Biomedical subjects

Charles L Feldman

Publications and source records attributed to Charles L Feldman.

9 recordsLinked to original sources

PubMed2003

Effect of endothelial shear stress on the progression of coronary artery disease, vascular remodeling, and in-stent restenosis in humans: in vivo 6-month follow-up study.

BACKGROUND: Native atherosclerosis and in-stent restenosis are focal and evolve independently. The endothelium controls local arterial responses by transduction of shear stress. Characterization of endothelial shear stress (ESS) may allow for prediction of progression of atherosclerosis and in-stent restenosis. METHODS AND RESULTS: By using intracoronary ultrasound, biplane coronary angiography, and measurement of coronary blood flow, we represented the artery in accurate 3D space and determined detailed characteristics of ESS and arterial wall/plaque morphology. Patients who underwent stent implantation and who had another artery with luminal obstruction <50% underwent intravascular profiling initially and after 6-month follow-up. Twelve arteries in 8 patients were studied: 6 native and 6 stented arteries. In native arteries, regions of abnormally low baseline ESS exhibited a significant increase in plaque thickness and enlargement of the outer vessel wall, such that lumen radius remained unchanged (outward remodeling). Regions of physiological ESS showed little change. Regions with increased ESS exhibited outward remodeling with normalization of ESS. In stented arteries, there was an increase in intima-medial thickness, a decrease in lumen radius, and an increase in ESS at all levels of baseline ESS. CONCLUSIONS: The present study represents the first experience in humans relating ESS to subsequent outcomes in native and stented arteries. Regions of low ESS develop progressive atherosclerosis and outward remodeling, areas of physiological ESS remain quiescent, and areas of increased ESS exhibit outward remodeling. ESS may have a limited role in in-stent restenosis. This technology can predict areas of minor plaque likely to exhibit progression of atherosclerosis.

Adult↗

PubMed2003

Reproducibility of coronary lumen, plaque, and vessel wall reconstruction and of endothelial shear stress measurements in vivo in humans.

The purpose of this study was to assess the reproducibility of an in vivo methodology to reconstruct the lumen, plaque, and external elastic membrane (EEM) of coronary arteries and estimate endothelial shear stress (ESS). Ten coronary arteries without significant stenoses (five native and five stented arteries) were investigated. The 3D lumen and EEM boundaries of each coronary artery were determined by fusing end-diastolic intravascular ultrasound images with biplane coronary angiograms. Coronary flow was measured. Computational fluid dynamics was used to calculate local ESS. Complete data acquisition was then repeated. Analysis was performed on each data set in a blinded manner. The intertest correlation coefficients for all arteries for the two measurements of lumen radius, EEM radius, plaque thickness, and ESS were r = 0.96, 0.96, 0.94, 0.91, respectively (all P values < 0.0001). The 3D anatomy and ESS of human coronary arteries can be reproducibly estimated in vivo. This methodology provides a tool to examine the effect of ESS on atherogenesis, remodeling, and restenosis; the contribution of arterial remodeling and plaque growth to changes in the lumen; and the impact of new therapies.

Adult↗

PubMed2003

The relative accuracies of ECG precordial lead waveforms derived from EASI leads and those acquired from paramedic applied standard leads.

Accurate precordial electrode placement can be difficult in emergency situations leading either to loss of time or diminished accuracy. A possible solution is the quasi-orthogonal EASI lead system, with only five electrodes and easily defined landmarks to provide a derived 12-lead electrocardiogram (ECG). The purpose of this study was to test the hypothesis that precordial waveforms in EASI-derived ECGs have no greater deviation from those in gold standard ECGs, than do the precordial waveforms in paramedic acquired standard ECGs. Twenty paramedics applied the standard precordial electrodes employing the routine procedure. A certified ECG technician applied the 6 standard precordial electrodes in their correct gold standard positions, and the EASI electrodes. 12-lead ECGs were obtained from the paramedics' standard leads, and derived from the EASI leads, for comparison with the gold standard ECG. In each precordial lead recording, 6 computer-measured QRS-T waveform parameters were considered. Differences between deltaEASI-gold standard versus deltaparamedic-gold standard were calculated for every waveform in every lead resulting in 720 comparisons. EASI and paramedic results were "equally accurate" in 47%, the paramedic was more accurate in 31%, and EASI was more accurate in the remaining 22%. The differences from gold standard recording of precordial waveforms in ECGs derived from the EASI leads and those acquired via paramedic-applied standard electrodes are similar. The results suggest that the EASI lead system may provide an alternative to the standard ECG precordial leads to facilitate data acquisition and possibly save valuable time in emergency situations.

Electrocardiography↗

PubMed2003

Comparison of waveforms in conventional 12-lead ECGs and those derived from EASI leads in children.

To investigate the possibility of simplifying electrocardiogram (ECG) recording in children, we compared waveforms in conventional 12-lead ECGs to those derived from EASI leads in 221 children of various ages. The conventional 12-lead ECGs and the ECGs using EASI electrode positions were collected simultaneously. We developed and determined the value of age-specific transformation coefficients for use in deriving 12-lead ECGs from the signals recorded at the EASI sites. We compared the results of using age-specific coefficients to the results of using adult coefficients and studied the "goodness-of-fit" between the conventional and the derived 12-lead ECGs. The age-specific coefficients performed slightly better than the adult coefficients, and good agreement was usually attained between the conventional 12-lead ECG and the EASI-derived 12-lead ECG. Our conclusion is that EASI leads in children have the same high levels of "goodness-of-fit" to replicate conventional 12-lead ECG waveforms, as reported earlier in adults.

Adolescent↗

PubMed2003

Prediction of sites of coronary atherosclerosis progression: In vivo profiling of endothelial shear stress, lumen, and outer vessel wall characteristics to predict vascular behavior.

PURPOSE OF REVIEW: Native atherosclerosis and in-stent restenosis are focal and evolve independently. The endothelium regulates arterial behavior by responding to its local environment of hemodynamic stresses, in particular, shear stress. Identification of endothelial shear stress and arterial wall characteristics may allow for the prediction of the progression of atherosclerosis. Accurate identification of arterial segments at high risk for progression may permit preemptive intervention strategies to avoid adverse coronary events. RECENT FINDINGS: In vitro studies indicate that low endothelial shear stress upregulates the genetic and molecular responses leading to the initiation and progression of atherosclerosis, and promotes inflammation and formation of other features characteristic of vulnerable plaque. Physiologic endothelial shear stress is vasculoprotective and fosters quiescence of the endothelium and vascular wall. High endothelial shear stress promotes platelet aggregation. Recent studies have now provided evidence that endothelial shear stress and vascular wall morphology along the course of human coronary arteries can be characterized in vivo, and, in serial studies, may actually predict the focal areas in which atherosclerosis progression occurs. SUMMARY: Rapidly evolving methodologies are able to characterize the arterial wall and the local hemodynamic environmental factors likely responsible for progression of coronary disease in humans. These new diagnostic modalities allow for identification of plaque progression. Future studies need to identify the factors responsible for vulnerable plaque formation. The current availability of drug-eluting stents with a low risk of restenosis allows for consideration of preemptive intervention strategies for these high-risk vascular sites such that future adverse coronary events can be averted.

Coronary Artery Disease↗

PubMed2002

Improved EASI coefficients: their derivation, values, and performance.

The EASI lead system, which is based on the dipole hypothesis of vectorcardiography, offers the possibility of deriving the standard 12-lead electrocardiogram (ECG) and other desired leads from ECGs recorded at only 4 sites; it uses the Frank E, A, and I electrode locations, a fourth electrode location (S) at the manubrium, and a reference electrode. Accordingly, the electrodes of this system can be applied rapidly on easy-to-locate, stable anatomical sites that leave the precordium free for other diagnostic procedures. In early EASI implementations, the derived leads differed from actual leads by more than some clinicians found acceptable. As these differences were thought to be caused by the fact that the coefficients that were used had been derived from a limited data set, we have calculated a new set of EASI coefficients for the standard 12 leads, and several other leads, by using a data set of 983 adult subjects with 120-lead ECGs and well-documented diagnoses. This database is a concatenation of 2 previously described ones: one consisting of 892 persons (normal subjects, postmyocardial-infarction patients with and without arrhythmias, and patients with ventricular arrhythmias but no history of myocardial infarction) and the other consisting of 91 patients with single-vessel coronary artery disease who underwent coronary balloon-inflation angioplasty. In addition to the coefficients for the standard 12 leads (derived for standard limb leads as well as for Mason-Likar leads), we derived coefficients for six additional unipolar leads (posterior V(7)-V(9), and right-sided V(3)R-V(5)R), the Frank orthogonal leads, and three bipolar, vessel-specific leads that have been previously shown to exhibit optimal sensitivity for acute myocardial ischemia. We also derived coefficients for the modified electrode locations of the EASI system that must be used with patients who have undergone a midline sternotomy. Optimal coefficients for lead transformations were determined by maximizing the ensemble average (over the entire data set) of the correlation between the derived and the true lead for the chosen interval of the averaged complex. For derived standard limb leads, the amplitude was adjusted to give the best root-mean-square fit over the entire PQRST interval, whereas for derived Mason-Likar leads it was adjusted to give the best ST-segment fit. The entire set of coefficients and their corresponding goodness-of-fit measures are presented.

Adult↗

PubMed2002

Comparability of 12-lead ECGs derived from EASI leads with standard 12-lead ECGS in the classification of acute myocardial ischemia and old myocardial infarction.

We compared 12-lead electrocardiograms (ECGs) derived with an improved transformation matrix from EASI leads and standard 12-lead ECGs in the detection of acute myocardial ischemia and old infarction (MI). For the ischemia test, we used ECGs of 40 patients recorded prior to and at peak inflation during percutaneous transluminal coronary angioplasty, and for old MI we used test ECGs of 382 non-MI subjects and of 472 patients with prior MI documented by enzyme findings. Two experienced ECG readers served as separate, independent standards for lead-set comparisons, and the Philips ECG analysis program also classified the ECGs. The results showed no significant differences between the two lead sets in the detection of acute inflation-induced ischemia or of old MI according to coding by the electrocardiographers or the computer program. No significant differences were found between the electrocardiographers and the lead sets for acute ischemia. Classification differences between the electrocardiographers were larger than those between the lead sets for acute and old MI and were significant for the latter (P <.001). A more detailed comparison of the lead sets suggested a possible need for modified old-MI criteria and optimization of ST classification thresholds for acute ischemic injury, specific for the EASI 12-lead ECG. We conclude that the EASI-derived 12-lead ECG deserves serious consideration as an alternative to the standard 12-lead ECG in emergency situations and for monitoring in acute-care setting.

Electrocardiography↗

PubMed2002

Statistical and deterministic approaches to designing transformations of electrocardiographic leads.

Two different approaches can be used to investigate the relationships among electrocardiographic leads: a statistical one, based on the analysis of recorded electrocardiograms (ECGs), and a deterministic one, based on physical principles that govern the current flow in irregularly shaped volume conductors such as the human body. The purpose of this study was to compare these two approaches. For the statistical investigation, the data set consisted of 120-lead ECGs recorded in a population including normal subjects (n = 290), post-myocardial-infarction patients (n = 497), patients with a history of ventricular tachycardia but no evidence of a previous myocardial infarction (n = 105), and patients with a single-vessel coronary artery disease who underwent coronary angioplasty (n = 91). Lead transformations of interest were obtained by fitting the multiple-regression model to this data set by the least-squares method. For the deterministic investigation, we used a boundary-element model of the human torso to simulate body-surface potentials in response to three orthogonal unit dipoles placed consecutively at 1,239 ventricular source locations, and the resulting body-surface potential distributions (instead of the recorded ECGs) were then fitted by the multiple-regression model. The results suggest that the lead transformations should be preferably designed by statistical analysis of recorded ECGs. Regression models with a small number of predictors (eg, those based on three ECG leads) are the most reliable; those using more predictors are fraught with the danger of collinearity when predictors are highly correlated (as occurs in the standard 12-lead ECG). Model-derived deterministic transformations are compatible with statistically derived ones, provided that the distributed character of the cardiac sources is taken into account. We conclude that statistical associations among electrocardiographic leads can be reliably quantified in sufficiently large and diverse databases of recorded data; the causality of these associations can be supported by appropriate deterministic models based on the laws of physics.

Angioplasty, Balloon, Coronary↗

PubMed2002

Determination of in vivo velocity and endothelial shear stress patterns with phasic flow in human coronary arteries: a methodology to predict progression of coronary atherosclerosis.

BACKGROUND: Although the coronary arteries are equally exposed to systemic risk factors, coronary atherosclerosis is focal and eccentric, and each lesion evolves in an independent manner. Variations in shear stress elicit markedly different humoral, metabolic, and structural responses in endothelial cells. Areas of low shear stress promote atherosclerosis, whereas areas of high shear stress prevent atherosclerosis. Characterization of the shear stresses affecting coronary arteries in humans in vivo may permit prediction of progression of coronary disease, prediction of which plaques might become vulnerable to rupture, and prediction of sites of restenosis after percutaneous coronary intervention. METHODS: To determine endothelial shear stress, the 3-dimensional anatomy of a segment of the right coronary artery was determined immediately after directional atherectomy by use of a combination of intracoronary ultrasound and biplane coronary angiography. The geometry of the segment was represented in curvilinear coordinates and a computational fluid dynamics technique was used to investigate the detailed phasic velocity profile and shear stress distribution. The results were analyzed with several conventional indicators and one novel indicator of disturbed flow. RESULTS: Our methodology identified areas of minor flow reversals, significant swirling, and large variations of local velocity and shear stress--temporally, axially, and cirumferentially--within the artery, even in the absence of significant luminal obstruction. CONCLUSIONS: We have described a system that permits, for the first time, the in vivo determination of pulsatile local velocity patterns and endothelial shear stress in the human coronary arteries. The flow phenomena exhibit characteristics consistent with the focal nature of atherogenesis and restenosis.

Blood Flow Velocity↗