large a lumen as possible.
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.
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
|%DS||=||percent diameter stenosis|
|ACC||=||American College of Cardiology|
|AHA||=||American Heart Association|
|MLD||=||minimal luminal diameter|
|PTCA||=||percutaneous transluminal coronary angioplasty|
|QCA||=||quantitative coronary analysis|
The following institutions and investigators participated in the Clinical Outcomes With Ultrasound Trial (CLOUT) study group.
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.
This study was supported in part by an unrestricted grant from Endosonics Corp, Pleasanton, Calif.
Reprint requests to Dr Gregg W. Stone, The Cardiovascular Institute, 2660 Grant Rd, Mountain View, CA 94040.
- Received July 16, 1996.
- Revision received November 19, 1996.
- Accepted November 25, 1996.
- Copyright © 1997 by American Heart Association
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