Biomedical subjects
Publications and source records attributed to D C Levin.
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The rate of complication and the time necessary to achieve thrombolysis remain major disadvantages of regional thrombolytic therapy. By lacing the entire length of arterial or arterial bypass graft occlusions in the lower extremities of 49 patients with one of two different bolus doses of urokinase (mean, 52,000 International U in 35 infusions = low-dose group [28 patients]; mean, 230,000 U in 23 infusions = high-dose group [21 patients]) prior to identical continuous infusions, it was possible to demonstrate a decrease in the time needed to complete thrombolysis from 33.6 hours in the low-dose group to 10.4 hours in the high-dose group (P less than .001). The total urokinase dose necessary for successful thrombolysis was also significantly less in the high-dose group (P less than .001). The major complication rate was 22.9% in the low-dose group and 8.7% in the high-dose group, although the difference was not statistically significant. The use of urokinase and a high-dose transthrombus bolus injection technique significantly accelerates thrombolysis, decreases the total urokinase dose needed, and may lower the major complication rate.
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Platypnea is a clinical syndrome of dyspnea worsened by assuming an erect position and is associated with a postural arterial oxygen desaturation known as orthodeoxia. The clinical incidence of this syndrome may be underestimated by its occurrence in the medical literature. Several subgroups have been identified: patients with basal pulmonary vascular shunts; patients with intracardiac shunts, generally atrial, and who often have loss of lung volume; and patients without detectable shunts. Severe congestive heart failure may accentuate an occult shunt. When a patient presents with platypnea and/or orthodeoxia, a careful search should be made for underlying correctable disease such as atrial septal defects. Evaluation should include orthostatic contrast echocardiography, which in skilled hands may obviate the need for invasive cardiac catheterization in diagnosing underlying cardiac defects. Hemodynamic changes with changes in position have been difficult to study, but may play a significant role in the pathogenesis of this syndrome and, ideally, should be documented to clarify the underlying pathophysiology.
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The authors report results of nonsurgical treatment of acute occlusion developing during percutaneous transluminal coronary angioplasty (PTCA). Of 514 consecutive PTCAs, acute occlusion of the dilated artery developed during or within 1 hour after PTCA in 44 patients (8.5%); of these acute occlusions, 11 (2.1%) were due to guide wire or catheter manipulation during PTCA, while 33 (6.4%) were due to abrupt closure occurring after initially successful dilation. In seven of the 11 patients with acute occlusions resulting from manipulation, PTCA was continued with attempts to cross the reoccluded segment; this was successful in two patients (29%). In 25 of the 33 patients with abrupt closure, repeat balloon dilation was immediately attempted rather than send the patients to surgery for emergency coronary artery bypass grafting. Sixteen of these 25 attempts were successful (64%) and resulted in conversion of a potential complication into a successful outcome. Abrupt closure following initial dilation seems more likely to be successfully treated by continuing with PTCA than is acute occlusion resulting from catheter and guide wire manipulation.
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Digital video coronary arteriography (DVCA) was used in 59 cases of percutaneous transluminal coronary angioplasty (PTCA) and found to be useful for display of imagery to facilitate choice of approach to a stenotic lesion; providing a "road map," simplifying guide wire manipulation and selective catheterization of vessels during PTCA; and archival of pre- and post-PTCA images. Use of DVCA for real-time display inside the catheterization laboratory expedites the successful performance of PTCA and is a convenient means of image archival.
A new method to assess the hemodynamic severity of arterial stenoses was proposed and evaluated. It is based on a previously developed finite element computer simulation model for laminar-separated flow in arteries of axially varying cross-section; the present modification allows use of angiographic stenosis shapes acquired by automatic edge-detection algorithms. The method was validated by comparing its results with published experimental and theoretic results for ideal stenosis shapes. At moderate flowrates (Reynolds number = 500), poststenosis flow separation was predicted for moderately severe (75% area reduction) but not for mild (25%) stenoses. For high flowrates (Reynolds number = 900) in a severe stenosis (89%), stagnation and reversed flow were predicted and the experimental nondimensional pressure drop of 48.5 was correctly determined. Bernoulli's Equation, which neglects viscosity, predicted a drop of only 40. For a severe stenosis (89%), even at low Reynolds numbers (50), reversed flow agreeing with other theoretic solutions was predicted. Predictions are especially useful at low flow rates, where experiments are difficult to conduct. The height of the curve on the graph of nondimensional pressure gradient vs. Reynolds number reflects the hemodynamic severity of a particular stenosis; these curves were predicted for moderate and severe ideal stenoses and agree with experiments. A similar analysis is applied to an actual human coronary artery stenosis, and the results are demonstrated to have use in assessing interventions during angiography.
For many years, atherosclerotic coronary artery lesions have been described by angiographers only in terms of location and degree of narrowing. However, it has become apparent that coronary stenoses generally have distinct morphologic features that can be recognized at angiography and that allow them to be classified as either "simple" or "complex" plaques. Complex plaques are those characterized by ulcerated or ruptured surfaces, subintimal hemorrhage, superimposed partially occluding thrombi, recanalized thrombi, or some combination. Pathologic studies have shown a very high frequency of these lesions at sites of total thrombotic occlusion of coronary arteries. Clinical and angiographic studies have demonstrated a high frequency of such lesions in living patients with both unstable angina and acute myocardial infarction. The presence of complex stenoses has also been found to increase the risk of future myocardial infarction. Plaque morphology thus appears to significantly affect the prognosis of patients with coronary disease and should be carefully evaluated in interpretation of all coronary angiograms.
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A frequent concern during angioplasty is the possibility of occluding important side branches that originate in arterial stenoses subjected to balloon dilatation. The effect of dilatation on 93 side branches (greater than or equal to 1 mm in diameter) was evaluated in 86 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) in whom those branches arose directly in dilated segments of the left anterior descending, circumflex, or right coronary arteries. Seventy-six of the 93 side branches had minor (less than 50%) narrowing at their origin. Among these side branches, nine (12%) were compromised by PTCA. Seventeen of the 93 side branches had greater than 50% ostial stenosis. Significantly more of these side branches (seven of seventeen, or 41%) were compromised by PTCA (P less than .01). Even when compromise does occur, it usually takes the form of increased stenosis rather than total occlusion. The presence of side branches originating in stenotic lesions is not a contraindication to PTCA since serious compromise of such branches rarely results from this procedure.
Ischemic heart disease remains a significant cause of morbidity and mortality in the United States. Thrombolytic therapy has given physicians the capability of limiting the amount of myocardial damage that occurs when there is an acute coronary artery thrombosis and resulting myocardial infarction. This review summarizes current concepts about action mechanisms of the major thrombolytic agents, the technique and clinical results of intracoronary thrombolytic therapy, intravenous vs intracoronary administration, postthrombolytic management of underlying coronary artery disease, new agents being developed, and directions for future investigations.
In a series of 44 occluded femoropopliteal grafts, streptokinase was used for thrombolytic therapy in 22 cases and urokinase in 22 cases. In most cases, thrombolytic agents were administered via an indwelling arterial catheter directly into the proximal thrombus. The catheter tip was advanced as thrombolysis occurred. Compared with streptokinase infusions, urokinase bolus injection followed by infusion had better results (77% vs 41%) and fewer complications (23% vs 50%). During thrombolytic infusion, concomitant heparin infusion was usually used to reduce the frequency of thrombus formation on the infusion catheter or recurrent thrombosis of the graft, once the tip of the infusion catheter was advanced distally. Follow-up in 23 of 26 successful cases showed that 11 of the grafts remained open at an average follow-up of 12 months or until the patient died. The 12 grafts that reoccluded remained open an average of 3 months. In none of the 18 failures was simple surgical thrombectomy or thrombectomy with graft revision effective in revascularizing the distal limb. The advantages of thrombolysis compared with thrombectomy are less trauma to the graft, which is especially important in vein grafts, and improved distal runoff due to lysis of infrapopliteal thrombus. Even among cases considered failures in this series, the surgical approach was often simplified because of partial thrombolysis. Thrombolysis requires a considerable amount of time, effort, and expense, but in certain patients where thrombectomy is indicated for the treatment of occluded femoropopliteal grafts this technique offers important advantages.
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