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W Combs

Publications and source records attributed to W Combs.

14 recordsLinked to original sources
PubMed2001

R-wave detection by subcutaneous ECG. Possible use for analyzing R-R variability.

BACKGROUND: Atrial arrhythmia (AA) discrimination remains a technological challenge for implanted cardiac devices. We examined the feasibility of R-wave detection by a subcutaneous far field ECG (SFFECG) and analysis of these signals for R to R variability as an indicator of atrial arrhythmia (AA). METHODS: Surface ECG and SFFECG (from the pacemaker pocket) were recorded in sixteen patients (61.5 +/- 11.4 years) with AA. The SFFECG was recorded with a pacemaker sized four electrode array acutely placed in the pacemaker pocket during implantation. The signals were analyzed to obtain peak-to-peak R wave amplitude and R to R interval variability (indicative of AAs). RESULTS: In sixteen patients R waves were visually discernible in all recordings. The percentage over and under detection for automatic R wave recognition SFFECG was 3 and 9%, respectively. R to R variability analysis using the SFFECG produced results concordant to those using the surface ECG. CONCLUSION: SFFECG might be a helpful adjunct in implantable device systems for detection of R waves and may be used for measurement of R to R variability.

Aged↗
PubMed2000

P wave and far-field R wave detection in pacemaker patient atrial electrograms.

This study was undertaken to develop and test a morphology-based adaptive algorithm for real-time detection of P waves and far-field R waves (FFRWs) in pacemaker patient atrial electrograms. Cardiac event discrimination in right atrial electrograms has been a problem resulting in improper atrial sensing in implantable devices; potentially requiring clinical evaluation and device reprogramming. A morphology-based adaptive algorithm was first evaluated with electrograms recorded from 25 dual chamber pacemaker implant patients. A digital signal processing (DSP) system was designed to implement the algorithm and test real-time detection. In the second phase, the DSP implementation was evaluated in 13 patients. Atrial and ventricular electrograms were processed in real-time following algorithm training performed in the first few seconds for each patient. Electrograms were later manually annotated for comparative analysis. The sensitivity for FFRW detection in the atrial electrogram during off-line analysis was 92.5% (+/- 10.9) and the positive predictive value was 99.1% (+/- 1.8). Real-time P wave detection using a DSP system had a sensitivity of 98.9% (+/- 1.3) and a positive predictivity of 97.3% (+/- 3.5). FFRW detection had a sensitivity of 91.0% (+/- 12.4) and a positive predictivity of 97.1% (+/- 4.2) in atrial electrograms. DSP algorithm tested can accurately detect both P waves and FFRWs in right atrium real-time. Advanced signal processing techniques can be applied to arrhythmia detection and may eventually improve detection, reduce clinician interventions, and improve unipolar and bipolar lead sensing.

Adolescent↗
PubMed1999

Automatic and efficient R wave discrimination in the right atrium using a two-state hidden Markov model.

INTRODUCTION: Discrimination of far-field R waves from atrial events in atrial electrograms (EGMs) is problematic in present implantable pacing systems. Adjustments of atrial refractory periods and sensitivity settings are the only options, and they will not provide optimal performance in many patients. The reliable detection or rejection of R waves in atrial EGMs would avoid problems of atrial undersensing or oversensing, thus benefiting DDD patients by providing more reliable and specific atrial arrhythmia detection. In addition, detection of far-field R waves could allow a measurement of AV conduction time in AAI and aid in discrimination of supraventricular tachyarrhythmia from ventricular tachyarrhythmia. METHODS AND RESULTS: Both atrial and ventricular unipolar EGMs were collected from 25 patients undergoing pacemaker implant or replacement. An average of 141 seconds of intrinsic or VVI paced EGMs was recorded and post analyzed. A new two-state hidden Markov model (HMM) was developed specifically for far-field R wave and P wave discrimination in the atrium. The recorded patients' EGMs were analyzed using this model, and the sensitivity and positive predictivity of far-field R wave detection were evaluated. The collected atrial EGMs were visually examined and marked as the control for verification of the detection analysis. Far-field R wave detection using this model had an overall sensitivity of 94% +/- 9.4% and a positive predictivity of 98.3% +/- 4.4%; and the far-field R wave rejection using the same model had a sensitivity and a positive predictivity of 98.8% +/- 3.8% and 99.1% +/- 1.7%, respectively. CONCLUSION: Far-field R wave detection in the right atrium by the two-state HMM is reliable and accurate, and can significantly improve atrial arrhythmia management for patients.

Adolescent↗
PubMed1998

A comparative study of activity and dual sensor: activity and minute ventilation pacing responses to ascending and descending stairs.

Previous studies with activity-based rate adaptive pacemakers have shown a somewhat paradoxical response when comparing ascending stairs to descending stairs. The objective of this investigation was to measure dual-sensor rate response provided by activity and minute ventilation (MV) compared with activity alone, and with a control group, during ascending and descending stairs. For dual sensor mode, measured mean peak pacing rate with 72 (92) steps per minute was 111 +/- 13 beats/min (124 +/- 14 beats/min) ascending stairs and 81 +/- 7 beats/min (97 +/- 13 beats/min) for descending. For activity mode alone, mean peak pacing rate was 90 +/- 12 beats/min (108 +/- 19 beats/min) ascending stairs and 97 +/- 12 beats/min (123 +/- 17 beats/min) descending. The mean peak control group heart rate ascending stairs for a step rate of 72 (92) steps/min were 116 +/- 11 beats/min (127 +/- 14 beats/min) ascending stairs and for descending 89 +/- 12 beats/min (95 +/- 11 beats/min). While for dual sensor controlled pacing there was a significant difference for ascending and descending stairs at both step rates, there was no difference between going upstairs and downstairs for activity mode alone. Rates with dual sensor did not significantly differ from respective rates of the control group. The mean correlation coefficient between MV and paced rate was 0.85. Pacing heart rates delivered by the dual sensor mode were appropriate for ascending and descending stairs. In contrast to activity mode alone, the peak heart rates for dual sensor mode are higher during ascending than during descending stairs.

Aged↗
PubMed1998

Electrogram signals recorded from acute and chronic pacemaker implantation sites in pacemaker patients.

Electrogram signals recorded from typical pacemaker implantation sites may be useful for a variety of pacemaker system functions including pacemaker follow-up, atrial and ventricular sensing (event detection), and triggered electrogram storage. We quantified the electrical characteristics of pacemaker pocket electrograms using a subcutaneous electrode array (SEA) in a population of 48 patients undergoing initial or replacement pacemaker implantation. SEA recorded intrinsic R wave amplitudes measured peak to peak averaged 118 microV and 65 microV for the two recorded SEA electrograms and were significantly different (P < 0.001); paced R wave amplitudes averaged 180 microV and 110 microV. P wave amplitudes averaged 39 microV and 26 microV. No statistically significant difference in amplitudes were observed between acute versus chronic pacemaker pocket or indication for pacing (AV block, sick sinus syndrome). Signal to noise ratios, using R wave amplitude as signal, were lower in the SEA electrogram on average (11 dB) compared to the intracardiac electrogram (27 dB), but sufficient for diagnostic assessment. R wave/P wave ratios for SEA signals were lower than surface and intracardiac values 3.1 and 2.7 compared to a range of 6.2-9.8, indicating a relative enhancement of P waves to R waves in SEA signals. In summary, SEA electrograms are of sufficient amplitude and signal quality (signal to noise ratio) to hold promise for future implantable device features such as electrogram telemetry, enhanced sensing, and diagnostic data storage.

Adult↗
PubMed1998

The influence of sensor orientation on activity-based rate responsive pacing. Sensor Orientation Study Group.

Piezoelectric activity-based rate responsive pacemakers are commonly implanted with the sensor facing inward. This study was conducted to assess the safe and effective rate response of an activity-based rate responsive pacemaker implanted with the sensor facing outward. A comparison were made to a previously studied patient group with sensor facing inward. Patient and pacemaker data was collected at predischarge and 2-month follow-up. Two-minute hall walks in conjunction with programmer-assisted rate response assessment were utilized to standardize initial rate response parameter settings for both patient groups. At 2-month follow-up, sensor rate response to a stage 3 limited CAEP protocol was recorded. Adequate sensor rate response was achieved for both patient groups. No difference was noted in reported patient complications for both groups. A statistically significant difference in programmed rate response curve setting and activity threshold for the two groups was noted at 2-month follow-up. Adequate sensor rate response was achieved for a patient population implanted with an activity-based rate responsive pacemaker with sensor facing outward. In this orientation, one higher rate response curve setting and an activity threshold one value more sensitive were required on average when compared to the normal sensor orientation group.

Aged↗
PubMed1995

Initial clinical experience with a new dual sensor SSIR pacemaker controlled by body activity and minute ventilation.

Fourteen patients were implanted with a single chamber dual sensor pacemaker (Legend Plus) that measures minute ventilation (VE) via variations in impedance between a bipolar lead and the pacemaker case, and activity via a piezoelectric crystal bonded to the pacemaker case. Chronotropic incompetent patients were exercised on a treadmill and a bicycle in dual sensor mode. Activity only indicated pacing rate was measured using a strap-on pacemaker. Both implanted and strap-on pacemakers were adjusted to yield a steady-state pacing rate of 100 beats/min during hall walk. Pacing rate, VE, and oxygen uptake (VO2) were measured continuously. Linear curve fit analysis slopes for plots of VE versus pacing rate during exercise (1.33-1.49) compared favorably to values reported in normals. Peak pacing rates achieved for treadmill and bicycle testing for dual sensor mode were higher than activity mode alone. Slopes of heart rate to VE or VO2 were not significantly different (P < 0.05) for dual sensor mode in contrast to activity alone. In conclusion, the Legend Plus dual sensor rate adaptive pacing therapy delivered pacing rates more proportional to VE and VO2 under different types of exercise than rates indicated by a strap-on pacemaker in activity mode.

Aged↗
PubMed1995

Surgical clips as a nidus for biliary stone formation: diagnosis and therapy.

Two cases in which a cystic duct stump clip migrated into the common bile duct and formed the nidus for a stone are reported. In one case, the diagnosis was made before ERCP, on the basis of CT findings. In the second case, a retrospective review of plain abdominal films showed evidence of clip migration. Both patients were treated successfully with endoscopic sphincterotomy, as have most such patients reported in the literature. Although clip migration can occur after both open and laparoscopic cholecystectomy, there is some evidence that this complication may be more common after the laparoscopic procedure. Clip migration can be diagnosed before cholangiography by carefully reviewing plain abdominal films and CT scans. ERCP confirms the diagnosis, and sphincterotomy with clip and stone removal is the therapeutic procedure of choice. Additional surgical procedures only rarely are required.

Aged↗
PubMed1992

Feasibility of using intracardiac impedance measurements for capture detection.

Energy consumption and longevity of modern pacemakers are determined by the controlling electronic circuitry and by the stimulation energy. While with technological progress the electronics' energy consumption has been reduced significantly, clinical practice shows that many cardiac pacemakers are programmed to suboptimal settings with regard to minimization of pacing energy consumption. Several methods for optimizing pacemaker output settings have been proposed in the past. The most promising concept is an output parameter optimizing pacemaker with automatic capture detection. We examined whether it is possible to distinguish between effective and ineffective pacemaker stimulus capture by analyzing high pass filtered intracardiac impedance signals that are derived from standard bipolar pacing leads. In one series of 11 patients undergoing replacement or implantation of chronic bipolar pacemakers, four patients during electrophysiology studies, and eight volunteers undergoing invasive electrophysiology trials, we examined intracardiac impedance signals obtained with various stimulation rates and output parameter settings. Additionally we analyzed a series of five patients with implanted pacemakers that can measure and telemeter intracardiac impedance signals. Several evaluation concepts have been analyzed regarding their ability to discriminate between effective and ineffective stimuli. We developed an adequate algorithm that detects capture or loss of capture at different output parameter settings based on intracardiac impedance analysis. The sensitivity is 98.5% and specificity is 91% to loss of capture for the currently investigated algorithm and this can be used to determine the optimal setting of pulse width and amplitude with regard to energy consumption. This concept is currently under realization in the external programmer and in the future an implementation of these algorithms within the pacemaker itself is intended.

Algorithms↗
PubMed1992

Feasibility of an implantable arrhythmia monitor.

Conventional Holter monitoring is of limited benefit in patients with infrequent symptoms suspected to be related to arrhythmia. A small recorder implanted subcutaneously might obviate many limitations of conventional monitoring. To determine the feasibility of obtaining adequate electrocardiographic signals from such a device, a prototype was temporarily implanted in 17 patients undergoing pacemaker implantation. The prototype contained four disc-shaped titanium electrodes, 0.21 inches in diameter embedded in epoxy. The four electrodes were in a square configuration spaced 0.72 inches center to center and were placed face down in a subcutaneous pocket in the left pectoral region. Bipolar recordings were made from a horizontal pair, a vertical pair, and both diagonal paris of electrodes (interelectrode distance 1.02 inches) and recorded on electromagnetic tape after filtering at 0.5-250 Hz. The mean peak-to-peak amplitude in each configuration was determined over a five-beat interval. Clear recordings were obtained from all 17 patients with recognizable P, QRS, and T waves. The amplitude of the signals obtained from the diagonal pairs of electrodes (175 +/- 51 and 170 +/- 54 microV) were greater than obtained from either the vertical pair (142 +/- 62 microV, P = 0.08 compared to diagonal electrodes) or the horizontal pair of electrodes (105 +/- 54 microV, P < 0.01). The maximum amplitude recorded from any configuration was 189 +/- 54 microV. In six patients the device was also tested with the electrodes face up in the subcutaneous pocket.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

In vivo and in vitro effects of beta-carotene and algae extracts in murine tumor models.

Phycotene, an algae extract with known antineoplastic activity, was demonstrated to prolong, but not sustain, an increased survival rate in a murine fibrosarcoma model when it was combined with immunotherapy. It was further shown that splenocytes from phycotene and beta-carotene-treated survivors could not confer protection to a fresh tumor cell challenge in virgin mice after adoptive transfer. In a series of cytotoxicity assays, phycotene combined with immunization was demonstrated to enhance cell-mediated and complement-dependent cytotoxicity in the first 14-21 days. However, after 21 days, the phycotene and immunization groups exhibited a decreased ability to mediate immune cytotoxicity compared with immunization-only controls. This may serve to explain the in vivo findings that while survival was increased early on in active immunization and phycotene-treated mice, it eventually dropped to the level of the active immunization controls.

Animals↗
PubMed1980

Indirect mean arterial pressure in the anesthetized dog.

Using the oscillometric method, indirect mean arterial pressure was measured in 14 pentobarbital-anesthetized dogs (8-24 kg) with mean arterial pressure ranging from 23 to 160 mmHg. The effect of cuff size, in relation to forelimb circumference was investigated. Indirect mean arterial pressure agreed with direct mean arterial pressure when the cuff width was about 40% of the forelimb circumference.

Anesthesia↗