Biomedical subjects

S C Nishimura

Publications and source records attributed to S C Nishimura.

4 recordsLinked to original sources

PubMed2001

Intraoperative study of polarization and evoked response signals in different endocardial electrode designs.

Some new generation pacemakers use an algorithm based on evoked response (ER) detection to verify beat-to-beat capture and to enable automatic adjustment of output. This is a prospective acute study of polarization signal (PS) and ER in nine currently available electrodes. Intraoperative testing of ventricular bipolar electrodes used the Autocapture (AC) algorithm. The intrinsic R wave, PS, ER, acceptance of AC function, and stimulation thresholds (STs) were obtained. Ventricular electrodes were categorized as follows: titanium nitride (TiN)-coated passive and active fixation, high impedance (HI), passive fixation (VP), iridium oxide-coated titanium (IROX) (VI), and platinum helix (PH) active fixation. Acute testing was performed in 217 patients with an average age of 74.26 years, 59.6% were men with primary pacing indication-SSS (46.3%). There were no significant differences found with respect to R wave and threshold between the various electrodes. PH active-fixation electrodes had significantly higher ER and PS than other groups including the TiN-coated active-fixation electrodes. TiN-coated electrodes (active and passive fixation) had significantly lower PS than other electrodes. As a result, TiN electrodes had a significantly higher functional rate of AC (91.7%), whereas PH had the lowest rate (0%). In conclusion, (1) polarization characteristics are significantly different for commercially available ventricular electrodes, (2) certain physical features at the tissue to electrode interface like TiN coating appears to be more important in determining PS than electrode tip size and fixation method, and (3) the current algorithm for AC requires electrodes that provide low polarization for satisfactory performance.

Adult↗

PubMed2000

A cardiac evoked response algorithm providing threshold tracking: a North American multicenter study. Clinical Investigators of the Microny-Regency Clinical Evaluation Study.

The purpose of this study was to evaluate a pacing system using the recognition of cardiac evoked response for the automatic adjustment of pacing output. Patients were prospectively followed after primary implantation of VVIR pacemakers using AutoCapture (St. Jude Medical CRMD). Sensing and pacing thresholds, polarization signal, evoked response, and AutoCapture performance were evaluated with serial visits and 24-hour Holter monitoring. Three hundred ninety-eight patients (mean age 71 +/- 15 years) were followed for an average duration of 1 year (3 days-1.75 years) with the algorithm functional in > 90% of patients. Backup pacing in the event of exit block was confirmed in all patients. Pacing thresholds remained stable at 0.89 +/- 0.34 V with a pulse width of 0.31 ms (with chronic output autoset at 0.3 V above the actual threshold). Evoked response exhibited a small but statistically significant increase with time (8.92 mV at implant, 9.60 mV at 12 months), however, this finding did not result in any change in AutoCapture function during our follow-up period. The polarization signal remained stable with minimal variation (1.12 mV at implant, 1.18 at 12 months). No clinical adverse events were observed using the AutoCapture algorithm. In this initial experience with the AutoCapture algorithm the evoked response and polarization measurements remained adequate, allowing the system to function in the majority of patients with safe, low output pacing. High energy backup pacing provided an added safety feature over fixed output devices in cases of unexpected threshold rises. Longer follow-up is required for continued long-term validation of the algorithm.

Aged↗

PubMed1997

Is this the natural history of the retention wire? A case report.

We report on a 71-year-old man who had a dual chamber pacemaker implanted in 1991. A Class IV fracture of the Telectronics Accufix 330-801 atrial lead was observed on a chest X ray in December 1993. Serial chest X ray and fluoroscopy documented stable position of the migrated fractured J wire. The patient remained asymptomatic and a decision for conservative monitoring was made. A subsequent finding of a right atrial mass on echocardiography and evidence of pulmonary embolism on lung scan prompted a change of strategy. The patient underwent atriotomy, and a right atrial thrombus was discovered associated with the fractured J retention wire, both of which were extracted uneventfully. This case is illustrative that despite apparent stability of a Class IV fracture, it may result in endothelial injury with a thrombogenic nidus and resultant complications.

Aged↗

PubMed1996

Maintaining physiological pacing in AV block using a new generation single lead VDD pacemaker.

OBJECTIVE: A prospective evaluation of patients with AV block using a single pass lead, VDD pacing system. DESIGN: Fifteen patients with AV block, eight males, seven females, average age 68.1 years (range 22.3 to 86.5) were implanted with the THERA VDD 8948 pacemaker and 5032 single pass steroid eluting lead (Medtronic, Inc). P wave sensing and ventricular thresholds were done predischarge and at one, three, and six months and subsequent six-month periods postimplant. P wave sensing was evaluated with exercise testing and other provocative tests. Twenty-four hour Holter monitoring was done before discharge. Patients were given a quality of life questionnaire pre- and postimplant. SETTING: Tertiary care hospital. RESULTS: Average follow-up was 6.4 months (1.5 to 18). Ventricular thresholds remained stable. P wave amplitude at implant (average 2.2 mV; 1.6 to 3.6) showed a significant decrease at the initial visit (average 1.1 mV, 0.5 to 2.4), however, it remained stable at subsequent visits. This initial decrease had no clinical significance as the maximum atrial sensitivity of the device is 0.18 mV. The 24 hr Holter monitoring confirmed reliable AV synchronous pacing in 14 of 15 patient pacemakers programmed in the VDD mode. The sleep function maintained AV synchrony during nocturnal bradycardia; atrial rate histograms available at follow-up imply appropriate intrinsic rate variation and provocative sensing tests and exercise protocol demonstrated reliable atrial sensing. There was a significant improvement in overall patient well-being score using a quality of life questionnaire. CONCLUSIONS: During the follow-up period, this new generation VDD pacemaker, using a single pass lead, provided reliable AV synchronous pacing for patients diagnosed with AV block and normal sinus node function, as well as improved patient well-being.

Adult↗