In vitro validation of three-dimensional intravascular ultrasound for the evaluation of arterial injury after balloon angioplasty.

OBJECTIVES: The hypothesis of this study was that three-dimensional ultrasound imaging would facilitate the evaluation of arterial dissection after balloon angioplasty. BACKGROUND: The presence and extent of arterial dissection occurring at the time of balloon angioplasty may be important predictors of abrupt vessel closure or late restenosis. METHODS: Forty-one human arterial segments obtained after death were imaged in an in vitro system at physiologic pressure (80 to 100 mm Hg) before and after balloon angioplasty. Images were acquired with a 20- to 30-MHz mechanical intravascular ultrasound imaging system (Cardiovascular Imaging Systems) with a constant pullback technique (1 mm/s). Standard 0.5-in. (1.27-cm) video tapes were used for data storage and later playback for analog to digital conversion. Digitized data were reconstructed to three-dimensional images with use of voxel space modeling. The vessels were opened longitudinally and subjected to pathologic examination, photographed and classified histologically as normal, fibrous or calcified. Dissection was defined as a disruption and separation of components of the arterial wall. The length and depth of arterial dissection were evaluated grossly and microscopically. RESULTS: Of the 41 arteries studied, 36 (88%) exhibited dissection on pathologic examination after balloon angioplasty. Three-dimensional reconstruction of intravascular ultrasound images identified dissection in 11 (92%) of 12 normal, 8 (100%) of 8 fibrous and 11 (69%) of 16 calcified arteries. Excellent agreement between ultrasound and pathologic findings was achieved in the evaluation of length and depth of dissection for histologically normal and fibrous arteries (kappa = 0.72 to 1.0). When the vessels were severely calcified, the agreement was not as good (kappa = 0.27 to 0.56), particularly in detection of small, non-raised intimal flaps. CONCLUSIONS: This histopathologic validation study suggests that three-dimensional intravascular ultrasound imaging facilitates the evaluation of both quantitative and morphologic features of arterial dissection induced by balloon angioplasty. The advantage of three-dimensional intravascular ultrasound is its ability to assess the length and morphology of arterial injury over an entire vessel segment.

Intravascular ultrasound imaging: a current perspective.

Catheter-based intravascular ultrasound imaging has evolved from a research tool to a device that has received Food and Drug Administration approval. Although it is currently employed as an adjunct to contrast angiography in both the peripheral and the coronary circulation, the indications for its use and its clinical utility have yet to be defined. Much of the research on the technique has explored its qualitative and quantitative capabilities to improve the assessment of atherosclerotic vascular disease. There is the hope that this imaging technique may ultimately improve the performance of endovascular interventions. This review describes the development of the technology from early in vitro validation studies to its present use in human subjects. Wherever possible, studies that validate the findings (that is, by comparison with histopathology results) of intravascular ultrasound are emphasized. Although there is great promise for this technology, limitations such as loss of image quality in severely diseased or heavily calcified vessels hinder its use. The application of imaging with endovascular intervention, imaging of intracardiac structures and the pulmonary circulation and new techniques such as computer image analysis are discussed.

Application of time series analysis to circadian rhythms: effect of beta-adrenergic blockade upon heart rate and transient myocardial ischemia.

Circadian variations of transient myocardial ischemia and heart rate have been identified, but the rhythms and their response to beta blockade have not been fully characterized. Time-series analysis, a mathematical technique to describe oscillatory activity occurring within a continuous data set was used, to address these issues. Nine men with coronary artery disease underwent 72 hours of ambulatory electrocardiographic monitoring during therapy with placebo or metoprolol. During administration of placebo, ischemic time and heart rate showed a primary peak with a periodicity of approximately 24 hours with a tight coupling between the 2 variables and a secondary peak with a periodicity of 5 to 8 hours. During metoprolol therapy, heart rate and ischemic variation were reduced and the 24-hour periodicity for heart rate only remained. The 24-hour periodicity for ischemia was eliminated, but the data with 5- to 8-hour periodicity became the major component of the signal.

Silent myocardial ischemia during daily activities in asymptomatic men with positive exercise test responses.

The usefulness of prolonged ambulatory electrocardiographic monitoring (AEM) for detecting ischemia was investigated in 17 asymptomatic men who had ischemic-type ST-segment depression (greater than or equal to 2.0 mm) during treadmill exercise testing. No patient took anti-ischemic medications and all patients underwent coronary angiography. A total of 1,154 hours (range 64 to 72 hours/patient) of high-quality AEM recordings was obtained. Silent ischemia (episodes of asymptomatic ischemic-type ST depression of 60 seconds or longer) occurred in 11 patients during daily activity detected by AEM. In 6 other patients, no myocardial ischemic episodes were found. But 1 of these patients withdrew after only 24 hours of AEM and the remaining 5 had no significant coronary artery disease (CAD). All 11 patients who had silent ischemia had significant CAD (at least 50% stenosis) on angiography. There was wide intrapatient variability in the frequency of silent ischemic episodes. Silent ischemia was identified in 6 of these 11 patients after 24 hours of AEM, in 2 after 48 hours and in 3 after 72 hours. Thus, asymptomatic men with positive exercise test responses and CAD have silent ischemic episodes during daily activity. AEM may be useful in helping to predict which patients with asymptomatic positive exercise test responses have CAD; however, extended AEM periods are required.