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Biomedical subjects

C M Gibson

Publications and source records attributed to C M Gibson.

At least 19 recordsLinked to original sources

A role for trigger factor and an rgg-like regulator in the transcription, secretion and processing of the cysteine proteinase of Streptococcus pyogenes.

The ability of numerous microorganisms to cause disease relies upon the highly regulated expression of secreted proteinases. In this study, mutagenesis with a novel derivative of Tn4001 was used to identify genes required for the expression of the secreted cysteine proteinase (SCP) of the pathogenic Gram-positive bacterium Streptococcus pyogenes. Designated as Rop loci (regulation of proteinase), ropB is a rgg-like transcriptional activator required for transcription of the gene which encodes the proteinase. In contrast, ropA contributes post-transcriptionally to the secretion and processing of SCP and encodes a homologue of Trigger Factor, a peptidyl-prolyl isomerase and putative chaparone which is highly conserved in most bacterial species, but of unknown function. Analysis of additional ropA mutants demonstrated that RopA acts both to assist in targeting SCP to the secretory pathway and to promote the ability of the proprotein to establish an active conformation upon secretion. This latter function was dependent upon the peptidyl-prolyl isomerase domain of RopA and mutants that lacked this domain exhibited a bipartite deficiency manifested as a kinetic defect in autologous processing of the proprotein to the mature proteinase, and as a catalytic defect in the mature proteinase. These results provide insight into the function of Trigger Factor, the regulation of proteinase activity and the mechanism of secretion in Gram-positive bacteria.

Amino Acid Sequence

Mechanical debulking versus balloon angioplasty for the treatment of diffuse in-stent restenosis.

Previous studies have shown a high rate of repeat intervention after treating diffuse in-stent restenosis with percutaneous transluminal coronary angioplasty (PTCA) alone. It is not clear whether debulking with atherectomy is more effective in this condition. Between January 1994 and February 1997, we treated 60 consecutive patients with diffuse in-stent restenosis of a native coronary artery using conventional PTCA (n=30) or debulking (with rotational or directional atherectomy) plus adjunctive PTCA (n=30). Paired angiograms were analyzed by quantitative angiography, and clinical follow-up was obtained in all patients at 1 month, 6 months, and 1 year after revascularization. The mean lesion lengths were 13.5+/-8.3 and 18.4+/-13.2 mm in the debulking and PTCA groups, respectively (p=0.09). Acute procedural success was 100% in both cohorts, with no major complications in either group. Treatment with atherectomy plus adjunctive PTCA resulted in lower postprocedure stenoses (18+/-10 vs 26+/-13%, p=0.01) than treatment with balloon angioplasty alone. At 1-year follow-up, repeat target vessel revascularization was required in 28% of patients in the debulking group compared with 46% in the PTCA group (p=0.18). Independent predictors of the need for repeat target vessel revascularization were longer lesion lengths, diabetes mellitus, and smaller postprocedure lumen diameter. Thus, the strategy of atherectomy and adjunctive PTCA for diffuse in-stent restenosis is safe, improves acute angiographic results compared with PTCA alone, and may decrease the need for target vessel revascularization.

Angioplasty, Balloon, Coronary

Coronary artery injection technique: a quantitative in vivo investigation using modern catheters.

To date, there have been no quantitative in vivo assessments of contrast volumes and injection rates using modern high flow catheters during coronary angiography. Contrast volumes (n = 554), injection durations (n = 563), and injection rates (n = 498) were collected during 88 cardiac catheterizations. With increasing cathetersize (6, 7, and 8 French), injection volume increased (P < 0.0001), duration decreased (P < 0.0001), and rate increased (P < 0.0001). Compared with injections into the right coronary artery, left coronary artery injections were larger (7.1 +/- 0.1 cc vs. 4.8 +/- 0.1 cc, p < 0.0001), longer (3.6 +/- 0.05 sec vs 3.0 +/- 0.07 sec, P < 0.0001) and faster (2.1 +/- 0.04 cc/sec vs. 1.7 +/- 0.06 cc/sec, P < 0.0001). Patients with a significant stenosis in the left main or proximal right coronary artery received less contrast (P < 0.0001) more slowly (P < 0.0001) over a similar duration of injection (P = NS). When collaterals arose from the injected artery, angiographers injected more contrast (P < 0.001) over a longer period (P < 0.0001) more slowly (P < 0.0001). Catheter size and the injected vessel's location and anatomy significantly affect coronary catheterization injection technique.

Angioplasty, Balloon, Coronary

Thrombolysis in Myocardial Infarction frame count in saphenous vein grafts.

BACKGROUND: Although the Thrombolysis in Myocardial Infarction flow grade system is a widely used index of coronary blood flow, it has important limitations. We recently described a new continuous measure of blood flow in native coronary arteries, the Thrombolysis in Myocardial Infarction frame count (TFC), and sought to extend this method to coronary artery bypass grafts. METHODS: We retrospectively analyzed cinefilms of patients' status after coronary artery bypass grafting, excluding patients with recent myocardial infarction and grafts with stenoses in the graft or native vessel. We counted the cineframes required for dye to travel from the ostium of the graft to the graft anastomotic site (TFCg) and to a standardized distal coronary landmark (TFC). RESULTS: For all vein grafts combined, TFCg was 19.2+/-5.7 frames (mean+/-SD, n = 93) and the TFC was 33.9+/-8.0 frames (n = 67). The upper limits for "normal" flow, calculated from the 95% confidence intervals, were 31 frames for TFCg and 50 frames for TFC. CONCLUSIONS: The Thrombolysis in Myocardial Infarction frame counting method has now been extended to normal saphenous vein grafts, and normal reference values are provided.

Cardiac Catheterization

Six-month angiographic and clinical follow-up of patients prospectively randomized to receive either tirofiban or placebo during angioplasty in the RESTORE trial. Randomized Efficacy Study of Tirofiban for Outcomes and Restenosis.

OBJECTIVES: This study sought to investigate the effects of tirofiban versus placebo on the incidence of adverse cardiac outcomes and coronary artery restenosis at 6 months. BACKGROUND: Tirofiban is a highly selective, short-acting inhibitor of fibrinogen binding to platelet glycoprotein IIb/IIIa. In a recent clinical study, tirofiban reduced the incidence of adverse cardiovascular events at both 2 and 7 days after coronary angioplasty or directional coronary atherectomy. This reduction persisted but was no longer statistically significant at 30 days. METHODS: The Randomized Efficacy Study of Tirofiban for Outcomes and Restenosis (RESTORE) trial was a randomized, double-blind, placebo-controlled trial of tirofiban in patients undergoing balloon angioplasty or directional atherectomy within 72 h of presentation with either unstable angina pectoris or acute myocardial infarction. All patients received an initial bolus (10 microg/kg body weight over 3 min), followed by a 36-h infusion (0.15 microg/kg per min) of either tirofiban or placebo. RESULTS: At 6 months the composite end point (either death from any cause, new myocardial infarction, bypass surgery for angioplasty failure or recurrent ischemia, repeat target vessel angioplasty or stent insertion for actual or threatened abrupt closure) occurred in 1,070 placebo group patients (27.1%) and 1,071 tirofiban group patients (24.1%, p = 0.11). Analysis of 6-month coronary arteriograms by means of quantitative coronary arteriography showed no significant difference between placebo- and tirofiban-treated patients in either the incidence of a > or =50% diameter stenosis (57% vs. 51%, p = NS), a loss of > or =50% of lumen diameter gained (50% vs. 50%, p = NS) or a loss of > or =0.72 mm of lumen diameter (44% vs. 42%, p = NS). CONCLUSIONS: The 3% absolute reduction in the incidence of the composite end point at 6 months (27.1% placebo vs. 24.1% tirofiban) was similar to that previously reported at 2 days (8.7% vs. 5.4%, p < 0.005), and there does not appear to be any late effect of tirofiban on clinical end points between day 2 and 6 months. Tirofiban did not reduce the incidence of restenosis at 6 months when defined in a number of ways.

Adult

Mechanical debulking versus balloon angioplasty for the treatment of true bifurcation lesions.

OBJECTIVES: The purpose of this study was to compare the immediate angiographic and long-term results of debulking versus balloon angioplasty for treatment of true bifurcation lesions. BACKGROUND: Previous studies have shown true bifurcation lesions to be a high risk morphological subset for percutaneous transluminal coronary angioplasty (PTCA). Although atherectomy devices have been used to treat bifurcation lesions, no studies have compared the outcomes of these alternative treatment modalities. METHODS: Between January 1992 and May 1997, we treated 70 consecutive patients with true bifurcation lesions (defined as a greater than 50% stenosis in both the parent vessel and contiguous side branch) with conventional PTCA (n = 30) or debulking (with rotational or directional atherectomy) plus adjunctive PTCA (n = 40). Paired angiograms were analyzed by quantitative angiography, and clinical follow-up was obtained in all patients. RESULTS: Acute procedural success was 73% in the PTCA group and 97% in the debulking group (p = 0.01). Major in-hospital complications occurred in two patients in the PTCA group and one in the debulking group. Treatment with atherectomy plus PTCA resulted in lower postprocedure residual stenoses than PTCA alone (16+/-15% vs. 33+/-17% in the parent vessel, and 6+/-15% vs. 39+/-22% in the side branch; p < 0.001 for both comparisons). At 1 year follow-up, the incidence of target vessel revascularization (TVR) was 53% in the PTCA group as compared with 28% in the debulking group (p = 0.05). Independent predictors of the need for repeat TVR were side branch diameter >2.3 mm, longer lesion lengths, and treatment with PTCA alone. CONCLUSIONS: For the treatment of true bifurcation lesions, atherectomy with adjunctive PTCA is safe, improves acute angiographic results, and decreases target vessel revascularization compared to PTCA alone. The benefits of debulking for bifurcation lesions were especially seen in lesions involving large side branches.

Aged

Angioplasty guidewire velocity: a new simple method to calculate absolute coronary blood velocity and flow.

The Thrombolysis In Myocardial Infarction (TIMI) frame count is a relative index of coronary flow that measures time by counting the number of frames required for dye to travel from the ostium to a standardized coronary landmark in a cineangiogram filmed at a known speed (frames/s). We describe a new method to measure distance along arteries so that absolute velocity (length divided by time) and absolute flow (area x velocity) may be calculated in patients undergoing percutaneous transluminal coronary angiography (PTCA). After PTCA, the guidewire tip is placed at the coronary landmark and a Kelly clamp is placed on the guidewire where it exits the Y-adapter. The guidewire tip is then withdrawn to the catheter tip and a second Kelly clamp is placed on the wire where it exits the Y-adapter. The distance between the 2 Kelly clamps outside the body is the distance between the catheter tip and the anatomic landmark inside the body. Velocity (cm/s) may be calculated as this distance (cm) divided by TIMI frame count (frames) x film frame speed (frames/s). Flow (ml/s) may be calculated by multiplying this velocity (cm/s) and the mean cross-sectional lumen area (cm2) along the length of the artery to the TIMI landmark. In 30 patients, velocity increased from 13.9 +/- 8.5 cm/s before to 22.8 +/- 9.3 cm/s after PTCA (p <0.001). Despite TIMI grade 3 flow both before and after PTCA in 18 patients, velocity actually increased 38%, from 17.0 +/- 5.4 to 23.5 +/- 9.0 cm/s (p = 0.01). For all 30 patients, flow doubled from 0.6 +/- 0.4 ml/s before to 1.2 +/- 0.6 ml/s after PTCA (p <0.001). In the 18 patients with TIMI grade 3 flow both before and after PTCA, flow increased 86%, from 0.7 +/- 0.3 to 1.3 +/- 0.6 ml/s (p = 0.001). Distance along coronary arteries (length) can be simply measured using a PTCA guidewire. This length may be combined with the TIMI frame count to calculate measures of absolute velocity and flow that are sensitive to changes in perfusion. TIMI grade 3 flow is composed of a range of velocities and flows.

Angioplasty, Balloon, Coronary

Rescue angioplasty in the thrombolysis in myocardial infarction (TIMI) 4 trial.

Rescue percutaneous transluminal coronary angioplasty (PTCA) has been used to establish reperfusion after failed thrombolysis, and the goal of this study was to examine the angiographic and clinical outcomes after rescue PTCA performed for an occluded artery 90 minutes after thrombolysis. Four hundred two patients with acute myocardial infarction were randomized to receive either anistreplase (APSAC), recombinant tissue plasminogen activator, or their combination in the Thrombolysis in Myocardial Infarction (TIMI) 4 trial. The angiographic and clinical outcomes of patients with a patent artery 90 minutes after thrombolysis were compared with those of patients with an occluded artery treated in a nonrandomized fashion with either rescue or no rescue PTCA. At 90 minutes, the number of frames required to opacify standard landmarks (corrected TIMI frame count) was significantly lower (i.e., flow was faster) after successful rescue PTCA (27 +/- 11) than that in patent arteries after successful thrombolysis (39 +/- 20, p < 0.001), and the incidence of TIMI grade 3 flow was correspondingly higher after successful rescue PTCA (87% vs 65%, p = 0.002). In-hospital adverse outcomes (death, recurrent acute myocardial infarction, severe congestive heart failure, cardiogenic shock or an ejection fraction <40%) occurred in 29% of successful rescue PTCAs and in 83% of failed rescue PTCAs (p = 0.01). Among all patients in whom rescue PTCA was performed (successes and failures combined), 35% of patients experienced an adverse outcome, which was the same as the 35% incidence observed in patients not undergoing rescue PTCA (p = NS) and tended to be higher than the 23% incidence observed in patients with patent arteries (p = 0.07). Although successful rescue PTCA for an occluded artery at 90 minutes results in restoration of flow that is superior to that of successful thrombolysis, the incidence of adverse events for the strategy of rescue PTCA as a whole was the same as that of undertaking no PTCA.

Age Factors

TNK-tissue plasminogen activator in acute myocardial infarction. Results of the Thrombolysis in Myocardial Infarction (TIMI) 10A dose-ranging trial.

BACKGROUND: TNK-tissue plasminogen activator (TNK-TPA) is a genetically engineered variant of TPA, which in experimental models has a slower plasma clearance and greater fibrin specificity and is 80-fold more resistant to plasminogen activator inhibitor-1 than alteplase TPA. METHODS AND RESULTS: The thrombolysis in Myocardial Infarction (TIMI) 10A trial was a Phase 1, dose-ranging pilot trial designed to evaluate the pharmacokinetics, safety, and efficacy of TNK-TPA in patients with acute myocardial infarction. One hundred thirteen patients with acute ST-segment elevation myocardial infarction presenting within 12 hours and without contraindications to thrombolysis were enrolled and treated with a single bolus of TNK-TPA over 5 to 10 seconds with doses ranging from 5 to 50 mg. TNK-TPA demonstrated a plasma clearance of 151 +/- 55 mL/min and a half-life of 17 +/- 7 minutes. Comparable values for wild-type TPA are 572 +/- 132 mL/min and 3.5 +/- 1.4 minutes, respectively. Systemic fibrinogen and plasminogen levels fell by only 3% and 13%, respectively, at 1 hour after TNK-TPA administration. TIMI grade 3 flow at 90 minutes was achieved in 57% to 64% of patients at the 30- to 50-mg doses. Seven patients (6.2%) experienced a major hemorrhage, which occurred at a vascular access site in six patients. CONCLUSIONS: TNK-TPA has a prolonged half-life so it can be administered as a single bolus. TNK-TPA appears to be very fibrin specific, and the initial patency and safety profiles are encouraging. Further study of this new thrombolytic agent is ongoing.

Adult

Myoglobin, creatine kinase MB, and cardiac troponin-I to assess reperfusion after thrombolysis for acute myocardial infarction: results from TIMI 10A.

BACKGROUND: The availability of a reliable, noninvasive serum marker of reperfusion may permit early identification of patients with occlusion after thrombolysis who might benefit from further interventions. METHODS: We measured myoglobin, creatine kinase MB (CK-MB), and cardiac troponin-I (cTnI) concentrations in sera obtained just before thrombolysis (T0) and 60 minutes later (T60) in 30 patients given TNK-tPA for acute myocardial infarction as part of the Thrombolysis in Myocardial Infarction (TIMI) 10A trial. RESULTS: Angiography at T60 showed reperfusion (TIMI flow grade 2 to 3; n = 19) or occlusion (TIMI flow grade 0 to 1; n = 8). The median serum T60 concentration, the ratio of the T60 and T0 serum concentration, and the slope of increase over a 60-minute period for each serum marker were significantly higher in patients with patent arteries compared with patients with occluded arteries. The areas under the receiver operator characteristics curve for diagnosis of occlusion were 0.96, 0.91, and 0.87 for the T60 concentration of myoglobin, CK-MB and cTnI, respectively. Although the T60 levels of <469 ng/ml for myoglobin, <11.5 ng/ml for CK-MB, and < 1.1 ng/ml for cTnI identified all patients with occlusion, the specificity of myoglobin (94%) was higher than that of CK-MB (61%) and cTnI (67%). Similar results were obtained for the 60-minute ratios and 60-minute slopes for each marker, with indexes for myoglobin having the highest specificity. CONCLUSIONS: In this pilot study, noninvasive diagnosis of occlusion 60 minutes after thrombolysis was achieved with a high degree of sensitivity and specificity with the myoglobin, CK-MB, and cTnI concentrations measured at that time point. These preliminary findings may permit a new strategy for assessment of the success of reperfusion, with triage to rescue angioplasty for patients in whom the 60-minute cardiac marker values or indexes are consistent with occlusion of the infarct-related artery.

Adult

Relation between injections before 90-minute angiography and coronary patency: results of the thrombolysis in myocardial infarction 4 trial.

The current goal of thrombolytic therapy is to achieve both full (Thrombolysis in Myocardial Infarction [TIMI] grade 3) and early reperfusion. Newer reperfusion strategies may now achieve a high degree of reperfusion even earlier than the traditional 90-minute end point. To determine whether injections before 90 minutes affect this traditional end point, the relation between the number of injections before 90-minute angiography and patency was examined in the TIMI 4 trial. The number of injections before 90-minute angiography was no different between occluded arteries (TIMI grade 0/1 flow) (2.46 +/- 1.78; n = 94) and patent arteries (TIMI grade 2/3 flow) (2.71 +/- 2.42; n = 295) (p = 0.24). The incidence of any injections before 90 minutes was no different in patent versus closed arteries (80.6% [77/98] vs 72.4% [22/304]; p = 0.10). The number of injections before 90 minutes was insignificantly smaller in patients with TIMI grade 3 flow (2.53 +/- 2.53 [n = 184] vs 2.76 +/- 2.03 [n = 204]; p = 0.31), but the incidence of any injections before 90 minutes was significantly smaller in patients with TIMI grade 3 flow (68.8% [132/192] vs 79.5% [167/210]; p = 0.01). No relation was identified between the number of injections before 90-minute angiography and patency at this traditional time point. This observation justifies the judicious use of a limited number of "earlier snapshots" of the infarct-related artery before 90 minutes to ascertain just how rapidly newer thrombolytic regimens achieve patency. Patients with TIMI grade 3 flow had a slightly lower incidence of injections before 90 minutes, perhaps because they did not require as urgent a definition of coronary anatomy.

Aged

Effect of combination therapy with lipid-reducing drugs in patients with coronary heart disease and "normal" cholesterol levels. A randomized, placebo-controlled trial. Harvard Atherosclerosis Reversibility Project (HARP) Study Group.

BACKGROUND: Combination drug therapy has been shown to decrease cholesterol levels in hyperlipidemic patients. However, its efficacy has not been well studied in patients previously considered to be normolipidemic, many of whom are now candidates for this therapy. OBJECTIVE: To determine the efficacy and tolerability of multidrug therapy designed to improve low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels in patients with coronary heart disease and average lipid levels. DESIGN: Randomized, placebo-controlled, 2.5-year trial comparing patients receiving usual care with patients receiving stepped-care drug therapy. INTERVENTION: Stepped-care therapy (pravastatin, nicotinic acid, cholestyramine, and gemfibrozil) to decrease total cholesterol levels to less than 4.1 mmol/L (160 mg/dL) and the ratio of LDL cholesterol to HDL cholesterol to less than 2.0. SETTING: 2 academic, urban, tertiary care hospitals. PATIENTS: 91 patients (80 men and 11 women) with coronary heart disease, a mean age of 60 years, total cholesterol levels less than 6.4 mmol/L (250 mg/dL) at baseline, and ratios of total cholesterol to HDL cholesterol greater than 4.0 at baseline. MEASUREMENTS: Fasting serum lipoprotein profile, fasting apolipoprotein levels, and frequency of adverse effects. Patients were assessed every 6 weeks during drug titration and every 3 months thereafter. RESULTS: Mean lipid levels at baseline were as follows: total cholesterol, 5.5 mmol/L (214 mg/dL); LDL cholesterol, 3.6 mmol/L (140 mg/dL); HDL cholesterol, 1.1 mmol/L (42 mg/dL); and triglycerides, 1.8 mmol/L (159 mg/dL). With pravastatin, changes in levels from baseline were -22% for total cholesterol, -32% for LDL cholesterol +8% for HDL cholesterol, and -15% for triglycerides (P < 0.001 for all comparisons). With the addition of 1.5 g of nicotinic acid, additional changes were -6% for total cholesterol (P < 0.002). -11% for LDL cholesterol, +8% for HDL cholesterol, and -10% for triglycerides (P < 0.001 for all comparisons). With 2.25 to 3 g of nicotinic acid, these changes were -7% for total cholesterol (P = 0.007), -14% for LDL cholesterol (P < 0.001), +6% for HDL cholesterol (P = 0.02), and -13% for triglycerides (P = 0.03). With cholestyramine, total cholesterol and LDL cholesterol levels were unchanged compared with the previous step; the change in HDL cholesterol level was -8% (P = 0.03); and the change in triglyceride level was +46% (P < 0.001). With gemfibrozil, total cholesterol level was unchanged; the additional change in LDL cholesterol level was +12% (P = 0.09); the change in HDL cholesterol level was +12% (P = 0.03); and the change in triglyceride level was -37% (P < 0.001). Apolipoprotein B levels decreased by 25% overall (P < 0.001); lipoprotein(a) levels did not change significantly. Adverse effects were primarily attributable to nicotinic acid or cholestyramine. In 18 of the 35 patients (50%) whose baseline LDL cholesterol levels were greater than 3.35 mmol/L (130 mg/dL), pravastatin decreased LDL cholesterol levels to 2.6 mmol/L (100 mg/dL) or less by 6 weeks; 70% of patients needed combination therapy to reach this National Cholesterol Education Program goal during the 2.5 years of the study. Adding nicotinic acid to pravastatin produced LDL cholesterol levels of 2.6 mmol/L or less in 15 more of these 35 patients, so that 94% (n = 33) of the patients receiving these two drugs reached this goal. CONCLUSIONS: To reach current goals for LDL cholesterol levels, most normolipidemic patients with coronary heart disease in this study needed combination therapy. Pravastatin with nicotinic acid and pravastatin with gemfibrozil are well-tolerated combinations that can maintain target LDL cholesterol levels, decrease triglyceride levels, and increase HDL cholesterol levels. Adding resin to these combinations produced no further benefit.

Algorithms

TIMI frame count: a quantitative method of assessing coronary artery flow.

BACKGROUND: Although the Thrombolysis in Myocardial Infarction (TIMI) flow grade is valuable and widely used qualitative measure in angiographic trials, it is limited by its subjective and categorical nature. METHODS AND RESULTS: In normal patients and patients with acute myocardial infarction (MI) (TIMI 4), the number of cineframes needed for dye to reach standardized distal landmarks was counted to objectively assess an index of coronary blood flow as a continuous variable. The TIMI frame-counting method was reproducible (mean absolute difference between two injections, 4.7 +/- 3.9 frames, n=85). In 78 consecutive normal arteries, the left anterior descending coronary artery (LAD) TIMI frame count (36.2 +/- 2.6 frames) was 1.7 times longer than the mean of the right coronary artery (20.4 +/- 3.0) and circumflex counts (22.2 +/- 4.1, P < .001 for either versus LAD). Therefore, the longer LAD frame counts were corrected by dividing by 1.7 to derive the corrected TIMI frame count (CTFC). The mean CTFC in culprit arteries 90 minutes after thrombolytic administration followed a continuous unimodal distribution (there were not subpopulations of slow and fast flow) with a mean value of 39.2 +/- 20.0 frames, which improved to 31.7 +/- 12.9 frames by 18 to 36 hours (P < .001). No correlation existed between improvements in CTFCs and changes in minimum lumen diameter (r=-.05, P=.59). The mean 90-minute CTFC among nonculprit arteries (25.5 +/- 9.8) was significantly higher (flow was slower) compared with arteries with normal flow in the absence of acute MI (21.0 +/- 3.1, P < .001) but improved to that of normal arteries by 1 day after thrombolysis (21.7 +/- 7.1, P=NS). CONCLUSIONS: The CTFC is a simple, reproducible, objective and quantitative index of coronary flow that allows standardization of TIMI flow grades and facilitates comparisons of angiographic end points between trials. Disordered resistance vessel function may account in part for reductions in flow in the early hours after thrombolysis.

Blood Flow Velocity

Involvement of S2 episomal sequences in the generation of NCS4 deletion mutation in maize mitochondria.

Cytoplasmic male sterility (CMS) and the abnormal-growth, nochromosomal stripe (NCS) phenotypes are cytoplasmically determined traits in plants. Mitochondrial DNA rearrangements involving short repeats appear to be responsible for the production of CMS reversions to fertility and NCS mutations. NCS4, a new mutant of maize CMS-S, exhibits both abnormal growth and male fertility. This mutant is unique because both mutations occurred within the same plant. Free S1 and S2 episomes normally found in CMS-S mitochondria have been lost from NCS4 plants. An S2 sequence has recombined aberrantly with a ribosomal protein coding region, rps3/rpl16. One end of the S2 sequence and the 5' end of the rps3/rpl16 transcription unit are absent from the NCS4 recombinant genome. Loss of mitochondrial ribosomal protein function is lethal; therefore, NCS4 plants are heteroplasmic for the rps3 deletion. Loss of S sequences from CMS-S mitochondria is not lethal and plants regain pollen function. Thus, although NCS4 plants have very abnormal plant phenotypes, they are male-fertile.

Base Sequence

Insertional inactivation of Streptococcus pyogenes sod suggests that prtF is regulated in response to a superoxide signal.

In establishing an infection, Streptococcus pyogenes has the capacity to bind to the host extracellular matrix protein fibronectin via its protein F adhesin. Previous studies have suggested that the expression of protein F is stimulated during aerobic growth or upon addition of superoxide-generating agents to the culture under O2-limited conditions. To further explore the role of superoxide, we have examined the transcription of the gene which encodes protein F (prtF), as well as the expression of superoxide dismutase (SOD) under conditions which promote or repress protein F expression. These studies show that prtF transcription is regulated in response to superoxide concentration and that SOD is regulated in different environments in a manner which directly parallels the expression of protein F. A mutant deficient in SOD activity was constructed by insertional mutation into the gene which encodes SOD (sod). The resulting mutant was sensitive to superoxide and aerobic conditions, showed hypersensitive induction of prtF in response to superoxide, and expressed prtF under normally unfavorable O2-limited conditions. These findings suggest that a streptococcal signal transduction system which senses superoxide may coordinately control expression of prtF and sod.

Adhesins, Bacterial

The influence of pretreatment low density lipoprotein cholesterol concentrations on the effect of hypocholesterolemic therapy on coronary atherosclerosis in angiographic trials. Harvard Atherosclerosis Reversibility Project Research Group.

Angiographic trials of coronary atherosclerosis treatment have demonstrated that lowering low density lipoprotein (LDL) cholesterol concentrations improves coronary artery stenosis. Most patients in previous trials have had at least mildly elevated LDL. Recently, however, the Harvard Atherosclerosis Reversibility Project (HARP) did not find such benefit in patients with lower baseline LDL levels compared with previous trials. We reviewed and analyzed all cholesterol-lowering trials that used angiographic endpoints. Unifactorial trials of hypocholesterolemic dietary or drug therapy demonstrated that the higher the baseline LDL, the greater the improvement in quantitatively determined stenosis in the treatment group compared with the controls (r = .83). Considering the change in stenosis in the treatment group alone, regression was more common in trials in which baseline mean LDL was > 170 mg/dl (> 4.4 mmol/liter), whereas progression occurred when baseline mean LDL was < 170 mg/dl (< 4.4 mmol/liter). HARP had the lowest baseline LDL (137 mg/dl [3.54 mmol/liter]), and showed no tendency for improvement in lesions. In contrast to the influence of baseline LDL levels, neither a low LDL level achieved on treatment nor a large percentage reduction in LDL was related to improvement in lesions. Sample size differences between HARP and the other trials are unlikely to be a major explanatory factor, since trials of comparable sample size to HARP, but with higher initial LDL, demonstrated favorable results. We conclude that coronary lesions that develop in the context of average LDL levels show less angiographic improvement in response to substantial LDL reduction than lesions in hypercholesterolemic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Angiographic predictors of reocclusion after thrombolysis: results from the Thrombolysis in Myocardial Infarction (TIMI) 4 trial.

OBJECTIVES: This study attempted to determine which lesion characteristics are associated with reocclusion by 18 to 36 h. BACKGROUND: Reocclusion of the infarct-related artery after successful reperfusion is associated with significant morbidity and up to a threefold increase in mortality. METHODS: Two hundred seventy-eight patients with acute myocardial infarction were randomized to receive either anisoylated plasminogen streptokinase activator complex (APSAC) or recombinant tissue-type plasminogen activator (rt-PA) or their combination. Culprit arteries were assessed for Thrombolysis in Myocardial Infarction (TIMI) flow grade, lesion ulceration, thrombus, collateral circulation and eccentricity. Minimal lumen diameter, percent diameter stenosis and lesion irregularity (power) were calculated using quantitative angiography. RESULTS: Reocclusion was observed more frequently in arteries with TIMI 2 versus TIMI 3 flow (10.4% vs. 2.2%, p = 0.003), in ulcerated lesions (10.7% vs. 3.0%, p = 0.009) and in the presence of collateral vessels (18.2% vs. 5.6%, p = 0.03). Similar trends were observed for eccentric (7.3% vs. 2.3%, p = 0.06) and thrombotic (8.4% vs. 3.3%, p = 0.06) lesions. Reocclusion was associated with more severe mean percent stenosis (77.9% vs. 73.9%, p = 0.04). Lesion length, reference segment diameter and Fourier measures of lesion irregularity were not associated with reocclusion. CONCLUSIONS: Several simply assessed angiographic variables, such as the presence of TIMI grade 2 flow, ulceration, collateral vessels and greater percent diameter stenosis at 90 min after thrombolytic therapy, are associated with significantly higher rates of infarct-related artery reocclusion by 18 to 36 h and may aid in identifying the subset of patients who are at significantly higher risk of early reocclusion and who potentially warrant further early pharmacologic or mechanical intervention.

Adult