Author + information
- Received February 8, 1997
- Revision received July 23, 1997
- Accepted August 14, 1997
- Published online November 15, 1997.
- Masashi Iwabuchi MDA,*,
- Seiichi Haruta MDA,
- Atsushi Taguchi MDA,
- Yoshito Ichikawa MDA,
- Tomoo Genda MDA,
- Satoshi Katai MDA,
- Takeshi Imaoka MDA,
- Yosihito Shimizu MDA and
- Mafumi Owa MDB
- ↵*Dr. Masashi Iwabuchi, Department of Cardiology, Fukuyama Cardiovascular Hospital, 1-26 Sumiyoshi-cho Fukuyama, Hiroshima, 720, Japan.
Objectives. This study sought to evaluate the intravascular structure as depicted by intravascular ultrasound after successful primary angioplasty (i.e., without thrombolytic therapy) for acute myocardial infarction and to investigate the related predictors of acute coronary occlusion.
Background. The usefulness of primary angioplasty for acute myocardial infarction is still limited by early reocclusion. There are few data regarding the intravascular ultrasound findings after primary angioplasty.
Methods. Intravascular ultrasound was performed in 27 patients after successful primary angioplasty. Repeat coronary angiography was performed 15 min later, on the following day and 1 month after angioplasty.
Results. Abrupt occlusion occurred in 8 of 27 patients. Angiographic variables in patients with versus those without abrupt occlusion were not significantly different. Intravascular ultrasound disclosed a significantly smaller lumen area ([mean ± SD] 2.49 ± 0.72 vs. 5.06 ± 1.52 mm2, p < 0.001) and a significantly greater percent plaque area (80.5 ± 9.1% vs. 63.7 ± 7.8%, p < 0.001) in patients with abrupt occlusion. There was no significant difference in external elastic membrane cross-sectional area. We classified the ultrasound appearance of the intravascular structure as smooth, irregular or filled. Abrupt occlusion occurred in none of 6 patients with a smooth intravascular structure, 24% of 17 patients with an irregular structure and in all 4 with a filled structure (p < 0.05). In the latter group, the lumen was filled with bright speckled or low echogenic material, although angiography revealed excellent coronary dilation in all these arteries.
Conclusions. Intravascular ultrasound revealed a narrow lumen in coronary arteries showing abrupt occlusion after successful primary angioplasty, even though angiography disclosed successful dilation. Arteries with a lumen filled with bright speckled or low echogenic material frequently develop abrupt occlusion.
Primary angioplastyrefers to angioplasty undertaken without thrombolytic therapy. The Primary Angioplasty in Myocardial Infarction (PAMI) Study Group reported that primary angioplasty for acute myocardial infarction results in greater patency of the infarct-related coronary vessel than does thrombolysis. Primary angioplasty is also associated with a lower incidence of intracranial hemorrhage, nonfatal reinfarction and death within 6 months compared with intravenous tissue-plasminogen activator therapy.
Nevertheless, the usefulness of primary angioplasty is still limited by the in-hospital reocclusion rate, which may approach 10% to 15% of vessels treated [1–8]. Previous studies [2, 3]revealed that abrupt vessel occlusion after angioplasty occurred at an incidence of 2% to 10%. An association of patient and angiographic factors with increased occlusion has also been reported . However, there are few data regarding intravascular ultrasound findings after primary angioplasty.
The objectives of the present study were to evaluate the intravascular structure as depicted by intravascular ultrasound after successful primary angioplasty for acute myocardial infarction and to investigate the related predictors of abrupt coronary occlusion after angioplasty.
Between December 1994 and June 1995, intravascular ultrasound was performed in 27 patients after successful primary angioplasty for acute myocardial infarction. The diagnosis of acute myocardial infarction was documented by a characteristic history of prolonged chest pain, diagnostic electrocardiographic changes, and elevation of serum cardiac enzyme levels. Intravascular ultrasound was not performed in patients with disease affecting the left main coronary artery or an artery supplying an equivalent amount of myocardium, when it was deemed that the affected arteries were too small to allow the passage of the intravascular ultrasound device. Intravascular ultrasound was also not performed when complex dissection, thrombus or residual stenosis ≥50% was observed on the coronary angiogram after primary angioplasty, to avoid complications such as distal embolization and progression of dissection .
The criteria for successfulprimary angioplasty were Thrombolysis in Myocardial Infarction (TIMI) flow grade 3 coronary flow; residual stenosis <50%; and no angiographic complex dissection or thrombus after the procedure.
1.2 Primary Angioplasty and Follow-Up Coronary Angiography
Patients underwent diagnostic cardiac catheterization through the femoral percutaneous approach with 5F Judkins catheters. Coronary angiography revealed an occluded infarct-related artery (TIMI flow grade 0 or 1) in all patients. Before primary angioplasty, patients were given oral aspirin (162 mg), intracoronary isosorbide (2.5 mg) and intravenous heparin (10,000 U), and 2,000 U of additional heparin was given at hourly intervals to maintain an activated clotting time >300 s. Primary angioplasty was performed in the conventional manner, and a variety of low profile angioplasty balloons and guide wires were used.
After primary angioplasty, the intravenous infusion of heparin was continued for at least 24 h to maintain an activated clotting time of 180 to 200 s. The sheath was removed 4 to 6 h after heparin was discontinued.
Repeat coronary angiography was performed 15 min after successful primary angioplasty, on the following day and 1 month after procedure.
1.3 Angiographic Definitions
Coronary angiograms were reviewed separately by two investigators (A.T., Y.I.) who had no knowledge of the outcome of primary angioplasty. Quantitative angiography was carried out on-line using the digital caliper method, with the diameter of the catheter used for calibration. Stenosis diameter was calculated by comparing the minimal diameter of the lesion with the proximal and distal normal vessel diameters. In accordance with TIMI criteria , angiographic evidence of thrombuswas defined as an intraluminal filling defect with a rounded, globular or polypoid shape that protruded into the lumen or as contrast medium staining at the site of coronary stenosis or occlusion. Coronary dissectionwas classified as simple or complex. Simple dissectionwas defined as 1) a dissection without discrete linear defects within the lumen or adjacent to the lumen, or 2) a lumen abnormality, defined as one or more distinct linear filling defects in the contrast column within the lumen of the vessel at the dilation site or an accumulation of contrast material in the apparent wall of the artery at the site of dilation. In simple dissection, the flow of contrast material through the dilated segment is normal, and there is no delay of washout from the segment. Complex dissectionwas defined as 1) the presence of one or more linear lumen abnormalities in the dilated segment plus the extraluminal accumulation of contrast material, or 2) the presence of a spiral lumen lucency beginning in the dilated segment that may propagate distally. In complex dissection, the flow of contrast material through the dilated segment may be normal, or there may be delayed flow through the segment with delayed washout.
Abrupt occlusionwas defined as stenosis with TIMI grade 0 to 1 distal flow after angioplasty in a previously patent vessel. Threatened occlusionwas defined as stenosis with TIMI grade 2 to 3 distal flow and myocardial ischemia after angioplasty in a previously patent vessel.
1.4 Intravascular Ultrasound System and Imaging Procedure
Studies were performed using one commercially available intravascular ultrasound imaging system consisting of an imaging catheter (Sonicath, Boston Scientific Corp.) and a Sonos Intravascular System imaging console (Hewlett-Packard). The imaging catheter has a 30-MHz single piezoelectric crystal transducer mechanically rotating at 1800 rpm within a 3.5F monorail over the wire catheter sheath.
Intravascular ultrasound was performed immediately after successful primary angioplasty for acute myocardial infarction. Imaging was performed after administration of 2.5 mg of intracoronary isosorbide. After the imaging catheter was advanced across the lesion to the distal portion of the vessel under fluoroscopic guidance, imaging was performed during slow manual retraction of the imaging catheter. The two-dimensional images were displayed on the Sonos imaging console and recorded on 0.5-in. high resolution s-VHS videotape for off-line analysis.
To evaluate the intravascular structure in detail, we injected ultrasound contrast medium through a guide catheter during the examination in all patients [11, 12]. The ultrasound contrast medium (Albunex, Molecular Biosystems Corp.) was diluted with the same volume of contrast medium, and 1 ml of the diluted medium was injected through the guide catheter as a bolus.
Patients were studied after giving written informed consent.
1.5 Imaging Analysis
Intravascular ultrasound images were analyzed off-line with the Sonos Intravascular System. Qualitative (plaque morphology and intraluminal structure) and quantitative (cross-sectional) analysis of the ultrasound images was performed by investigators (Y.I., T.G.) who had no knowledge of the immediate angiographic and clinical results. Single images of the lesion sites were selected for quantitative and qualitative analysis. By computer planimetry, the external elastic membrane and lumen cross-sectional areas both in mm2were measured, and the plaque plus media cross-sectional area (mm2) was calculated as the external elastic membrane cross-sectional area (mm2) minus the lumen cross-sectional area (mm2), and the percent cross-sectional narrowing was calculated as the plaque plus media cross-sectional area (mm2) divided by the external elastic membrane cross-sectional area (mm2) times 100.
1.5.1 Qualitative Analysis
We classified the ultrasound appearance of the intravascular structure as follows: smooth= no visible dissection, with a smooth lumen border (Fig. 1A); irregular= visible dissection, with an irregular lumen border (Fig. 1B); or filled= lumen filled with bright speckled material (Fig. 2CFig. 2D) or low echogenic material (Fig. 3CFig. 3D), despite angiographic findings of successful dilation. Dissection or tearsin the plaque were classified as abrupt focal interruptions in the continuity of the plaque or intima that spanned the normal tissue planes circumferentially.
1.6 Statistical Analysis
Results are expressed as mean value ± SD. Differences between patients with and those without abrupt closure were compared by the chi-square test for discrete variables and an independent Student ttest for continuous variables. Multiple logistic regression analysis was used to assess the relation between abrupt closure and multiple clinical, angiographic and intravascular ultrasound variables, including age; reference diameter, minimal lumen diameter and percent stenosis after angioplasty by angiography; and external elastic membrane cross-sectional area, lumen cross-sectional area, plaque plus media cross-sectional area, cross-sectional narrowing, degree of dissection and type of lumen structure after angioplasty by intravascular ultrasound. A p value <0.05 was considered statistically significant. All statistical analyses were performed with SPSS 7.5 statistical package programs (SPSS Institute).
2.1 Baseline Clinical Characteristics
The baseline clinical characteristics of the 27 study patients are summarized in Table 1.
2.1.1 Angiographic Results
Table 2summarizes the angiographic characteristics before and after successful primary angioplasty for acute myocardial infarction. The reference lumen diameter, minimal lumen diameter and percent stenosis measured after the procedure were 2.95 ± 0.45 mm, 2.34 ± 0.38 mm and 20.1 ± 12.8%, respectively. Coronary flow after the procedure was TIMI grade 3 in all patients. Coronary dissection occurred in 12 patients (44.4%) and were all simple dissections; and no complex dissection was noted.
Fig. 4is a flowchart showing the clinical and angiographic outcome after primary coronary angioplasty. Fifteen minutes after the procedure, abrupt or threatened occlusion occurred in 8 (30%) of 27 patients. Repeat balloon angioplasty was performed in all eight patients and was successful in five. In the three patients with abrupt coronary occlusion, repeated stenting was successful, and reperfusion was ultimately successful in all 27 patients. Residual coronary stenosis was 29.3 ± 11.7% on the day after angioplasty and 15.6 ± 13.6% 1 month later. Recurrent occlusion or restenosis has not occurred in any patient.
2.2 Intravascular Ultrasound Findings
Intravascular ultrasound studies were completed without any vascular complications, and quantitative and qualitative analyses were performed using the data for all 27 patients.
Mean external elastic membrane cross-sectional area, lumen cross-sectional area and plaque plus media cross-sectional area were 14.31 ± 4.88 mm2, 4.29 ± 1.78 mm2, and 10.01 ± 4.36 mm2, respectively (Fig. 5). The cross-sectional narrowing was 68.65 ± 11.23%. On qualitative analysis of the infarct-related artery after primary angioplasty, a smooth intravascular structure was observed in 6 patients (22%), an irregular structure in 17 (63%) and a filled structure in 4 (15%; bright speckled material where the contrast medium flowed into the space in 3 patients, low echogenic material in the other) despite angiographic findings of exellent coronary dilation in all 4 patients (Figs. 2 and 3).
2.2.1 Abrupt Coronary Occlusion and Intravascular Ultrasound and Angiographic Findings
Tables 3 and 4⇓⇓show the quantitative and qualitative intravascular ultrasound and angiographic findings in, respectively, individual patients and patients grouped according to those without (Patients 1 to 19) and those with (Patients 20 to 27) abrupt occlusion. There was no significant difference between groups in any angiographic variable, including minimal lumen diameter, percent stenosis, thrombus, degree of dissection or external elastic membrane cross-sectional area. Intravascular ultrasound revealed a significantly smaller lumen area (2.49 ± 0.72 vs. 5.06 ± 1.52 mm2, p < 0.001) and a significantly greater cross-sectional narrowing (80.5 ± 9.1% vs. 63.7 ± 7.8%, p < 0.001) in patients with abrupt coronary occlusion. There was no difference in degree of dissection.
Abrupt occlusion occurred in none of 6 patients with a smooth intravascular structure, in 4 (24%) of 17 with an irregular structure and all 4 with a filled structure (p < 0.05, Kruskal-Wallis analysis of variance). Repeat balloon angioplasty was successful in patients with an irregular structure. In contrast, abrupt coronary occlusion repeatedly occurred in the three patients with a filled structure and was resolved by stenting.
Among a set of 10 variables included in the logistic regression analysis (age; reference diameter, minimal lumen diameter and percent stenosis after angioplasty by angiography; external elastic membrane cross-sectional area, lumen cross-sectional area, plaque plus media cross-sectional area, cross-sectional narrowing, degree of dissection and type of the lumen structure after angioplasty by intravascular ultrasound), lumen cross-sectional area, cross-sectional narrowing and type of lumen structure were chosen as independent predictors of abrupt coronary occlusion (Table 4).
3.1 Intravascular Ultrasound Findings After Angioplasty For Acute Myocardial Infarction
In a previous report, Bocksch et al. performed intravascular ultrasound in patients with an acute myocardial infarction before percutaneous transluminal coronary angioplasty. Intracoronary ultrasound permitted differentiation between pulsatile, low echogenic intraluminal material suggesting thrombus and mural highly echogenic atherosclerotic plaque in 22 (88%) of 25 patients. A negative silhouette of the intravascular ultrasound device was documented within the low echogenic material in 17 (68%) of 25 patients. Low echogenic intraluminal material was found in 18 (72%) of 25 segments proximal to and in 12 (48%) of 25 segments distal to the highly echogenic plaque, indicating prestenotic and post-stenotic thrombus . Walton et al. reported a case in which the intravascular ultrasonographic images obtained before angioplasty revealed total occlusion of the vessel, with plaque and bright speckled material suspected of being thrombus.
In the present study, there were four patients with material filling the blood vessel lumen despite successful dilation depicted on angiography. All four of these patients later showed abrupt occlusion. The low echogenic and bright speckled material filling the lumen of the infarct-related vessel in these patients was probably thrombi. Because the bright speckled material was partially enhanced by injection of ultrasound contrast media, it may have consisted of intimal plaque disruption and thrombi.
Factors predictive of abrupt occlusion could not be identified angiographically because only patients showing successful angiographic dilation were examined in this study. Minimal lumen diameter and lumen cross-sectional area as depicted by this modality after primary angioplasty differed from those depicted by angiograms, and ultrasound revealed the existence of a subgroup of patients without sufficient lumen cross-sectional area despite successful dilation on angiography. In previous studies, discrepancies between angiographic and intravascular ultrasound findings before and after angioplasty, directional coronary atherectomy or rotational atherectomy were reported [15–20]. Although angiography demonstrates a two-dimensional silhouette of the lumen, intravascular ultrasound provides a three-dimensional image of the lumen, enabling more detailed studies of intravascular structure. Reocclusion did not occur in any patient with a smooth intravascular surface but did occur in 24% of patients with an irregular intravascular surface and in all patients demonstrating thrombi and disruption within the blood vessels. Of the patients with reocclusion, those with an irregular intravascular surface were successfully managed by repeated angioplasty, whereas those with a filled lumen demonstrated repeated occlusion, and salvage by balloon angioplasty was difficult. We found that even when successful angiographic dilation was seen after primary angioplasty, obstruction occurred repeatedly in some patients because of intimal disruption, dissection and thrombi. The outcome after successful primary angioplasty can be predicted from the postprocedural lumen area and characteristics of the intravascular structure, which are identifiable by intravascular ultrasound.
3.2 Limitations of the Study
We studied only a small group of patients with successful primary angioplasty for acute myocardial infarction; thus, our patients may not be representative of all patients treated with primary angioplasty.
The capacity of intravascular ultrasound to define thrombus is limited . In most patients with an acute myocardial infarction, thrombi are observed by angioscopy in the infarct-related artery. However, intravascular ultrasound has limited capacity to detect thrombi. In only four of our patients, were materials filling the lumen demonstrated by intravascular ultrasound, revealing the involvement of thrombi. Because thrombi are considered significantly involved in abrupt coronary obstruction after primary angioplasty for acute myocardial infarction, improvement of the intravascular ultrasound device to facilitate more detailed examination would be desirable.
In previous studies, acute arterial patency after primary angioplasty was attained in ∼90% to 95% of patients, with a reocclusion rate of 10% to 15% at 6-month follow-up angiography [1–8]. In the present study, abrupt or threatened occlusion occurred in 30% of patients after primary angioplasty. In three patients, repeated occlusion was observed after conventional balloon angiography but could not be resolved. Such cases would conventionally be judged as treatment failures. After exclusion of these three patients, five (19%) showed abrupt coronary obstruction, which is still slightly higher than the rates cited in other reports. The passage of the intravascular ultrasound device may affect the angioplasty result in patients without an adequate lumen area after primary angioplasty for acute myocardial infarction .
Abrupt occlusion after successful primary angioplasty for acute myocardial infarction was found to occur in coronary arteries with a narrow lumen by intravascular ultrasound, despite successful angiographic dilation. Abrupt occlusion frequently occurred when the lumen was filled with bright speckled or low echogenic material. Intravascular ultrasound is more sensitive than conventional angiography in the evaluation of the intraluminal structure and can be useful in risk stratification of lesions with the potential for abrupt occlusion.
- Received February 8, 1997.
- Revision received July 23, 1997.
- Accepted August 14, 1997.
- The American College of Cardiology
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