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At least 1,603 records · Page 89Linked to original sources
PubMed2000

Long-term outcome of patients with multiple (> or = 3) noninfected transvenous leads: a clinical and echocardiographic study.

To prospectively assess the incidence and clinical significance of thromboembolic complications in patients with multiple (> or = 3) noninfected transvenous leads; 48 consecutive patients were evaluated. Half of the patients had two ventricular leads and one atrial lead, 15 patients had two atrial leads and one ventricular lead, while 9 patients had two ventricular and two atrial leads. No additional care was provided except for aspirin (80 mg bid) and annually performed echo-Doppler studies. Clinical follow-up included signs and symptoms of subclavian and/or axillary vein thrombosis, the presence of right congestive heart failure, the number of hospital admissions, and death. Echo-Doppler studies assessed the presence of an enlarged right atrium or ventricle, right atrial or ventricular spontaneous contrast, and the presence of tricuspid regurgitation. During a total follow-up of 7.4 +/- 2.2 years there were no differences in the incidence of clinical variables as compared to age-matched controls with DDD pacemakers. The most common complication was transient venous thrombosis (mostly presenting as venous prominence 1-2 weeks after implantation), which was seen in 17% of the study group versus 15% in controls (NS). Cumulative mortality was not different in both groups (13% in the study group vs 15% in controls). No differences were present with respect to hospital admissions (1.1 +/- 0.27/year in the study group vs 1.2 +/- 0.30/year in the controls). In patients with multiple ventricular leads, tricuspid regurgitation on echo-Doppler studies was more frequent (24%) as compared to controls (4%); however, clinical signs of right heart failure were equally distributed. Thus, patients with multiple (> or = 3) noninfected leads have no clinical adverse outcome during long-term follow-up.

Catheterization, Peripheral↗
PubMed2005

Finite volume analysis of temperature effects induced by active MRI implants with cylindrical symmetry: 1. Properly working devices.

BACKGROUND: Active Magnetic Resonance Imaging implants are constructed as resonators tuned to the Larmor frequency of a magnetic resonance system with a specific field strength. The resonating circuit may be embedded into or added to the normal metallic implant structure. The resonators build inductively coupled wireless transmit and receive coils and can amplify the signal, normally decreased by eddy currents, inside metallic structures without affecting the rest of the spin ensemble. During magnetic resonance imaging the resonators generate heat, which is additional to the usual one described by the specific absorption rate. This induces temperature increases of the tissue around the circuit paths and inside the lumen of an active implant and may negatively influence patient safety. METHODS: This investigation provides an overview of the supplementary power absorbed by active implants with a cylindrical geometry, corresponding to vessel implants such as stents, stent grafts or vena cava filters. The knowledge of the overall absorbed power is used in a finite volume analysis to estimate temperature maps around different implant structures inside homogeneous tissue under worst-case assumptions. The "worst-case scenario" assumes thermal heat conduction without blood perfusion inside the tissue around the implant and mostly without any cooling due to blood flow inside vessels. RESULTS: The additional power loss of a resonator is proportional to the volume and the quality factor, as well as the field strength of the MRI system and the specific absorption rate of the applied sequence. For properly working devices the finite volume analysis showed only tolerable heating during MRI investigations in most cases. Only resonators transforming a few hundred mW into heat may reach temperature increases over 5 K. This requires resonators with volumes of several ten cubic centimeters, short inductor circuit paths with only a few 10 cm and a quality factor above ten. Using MR sequences, for which the MRI system manufacturer declares the highest specific absorption rate of 4 W/kg, vascular implants with a realistic construction, size and quality factor do not show temperature increases over a critical value of 5 K. CONCLUSION: The results show dangerous heating for the assumed "worst-case scenario" only for constructions not acceptable for vascular implants. Realistic devices are safe with respect to temperature increases. However, this investigation discusses only properly working devices. Ruptures or partial ruptures of the wires carrying the electric current of the resonance circuits or other defects can set up a power source inside an extremely small volume. The temperature maps around such possible "hot spots" should be analyzed in an additional investigation.

Body Temperature↗
PubMed2005

Comparison of subtraction arthrography, radionuclide arthrography and conventional plain radiography to assess loosening of total knee arthroplasty.

The value of plain radiographs, digital subtraction arthrography and radionuclide arthrography was analysed in 23 cases of failed total knee arthroplasty. The preoperative diagnosis was compared with the intraoperative assessment. Sensitivity, specificity and the positive and negative predictive value for assessing a loose component were determined separately for the femoral and tibial components. At revision we found 13 loose femoral and 12 loose tibial implants. In eight cases both components were unstable. Plain radiography had a sensitivity of 77% for loosening of the femoral and 83% for the tibial component; digital subtraction arthrography 77% for the femoral and 8% for the tibial component and radionuclide arthrography 31% and 8%. The specificity for plain radiography was 90% for the femoral and 72% for the tibial implant. For subtraction arthrography it was 50% and 82% and for subtraction arthrography 70% and 82%. Radiography had the highest positive and negative predictive values for both components compared with the other two techniques. As a diagnostic tool to detect implant loosening, plain radiography is the most effective in this study. Subtraction arthrography and radionuclide arthrography are not suitable for use as routine methods for detection of total knee arthroplasty loosening.

Adult↗
PubMed1991

The excessive loss of Branemark fixtures in type IV bone: a 5-year analysis.

The predictability of branemark implants has been well documented. High success rates in the maxilla and mandible in fully and partially edentulous patients can be expected. A host of factors may be attributed to the etiology of fixture loss. However, the quality of bone stands out as the single greatest determinant in fixture loss. Types I, II, and III bone offer good strength. Type IV bone has a thin cortex and poor medullary strength with low trabecular density. Ninety percent of 1,054 implants placed were in Types I, II, and III bone. Only 3% of these fixtures were lost; of the 10% of the fixtures placed in Type IV bone, 35% failed. Presurgical determination of Type IV bone may be one method to decrease implant failure.

Dental Implantation, Endosseous↗
PubMed2001

Risks of fracture of Björk-Shiley 60 degree convexo-concave prosthetic heart valves: long-term cohort follow up in the UK, Netherlands and USA.

BACKGROUND AND AIM OF THE STUDY: Approximately 82,000 Björk-Shiley convexo-concave (BSCC) 60 degree prosthetic heart valves were implanted in patients worldwide between 1979 and 1986. Outlet strut fractures (OSF) of some of the valves were first reported shortly after their introduction. Here, the determinants of OSF are examined, and the between-country variation and long-term risk are assessed. METHODS: Cohorts of patients in the UK, Netherlands and USA with 15,770 BSCC 60 degree heart valves were followed up to 18 years for the occurrence of OSF. RESULTS: Crude rates of OSF were highest in the UK (0.18% per year), intermediate in the Netherlands (0.13%), and lowest in the USA (0.06%), although risk factor adjustment reduced the inter-country differences. Furthermore, in the UK and Netherlands, OSF rates (particularly for mitral valves) declined with time since implantation, and between-country differences were considerably diminished 10 or more years post implantation. The risk of OSF decreased steadily with advancing patient age. Fracture rates were lower among women than men, and also varied significantly with valve size and position and OSF status of other valves in the same shoporder. CONCLUSION: This long-term follow up of BSCC 60 degree heart valve patients indicates that risk factors for valve fracture are generally similar in the UK, Netherlands and USA. It also identifies a strong association between fracture risk and age, newly reveals gender-related differences, and shows that the risk of valve fracture persisted, albeit at a reduced rate, into the 1990s.

Adult↗
PubMed2001

[Revision arthroplasty of the shoulder for painful glenoid loosening: a series of 14 cases with acromial prostheses reviewed at four year follow up].

PURPOSE OF THE STUDY: We present the results of a continuous series of 14 patients who underwent revision arthroplasty of the shoulder for painful major loosening of the glenoid component. MATERIAL AND METHODS: Mean follow-up was four years after revision. Loosening was diagnosed seven and a half years after the primary arthroplasty. The diagnosis of loosening was based on the association of a painful impairment of the shoulder with increasing radiolucency or migration of the component. The degree of pain alone guided the surgical decision. The posterior approach provided wide exposure. A glenoid component with an acromial fixation was used in all cases. RESULTS: The loosening was confirmed in all cases at surgery. Two were early failures of the fixation. The glenoid required a bone graft in all cases. The acromion was a useful landmark for proper positioning of the prosthesis. Fixation with cement and screws provided a strong fixation allowing immediate rehabilitation exercises. Good fixation of the glenoid component was achieved in all cases. After seven years follow-up there has been evidence of iterative loosening in one patient. In another case, one screw broke, suggesting forthcoming loosening. Twelve cases had no or very little pain. Two painful cases were associated with anterior migration of the humeral head. DISCUSSION: Even when the local conditions are unfavorable, good implant fixation can be achieved by grafting the glenoid bone loss. Functional improvement is essentially due to pain relief. CONCLUSION: This series, the largest published to date on revision surgery of painful loosening of total shoulder arthroplasty, demonstrated that iterative fixation is technically possible and can provide highly significant pain relief.

Adult↗
PubMed2003

The dilemma of reporting device-related adverse events.

One of the most difficult decisions that medical device companies may face is whether or not to report an adverse event to regulatory authorities. This article discusses a series of UK vigilance guidance documents for device implants designed to assist manufacturers in making these decisions and the wider value to industry that these documents may have.

Disclosure↗
PubMed1996

Effect of repetitive impact on the mechanical strength of pyrolytic carbon.

Impact loading is experienced by mechanical heart valve components when the leaflet comes into contact with the housing orifice as the valve opens and closes during the cardiac cycle. Since the human heart beats approximately 40 million times per year, a large number of impact loading cycles are imposed on the carbon valve components. Contact loading can produce high mechanical stress at the contact area, leading to potential material damage and fracture. This paper describes a procedure for characterizing the effect of repetitive impact on the mechanical strength of pyrolytic carbon. The results shed light on the basic understanding of the damage formation and its strength degradation effect. In particular, fatigue crack growth was identified as the primary mechanism which causes the observed strength degradation. Design procedures based on fracture mechanics and contact mechanics are used in mechanical heart valve design to prevent structural failure associated with impact fatigue.

Biocompatible Materials↗
PubMed1994

[Redo valve replacement for primary tissue failure of bioprosthetic heart valve].

We evaluated long-term results of valve replacement with bioprosthesis in 59 patients. Freedom from primary tissue failure and reoperation declined more than seven years after valve replacement. Seven patients underwent repeat operations because of primary tissue failure in our hospital. Their ages ranged from 32 to 54 years, two cases were male and five were female. At repeat operation, mechanical valve prosthesis were implanted to mitral position in all seven patients, tricuspid annuloplasty was added in five patients, and aortic valve replacement was added in one patients. The New York Heart Association (NYHA) functional classifications were grade II for 1 patient, III for 1, and IV for 5 preoperatively. Five patients had severe pulmonary hypertension preoperatively, and three of them were died after operation. The removed bioprostheses showed tears, perforations or calcifications of cusps and commissural detachments.

Adolescent↗