Is tranexamic acid safe in patients undergoing coronary endarterectomy?

BACKGROUND

Patients undergoing coronary endarterectomy during coronary artery bypass grafting (CABG) are at increased risk of perioperative myocardial infarction due to coronary intimal disruption. Data assessing the safety of the antifibrinolytic drug tranexamic acid (TA) in patients undergoing this procedure are lacking.

METHODS

From September 1997 to December 1999, 221 patients underwent nonemergency primary CABG with endarterectomy of the right coronary artery alone in 149, the left anterior descending in 35, or both right and left anterior descending in 27. TA was administered intraoperatively to 87 patients (TA group: average total dose 62 +/- 4.4 mg/kg; range 20 to 109 mg/kg), and was not administered to 134 patients (No TA group).

RESULTS

The patient characteristics of the 2 groups were similar. In-hospital mortality consisted of 2 patients in the TA group and 4 patients in the No TA group. Perioperative myocardial infarction rates were 2% and 5% in the TA and No TA groups, respectively (p = 0.49). The relative risk for any type of perioperative cardiac ischemic event in the TA group versus the No TA group was 0.77 (95% CI; 0.4, 1.2). Patients in the TA group had a significant reduction in postoperative chest tube drainage (685 versus 894 mL in the TA versus No TA groups, respectively) and in the use of fresh-frozen plasma (p = 0.03).

CONCLUSIONS

These results suggest that the clinical effectiveness of tranexamic acid in reducing postoperative blood loss in patients undergoing coronary endarterectomy is not associated with a higher incidence of myocardial ischemia-related complications.

Comparative clinical outcomes with St. Jude Medical, Medtronic Hall and CarboMedics mechanical heart valves

BACKGROUND AND AIM OF THE STUDY

Whether the St. Jude Medical (SJM), Medtronic Hall (MH) or CarboMedics (CM) heart valves confer any relative benefits to patient outcome remains controversial. While numerous studies have analyzed clinical results with a single brand, and a few studies have compared two brands, there are no single-center trials comparing all three valves.

METHODS

Our experience with patients who had either a SJM, MH or CM mechanical valve in isolated aortic valve (AVR) or mitral valve (MVR) replacement was reviewed. AVR was performed in 953 patients (SJM = 394, MH = 314, CM = 245) and MVR in 591 patients (SJM = 193, MH = 264, CM = 134). Survivors were assessed annually; follow up consisted of 3336 patient-years (pt-yr) after AVR and 1693 pt-yr after MVR.

RESULTS

Preoperatively, in the AVR group, more MH patients had previous valve surgery (p = 0.001) or were in NYHA class III/IV (p = 0.03), and more CM patients had a concomitant surgical procedure (p = 0.005). The hospital mortality after AVR with SJM, MH and CM valves was 3.8, 4.7 and 5.3%, respectively (p = 0.65). In the MVR group, there were more males in the CM group (p = 0.011), more CM patients had concomitant surgery (p = 0.001), and more MH patients had previous surgery (p = 0.006). The hospital mortality after MVR with SJM, MH and CM valves was 8.3, 10.2 and 6.0%, respectively (p = 0.35). There was no late survival advantage in either the AVR or MVR group according to the valve used (p = 0.24 and p = 0.90, respectively). For the AVR group the five-year actuarial freedom from thromboembolism was: SJM 85.8 +/- 2.5%, MH 80.1 +/- 2.7% and CM 85.9 +/- 3.5% (p = 0.04), and for MVR it was: SJM 84.2 +/- 4.0%, MH 77.5 +/- 3.4% and CM 86.9 +/- 5.2% (p = 0.27). Bleeding occurred with a similar frequency in the AVR (p = 0.36) and MVR (p = 0.70) groups. No cases of structural failure were identified in this study. At follow up, among AVR patients NYHA class III/IV was present in: SJM 5%, MH 6% and CM 3% (p = 0.50), while among MVR patients this was identified in: SJM 7%, MH 10% and CM 4% (p = 0.22).

CONCLUSION

It is concluded that the SJM, MH and CM mechanical valves offer similar clinical results when used for isolated AVR or MVR. While there is a suggestion of an advantage with bileaflet valves, any differences detected may simply reflect differences in the preoperative patient variables.

The HeartSaver left ventricular assist device: an update

BACKGROUND

Ventricular assist devices have been shown to be effective as bridges to transplantation and recovery for patients with end-stage heart failure. Current technology has been limited because of the need for percutaneous connections with controllers. The HeartSaver ventricular assist device (VAD) (World Heart Corporation, Ottawa, Ontario, Canada) was developed with the intention of having a completely implantable, portable VAD system. The system consists of an electrohydraulic blood pump, internal and external battery power, and a transcutaneous energy transfer and telemetry unit that allows for power transmission through the skin. Control of the device may be achieved locally or remotely through a variety of communication systems.

METHODS

The device has been modified with the Series II preclinical version being available for in vitro (mock loop) and in vivo (bovine model) testing.

RESULTS

Seventeen Series II devices have been functional on mock loops or other testing trials for an accumulated 900 days of operation. There have been eight acute experiments using a bovine model to test various components as they have become available from manufacturing. Mean pump output was 10.4 +/- 1.1 L/min in full-fill/full-eject mode. Changes in the last 24 months include (1) cannula redesign for better port alignment and integration of tissue valves; (2) battery redesign to convert to new lithium-ion cells; (3) optimized infrared information and electromagnetic inductance energy transmission through various skin thicknesses and pigmentation; and (4) improved reliability of internal and external controller hardware and software.

CONCLUSIONS

Modifications have been required to optimize the HeartSaver VAD's performance. The final HeartSaver VAD design will be produced in the near future to allow for formal in vitro and in vivo testing before clinical implantation.

Endoglin is overexpressed after arterial injury and is required for transforming growth factor-beta-induced inhibition of smooth muscle cell migration

Endoglin is a homodimeric membrane glycoprotein primarily expressed on endothelial cells. In association with transforming growth factor (TGF)-ss receptors I and II, it can bind TGF-beta1 and -beta3 and form a functional receptor complex. There is increasing evidence that endoglin can modulate the cellular response to TGF-beta, a factor implicated in vascular lesion formation in human and experimental models. The purpose of this study was to analyze the expression of endoglin in normal and balloon-injured porcine coronary arteries and in normal and atherosclerotic human coronary arteries and to determine its ability to mediate the effects of TGF-beta on the migration of vascular smooth muscle cells (SMCs). In normal porcine coronary arteries, endoglin was of low abundance and was found primarily on endothelial cells and adventitial fibroblasts, as well as on a minority of medial SMCs. On days 3, 7, and 14 after angioplasty, endoglin was present not only on endothelial cells but also on adventitial myofibroblasts and medial SMCs of porcine coronary arteries. By day 28, few or no cells expressed endoglin. In situ hybridization revealed that endoglin mRNA expression appeared to be highest in endothelial cells on days 3, 7, and 14 days after injury and absent thereafter. With a second balloon injury, a similar pattern of endoglin protein and mRNA expression was observed. In human vascular tissue, endoglin immunolabeling was higher in endarterectomy specimens removed from diseased coronary arteries than in normal internal mammary arteries. In vitro, antisense oligonucleotides to endoglin decreased its expression and antagonized the TGF-beta-mediated inhibition of human and porcine SMC migration. In summary, upregulation of endoglin occurs during arterial repair and in established atherosclerotic plaques and may be required for modulation of SMC migration by TGF-beta.

HeartSaver VAD: a totally implantable ventricular assist device. Results of in vivo studies

Currently, the most widely utilized ventricular assist devices (VADs) require percutaneous connections and are located either externally (e.g., Thoratec, Abiomed) or intra-abdominally (e.g., Novacor, TCI). These attributes have been implicated in a variety of complications (infection, thromboembolic, gastrointestinal, etc.). To address these concerns, a totally implantable VAD that requires no percutaneous connections and can be implanted in the left hemi-thorax has been developed. The developed device has undergone in vivo evaluation as part of the design and development process. A total of 43 implants in the bovine model, with 5 device versions, have been conducted between July 1992 and February 2000. These studies successfully have demonstrated several important aspects of the developed device, including 1) feasibility of a totally implantable system; 2) capability of the device to support a dysfunctional heart; and 3) ability of the device to provide flows up to 10 L/min in a physiological setting. The studies to date have played a vital role in the design and development process as well as demonstrating the feasibility of a totally implantable intrathoracic VAD. Based on these studies, design optimization was conducted, resulting in the development of the pre-clinical version of the device in preparation for clinical trials.

Early and follow-up angiography in minimally invasive coronary bypass without mechanical stabilization

BACKGROUND

This study was undertaken to assess the early and late outcome of coronary anastomosis constructed on a beating heart without the help of mechanical stabilization.

METHODS

All consecutive patients (51) from January 1996 to September 1997 who had bypass done by one surgeon using a left minithoracotomy (39) or median sternotomy (12) on a beating heart with occlusive local snares without mechanical stabilization underwent follow-up angiography early (100%) (within 6 hours) and late (63.5%) at a mean of 9.6+/-4.48 months (range, 3.3 to 19.1 months).

RESULTS

The cumulative late patency was 95.4% (83 of 87 patients), with two early and two late occlusions. There was no early or late mortality or perioperative myocardial infarction. Two patients (3.9%) developed recurrent angina. Four anastomotic irregularities (4 of 32 patients, 12.6%) have cleared up on follow-up angiography. There was no evidence of late stenosis at the snare sites used for local occlusion.

CONCLUSIONS

Minimally invasive coronary bypass is safe and effective. Early angiographic abnormalities should be interpreted with caution and we could not demonstrate any long-term deleterious effects of local snaring.

Are older patients with mechanical heart valves at increased risk?

BACKGROUND

Controversy exists regarding the use of mechanical valves in older patients. Many authorities believe that the use of anticoagulants in the elderly is associated with an increased risk of warfarin-related complications. Therefore, we compared the results with mechanical valves in older patients to a cohort of younger patients.

METHODS

Aortic (AVR) or mitral valve replacement (MVR) with a mechanical valve was performed in 1,245 consecutive patients who were followed prospectively. They were grouped by age (group 1, < or = 65 years; group 2, > 65 years). The study groups consisted of AVR (group 1, 459 patients; group 2, 323 patients) MVR (group 1, 313 patients; group 2, 150 patients).

RESULTS

The average age for the groups was: AVR (group 1, 51 years; group 2, 70 years; p = 0.03) and MVR (group 1, 53 years; group 2, 70 years; p = 0.03). For AVR the incidence of thromboembolism was 0.050 (group 1) and 0.038 (group 2) (p = 0.37) and the actuarial freedom from thromboembolism was 83.0%+/-3.0% and 86.5%+/-1.0%, respectively (p = 0.13). The incidence of bleeding after AVR was 0.021 for group 1 and 0.028 for group 2 (p = 0.49). For MVR the incidence of thromboembolism was 0.059 for group 1 and 0.051 for group 2 (p = 0.75) and the actuarial freedom from thromboembolism was 78.8%+/-3.0% and 75.4%+/-8.7%, respectively (p = 0.71). The incidence of bleeding after MVR was 0.020 for group 1 and 0.027 for group 2 (p = 0.62).

CONCLUSIONS

Mechanical valves perform well in selected older patients with no increased risk of bleeding or thromboembolism.

Successful surgical endarterectomy of a stented coronary artery

An occlusion in this 61-year-old male's distal right coronary artery was initially successfully opened with balloon angioplasty and three "half" Palmaz-Schatz stents (Johnson and Johnson International Systems, Warren, NJ). Subsequent occlusion of the RCA occurred and prompted bypass grafting 2 years later. An extensive manual surgical endarterectomy removed the stents, demonstrating the technical feasibility of surgically removing failed stents in accessible coronary arteries.

Determinants of hospital survival following reoperative single valve replacement

OBJECTIVE

To determine the indicators of risk for hospital death, patients undergoing reoperative valve replacement were analyzed

METHODS

Four hundred and eighteen consecutive patients undergoing reoperative valve replacement from 1977 to 1994 were reviewed using univariate and multivariate analysis.

RESULTS

Overall hospital mortality was 11.2% with 9.4% mortality with aortic valve replacement and 14.2% with mitral valve replacement (P=0.52). Mortality was 9.7% for patients less than 70 years of age compared with 19.4% for older patients (P=0.03), and was 8.5% for those with anoxia times less than 90 mins versus 21.9% for those with longer anoxia times (P=0.001). For first reoperations, 9.5% of patients died, while for patients undergoing second or more reoperation, mortality was 23.2% (P=0.01). While mortality increased from 8.9% to 19.0% with the addition of a concomitant procedure (P=0.008), it was not affected if the additional procedure was a coronary bypass (P=0. 96). The indication for surgery influenced outcome. Mortality was zero for thromboembolism, 9% for structural failure, 23% for nonstructural failure and 22% for endocarditis (P=0.006). For New York Heart Association (NYHA) functional class I patients, mortality was 1.6% compared with 22.3% for those in NYHA class IV (P=0.006). By multivariate analysis, however, only the indication for surgery and the NYHA functional class influenced survival.

CONCLUSIONS

Reoperative valve surgery can be performed with a survival (88.8%) that is similar to the initial procedure (91.2%). The indication for surgery and NYHA functional class alone influenced outcome; therefore, possible early reoperation is indicated before clinical deterioration occurs.

Circulatory support for cardiogenic shock due to acute myocardial infarction: a Canadian experience

BACKGROUND

Cardiogenic shock due to acute myocardial infarction (AMI) is associated with high mortality. Circulatory support devices may be used to assist these patients while they await cardiac transplantation.

METHODS AND RESULTS

From 1986 to 1997, 25 patients in cardiogenic shock complicating AMI within 3.6+/-0.7 days of the event were supported with artificial hearts. Of the 25 patients, 21 were men with a mean age of 48.4 +/- 1.8 years. The age range was 26 to 62 years. Patients were considered for a device when the following criteria were met: cardiac index less than 1.8 L/min/m2, wedge pressure greater than 20 mmHg despite one or two inotropes and/or intra-aortic balloon support. They received either a CardioWest total artificial heart (n=13), a Thoratec biventricular assist device (n=6) or left ventricular assist device (LVAD) (n=6). Three patients were not considered transplant candidates and died while on the devices (two with multiorgan failure and one found to have a bronchogenic carcinoma after implant), with 22 undergoing cardiac transplantation within 8.6+/-2.2 days of device implant. Six patients died in hospital after the transplants (27.3% mortality). Complications included bleeding or tamponade in seven (28%), pneumonia in six (24%) and right ventricular failure in three LVAD patients (12%). Post-transplant actuarial one-, two- and five-year survival rates were 71.4%, 71.4% and 51%, respectively.

CONCLUSIONS

Circulatory support devices offer a means to maintain organ perfusion in patients who develop cardiogenic shock due to AMI. Patients can then undergo transplantation with a reasonable expectation for survival when the alternative is death. Eventually the availability of permanent support devices may obviate the need for transplant in these patients.

Ochronosis: an unusual finding at aortic valve replacement

The condition known as ochronosis refers to the accumulation of oxidized homogentisic acid in the connective tissues of alkaptonuric patients. The diagnosis is usually made from the triad of degenerative arthritis, ochronotic connective tissue pigmentation and urine that turns dark brown or black on alkalinization. Cardiovascular disease is a less well appreciated aspect of this disorder. A patient with ochronosis of his stenotic aortic valve is reported. The role of the pigment in the genesis of the valve degeneration is discussed.

Progress with the HeartSaver Ventricular Assist Device

BACKGROUND

Ventricular assist devices (VADs) have been shown to be effective for short- or long-term circulatory support. Devices are either being adapted or newly designed for longer term or permanent support, with the goal to provide patients with improved quality of life. Since 1990, a program has been in place to develop a totally implantable, permanent VAD.

METHODS

A multidisciplinary team is developing this VAD with specific goals in mind: (1) that it have an intrathoracic position, (2) that it be a totally implantable device without any percutaneous connections, and (3) that it be possible to communicate with the device from remote locations. These goals would allow for complete patient mobility and flexibility for follow-up.

RESULTS

The electrohydraulically actuated VAD combines the blood pump, volume displacement chamber, energy converter, and internal electronic module into a single compact unit. The device called the HeartSaver VAD is powered by a transcutaneous energy transfer system and can be remotely monitored and controlled. Prototypes of different versions of the device have been tested in vitro and in vivo with satisfactory performance.

CONCLUSIONS

The prototypes of the HeartSaver VAD have functioned well under test conditions and fulfilled the outlined goals. Further development and testing of the design are being conducted before clinical availability.

Heart transplantation in perspective

Heart disease remains one of the leading causes of death in the western world. In the 35 years since the first human heart transplants, cardiac transplantation has become established as the therapeutic option of choice in the management of terminal cardiac failure. Since 1981, the introduction of cyclosporin for immunosuppression has dramatically increased cardiac transplantation. However, several obstacles limit further utilization, including limited availability of donor hearts, limited ischemic time tolerated by donor hearts, and chronic rejection. Research is underway into donor heart preservation and new immunosuppressant drugs in an effort to increase donor organ availability. Due to these constraints, alternative therapies are under development. More than 2,000 circulatory assist devices have been implanted with >25% used as a bridge to heart transplantation. The University of Ottawa Heart Institute began the first Canadian implantation of circulatory assist devices in 1986 and has implanted 23 total artificial hearts and 23 ventricular assist devices. The Heart Institute is also developing a totally implantable electrohydraulic ventricular assist device (EVAD) for long-term mechanical support outside the hospital. Another alternative being evaluated for clinical use is xenotransplantation. The major obstacle for widespread use of clinical xenotransplantation remains graft rejection, and fundamental research is ongoing to address hyperacute and delayed xenograft rejection. While cardiac transplantation is the most effective treatment of terminal heart failure, limited donor hearts compel us to rely on alternatives. In the future, the research underway on xenotransplantation and mechanical circulatory assist devices will provide new options for the clinical treatment of terminal cardiac failure.

Development of a ventricular assist device for out-of-hospital use

BACKGROUND

Success with temporary ventricular assist devices, has prompted interest in devices developed for long term use outside of the hospital setting.

METHODS

A totally implantable intrathoracic electro-hydraulic ventricular assist device has been developed. Design focused on providing the recipient with a near normal quality of life. To meet this goal the system utilizes transcutaneous energy transfer and biotelemetry to eliminate percutaneous drive-lines/cables as well as a displacement chamber capable of pressure equalization to atmospheric pressures, so as to eliminate the need for percutaneous venting. An implanted battery provides backup power to allow the recipient the ability to bathe, shower, or swim without connection to an external power source. An integrated telemedicine capability allows the device to be monitored/controlled remotely, using telephone lines.

RESULTS

The system has been tested in vitro with early prototypes running for up to 5 1/2 years. The system was studied in calves (n = 25) with durations of support of up to 30 days, demonstrating the ability of the device to function as a totally implantable device without percutaneous connections.

CONCLUSIONS

The various in vitro and in vivo studies have demonstrated the feasibility of the totally implantable device. Chronic in vivo experiments will follow in preparation for regulatory submissions for human use.

The Ottawa telehealth project

OBJECTIVE

To examine the telehealth system as a means of improving access to cardiac consultations and specialized health services in remote areas of Ontario.

METHODS

The University of Ottawa Heart Institute has set up a telehealth test program, Healthcare and Education Access for Remote Residents by Telecommunications (HEARRT), in collaboration with industry and the provincial and federal government, as well as several remote clinical test sites. The program makes off-site cardiology consultations possible. History taking and physical examinations are conducted by video and electronic stethoscope. Laboratory results and echocardiograms are transmitted by document camera and VCR. The technology is being tested in both stable outpatient and emergency situations. Various telecommunications bandwidths and encoding systems are being evaluated, including satellite and terrestrial-based asynchronous transfer-mode circuits. Patient satisfaction and cost-effectiveness are also being assessed.

RESULTS

Bandwidths from as low as 384 kbps using H.320 encoders to 40 Mbps using digital transport of NTSC video signals have been evaluated. Although lower bandwidths are sufficient for sending echocardiographic and electrocardiogram data, bandwidths with transport speeds of 4 to 6 Mbps appear necessary to capture the nuances of the cardiac physical examination. A preliminary satisfaction survey of 19 patients noted that all felt that they could communicate effectively with the cardiologist by video, and each had confidence in the advice offered. None reported that he or she would rather have traveled to the doctor in person. Initial and projected examination of the costs suggested that telehealth will effectively reduce overall health care spending while decreasing travel expenses for rural patients.

CONCLUSION

Telehealth technology is sufficiently sophisticated to allow off-site cardiology assessments. Preliminary results suggest there is a sound business case for the implementation of telehealth technology to meet the needs of remote residents in northern Ontario. Working closely with government and industry, we will develop a marketing and commercialization plan to support the use of this technology throughout Ontario and expand application to patient education and continuing medical education.

Cardiac operations in the elderly: who is at risk?

BACKGROUND

With the growing number of elderly patients presenting for cardiac operations we analyzed their early survival data to determine whether any preoperative variables might be indicative of increased risk.

METHODS

From 1990 to 1995, 436 consecutive patients who were 75 years old or older had either coronary artery bypass, valve replacement(s), or a combination of these. A total of 34 preoperative variables were assessed for their effect on hospital survival by using univariate and multivariable analysis.

RESULTS

There were 266 men and 170 women, with 292 patients being 75 to 80 years old and 144 patients being older than 80 years. Coronary artery bypass was performed in 242 patients, valve replacement was performed in 93 patients, and a combination of these in 101 patients. The operation was considered elective in 202 patients, urgent in 209, and emergent in 25 patients of whom 21 were in cardiogenic shock. Overall there were 61 hospital deaths (13.9%). The most common cause of death, low cardiac output syndrome, occurred in 34 patients of whom 26 suffered a perioperative myocardial infarction. Stroke was the cause of death in eight and multiple organ failure accounted for nine deaths. In the univariate analysis, variables that influenced survival included heart failure (p = 0.004), pulmonary edema (p = 0.004), cardiomegaly (p = 0.02), elevated serum creatinine (p = 0.009), surgical priority (p = 0.002), and cardiogenic shock (p = 0.002). In the multivariable analysis there were three independent determinants of hospital survival: cardiomegaly (odds ratio, 1.8:1) serum creatinine level higher than 150 micromol/L (odds ratio, 5.5:1) and emergency procedure (odds ratio, 2.5:1).

CONCLUSIONS

Although cardiac operations can be performed safely in many elderly patients, we identified several factors that might help both in case selection and in perioperative decisions.

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.

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.

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).

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.

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.

Early release after cardiac surgery

Early release after cardiac surgery can be facilitated by the implementation of a standard protocol for pre- and postoperative care. This protocol involves aggressive pharmacological therapy, in combination with education and support. Accelerated recovery and release is inherently attractive because the duration of intensive care unit stay and of total hospital stay are the most important determinants of costs. However, in addition to the desire for reduced costs, the patients must be clearly seen to benefit from earlier rehabilitation and release. Retrospective studies have shown no significant differences in mortality or morbidity between patients who have received conventional care and those given 'fast-tracked' care after cardiac surgery, and follow-up surveys have shown a high level of patient satisfaction with the care. Some centres report that all cardiac surgery patients are now fast-tracked.

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.

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.

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.

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.

Evolution of an electrohydraulic ventricular assist device through in vivo testing. The EVAD Team

A totally implantable intrathoracic electrohydraulic ventricular assist device has been developed at the University of Ottawa Heart Institute. In vivo testing has been instrumental in its progressive development. A total of 15 experiments (4 acute, 11 performance) have been performed using male calves (62-117 kg). Data from the acute experiments, human fit trials, fluid dynamic studies, and hydraulic/energy efficiency analyses formed the basis for the development of a compact, single piece ventricular assist device called the Unified System in which the volume displacement chamber, motor, and blood chamber are housed within a compact 600 cc, 740 g unit. The performance experiments indicated that the unified system could support calves for periods up to 96 hr. The mean postoperative cardiac output was 7.1 +/- 0.7 L/ min (range = 4.9-11), mean blood pressure was 99.7 +/- 5.8 mmHg, and mean pulmonary artery pressure was 32.1 +/- 1.2 mmHg. The operative technique for intrathoracic implantation has been developed. The major problems encountered were of respiratory failure, improved by device repositioning in the calf; decreased blood inflow to the device that was improved by cannula redesign; circuit board fracture corrected by design modification; and a power supply problem that was limited to a single unit. The preliminary experiments have helped in the design modifications of the Unified System. The improved version of the system will undergo formal performance, reliability, and chronic in vivo testing before human implantation.

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.

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.

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.

A fenestrated aortic valve contributing to iatrogenic aortic insufficiency post mitral valve replacement

A case of an unusual local complication of cardiac valvular surgery is presented. Distortion of the geometry of the aortic valve base by a prosthetic mitral valve sewing ring allowed aortic insufficiency through the aortic valve's central orifice, as well as through an aortic valve cusp fenestration. During the 6 years after valve surgery, this patient developed chronic left heart failure contributed to by the aortic insufficiency and eventually, at age 65, required cardiac transplantation. Surgeons and pathologists should be aware of this unusual local complication of cardiac valve surgery, as it may have serious consequences.

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.

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.

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.

Coronary subclavian steal: a recurrent case with notes on detecting the threat potential

A 43-year-old military patient with silent myocardial ischemia due to proximal anterior descending coronary artery and major diagonal branch stenoses had left and right internal mammary artery grafts in 1973, with excellent angiographic results. In 1984, silent ischemia recurred, due to proximal subclavian occlusion with collateral subclavian steal from the left internal mammary artery. A carotid-subclavian artery graft required replacement in 1987 and in 1989 for steal recurrence from graft stenosis due to thrombosis/atherosclerosis. The final 12-mm graft remained smooth with conventional anticoagulant therapy. However, in 1994, ostial compromise of the left internal mammary artery reduced flow enough to require relief of the original and unchanged anterior descending stenosis by transluminal angioplasty and stent placement. Observations are made on subclavian steal and simple methods for detecting its potential for occurrence.

Preservation of cell organelles during storage of human atrial tissue in the University of Wisconsin solution

AIM OF THE STUDY

The University of Wisconsin storage solution (UW) (E.I. du Pont de Nemours, Wilmington, DE) has been successful in extending the storage period using some model systems of donor heart preservation for cardiac transplantation. The ability of UW to preserve human cardiac cell organelle (sarcoplasmic reticulum, mitochondria and sarcolemmal) membrane composition (enzyme activity, protein, cholesterol and phospholipid content) was compared to St. Thomas's Hospital Solution (ST) and saline.

METHODS

Human atrial appendages were stored at 4 degrees C for 24 h in saline, ST or UW or not stored (controls) and the cell organelles isolated. Each fraction was assayed for enzyme activity (mitochondria: azide sensitive Ca2+ ATPase, cytochrome C oxidase; sarcolemmal membrane: Na+K+ ATPase, p-nitrophenylphosphatase; sarcoplasmic reticulum: CA2+ uptake, Ca2+ ATPase, NADPH cytochrome C reductase), protein, cholesterol and phospholipid content.

RESULTS

"Protein yield" proved to be the most sensitive marker for cell organelle preservation. Only the sarcolemmal membrane showed no decrease in either enzyme activities of "protein yield" after storage in saline, ST or UW. Mitochondria showed no decrease in enzyme activities but a decrease in "protein yield" after storage in all 3 solutions. The "protein yield" of sarcoplasmic reticulum was significantly reduced after storage in UW, saline and ST. No correlation could be drawn between cholesterol and phospholipid content and the preservation of cell organelle function.

CONCLUSIONS

It is possible to distinguish between the ability of solutions to preserve the membrane composition of human cardiac tissue during hypothermic storage. Using simple assays to assess preservation provides preliminary screening for a superior solution which can then be used in more complicated transplantation models to more fully assess cardiac function.

Comparative results with the St. Jude Medical and Medtronic Hall mechanical valves

This study compared the clinical performance of the St. Jude Medical and Medtronic Hall mechanical valves in isolated aortic or mitral valve replacement. From 1984 to 1993, 349 St. Jude Medical valves (aortic 237, mitral 112) and 465 Medtronic Hall valves (aortic 272, mitral 193) were implanted in 814 patients at the University of Ottawa Heart Institute. The patients had similar preoperative characteristics. The hospital mortality rate for aortic valve replacement was 3.4% with the St. Jude Medical valve and 5.8% with the Medtronic Hall valve (p = 0.26) and the rate for mitral valve replacement was 8.9% with the St. Jude Medical valve and 11.9% with the Medtronic Hall valve (p = 0.54). Actuarial estimates of survival and freedom from complications were calculated. At 5 years the actuarial probability of survival (including hospital deaths) for aortic valve replacement was 86% +/- 3% with the St. Jude Medical valve and 68% +/- 4% with the Medtronic Hall valve (p = 0.0001) and for mitral valve replacement was 75% +/- 7% with the St. Jude Medical valve and 70% +/- 4% with the Medtronic Hall valve (p = 0.54). The most common cause of late death was cardiac failure and no deaths were caused by structural failure. The 5-year probability of freedom from bleeding after aortic valve replacement was 99% +/- 1% with the St. Jude Medical valve and 95% +/- 2% with the Medtronic Hall valve (p = 0.06) and after mitral valve replacement 99% +/- 1% with the St. Jude Medical valve and 97% +/- 2% with the Medtronic Hall valve (p = 0.37). The 5-year probability of freedom from thromboembolism after aortic valve replacement was 88% +/- 4% with the St. Jude Medical valve and 81% +/- 3% with the Medtronic Hall valve (p = 0.08) and after mitral valve replacement was 85% +/- 7% with the St. Jude Medical valve and 77% +/- 5% with the Medtronic Hall valve (p = 0.17). Reoperation was uncommon and there were no cases of structural valve failure. The 5-year actuarial estimate of freedom from reoperation therefore for aortic valve replacement was 99% +/- 1% with the St. Jude Medical valve and 96% +/- 2% with the Medtronic Hall valve (p = 0.09) and for mitral valve replacement was 98% +/- 2% with the St. Jude Medical valve and 95% +/- 3% with the Medtronic Hall valve (p = 0.40).(ABSTRACT TRUNCATED AT 400 WORDS)

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)

Assessment of reused catheters

Demands for health care cost containment have prompted the assessment of recycling medical devices, including catheters. The investigation of catheter reuse for effectiveness and safety began at the University of Ottawa Heart Institute in early 1994. This report provides the preliminary results from this ongoing assessment on the feasibility of catheter reuse. Burst tests were conducted to detect changes in catheter mechanical integrity. Scanning electron microscopy (SEM) was performed to assess surface changes and protein deposition after use and the subsequent cleaning process. Results of burst testing showed no significant difference in burst patterns or burst pressures between single use and unused catheters. Surface differences were observed between used and unused catheters. SEM studies detected physical changes such as scratches, gouges, cuts, and deposits on the used catheters. Unused balloon surfaces appeared to be clean and uniform compared to used ones. Residue and cracking were identified on other used devices. In conclusion, the methods used can assess various effects of recycling. A blind study of large samples of used catheters is planned to establish statistically the level and variance of structural damage to catheters during typical use.

A transcutaneous energy and information transfer system for implanted medical devices

During the last four decades there has been a rapid increase in the development and usage of medical devices. Currently, there are more than 500,000 devices on the market and 25,000 new devices enter the market each year. Many medical devices are now designed to be implantable (pacemakers, defibrillators, circulatory assist devices, artificial hearts, cochlear implants, neuromuscular stimulators, biosensors, etc.). Almost all of the active devices (those that perform work) and many of the passive devices (those that do not perform work) require a source of power. In addition, these devices need to be monitored and controlled, which can be accomplished by utilizing remote communication methods. A transcutaneous energy transfer system combined with a remote communications system has been developed and evaluated in vitro and in vivo (bovine, porcine, and human cadaver experiments). The energy transfer system can deliver up to 60 W with power transfer efficiencies between 60 and 83%. An automatically tuned, resonant frequency tracking method is used to obtain optimum power transfer over a range of operating conditions. The remote communications system can transfer digital data bidirectionally through intact skin at rates up to 9600 baud. The system transmits information by frequency modulating an 890 nm infrared carrier signal. The system has demonstrated satisfactory performance during multicenter evaluation with ventricular assist and total artificial heart devices. Design improvements have been identified, which will be implemented to produce an optimized system for energy transfer to and remote communications with various implantable medical devices.

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.

The role of magnesium in myocardial preservation

The purpose of this review is to look at the role of magnesium in the formation of preservation and reperfusion solutions for the ischaemic heart. Preservation of the heart during cardiac surgery procedures, including cardiac transplantation, can be divided into distinct phases: arrest, cold storage in the case of transplantation, global ischaemia during implantation or cardiac surgery procedures, followed by reperfusion when the heart is rewarmed and restarted. Although the magnesium ion can play a significant role in myocardial protection, it is important to recognize the different types of protection required during these different phases of surgical procedures. The rationale for the inclusion of magnesium in cardioplegic solutions is threefold: (i) for its negative inotropic effect; (ii) to prevent ischaemia-induced magnesium loss; (iii) to influence cellular ionic movements. Preservation temperature as well as the concentration of other ionic constituents present in the preservation solution alter the effects of magnesium. Results obtained from animal models suggest that elevated magnesium (16 mM) is beneficial to the hypothermic preservation of hearts with extracellular type solutions, especially when calcium is elevated in the solution formulation. Research has shown that the amplitude of the inotropic effect of magnesium varies from one species to another so that the beneficial effect of magnesium is inferior in the less sensitive species. Using the human atrial trabecular preparation as a model for myocardial preservation, we have assessed the effects of elevated magnesium on the recovery of developed force, both for long-term preservation (24 h) during hypothermic arrest (4 degrees C) and for reperfusion during rewarming of the trabeculae. No clear pattern emerged when the ratio of calcium to magnesium was altered in St Thomas' I and II solutions used for the storage. However, when the atrial trabecular preparation was rewarmed in a Krebs Henseleit buffer containing an elevated level of magnesium (16 mM), a greater number of trabeculae reached a greater developed force and had higher levels of energetic metabolites than when the magnesium in the Krebs Henseleit buffer was 1.2 mM. Several studies have suggested that an elevated magnesium prevents calcium overload by competing with this ion at the membrane, and reduces the workload, while ATP reserves and ion homoeostasis are re-established. The role of the magnesium ion in hypothermic preservation of the human myocardium is still not clear after many clinical and experimental studies and requires further investigation.(ABSTRACT TRUNCATED AT 400 WORDS)

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.