Large multicenter evaluation of clinical outcomes of transcatheter aortic valve implantation in different age groups: results from the Israeli TAVI registry

Introduction

Transcatheter aortic valve implantation (TAVI) is becoming the preferred treatment for elderly patients with severe aortic stenosis. Clinical outcomes of these patients according to different age groups and especially in the very old population are under reported.

Purpose

To describe clinical characteristics at baseline, according to different age groups, and to compare clinical outcomes in the very old population with other patients undergoing the procedure.

Methods

Data was extracted from the Israeli National TAVI Registry. Clinical outcomes in very old patients (above the age of 90 years) were compared with younger patients. Multivariable analysis for 30-day and 1-year mortality were performed. Procedural complication was defined as one or more of the following: need for permanent pacemaker, major vascular complication, severe acute kidney injury and major stroke.

Results

A total of 5,936 patients who underwent TAVI from 2008 to 2021 were analyzed (age 81.6±7.1 years, 50.6% female). Patients older than 90 years of age had more comorbidities than the younger population (STS score for mortality 6.4%±3.8% vs. 4.1%±4.8%, p<0.001). Independent correlates for 30-day mortality included STS score (OR=1.01, 95% CI [1.03–1.13], p<0.001) and procedural complication (OR=4.29, 95% CI [2.24–8.20], p<0.0001). Independent correlates for 1-year mortality included chronic obstructive pulmonary disease (OR=1.83, 95% CI [1.28–2.60]; p=0.001), atrial fibrillation (OR=1.71, 95% CI [1.31–2.23]; p<0.001 (STS score); OR=1.13 95% CI [1.09–1.18]; p<0.001), and procedural complication) OR=2.58, 95% [1.89–3.50]; p<0.001).

Conclusions

Although older patients undergoing TAVI had a higher risk profile, short- and long-term survival of these patients were associated significantly more with procedural complications than with patient age. It seems that extreme patient age alone should not be viewed as a consideration for not performing valve replacement, as long as the risk for procedural complications does not seem to be severely elevated.

Funding Acknowledgement

Type of funding sources: None.

Increased rate of new-onset left bundle branch block in patients with bicuspid aortic stenosis undergoing TAVR; data from a national registry

Background

There is a growing interest in transcutaneous aortic valve replacement (TAVR) therapy among patients with bicuspid severe aortic stenosis (BAV). Conduction disturbances remain a frequent complication of TAVR, and new-onset permanent LBBB (NOP-LBBB) post-TAVR may be a marker of worse outcomes.

Purpose

To evaluate primarily the rate of NOP-LBBB following TAVR among patients with BAV as compared to tricuspid severe aortic stenosis (TAV).

Methods

Patients enrolled in the multicenter (5 centers) Bicuspid AS TAVR Registry were reviewed and compared with patients with TAV. Patients with prior aortic valve replacement, other valve morphologies and those with preprocedural LBBB or pacemaker were excluded. NOP-LBBB was defined as LBBB first detected and persisting 30-days following TAVR.

Results

A total of 387 patients (66 with BAV, 321 with TAV), age 80.3±7.3, 47% females were analyzed. The device success rates were 95% in both groups without any conversions to surgery. The rate of NOP-LBBB was significantly higher among patients with BAV vs. TAV (29.2% vs. 16.9%, p=0.02). However, the rate of post procedural pacemaker implantation was similar (14.8% vs. 12.5%; respectively, p=0.62). In BAV and TAV groups, 1-year mortality (6.1% vs. 7.2%; respectively, p=0.75) and stroke rates (6.1% vs. 3.5%; respectively, p=0.3) were not significantly different. Multivariate analysis identified BAV as an independent predictor of NOP-LBBB (OR=2.7, 95% CI 1.3–5.4). Furthermore, BAV subtypes with raphe (type 1) were identified as independent predictors of NOP-LBBB (OR=3.2, 95% CI: 1.5–6.7).

Conclusions

Patients with BAV undergoing TAVR have greater risk for developing NOP-LBBB compared with patients with TAV and the presence of raphe was associated with increased risk of NOP-LBBB. The prognostic significance for this finding warrants further evaluation in future studies.

Funding Acknowledgement

Type of funding sources: None.

Characteristics of aortic root and vascular anatomy in bicuspid versus tricuspid aortic valve anatomy

Background

Transcatheter aortic valve replacement (TAVR) is being increasingly performed in patients with bicuspid aortic valve stenosis (AS).

Purpose

This study sought to compare aortic root, aorta and iliofemoral artery anatomy in patients with bicuspid versus tricuspid AS.

Methods

172 patients with bicuspid AS and 331 patients with tricuspid AS underwent pre-procedural computed tomography (CT) evaluation before TAVR. Dimensions, calcification, and tortuosity of the iliofemoral arteries were evaluated and the dimensions of aortic root, aorta, and left subclavian arteries were determined.

Results

Dimensions of aortic root, aorta, left subclavian, and iliofemoral arteries were consistently and significantly larger in bicuspid than in tricuspid AS (P<0.001). Patients with bicuspid AS had significantly lower subclavian, aorta, and iliofemoral arteries calcification, lower tortuosity index and lower maximal tortuosity angle compared to patients with tricuspid AS (P<0.001 for all) even after adjustment for baseline characteristics (Figure). Compared to tricuspid AS the prevalence of porcelain aorta and aneurysm in the descending aorta and iliofemoral arteries were significantly less common in bicuspid valve anatomy. After adjustment for baseline characteristics Bicuspid valve anatomy was associated with lower odds of vascular calcification (odds ratio (OR) 0.82: 95% CI 0.52–0.93; P=0.001).

Conclusions

Bicuspid AS was associated with larger dimensions of aortic root, aorta, subclavian, and iliofemoral arteries compared with tricuspid AS. Low vascular calcification and decreased tortuosity index of iliofemoral arteries characterized bicuspid anatomy. Further studies are needed to evaluate the impact of bicuspid vascular anatomy on vascular complications after TAVR.

Funding Acknowledgement

Type of funding sources: None.

Invasive- versus computed tomography-angiography for the evaluation of coronary artery disease among elderly patients undergoing transcatheter aortic valve implantation

Background

Coronary artery disease (CAD) is common among elderly patients with severe aortic stenosis undergoing transcatheter aortic valve implantation (TAVI). Current guidelines recommend that percutaneous coronary intervention (PCI) of >70% proximal coronary lesions prior to TAVI. The aim of the current study was to evaluate two approaches to CAD diagnosis pre-TAVI.

Methods

We investigated 2,027 patients undergoing TAVI for severe aortic stenosis at two large centers with different pre-procedural CAD assessment: pre-TAVI computed tomography angiography (CTA) with selective invasive angiography according to CTA results (N=831) or mandatory invasive angiography (IA) (N=1,196). Peri-procedural complications were documented according to the VARC-2 criteria. Mortality rates were prospectively documented.

Results

Mean age of the study population was 86±4, of whom 55% were female. Patients in the IA group had significantly higher rates of pre-TAVI PCI compared to the CTA group (32% vs. 17%, p<0.001). Following TAVI, peri-procedural myocardial infarction (MI) rates were significantly lower among the IA group (0.1% vs. 1.5%, p=0.001). However, multivariate binary logistic regression analysis adjusted for age, gender and cardiovascular risk factors failed to show association between centers strategy and peri-procedural MI. Periprocedural bleeding rates were similar between the groups (3.5% vs. 2.9%, p=0.477). Thirty day, and 1-year mortality crude rates were similar between the groups (2.5% vs. 3.4%, p=0.25, and 10.2% vs. 12.0%, p=0.19). Multivariate cox regression adjusted for age, gender and cardiovascular risk factors did not find association between CAD clearance strategy and outcome.

Conclusions

In elderly patients, CTA driven approach for CAD evaluation pre-TAVI is a valid strategy with similar outcome as compared to invasive approach. CTA strategy significantly reduces invasive procedures rates without compromising patient's outcome.

Funding Acknowledgement

Type of funding source: None

Procedural and remote outcome among patients undergoing urgent trans-catheter aortic valve implantation

Background

Severe aortic stenosis patients suffer frequent heart failure decompensations events often requiring hospitalization. In extreme situations patients can be found with pulmonary edema and cardiogenic shock, unresponsive to medical treatment. Urgent trans-catheter aortic valve implantation (TAVI) has emerged as a treatment option for these high-risk patients.

Methods

We investigated 3,599 patients undergoing TAVI. Subjects were divided into two groups based on procedure urgency: patients who were electively hospitalized for the procedure (N=3,448) and those who had an urgent TAVI (N=151). Peri-procedural complications were documented according to the VARC-2 criteria. In hospital and 1-year mortality rates were prospectively documented.

Results

Mean age of the study population was 82±7, of whom 52% were female. Peri-procedural complication rates was significantly higher among patients with an urgent indication for TAVI compared to those having an elective procedure: valve malposition 3.6% vs. 0.6% (p-value=0.023), valve migration 3.2% vs. 0.9% (p-value=0.016), post procedure myocardial infarction 3.7% vs. 0.3% (p-value=0.004), and stage 3 acute kidney injury 2.6% vs. 0.5%, (p-value=0.02). Univariate analysis found that patients with urgent indication for TAVI had significantly higher in hospital mortality (5.8% vs. 1.4%, p-value<0.001). similarly, multivariate analysis adjusted for age, gender and cardio-vascular risk factors found that patients with urgent indication had more than 5-folds increased risk of in-hospital mortality (OR 5.94, 95% CI 2.28–15.43, p-value<0.001). Kaplan-Meier's survival analysis showed that patients undergoing urgent TAVI had higher 1-year mortality rates compared to patients undergoing an elective TAVI procedure (p-value log-rank<0.001, Figure). Multivariate analysis found they had more than 2-folds increased risk of mortality at 1-year (HR 2.27, 95% CI 1.53–3.38, p<0.001 compared to those having an elective procedure.

Conclusions

Patients with urgent indication for TAVI have higher in-hospital mortality and higher peri-procedural complication rates. However, if these patients survive the index hospitalization, they enjoy good prognosis.

Kaplan-Meier's survival analysis

Funding Acknowledgement

Type of funding source: None

Differences in valve morphology between patients with bicuspid and tricuspid aortic valve

Background

Bicuspid aortic valve (BAV) patients represent a significant minority of severe aortic stenosis (AS) patients undergoing transcutaneous aortic valve implantation (TAVI). These patients demonstrate anatomic differences compared to tricuspid aortic valve (TAV). Ethnicity is associated with different valve morphologies characterized by Siever's classification.

Purpose

We aim to evaluated the prevalence of BAV subtypes and the differences in valve morphology and aortic root dimensions between BAV and TAV in patients undergoing computed tomography (CT) before TAVI.

Methods

In five Israeli medical centers, 131 patients with BAV and 674 patients with TAV underwent CT angiography. BAV morphology was defined according to the number of commissures and raphe, following Siever's classification. Aortic root dimensions were measured at the level of the aortic annulus, sinus of Valsalva (SOV), and sino-tubular junction (STJ). Finally, Agatston score unit (AU) for valve calcification was evaluated.

Results

Type 0 accounted for 27% (36/131), Type IA for 63% (82/131), Type IC for 9% (12/131), and Type 2 for 1% (1/131). Calcium score in BAV patients was significantly higher compared to TAV patients, 4000±1897 vs. 2152±1216 AU; respectively (P<0.001). Distance from the annulus to the left main coronary artery was greater in BAV patients compared to TAV (13.8±3.6 mm vs. 12.8±2.8 mm; respectively, P<0.001), similar distance from annulus to right coronary artery was observed in BAV and TAV patients (16.7±3.7 mm vs. 15±3 mm; respectively, P<0.001). Aortic annulus perimeter was greater in BAV than TAV patients (79.3±11mm vs. 73±8.7mm, respectively, P<0.001), as well as SOV perimeter (35.7±4.5mm vs. 32±3.7mm, respectively, P<0.001), and STJ perimeter (32.3±5mm vs. 27±3.3 mm; respectively, P<0.001).

Conclusion

In Israel, AS patients showed more frequently type 1A BAV. BAV patients have larger aortic root dimensions and higher calcium burden than TAV patients.

Funding Acknowledgement

Type of funding source: None

P1423 Significantly higher 1-year mortality rate in patients undergoing TAVR with higher right ventricular volumes, as calculated by pre-procedural CT angiography

Background

Cardiac gated computed tomography angiography (CCTA) is the mandatory pre-interventional imaging planning procedure in patients eligible for trans-catheter valve implantation (TAVR). Automated analysis of the cardiac chambers" volumes including the right ventricle (RV), can be obtained from the CCTA and thus contribute to patient selection.

Objectives

To assess the prognostic implications of increased RV volume using a fast automated volumetric analysis software on preprocedural CCTA data among patients undergoing TAVR.

Methods

CCTA of patients who underwent TAVR at two medical centers – Stanford University Medical Center (California, USA) and Tel Aviv Medical Center (Israel) – between 2013 and 2016 were analyzed by an automatic four chamber volumetric analysis (4CVA) software, and grouped according to their RV volume index, into those with the largest RV (upper 5th percentile of RV volume index (>120 ml/m2; n = 16) versus those within the 95th percentile lower volumes index (≤120 ml/m2; n = 307). Differences in baseline characteristics between the groups were adjusted for with a propensity score. The risk for one year mortality following the TAVR was compared between the two groups.

Results

In total 323 patients were included. There were no major differences in background and demographic characteristics between the study groups. A significantly higher 1-year mortality rate was found for patients with large RV (31.3% vs. 7.5%, p = 0.008). After adjustment for clinical characteristics, patients with RV volume index >120 ml/m2 were at almost a 5 times higher risk for 1-year mortality compared to patients with smaller RV (HR 4.9, 95% CI 1.8-13.1, p = 0.002). The addition of echocardiographic parameters to the propensity score did not eliminate the significance of RV volume index >120 ml/m2 as an independent predictor for mortality at 1-year. An analysis of RV as a continuous variable demonstrated that the risk for 1-year mortality increased by 2% for every 1 ml/m2 RV volume enlargement (p = 0.013).

Conclusions

Cardiac volumetric data by CCTA performed for procedural planning may help predict outcome in patients undergoing TAVR.

Abstract P1423 Figure. Cox survival curves according to RVi

Barriers and facilitators of health behavior engagement in ultra-Orthodox Jewish women in Israel

Background

The ultra-Orthodox Jewish (UOJ) community is a primarily low socio-economic, culturally insular minority sub-sect in Israel. Compared with the general population, UOJ women report higher rates of diabetes and overweight, lower physical activity rates, and have lower breast cancer survival rates. Research in this sub-sect is limited. Identifying the facilitators and barriers to health behavior engagement would facilitate public health intervention design in this population.

Methods

This study describes UOJ women’s barriers and facilitators to engagement in targeted health behaviors (i.e. health nutrition, physical activity), identified through mixed methods analysis. Qualitative and quantitative analyses of interviews (N = 5), focus groups (5, including 35 women), and questionnaires (N = 239) identified barriers to engaging in preventive health behaviors and intervention preferences.

Results

Most of the barriers identified (financial and time limitations, personal preferences, lack of education/awareness, and family-related obstacles) are similar to those reported by women from the general population. Cultural aspects such as women’s role in the home, religious restrictions, and modesty were also identified as barriers to health behavior engagement, comparable to women from other insular communities.

Conclusions

Utilizing a mixed methods approach in identifying barriers and facilitators informed intervention development and improved cultural tailoring, potentially serving as a model for intervention design with additional UOJ communities as well as other difficult to access, low socio-economic, culturally insular populations.

Key messages

This is the first study identifying facilitators and barriers to UOJ women’s health behavior engagement. Findings can inform intervention design in difficult to access, culturally insular populations.

P3378Differences in valve morphology and aortopathy between patients with bicuspid and tricuspid aortic valves: a Computed Tomography Study

Background

Transcatheter aortic valve implantation (TAVI) has been shown safe and feasible in patients with bicuspid aortic valve (BAV) morphology. Evaluation of differences in valve morphology and aortic root dimensions in patients with BAV in comparison to patients with tricuspid aortic valve (TAV) is important for the spread of TAVI in patients with BAV.

Purpose

The present study evaluated the prevalence of BAV subtypes and the differences in valve morphology and aortic root dimensions between BAV and TAV in patients undergoing computed tomography (CT) before TAVI.

Methods

In five medical centers in Israel, 104 patients (69±13.5 years) with BAV and 105 patients (81±8.22 years) with TAV underwent CT angiography. BAV morphology was defined according to the number of commissures and raphe following Siever's classification. Functional BAV was defined as 3 cusps with focal fusion of 1, 2, or 3 commissures. Aortic root dimensions were measured at the level of the aortic annulus, sinus of Valsalva (SOV), sino-tubular junction (STJ), and ascending aorta (AA). Membranous septum (MS) length was measured in coronal view. The volume and agatston score of aortic valve calcification were evaluated.

Results

Type 0 account for 22% (23/104), type IA for 58% (60/104), Type IC for 9% (9/104), functional BAV for 11% (12/104). Type IB and II were not found in the studied population. As compared with TAV, patients with BAV have significantly larger aortic annulus area, SOV area, STJ area and AA Area; however, the ellipticity index of aortic annulus, SOV, STJ, and AA were similar. MS length was significantly smaller in patients with BAV compared to patients with TAV (6.4±2.3 mm vs. 8.1±2.7mm; retrospectively; P<0.001) and the volume of aortic valve calcifications was significantly higher in BAV compared to TAV patients: 2.3±1.6 ml3 vs. 1.4±1.2 ml3 retrospectively; P=0.003).

Conclusions

In Israel, patients with BAV showed more frequently type 1A BAV. BAV patients have larger aortic root dimensions than patients with TAV without difference in regard to the ellipticity index. MS length was smaller and the amount of aortic leaflet calcifications was higher in patients with BAV. These findings may have important impact on procedural outcome.

P3857Validation of the cardiac damage classification and additional effects of albumin levels in a large cohort of patients undergoing transcatheter aortic valve replacement

Background

Risk stratification in patients undergoing transcatheter aortic valve replacement (TAVR) is limited and based on clinical judgment and surgical AVR scoring systems. Recently, extent of cardiac damage using an echocardiographic classification was purposed to assess prognosis of patients undergoing TAVR. We aimed to validate this new scoring system in a real-world cohort and to examine the addition of baseline albumin in risk assessment.

Methods

We investigated 2,608 patients undergoing TAVR. All subjects had an echocardiography test prior to TAVR. Subjects were divided into five groups based on their echocardiography findings: stage 0 – 758 (29%) patients, stage 1 – 769 (30%), stage 2 – 730 (28%), stage 3 – 320 (12%) and stage 4 (1.2%). Patients were further assessed by incorporating baseline albumin.

Results

Mean age of study population was 82±7 years. Kaplan-Meier's survival analysis showed that the cumulative probability of mortality was significantly higher among subjects with increased stage compared to the lower stages (p<0.001). Multivariable analysis demonstrated that each increase in stage was associated with significant increased risk of 1-year mortality (HR 1.37, 95% CI 1.23–1.54, p<0.001). Among patients at increased stage (3–4), incorporation of baseline of albumin identified the highest risk group, such that each 1 decrement in albumin levels was associated with more than triple increase in mortality among patients at stage 3 and 4 (HR 2.77, 95% CI 1.48–5.18, p-value=0.001)[figure]. When added to the scoring risk prediction model, albumin allowed more accurate risk stratification: continuous NRI analysis showed an overall improvement of 11% (95% CI 6%-16%) in the accuracy of classification.

KM according to stage and albumin

Conclusions

Cardiac damage classification is validated in a real-world cohort of patients undergoing TAVR. Incorporation of low baseline albumin may further identify patients at the highest risk group.

The validity of an experiment testing the influence of acceleration on time dilation using a rotating Mössbauer absorber and a Synchrotron Mössbauer Source

Three experiments are reviewed, performed (in 2014-2016) at ID18 of ESRF to measure the influence of acceleration on time dilation by measuring the relative shift between the absorption lines of two states of the same rotating absorber with accelerations anti-parallel and parallel to the incident beam. Statistically significant data for rotation frequencies up to 510 Hz in both directions of rotation were collected. For each run with high rotation, a stable statistically significant `vibration-free' relative shift between the absorption lines of the two states was measured. This may indicate the influence of acceleration on time dilation. However, the measured relative shift was also affected by the use of a slit necessary to focus the beam to the axis of rotation to a focal spot of sub-micrometre size. The introduction of the slit broke the symmetry in the absorption lines due to the nuclear lighthouse effect and affected the measured relative shift, preventing to claim conclusively the influence of acceleration on time dilation. Assuming that this loss of symmetry is of first order, the zero value of the relative shift, corrected for this loss, falls always within the experimental error limits, as predicted by Einstein's clock hypothesis. The requirements and an indispensable plan for a conclusive experiment, once the improved technology becomes available, is presented. This will be useful to future experimentalists wishing to pursue this experiment or a related rotor experiment involving a Mössbauer absorber and a synchrotron Mössbauer source.

Correlates of burnout among professionals working with people with intellectual and developmental disabilities

BACKGROUND

Although burnout has been recognised as an important stress-related problem among staff working with people with intellectual and developmental disabilities (IDD), literature on the subject is limited yet emerging. The aim of this study is twofold: (1) to evaluate the level of burnout within different professions working with IDD; (2) to examine the association between socio-demographic, professional and organisational characteristics and burnout.

METHOD

One hundred ninety-nine professionals working with people with IDD were enrolled in the study (66% response rate). Participants were recruited from several facilities that provide care for people with IDD of all ages, in the Jerusalem area and in other cities in central Israel. The anonymous questionnaires included valid and reliable measures of burnout, socio-demographic variables, professional variables and organisational variables.

RESULTS

Participants' mean age was 38.3 years, and most were women. There were no significant differences in burnout levels among the different professionals. Role ambiguity, perceived overload, care-recipient group and job involvement were significant predictors of burnout. The model explained a high percentage (46.8%) of the observed variance.

CONCLUSIONS

Most of these predictors are organisational measures. These findings demonstrate that organisational variables are more significantly associated with burnout of staff working with people with IDD than the socio-demographic factors or professional characteristics. Identifying and better understanding the specific factors associated with burnout among professionals working with IDD could facilitate unique intervention programs to reduce burnout levels in staff.

Synchrotron radiation Mössbauer spectra of a rotating absorber with implications for testing velocity and acceleration time dilation

Many Mössbauer spectroscopy (MS) experiments have used a rotating absorber in order to measure the second-order transverse Doppler (TD) shift, and to test the validity of the Einstein time dilation theory. From these experiments, one may also test the clock hypothesis (CH) and the time dilation caused by acceleration. In such experiments the absorption curves must be obtained, since it cannot be assumed that there is no broadening of the curve during the rotation. For technical reasons, it is very complicated to keep the balance of a fast rotating disk if there are moving parts on it. Thus, the Mössbauer source on a transducer should be outside the disk. Friedman and Nowik have already predicted that the X-ray beam finite size dramatically affects the MS absorption line and causes its broadening. We provide here explicit formulas to evaluate this broadening for a synchrotron Mössbauer source (SMS) beam. The broadening is linearly proportional to the rotation frequency and to the SMS beam width at the rotation axis. In addition, it is shown that the TD shift and the MS line broadening are affected by an additional factor assigned as the alignment shift which is proportional to the frequency of rotation and to the distance between the X-ray beam center and the rotation axis. This new shift helps to align the disk's axis of rotation to the X-ray beam's center. To minimize the broadening, one must focus the X-ray on the axis of the rotating disk and/or to add a slit positioned at the center, to block the rays distant from the rotation axis of the disk. Our experiment, using the (57)Fe SMS, currently available at the Nuclear Resonance beamline (ID18) at the ESRF, with a rotating stainless steel foil, confirmed our predictions. With a slit installed at the rotation axis (reducing the effective beam width from 15.6 µm to 5.4 µm), one can measure a statistically meaningful absorption spectrum up to 300 Hz, while, without a slit, such spectra could be obtained up to 100 Hz only. Thus, both the broadening and the alignment shift are very significant and must be taken into consideration in any rotating absorber experiment. Here a method is offered to measure accurately the TD shift and to test the CH.

Using a Systems Pharmacology Approach to Study the Effect of Statins on the Early Stage of Atherosclerosis in Humans

More than 100,000 people have participated in controlled trials of statins (lowering cholesterol drugs) since the introduction of lovastatin in the 1980s. Meta-analyses of this data have shown that statins have a beneficial effect on treated groups compared to control groups, reducing cardiovascular risk. Inhibiting the HMG-CoA reductase in the liver, statins can reduce cholesterol levels, thus reducing LDL levels in circulation. Published data from intravascular ultrasound studies (IVUS) was used in this work to develop and validate a unique integrative system model; this consisted of analyzing control groups from two randomized controlled statins trials (24/97 subjects respectively), one treated group (40 subjects, simvastatin trial), and 27 male subjects (simvastatin, pharmacokinetic study). The model allows to simulate the pharmacokinetics of statins and its effect on the dynamics of lipoproteins (e.g., LDL) and the inflammatory pathway while simultaneously exploring the effect of flow-related variables (e.g., wall shear stress) on atherosclerosis progression.

A composite computational model of liver glucose homeostasis. II. Exploring system behaviour

Using a composite model of the glucose homeostasis system, consisting of seven interconnected submodels, we enumerate the possible behaviours of the model in response to variation of liver insulin sensitivity and dietary glucose variability. The model can reproduce published experimental manipulations of the glucose homeostasis system and clearly illustrates several important properties of glucose homeostasis-boundedness in model parameters of the region of efficient homeostasis, existence of an insulin sensitivity that allows effective homeostatic control and the importance of transient and oscillatory behaviour in characterizing homeostatic failure. Bifurcation analysis shows that the appearance of a stable limit cycle can be identified.

A composite computational model of liver glucose homeostasis. I. Building the composite model

A computational model of the glucagon/insulin-driven liver glucohomeostasis function, focusing on the buffering of glucose into glycogen, has been developed. The model exemplifies an 'engineering' approach to modelling in systems biology, and was produced by linking together seven component models of separate aspects of the physiology. The component models use a variety of modelling paradigms and degrees of simplification. Model parameters were determined by an iterative hybrid of fitting to high-scale physiological data, and determination from small-scale in vitro experiments or molecular biological techniques. The component models were not originally designed for inclusion within such a composite model, but were integrated, with modification, using our published modelling software and computational frameworks. This approach facilitates the development of large and complex composite models, although, inevitably, some compromises must be made when composing the individual models. Composite models of this form have not previously been demonstrated.

Equivalent Circuits as Related to Ionic Systems

The purpose of this paper is to clarify the relationship between certain "equivalent circuits" and the fundamental flux equations of Nernst and Planck. It is shown that as a direct algebraic consequence of these equations one may construct two types of equivalent circuits for a homogeneous (charged or uncharged) membrane. The one, which we term the "pure electrical equivalent circuit," correctly predicts all of the electrical properties of the membrane for both steady and transient states. The other, which we call the "mixed equivalent circuit," predicts the steady state I, Psi characteristics of the membrane and the steady state ionic fluxes; it is not applicable to non-steady state properties or measurements. We emphasize that with regard to the portrayal of the physical basis of the properties of a homogeneous membrane, the mixed equivalent circuit can be misleading. This is particularly significant because this same circuit can also be used to depict a mosaic membrane, in which case the circuit gives a realistic pictorialization of the physical origin of the membrane properties. It is hoped that our analysis will be of aid to workers in electrophysiology who make use of equivalent circuit terminology in discussing the behavior of the plasma membrane.

An improved morphological approach to background normalization of ECG signals

This paper describes an improved morphological approach to remove baseline wander from neonatal electrocardiogram (ECG) signals, with particular emphasis on preserving the ST segment of the original signal. The algorithm consists of two stages of morphological processing. First, the QRS complex and impulsive noise component due to skeletal muscle contractions etc., are detected and removed from the input signal. Second, the corrected QT interval (QTc) and RR interval are used to determine a structuring element. With this structuring element, the same morphological operation as in the first stage is then applied to the QRS-removed signal to obtain and remove the baseline wander. The performance of the algorithm is evaluated with simulated and real ECGs. Compared with an existing morphological method, there is a substantial improvement, especially in reducing distortion of the baseline waveform within the PR and QT intervals.

Intravenous magnesium in experimental stent thrombosis in swine

We investigated the effects of magnesium on acute platelet-dependent stent thrombosis in an ex vivo porcine arteriovenous shunt model of high-shear blood flow. Control nitinol stents were expanded to 2 mm in diameter in a tubular perfusion chamber interposed in the shunt and exposed to flowing arterial blood at a shear rate of 2100 s(-1) for 20 minutes (n=156 perfusion runs in 10 swine). Animals were treated with intravenous heparin or MgSO(4) alone (2 g bolus over 20 minutes, followed by 2 g/h infusion) and combined heparin plus MgSO(4) in random fashion. Effects on thrombus weight (TW), platelet aggregation, bleeding time, activated clotting time, mean arterial blood pressure, and heart rate were quantified. Data points in the magnesium-treated animals were examined within 20 minutes after bolus (Mg-early) and >40 minutes after bolus (Mg-late). Stent TW (20+/-3 mg, pretreatment) was reduced by 42+/-21%, 47+/-19%, 48+/-16%, 67+/-12%, and 86+/-8% in the groups treated with Mg-early alone, Mg-late alone, heparin alone, heparin+Mg-early, and heparin+Mg-late, respectively (all P<0.001 versus pretreatment, P<0.001 for heparin+Mg-early and Mg-late versus heparin or magnesium alone, and P<0.05 for heparin+Mg-late versus heparin+Mg-early, ANOVA). Magnesium had no significant effect on platelet aggregation, activated clotting time, or bleeding time. There were no significant effects on heart rate or mean arterial blood pressure. The serum magnesium level was inversely correlated with TW (r=-0.70, P=0.002). In conclusion, treatment with intravenous MgSO(4) produced a time-dependent inhibition of acute stent thrombosis under high-shear flow conditions without any hemostatic or significant hemodynamic complications. Thus, magnesium may be an effective agent for preventing stent thrombosis.

The diphtheria toxin channel-forming T-domain translocates its own NH2-terminal region and the catalytic domain across planar phospholipid bilayers

The T-domain of diphtheria toxin, which extends from residue 202 to 378, causes the translocation of the catalytic A fragment (residues 1-201) across endosomal membranes and also forms ion-conducting channels in planar phospholipid bilayers. The carboxy-terminal 57-amino acid segment (residues 322-378) in the T-domain is all that is required to form these channels, but its ability to do so is greatly augmented by the portion of the T-domain upstream from this. Here we show that in association with channel formation by the T-domain, its hydrophilic 63-amino acid NH2-terminal region (residues 202-264) as well as the entire catalytic A fragment (residues 1-201) cross the lipid bilayer. The phenomenon that enabled us to demonstrate this was the rapid closure of channels at cis negative voltages when a histidine tag was placed at various positions in the NH2-terminal region of the T-domain or in the A fragment; the inhibition of this effect by trans nickel established that the histidine tag was present on the trans side of the membrane. Thus, all of the machinery necessary to translocate the A fragment across membranes is built into the 114 residues at the carboxy-terminal end of the T-domain (residues 265-378), without the requirement of any proteins in the plasma membrane (e.g., toxin receptor) or of any other cellular components.

Protein translocation across planar bilayers by the colicin Ia channel-forming domain: where will it end?

Colicin Ia, a 626-residue bactericidal protein, consists of three domains, with the carboxy-terminal domain (C domain) responsible for channel formation. Whole colicin Ia or C domain added to a planar lipid bilayer membrane forms voltage-gated channels. We have shown previously that the channel formed by whole colicin Ia has four membrane-spanning segments and an approximately 68-residue segment translocated across the membrane. Various experimental interventions could cause a longer or shorter segment within the C domain to be translocated, making us wonder why translocation normally stops where it does, near the amino-terminal end of the C domain (approximately residue 450). We hypothesized that regions upstream from the C domain prevent its amino-terminal end from moving into and across the membrane. To test this idea, we prepared C domain with a ligand attached near its amino terminus, added it to one side of a planar bilayer to form channels, and then probed from the opposite side with a water-soluble protein that can specifically bind the ligand. The binding of the probe had a dramatic effect on channel gating, demonstrating that the ligand (and hence the amino-terminal end of the C domain) had moved across the membrane. Experiments with larger colicin Ia fragments showed that a region of more than 165 residues, upstream from the C domain, can also move across the membrane. All of the colicin Ia carboxy-terminal fragments that we examined form channels that pass from a state of relatively normal conductance to a low-conductance state; we interpret this passage as a transition from a channel with four membrane-spanning segments to one with only three.

Selective consumption of thyroxine-binding globulin during cardiac bypass surgery

A study of serum thyroid hormone binding proteins and thyroid hormone concentrations during and after coronary artery bypass graft (CABG) surgery shows a marked difference in the response of thyroxine binding globulin (TBG) and transthyretin (TTR). The effects of CABG on TBG and TTR were compared in 32 patients during the day of surgery. In a few of these patients, additional determinations were performed to 5 days. When corrected for dilution, TTR concentrations decline gradually after surgery, with no significant decrease over the first 24 hours. In contrast, a rapid decrease of TBG to a mean level of 60% of the preoperative control at 12 hours after the start of surgery appears to account for the concomitant decrease of serum T4. The rate at which the TBG concentration decreased far exceeds the reported fractional clearance of TBG and therefore implies accelerated consumption rather than inhibition of production. TBG is a member of the serine protease inhibitor (SERPIN) superfamily. We propose that its rapid consumption is due to protease cleavage at inflammatory sites. This may explain the previously observed accumulation of thyroxine iodine at such sites.

Direct ultrasound application had no effect on cardiac hemodynamic performance in a baseline isolated rat heart model

Therapeutic ultrasound (US) has been used for more than 3 decades to promote tissue healing in cases of tissue injury and muscle soreness. It was previously suggested that US may have vasorelaxatory and inotropic properties. However, the direct effect of therapeutic US in a whole heart model has not yet been investigated. Our hypothesis was that application of US might enhance cardiac function. The Langendorf model was modified in a special manner to allow application of US to the heart. Using this model, 20 male rats were equally divided into two groups. Group 1: the hearts were perfused for 15 min, to obtain baseline measurements, and then they were perfused for another 15 min in a special bath full of perfusate. Group 2: after 15 min of baseline measurements, continuous US of 1 MHz 2 W/cm(2) was applied for another 15 min. The parameters that were measured at 5-min intervals were: left ventricular pressure P(max), first derivative of the rise and fall in left ventricular pressure (dP/dt(max), dP/dt(min)), and pressure-time integral. There was no significant difference between the two groups in all parameters at baseline and during US application. P(max) and dP/dt(max) remained constant. After 15 min of US propagation, P(max) was 98% +/- 3 from baseline level vs. 98% +/- 7 in the control group, and dP/dt(max) was 98% +/- 3 vs. 99% +/- 9 in the control. In dP/dt(min), a gradual decline after 15 min of perfusion was measured. In the US- treated group, it declined to 80% +/- 10 vs. 83% +/- 5 in the controls. In conclusion, US radiation at the dose specified does not improve healthy isolated heart hemodynamic performance. We established a model that may be used for further investigation.

Translocation of the catalytic domain of diphtheria toxin across planar phospholipid bilayers by its own T domain

The T domain of diphtheria toxin is known to participate in the pH-dependent translocation of the catalytic C domain of the toxin across the endosomal membrane, but how it does so, and whether cellular proteins are also required for this process, remain unknown. Here, we report results showing that the T domain alone is capable of translocating the entire C domain across model, planar phospholipid bilayers in the absence of other proteins. The T domain therefore contains the entire molecular machinery for mediating transfer of the catalytic domain of diphtheria toxin across membranes.

The Effect of Agmatine on Ischemic and Nonischemic Isolated Rat Heart

OBJECTIVE: the natural polyamines play a protective role during ischemic injury. We studied the effects of agmatine on ischemic and nonischemic isolated rat hearts. METHODS: Thirty-one rats were randomly assigned to one of four experimental groups. Sixteen rats were injected with saline (group 1, n = 9; group 3, n = 7), and 15 rats were injected with 100 mg/kg of agmatine (group 2, n = 8; group 4, n = 7). Injections were given twice: 24 hours and 1 hour before the experiment. Using the modified Langendorf model, rat hearts were perfused with Krebs-Henseleit solution for 105 minutes during phase 1 of the experiment (groups 1 and 2). During phase 2, hearts were exposed to 45 minutes of global ischemia (groups 3 and 4). RESULTS: During phase 1, no statistically significant differences were observed between the agmatine and the control groups. During phase 2, agmatine caused a significant increase in left ventricular pressure (P <.003). At the end of reperfusion, P(max) was 111% +/- 10% from the baseline levels versus only 82% +/- 5% in the control group. After 20 minutes of reperfusion, dP/dt (first-time derivative of the ventricular pressure) in the agmatine group reached full recovery of 106% +/- 12% versus only 64% +/- 14% in the saline group (P =.059). Agmatine also caused a significant increase in coronary flow rate (P <.004) throughout the reperfusion period. Quantitative immunohistochemical staining disclosed reduced cell damage in the agmatine-treated hearts (P <.02) versus the control group. CONCLUSION: Agmatine injection given before induced ischemia improves hemodynamic recovery by mechanisms that may be attributed to its vasodilatory properties.

Channel-forming colicins: translocation (and other deviant behaviour) associated with colicin Ia channel gating

1. Introduction 189

2. Channel properties 191

2.1 Voltage-dependent gating 191

2.2 Ion permeability 193

2.2.1 Selectivity between potassium and chloride 193

2.2.2 Permeability to large cations and large anions 193

2.3 Single-channel characteristics 194

2.4 Molecularity of the channel 195

3. Colicin Ia channel topology and protein translocation 195

3.1 Channels formed by whole colicin Ia 195

3.1.1 General channel topology 196

3.1.2 The translocated region 199

3.1.3 The nonuniqueness of the upstream membrane-inserted segment 199

3.2 Channels formed by the C-terminal domain of colicin Ia 200

4. Concluding remarks 202

5. Acknowledgement 203

6. References 203

Colicins are plasmid-encoded proteins, produced by some strains of E. coli, that kill other strains lacking the specific immunity protein encoded by the same plasmid. Most of the colicins have a three-domain structure: a central domain that binds to a receptor in the outer membrane of the target cell; an N-terminal domain that interacts with target cell proteins to move the C-terminal domain across the outer membrane and periplasmic space to the inner membrane; and a C-terminal domain that carries the toxic activity. In some colicins the C-terminal domain is an enzyme that kills the cell by entering the cytoplasm and attacking its DNA (e.g. colicin E2), its ribosomal RNA (e.g. colicin E3), or another target (Schaller et al. 1982; Ogawa et al. 1999). In other colicins, the C-terminal domain forms an ion-conducting channel in the inner membrane that ultimately leads to cell death by allowing essential solutes to leak out of the cell. These colicins, or their isolated C-terminal domains, can also form voltage-dependent channels in planar phospholipid bilayers. (For a review of the E colicins, including enzymatic colicins, see James et al. 1996; for a review of channel-forming colicins, see Cramer et al. 1995; and for a review of colicin import into E. coli, see Lazdunski et al. 1998.) The channel-forming colicins are the subject of this review, with particular emphasis on one member of this group, colicin Ia, and the protein translocation associated with the gating of its channel.

Effects of mutations in proline 345 on insertion of diphtheria toxin into model membranes

Translocation of the catalytic domain of diphtheria toxin (DT) across the endosomal membrane to the cytoplasm of mammalian cells requires the low-pH-dependent insertion of a hydrophobic helical hairpin (TH8-TH9) that is buried within the T domain of the native protein. Mutations of Pro345, which terminates helix TH8, have been reported to block toxicity for Vero cells. We found that mutant toxins in which Pro345 had been replaced by Cys, Glu, or Gly were profoundly defective at low pH in forming channels in planar phospholipid bilayers and in permeabilizing phospholipid vesicles to entrapped fluorophores. Experiments with isolated T domain containing a polarity-sensitive fluorophore attached to Cys at position 332 suggest that the P345E mutation blocks membrane insertion. None of the Pro345 mutations shifted the pH-dependence of binding in solution of the hydrophobic fluorophore, 2-p-toluidinyl-naphthalene 7-sulfonate. The results indicate that proline at position 345 is required for the T domain to insert into phospholipid bilayers or to adopt a functional conformation within the bilayer.

The diphtheria toxin channel-forming T domain translocates its own NH2-terminal region across planar bilayers

The T domain of diphtheria toxin, which extends from residue 202 to 378, causes the translocation of the catalytic A fragment (residues 1-201) across endosomal membranes and also forms ion-conducting channels in planar phospholipid bilayers. The carboxy terminal 57-amino acid segment (322-378) in the T domain is all that is required to form these channels, but its ability to do so is greatly augmented by the portion of the T domain upstream from this. In this work, we show that in association with channel formation by the T domain, its NH2 terminus, as well as some or all of the adjacent hydrophilic 63 amino acid segment, cross the lipid bilayer. The phenomenon that enabled us to demonstrate that the NH2-terminal region of the T domain was translocated across the membrane was the rapid closure of channels at cis negative voltages when the T domain contained a histidine tag at its NH2 terminus. The inhibition of this effect by trans nickel, and by trans streptavidin when the histidine tag sequence was biotinylated, clearly established that the histidine tag was present on the trans side of the membrane. Furthermore, the inhibition of rapid channel closure by trans trypsin, combined with mutagenesis to localize the trypsin site, indicated that some portion of the 63 amino acid NH2-terminal segment of the T domain was also translocated to the trans side of the membrane. If the NH2 terminus was forced to remain on the cis side, by streptavidin binding to the biotinylated histidine tag sequence, channel formation was severely disrupted. Thus, normal channel formation by the T domain requires that its NH2 terminus be translocated across the membrane from the cis to the trans side, even though the NH2 terminus is >100 residues removed from the channel-forming part of the molecule.

Translocation of inserted foreign epitopes by a channel-forming protein

Certain bacterial protein toxins are able to insert themselves into, and at least partially across, lipid bilayer membranes in the absence of any auxiliary proteins, by using unknown mechanisms to overcome the high energy barrier presented by the hydrophobic bilayer core. We have previously shown that one such toxin, colicin Ia, translocates a large, hydrophilic part of itself completely across a lipid bilayer in conjunction with the formation of an ion-conducting channel. To address the question of whether the colicin can translocate any arbitrary amino acid sequence, we have altered the translocated segment by inserting, singly, two different foreign epitopes. Colicins containing either epitope retain significant bactericidal activity and form channels of normal conductance in planar bilayers. Furthermore, antibodies added on the side of the bilayer opposite that to which the colicin was added interact specifically with the corresponding epitopes, producing an inhibition of channel closing. Thus, the inserted epitopes are translocated along with the rest of the segment, suggesting that a surprisingly small part of colicin Ia, located elsewhere in the molecule, acts as a nonspecific protein translocator.

Functions of the N- and C-terminal domains of human RAP74 in transcriptional initiation, elongation, and recycling of RNA polymerase II

Transcription factor IIF (TFIIF) cooperates with RNA polymerase II (pol II) during multiple stages of the transcription cycle including preinitiation complex assembly, initiation, elongation, and possibly termination and recycling. Human TFIIF appears to be an alpha2beta2 heterotetramer of RNA polymerase II-associating protein 74- and 30-kDa subunits (RAP74 and RAP30). From inspection of its 517-amino-acid (aa) sequence, the RAP74 subunit appears to comprise separate N- and C-terminal domains connected by a flexible loop. In this study, we present functional data that strongly support this model for RAP74 architecture and further show that the N- and C-terminal domains and the central loop of RAP74 have distinct roles during separate phases of the transcription cycle. The N-terminal domain of RAP74 (minimally aa 1 to 172) is sufficient to deliver pol II into a complex formed on the adenovirus major late promoter with the TATA-binding protein, TFIIB, and RAP30. A more complete N-terminal domain fragment (aa 1 to 217) strongly stimulates both accurate initiation and elongation by pol II. The region of RAP74 between aa 172 and 205 and a subregion between aa 170 and 178 are critical for both accurate initiation and elongation, and mutations in these regions have similar effects on initiation and elongation. Based on these observations, RAP74 appears to have similar functions in initiation and elongation. The central region and the C-terminal domain of RAP74 do not contribute strongly to single-round accurate initiation or elongation stimulation but do stimulate multiple-round transcription in an extract system.

Identification of residues lining the anthrax protective antigen channel

In its activated 63 kDa form, the protective antigen (PA) component of anthrax toxin forms a heptameric prepore, which converts to a pore (channel) in endosomal membranes at low pH and mediates translocation of the toxin's enzymic moieties to the cytosol. It has been proposed that the prepore-to-pore conversion involves a conformational rearrangement of a disordered amphipathic loop (D2L2; residues 302-325), in which loops from the 7 protomers combine to form a transmembrane 14-stranded beta barrel. To test this model, we generated Cys substitutions in 24 consecutive residues of the D2L2 loop, formed channels in artificial bilayers with each mutant, and examined changes in channel conductance after adding the thiol-reactive, bilayer-impermeant reagent methanethiosulfonate ethyltrimethylammonium (MTS-ET) to the trans compartment. The rationale for these experiments is that reaction of MTS-ET with a Cys residue adds a positively charged group and therefore would likely reduce channel conductance if the residue were in the ion-conducting pathway. We found alternating reduction and absence of reduction of conductance in consecutive residues over two stretches (residues 302-311 and 316-325). This pattern is consistent with alternating polar and apolar residues of the two stretches projecting into the pore lumen and into the bilayer, respectively. Residues connecting these two stretches (residues 312-315) were responsive to MTS-ET, consistent with their being in a turn region. Single channels formed by selected mutants (H304C and N306C) showed multiple conductance step changes in response to MTS-ET, consistent with an oligomeric pore. We also found that the binding site for the channel-blocking tetraalkylammonium ions is located cis relative to the inserted D2L2 loops. These findings constitute strong evidence in favor of the model of conversion of the prepore to a 14-stranded beta barrel pore and solidify the foundation for studies to understand the mechanism of translocation by anthrax toxin.

Probing the structure of the diphtheria toxin channel. Reactivity in planar lipid bilayer membranes of cysteine-substituted mutant channels with methanethiosulfonate derivatives

Previous work has established that the 61 amino acid stretch from residue 322 to 382 in the T-domain of diphtheria toxin forms channels indistinguishable in ion-conducting properties from those formed by the entire T-domain. In the crystal structure of the toxin's water-soluble form, the bulk of this stretch is an alpha-helical hairpin, designated TH8-9. The present study was directed at determining which residues in TH8-9 line the ion-conducting pathway of the channel; i.e., its lumen or entrances. To this end, we singly mutated 49 of TH8-9's 51 residues (328-376) to cysteines, formed channels with the mutant T-domain proteins in planar lipid bilayers, and then determined whether they reacted with small, charged, lipid-insoluble, sulfhydryl-specific methanethiosulfonate (MTS) derivatives added to the bathing solutions. The indication of a reaction, and that the residue lined the ion-conducting pathway, was a sudden change in single-channel conductance and/or flickering behavior. The results of this study were surprising in two respects. First, of the 49 cysteine-substituted residues in TH8-9 tested, 23 reacted with MTS derivatives in a most unusual pattern consisting of two segments: one extending from 329 to 341 (11 of 13 reacted), and the other from 347 to 359 (12 of 13 reacted); none of the residues outside of these two segments appeared to react. Second, in every cysteine mutant channel manifesting an MTS effect, only one transition in single-channel conductance (or flickering behavior) occurred, not the several expected for a multimeric channel. Our results are not consistent with an alpha-helical or beta-strand model for the channel, but instead suggest an open, flexible structure. Moreover, contrary to common sense, they indicate that the channel is not multimeric but is formed from only one TH8-9 unit of the T-domain.

Transmembrane insertion of the colicin Ia hydrophobic hairpin

Colicin Ia is a bactericidal protein that forms voltage-dependent, ion-conducting channels, both in the inner membrane of target bacteria and in planar bilayer membranes. Its amino acid sequence is rich in charged residues, except for a hydrophobic segment of 40 residues near the carboxyl terminus. In the crystal structure of colicin Ia and related colicins, this segment forms an alpha-helical hairpin. The hydrophobic segment is thought to be involved in the initial association of the colicin with the membrane and in the formation of the channel, but various orientations of the hairpin with respect to the membrane have been proposed. To address this issue, we attached biotin to a residue at the tip of the hydrophobic hairpin, and then probed its location with the biotin-binding protein streptavidin, added to one side or the other of a planar bilayer. Streptavidin added to the same side as the colicin prevented channel opening. Prior addition of streptavidin to the opposite side protected channels from this effect, and also increased the rate of channel opening; it produced these effects even before the first opening of the channels. These results suggest a model of membrane association in which the colicin first binds with the hydrophobic hairpin parallel to the membrane; next the hairpin inserts in a transmembrane orientation; and finally the channel opens. We also used streptavidin binding to obtain a stable population of colicin molecules in the membrane, suitable for the quantitative study of voltage-dependent gating. The effective gating charge thus determined is pH-independent and relatively small, compared with previous results for wild-type colicin Ia.

Enhancement of recombinant tissue-type plasminogen activator thrombolysis with a selective factor Xa inhibitor derived from the leech Hirudo medicinalis: comparison with heparin and hirudin in a rabbit thrombosis model

OBJECTIVE

To compare the efficacy of Yagin, a factor Xa inhibitor derived from the leech Hirudo medicinalis, with those of heparin and hirudin as adjuncts to recombinant tissue-type plasminogen activator (rTPA) thrombolysis in a rabbit thrombosis model.

METHODS

Thirty-one animals were allocated randomly to three groups, all administered four boluses of 0.25 mg/kg rTPA every 10 min for 30 min, 17 mg/kg aspirin intravenously, and heparin (as a 100 IU/kg bolus followed by infusion of 50 IU/kg heparin per h), hirudin (as a 2 mg/kg bolus followed by infusion of 1 mg/kg hirudin per h), or Yagin (as an 80 micrograms/kg bolus followed by infusion of 43 micrograms/kg Yagin per h).

RESULTS

Administration of Yagin was associated with a significant acceleration of the reflow time, this time being 14.5 +/- 1.2 min with Yagin, 25.8 +/- 5.2 min with heparin (P < 0.0001, versus Yagin), and 28.7 +/- 16.0 min with hirudin (P = 0.012, versus Yagin). Overall patency did not differ significantly among the three groups.

CONCLUSIONS

At the indicated single doses, inhibition of factor Xa by a relatively low concentration of Yagin was found to be superior than that with either heparin or hirudin for accelerating rTPA thrombolysis.