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Biomedical subjects

N E Fearnot

Publications and source records attributed to N E Fearnot.

At least 19 recordsLinked to original sources
PubMed1994

Five-years experience with intravascular lead extraction. U.S. Lead Extraction Database.

From December 1988 to April 1994, the extraction of 2,195 intravascular pacing leads from 1,299 patients was attempted at 193 centers. Indications were: infection (54%, including 10% septicemia), pacemaker reoperation with removal of nonfunctional or incompatible leads (40%), and other causes (6%). Extraction was attempted via the implant vein using locking stylets and dilator sheaths, via the femoral vein using snares, retrieval baskets, and sheaths, or via both approaches. Leads had been implanted for 0.2 months to 24 years (mean 56 months). At the conclusion of the intravascular procedure, 86.8% of the leads were completely removed, 7.5% were partially removed, and 5.7% were not removed. For physicians performing their first case, 12% of leads were not removed; for physicians who had performed more than 10 cases, only 2% of leads were not removed. Of the 189 leads where extraction attempts had previously failed, 75.1% were completely removed, 14.8% were partially removed, and 10.1% were not removed. Scar tissue increased in severity with implant duration, was a complicating factor, and was the main cause of failure to remove leads. Use of the femoral approach increased with implant duration (5% of leads implanted 12 months or less, 11% of leads 13 months to 3 years, 20% of leads 4-7 years, and 31% of leads 8-24 years), primarily because of increasingly abundant scarring and prior lead damage. Fatal and near fatal complications occurred in 2.5%, including 8 (0.6%) deaths (3 hemopericardium/tamponade, 1 hemothorax, 3 pulmonary embolus, 1 stroke).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Design and evaluation of closed-loop feedback control of minimum temperatures in human intracranial tumours treated with interstitial hyperthermia.

The dynamic nature of blood flow during hyperthermia therapy has made the control of minimum tumour temperature a difficult task. The paper presents initial studies of a novel approach to closed-loop control of local minimum tissue temperatures utilising a newly developed estimation algorithm for use with conductive interstitial heating systems. The local minimum tumour temperature is explicitly estimated from the power required to maintain each member of an array of electrically heated catheters at a known temperature, in conjunction with a new bioheat equation-based algorithm to predict the 'droop' or fractional decline in tissue temperature between heated catheters. A closed loop controller utilises the estimated minimum temperature near each catheter as a feedback parameter, which reflects variations in local blood flow. In response the controller alters delivered power to each catheter to compensate for changes in blood flow. The validity and stability of this estimation/control scheme were tested in computer simulations and in closed-loop control of nine patient treatments. The average estimation error from patient data analysis of 21 sites at which temperature was independently measured (three per patient) was 0.0 degree C, with a standard deviation of 0.8 degree C. These results suggest that estimation of local minimum temperature and feedback control of power delivery can be employed effectively during conductive interstitial heat therapy of intracranial tumours in man.

Adult↗
PubMed1990

Theoretical basis for controlling minimal tumor temperature during interstitial conductive heat therapy.

This paper describes simulation of steady-state intratumoral temperatures achieved by a simple modality of local heat therapy: interstitial treatment with parallel arrays of warmed, conductive heating elements. During "conductive heating" power is directly deposited only in the interstitial probes. Adjacent tissue is warmed by heat conduction. Simulations of interstitial conductive heating involved solution of the bioheat transfer equation on a digital computer using a finite difference model of the treated tissue. The simulations suggest that when the complete temperature distributions for conductive interstitial hyperthermia are examined in detail, substantial uniformity of the temperature distributions is evident. Except for a thin sleeve of tissue surrounding each heating element, a broad, flat central valley of temperature elevation is achieved, with a well defined minimum temperature, very close to modal and median tissue temperatures. Because probes are inserted directly in tumor tissue, the thin sleeve of overheated tissue would not be expected to cause normal tissue complications. The temperature of the heated probes must be continuously controlled and increased in the face of increased blood flow in order to maintain minimum tumor temperature. However, correction for changes in blood flow is possible by adjusting probe temperature according to a feedback control scheme, in which power dissipation from each probe is the sensed input variable. Conductive interstitial heating with continually controlled probe temperature deserves investigation as a technique for local hyperthermia therapy.

Computer Simulation↗
PubMed1990

Intravascular lead extraction using locking stylets, sheaths, and other techniques.

UNLABELLED: Septicemia necessitates extraction of chronic pacemaker leads. Using locking stylets and sheaths to extract leads via the implantation vein (subclavian, cephalic, or jugular) and maneuvering devices, sheaths, and retrieval baskets via the femoral approach, extraction of 228 leads implanted 5 days to 240 months (mean 55 months) was attempted in 136 patients (mean 62 years) at 34 institutions. In addition to septicemia (9%) and infection (39%), total 48%, indications included prophylaxis/replacement (40%), and other (12%). Seventy-seven leads were atrial, 151 ventricular; 147 were unipolar, 81 bipolar; 96 had silicone insulation, 127 polyurethane, 1 poly/silicone, and 2 undetermined. Fixation included tines or fins (160), screw (40), flange (12), and other (16). One hundred and ninety-four leads were completely extracted, 19 partly extracted, and 15 not extracted. Procedural complications were: torn atrium requiring open heart repair (1), hemothorax requiring a chest tube and blood transfusions (1), subacute hemothorax requiring drainage 18 days after discharge (1), thrombosis treated by drugs (1), and myocardial avulsion without sequela (1). Important observations included the significant training required due to the large number of possible clinical variables, and the need to be prepared for life-threatening cardiovascular complications. With training, procedures done at higher volume and lower volume institutions met with similar success. CONCLUSION: Intravascular lead extraction is a viable technique whose benefits outweigh the risks, given the proper intensive training and open heart surgical backup, and may obviate the need for open heart surgery for lead extraction.

Adult↗
PubMed1990

Intravascular lead extraction using locking stylets and sheaths.

Chronic lead extraction using intravascular countertraction techniques was studied in patients with over 65 different lead models including passive and active fixation devices. Indications for removal of 115 leads implanted 5 days to 264 months (mean 58 months) in 62 patients (mean 65 years) included septicemia, subcutaneous tissue infection, preerosion, free-floating lead, lead trapped in valve, too many leads, pain, and vein thrombosis. The superior vena cava (SVC) approach was attempted in 101 leads and was successful in 82 attempts (71% of total leads). The inferior vena cava (IVC) approach via the femoral vein was required to extract 14 (12%) leads inaccessible to the SVC approach and the 19 leads that failed the SVC approach (29% of total leads). The SVC procedure includes a sized stylet locked at the tip and telescoping sheaths advanced over the lead to the heart. An IVC procedure includes placement of a 16 F sheath workstation via a femoral vein into the right atrium. A deflection catheter and Dotter snare in an 11 F sheath were advanced through the workstation into the right atrium. The lead was maneuvered into position, snared, and pulled into the workstation. For both the SVC and IVC approaches, the leads were removed by applying traction on the lead and countertraction with the sheaths. In experienced hands, these techniques have proven safe and effective for removing chronic transvenous leads.

Adult↗
PubMed1990

Hyperthermia catheter implantation and therapy in the brain. Technical note.

For the treatment of malignant gliomas, a technique for implanting hyperthermia catheters was developed that utilized a stereotactic template and head-stabilization frame mounted on a computerized tomography (CT) scanner. Computerized tomography scans were used to measure tumor dimensions and to determine the number, implantation depths, and active heating lengths of the catheters, which were implanted through twist-drill holes while the patient was in the CT room. Heat was subsequently delivered via implanted catheters using a computer-controlled hyperthermia system, which partially compensates for heterogeneous and time-varying tumor blood flow.

Brain Neoplasms↗
PubMed1989

Evaluation of the temperature response to exercise testing in patients with single chamber, rate adaptive pacemakers: a multicenter study.

UNLABELLED: Temperature responsive pacemakers were implanted in 45 patients (ages 44 to 90); 31 patients were evaluated by randomized, paired treadmill exercise tests 1 month postimplant. Of 28 males and 17 females, 19 had coronary artery disease; 8 had congestive heart failure. Pacing indications included sinus node disease (26), atrial fibrillation (15), AV block (10), and brady/tachy syndrome (10); some had multiple indications. Blood temperature (every 10 seconds, resolution = 0.004 degrees C) and pacing rate (every minute) were telemetered from the pacemaker. Average heart rate, exercise duration (5.7 min VVI; 6.7 min VVIR), VVIR response time (22 sec), initial temperature drop (0.23 degrees C) and maximum rate of drop (0.65 degrees C/min), temperature rise (0.31 degrees C VVI; 0.38 degrees C VVIR) and rate of rise (0.27 degrees C/min) were studied in a subset of patients. In pacer-dependent patients, average paired increases in exercise duration and heart rate was 56% and 34%, respectively. Including all (31) patients, some with intermittent sinus rhythm, increases were 28% and 9%, respectively. Because exercise duration increased, temperature rise was higher with rate adaptation. Rate adaptation was obtainable in all patients and patients averaged 99 +/- 48 increases above basic pacing rate per day at nominal temperature sensitivity. CONCLUSION: Beneficial rate adaptation is achievable using blood temperature to modify rate in a sensor based system.

Aged↗
PubMed1989

Case studies on the effect of exercise and hot water submersion on intracardiac temperature and the performance of a pacemaker which varies pacing rate based on temperature.

The effectiveness of using blood temperature change as an indicator to automatically vary heart rate physiologically was evaluated in 3 patients implanted with Model Sensor Kelvin 500 (Cook Pacemaker Corporation, Leechburg, PA, USA) pacemakers. Each patient performed two block-randomized treadmill exercise tests: one while programmed for temperature-based, rate-modulated pacing and the other while programmed without rate modulation. In 1 pacemaker patient and 4 volunteers, heart rates were recorded during exposure to a hot water bath. Blood temperature measured at 10 sec intervals and pacing rate measured at 1 min intervals were telemetered to a diagnostic programmer and data collector for storage and transfer to a computer. Observation comments and ECG-derived heart rates were manually recorded. The temperature-based pacemaker was shown to respond promptly not only to physical exertion but also to emotionally caused stress and submersion in a hot bath. These events cause increased heart rate in the normal heart. Using a suitable algorithm to process the measurement of blood temperature, it was possible to produce appropriate pacing rates in paced patients.

Aged↗
PubMed1988

Cardiac output versus pacing rate at rest and with exercise in dogs with AV block.

To achieve maximum benefit from exercise (rate)-responsive pacing in subjects with sinus node dysfunction and AV block, it is necessary to determine the pacing rate (HR) which produces maximum cardiac output (CO) under specified exercise conditions. However, the CO-HR relationship for exercise has not been systematically investigated. To permit determination of the optimum HR, CO was measured at rest and with exercise for different pacing rates. Seven dogs with complete AV block and permanently implanted ventricular pacemakers were exercised on a treadmill for 5 min at each of four pacing rates (55, 76, 101, 116/min) and at two constant exercise levels (225 and 560 kg.m/min). CO was determined by impedance cardiography during the resting state preceding exercise and during a brief period (10-20 s) immediately after exercise, and was expressed as a percent of the CO determined at rest with HR = 55/min. A three-phase pattern of CO versus HR appears to exist for exercise as for rest. For exercise, starting from a low HR, CO increases markedly; a "plateau" is reached during which moderate increase in CO is achieved by increasing HR. At very rapid pacing rates, CO may actually decrease with further increase in HR. The results of this study suggest that a subject-specific optimum HR exists for each constant exercise level. Moreover, the methodology employed in the study is applicable to the identification of optimum HR for any exercise (rate)-responsive pacemaker.

Animals↗
PubMed1988

Heart rate correlation, response time and effect of previous exercise using an advanced pacing rate algorithm for temperature-based rate modulation.

A temperature-based algorithm to produce pacing rate that resembles chronotropic response to activity was developed. Measurement criteria for the algorithm included workload dependent rate increases with activity and response time within 60 seconds of exercise onset. To evaluate the algorithm, right ventricular blood temperature was recorded during rest and treadmill exercise in 25 patients with implanted Kelvin 500 pacemakers (Cook Pacemaker). Patients included 16 males and nine females, ages 44-81 (mean 72). Indications for pacing were sinus node disease, atrioventricular block and atrial fibrillation with slow ventricular response. Temperature changes reflected physical activity as well as emotional stress. The algorithm was based on the rate of change (dT/dt), the relative change (delta T) and the baseline history (T) of temperature. At exercise onset, a rapid, brief drop in temperature (dT/dt) typically occurred due to peripheral vasodilation, causing prompt increase in pacing rate. As exercise continued, the increase in metabolic rate caused dT/dt as well as delta T to increase, further increasing pacing rate. After exercise, temperature returned to resting level which correspondingly decreased the pacing rate. Sensitivity of the algorithm to temperature variations, and the upper and lower pacing rate limits were programmable to adapt to individual patient needs. The rates produced by the algorithm mimicked intrinsic rate response for various activity levels and produced a mean response time of 16 seconds from exercise onset. Previous exercise had no significant effect on response time. Correlation between normal chronotropic response and simulated pacing rate from five exercise tests was 0.92. These results show good specificity and refute the statement that blood temperature yields a slow response.

Adult↗
PubMed1988

Evaluation of the pacing rate response to treadmill exercise using computer simulation of a temperature-based, rate-adaptive algorithm.

A temperature-based, rate-adaptive, pacing algorithm was developed to benefit the patient. Rate-adaptive pacemakers use a physiologic parameter to identify the need for increased pacing rate. Parameters that have been clinically investigated include venous pH, Q-T interval, respiration, body motion, and blood temperature. The objective of this study was to provide pacing rates resembling normal heart rates in response to various levels and types of activity. A rapid response time (within 30 s of exercise onset) was also sought. Blood temperature, which reflects metabolic activity of all regions, was selected as the physiologic parameter. Right ventricular blood temperature was recorded in 25 patients with implanted Kelvin 500 pacemakers (Cook Pacemaker) during rest and treadmill exercise. The patient population included 16 men and 9 women, age 44-81 years (mean = 72). Indications for pacing were sinus node disease, atrioventricular block, and atrial fibrillation with slow ventricular response. The temperature changed with physical activity and emotional stress. Temperature typically dropped briefly at exercise onset, increased with continued exercise, and returned to the resting level after exercise. These components were employed in developing the temperature-based rate-adaptive algorithm, which was designed to use the rate of temperature change (dT/dt), temperature change (delta T), and baseline temperature (T). The temperature profiles were used to produce simulated pacing rates as determined by the algorithm. The drop in temperature at onset of activity was utilized to provide a rapid increase in pacing rate. As dT/dt became positive and delta T increased, pacing rate was further increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Right ventricular blood temperature profiles for rate responsive pacing.

To establish the efficacy of a temperature-based pacemaker control algorithm, right ventricular temperature and heart rate were measured for 12-70 hours in eight patients (51 +/- 17 years) and in one normal volunteer (28 years) during a variety of activities including exercise, rest, sleeping, eating, drinking, and bathing. A diurnal variation in heart rate and temperature was observed. Drinking caused transient temperature changes (less than one minute); during eating, increases of 0.07-0.36 degrees C over 3-12 minutes were observed. An increase of 0.24 degrees C over 8.5 minutes was observed in one patient during bathing. An abrupt drop in temperature was typically observed at the onset of exercise, followed by a steady temperature rise. During treadmill exercise, after a drop (0.13-0.48 degrees C, Bruce n = 4; 0.16-0.34 degrees C, Naughton, n = 3) during the first 1-2 minutes, temperature rose steadily through the end of peak exercise (0.45-1.01 degrees C, Bruce; 0.28-0.47 degrees C, Naughton). A temperature dip was also observed when a patient was told exercise would start but the treadmill failed to turn on. The dip is probably secondary to changes in blood flow from the peripheral circulation to the central system at the onset of exercise. Repeated exercise separated by short rests caused progressive blunting of the initial dip. Right ventricular temperature changes in a predictable manner with daily activity, allowing a temperature algorithm to detect rest and exercise.

Adult↗
PubMed1986

Trends in pacemakers which physiologically increase rate: DDD and rate responsive.

Exercise (rate) responsive pacemakers benefit patients by providing increased cardiac output when needed and permitting lower rate during rest. This paper briefly reviews trends in reported studies on rate responsive pacemakers. For patients with reliable atrial rhythms, atrial-triggered pacemakers (DDD) provide physiological ventricular rates unless complications arise. At low rates, A-V synchrony benefits patients with refractory cardiac decompensation; however, in patients with healthy myocardiums, achieving higher pacing rates is more significant than maintaining synchrony. If atrial rhythms are unreliable, an alternative sensor for determining pacing rate is indicated. Pacemakers that respond to changes in right ventricular blood temperature, respiratory rate, QT interval, body vibration (motion), and pH have been implanted in humans. Clinical evaluations have shown that increased pacing rate leads to increased exercise tolerance and cardiac output when needed, independent of the sensor type (DDD, QT, respiratory rate, etc.). The effectiveness of any sensor type to increase pacing rate appropriately requires reliable sensors that respond specifically to the need for increased pacing rate. Sensors for stroke volume, venous oxygen saturation, right atrial or ventricular pressure and catecholamines are also under preclinical investigation. The availability of a reliable, long-term sensor is a key limitation to several techniques including pH, stroke volume, oxygen saturation, pressure, and catecholamines. Sensor technology and clinical effectiveness are the keys to rate responsive pacing.

Blood↗