PubMed Health⌕ Search

Biomedical subjects

M D Herr

Publications and source records attributed to M D Herr.

7 recordsLinked to original sources
PubMed1994

The effects of pacing site on left ventricular epicardial surface velocity patterns during systole.

Changes in epicardial LV velocity patterns during isovolumic contraction and ejection as induced by ventricular pacing were studied in 15 canines. A noninvasive imaging technique that provided high temporal resolution was used to study the timing of an outward expansion of the LV during isovolumic contraction and the propagation pattern of an inward LV velocity wavefront during ejection. With this technique, surface displacements were measured (+/- 0.1 mm SD) at 50-70 locations on the LV free wall at 5-msec intervals. Velocities were calculated by differentiating the surface displacement waveforms and an interpolation procedure was used to provide detailed color coded velocity maps of the LV surface. LV surface velocities were determined from data obtained during closed-chest endocardial pacing from each of four sites: right atrium, right ventricular apex, left ventricular apex, and right ventricular outflow tract. These surface velocities showed a distinct spatial and temporal pattern for each pacing site. The results show that this noninvasive mapping procedure has potential for determining the location of an ectopic ventricular focus.

Animals↗
PubMed1989

High precision Compton backscatter maps of myocardial wall dynamics. Theory and applications.

Compton backscatter imaging (CBI) is a technique that uses x-rays scattered from the closed-chest surface of the heart to obtain high frequency (5 msec) and high precision (+/- 0.1 mm SD) measurements of regional surface displacements and velocities. These measurements are acquired in a three-dimensional format that allows the reconstruction of the epicardial surface and the creation of color coded displacement and velocity maps at many time points during the cardiac cycle. Applications of the technique are shown to characterize detailed regional normal wall displacement and velocity patterns, and the significant alteration of those patterns after coronary embolization. The technique is also applied to the characterization of early diastolic wall dynamics. CBI measurements show that a brief and somewhat paradoxical inward displacement of the anterior ventricular wall occurs during early diastole in normal canines. The wall dynamics associated with this inward displacement suggest a brief collapse of the ventricle subsequent to aortic valve closure. Diastolic collapse velocities and displacements are significantly altered subsequent to coronary occlusion with mean and maximum collapse velocities decreasing by 50% and concomitant inward displacements decreasing by 40%. Data acquisition with CBI is non-invasive, does not require contrast agents or radioisotopes, and uses low irradiation levels (125 kVp, 3-5 ma). The average radiation dose to the heart for a typical study is 250 mrem, significantly lower than that of other radiation based imaging techniques.

Animals↗
PubMed1988

Coronary artery embolization in closed-chest canines using flexible radiopaque plugs.

A new technique induces localized myocardial infarction in closed-chest dogs by placing discrete plugs in coronary arteries without using cumbersome coaxial catheters or guide wires. Flexible plugs, essential to this method, are formed by extruding a dental impression polymer, rendered radiopaque with sodium iodide, into spaghetti-like strands. Segments of these strands can be injected through a catheter into a selected coronary artery. Contact with blood or saline causes plugs to swell. The mean increase in plug diameter due to swelling was 27 +/- 20%. Eight anesthetized dogs were embolized via carotid approach [6 left anterior descending (LAD), 1 left circumflex (LCX), and 1 LAD and LCX]. Plug positions were monitored fluoroscopically. One animal died at 2 days postembolization. The remaining seven dogs were killed after 14-37 days. Autopsies showed complete vessel occlusion and localized infarction. Infarcts resulting from coronary artery occlusion with one, two, or three plugs involved 2-26% of the left ventricular mass.

Animals↗
PubMedDate not supplied

The measurement of multidimensional myocardial dynamics using scattered radiation fields.

A new radiographic device, based upon the analysis of scattered radiation fields, has been developed to measure myocardial dynamics. The device consists of an array of detectors arranged to monitor photons scattering from the epicardial surface. Data synthesis permits real-time dynamic displays of the epicardial surface in two and three dimensions. The system has been tested on close-chest canines. Epicardial surface displacements within the closed chest cavity can be measured to 0.1 mm (S.D.). Right or left ventricular surfaces may be monitored on a given scan. Surfaces behind or in front of outer myocardial boundaries within the direct field of view of the detectors are located with equal accuracy. Except for the use of low levels of fluoroscopic x-rays, the procedure is completely noninvasive. Radiation dose levels and component costs for the prototype system are modest. The detector system attaches to a standard fluoroscopic x-ray generator.

Animals↗