Study of two different thin film coating methods in transmission laser micro-joining of thin Ti-film coated glass and polyimide for biomedical applications.

Biomedical devices and implants require precision joining for hermetic sealing which can be achieved with low power lasers. The effect of two different thin metal film coating methods was studied in transmission laser micro-joints of titanium-coated glass and polyimide. The coating methods were cathodic arc physical vapor deposition (CA-PVD) and electron beam evaporation (EB-PVD). Titanium-coated glass joined to polyimide film can have neural electrode application. The improvement of the joint quality will be essential for robust performance of the device. Low power fiber laser (wave length = 1100 nm) was used for transmission laser micro-joining of thin titanium (Ti) film (approximately 200 nm) coated Pyrex borosilicate 7740 glass wafer (0.5 mm thick) and polyimide (Imidex) film (0.2 mm thick). Ti film acts as the coupling agent in the joining process. The Ti film deposition rate in the CA-PVD was 5-10 A/s and in the EB-PVD 1.5 A/s. The laser joint strength was measured by a lap shear test, the Ti film surfaces were analyzed by atomic force microscopy (AFM) and the lap shear tested joints were analyzed by optical microscopy and scanning electron microscopy (SEM). The film properties and the failure modes of the joints were correlated to joint strength. The CA-PVD produced around 4 times stronger laser joints than EB-PVD. The adhesion of the Ti film on glass by CA-PVD is better than that of the EB-PVD method. This is likely to be due to a higher film deposition rate and consequently higher adhesion or sticking coefficient for the CA-PVD particles arriving on the substrate compared to that of the EB-PVD film. EB-PVD shows poor laser bonding properties due to the development of thermal hotspots which occurs from film decohesion.

Coronary bypass after ascending aorta to femoral graft placement running head: CABG after ascending aorta-bifemoral graft.

A 73-year-old woman had undergone ascending aorta-bifemoral bypass 9 years previously and now required coronary artery bypass for unstable angina. The technical considerations for the operation had never been described. We successfully completed the operation by mobilization of the pre-existent graft as it exited the thorax and by intermittent aortic root perfusion of the graft. Postoperatively she had no lower extremity complications, despite what was likely a graft dependent circulation. The same technique for coronary bypass can likely be used for all extra-anatomic bypass grafts originating from the ascending aorta. An alternate theoretical method is also discussed.

Sinus of Valsalva repair for annulo-aortic ectasia and aortic insufficiency.

OBJECTIVE: The standard treatment of ascending aortic aneurysms (AsAAs) with annulo-aortic ectasia and aortic insufficiency has been composite graft replacement of the valve and ascending aorta. The authors propose a method of repair which preserves the native aortic valve and correct the aneurysmal dilation of the sinus of Valsalva yet preserves its normal shape. PATIENTS/INTERVENTIONS: Two patients with large AsAAs and severe aortic insufficiency had operative repair by plication of the sinuses of Valsalva which maintained the normal sinus shape and restored coaptation of the aortic leaflets. MAIN RESULTS: Late postoperative echocardiography revealed only mild aortic insufficiency in both patients and no evidence of further sinus dilation. CONCLUSIONS: Repair of the sinus of Valsalva preserves the aortic valve and native coronary ostia, can correct existing aortic insufficiency and can provide a good functional result without the need for anticoagulation.

Thoracic aortic surgery.

Between 1982 and 1989, 119 patients had repair of thoracic aortic pathology. Thirty-seven had repair of ascending aortic aneurysms, with an 11% hospital mortality. Forty-one patients had urgent repair of acute type A aortic dissections, with a 32% hospital mortality. The independent predictors of mortality were the use of crystalloid cardioplegia, aortic dissection, and the use of an intraluminal prosthesis or the inclusion surgical technique. Better grafts and the resection technique has reduced mortality since 1986. Seventeen patients had their primary pathology in the aortic arch, with a 47% hospital mortality. The urgency of the procedure and crystalloid cardioplegia predicted an unsuccessful outcome. Seventeen patients had descending aortic aneurysms repaired, with an 18% mortality. The urgency of surgery was the predictor of mortality. Seven patients had a descending thoracic aortic disruption repaired, with one death (14%). Better graft materials, surgical techniques, and methods of myocardial protection have contributed to the improved results of thoracic aortic surgery in recent years.

Ancrod anticoagulation for cardiopulmonary bypass in heparin-induced thrombocytopenia and thrombosis.

Heparin-induced thrombocytopenia and thrombosis was diagnosed in a 50-year-old man undergoing a repeat heart operation after heparinization led to microemboli and an eventual left transmetatarsal amputation. A third heart operation was aborted when anticoagulation with low molecular weight heparin produced intraoperative thrombi. The patient was referred to Toronto where ancrod (Arvin) was used to lower plasma fibrinogen level, allowing successful repair of a ventricular septal defect using cardiopulmonary bypass support. The patient made an uneventful recovery.

Clinical performance of Bjork-Shiley mechanical heart valves: a perspective on outlet strut fractures in the 60 degrees and 70 degrees convexo-concave disc models.

The convexo-concave disc model of Bjork-Shiley mechanical heart valve is a significant improvement over the spherical disc model and compares favourably to other valves, including bioprostheses, with respect to hemodynamics, thromboembolism, anticoagulant related hemorrhage and prosthetic endocarditis. A small number of the 60 degrees and 70 degrees welded outlet strut Bjork-Shiley convexo-concave valves are at risk of sudden structural failure. The risk is constant or decreasing with time. Elective explanation is not recommended. The integral outlet monostrut 70 degrees Bjork-Shiley convexo-concave valve demonstrates further improvements in design and durability, and is recommended for use in patients who are appropriate candidates for mechanical cardiac prostheses.

5-year results of a prospective study of percutaneous transluminal angioplasty.

This paper presents the results of a prospective study of percutaneous transluminal angioplasty (PTA) for the treatment of patients with peripheral arterial occlusive disease and identifies the variables that are predictive of long-term success. The variables believed to be important prognostically were recorded for 984 consecutive PTAs performed between July 1978 and July 1986. Success or failure was defined using a combination of clinical and objective vascular laboratory criteria. The overall long-term success was estimated by the Kaplan-Meier method and differences between curves of success rate versus time for each variable were determined by the Wilcoxon and log-rank statistics. The combination of variables associated with success were determined by the Cox proportional hazards regression model. For all cases, the initial success rate was 88.6 +/- 1.0% and at 5 years was 48.2 +/- 2.3%. The following variables, when considered individually, were associated with success (p less than 0.05): indication for PTA, site of PTA, severity of lesion, runoff, number of sites dilated, diabetes, and the occurrence of a complication. From the Cox model, by using a stepwise multiple regression procedure, the following combination of variables were found to be predictive of success (p less than 0.05): (1) indication (claudication vs. salvage), (2) site (common iliac vs. other), (3) severity of lesion (stenosis vs. occlusion), and (4) runoff (good vs. poor). For all combinations of these four significant variables, curves of the success rate versus time were calculated. In conclusion, this study has identified the combination of four variables that together predict if PTA is likely to be successful in the management of a patient with peripheral arterial occlusive disease.

The determinants of mortality and morbidity after multiple-valve operations.

The factors predictive of hospital mortality and morbidity after contemporary multiple-valve surgical procedures were identified to develop strategies to improve the results of such procedures. Preoperative, intraoperative, and postoperative information was collected prospectively on 90 consecutive patients undergoing surgical procedures between 1982 and 1984. The operative mortality was 5.6%, and the incidence of postoperative low-output syndrome was 16.7%. Multivariate logistic regression analysis identified tricuspid regurgitation (p less than .03, improvement-of-fit chi square) and the aortic valve lesion (p less than .03) as the independent predictors of postoperative complications (mortality or low-output syndrome). Patients with tricuspid regurgitation and right ventricular decompensation and those with aortic stenosis and left ventricular hypertrophy had limited ventricular functional reserve and faced an increased risk. Improved methods of myocardial protection may reduce the risk in these patients.

Increased risk of urgent revascularization.

To determine the risk factors for operative mortality and morbidity, we performed a prospective analysis of 1,980 patients undergoing isolated coronary artery bypass operations between 1982 and 1984. The operative mortality was 3.5%, and the incidence of perioperative myocardial infarction was 8.6% and low output syndrome, 12.0%. Stepwise logistic regression identified sex, preoperative left ventricular ejection fraction, and the urgency of operation as independent risk factors for postoperative mortality. Urgent revascularization was performed in patients with unstable angina refractory to maximal medical therapy. In these patients the operative mortality was 8.5%. Independent risk factors of postoperative morbidity, in addition to sex, ejection fraction, and urgent revascularization, included a previous bypass procedure, age, and New York Heart Association functional class. Unstable angina unresponsive to medical therapy contributed significantly to the operative risk. Interventions to reduce perioperative ischemic injury, such as improved methods of myocardial protection, may improve the results in high-risk patients.

Diltiazem cardioplegia. A balance of risk and benefit.

Calcium channel blockers may prevent myocardial injury during cardioplegia and reperfusion. A prospective, randomized trial was instituted to evaluate the hemodynamic and myocardial metabolic recovery in 40 patients undergoing elective aorta-coronary bypass with either diltiazem in crystalloid potassium cardioplegia (n = 20) or crystalloid potassium cardioplegia (n = 20). In a preliminary trial, doses between 150 and 250 micrograms/kg reduced the period of heart block after cross-clamp removal (90 +/- 110 minutes) from that found with higher doses and improved myocardial metabolism. In the randomized trial, diltiazem cardioplegia (150 micrograms/kg) produced coronary vasodilatation during cardioplegia and produced less reactive hyperemia during reperfusion. Myocardial oxygen extraction was lower and myocardial lactate production was less after diltiazem cardioplegia during reperfusion. Tissue adenosine triphosphate and creatine phosphate concentrations were preserved better after diltiazem cardioplegia. The postoperative creatine kinase MB levels were less (p less than 0.05) after diltiazem cardioplegia, which indicated less myocardial injury. Postoperative volume loading demonstrated that systolic function (the relation between systolic blood pressure and end-systolic volume index) was depressed after diltiazem cardioplegia compared to crystalloid cardioplegia, but cardiac index was higher because afterload (mean arterial pressure) was lower and preload (end-diastolic volume index) was higher. Diltiazem cardioplegia preserved high-energy phosphates, improved postoperative myocardial metabolism, and reduced ischemic injury after elective coronary bypass. However, diltiazem was a potent negative inotrope and produced prolonged periods of electromechanical arrest. Diltiazem cardioplegia may be of value in patients with severe ischemia but should be used with caution in patients with ventricular dysfunction, and a dose-response relation must be established at each institution before clinical use.

Endocardial excision versus encircling endocardial ventriculotomy. A comparison of effects on ventricular structure and function.

Although endocardial excision and encircling endocardial ventriculotomy are being performed in patients with extensive triple-vessel disease and compromised ventricular function, long-term effects of the operative intervention on structure and function of the left ventricle have not been determined. These procedures were performed in healthy dogs in three groups: control (ventriculotomy alone), endocardial excision, and encircling endocardial ventriculotomy (five dogs per group). Six weeks later, through a left thoracotomy, an arterial line, left atrial line, and Swan-Ganz catheter were inserted. Cardiac output measurements permitted calculation of left ventricular stroke work index, and gated nuclear ventriculograms permitted calculation of left ventricular volume indices. Myocardial performance (stroke work index/end-diastolic volume index relation), systolic elastance (systolic blood pressure/end-systolic volume index relation) and diastolic pressure-volume relationship (left atrial pressure/end-diastolic volume index relation) were determined from volume loading studies. In the endocardial excision group, the left atrial pressures were increased at similar end-diastolic volumes (p less than 0.05 by performance and systolic elastance were similar in the three groups. On completion of hemodynamic studies, the hearts were excised. Gross and light microscopic examination showed that the inner layer of myocardium was scarred in the area of intervention after both endocardial excision and encircling endocardial ventriculotomy. In neither group was there significant morphologic change elsewhere in the myocardium. Both endocardial excision and encircling endocardial ventriculotomy have little effect on long-term structure and function when performed in healthy canine hearts.

Cardiac dysfunction during abdominal aortic operation: the limitations of pulmonary wedge pressures.

The mortality rate for elective abdominal aortic operations remains between 3% and 8% despite careful hemodynamic monitoring, and half of these deaths are cardiac in origin. An extensive evaluation of ventricular function was performed during abdominal aortic operation to detect subtle abnormalities in systolic or diastolic ventricular function that could precipitate progressive ischemic cardiac injury. Twenty-three patients undergoing elective abdominal aortic operations (14 patients with abdominal aortic aneurysm [AAA] and nine patients with aortoiliac occlusive disease [AIOD] ) had hemodynamic and nuclear ventriculographic measurements performed preoperatively, during aortic clamping, and immediately after aortic declamping. No differences were found in the hemodynamic response to operation between patients with AAA or AIOD. Volume loading was performed at each time period to assess ventricular function. Myocardial performance (the relation between cardiac index and end-diastolic volume index) and systolic function (the relation between systolic blood pressure and end-systolic volume index) were depressed during aortic clamping (p less than 0.05), suggesting decreased contractility, but returned to baseline values after declamping. Diastolic compliance (the relation between pulmonary capillary wedge pressure and end-diastolic volume index) decreased after declamping (p less than 0.05), suggesting early myocardial ischemia. The decrease in diastolic compliance rendered pulmonary capillary wedge pressure a poor index of left ventricular preload after declamping. Higher pressures were required to maintain adequate diastolic volumes. Despite careful hemodynamic monitoring, potentially ischemic ventricular dysfunction was found during abdominal aortic operation.

Ascending aorta to bifemoral bypass--a ventral aorta.

In the decade since April 1975 we accumulated a series of 18 patients with arterial conduits from the ascending aorta to the femoral arteries, 10 men aged 53 to 75 years (mean, 60 years) and eight women aged 33 to 56 years (mean, 50 years). In the first two patients, the conduit was placed subcutaneously; in the remaining 16 patients, it was placed behind the rectus muscle and in front of the posterior rectus fascia, thus following the ventral anastomotic axis of the internal mammary and inferior epigastric arteries. The conduit is not visible, palpable, or compressible in this position. This approach was usually chosen because of multiple failures of standard intra-abdominal and axillofemoral vascular reconstructions. Five patients had concurrent intramediastinal procedures, mostly coronary bypass or innominate artery repair. The early operations were performed with Dacron grafts with a bifurcation constructed just below the umbilicus. In the last nine patients, we have used an 8 or 10 mm polytetrafluoroethylene (PTFE) prosthesis and connected it to a 6 or 8 mm PTFE crossfemoral bypass. No operative deaths occurred. The 5-year patency rate by life-table analysis is 70%. This operation is an alternative to axillofemoral bypass in patients with an inoperable abdominal aortic aneurysm.

Comparison between antibiotic irrigation and mobilization of pectoral muscle flaps in treatment of deep sternal infections.

Between January of 1978 and December of 1983, 41 patients developed deep sternal infections with mediastinitis after cardiac operations. Between January of 1978 and December of 1981, 19 of these patients were treated with débridement, primary wound closure, and mediastinal antibiotic irrigation (Group I). Between January of 1982 and December of 1983, 22 patients were treated with débridement, open "clean" packing, and delayed wound closure by the technique of pectoral muscle flap mobilization, which preserves the thoracoacromial pedicles and the pectoral humeral attachments (Group II). The purpose of this study was to compare the results of the treatment of deep sternal infections after cardiac operations with these two techniques. The perioperative hemodynamic, operation, functional, and pathological profiles of both groups of patients were the same. The cosmetic and functional results were the same in both groups as were shoulder girdle and torso mobility. We conclude that either technique is equally effective in the management of patients in whom the serious complication of deep sternal infection with mediastinitis develops after cardiac operation, and we now recommend débridement and pectoral muscle flap closure in one stage.

Permanent cardiac pacing after open heart surgery: congenital heart disease.

A retrospective review of 6,004 patients who underwent open repair of congenital heart defects revealed that 132 patients (2.2%) required permanent cardiac pacing postoperatively. The indications for pacing were early atrioventricular (AV) block in 55%, late onset AV block in 31%, and sick sinus syndrome in 14%. A ventricular septal defect (VSD) was the most common congenital anomaly present alone or in association with other lesions in 67% of the patients. Atrial surgery accounted for 21% of the patients requiring pacing. Ten-year patient survival was found to be 66% (+/- 6%). Thirty-five percent of the deaths were sudden and unexpected, presumably due to an arrhythmia. Reoperation for pacing system failure has occurred too frequently (12% per year). The most common causes for reoperation were battery failure (44%) and exit block (25%).

Myocardial metabolism and ventricular function following cold potassium cardioplegia.

Transient alterations in myocardial metabolism and ventricular function were observed after elective coronary bypass grafting despite apparently adequate intraoperative protection with cold potassium cardioplegia. Ninety patients had serial hemodynamic measurements and coronary sinus catheters inserted. Thirty-three patients had thermodilution coronary sinus flow catheters inserted to measure coronary sinus blood flow and to evaluate the myocardial utilization of oxygen and lactate. Nuclear ventriculograms were performed in 43 patients to assess ventricular function. Cardiac index fell after discontinuation of cardiopulmonary bypass and then rose between 2 and 24 hours postoperatively. Myocardial oxygen consumption steadily increased during this period. Myocardial lactate production reverted to lactate extraction 30 minutes after reperfusion. Reactive hyperemia was present during the first 10 minutes after cross-clamp release, and coronary sinus blood flow increased gradually during the first 24 hours postoperatively. The response to the stress of volume loading (the infusion of 250 to 500 ml of a colloid solution) and atrial pacing (at a rate of 110 beats/min) was evaluated 2 to 4 hours postoperatively (EARLY) and between 4 to 6 hours postoperatively (LATE). Volume loading resulted in a decrease in lactate extraction EARLY and an increase LATE (EARLY: -0.07 +/- 0.35 mmol/L; LATE: 0.08 +/- 0.32 mmol/L, mean +/- standard deviation not significant). Atrial pacing resulted in a decrease in lactate extraction EARLY and an increase LATE (EARLY: -0.11 +/- 0.34 mmol/L; LATE: 0.14 +/- 0.36 mmol/L, p less than 0.05). Diastolic compliance (the relation between the end-diastolic volume index) decreased between EARLY and LATE. Systolic function (the relation between the systolic blood pressure and the end-systolic volume index) and myocardial performance (the relation between the left ventricular stroke work index and the end-diastolic volume index) were unchanged. Ejection fraction correlated inversely with the end-diastolic volume index and did not represent an independent index of contractility. After elective coronary bypass grafting and cold crystalloid cardioplegia, myocardial metabolism recovered slowly. Hemodynamic stresses should be avoided in the early postoperative period to prevent progressive ischemic injury.

Improved myocardial protection with blood and crystalloid cardioplegia.

Although the results of coronary artery bypass surgery have been excellent, recent studies have demonstrated transient alterations in myocardial function and metabolism in spite of apparently adequate cardioplegic protection. Blood cardioplegia may provide better protection than crystalloid cardioplegia, but clinical studies remain inconclusive. Critical coronary stenoses limit cardioplegic delivery, and myocardial protection would be improved with either blood or crystalloid cardioplegia if the solution could be delivered beyond the coronary stenosis. The construction of proximal as well as distal anastomoses during a prolonged cross-clamp period permits more uniform cardioplegic delivery and immediate reperfusion when the cross clamp is released. This technique was used in a prospective randomized trial comparing blood and crystalloid cardioplegia. The long cross-clamp technique eliminated temperature gradients induced when cardioplegia was delivered into the aortic root. The technique of cardioplegic delivery may be as important as the solution used for cardioplegic protection.