Clinical evaluation of a microsample coagulation analyzer, and comparison with existing techniques

A new microsample coagulation analyzer (Hemochron Jr.) has recently been developed which performs a modified activated clotting time (ACT+) and an aPTT by using different reagents. The Hemochron Jr. measures the clotting time of a 5-microliter whole-blood sample by an optical detector and extrapolates the results to the activated clotting time (ACT+) or the plasma-activated partial thromboplastin time by using a validated regression analysis. We compared 124 simultaneous ACT+ and Hemochron ACTs, and 53 paired Hemochron Jr. aPTTs and hospital laboratory aPTTs, in 44 patients during coronary intervention. The Hemochron Jr. aPTT closely correlated with the lab aPTT (r = .79, P < .0001), and the test results were available much more rapidly than the lab aPTT (3.5 +/- 1.1 vs. 56.3 +/- 25.5 min, P = 0.0029). A comparison of duplicate ACT+ measurements did not identify a significant difference in the means (292 +/- 115 sec vs. 293 +/- 112 sec, P = 0.72). The ACT+ closely correlated with the Hemochron ACTs (r = .85, P < .0001). At baseline, the mean ACT+ (175 +/- 43 sec) exceeded the Hemochron ACT (144 +/- 36 sec) by 22% (P < .001). After heparin administration, the mean ACT+ (378 +/- 74 sec) exceeded the Hemochron ACT (332 +/- 65) by 12% (P < .001). The Hemochron Jr. provides a fast and reproducible methodology for measuring ACT and aPTT, using a small blood volume. Further studies are required to determine the optimal anticoagulation range when using the Hemochron Jr. during or after interventional procedures.

The beta-particle-emitting radioisotope stent (isostent): animal studies and planned clinical trials

Radiation delivered by intravascular stent is an appealing approach to prevent neointimal hyperplasia, since it nonselectively kills dividing cells. In particular, beta-particle-emitting radioisotope stents may prove to be an ideal means of local irradiation in that 95% of the dose is delivered within 4 mm of the stent edge and the dose drops off rapidly to < 1/1,000 of the original dose at 5 months postimplantation. In the in vitro smooth muscle cell model, one can observe a zone of growth inhibition around radioactive stent wires that averages about 6 mm at very-low-activity levels (0.006 microCi/cm of wire). In vivo studies in animal models, including porcine iliac and coronary arteries and rabbit iliac arteries, have shown the effectiveness of radioisotope stents in inhibiting neointimal proliferation. Proliferating endothelial cells appear to be relatively radioresistant. A computer model was employed to look at the radiation dose delivered as a function of distance from the stent. With very-low-activity stents, presumably, DNA of the smooth muscle cells is damaged as they migrate through the "electron fence" on the way to the neolumen, diminishing the population of myofibroblasts and reducing hyperplasia. Catheter-based radiation therapies may disable these cells before they migrate, although such an approach may not inhibit early recoil or late contraction. Based on the characteristics of beta emissions (i.e., rapid drop-off, minimal leaching), radioisotope stents containing phosphorus-32 appear to be safe. A randomized triple-blind clinical trial is planned to assess restenosis at 6 months in native coronary arteries treated with radioisotope stents.

Coronary stenting with a novel stainless steel balloon-expandable stent: determinants of neointimal formation and changes in arterial geometry after placement in an atherosclerotic model

OBJECTIVES

This study evaluated the delivery characteristics and vascular response to placement of a novel balloon-expandable stent in swine with experimentally induced atherosclerosis.

BACKGROUND

The Multi-Link stent is a balloon-expandable stainless steel stent with an interconnected ring structure designed to provide a high degree of compressive resistance while preserving longitudinal flexibility. The placement characteristics and vascular response to this stent in atherosclerotic coronary arteries have not been characterized.

METHODS

We tested the delivery characteristics and vascular response to the Multi-Link stent in 19 miniature swine with experimentally induced coronary atherosclerosis created in 37 coronary artery segments by overstretch balloon injury and high cholesterol diet. Quantitative coronary angiography was used to define stent performance characteristics, such as lesion dilation and compressive resistance. Pathologic assessment of the stented arteries was used to evaluate the immediate and long-term vascular response to stent placement.

RESULTS

Nineteen (95%) of 20 stents were successfully implanted in the left anterior descending (n = 11), left circumflex (n = 7) or right (n = 1) coronary artery. The baseline angiographic minimal lumen diameter of the stented coronary segment was 2.48 +/- 0.09 mm (reference diameter 2.87 +/- 0.06 mm, mean +/- SE) and increased to 2.82 +/- 0.05 mm (p < 0.001) after stent placement. The balloon-inflated stent diameter was 2.98 +/- 0.06 mm with minimal recoil to a final minimal lumen diameter of 2.82 +/- 0.06 mm at 15 min after implantation (p = 0.001). Angiographic and histologic follow-up at 72 h (n = 7), 14 days (n = 4) and 56 days (n = 8) demonstrated that all stents were patent, without evidence of migration, intraluminal filling defects or side branch occlusion. At 56 days, mean neointimal thickness was significantly greater at the stent wire sites in the region of the plaque where the media was absent than the stent wire sites, where the internal elastic lamina was intact with underlying normal media (0.48 +/- 0.01 vs. 0.27 +/- 0.02 mm, p < 0.0001). Compared with the nonstented atherosclerotic lesions, after 56 days the stented vessels had a mildly reduced lumen area when normalized to the proximal reference vessel (2.81 +/- 0.27 vs. 2.68 +/- 0.30 mm2, p = 0.07). The mean change in the area within the external elastic lamina relative to a normal proximal reference segment was significantly greater in stented vessels (1.45 +/- 0.34 mm2) than nonstented atherosclerotic vessels (0.44 +/- 0.28 mm2, p = 0.033).

CONCLUSIONS

Morphologic data confirm that the principal beneficial effect of stent placement is vessel expansion and attenuation of constrictive remodeling. In vessels with eccentric atherosclerotic fibrocellular plaques, the presence of normal media underlying the stent determines the degree of neointimal formation. These data may be useful in understanding the mechanism of stent restenosis in patients with prior percutaneous transluminal coronary angioplasty.

Angiographic and procedural outcome after coronary angioplasty in high-risk subsets using a decremental diameter (tapered) balloon catheter. Tapered Balloon Registry Investigators

The angiographic and clinical outcomes of 115 patients (129 lesions) treated at 11 clinical centers using a decremental diameter (tapered) balloon catheter were evaluated. The presence of marked tapering of the reference vessel, lesion location involving a bifurcation or anastomosis of a saphenous vein graft, or total coronary occlusion where estimation of the distal vessel size was difficult were indications for this device. The tapered balloon was used as the initial dilatation device in 62 patients (73 narrowings), and as a secondary device in 53 patients (56 narrowings). Lesions selected for tapered balloon angioplasty were generally complex (95% had > or = 1 and 60% had > or = 2 adverse morphologic features). Vessel diameters were larger in the proximal reference segments (3.07 +/- 0.52 mm) than in distal ones (2.48 +/- 0.45 mm) (p<0.001). After tapered balloon angioplasty, the minimal lumen diameter increased from 0.85 +/- 0.34 mm to 2.13 +/- 0.50 mm (p<0.001), and the percent diameter stenosis decreased from 69 +/- 12% to 24 +/- 12% (p<0.001). Coronary dissections occurred in 20% of lesions; they were severe in 4% (National Heart, Lung, and Blood Institute grade C to F). Abrupt closure occurred in 4.3% of patients (2.6% immediate; 1.7% delayed). Procedural success was obtained in 110 patients (96%); major complications (in-hospital death, myocardial infarction, or emergency coronary bypass surgery) occurred in 3 patients (2.7%). Coronary angioplasty using the tapered balloon catheter appears to be a safe and effective technique for the treatment of complex lesion subsets, particularly those involving coronary arteries with marked segmental tapering.

Inhibition of neointimal proliferation with low-dose irradiation from a beta-particle-emitting stent

BACKGROUND

Restenosis after successful percutaneous transluminal coronary angioplasty is the major factor limiting the long-term effectiveness of this procedure. Neointimal proliferation in response to arterial injury is an important contributor to restenosis. The use of radiation for the treatment of malignant and benign proliferative conditions has been well established. External beam irradiation and endovascular irradiation by use of an after-loading technique have been shown to inhibit neointimal proliferation in experimental models of restenosis. The objective of this study was to investigate whether low-dose irradiation from a beta-particle-emitting stent would inhibit neointimal proliferation after placement in porcine iliac arteries.

METHODS AND RESULTS

Fourteen titanium-mesh stents were implanted in the iliac arteries of nine NIH miniature swine. There were seven beta-particle-emitting radioisotope stents (32P, activity level 0.14 microCi) and seven control stents (31P, nonradioactive). Treatment effect was assessed by angiography and histomorphological examination of the stented iliac segments 28 days after implantation. There was a significant reduction in neointimal area (1.76 +/- 0.37 mm2 versus 2.81 +/- 1.22 mm2, P = .05) and percent area stenosis (24.6 +/- 2.9% versus 36.0 +/- 10.7%, P = .02) within the beta-particle-emitting stents compared with the control stents. Neointimal thickness, which was assessed at each wire site, was also significantly less within the treatment stents (0.26 +/- 0.04 mm versus 0.38 +/- 0.10 mm, P = .012). Scanning electron microscopy was performed on sections from four stents. This demonstrated endothelialization of both the treatment and control stents. There was no excess inflammatory reaction or fibrosis in the media, adventitia, or perivascular space of vessels treated with the beta-particle-emitting stent compared with control vessels. At 28 days, there was no difference in smooth muscle cell proliferation as measured by the proliferating cell nuclear antigen index.

CONCLUSIONS

A local, continuous source of low-dose endovascular irradiation via a beta-particle-emitting stent inhibits neointimal formation in porcine arteries. This low dose of local irradiation did not prevent endothelialization of the stents. This novel technique offers promise for the prevention of restenosis and warrants further investigation.

Spring coil embolization of a patent ductus arteriosus in an adult

To date, coil embolization has been reserved for occlusion of the small patent ductus arteriosus (PDA) because of potential dislodgement of the coils. We report a case of a larger, hemodynamically significant PDA in an adult which was successfully closed by two spring coils using a "crossed catheter" technique for coil delivery.

Morphologic characteristics of lesion formation and time course of smooth muscle cell proliferation in a porcine proliferative restenosis model

OBJECTIVES

This study was performed to define the evolution of lesion morphology and its relation to thrombus formation and smooth muscle cell proliferation after experimental coronary stent placement.

BACKGROUND

Restenosis after percutaneous revascularization may develop because of thrombus accumulation and smooth muscle cell proliferation. In animal models of restenosis, thrombus may assume a significant role in neointimal formation by providing an absorbable matrix into which smooth muscle cells proliferate.

METHODS

Twenty-eight oversized stents were placed in the coronary arteries of 23 juvenile domestic pigs. The histologic degree of vessel injury, lesion morphometry and smooth muscle cell proliferation measured by immunolocalization with a monoclonal antibody to proliferating cell nuclear antigen (PCNA) were assessed at 24 h and 7, 14 and 28 days after stent placement.

RESULTS

The area of thrombus was minimal at 24 h ([mean +/- SE] 0.44 +/- 0.12 mm2). Neointimal area at 7 days (0.72 +/- 0.20 mm2) was similar to the area of thrombus, followed by a significant increase at 14 days (3.15 +/- 0.39 mm2) and 28 days (3.30 +/- 0.28 mm2) (p < 0.0036, 24 h and 7 days vs. 14 and 28 days). At 14 and 28 days, neointimal thickness correlated with the histologic degree of vessel injury (p < 0.003). In arteries with severe injury, the increase in neointimal thickness is accounted for by replacement of the damaged media. The smooth muscle cell proliferation index was 18.6 +/- 3.5% at 7 days compared with 9.6 +/- 1.3% by 14 days (p = 0.0247) and declined to 1.1 +/- 0.97% by 28 days (p < 0.008, 7 and 14 days vs. 28 days).

CONCLUSIONS

Early thrombus formation is minimal, and thrombus accounts for a small portion of subsequent neointimal formation. Smooth muscle cell proliferation and matrix formation are the major factors relating to neointimal formation in this proliferative model of restenosis. The evolution of neointimal formation after coronary stenting shows maximal smooth muscle cell proliferation at 7 days, with a decline to low levels by 28 days. Therefore, these data may be useful for developing effective therapies for restenosis.

Side-branch occlusion with directional coronary atherectomy: incidence and risk factors

Side-branch occlusion is a recognized complication of directional coronary atherectomy (DCA). To evaluate the incidence, risk factors, and clinical outcome of side-branch compromise, we analyzed our first 100 consecutive atherectomies of native coronary arteries. Seventy-eight patients had 122 side branches at risk, 21 (17%) of which demonstrated compromised flow after DCA. Origin of the side branch from the culprit atheroma and preexisting side-branch ostial stenosis were highly predictive of this complication in 20 of 55 (p < 0.05) and 14 of 31 (p < 0.05) lesions, respectively. There was one non-Q-wave myocardial infarction, no emergency surgeries, and no deaths. In conclusion, side-branch loss after DCA occurs with a frequency similar to balloon angioplasty and was well tolerated in our patient population. Side branches that originate directly from culprit lesions or that have significant ostial narrowing have a higher incidence of this complication.

Placement and angiographic patency of the Strecker coronary stent

The Strecker stent is a newer, balloon-expandable vascular prosthesis consisting of a single tantalum filament knitted into a flexible mesh tube. To test the placement characteristics and patency of this device, we implanted 29 stents in the coronary arteries of 24 juvenile Yorkshire swine. Seventeen stents were placed in the left anterior descending artery, and 12 were placed in the left circumflex system. All stents were deployed successfully. Four animals died within the first 24 hr of anesthesia-related complications. The remaining animals were sacrificed at 24 hr, 1 week, 2 weeks, or 4 weeks. Follow-up angiography demonstrated the patency of all stents. There were no episodes of stent migration or side branch occlusion. The Strecker stent has several favorable characteristics, including its unique delivery system, ease of deployment, flexibility, radiopacity, and radial strength. There was 100% patency at up to 4 weeks in this animal model. Further studies are required to define whether the knitted mesh design offers any advantage over previous models.

Transcoronary cardiac pacing during myocardial ischemia

Severe bradyarrhythmias are a rare but potentially life threatening complication of percutaneous transluminal coronary angioplasty (PTCA). Previous work has outlined a technique for coronary pacing using the angioplasty guidewire. To examine the effectiveness of this technique during severe ischemia, seven swine underwent placement of an unmodified 0.014 inch angioplasty guidewire and 3.0 mm balloon catheter in the left anterior descending (LAD) artery. Baseline pacing thresholds were obtained. Pacing was begun at twice diastolic threshold and ischemia was produced by balloon inflation. Repeat capture thresholds were obtained after 1 and 8 minutes of ischemia. Transcoronary pacing was successfully performed in all seven animals and was continued for a mean of 13.8 +/- 1.5 minutes. The baseline capture threshold was 4.0 +/- 0.5 mA. The mean capture threshold was 3.3 +/- 0.3 mA and 4.5 +/- 0.9 mA at 1 and 8 minutes of ischemia, respectively. We conclude that transcoronary pacing using the angioplasty guidewire can be successfully performed during myocardial ischemia and may serve as a reliable backup system during interventional procedures complicated by bradyarrhythmias.

Coronary arterial ectasia: increased prevalence in patients with abdominal aortic aneurysm as compared to occlusive atherosclerotic peripheral vascular disease

Coronary artery ectasia (CAE) is the saccular or fusiform dilatation of a coronary artery. CAE is found in 1.2% to 4.9% of patients at autopsy or during angiographic studies, with a similar prevalence of CAE found in patients with atherosclerotic peripheral vascular disease (PVD). Abdominal aortic aneurysm (AAA) and CAE are similar in pathogenesis and histology. To determine whether CAE occurs more frequently in patients with AAA than in occlusive forms of atherosclerotic PVD, a review of coronary angiograms was performed in patients who underwent cardiac catheterization and vascular reconstruction for AAA or occlusive atherosclerotic PVD of the lower extremities. Of 72 patients with AAA, 15 had CAE (20.8%) compared with only 2 of 69 patients with atherosclerotic PVD (2.9%) (p < 0.003). CAE was predominantly discrete, located in the left coronary system, and associated with significant coronary atherosclerosis. CAE may be more prevalent in patients with AAA resulting from a similar pathogenetic process.

Tolerance of normal aorta to oversized dual balloon valvuloplasty. Observations in a swine model: technical note

The damage threshold during aortic valvuloplasty was determined in 12 normal swine subjected to inflation of oversized dual balloons. Catheters with combined balloon diameters of 1.2-2.0 times the aortic annulus were selected. Following completion of the procedure, the animals were sacrificed and examined for pathology. With combined balloon diameters less than or equal to 1.7 times the aortic annulus, there was no gross or microscopic damage. In animals with combined diameters equal to 2 times the aortic annulus, there was rupture of the aorta. This data provides further basis for the selection of catheter sizes in dual balloon aortic valvuloplasty.

Swallow syncope associated with complete atrioventricular block: a case report and review of the literature

Swallow or deglutition syncope is a very unusual but treatable disorder. A 44-year-old male presented with multiple, recurrent episodes of complete atrioventricular block associated with swallowing. Over a 24-hour period, 92 episodes of complete atrioventricular block occurring with meals were recorded by Holter monitoring. Evaluation did not demonstrate any underlying esophageal or cardiac disease. A trial of anticholinergic medications was unsuccessful. The patient's symptoms resolved following placement of a demand cardiac pacemaker. This is a rare but potentially lethal disorder that can be successfully treated if recognized. Physicians should be alerted to symptoms of lightheadedness or syncope during meals.