Intravascular ultrasound study of angiographically mildly diseased coronary arteries

Evaluation of patients with minimally obstructive coronary artery disease and angina

Atherosclerotic coronary artery disease is a progressive process adversely affecting the integrity of the coronary vasculature. In past years, most studies have focused on the morphological changes leading to compromised coronary blood flow in atherosclerosis. However, in recent years it has become apparent that abnormal coronary vasomotor regulation may precede or accompany gross morphological changes in coronary atherosclerotic disease. In fact, the pathophysiology of angina pectoris in many patients with risk factors for atherosclerosis and minimally obstructive disease may involve abnormal coronary vasomotor tone regulation. The aim of the present article is to describe a clinical approach to patients with angina pectoris and minimally obstructive coronary artery disease based on current knowledge of coronary vasomotor regulation.

Determination of aortic valve area in valvular aortic stenosis by direct measurement using intracardiac echocardiography: a comparison with the Gorlin and continuity equations

OBJECTIVES

This study sought to 1) show that intracardiac echocardiography can allow direct measurement of the aortic valve area, and 2) compare the directly measured aortic valve area from intracardiac echocardiography with the calculated aortic valve area from the Gorlin and continuity equations.

BACKGROUND

Intracardiac echocardiography has been used in the descriptive evaluation of the aortic valve; however, direct measurement of the aortic valve area using this technique in a clinical setting has not been documented. Despite their theoretical and practical limitations, the Gorlin and continuity equations remain the current standard methods for determining the aortic valve orifice area.

METHODS

Seventeen patients underwent intracardiac echocardiography for direct measurement of the aortic valve area, including four patients studied both before and after valvuloplasty, for a total of 21 studies. Immediately after intracardiac echocardiography, hemodynamic data were obtained from transthoracic echocardiography and cardiac catheterization.

RESULTS

Adequate intracardiac echocardiographic images were obtained in 17 (81%) of 21 studies. The average aortic valve area (mean +/- SD) determined by intracardiac echocardiography for the 13 studies in the Gorlin analysis group was 0.59 +/- 0.18 cm2 (range 0.37 to 1.01), and the average aortic valve area determined by the Gorlin equation was 0.62 +/- 0.18 cm2 (range 0.31 to 0.88). The average aortic valve area determined by intracardiac echocardiography for the 17 studies in the continuity analysis group was 0.66 +/- 0.23 cm2 (range 0.37 to 1.01), and that for the continuity equation was 0.62 +/- 0.22 cm2 (range 0.34 to 1.06). There was a significant correlation between the aortic valve area determined by intracardiac echocardiography and the aortic valve area calculated by the Gorlin (r = 0.78, p = 0.002) and continuity equations (r = 0.82, p < 0.0001).

CONCLUSIONS

In the clinical setting, intracardiac echocardiography can directly measure the aortic valve area with an accuracy similar to the invasive and noninvasive methods currently used. This study demonstrates a new, quantitative use for intracardiac echocardiographic imaging with many potential clinical applications.

Computation of a location shift between two subsequent intra vascular ultrasound registrations by cross-correlation analysis of the lumen area functions

For longitudinal studies on atherosclerosis and restenosis after angioplasty by intravascular ultrasound (IVUS), it is essential that repeated studies are performed at exactly the same location along an arterial section. In human femoral arteries, lumen and plaque area functions of two subsequent IVUS pullback maneuvers were compared by cross-correlation analysis. In cross-correlation analysis of two functions with equal abscissa values, the data sets are repetitively correlated after incremental shifts of the two functions along the abscissa. This results in multiple correlation coefficients with a maximum at the relative position where the two functions show the closest match. In group A (12 patients), both pullbacks were performed after angioplasty and in group B (17 patients) one pullback was performed before angioplasty and the second immediately after angioplasty. In group A, cross-correlation showed a shift between lumen area functions of 5 mm in one patient and no shift in the other patients. Maximum correlation coefficients in group A ranged from 0.644 to 0.978. Four patients from group B showed shifts from 2.5 to 35 mm. Maximum coefficients were significantly smaller than in group A: 0.259-0.864 (p < 0.01). Plaque area functions in group B showed higher correlations (0.468-0.862, p = 0.034) and only two shifts. Cross-correlation of lumen and plaque area functions may be used to compute location shifts between two subsequent IVUS registrations and to correct such shifts.

Influence of the selection of angiographic projections on the results of coronary angiographic follow-up trials. International Nifedipine Trial on Antiatherosclerotic Therapy Investigators

In recent years follow-up trials on coronary artery disease with angiographic end points analyzed quantitatively have gained increasing relevance and popularity. There is no consensus, however, on the method of calculation of progression or regression from multiple angiographic projections. Therefore the influence of the selection of angiographic projections on the outcomes of such trials was investigated with the data of the International Nifedipine Trial on Antiatherosclerotic Therapy. In 348 patients with coronary artery disease, repeated coronary angiograms were compared in multiple identical angiographic projections. Changes in angiographic parameters were averaged over the 1063 stenoses analyzed. Five methods of evaluation of multiple projections in the individual stenoses were applied, resulting in different extents of overall progression, or even regression of coronary artery disease (p < 0.01). It is concluded that in quantitative coronary angiographic follow-up trials changes should be averaged over all angiographic projections available for a stenosis to avoid overestimation of progression or regression.

Three-dimensional intravascular ultrasound assessment of plaque volume after successful atherectomy

The primary purpose of directional coronary atherectomy is the removal of intraluminal plaque. Angiography allows assessment of residual lumen narrowing but is limited in the assessment of residual plaque burden. Intravascular ultrasound has proven useful in assessing plaque size, but current use has been limited to a single, representative cross-sectional image rather than an evaluation of the entire plaque volume. To determine the volume of residual plaque after angiographically successful directional coronary atherectomy ( < or = 20% residual stenosis), we performed intravascular ultrasound in 19 patients before and after atherectomy. Only coronary lesions optimal for three-dimensional analysis (a single, discrete stenosis in a nontortuous, noncalcified native coronary artery) were selected. A 2.9F sheath-design intravascular ultrasound catheter with a motorized pullback device was used in all patients. The cross-sectional area of the artery (defined by the medial-adventitia border), the lumen, and the plaque were measured at 1 mm intervals over a 15 to 20 mm segment, which included the target lesion and a proximal reference segment (n = 362 cross-sections), before and after atherectomy. The volumes of the artery, vessel lumen, or plaque were calculated with a modified Simpson's equation and compared with standard area measurements at the point of maximal stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic expansion of the coronary arteries: implications for intravascular ultrasound measurements

The majority of coronary artery blood flow occurs in diastole; however, systolic epicardial coronary artery expansion has been described. With the advent of intravascular ultrasound, precise measurements of arterial structures with excellent spacial and temporal resolution are now readily available. However, the effect of dynamic expansion of the coronary arteries on routine intravascular ultrasound measurements has not been assessed. The purpose of this study was to determine in vivo the presence, timing, and extent of dynamic changes in the coronary arteries and saphenous vein grafts and to assess their implications for intravascular ultrasound measurements. Intravascular ultrasound images were obtained with simultaneous electrocardiographic monitoring in 202 coronary artery and 50 saphenous vein graft sites in 32 patients with varying plaque burden and morphologic features. Arterial, luminal, and plaque area were measured at end-diastole and early, mid-, and end-systole. Coronary luminal diameter increased 2.1%; luminal area increased 8.1%; arterial area increased 3.7%; and plaque area decreased 4.9% during mid and late systole (p < 0.01). There was no detectable cyclic change in saphenous vein graft dimensions. In coronary arteries there was significant systolic expansion of the artery and lumen and systolic thinning of the plaque. The magnitude of dynamic luminal area change was greater than the variability in measurement and thus warrants gating to the cardiac cycle. The lack of dynamic change in saphenous vein grafts and the relatively small dynamic change in luminal diameter and arterial and plaque areas suggest nominal utility in gating these measurements to the cardiac cycle.

Anatomic and physiologic heterogeneity in patients with syndrome X: an intravascular ultrasound study

OBJECTIVES

We used intravascular ultrasound imaging of the epicardial vessels to assess coronary morphology, vasomotor response to exercise and exercise-vasomotion after beta-adrenoceptor blockade in patients with syndrome X.

BACKGROUND

Syndrome X is defined as chest pain, abnormal exercise test results and normal coronary angiographic findings. Because of the limitations of coronary angiography, intravascular ultrasound was used to define coronary pathophysiology.

METHODS

Thirty patients with syndrome X were studied with intravascular ultrasound imaging (30 MHz, 4.3F catheter) of all three major epicardial vessels. Supine arm exercise was performed during coronary imaging. Lumen area was assessed at rest and during peak exercise. The exercise-imaging protocol was repeated after loading with 0.1 mg/kg body weight of intravenous propranolol.

RESULTS

Three morphologic groups were identified using intravascular ultrasound: normal coronary arteries (no plaque, intimal thickness < 0.25 mm, n = 12), atheromatous disease (mean [+/- SD] area stenosis 37.9 +/- 7.2%, n = 10) and marked intimal thickening (0.73 +/- 0.11 mm, n = 8). Patients with normal coronary arteries displayed a vasodilatory response to exercise (+16.9% area increase); patients with abnormal coronary arteries displayed a vasoconstrictive response to exercise (-17.4% in the group with plaque; -17.6% in the group with intimal thickening). Propranolol loading attenuated the vasodilatory response in the group with normal coronary arteries (+6.4% area increase) and attenuated the vasoconstrictive response in the two groups with abnormal coronary arteries (-8.0% in the group with plaque; -8.8% in the group with intimal thickening).

CONCLUSIONS

Most patients with syndrome X have abnormal coronary arteries by intravascular ultrasound. Intravascular ultrasound identifies three distinct morphologic groups: normal coronary arteries, atheromatous plaque and intimal thickening. Exercise-vasomotion is normal in patients with syndrome X who have normal coronary arteries by ultrasound; patients with abnormal arteries (plaque or intimal thickening) have an abnormal (constrictive) response to exercise. Propranolol loading attenuates vasoreactivity in all subgroups, suggesting divergent therapeutic utility.

Intracoronary ultrasound: current state of the art

Images

An explanation for discrepancy between angiographic and intravascular ultrasound measurements after percutaneous transluminal coronary angioplasty

OBJECTIVES

This study attempted to determine why there is a discrepancy between angiographic and intravascular ultrasound measurements after coronary balloon angioplasty.

BACKGROUND

Previous studies have shown a poor correlation between angiographic and intravascular ultrasound measurements after percutaneous coronary balloon angioplasty.

METHODS

After successful balloon angioplasty, 91 lesions in 84 patients were studied by intravascular ultrasound. Plaque morphology on intravascular ultrasound was classified as demonstrating a superficial injury if there was either no fracture or only a small tear that did not extend to the media versus a deep injury defined as the presence of a plaque fracture that reached the media. Measurements of minimal lumen diameter were compared between angiography and intravascular ultrasound.

RESULTS

On ultrasound imaging, a superficial injury pattern was observed in 44 lesions, whereas a deep injury was seen in 47 lesions. There were no statistical differences at baseline in patient or lesion characteristics. In the superficial injury group there was a significant correlation between angiography and intravascular ultrasound for minimal lumen diameter (r = 0.67) and lumen cross-sectional area (r = 0.69). In the deep injury group there was a poor correlation for minimal lumen diameter (r = 0.05) and lumen cross-sectional area (r = 0.28). After balloon angioplasty, the angiographic appearance showed a normal contour in 34%, the presence of dissection in 38% or a hazy appearance in 23%. On ultrasound imaging after angioplasty, the superficial injury group comprised 65% of lesions with a normal angiographic appearance and 67% of lesions with a hazy appearance, whereas 77% of lesions with an angiographic diagnosis of dissection were in the deep injury group by ultrasound (p = 0.0005).

CONCLUSIONS

These observations suggest that the discrepancies between angiographic and ultrasound measurements are due to differences in plaque morphology created by balloon dilation. Superficial injuries demonstrate similar results by angiography or ultrasound, whereas a deep injury to the plaque produces a difference in measurements between angiography and ultrasound. When angiography reveals a dissection, there is a high probability that intravascular ultrasound will demonstrate a plaque fracture extending to the media.

Angioscopic evaluation of incompletely obstructing coronary intraluminal filling defects: comparison to angiography

At 66 sites in 40 patients, we evaluated the sensitivity and specificity of coronary angiography in detecting intraluminal filling defects of varying sizes and in characterizing the contents (thrombus, intimal flap, both) of such defects using coronary angioscopy as "the gold standard." Overall angiographic sensitivity for thrombus was 37% and for intimal flap 45%. Specificity for thrombus was 100% and intimal flaps 96%. Angioscopically small flaps were less frequently seen angiographically (28%) than larger sizes (65%, p = 0.03). Angioscopically small thrombi were seen less often angiographically (30%) than larger ones (75%, p = 0.13). Filling defects (intimal flaps, thrombus, both) were characterized correctly in only 37% of sites. Angiography is relatively insensitivity in detecting intraluminal filling defects. Angioscopy may be preferred to or adjunctive with angiography in detecting these lesions.

Coronary artery ectasia: local pathology or diffuse disease?

It is not known whether general or local factors influence the pathogenesis of coronary ectasia. We analyzed prospectively coronary angiograms from 2,186 consecutive patients with 32 patients (1.5%), identified as having coronary artery ectasia. Sixteen subjects had coronary ectasia in more than one segment of the same or a different artery. In 20 of 72 (28%) ectatic segments there was a proximal, related stenosis. In these cases ectasia was more often saccular than fusiform (16 vs. 4) compared to ectasia without a proximal, related stenosis (21 vs. 31, P = 0.003), and the mean length of the ectatic segment was shorter (8.0 vs. 15.1 mm, P = 0.013). Subjects with ectasia after a stenosis often had other ectatic segments unrelated to stenoses. The high incidence of multisegment involvement suggests that coronary ectasia results from a diffuse abnormality of the vessel wall. In predisposed individuals localized ectasia may follow a stenosis, suggesting poststenotic dilatation.

False positive dobutamine stress echocardiograms: characterization of clinical, echocardiographic and angiographic findings

OBJECTIVES

This study was designed to characterize the clinical, echocardiographic and angiographic findings in patients who have regional wall motion abnormalities predictive of coronary artery disease on dobutamine stress echocardiograms, although coronary angiography reveals no critical stenoses.

BACKGROUND

The specificity of dobutamine stress echocardiography has been reported to be lower than its sensitivity; the sources of false positive findings on dobutamine stress echocardiograms have not been previously defined.

METHODS

Clinical and echocardiographic characteristics were retrospectively reviewed for patients who had both a dobutamine stress echocardiogram indicative of coronary artery disease on the basis of wall motion abnormalities and < 50% stenoses reported on coronary angiography performed within 6 weeks of the echocardiogram. A 16-segment model was used to perform wall motion scoring. Angiograms were independently reviewed, and stenosis severity was quantified with the use of digital calipers.

RESULTS

Thirty-nine (11.4%) of 342 studies met criteria for false positive test results, which occurred predominantly in women (72%, p < 0.001). Regional wall motion abnormalities were evident more often in the posterior circulation (62%), and 65% of them were limited to the basal segments. Twelve (28%) of 43 wall motion abnormalities were associated with coronary stenoses of at least intermediate grade (lumen diameter 40.3% to 68.1%). Abnormalities confined to basal segments of the posterior circulation were unlikely to have associated coronary lesions (p = 0.03).

CONCLUSIONS

False positive findings on dobutamine stress echocardiograms tend to involve small wall motion abnormalities that are frequently located in basal segments of the posterior myocardial circulation. Approximately one third of false positive results occurred in patients with intermediate-grade coronary stenoses, and these studies may reflect true inducible ischemia. Additional sources of false positive study results may include poor endocardial visualization and abnormal motion due to tethering to the fibrous skeleton of the heart. Altered echocardiographic diagnostic criteria may be appropriate for small wall motion abnormalities confined to basal segments of the posterior circulation.