Incidence and treatment of 'no-reflow' after percutaneous coronary intervention

BACKGROUND

Profound reduction in antegrade epicardial coronary flow with concomitant ischemia is seen occasionally during percutaneous coronary intervention despite the absence of evident vessel dissection, obstruction, or distal vessel embolic cutoff. In a prior small series of cases, this "no-reflow" phenomenon appeared to be promptly reversed by the intra-coronary administration of verapamil.

METHODS AND RESULTS

To further understand the prevalence of this syndrome and its responsiveness to the proposed therapy, we reviewed 1919 percutaneous interventions performed between January 1991 and April 1993. During the study period, 39 patients (2.0%) met our criteria for no reflow, 37 of whom were treated with intracoronary nitroglycerin followed by intracoronary verapamil and 2 of whom received intracoronary nitroglycerin alone. An additional 16 patients (0.8%) were given verapamil as part of the management of a flow-limiting dissection or distal embolus (mechanical obstruction). Intracoronary verapamil (50 to 900 micrograms, total dose) improved TIMI flow grade in 89% of no-reflow patients and markedly reduced the number of cineframes between contrast injection and opacification of a selected distal landmark (from 91 +/- 56 to 38 +/- 21 frames, P < .001). By contrast, only 19% of patients with epicardial mechanical obstruction showed improvement in TIMI flow grade after verapamil, with minimal reduction in frames to opacification (from 107 +/- 42 to 101 +/- 69, P = .73).

CONCLUSIONS

The no-reflow phenomenon--reduction in distal flow without apparent dissection or distal embolization--occurs in 2% of coronary interventions. It generally responds promptly to intracoronary verapamil administration, suggesting that distal microvascular spasm may be its etiology.

The identification of rofA, a positive-acting regulatory component of prtF expression: use of an m gamma delta-based shuttle mutagenesis strategy in Streptococcus pyogenes

Binding of the Gram-positive pathogenic bacterium Streptococcus pyogenes (group A streptococcus) to respiratory epithelium is mediated by the fibronectin-binding adhesin, protein F. Most strains of streptococci regulate the expression of protein F in response to oxygen levels and redox potential; however, JRS4 constitutively binds high levels of fibronectin under all environmental conditions. In this study, we have examined the regulation of protein F expression in JRS4 using a shuttle mutagenesis strategy novel to S. pyogenes. Cloned DNA representing the chromosomal loci adjacent to the gene which encodes protein F (prtF) was subjected to transposon mutagenesis in Escherichia coli using a derivative of transposon m gamma delta that was modified to contain a streptococcal antibiotic-resistance gene. mutagenized DNA was then returned to the streptococcal chromosome by allelic replacement. Analysis of the resulting fibronectin-binding phenotypes revealed that insertions in a region upstream of prtF abolished the constitutive phenotype. However, these mutants now demonstrated regulation in response to both oxygen levels and redox potential. Because these insertions define a locus responsible for the constitutive phenotype, it has been designated rofA (regulator of F). Chromosomal interruption studies using integrational plasmids together with complementation data from a previous study (VanHeyningen et al., 1993) suggested that rofA acts as a positive trans-acting regulator of prtF. Construction of prtF-lacZ fusions indicated that transcription of prtF is constitutive in JRS4 but is regulated in rofA mutants. Analysis of the DNA sequence defined by the rofA insertions revealed a 1495 bp open reading frame, whose predicted product (RofA) possessed both a putative helix-turn-helix motif and limited homology to two other transcriptional activators (Mry, PrgR) of Gram-positive surface proteins. Sequences homologous to rofA were found in regulated strains of S. pyogenes, which suggests that rofA may act as an activator of prtF in response to an unidentified environmental signal. We speculate that the allele reported here contains a mutation that renders it constitutively active.

Natural history of coronary atherosclerosis using quantitative angiography in men, and implications for clinical trials of coronary regression. The Harvard Atherosclerosis Reversibility Project Study Group

Previous studies of the natural history of coronary disease generally relied on estimates of percent stenosis derived from visual assessment of the coronary angiogram. In a study of 26 patients, serial quantitative angiography was performed 3 years apart to determine changes in both absolute measurements of the luminal diameter and relative percent stenosis. Initially, the mean minimal diameter of 74 coronary obstructions was 1.94 +/- 0.09 mm, the mean "normal" reference diameter was 3.06 +/- 0.11 mm, and the mean percent stenosis was 37%. At follow-up, there was a mild reduction of 0.12 +/- 0.04 mm (6%) in the minimal diameter (p < 0.005), and an increase in percent stenosis to 39% (p = 0.03). The average diameter of 85 arterial segments without a focal obstruction either initially or at follow-up showed mild but significant progression (-0.11 +/- 0.04 mm; p = 0.02). Using a minimal change of 0.27 mm in arterial diameter as a categoric variable, progression occurred in 26% of 74 arterial segments, no significant change in 65%, and regression in 9%. The only significant determinant of disease progression was the initial severity of disease. Obstructed arteries with a larger initial minimal diameter and presumably milder disease progressed more rapidly than did those with a smaller diameter (r = -0.42; p = 0.0002). There was no effect of age on the rate of progression (r = 0.02; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of restenosis and redilation within coronary stents--quantitative angiographic assessment

OBJECTIVES

This study was designed to assess the relative contributions of intimal hyperplasia and stent compression to the lumen narrowing seen after intracoronary stenting and to determine whether the lumen enlargement produced by angioplasty of in-stent restenosis results primarily from compression or extrusion of intimal hyperplasia through the stent or from additional stent expansion.

BACKGROUND

Palmaz-Schatz stent placement outwardly displaces plaque and eliminates elastic vessel recoil to provide a large and smooth lumen. Some degree of late lumen narrowing occurs within each stent and causes significant restenosis (> or = 50% stenosis) in 25% to 30% of treated lesions. It has not been clear, however, whether this narrowing results from stent compression (crush) or from in-stent intimal hyperplasia. Because the Palmaz-Schatz stent has a distinct radiographic shadow, it is possible to determine the late diameter of both the stent and the enclosed vessel lumen to assess the relative contributions of these two processes.

METHODS

From cineangiograms, initial (after stenting) and late (follow-up) lumen and stent diameters were examined in 55 patients (59 stents, group I) who had both immediate and 6-month (192 +/- 117 days) angiography. Lumen and stent diameter were also examined before and after dilation in 30 patients (30 stents, group II) who underwent angioplasty of severe in-stent restenosis.

RESULTS

Late loss in minimal lumen diameter was 0.99 +/- 0.87 mm for group I despite only a slight (0.03 +/- 0.23-mm) reduction in the corresponding stent diameter. After redilation for in-stent restenosis, the acute gain in minimal lumen diameter was 1.51 +/- 0.82 mm for group II, again without appreciable increase (0.06 +/- 0.20 mm) in stent diameter.

CONCLUSIONS

Restenosis after intracoronary Palmaz-Schatz stenting appears to be due predominantly to lumen encroachment by intimal hyperplasia within the stent, with minimal contribution of stent compression. Lumen enlargement after coronary angioplasty of in-stent restenosis appears to be due primarily to compression or extrusion of intimal hyperplasia through the stent, or both, rather than to further stent expansion.

Lesion-to-lesion independence of restenosis after treatment by conventional angioplasty, stenting, or directional atherectomy. Validation of lesion-based restenosis analysis

BACKGROUND

Since many restenosis trials include patients in whom more than one lesion is treated, analysis of the angiographic data on a "per lesion" basis might be confounded by potential correlations of restenosis among multiple treated lesions within each patient. The goals of this study were: 1) to determine whether there was any correlation in the rate of restenosis among multiple lesions that underwent conventional angioplasty, stenting, or directional atherectomy within the same patient and 2) to determine whether lesions treated in a multilesion intervention experience a different magnitude of restenosis than lesions undergoing single-lesion procedures.

METHODS AND RESULTS

Of 441 patients treated by Palmaz-Schatz stenting (n = 114), directional atherectomy (n = 100), or conventional balloon angioplasty (n = 227), 67 underwent multilesion procedures involving treatment of 146 lesions. A general linear model with intraclass correlation (GLIMIC) was used to calculate the coefficient of correlation (rho) of the change in the measured minimum luminal diameter (late loss) from the time of the initial procedure to 6-month angiogram among the multiple lesions within the same patient for all 441 patients. This showed no correlation among multiple lesions within the same patient for the late loss in minimum luminal diameter (rho = -0.12 [95% CI: -0.40, 0.12]), among lesions in the same vessel (rho = 0.14 [95% CI: -0.34, 0.62]), or among different vessels (rho = -0.18 [95% CI: -0.52, 0.16]), suggesting that the magnitude of late loss is independent among multiple lesions within the same patient. There was no difference (p = 0.96) between the observed incidence of zero-, one-, and two-vessel restenosis (> or = 50% diameter stenosis at follow-up) for patients with multiple-lesion treatment and that predicted assuming lesion-to-lesion independence. Similarly, there was no difference in late loss or in the overall binary restenosis rate when single-lesion procedures were compared with multilesion procedures. Multivariable analysis of the late loss in lumen diameter (which adjusted for the effects of the acute result and the device used) demonstrated no independent effect (p = 0.20) of single-lesion versus multilesion status.

CONCLUSIONS

Luminal encroachment appears to occur at independent rates among multiple lesions treated in a single patient. The observed incidence of restenosis for patients with multiple treated lesions is accurately predicted assuming independent probabilities of restenosis. Lesion-based analysis, even when including multiple treated lesions within the same patient, is thus valid for evaluating conventional angioplasty, stenting, or directional atherectomy.

Relation of vessel wall shear stress to atherosclerosis progression in human coronary arteries

The purpose of this study was to determine the relation between vessel wall shear stress and the rate of atherosclerosis progression. Quantitative angiography was used to calculate the change in coronary arterial diameter over 3.0 years in patients enrolled in the Harvard Atherosclerosis Reversibility Project pilot study (n = 20 arterial segments). Vessel wall shear stress was calculated by means of a validated finite-difference model of the Navier-Stokes' equation that assumes a coronary flow rate of 8 ml/sec. The correlation between vessel wall shear stress and the change in arterial diameter at multiple points (mean, 70) along the length of the artery was then calculated for each of the 20 segments with a focal stenosis. In 15 of the 20 arterial segments there was a significant correlation (p < 0.05) between low shear stress and an increased rate of atherosclerosis progression. A Fisher's z transformation was then used to combine the correlation coefficients from all 20 segments. Low shear stress was significantly correlated (z = 0.37 +/- 0.00074, p < 0.0001) with an increased rate of atherosclerosis progression. This serial quantitative evaluation of human coronary arteries is consistent with previous data that have suggested that low shear stress promotes atherosclerosis progression. Variations in local vessel wall shear stress may explain the previously reported near-independent rate of atherosclerosis progression in multiple lesions within the same patient despite exposure to the same circulating lipoprotein values and systemic hemodynamics.

Generalized model of restenosis after conventional balloon angioplasty, stenting and directional atherectomy

OBJECTIVES

This study was designed to extend the results of a quantitative model originally developed for restenosis after stenting or atherectomy to include restenosis after conventional balloon angioplasty.

BACKGROUND

We have previously described a continuous regression model that explains late (6-month) lumen narrowing as the difference between the immediate gain and the subsequent normally distributed late loss in lumen diameter after Palmaz-Schatz stenting or directional atherectomy.

METHODS

Lumen diameter was measured immediately before and after coronary intervention on 524 consecutive lesions including those treated by Palmaz-Schatz stenting (102), directional atherectomy (134) and conventional balloon angioplasty (288). Of these lesions, 475 (91%) underwent follow-up angiography 3 to 6 months after treatment. The immediate increase in lumen diameter produced by the intervention (immediate gain) and the subsequent reduction in lumen diameter between the time of intervention to follow-up angiography (late loss) were examined. Association between demographic or angiographic variables and continuous measures of restenosis (late lumen diameter or late percent stenosis) was tested with linear regression techniques; a traditional binary measure of restenosis (late diameter stenosis > or = 50%) was evaluated with logistic regression analysis.

RESULTS

Regression models relating late lumen diameter to the immediate lumen result were successfully fitted to all segments studied. According to these models, three indexes of restenosis (late lumen diameter, late percent stenosis and binary restenosis) were found to depend solely on the immediate lumen diameter after the procedure and the immediate residual percent stenosis, but not on the specific intervention used. Moreover, the late loss in lumen diameter was found to vary directly with the immediate gain provided by an intervention, and the "loss index" (a measure that corrects for differences in immediate gain) was uniform among all three interventions.

CONCLUSIONS

The quantitative model originally developed for restenosis after stenting or atherectomy may thus be generalized to include conventional balloon angioplasty. It shows that the apparent differences in restenosis among the three interventions studied are due solely to differences in the immediate result provided and not to differences in the behavior of subsequent late loss. Moreover, although the late loss in lumen diameter was found to correlate with differences in the immediate gain provided by an intervention, the "loss index" (a measure that corrects for differences in acute gain) was uniform across all three interventions. It is thus the immediate result (and not the procedure used to obtain that result) that determines late outcome after coronary intervention.

Angiographic and clinical outcome of intracoronary stenting: immediate and long-term results from a large single-center experience

OBJECTIVES

The purpose of this study was to determine the immediate and long-term angiographic and clinical results of coronary stenting.

BACKGROUND

Although preliminary trials of endovascular stenting have demonstrated promising results, lack of long-term follow-up has limited the critical evaluation of the role of coronary stenting in the treatment of obstructive coronary artery disease.

METHODS

A total of 250 procedures using the Palmaz-Schatz stent, performed in 220 patients between June 1988 and July 1991, were examined. Minimal lumen diameter of the treated segments was measured on angiograms obtained before, after and 6 months after intervention.

RESULTS

Stent placement was successful in 246 (98%) of 250 lesions, reducing diameter stenosis from 77% to -2.5%. There were no deaths or Q wave myocardial infarctions. One patient (0.4%) required emergency bypass surgery and one (0.4%) developed subacute thrombosis. Femoral vascular complications occurred in 36 patients (16%). Six-month angiographic follow-up was obtained in 91% of eligible patients. The overall angiographic restenosis rate (stenosis greater than or equal to 50%) was 25%. By univariable analysis, the rate of restenosis was significantly higher for stents in the left anterior descending versus the right coronary artery (44% vs. 12%; p = 0.002); in diabetic patients (56% vs. 20%; p = 0.006), and in vessels with post-stent lumen diameter less than 3.31 mm (34% vs. 16%; p = 0.05). Stenting of the left anterior descending artery was the strongest predictor (p = 0.01) of restenosis in a multivariable model. Total survival was 97% and event-free survival (freedom from death, myocardial infarction or revascularization) was 70% at 36 months.

CONCLUSIONS

Palmaz-Schatz stents can be placed successfully with a low incidence of major complications. The angiographic restenosis rate was 25%, and 70% of patients remained free of cardiovascular events at 3 years. Diabetes, small postprocedure lumen diameter and stenting of the left anterior descending artery are associated with higher rates of restenosis.

Quantitative angiographic and statistical methods to assess serial changes in coronary luminal diameter and implications for atherosclerosis regression trials

The purpose of this study was (1) to determine a threshold for categorizing individual coronary lesions as either significantly progressing or regressing, (2) to determine whether multiple lesions within individual patients progress at independent rates, and (3) to calculate sample sizes for atherosclerosis regression trials. Seventeen patients with 46 significant lesions (2.7 lesions/patient) underwent repeat coronary arteriography 3.0 years apart. With use of the standard error of the mean change in diameter from initial to repeat catheterization across 5 pairs of consecutive end-diastolic frames, individual lesions were categorized as either significantly (p less than 0.01) progressing or regressing if there was a 0.27 mm change in minimum diameter or a 7.8 percent point change in percent stenosis. The mean diameter change of a sample of lesions can also be analyzed as a continuous variable using either the lesions or the patient as the primary unit of analysis. A lesion-specific analysis can be accomplished using a multiple regression model that accounts for the intraclass correlation (rho) in the degree of change among multiple lesions within individual patients. The intraclass correlations in percent stenosis (rho = 0.01) and minimum diameter (rho = -0.24) were low, indicating that disease progression in different lesions within individual patients is nearly independent. With use of this model, 50 patients per treatment group would permit the detection of a 5.5% difference between treatment group means in the change in minimum diameter and a 2.7% percentage point (not percent) difference in the change in percent stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on cyclic erythropoiesis in mice

When young adult female W/Wv mice are given 0.5 micro+Ci 89Sr/g body weight intravenously, their hematocrit values oscillate from nadirs of 26% to zeniths of 42% with a periodicity of 16 days [1]. The response of the W/Wv mouse to an assortment of radioactive and hematologic stresses have been examined in an effort to understand better the pathophysiology of cyclic erythropoiesis. When the dose of 89Sr is increased, the amplitude of cycling increases as nadirs are lowered, but periodicity is unchanged. When the dose of 89Sr is lowered to 0.3 microCi or less, cyclic erythropoiesis of substantial amplitude is observed only after five or six microoscillations. A single hematopoietic insult of 80 rad x-irradiation coupled with phlebotomy produces a transient form of cyclic erythropoiesis, namely, a series of dampened oscillations prior to recovery. Finally, we report that Wv/Wv mice exhibit a form of cyclic erythropoiesis in response to 0.5 microCi 89Sr/g body weight, in which the hematocrit values of successive nadirs gradually increase, and stabilize at about 100 days. 89Sr does not induce cyclic erythropoiesis in the +/+, W/+, or W/v/+ mice, the Hertwig strain of anemic mice, or in normal BDF1 mice.

Cyclic erythropoiesis in the S1/S1d mouse

Previously we reported that when young adult female W/Wv mice are given 0.5 microCi strontium-89 per gram body weight IV, their hematocrit values oscillate from nadirs of 26% to zeniths of 42% with a periodicity of 16 days. We now report that a second strain of congenitally anemic female mice, the S1/ S1d , also exhibit large fluctuations in their hematocrit values following a dose of 0.5 microCi 89Sr/g body weight. The zeniths through which these mice cycled averaged 37% (range 35%-38%) and the nadirs averaged 13% (range 12%-14%). Reticulocytes fluctuated from highs averaging 40% (range 35%-45%) to lows that averaged 3% (range 1%-5%). The periodicity of cycling in these eight mice ranged from 16 to 19 days. The hematocrits of three out of five non-strontium-treated mice were found to cycle spontaneously in the absence of 89Sr-mediated hematopoietic insult, with nadirs averaging 22% and zeniths averaging 39%. Similarly, doses as small as 0.1 microCi 89Sr/g body weight coupled with antecedent phlebotomy induced cyclic erythropoiesis of substantial amplitude (average nadir 16% and average zenith of 39%). Splenectomy in the S1/ S1d mouse eliminates both spontaneous and 89Sr-induced cyclic erythropoiesis. If the spleen is removed prior to radiostrontium treatment, then cyclic erythropoiesis is not observed following a dose of 0.5 microCi 89Sr/g body weight.