Biomedical subjects

W J Keon

Publications and source records attributed to W J Keon.

At least 19 recordsLinked to original sources

PubMed1998

Left anterior descending endarterectomy and internal thoracic artery bypass for diffuse coronary disease.

BACKGROUND: The risk and efficacy of using an arterial conduit to bypass an endarterectomized coronary artery remain incompletely defined. To address this question we analyzed retrospectively 74 patients from 1989 to 1994 in whom bypass grafting using the left internal thoracic artery to an endarterectomized left anterior descending artery was performed. METHODS: There were 60 men and 14 women with a mean age of 60.1 +/- 8.6 years. Of this cohort, 55 patients (74.3%) had a previous infarction, 18 (24.3%) were diabetic, and 5 (6.7%) had reoperations; 25 patients (34%) had a totally occluded left anterior descending artery and the average ejection fraction was 45%. Each patient had 2.95 +/- 0.52 grafts with 48 patients (65%) requiring multiple endarterectomies. The average length of the endarterectomized segment was 3.1 +/- 1.6 cm. Average anoxia time was 49 +/- 13 minutes. Postoperatively 19 patients (25.6%) required intraaortic balloon and 18 (24.3%) required inotropic support. Perioperative infarction in the left anterior descending artery distribution occurred in 5 patients (6.7%). RESULTS: There were 3 (4.0%) early and 4 (5.4%) late deaths at a mean follow-up of 36 +/- 16 months. Recurrent angina was present in 9 patients (14.7%). Actuarial 5-year survival was 84.5%. Angiographic follow-up obtained in 23 patients (37.4%) demonstrated 74% anastomotic patency, with good distal run-off in 13 (65%). The anterior segmental wall motion was preserved. CONCLUSIONS: The use of the left internal thoracic artery bypass and adjunctive left anterior descending artery endarterectomy to expand the scope of myocardial revascularization in carefully selected circumstances appears to be beneficial.

Coronary Artery Bypass↗

PubMed1997

Minimally invasive coronary artery bypass: a series with early qualitative angiographic follow-up.

BACKGROUND: Notwithstanding the advantages offered by minimally invasive coronary bypass, valid concerns have been raised about the technical accuracy of the distal anastomoses that can be fashioned on a beating heart. The main objective of our study was to undertake early and complete qualitative angiographic graft analysis in all patients undergoing this procedure. METHODS: All enrolled patients (25) from January to October 1996 who had bypass done by one surgeon via left minithoracotomy (19) or median sternotomy (6) on a beating heart underwent postoperative angiography within 4 to 6 hours. These angiograms were then reviewed for qualitative analysis and compared with a similar series done under conventional cardioplegic arrest. RESULTS: There was 97.5% graft patency (28/29) and no anastomotic occlusions. One internal thoracic artery was damaged. There was no mortality and no perioperative myocardial infarctions. All patients are alive and symptom free. The follow-up is 100% complete and ranges from 15 days to 11 months. Of the 26 anastomoses that could be assessed, 21 (81%) were grade A and 5 (19%) were grade B. In comparison, 24/25 (96%) of the anastomoses fashioned on an arrested heart by the same surgeon were grade A (p = 0.175). CONCLUSIONS: Minimally invasive coronary bypass can be carried out effectively and safely in a select group of patients, and the development of stabilizing devices and proper instrumentation should further improve results.

Anastomosis, Surgical↗

PubMed1997

Wireless monitoring and control for implantable rotary blood pumps.

A wireless biotelemetry system for the transfer of digital data through intact skin and tissue has been developed to provide a safe and noninvasive means of communication between implanted medical devices and the outside of the body. The system utilizes 2 miniature infrared transmitter/receiver modules. Data are transmitted through intact skin and subcutaneous tissue on an 890 nm infrared carrier signal. The system has been evaluated in human cadavers and during in vivo implantation of artificial hearts and ventricular assist devices for durations of up to 96 h. Acceptable data transfer (error rate < 10(-5)) through a typical tissue thickness of 5-25 mm has been demonstrated. The ability to monitor and control a device from a remote site using public communication systems such as telephone lines and asynchronous transfer mode (ATM) systems has also been demonstrated. Design optimization is currently ongoing in preparation for clinical utilization with artificial heart systems and other implantable devices (such as rotary blood pumps).

Animals↗

PubMed1997

Multi-purpose mechanical circulatory device.

A mechanical circulatory assist device for long term use outside the hospital setting has been developed. The device can be used for left, right or bi-ventricular support, and several of the developed technologies are applicable for total artificial hearts and non-pulsatile flow systems. The totally implantable device is principally designed for left ventricular support with implantation in the left hemithorax. The system utilizes transcutaneous energy and information transfer sub-systems, and has no percutaneous connections. In vitro durability testing has been conducted for periods from 1-4 years. Bovine experiments have been conducted with sustained circulation for periods form 1.5 to 96 hours. The in vitro and in vivo evaluation to date has demonstrated that the system can function effectively as a totally implantable ventricular assist device. The transcutaneous energy and information transfer sub-systems provided the ability to power, monitor and control the device, without the need for percutaneous connections. Design optimization and chronic in vivo evaluation is planned.

Animals↗

PubMed1997

International experience with the CardioWest total artificial heart as a bridge to heart transplantation.

As the number of potential heart donors remains constant and the number of potential recipients continuous to increase, the need for circulatory devices to bridge patients becomes more important. The CardioWest total artificial heart (TAH) is a pneumatic, implantable system that totally replaces the failing ventricles. It has been utilized worldwide as a bridge to heart transplantation in 79 patients. There were 73 males and six females who received the TAH. Currently three patients remain on the device waiting for transplantation. A total of 55 patients (70%) were transplanted of which 50 survived (91% of patients transplanted) and were discharged home. Idiopathic/dilated cardiomyopathy was the most common etiology followed by ischemic cardiomyopathy. The mean duration of implant was 34 days (range 0-186 days) and the mean age of the group was 45 years (range 16-62 years). Twenty-one patients died while on the device. Multiple organ failure was the major cause of death. There were a total of 255 complications in this group that included reoperation, bleeding, hepatic failure, renal failure, respiratory failure, neurologic events, thromboembolic events, infections, device malfunction, and fit complications. This represented a mean complication rate of three events per patient. The survival rate for the CardioWest TAH of 91% of the patients who reached transplantation is an improvement over that of the Symbion registry (55% of those transplanted) probably as a result of a better patient selection and better control of the coagulation system. These results are also comparable to those survival results obtained with other biventricular and left ventricular assist devices currently available.

Adolescent↗

PubMed1996

Totally implantable intrathoracic ventricular assist device.

BACKGROUND: A totally implantable, intrathoracic electrohydraulic ventricular assist device (EVAD) is being developed for permanent use or as a bridge to transplantation. METHODS: The blood pump with 70-mL nominal stroke volume, volume displacement chamber, reversible turbine, internal electronics and infrared diaphragm position sensor are combined in one compact unit (unified system). The size and geometry are based on human anatomic measurements and fluid dynamic studies. A transcutaneous energy transfer powers the system and recharges the implantable nickel-cadmium battery pack. Autotuning circuitry optimizes energy transfer efficiency over a range of transcutaneous energy transfer coil spacings and misalignments. An infrared diaphragm position sensor detects end-systole and diastole points. RESULTS: In vitro and acute in vivo tests have demonstrated flow rates greater than 6 L/min. The transcutaneous energy transfer system demonstrated power transfer efficiencies of 60% to 80% for power demands from 5 to 60 W. Thirteen systems are currently undergoing durability testing; one has run for more than 750 days failure-free. The system recently sustained circulation in an acute calf implantation for 96 hours. CONCLUSIONS: Results of the in vitro and in vivo testing to date have demonstrated that the developed system can function effectively as a totally implantable ventricular assist device. Chronic in vivo evaluation is planned.

Animals↗

PubMed1996

Cardiac transplantation after mechanical circulatory support: a Canadian perspective.

BACKGROUND: To assess the relative efficacy of cardiac transplantation after mechanical circulatory support with a variety of support systems, we analyzed our consecutive series of patients who had and did not have mechanical support before transplantation. METHODS: A review of 209 patients undergoing cardiac transplantation from 1984 to May 1995 was performed. Group 1 consisted of 110 patients who were maintained on oral medications while awaiting transplantation, and group 2 consisted of 60 patients who required intravenous inotropic support. Group 3 included 39 patients who had transplantation after mechanical circulatory support for cardiogenic shock. The indication for device implantation was acute onset of cardiogenic shock in 38 patients and deterioration while awaiting transplantation in 1 patient. The support systems were an intraaortic balloon pump in 13 (subgroup 3A), a ventricular assist device in 7 (subgroup 3B), and a total artificial heart in 19 patients (subgroup 3C). RESULTS: After transplantation, infection was more common in group 3 (56%) than in group 1 (28%) or group 2 (32%) (p = 0.005). Survival to discharge was lower for group 3 (71.7%) than for group 1 (90.9%) or 2 (88.3%) (p = 0.009). For mechanically supported patients, survival to discharge was 84.6% in subgroup 3A, 71.4% in subgroup 3B, and 63.1% in subgroup 3C (p = not significant). CONCLUSIONS: Transplantation after mechanical support offers acceptable results in this group of patients for whom the only alternative is certain death. Patient selection and perioperative management remain the challenge to improving these results.

Administration, Oral↗

PubMed1996

Coronary-pulmonary steal syndrome.

The development of an internal thoracic artery-pulmonary artery fistula after operation is a rare entity of no clear etiology. We report a patient who underwent coronary bypass reoperation, presented 3 years later with angina on exertion, and upon investigation was found to have an internal thoracic artery-pulmonary artery fistula. This patient was managed conservatively.

Aged↗

PubMed1996

Coronary bypass graft fate and patient outcome: angiographic follow-up of 5,065 grafts related to survival and reoperation in 1,388 patients during 25 years.

OBJECTIVES: We sought to examine, angiographically, the longterm fate of a large number of mainly venous coronary bypass grafts and to correlate graft patency and disease with patient survival and reoperation. BACKGROUND: Much is known about bypass graft patency and disease, but the precise relation between graft fate and patient outcome has not been substantiated and documented. METHODS: A total of 1,388 patients underwent a first coronary artery bypass graft procedure at a mean age of 48.9 years, 234 had a second bypass procedure at a mean age of 53.3 years, and 15 had a third bypass procedure at a mean age of 58.2 years during the 25-year period from 1969 to 1994. Most were male military personnel or veterans; 12% were < or = 39 years old. Of 5,284 grafts placed, 91% were venous and 9% arterial. Angiograms were performed on 5,065 (98% of surviving) grafts early, on 3,993 grafts at 1 year and on 1,978 grafts at 5 years after operation; other examinations were also performed up to 22.5 years after operation, and 353 grafts were examined after > or = 15 years. Grafts were graded for patency and disease. The status of all patients was known at the study's end. RESULTS: The perioperative mortality rate was 1.4% for an isolated first coronary bypass procedure, 6.6% for reoperation. Vein graft patency was 88% early, 81% at 1 year, 75% at 5 years and 50% at > or = 15 years; when suboptimal grafts, graded B, were excluded from calculation, the proportion of excellent grafts, graded A, decreased to 40% after > or = 12.5 years. After the early study, the vein graft occlusion rate was 2.1%/year. Internal mammary artery graft patency was significantly better but decreased with time. Vein graft disease appeared by 1 year and the rate accelerated by > or = 2.5 years, involving 48% of grafts at 5 years and 81% at > or = 15 years; 44% of the latter grafts were narrowed > 50%. Survival of all patients was 93.6% at 5 years. 81.1% at 10 years, 62.1% at 15 years, 46.7% (150 patients) at 20 years and 38.4% (25 patients) at 23 years after operation. Survival decreased as age increased, but curves approximated "normal" life expectancy for older patients. Survival curves at all ages showed a steeper decline after 7 years. The rate of reoperation increased between 5 years and 10 to 14 years, then decreased to stable levels. Coronary atheroembolism from vein grafts was the major cause of morbidity and mortality associated with reoperation. Vein graft patency and disease were temporally and closely related to reoperation and survival. CONCLUSIONS: Coronary bypass graft disease and occlusion are common after coronary artery bypass grafting and increase with time. They are major determinants of clinical prognosis, specifically measured by reoperation rate and survival. Intraoperative graft atheroembolism was a major reoperation hazard. Reoperation is definitely worthwhile but entails identifiable risks that must be dealt with.

Adult↗

PubMed1996

Early release following cardiac surgery.

Early release following cardiac surgery can be facilitated by the implementation of a standard protocol for pre- and postoperative care. This protocol involves aggressive pharmacologic therapy together with education and support. Accelerated recovery and release is inherently attractive because the duration of intensive care unit stay and hospital stay are the most important determinants of costs. However, in the desire for reduced costs, patients must clearly benefit from earlier rehabilitation and release. Retrospective studies have shown no significant differences in mortality or morbidity in patients who have undergone conventional versus "fast-tracked" care following cardiac surgery, and follow-up surveys have shown a high level of patient satisfaction with the care. Some centers report that, without exception, all cardiac surgery patients are now fast-tracked.

Cardiac Surgical Procedures↗

PubMed1996

A remotely controlled and powered artificial heart pump.

An intrathoracic pulsatile artificial heart pump has been developed. Transcutaneous energy transfer and biotelemetry systems provide continuous power and remote monitoring and control, with no percutaneous connections required. The electrohydraulic system can be used either as a ventricular assist device or with modifications as a total artificial heart. The device uses a unidirectional axial flow pump coupled with a pressure activated one-way valve to allow hydraulic fluid to passively return to the volume displacement chamber during diastole. The transcutaneous energy transfer system provides power to the device and recharges the implantable battery pack. A wearable external controller and external battery pack provide the patient enhanced mobility and thus an improved quality of life. The biotelemetry system allows control and monitoring of the device after implantation, as well as an added capability to monitor and control the device remotely over public communication lines. Early prototypes have functioned failure free for up to 3 years in vitro. The device has sustained circulation in vivo for up to 4 days. Design optimization is continuing, and chronic in vivo evaluation is planned.

Animals↗

PubMed1996

Shared care for open heart surgery: 21 years' experience.

OBJECTIVES: To determine whether patients undergoing open heart surgery, the majority coronary artery bypass grafting (CABG), can safely be returned early to the smaller nonspecialized hospital that referred them for postoperative care by a cardiological team. Another objective is to determine what benefits might accrue from this practice and to whose credit. DESIGN: All 1696 patients, 1512 having coronary bypass alone or with ventricular aneurysm repair in 6%, referred from a military hospital with investigative facilities from November 1971 to November 1992 were studied with attention to length of postoperative stay in both hospitals, perioperative mortality and major complications mandating return to the surgical centre (which was almost always for reoperation). Time between initial coronary angiography and CABG was examined to see whether it related to the early return policy. RESULTS: After the first two years, postoperative care at the surgical hospital following CABG was reduced from a mean of 10.4 to 2.4 days, with an 18% reduction in the combined time spent at both hospitals, an estimated reduction of some 48 patient-years at the surgical hospital. A perceived need for active in-patient-rehabilitation and formal postoperative assessment explains the somewhat higher than average 23-day combined hospital stay after CABG. There have been no cardiovascular problems associated with the process of patient transfer and the three postoperative deaths that occurred in the referring hospital do not appear related to early transfer. Most of the 29 patients (2%) returned to the surgical hospital during the postoperative phase to have reoperations; there were three deaths, inevitable in one, scarcely preventable in two and unrelated to the early transfer in all three. Overall perioperative mortality was 2.7%; it was 1.3% for isolated primary CABG, 7.7% for reoperation. Delay between angiography and CABG was less than one day in 9%, less than four weeks in 69% and less than 12 weeks in 96%. It is believed that rapid access to surgical treatment was facilitated by cardiologists' willingness to undertake postoperative care and by the amicable trusting relationship between staff of the two hospitals. CONCLUSIONS: It is possible to transfer patients safely after open heart surgery to a smaller, nonspecialized hospital for postoperative care; there are no significant ill effects from the practice and obvious benefits accrue to several involved parties. This model of shared care may have lessons for those designing or modifying cardiac surgical care programs.

Adolescent↗

PubMed1996

Transcutaneous energy transfer with voltage regulation for rotary blood pumps.

Rotary blood pumps often require a constant operating voltage. To meet this requirement and to eliminate the need for percutaneous leads, a voltage-regulated transcutaneous energy transfer (TET) system has been developed. Voltage regulation is achieved by using a transcutaneous infrared feedback control loop operating on a 890 nanometer (nm) wavelength. In vitro testing of the system developed has shown that output voltage can be maintained to within 0.2 V of nominal (14.5 V) for delivered powers up to 50 watts (W) and coil separations of between 3 and 10 mm. Power transfer efficiencies were determined to be from 68% to 72% over the tested range of coil separations and output currents from 1.5 to 3.6 amperes (A). This system has demonstrated acceptable performance in regulating output voltage while transferring power inductively without using percutaneous connections. By integrating this type of TET system with an implanted rotary blood pump, the quality of life for the device recipient could be improved.

Energy Transfer↗

PubMed1996

Bridge to transplantation with the CardioWest total artificial heart: the international experience 1993 to 1995.

BACKGROUND: After reapproval by the Food and Drug Administration of the CardioWest total artificial heart for clinical investigation, an international study was started in January 1993 to ascertain the safety and efficacy of this device for bridging to heart transplantation. To date, 40 devices have been implanted in five centers. METHODS: Retrospective data collection from participating centers provided enough material for analysis of patient selection, patient survival, adverse events, and comparison with contemporary devices used for bridge to transplantation. RESULTS AND CONCLUSIONS: Twelve patients (30%) died after implantation and before transplantation after an average of 10.6 +/- 10 days of support. The major cause of death in this group was multiorgan failure. Twenty-eight patients (70%) were supported 36 +/- 36 days before transplantation. There were two deaths after transplantation (1 rejection, 1 multiorgan failure) leaving 26 patients (65% of the total patients and 93% of those who were transplanted) who survived to discharge from the hospital. There was one late death from rejection at one month post discharge. The mean survival time of the 25 surviving patients is 12 months. These results compare favorably with those of other contemporary devices used for bridge to transplantation.

Adult↗

PubMed1996

Mechanical circulatory support as a bridge to transplantation: past, present and future.

OBJECTIVE: Historical and state-of-the-art review of clinical mechanical circulatory assist and replacement devices. Recent clinical experience at the University of Ottawa Heart Institute with various mechanical circulatory assist devices as a bridge to transplant, and experimental results with the development and testing of a new electrohydraulic ventricular assist device, are described in detail. DATA SOURCES: A Medline search of the English literature from 1980 to 1996 was done using the following words: artificial heart; ventricular assist device; and transplantation. STUDY SELECTION: Papers were selected to provide both a historical perspective and an overview of the current status and future prospects of mechanical circulatory assist devices and artificial hearts. DATA SYNTHESIS: Since the implantation in animals of the first devices in the 1960s and 70s, there have been astounding improvements in design, available materials and implementation of these devices. Increases in the understanding and management of thrombogensis and immunosuppressive drugs as well as developments in the fields of miniaturization, pumps and power sources will lead to concomitant improvements in these devices. CONCLUSIONS: The use of these devices has become an accepted treatment for end-stage heart disease. Additional development and testing is required to address persistent complications in most models if they are to become alternatives to cardiac transplantation. The basis of the future successes is dependent on both technological refinements in the developments of new devices and on continued research into the physiological effects of mechanical circulatory support. However, these devices are used both as a bridge to recovery and a bridge to cardiac transplant and it is expected that they will be used increasingly to provide permanent circulatory assistance or replacement.

Adult↗

PubMed1995

Postoperative symptomatic internal thoracic artery stenosis and successful treatment with PTCA.

From 1988 to 1992, 4,182 coronary bypass grafting procedures were performed at the University of Ottawa Heart Institute. The left internal thoracic artery (ITA) was used in 2,913 patients, the right ITA in 79, and bilateral ITAs in 61 for a total of 3,053 patients with ITAs. This study assessed patients requiring angioplasty for symptomatic ITA stenosis after operation. A total of 29 patients (0.95%) with a mean age of 55.3 +/- 1.9 years underwent angioplasty for ITA stenosis from 4 days to 34 months after operation (mean, 6.5 +/- 1.6 months). Internal thoracic artery stenosis was identified in 18 patients (62.1%) within 3 months after operation. Angina was present in 26 patients (89.7%), a positive stress test in 8 (27.6%), and myocardial infarction in 1 (3.4%). At angiography, a total of 34 stenotic sites were identified in ITA grafts. Angioplasty was successful (< 50% residual stenosis) in 31 sites (91.2%). Follow-up was available for 28 of 29 patients (96.6%) at 24.6 +/- 2.3 months. Four patients (14.3%) returned with restenosis within 3 months, 2 of whom had successful repeat angioplasty, and 1 required reoperation. Canadian Cardiovascular Society anginal class after angioplasty was less than class II in 84.6% of patients. In conclusion, symptomatic postoperative ITA stenosis is uncommon, occurs most frequently at the site of distal anastomosis, and generally presents within 3 months of operation. It may be safely and effectively treated with angioplasty with a low recurrence rate.

Adult↗

PubMed1995

Determinants of hospital survival after cardiac transplantation.

To identify the preoperative factors that influence hospital survival after transplantation we analyzed our consecutive experience of 183 transplantations in 179 patients over a 10-year period. There were 151 male and 29 female transplant recipients ranging in age from 10 days to 70 years (mean, 48 +/- 1 years). Diagnoses included coronary disease in 110 patients, cardiomyopathy in 55 patients, valvular disease in 6 patients, and congenital heart disease in 9 patients. Seventy-seven had undergone a previous cardiac operation, and 30 patients required preoperative mechanical support. Forty patients received hearts from donors who were 40 years old or older (range, 40 to 62 years). Ischemic time was greater than 240 minutes in 32 cases, and pulmonary vascular resistance was greater than 3 Wood units in 40 patients (range, 3.1 to 10.0 Wood units). Cyclosporine induction was used in 52 patients, whereas 128 recipients received polyclonal antibody prophylaxis. There were 25 hospital deaths. Recipient diagnosis, use of mechanical support, donor age, and the immune suppression protocol were related to hospital survival according to univariate analysis. Using multiple logistic regression, only the method of immune suppression induction and the use of mechanical assists were significant independent determinants of survival. In conclusion, we believe that extended ischemic times and donor age do not adversely affect the early success of transplantation, whereas induction with immune globulin may reduce early mortality. Patients requiring mechanical support before transplantation continue to be a challenge.

Adolescent↗

PubMed1995

Long-term experience with the Ionescu-Shiley pericardial valve.

To determine the long-term durability of the Ionescu-Shiley valve, we analyzed our experience with this valve at the University of Ottawa Heart Institute. To 1988, 780 patients have had aortic valve replacement (AVR = 528) or mitral valve replacement (MVR = 252). Of the aortic valves, 310 were standard profile and 218 were low profile. Of the mitral valves, 143 were standard profile and 109 were low profile. Actuarial survival at 10 years was as follows: AVR, 62% +/- 3%; MVR, 58% +/- 4%; p = 0.42. At 14 years, the results were AVR, 44% +/- 1% and MVR, 46% +/- 5%; p = 0.40. Reoperation was required in 197 patients. Structural failure was present in 85% of these valves, with leaflet tears alone in 69%, tears with calcification in 21%, and calcification alone in 10%. Leaflet tears occurred in 95% after AVR and in 78% after MVR (p = 0.006) and were seen in 95% of low-profile valves and 87% of standard-profile valves (p = 0.16). The actuarial freedom from reoperation at 10 years was: AVR, 58% +/- 3%; MVR, 62% +/- 5%; p = 0.49. At 13 years, these rates were 38% +/- 4% for AVR and 25% +/- 9% for MVR (p = 0.79). For AVR, the 10-year rate of freedom from reoperation was 57% +/- 4% for standard-profile valves and 57% +/- 8% for low-profile valves (p = 1.0). Similarly for MVR, the 10-year freedom from reoperation was 61% +/- 6% for standard-profile valves and 68% +/- 8% for low-profile valves.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗