Noncontact Endocardial Mapping: Reconstruction of Electrograms and Isochrones From Intracavitary Probe Potentials

Noncontact Endocardial Mapping. Introduction : Mapping endocardial activation and repolarization processes is critical to the study of arrhythmias and selection of therapeutic procedures. Previously, we developed methodology for reconstructing endocardial potentials from potentials measured with a noncontact, intracavitary probe. This study further develops and evaluates the ability of the approach to provide detailed information on the spatiotemporal characteristics of the activation process. Specifically, we reconstructed endocardial electrograms and isochrones throughout the activation process over the entire endocardium during a single beat.
Methods and Results : Cavity potentials were measured with a 65-electrode probe placed inside an isolated canine left ventricle. Endocardial potentials were measured simultaneously using 52 electrodes. Potentials were acquired during subendocardial pacing from different locations. Computed electrograms at various sites closely resemble the measured electrograms (correlation coefficient > 0.9 at 60% of the electrodes). Computed isochrones locate subendocardial pacing sites with 10-mm accuracy. Two pacing sites, 17 mm apart, were resolved. Critical regions, such as areas of isochrone crowding, were accurately reconstructed.
Conclusions : Results indicate the applicability of the approach to mapping the cardiac excitation process on a beat-by-beat basis without occluding the ventricle. The ability of locating electrical events (e.g., single or multiple initiation sites) is demonstrated. Importantly, the method is shown to be capable of reconstructing electrograms over the entire endocardium and determining nonuniformities of activation spread (e.g., areas of slow conduction). These capabilities are important to clinical application in the electrophysiology laboratory and experimental studies of arrhythmias in the intact animal.     

The Vulnerable Window for Unidirectional Block in Cardiac Tissue:

Vulnerable Window of Unidirectional Block. Introduction: Unidirectional block is a requisite event in the initiation of reentry in cardiac tissue, but its initiation and behavior in the presence of tissue pathologies remain poorly understood. Previous experimental and theoretical reports on vulnerability to unidirectional block under conditions of reduced cellular coupling and reduced membrane excitability have varied due to differences in experimental and simulation protocols. Methods and Results: We have addressed the issue of vulnerability to unidirectional block using the recent Luo-Rudy membrane model and computer simulations of propagation in a one-dimensional cardiac fiber. The vulnerable window (VW) of unidirectional block from premature stimulation is expressed in units of time, VW_time, and as a range of membrane potentials at the stimulus site, VW_pot VW_pot and VW_time, were quantified over a range of membrane excitability and gap junction resistances (intercellular coupling). With normal membrane excitability and intercellular coupling, VW_pot, and VW_time, were small (VW_Pot, = 0.44 mV, VW_time, = 0.39 msec). A uniform reduction (0.25 ×) in the degree of intercellular coupling increased VW_time, and VW_pot, by factors of 3.6 and 4.7, respectively, whereas a uniform decrease (0.25 ×) in membrane excitability (same resulting velocity) increased VW_time, by only a factor of 0.4 and decreased VW_pot, to negligible levels. When inhomogeneities in fiber properties were introduced (intercellular coupling and membrane excitability), VW_time, increased more due to inhomogeneity in membrane excitability (VW_time= 4.5 msec) than to inhomogeneity in intercellular coupling (VW_time, = 1.5 msec). The simulations also clarify the dependence of the VW on the dimensions of the stimulating electrode. The length of the stimulating electrode added a factor, equal to the propagation time across the eiectrode length, to the intrinsic VW of the fiber. Conclusions: VW_pot, and VW_time, are both important parameters for quantifying vulnerability to unidirectional block. In an environment with uniform distribution of fiber and membrane properties, reduced intercellular coupling bas a greater effect on the VW than reduced membrane excitability. Inhomogeneous reduction of membrane excitability can significantly enhance vulnerability to unidirectional block, much more so than inhomogeneous reduction of intercellular coupling. Theoretically, stimulation at a point should be used to define the VW. Finite electrode dimensions introduce a geometrical factor that affects the measurement of the VW.     

Role of the Popliteal Lymph Node in Infection with Mycobacterium marinum of the Hind Footpad of the Mouse, and Source of the Cells that Characterize the Process

We examined the possibility that the popliteal lymph node serves as the source of the lymphocytes that, together with macrophages, characterize Ihc lesion produced by infection with Mycobacterium marinum in the hind footpad of Ihc mouse. Naive mice were partially protected against challenge with M. marinum in the hind footpad by intravenous infusion of lymphoc) its harvested from the popliteal nodes of donor mice infected with M. marinum 7 days earlier. Lymphocytes harvested from the popliteal nodes of infected donors, labelled in vitro with ³H-uridine, and infused intravenously into naive mice that were immediately challenged in the hind footpads with M. marinum, localized in the popliteal nodes of the recipient mice but nol in the footpad lesions. Lymphocytes harvested from the spleens of naive donors and labelled in vitro appeared to home to the popliteal nude draining the M. marinum-infected footpad. Thus, the primary rule of the popliteal lymph node appeared to be passive trapping of the lymphocytes brought to it by the circulairon or afferent lymphatics. We then tried lo locate the sources of bolh lymphocytes and macrophages that characterize the lesion. Temporary occlusion of the abdominal aorta prevented labelling by intravenously infused ³H-thymidine (³H-TdR) of the mononuclear cells of both footpad lesion and popliteal node. Temporary occlusion of the left common iliac artery during ³H-TdR infusion prevented immediate labelling on the ipsilateral side. After 24 and 48 h, however, small numbers of labelled lymphocyles were found in the left hind footpad lesion. Amputation of the right leg at the hip joint, but run right poplitial lymphadenectomy, performed immediately after re-estublishment of patency of the left common iliac artery, prevented the late influx of labelled lymphocytes into the lesion of the left hind footpad. Thus, the chief source of both the lymphocytes and the macrophages of the footpad lesion appeared lo be the lesion ilself.     

THE IMPACT OF PROSTATE BIOPSY ON PATIENT WELL-BEING: A PROSPECTIVE STUDY OF VOIDING IMPAIRMENT

PURPOSE: We studied the possible association of transrectal ultrasound guided prostate biopsy with voiding impairment. MATERIALS AND METHODS: A total of 211 consecutive patients were prospectively enrolled. International Prostate Symptom Score (I-PSS), subjective voiding complaints and retention were recorded in 3 personal interviews before biopsy, and on postoperative days 7 and 30. RESULTS: Of the 204 patients who voided via the urethra at biopsy 52 (25%) reported subjective voiding impairment on postoperative day 7, including 12% who defined difficult voiding as mild-1 to 2 points on a 0 to 5 scale, 8% as moderate-3/5 and 5% as severe-4 to 5/5. In 5 of the latter cases (2.5%) acute urinary retention necessitated urethral catheter insertion. Transition zone volume, which was 42 ml. or larger in all patients in urinary retention, was the only independent variable associated with patient report of subjective difficult voiding and acute urinary retention during week 1 after biopsy (p = 0.03). Baseline I-PSS greater than 20 points indicated a risk of an acute transient increase in I-PSS on postoperative day 7. CONCLUSIONS: Transient voiding impairment may be precipitated by ultrasound guided prostate biopsy. To decrease this morbidity appropriate evaluation and possible treatment for bladder outlet obstruction are justified in patients with a larger transition zone and in those with preoperative baseline I-PSS greater than 20 points.