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J R Resar

Publications and source records attributed to J R Resar.

29 records · Page 2Linked to original sources
PubMed1993

Fragmentation and embolization of a plastic-coated guidewire.

We report a case of fragmentation and embolization to the pulmonary artery of sheared pieces of a recently introduced hydrophilic plastic-coated guidewire. The propensity for this to occur, the lack of initial recognition, and the ability to retrieve the fragments by catheter techniques are emphasized. As these guidewires are more frequently used, physicians should be aware of this potential complication.

Angioplasty, Balloon, Coronary↗
PubMed1993

Estimation of myocardial mechanical properties with dynamic transverse stiffness.

There are currently no validated methods for accurately estimating regional ventricular mechanical properties. We recently developed a dynamic indentation system that can determine dynamic transverse stiffness (the slope of the relation between the indentation stress and indentation strain during high frequency indentations) in as little as 10 msec. The apparatus consists of an indentation probe coupled to a linear-motor and a computerized control system. This indentation system was tested on beating, canine ventricular septa that were mounted in a biaxial system that could apply strains in the plane of the septum and measure the resulting in-plane stresses. The probe indented the septa with peak displacements of 0.1-0.5 mm at frequencies of 20 and 50 Hz. The transverse stiffness was shown to be related to the in-plane stress and stiffness in the isolated septa. Dynamic transverse stiffness was then used to study the effects of myocardial perfusion on passive tissue stiffness and on contractility. In addition, the transverse stiffness was studied in intact canine hearts during diastole, where it was related to the chamber stiffness. Thus, dynamic transverse stiffness appears to allow estimation of myocardial mechanical properties.

Animals↗
PubMed1993

Percutaneous transluminal coronary angioplasty through 6F diagnostic catheters: a feasibility study.

This study evaluated the feasibility of performing coronary angioplasty through 6F diagnostic catheters by mainly using over-the-wire balloon systems on 84 lesions in 70 patients. Procedural variables, including vessel opacification and angioplasty outcome, were assessed. Changes in hematocrit after angioplasty were compared for 6F versus 7F and 8F systems. Successful 6F dilatation was performed in 72 (85.7%) of 84 lesions and 58 (82.9%) of 70 patients. Seven of the 12 lesions unable to be dilated with 6F systems were successfully dilated with larger French systems. Coronary artery opacification with the 6F catheters after balloon dilation was less than optimal with the balloon and guidewire still in the catheter. Changes in hematocrit after 6F procedures were significantly less than for 8F procedures (-2.1% vs -4.2%, respectively, p < 0.01) but not for 7F procedures (-2.4%, p = not significant). Potential cost savings for angioplasty with 6F diagnostic catheters could be significant. Thus angioplasty with over-the-wire balloon systems in which 6F nontapered diagnostic catheters are used can be performed safely and with less procedural blood loss than with 8F systems. Significant problems encountered with the current catheter design were poor vessel opacification after balloon dilation and difficulties with balloon retraction.

Angioplasty, Balloon, Coronary↗
PubMed1993

Preprocedural anticoagulation does not reduce angioplasty heparin requirements.

To determine whether continuous preprocedural heparin influences the need for anticoagulation during percutaneous transluminal coronary angioplasty (PTCA), we compared heparin requirements in patients therapeutically anticoagulated after continuous heparinization for > or = 12 hours with patients not pretreated with heparin (controls). A Hemochron device was used to monitor the activated clotting time (ACT) values during the procedure. An ACT > or = 300 seconds was used as a measure of optimal anticoagulation. Patients pretreated with heparin had significantly higher preprocedural ACT measurements (163 +/- 31.5 vs 126 +/- 13 seconds, p < 0.001) and partial thromboplastin time (PTT) measurements (46 +/- 15 vs 25 +/- 3 seconds, p < 0.001) than controls. While the amount of heparin needed to achieve an initial ACT > 300 seconds was slightly greater in control patients (10,682 +/- 1,852 vs 9,269 +/- 2,993 units, p < 0.001), the total heparin required to maintain an ACT > 300 seconds throughout the procedure was similar between the two groups (11,551 +/- 3,181 units vs 12,136 +/- 2,575 units, p = NS). Thus preprocedural anticoagulation does not significantly reduce total heparin requirements, and these patients should receive the same initial heparin regimen as patients not pretreated with intravenous heparin.

Angina, Unstable↗
PubMed1993

Brachial approach for intracoronary stent implantation: a feasibility study.

Implantation of coronary artery stents via the percutaneous femoral approach is associated with a high rate of vascular complications at the access site related to the size of the entry hole and the intense anticoagulation required to prevent stent thrombosis. Therefore we studied the feasibility of using the left brachial approach utilizing open arterial repair for implantation of coronary artery stents. Intracoronary stent implantation via the femoral approach in 24 patients (group A) was compared with implantation via the brachial approach in 16 patients (group B). Baseline lesion characteristics were similar in the two groups. All stents in group A (n = 27 stents) were successfully delivered to their target vessel. One stent in group B (n = 18 stents) could not be delivered because of an inability to engage the coronary artery from the brachial approach. There were no significant differences in the angiographic outcome between the two groups. Complications including hematomas, hemorrhage requiring blood transfusion, vascular injury requiring surgery, and pseudoaneurysm formation were significantly more common in group A than in group B (8/24 [33%] versus 1/16 [6%], respectively; p < 0.05). In addition, the length of hospital stay was significantly longer for the femoral approach than the brachial approach (9.4 vs 6.5 days, respectively; p < 0.05). Thus the left brachial approach for intracoronary stent implantation is technically feasible, safe, and associated with fewer local vascular complications and a shorter hospitalization than the femoral approach.

Brachial Artery↗
PubMed1993

Direct evidence that coronary perfusion affects diastolic myocardial mechanical properties in canine heart.

OBJECTIVE: The effect of coronary perfusion on left ventricular chamber distensibility is only indirect evidence that perfusion alters the mechanical properties of the myocardium. The aim of this study was to demonstrate explicitly the effects of coronary perfusion on these mechanical properties. METHODS: The effects of different levels of coronary perfusion were studied both on in-plane stress-strain relations and on transverse stiffness in an isolated, perfused canine interventricular septal preparation. Additionally, to determine the vascular compartment responsible for the mechanical effects of perfusion on tissue properties, we examined the in-plane stress-strain responses and transverse stiffness after embolisation of the vasculature with 15 microns microspheres. RESULTS: The data show a clear dependence of tissue stress-strain properties on perfusion. The in-plane stress-strain relations were shifted to the left and transverse stiffness increased linearly as septal artery perfusion pressure increased. The dependence of both the in-plane stress-strain relations and transverse stiffness on perfusion was significantly decreased following embolisation. CONCLUSIONS: Myocardial tissue stiffness is directly related to perfusion. The linear relationship between transverse stiffness and perfusion makes it easier to assess the effects of perfusion on tissue stiffness than with in-plane stress-strain relations. Perfusion of capillaries and/or venules is largely responsible for these alterations in myocardial stiffness.

Animals↗
PubMed1993

Rapid measurements of diastolic intramyocardial vascular volume.

Rapid measurements of coronary vascular volume are necessary for a complete understanding of phasic coronary flow. Because no standard method is capable of making these measurements, we developed a method that uses digital subtraction angiography to image an intravascular contrast agent. The method is capable of measuring vascular volume in 33 ms and can be repeated three times per second. The method was first validated in phantoms. We then used this method to measure coronary vascular volume in the isolated, perfluorochemical-perfused, interventricular canine septum. The speed of the measurements allowed us, for the first time, to directly measure transients in vascular volume following sudden changes in perfusion pressure. At the steady-state and maximal vasodilation, coronary vascular volume varied from 7.5 +/- 1.2 (SE) ml/100 g at a perfusion pressure of 20 mmHg to 12.1 +/- 1.9 ml/100 g at 90 mmHg, which is similar to other reports. After a sudden change of 40 mmHg in perfusion pressure, vascular volume changed with a time constant of 3.2 +/- 0.3 (SE) s. Increasing ventricular wall stretch had no effect on either the steady-state volumes (P = 0.25) or the time constant for volume changes (P = 0.17). The fact that the time constant is longer than the cardiac cycle, yet much shorter than the time necessary to measure vascular volume using other methods, highlights the need for rapid measurements of vascular volume.

Absorptiometry, Photon↗
PubMed1993

Effect of tetanic myocardial contraction on coronary pressure-flow relationships.

Cardiac contraction causes a decrease in coronary flow. Despite many studies, it is still not clear what mechanism or mechanisms are responsible for this flow decrease. The phasic nature of myocardial contraction and the complexities intrinsic to intact heart preparations make it difficult to elucidate the mechanisms. We therefore studied coronary pressure-flow relationships during steady-state (tetanic) contractions in the maximally vasodilated isolated canine interventricular septum to see whether waterfall-type behavior is present. Using ryanodine and electrical stimulation allowed the production of reproducible and reversible tetani. This preparation minimizes the difficulties associated with transmural variations and also the effects of intramyocardial capacitance. Two separate protocols were performed to delineate the pressure-flow relationships in the passive and tetanized states. The first compared diastolic and tetanized pressure-flow relationships. In the second protocol, 2,3-butanedione monoxime was added to obtain an intermediate contractile level, thus allowing the comparison of two contractile states. Both the diastolic and tetanized pressure-flow relationships were curvilinear in the low-pressure range. Linear and nonlinear fits to the data showed that the primary effect of contraction was a shift of the pressure-flow relationships to higher pressures at a given flow. This effect was graded by the level of contractility and was independent of developed stress. Although other mechanisms may also be operative, these results support the presence of waterfall behavior in the coronary vascular bed.

Animals↗
PubMed1992

Early coronary artery stent restenosis: utility of percutaneous coronary angioscopy.

Restenosis of an endovascular stent may be caused by thrombus, intimal hyperplasia, or extrinsic compression. Angiography may not adequately define the etiology of restenosis. We describe a patient in whom angioscopy proved important in diagnosing intimal hyperplasia obviating the need for thrombolytic therapy and prolonged anti-coagulation.

Aged↗
PubMed1992

In-plane myocardial wall stress is not the primary determinant of coronary systolic flow impediment. A study in the isolated, perfused dog septum.

The hypothesis that ventricular in-plane tensile wall stresses are the major determinant of systolic coronary flow was investigated in this study. We measured coronary artery inflow in the maximally vasodilated bed of the isolated beating septum (n = 10) during two modes of contraction characterized by markedly different levels of developed in-plane stress. An increase in contractility was induced by changing from the control steady-state pacing state to a postextrasystolic potentiated state induced by a modified rapid pacing protocol. Over a range of increments of passive stretch, the systolic flow impediment versus the diastolic wall strain was described by an inverse linear relation. Despite the differences in developed in-plane wall stresses between the two modes of contraction (p less than 0.001), the slope and intercept of these relations in both the control and potentiated states were not different for the low versus high developed stress modes. The systolic flow impediment versus diastolic wall strain relation for the potentiated beats, compared with the control beats, was characterized by an increase in the intercept in both the low developed stress beats (p less than 0.05) and the high developed stress beats (p less than 0.05). These data indicate that the impediment to coronary flow during systole is not primarily determined by systolic myocardial in-plane tensile wall stresses but rather by the contractile state of the muscle.

Animals↗